Development of 3D Braiding Concept for Multi-Axial Textile Preforms

A thesis submitted to The University of Manchester for the degree of PhD in the Faculty of Engineering and Physical Sciences

2015

KHAYALE JAN

Textile Composite Group SCHOOL OF MATERIALS

Table of Contents Development of 3D Braiding Concept for Multi-Axial Textile Preforms ...... 1 List of Figures ...... 5 Abstract ...... 11 Declaration...... 12 Copyright Statement ...... 13 Dedication ...... 14 Acknowledgement ...... 15 1 CHAPTER 1 INTRODUCTION ...... 16 1.1 Brief Account of Textile Preforms and Preforming Techniques ...... 16 1.2 Research Aims ...... 18 1.3 Research Objectives ...... 19 1.4 Thesis Outlines ...... 20 2 CHAPTER 2 LITERATURE REVIEW ...... 22 2.1 Introduction ...... 22 2.2 Composites...... 22 2.3 Textile Composites ...... 23 2.4 Scope and Applications ...... 24 2.5 Brief Account of Textile Preforms for Composites ...... 26 2.5.1 2D Textile Preforms ...... 27 2.5.2 3D Woven Preforms ...... 29 2.5.3 Multi-Axial Textile Preforms ...... 31 2.5.4 3D Knitted Preforms...... 32 2.5.5 3D Stitched Preforms ...... 33 2.5.6 3D Braided Preforms ...... 34 2.5.7 Filament Wound Preforms ...... 35 2.6 Textile Preforming Techniques ...... 35 2.6.1 Weaving ...... 35 2.6.2 Tubular Preforming Techniques ...... 39 2.6.3 Filament Winding ...... 39 2.6.4 Braiding ...... 43 2.6.4.1 Horngear Braiding ...... 44 2.6.4.2 3D Solid ...... 49 2.6.4.3 Cartesian Braiding ...... 55

2.6.4.3.1 Two-Step Cartesian Braiding ...... 55 2.6.4.3.2 Four-Step Cartesian Braiding ...... 57 2.6.4.3.3 Circular Braiding Machine ...... 68 2.7 Critical Review & Conclusion ...... 76 3 CHAPTER 3 CONCEPTUAL DESIGN OF 3D NOVEL MACHINE ...... 78 3.1 Preliminary Concepts ...... 78 3.1.1 Concept-1: Cartesian Braiding with Continuous Supply of Yarn from a Creel .... 78 3.1.1.1 Cartesian Braiding Bed ...... 79 3.1.1.2 Braid Locking Set-Up ...... 81 3.1.1.3 A Hand Operated Prototype ...... 81 3.1.1.4 Advantages ...... 82 3.1.1.5 Limitations ...... 83 3.1.2 Concept-2: Cartesian Braiding with a Mini-Braiding Bed ...... 83 3.1.3 Concept-3: Cartesian Braiding Machine Inter-twining Braiding, Axial & Semi- Axial Yarns ...... 86 3.1.3.1 Axial Yarns ...... 86 3.1.3.2 Braiding Yarns ...... 86 3.1.3.3 Semi-Axial Yarns ...... 86 3.2 Modifications in Concepts ...... 87 3.2.1 First modification: Cartesian Circular Braiding Machine incorporating Braiding, Axial & Binder Yarns ...... 88 3.2.2 Second modification: Circular Braiding cum Winding Machine for Multi-Layer Multi-axial Textile Preforms Incorporating Braiding, Axial & Binder Yarns ...... 91 3.2.2.1 Bobbin Transfer System ...... 93 3.2.3 Final Modification ...... 98 3.3 Conclusion ...... 100 4 CHAPTER 4 DEVELOPMENT OF THE NOVEL 3D TEXTILE PREFORMING MACHINE ...... 102 4.1 Construction of the Machine ...... 104 4.1.1 Braiding Rings ...... 104 4.1.2 Pneumatic Actuators ...... 106 4.1.3 Pneumatic Internal Grippers ...... 107 4.1.4 Miniature Shuttle ...... 108 4.1.5 Axial Yarn Supply ...... 110 4.2 Bobbin Transfer Mechanism ...... 111 4.3 Braiding Yarn Placement ...... 119

4.4 Process Layout of the Machine Operations ...... 121 4.5 Conclusion ...... 123 5 CHAPTER 5 DEVELOPMENT OF MULTI-AXIAL BRAIDED PREFORMS ...... 124 5.1 Prospective Fibre Architectures ...... 124 5.2 Development of Multi-Axial Textile Preforms ...... 127 5.2.1 Preparation ...... 127 5.2.2 Tensions Adjustment ...... 129 5.3 Validation of the Weave Architecture ...... 130 5.4 Initial Trials to Develop Preforms...... 131 5.5 Preform with Various Structure Compactness ...... 135 5.6 Braided Yarn Placement at ±45o ...... 141 5.7 Sample Development for Tomography ...... 141 5.8 Weave Topology of Novel Braided Preform ...... 144 5.9 Conclusion ...... 145 6 CHAPTER 6 GEOMETRICAL ANALYSIS OF BRAIDED STRUCTURES USING COMPUTED TOMOGRAPHY ...... 147 6.1 Computed Tomography (CT) ...... 147 6.2 Mechanical Testing ...... 161 6.2.1 Composite Forming ...... 161 6.2.2 Compression Testing ...... 162 6.2.2.1 Material ...... 162 6.2.2.2 Methodology ...... 163 6.2.2.3 Results and Discussion ...... 164 6.2.3 Tensile Testing...... 166 6.2.3.1 Material ...... 166 6.2.3.2 Methodology ...... 167 6.2.3.3 Results and Discussion ...... 168 6.3 Conclusion ...... 171 7 CHAPTER 7 CONCLUSION AND FUTURE WORK...... 172 7.1 Conclusion ...... 172 7.2 Future Work ...... 173 References: ...... 175 Appendix ...... 182

List of Figures

Figure 1.1 3D woven fabric 16 Figure 1.2 Braided shaped architectures and preforms 17 Figure 2.1 Some applications of fibre reinforced composites 25 Figure 2.2 Classification of 2D & 3D textile preforms 27 Figure 2.3 2D Woven fabrics 27 Figure 2.4 Maypole braid pattern 28 Figure 2.5 Braid structure illustrations 29 Figure 2.6 Examples of 3D woven preforms 30 Figure 2.7 Angle-interlock and Orthogonal weave architecture 30 Figure 2.8 Possible axes, and fibre architecture in a 3D cube of textile preform 31 Figure 2.9 Distance fabric 32 Figure 2.10 3D knitted fabric for helmet 33 Figure 2.11 Various stitched preforms 33 Figure 2.12 Braid architectures 34 Figure 2.13 Braided shapes 35 Figure 2.14 3D Weaving demonstration 36 Figure 2.15 Multi-layer fabric 36 Figure 2.16 Fukuta’s machine for 3D fabric 37 Figure 2.17 Annahara’s 5-axes 3D fabric and its method 37 Figure 2.18 Kimbara’s 3-D fabric architecture 38 Figure 2.19 Machine developed by Muhammad for 5-axes 3D-fabric 38 Figure 2.20 Khokar’s 3D woven fabric 39 Figure 2.21 Schematic of filament winding 40 Figure 2.22 Schematic of winding 41 Figure 2.23 Three basic winding patterns 42 Figure 2.24 Pin wheels for placing unidirectional fibre using filament winding 43 Figure 2.25 First prototype of LOTUS 43 Fig 2.26 Biaxial and tri-axial braids 44 Figure 2.27 Horngear braiding machines 45 Figure 2.28 (a) Horn gear with yarn carrier arrangement; (b) track plate 45

Figure 2.29 Mega-braider for up to 100 inches diameter and 15 feet long mandrels 46 Figure 2.30 A side view of three deck braiding set-up 47 Figure 2.31 Demonstration of two inter-locked layers with cross over points 47 Figure 2.32 Configuration of the braiding bed for an I-beam 48 Figure 2.33 Apparatus and braiding track for two layers with a cross over point 48 Figure 2.34 (a) Configuration for a circular braid with another layer inter-connected in the core (b) A circular solid braid 49 Figure 2.35 Braiding bed configured in two regions for an I-beam shaped structure 49 Figure 2.36 3D Solid braid configuration & 3D solid braiding machine 50 Figure 2.37 A demonstration of rotors and yarn carriers movement 51 Figure 2.38 Circular and rectangular braiding bed configurations 51 Figure 2.39 Mungalov’s 3D braiding machine 52 Figure 2.40 Featured machine parts of Mungalov’s 3D braiding 52 Figure 2.41 Braiding bed configurations for different shapes 52 Figure 2.42 1st generation hexagonal braiding machine with single carrier position 53 Figure 2.43 2nd generation hexagonal braiding machine with two carrier positions 53 Figure 2.44 Braid pattern for 3D solid round and triangle structures showing yarn groups 54 Figure 2.45 The yarn carrier switch mechanism 54 Figure 2.46 2-step Braiding machine developed by Ronald F McConnell et al. 56 Figure 2.47 Two-step braiding bed with carrier paths 56 Figure 2.48 Braiding machine developed by Du et al. 57 Figure 2.49 Track plates of the machine 57 Figure 2.50 Cartesian braiding arrangement 58 Figure 2.51 Cartesian braiding process 59 Figure 2.52 A prototype of multi-step braider with Eight-step 1×1 braid cycle 60 Figure 2.53 Cartesian braiding machine developed by Bluck et al. 61 Figure 2.54 Cartesian braiding machine developed by Florentine 61 Figure 2.55 Cartesian braiding blocks with magnets and bobbin on the top 62 Figure 2.56 Yarn carrier paths on Florentine rectangular braiding bed 62 Figure 2.57 Yarn carrier trajectory on Florentine circular braiding bed 63 Figure 2.58 A schematic arrangement of row and columns on the braiding bed 63 Figure 2.59 an array of self supporting elements and floating creel 64 Figure 2.60 A Cartesian braiding bed with yarn carrier trajectory on it 64

Figure 2.61 Set-up-A with take-up on both side and braiding bed between them 65 Figure 2.62 Set-up-B with creel on one side and take-up on the other 65 Figure 2.63 Prototype braider showing some basic components by Farley et al. 66 Figure 2.64 Schematic representation of shuttle plate braider operation 67 Figure 2.65 Schematic representation of Nayfeh bias weaving operation 68 Figure 2.66 Front & Side elevational views of circular braiding machine by Brown 69 Figure 2.67 Discrete elements of the ring for the fibre carrier on Brown’s machine 69 Figure 2.68 Side views of portions of the modified belts 70 Figure 2.69 Circular preforming machine 71 Figure 2.70 A multi-axial 3D circular preform and an interlacement unit. 71 Figure 2.71 An isometric view of the mechanism with equidistant fibre carriers 72 Figure 2.72 Braiding machine developed by Micheal J. Hurst et al. 73 Figure 2.73 True Tri-axial Braiding Machine 73 Figure 2.74 Axially stable tri-axial tubular fabric and its interlacement pattern 74 Figure 2.75 Front view of the machine with inner rotating spools and outer interlacing spools. 75 Figure 3.1 Isometric view of the braiding machine presented in concept-1 79 Figure 3.2 Cartesian braiding bed with pneumatic actuators 80 Figure 3.3 Comber boards in rectangular and square shapes 81 Figure 3.4 A schematic view of the prototype 82 Figure 3.5 A 4-step vertical Cartesian braiding bed 82 Figure 3.6 Line diagram of braiding machine with robotic arm 84 Figure 3.7 Line diagram of Cartesian braiding machine with a mini-braiding bed 85 Figure 3.8 Self supporting mini-braiding bed with axial and braiding yarns 85 Figure 3.9 (a) Braiding yarn Carrier (b) Axial Yarn Carrier (c) Spacer 87 Figure 3.10 Cartesian braiding machine with 3 Sets of yarns 89 Figure 3.11 Segmented piece of the ring with braiding bobbin 90 Figure 3.12 Single ring & an array of rings arranged side by side 90 Figure 3.13 Circular Braiding Machine based on Cartesian principle incorporating Braiding, Axial & Semi-Axial 92 Figure 3.14 Modified ring 92 Figure 3.15 A solid & an aluminium Central support frames for holding the rings 93 Figure 3.16 Central guide plates as positioned between the rings 94 Figure 3.17 Bobbin transfer system 95

Figure 3.18 An assembly with bobbins mounted on it 96 Figure 3.19 Casing of transverse bobbin for external gripper 97 Figure 3.20 Specially designed transverse bobbin for internal gripper 97 Figure 3.21 Internal gripper with sleeve 98 Figure 4.1 a full view of the machine 103 Figure 4.2 Main braiding area of the machine 105 Figure 4.3 Braiding bobbin attached to the ring 106 Figure 4.4 A view of the machine showing pneumatic actuators 107 Figure 4.5 Pneumatic bellow gripper (a) without sleeve (b) with sleeve 108 Figure 4.6 Bellow gripper’s outer sleeve 108 Figure 4.7 Miniature shuttle 109 Figure 4.8 Axial yarn assembly 110 Figure 4.9 Bobbin transfer arrangement 113 Figure 4.10 Machine view showing pneumatic actuators 114 Figure 4.11 Bobbin transfer mechanism 115 Figure 4.12 Miniature shuttle in bellow gripper 116 Figure 4.13 Shuttle weft insertion system 118 Figure 4.14 Rapier insertion system 119 Figure 4.15 Rings’ rotations in four steps 121 Figure 4.16 Process layout 122 Figure 5.1 CAD models of double layered fibre architecture 124 Figure 5.2 CAD models of fibre architecture 125 Figure 5.3 Cross wound preform with axial yarns 125 Figure 5.4 Multi-layered preform using different fibres in different layers 126 Figure 5.5 A sample in which braiding layers are not cross-wound 126 Figure 5.6 braiding bobbin with 38mm diameter & regular size binder yarn bobbin with 14mm diameter 128 Figure 5.7 Winding set-up, a simple winder and braiding bobbin 128 Figure 5.8 Interlocked braided structure with different spacing of braid 131 Figure 5.9 Sample-1 of the braided structure 132 Figure 5.10 Sample-2 of the braided structure 132 Figure 5.11 Sample-3 of the braided structure 133 Figure 5.12 Sample-4 of the braided structure 133 Figure 5.13 Sample-5 of the braided structure 134

Figure 5.14 Sample-6 of the braided structure 134 Figure 5.15 A 30cm long uniform braided structure 135 Figure 5.16 Sample-1a 136 Figure 5.17 Sample-1b 136 Figure 5.18 Sample-2a 137 Figure 5.19 Sample-2b 137 Figure 5.20 Sample-3 138 Figure 5.21 Sample-4a 139 Figure 5.22 Sample-4b 139 Figure 5.23 Sample-4c 140 Figure 5.24 Sample-5 140 Figure 5.25 Preforms braided at ±60o and ±45o 141 Figure 5.26 Sample developed for tomography 142 Figure 5.27 Sample-1 142 Figure 5.28 Sample-2 143 Figure 5.29 Sample-3 143 Figure 6.1 Sample mounted on the Zeiss-Versa 520 system during CT acquisition 148 Figure 6.2 3D structure of the braid showing braid angle and braid axis 148 Figure 6.3 Axial yarn extracted from 3D novel braided structure 149 Figure 6.4 Binder yarn extracted from 3D novel braided structure 149 Figure 6.5 Cross-sectional views of the CT image 150 Figure 6.6 3-D reconstruction of the braided sample 151 Figure 6.7 Cross-sectional views of the sample 152 Figure 6.8 Cross-sectional views of the sample 153 Figure 6.9 3-D reconstruction of the braided sample 154 Figure 6.10 Transverse cross-sectional views of the sample 155 Figure 6.11 Longitudinal cross-sectional views of the sample 155 Figure 6.12 3-D reconstruction of the 3D novel braided structure 156 Figure 6.13a Binder yarns in the 3D novel braided structure 157 Figure 6.13b Binder yarns in the 3D novel braided structure 157 Figure 6.14 Cross-sectional views of the 3D novel braided structure 158 Figure 6.15 3-D reconstruction of the 3D novel braided structure 159 Figure 6.16 Vacuum Bagging & Resin Infusion for composite forming 161 Figure 6.17 Curing cycle for resin infused carbon composite 162

Figure 6.18 Instron 5569 testing machine set-up for compression 163 Figure 6.19 Damaged sample at failure after compression loading 164 Figure 6.20 Compressive stress vs Compressive strain 165 Figure 6.21 Compression modulus of Novel braided samples &2D braided samples 166 Figure 6.22 Sample clamped in Instron machine 167 Figure 6.23 Fixture for clamping the braided composite tubes 167 Figure 6.24 Fracture in the sample during tensile loading 168 Figure 6.25 Tensile stress vs Tensile strain 169 Figure 6.26 Tensile modulus of Novel braided samples & 2D braided samples 170

Abstract

Significant research has been conducted to develop new preforming techniques as the conventional textile technologies have certain limitations in producing purpose built products. The successful attempts have opened new horizons for future prospects. 3D weaving has been one of the prominent technologies whilst 3D braiding has appeared to be more versatile in preforming quasi-isotropic near-net-shape preforms. The following study includes a review of the textile preforming techniques. Three- dimensional (3D) textiles are discussed on a broader scale and more specifically concentrating on multi-axial 3D preforming techniques. Cartesian braiding is the focal point of this research. Two-step and four-step braiding methods are investigated as being the core areas of interest. The experimental work was initiated by drawing preliminary concepts that ultimately converged into a final concept of developing a novel 3D textile preforming machine capable of producing multi-axial textile preforms with the inclusion of z-axis yarn through-the-thickness of the structure. Such preforms are multi-layered and interlocked together by means of binder yarns. The final concept for the development of the machine incorporates the insertion of braiding yarns, axial yarns and binder yarns simultaneously. The development of a fully automated machine has been outlined in detail. Insertion of through-the-thickness yarn along the z-axis is a characteristic feature of the concept which distinguishes this development among the existing preforming technologies. The insertion of binder yarn along the z-axis and the transfer of a miniature shuttle with the help of a rapier system has been the pivotal area of this research. Following the development of the machine, sample development has been explained with all necessary details. This part covers the preparation for sample development, yarn tensioning and finally the development of the preforms. The description of various preforms using different numbers of yarns and tow sizes has been given. In the last phase, tomographic analysis of the preforms has been conducted in order to study the tow geometry and fibre architecture. This study creates a very clear understanding of fibre architecture and shows a good comparison of weave pattern between various textile preforms. Besides preform geometry, an analysis of the mechanical performance of the produced preforms has been presented. The preforms have been infused with epoxy resin to turn them into composites for tensile and compression tests. Tests results indicate the likely behaviour and trend of the manufactured preforms.

Declaration

That no portion of the work referred to in the thesis has been submitted in support of an application for another degree or qualification of this or any other university or other institute of learning.

The report is a presentation of my original research. Contributions of others, wherever involved, are indicated clearly with reference to literature.

The work is done under the guidance of Prof. Dr. Prasad Potluri, at The University of Manchester.

i. The author of this dissertation (including any appendices and/or schedules to this dissertation) owns any copyright in it (the “Copyright”) and he has given The University of Manchester the right to use such Copyright for any administrative, promotional, educational and/or teaching purposes. ii. Copies of this thesis, either in full or in extracts and whether in hard or electronic copy, may be made only in accordance with the Copyright, Designs and Patents Act 1988 (as amended) and regulations issued under it or, where appropriate, in accordance with licensing agreements which the University has from time to time. This page must form part of any such copies made. iii. The ownership of certain Copyright, patents, designs, trademarks and other intellectual property (the “Intellectual Property”) and any reproductions of copyright works in the thesis, for example graphs and tables (“Reproductions”), which may be described in this thesis, may not be owned by the author and may be owned by third parties. Such Intellectual Property and Reproductions cannot and must not be made available for use without the prior written permission of the owner(s) of the relevant Intellectual Property and/or Reproductions. iv. Further information on the conditions under which disclosure, publication and commercialisation of this thesis, the Copyright and any Intellectual Property and/or Reproductions described in it may take place is available in the University IP Policy (see http://www.campus.manchester.ac.uk/medialibrary/policies/ intellectual-property.pdf) in any relevant Thesis restriction declarations deposited in the University Library, The University Library’s regulations (see http://www.manchester.ac.uk/library/aboutus/regulations) and in The University’s policy on presentation of Theses.

Dedication

I Dedicate This Work

My Parents

Acknowledgement

I am deeply indebted to my supervisor, Prof. Prasad Potluri for his outstanding advice, support and encouragement. His inspiring mode of leading and encouragement during the course of my research has always been a source of motivation for me. It has become possible for me to conduct this research mainly with his help and support.

I express my sincere thanks to my co-supervisor, Dr. Richard Kennon for his compassionate supervision and valuable guidance. His wonderful personality has always been a source of light for me, and his soft and gentle nature has left a serene impact on my performance.

I would also like to express my gratitude to Bahauddin Zakariya Univeristy Multan and Higher Education Commission (HEC) of Pakistan for their financial support to pursue my higher studies.

I highly appreciate the help I received from Dr. Dhavalsinh Jetavat (Research Associate), Mr. Roy Conway and Mr. Alvaro Silva Caballero without whom I would have had a much harder time.

I would like to thank the technical staff particularly Mr. Thomas Kerr (Experimental Officer Weaving), Mr. Mark Chadwick (Technician), Mr. Alan Nesbit, Mr. Bill, Mr. Bary Gleeve, Mr. Mark Harris, Engineer Stephen Cowling, Mr. Ryan Delve (Mechanical Engineering Technician), Technician Thomas Neild and Mechanical Workshop Technician Christopher Hyde for their help to make various parts and jobs for me in time for the construction of the machine.

It has been great pleasure to have the company of all my research fellows including Dr. Zeeshan Yousaf, Dr. Sabahat Nawaz, Dr. Mazhar Hussain Perzada, Dr. Haseeb Arshad, Mr. Rishad Rayyan, Dr. Shankhachur Roy, Dr. Vivek Konchery, Mr. Mayank Gautam, Dr. Dhaval Patel and Mr. Hussein Dalfi. I am grateful to all of them for their advice and support.

Most importantly, I acknowledge the love and patience of my parents and my family members. I am thankful to them for their constant source of love, concern, support and strength all these years.

1 CHAPTER 1 INTRODUCTION

1.1 Brief Account of Textile Preforms and Preforming Techniques Textile preforms for advanced composites have gained significant attention in the last few decades. This advancement derives significantly from the design and development of preforming techniques. The understanding of the process-structure-property relationship is critical in realising the maximum advantages of textile preforming [1].

Textile composites reinforced with two-dimensional (2D) laminates have been used for over forty years in aircraft, for over sixty years in maritime craft, and for nearly thirty years in high performance automobiles and civil infrastructure. The use of through-the- thickness z-yarns has improved the out of plane properties of composites considerably.

Composites reinforced with 3D textile preforms have contributed significantly to overcome issues with 2D laminates like drapeability and delamination as these preforms can be produced in near-net shapes [2] as shown in Figure 1.1. Angle interlock and through-the-thickness fabrics are the most common 3D woven fibre architectures. Despite their advantageous potential, the absence of bias yarns in 3D woven preforms is one of their major shortcomings, and it results in low shear and torsion properties.

Figure 1.1 3D woven fabric

Braided preforms, on account of the diversity of manufacturing configurations, offer a wide range of fibre architectures as shown in Figure 1.2. Two-step braided preforms encompass axial yarns intertwined by braider yarns that result in higher stiffness and axial strength with improved out-of-plane properties [4]. In a way two-step braided preforms are more versatile for creating complex shapes.

Cartesian braided textile preforms for composites are known for their excellent shear resistance, quasi isotropic elastic behaviour, low stiffness and strength and high Poisson effect. Their poor mechanical characteristics are because of the lack of axial yarns. However, two-step braided preforms include axial yarns intertwined by braiding yarns and these preforms can be braided into complex shapes. The need for composites with a variety of cross sectional shapes has led researchers to exploit the potential of 3D multi- step braiding [1].

Figure 1.2 Braided shaped architectures and preforms

A range of textile preforming techniques are being used currently; weaving, braiding, knitting, stitching and a combination of two or more of these. Each of these procedures has its own importance and potential regarding various features during and after manufacturing. Weaving has been traditionally used for bi-axial textile fabrics in significantly wider widths. The speed of manufacturing is the major strength of weaving. It has been applied to 3D textiles successfully by making minor modifications to the existing technology. Subsequently a number of specially designed weaving machines have been developed which indicates significant progress towards textile composites. The limited scope of versatility in shapes and forms of the textile preform has been a major drawback.

Braiding has been considered to be less adaptable for technical textiles in the form of textile composites. Previously braids were only considered to be used for ropes, hoses etc. However, over the last 50 years, new braiding techniques have been introduced. It has been appreciated that braiding has great potential in the preforming of textile composites in versatile approaches with greater flexibility in the shapes, forms, architectures and mechanical properties. The major limitation of braiding technology is the ratio of preform size to machine bed size. The second important constraint of 3D braiding is the length of the element to be braided.

The complexity of the mechanism, the adaptability of the mechanism for different preforms with fewer changes, and near net shape preforming are still the main focus of ongoing research. A number of attempts have been made but still a level that can give confidence to the designer, manufacturer and the end user, has not yet been achieved.

The following research concentrates on 3D braiding technology on account of its capability for bias inter-twining and versatility in shapes and sizes, for the development of multi-axial textile preforms with bias orientations. The focus is to design and develop a novel 3D braiding machine capable of producing multi-axial textile preforms featuring through-the-thickness yarn along the z-axis. In existing 3D braided preform there is no provision for fibre placement perpendicular to the plane of the preform. The available conventional (2D) braiding technology offers to intertwine the diagonal (bias) yarns along the spiral periphery of the tubular structure with an addition of axial yarns along the braiding axis (at 0o) by variety of methods, and multi-layers can be over-braided to get the required thickness of the preform. The fibre architecture and its intertwining pattern in both 3D solid braiding and Cartesian braiding is the same although the working principle of each is entirely different. 3D solid braiding makes use of horngears to move the bobbin carriers in sinusoidal motion whereas in Cartesian braiding the bobbin carriers are moved along rows and columns. Each of these techniques can incorporate the axial yarn but there is no fibre placement through-the-thickness. Shear, both in-plane and out-of-plane, Poisson’ effect, delamination and damage propagation are the major issues because of the absence of z-axis and locking yarns. So it is noticeable that the performance of the braided structure can be improved by adding binder yarns along the z-axis. The presence of z-axis yarn in the braided structure could be a source for binding the structure and it can overcome the related issues. The concept presented in the following study/ research offers to incorporate binder yarns through- the-thickness along the z-axis with braiding and axial yarns simultaneously. A number of aims and targets have been set for this research.

1.2 Research Aims This research aims to develop a novel 3D braiding concept for the manufacture of multi- axial 3D textile preforms.

This research is focussed on the development of a novel 3D textile machine to produce multi-axial braided preforms with enhanced properties and more stable structure by the insertion of through thickness reinforcement.

1.3 Research Objectives The following are the set objectives of the research to achieve the main goal and aims.

 Conceptual design of a novel 3D textile preforming machine based on the braiding principle. o The proposition of a concept for the development of a novel 3D textile preforming machine considering the braiding technique as a foundation. o Drawing and sketching the 2D and 3D diagrams illustrating all the required features and specifications.

 Development of the novel 3D textile preforming machine based on the braiding principle. o Construction of an automated machine with a fully programmable control and command system for its motions. o Development of the machine with the least mechanical complexity that clearly facilitates the concept. o The machine should be adaptable for various fibre architectures of “over- mandrel” and “without mandrel” preforms.

 Development of multi-axial 3D textile preforms in various sizes and fibre architectures with better mechanical properties. o Once the machine is developed, the samples are to be produced with fibre architectures different from those produced on conventional braiding machines. o Development of multi-axial fibre architectures comprising diagonal braiding yarns, axial yarns and binder yarns. o Development of multi-axial fibre architectures in which the layers are bound together by means of binder yarns.

 Comparison of fibre architecture of preforms produced on the novel 3D textile machine with conventional circular braided preforms keeping the basic parameters the same. o Development of the samples on the novel 3D textile preforming machine and conventional braiding machine with an equal number of braiding and axial yarns. o Keeping the preforming parameters such as tow size, braiding angle and mandrel diameter the same. o Microscopic analysis of the fibre architecture of the preforms so produced.

 To compare the test performance of the preforms produced on the novel 3D textile preforming machine with that of conventional circular braided preforms in respect of their mechanical properties. o Mechanical testing including tensile and compression tests under the same loading conditions and test environments. o Tensile testing to check the performance deriving from the inclusion of the axial yarns. o Compression testing to check the out-of-plain properties.

1.4 Thesis Outlines The thesis has been concisely outlined to focus on the subject and an effort is made to present and elaborate the subject matter.

Chapter 1 introduces the project with a brief account of the context of the research. Here in this chapter, the research aims and objectives are defined, and finally the thesis is outlined.

Chapter 2 presents a review of the literature. Broadly it deals with a survey of 3D textile preforms and preforming techniques including weaving, winding and particularly braiding. This study shows various methods of preforming with their potentials and limitations. The study identifies the design gaps where improvement can be made.

Chapter 3 describes the conceptual design of the machine. The steps are illustrated to show how the research has been forwarded phase by phase. The modifications to the concept and eventually the design of the machine have been discussed.

Chapter 4 illustrates the development of the machine. The detailed explanation of each and every part and their functions is given in this chapter. The machine working and the principles have been described with all necessary details.

Chapter 5 includes a description of the development of the structures on the novel textile preforming machine. The processes and methods used in forming these structures have been detailed in this section. A variety of fibre architectures has been discussed. Furthermore an account of vacuum bagging, resin infusion, and composite forming has been included as they are an essential part of specimen preparation prior to testing.

Chapter 6 describes the mechanical testing and Tomographic analysis. A few tests including tensile and compression have been conducted to find the properties and understand the behaviour of the structures produced by the novel textile preforming machine. The results are presented in the form of graphs. Tomographic imaging has been carried out for a number of the samples produced by the novel textile preforming machine and conventional braiding machines. This is done to understand and elaborate the fibre architecture of the structures produced by the novel textile preforming machine in comparison with those produced by conventional braiding machine.

Chapter 7 is the last chapter of the thesis where a conclusion of the entire project and research has been derived. The capacity of the developed novel textile preforming machine to produce a variety of fibre architectures has been defined. Finally the potential areas for future work and research have been indicated.

2 CHAPTER 2 LITERATURE REVIEW

2.1 Introduction The existence of textiles is evident earlier to the recorded history. Archaeologists report that man used to fabricate coarse cloth from a range of fibres for at least 20,000 years and elaborate textiles were traced in tombs in Egypt and Asia dated to several thousand years before Christ. Various processes developed in olden times are still in use in remote areas of the world [3]. However, with the industrial revolution, textile technology has seen more rapid developments for the last one hundred years in its history so far [3]. Owing to the advances in textiles like computer-programmed machine with high rate of production, in the last thirty years applications of textiles composites have gained a substantial attraction. Both 2D and 3D textile preforms offer the potential of low-cost, mass-produced composite structures [5].

Textiles have been used in composite materials since the mid-1800s. The first use of textiles to reinforce a matrix material is attributed to Thomas Hancock by Hearle [6]. Thomas Hancock’s patent in 1824 describes “using flax, hemp, cotton and wool fibres that are previously arranged or disposed as to shape and dimension according to the purpose they are afterwards to be applied and saturating them with a liquid which, when partially evaporated, becomes flexible and adhesive.” This development led to the field of flexible composites such as tyres and conveyor belts. In the recent times the scope of textile composites particularly the 3D textile composites are extensively investigated for wide range of applications because of their damage tolerance and near-net shape manufacturing [5].

2.2 Composites Composites are regarded as an important class of engineering materials on account of their unique material properties. Composites can be defined as macroscopic combination of two or more distinct materials (reinforcement and binder or matrix) with an identifiable interface between them [7]. Both the constituents persist at macro and microscopic scale within the finished structure which results in a composite with greater performance characteristics. Composite materials are either available naturally or are

22 engineered. Generally a composite is composed of a continuous part, the matrix and a discontinuous part, the reinforcement [8].

The matrix itself is made from resin and fillers. Fillers reduce the cost while improving or modifying the characteristics of resin. The matrix passes on the external loads to the reinforcements whereas protecting them from environmental strains. Resins should be compatible with the reinforcements for better mechanical properties [8]. Two large families of resins are thermoplastic and thermo-set. Thermoplastic resins are characterised by low cost, able to be processed many times, and recycled. Thermosetting resins can only be processed once. They have higher thermo-mechanical properties than thermoplastics as they lead to geometric structures after polymerization [8].

Reinforcements incorporate into composites their distinct properties like mechanical, physical, thermal, electrical impact, compression, and torsion. Commercial forms of fibre reinforcements are listed below.

1. Linear (include strands, yarns, roving) 2. Surface tissues (woven fabrics, mats) 3. Multidirectional (preforms, complex shaped cloths etc)

The selection of the reinforcement and matrix is based on their compatibility, high mechanical properties, coefficient of thermal expansion, resistance to corrosion, damage tolerance, ease of manufacture, cost and a number of other factors of consideration [8].

2.3 Textile Composites Composite materials reinforced with fibrous, laminated or 3D structural textile preforms are termed as textile composites. One of the essential constituent of textile composites is textile preform for reinforcement purpose, and is usually manufactured from high performance fibres such as carbon, glass, aramid [9].

Major advances in composite materials with fibre reinforcement have been achieved since 1970. A variety of 3D fibre composites have been created, with the most important types being 3D woven, stitched, z-pinned and non-crimp knitted materials. The motive to use variety of 3D fibre composites is their superior delamination resistance, impact resistance and damage tolerance compared to traditional laminates

[10]. The potential of composite materials are well known for realizing light-weight and high strength applications. Variety of preforming techniques including weaving, braiding and fibre placement and preforms like non-crimp fabrics, tubular braids and unidirectional fabrics, near net shaped preforms complex three-dimensional braids have been developed during the past years. Today’s research is focused on improvements of mechanical performance like damage tolerance and cost-effective manufacturing methods. The next step is to combine the textile preforming technology with advanced impregnation techniques that may offer a high potential to reach these goals [11].

Textile reinforcement structure also known as preform is an integral components of textile composites which is usually manufactured from high performance fibres like carbon, glass, aramid [9]. Textile preforms (especially 2D fabrics) have long been in use mainly for made-ups and aesthetic purposes. The use of textiles in composites as a potential reinforcement dates very late in the history compared to metal composites and ceramics. Textile structures are famous for their unique features of being light weight, flexible and offering strength and stiffness to the composite. These are considered as a structural backbone for net shape manufacturing and toughness [13].

However, the physical properties of fibre reinforced composites are typically anisotropic in nature. Textile composites can fail on the micro and macro scale. These composites may undergo fibre pull-out, delamination caused by shock, impact, or repeated cyclic stresses. To aid in predicting and preventing failures, composites are modelled before construction and tested afterwards. Pre-construction analysis may use finite element analysis (FEA) and may be tested after construction through several non-destructive methods.

2.4 Scope and Applications Fibre-reinforced composite materials, though costly in general, have become popular in high-performance applications. 3D textile composites have unique features, which can be tailored for the desired properties for a particular end use. These distinguishing attributes make textile composites more attractive and adoptable for high performance applications. In harsh load bearing conditions the composites need to be light in weight, and strong such as for aerospace components. Examples of their applications are aircraft tails, wings, fuselages, connectors, spars, boat structures, racing car bodies, and bicycle

24 frames. An aerospace application is the new Boeing787 structure including the wings and fuselage, which is composed largely of composites.

Figure 2.1 Some applications of fibre reinforced composites

Aerospace, military, marine and civil engineering fields have become known to be the latest applications of textile reinforced composites with polymers [2] in addition to medical prosthesis and developments in the field of orthopaedic surgery [14]. 3D woven fabric preforms that can be found in numerous forms could lessen aircraft weight by 30% [15].

Carbon composites have a vital role in launch vehicles, heat shields and yoke of spacecrafts, solar panel substrates, antenna reflectors, payload adapters and inter-stage structures. In addition, composite materials with carbon fibres and silicon carbide matrix in luxury vehicles and sports cars and carbon/carbon material in disk brake systems of airplanes and racing cars are being used. Distance fabric composites are primarily used to produce double walled tanks or the wall lining for storage tanks, cars and truck spoilers/ fairings, lightweight walls, dome structures and composite tooling [14]. The application of 3D woven composites in aircrafts is considered more crucial and critical so they are less adopted; however in non-aerospace industries they are widely and potentially used. A vast range of their applications include floors, floor beams in trains and fast ferries, flat load trays in trucks, crash members in cars, buses and trucks, shipping containers and other container transport applications [14].

In order to take full advantage of textile composites, a sound testing database and reliable methodology is needed. Besides a practical approach towards the technology, modelling can play a vital role to predict behaviour of textile composites, especially to understand the failure phenomenon.

2.5 Brief Account of Textile Preforms for Composites Textile composites have attained a significant position in the realm of advanced composite materials and high performance applications. The chief advantages of textile composites over other composites using isotropic reinforcements are their high strength- to-weight ratio, near-net shaped complex preforms, enhanced mechanical, flexural and torsional properties, better in-plane and out-of-plane properties, improved impact resistance, damage tolerance and resistance to delamination. Applications of textile composites as high performance materials have made this class a competitor to existing technologies. 3D textile reinforced composites have made significant advancements to overcome issues such as drapeability, delamination and offer near-net shaped preforms for high structural applications [2]. However, research conducted so far in this field is still insufficient and the testing database is limited.

Textile preforms are of various types that can be categorised as 1D, 2D 2.5D and 3D. TW Chou further classified 3D textile preforms on the basis of manufacturing technique as shown in Figure 2.2 [5].

Biaxial

woven Triaxial Biaxial Mutiaxial woven Triaxial 2 Step

Flat Braid 4 Step 2D Braid Preforms 3D Circular Preforms Solid

Warp Warp Knit Knit Weft Weft

Lock Stitched Chain

Figure 2.2 Classification of 2D & 3D textile preforms

2.5.1 2D Textile Preforms 2D textile preforms are the structures having considerable larger outspread along two axes and a negligible thickness along the third direction. These preforms have good drapeability, in-plane properties and tensile strength but poor shear along in-plane and out of the plane. Conventionally 2D textile preforming techniques include weaving, knitting, stitching and braiding.

2D woven preforms comprise two sets of yarns running perpendicular to each other and being interlaced at various patterns. These preforms are cost effective, having better yarn packing, and good impact resistance but lower shear resistance and elastic in-plane properties [13]. Composites made with 2D woven preforms show inferior out of plane mechanical properties to 3D fabrics, however somewhat better than unidirectional laminates.

Figure 2.3 2D Woven fabrics

Braided preform is defined as “a narrow tubular textile structure produced by the intertwining of three or more parallel strands together” [16]. The diagonal intertwining is carried out at a certain angle ranging from 10o to 85o [17]. The classical braiding pattern is exactly similar to maypole dancing as shown in Figure 2.4.

Mandrel along Take-up axis Braiding bed with rotating bobbins

Figure 2.4 Maypole braid pattern

The applications expanded to cords then ropes with the development of industrial braiding equipment [18]. An aircraft company McDonnel Douglas was first to exploit braided preform as engineered materials particularly to be used in composite structures [19]. Whereas high production rate of manufacturing of braided preforms for composite has attained great attention [20]. The most recent advancement in braiding has been made by The Airbus Group for aircraft frame manufacturing together with filament winding technique [21]. The applications ranges to over braided fuel lines, air ducts [22], bike frame [23], stiffening tubes and sail boat spars etc [24].

2D braids may be bi-axial and tri-axial. Tri-axial 2D braiding incorporates axial laid-in yarns which result in an increase in longitudinal stiffness [13]. 2D braiding is capable of producing structures for hoses, expansion joints and even for over braiding on a mandrel to attain a final shape of the composites.

Diagonally interlacing yarns shown with different colours

Figure 2.5 Braid structure illustrations

S.L. Phoenix found that increase in braid angle, increase in number of strands or their cross-sectional area causes increase in crimp angle that results in lowering the braid strength and stiffness [25]. This leads to a derivation that lower crimp value is preferable for braid structure.

Knitted preforms are produced by interloping or intermeshing one set of yarns either longitudinally or horizontally with the help of needles. The structure so produced may be circular or flat depending on the choice of machine accordingly. Knitted fabrics exhibit better formability and in-plane shear resistance [13].

2.5.2 3D Woven Preforms 3D woven preforms have shown the capability of being preformed in near-net shapes minimizing the cost, reducing waste, labour, need for machining and joining. Some examples are shown in Figure 2.6. They offer higher delamination resistance, ballistic damage resistance and impact damage tolerance [5].

Figure 2.6 Examples of 3D woven preforms

A wide range of fibre architectures can be made through the 3D weaving processes, out of which angle interlock and orthogonal are most common. 3D woven preforms permit the possibility of hybrid composites [14].

Filling yarns Filling yarns Stuffer Warps Stuffer Warps

Binder Binder Warp Warp Figure 2.7 Angle-interlock and Orthogonal weave architecture

Mouritz [14] reported that composites with 3D woven preforms have limited commercial applications despite their distinguishing performance, enlisting only in manhole and the roof of ski chair lifts. There is only one structural application in aircrafts, which is the H-joint connectors in wing panels, and there are minimal uses in medical applications such as leg prosthesis. Additional applications in aerospace components are turbine engine thrust reversers, rotors, rotor blades, insulation, structural reinforcement, heat exchangers, rocket motors, nozzles and fasteners, engine mounts, T-section elements for primary fuselage frame structures, rib, cross-blade and multi-blade stiffened panels, T- and X-shape elements for filling the gap at the base of stiffeners when manufacturing stiffened panels, leading edges to wings.

3D woven composites are still incapable to replace 2D composites in structural applications. Besides many other reasons, one of the major inadequacies is the absence of bias yarns resulting in low shear and torsion properties. A number of researchers have reported stiffness of 3D composites are similar to 2D where as the tension and compression strength are lower by 15-20 % than 2D due to crimp and in-plane fibre distortion. Yet Mouritz expressed the lack of databases and information of 3D woven composites, on account of which the designers and manufacturers seem reluctant towards the potential utilization as they encounter difficulties in making reliable predictions and models [14].

Some issues hindering the use of 3D woven composites are:

 difficult and expensive to manufacture quasi-isotropic 3D woven composites,  3D woven composites generally have lower tension, compression, shear and torsion properties,  in-plane mechanical properties and failure mechanisms of 3D woven composites are not well characterised,  validated methods are not available for predicting many of the properties and long- term durability of 3D woven composites,

2.5.3 Multi-Axial Textile Preforms Multi-axial states the numbers of axes along which fibres or yarns are oriented within a textile preform. A 3D textile preform may have three or even more axes. Fibres/ yarns may be inclined at various angles within a three dimensional frame of reference, acquiring the shape of a 3D object. It is clearly demonstrated in Figure 2.8.

Figure 2.8 Possible axes, and fibre architecture in a 3D cube of textile preform

The requirement of achieving various fibre architectures and weave patterns to give desired characteristics to the preforms for their respective application led the researchers to develop multi-axis 3D woven preforms. K. Bilisik states that 3D multi-axis woven preforms having multi-layers exhibit no delamination on account of z-fibres and enhanced in-plane properties due to bias yarn layers, though it is in early phase of automation [26].

A specialized sub group of 3D woven composites, termed as ‘distance fabric’, is in the form of two layers interlocked with one another at a certain distance as shown in Figure 2.9. Some researchers also classify them as 2.5D woven structures. On the basis of better mechanical properties they are a good alternative to foam and honeycomb materials.

Figure 2.9 Distance fabric

2.5.4 3D Knitted Preforms Composites reinforced with knitted preforms may be categorised as sandwich, non- crimp, and near-net shape composites. Composites with knitted preforms have better drape and energy absorption capacity but poor flexural stiffness. Instead of structural applications these composites are more successfully applicable in structures such as bicycle helmets as shown in Figure 2.10. Knitted composites are cost effective with off axis reinforcement, having better formability and can be moulded into more complex shapes. However, they exhibit lower stiffness and strength. Knit preforms has been less utilised as reinforcement in textile composites. Only a niche of applications like curves and domes is found so far [14, 13, 27]. Knitted composites still need to be understood for better prediction of their properties. Machines for manufacturing knitted preforms are still in the phase of development.

Figure 2.10 3D knitted fabric for helmet

3D knitted preforms make use of laid-in yarns in the orthogonal direction to achieve the goal strength. Multi-axial warp knits are similar to unidirectional laminates in characteristics but exhibit improved through the thickness stiffness and strength [1].

2.5.5 3D Stitched Preforms Stitched preforms incorporate high strength sewing yarn through the thickness of prepreg or dry laminates. Stitching has been investigated as an alternative to binder or rivet in composite applications in aircrafts on the basis of its higher degree of joint strength. Stitched preforms are less expensive, with improved damage tolerance, delamination resistance and inter laminar fatigue resistance. However, stitching comes in combination with other preforming techniques. Stitching of thicker and curved composites, degrading in-plane properties, ageing and stitch durability are weak aspects of these preforms.

Figure 2.11 Various stitched preforms

The processes of weaving, knitting and stitching have limitations of poor shear resistance, exhibit reduced strength in primary loading direction and are unable to produce net-shaped preforms [28].

2.5.6 3D Braided Preforms The fundamental principle of 3-D braiding is the mutual intertwining or twisting of yams drawn from yarn carriers arranged in an array on a braiding bed (rectangular, annular, or cylindrical), whose leading ends are joined together at a certain distance perpendicular to the plane of yam carrier bed [29]. 3D braided textile preforms can be manufactured either by conventional horngear braiding or by modifying conventional braiding techniques. Other recognised methods are 2-step [30], 4-step [31], row and column [32]. Yarns braided by means of any of these methods are offset oriented. Braided preforms, on account of diversity of manufacturing configurations, offer a wide range of fibre architectures as shown in Figure 2.12. The mechanical properties of braided composites generally depend upon yarn size, orientation, spacing, fibre volume fraction and braid architecture.

Figure 2.12 Braid architectures [34, 35]

Composites with woven, knit and stitched preforms offer poor shear resistance, low strength against primary loading and incapability of producing complex shaped structures compared to those with braided preforms. [13]. Braided preforms can be tailored into more complex 3D shapes than any other textile preform. Complex braided preforms can easily be produced in near-net shapes of the required finished products, eliminating the need of trimming and post process machining [33]. A variety of shapes including hollow, tubular, solid, and I-beams can be manufactured for composite applications [34]. Some of these are shown in Figure 2.13. 3D braided composites offer better shear, torsional and out of plane properties, inexpensive manufacturing, higher delamination resistance and impact damage tolerance [14]. One major limitation of braided preforms is the production of small sized narrow preforms, in addition to lower stiffness and strength compared to 2D laminates [14], poor in-plane properties, and slow production rate [14, 30]. F Schreiber presented in his paper that 3D circular and

34 multilayer braided preforms can effectively be utilised in lightweight applications and medical prostheses [27].

Figure 2.13 Braided shapes [28]

2.5.7 Filament Wound Preforms Filament wound preforms are usually circular preforms in which the fibres are either in helical spiral shape or in hoop formation. Filament wound preforms generally acquire the shape of the object over which they are wound. They may have uniform or variable diameter or cross-section. Composites with filament wound preforms have potential applications like pressure vessels, storage tanks and pipes, rocket motors, launch tubes, drive shafts etc.

2.6 Textile Preforming Techniques Various textile preforming techniques such as weaving, braiding, knitting, stitching and a combination of two or more of these are in use currently. Each of these has its own importance and potential regarding various features during and post manufacturing.

2.6.1 Weaving Weaving has been traditionally used for bi-axial textile fabrics in significantly wider widths. Many papers have been published revealing the mechanisms specifically designed for the manufacture of 3D woven preforms. The leading names are Mohamed et al, Bennister and Herszberg [14].

A set of warp yarns (0o) is supplied to the weaving machine from a creel of warp spools individually or from a small number of cylindrical beams in the form of sheets. The warp yarns are passed through a lifting mechanism that is controlled either mechanically or electronically, which is responsible for lifting and lowering the particular warps

35 according to the pattern to be woven. The wefts are inserted from one side of the machine at right angle to the warp (90o). The weft insertion may be single weft or multiple weft insertion systems. Warps may also be either stuffer yarns or binder yarns or both. The binders may be introduce both warp way or weft way and they serve as through-the-thickness yarns along the z-axis. A simple demonstration is given in Figure 2.14.

Binder yarn Filling yarns

Warp yarns

Figure 2.14 3D Weaving demonstration

The speed of manufacturing is the major strength of weaving. It has been exploited to produce 3D textiles successfully by minor modifications to the existing technology. Subsequently a number of specially designed weaving machines have been developed which is a significant progress towards textile composites. The limited scope of versatility in shapes and forms of the textile preform has been a major drawback.

Fetterly in 1910 [35], developed a multi-layer woven fabric as an evolutionary step towards 3D-woven preforms. The fabric as shown in Figure 2.15 is a fantastic attempt. It was possible simply by playing with weave designs of the fabric and shedding on a conventional weaving machine.

Figure 2.15 Multi-layer fabric [35]

In 1974, Fukuta [31] designed a weaving machine for a real 3D-fabric with 3-axes in which he made use of z-axis yarns as shown in Figure 2.16. The z-axis yarns served as binder which themselves were held and locked by way of a stitching needle.

Figure 2.16 Fukuta’s machine for 3D fabric [31]

The fabrics produced by Fetterly and Fukuta are having 3-axes. 3D fabrics with more axes were attempted later on. Anahara et al [36-37] disclosed a method of 3D fabric formation consisting of 5-axis. This method employed a warp layer, sets of bias threads and a vertical thread arranged perpendicular to the warps and double inserted wefts. Vertical yarns serve to tie up all of these sets of yarn together. The apparatus and procedural scheme for fabric formation is shown in Figure 2.17.

Figure 2.17 Annahara’s 5-axes 3D fabric and its method [36]

Another method of fabricating multi-axial fabric architecture was presented by Kimbara et al in 1991 [38]. The process includes the grouping of warp yarns together by a pultrusion process. Several such rods were arranged in a hexagonal array and interlaced by three sets of rods at an angle of 60º. The fabric architecture is shown in Figure 2.18.

Figure 2.18 Kimbara’s 3-D fabric architecture [38]

Muhammad [39], in 1995, developed a machine to produce 5-axes 3D woven fabrics as ◦ shown in Figure 2.19. The concept employs 3 groups of yarns along the x-axis (0 & ◦ +45 ), one group along the y-axis and one group along the z-axes. The produced ◦ preform has two outer layers of oblique threads on each side at +45 orientations. These layers would be least useful for the tensile strength of the preform but would certainly increase the shear strength along the x-direction, compared to that of Fukuta’s preform.

Carrier for straight X- Needle for Z- yarns yarns Carrier for +/- X-yarns Fabric Take Up

Needle for Y- yarns

Figure 2.19 Machine developed by Muhammad for 5-axes 3D-fabric [39]

Khokar [40] designed a process of making a 3D fabric without using binding threads but minimizing the risk of delamination as shown in Figure 2.20. He termed it as true 3D fabric. According to Khokar’s model a true 3D fabric must always have mutual interlacing between all the three orthogonal yarn sets. He gave a new concept of shedding with a dual shedding system. In this model the first shedding is for normal

38 horizontal weft insertion (along y-axis) and second shedding is for vertical weft insertion (along z-axis). The distance between the two consecutive warps determines the shed size which may be decreased to a minimal enough for insertion of weft carriers. Beyond this limit the shed opening would not be sufficient to accommodate carriers and hence a limited warp density would be achieved.

Figure 2.20 Khokar’s 3D woven fabric [40]

2.6.2 Tubular Preforming Techniques Either 3D preform or multi-layers of 2D preforms can be used to make a tubular composite. Commonly used methods for tubular preforming are filament winding, wrapping of 2D woven fabric and braiding. Braiding and filament winding independently and/ or collectively can produce tubular preform. Dry fabric wrapping method is adopted for the manufacture of composite tubes using quickstep method [41].

2.6.3 Filament Winding Filament winding is a method of producing non-interlaced preform especially for cylindrical structures. Filament winding process has been in use since mid-19th century [42]. The applications of filament wound composite structures include aerospace, hydrospace, military, industrial pipelines for fuel [42], pressure vessels, storage tank, tube or solid rods, drill pipe [43], drive shaft, natural gas transportation [44], rocket motor case, tent pole, fishing rod etc.

In the process of filament winding the continuous fibres are accurately positioned in a prearranged pattern to form a cylindrical shape. The continuous fibre reinforcement is laid down at high speed to produce a preform with a specific winding pattern. Generally

39 filament winding machines make use of a resin bath to wind pre-impregnated fibres. The delivery assembly traverses laterally whereas the mandrel rotates on its longitudinal axis.

Winding layers

Nip Rollers Winding layers Resin Bath

Traverse Moving Carriage

Fibres from Creel

Figure 2.21 Schematic of filament winding

Figure 2.21 shows a basic filament winding process. A number of fibres are pulled from a series of creels and tensioners that control the tension of the fibres into the resin bath. Once the fibres are thoroughly impregnated and wiped, they are collected together in a flat band, passed through the carriage and located on the mandrel. The traversing speed of carriage and the winding speed of the mandrel are controlled to generate the desired winding angle patterns. After the appropriate number of layers has been applied, curing is carried out in an oven or at room temperature, after which the mandrel is removed. Figure 2.22 is another view of real time simple winding machine.

Traverse Cross wound track layers

Mandrel Fibre spool on Resin bath creel

Figure 2.22 Schematic of winding [45]

Such winding machines carry out helical winding, hoop winding and polar winding. Figure 2.23 has clearly shown the basic difference among them.

Hoop Hoop winding is circumferential winding normally with an angle just below 90° degrees. For hoop winding the fibre can be wound at an angle between 5° and 89° [46] by controlling the mandrel rotation and traverse speed of delivery assembly.

Helical The fibres are placed in the form of a helix at a certain angle and the second layer cross wind the first one making full fibre coverage. Helical winding can be carried out within a range of 0° to 90° of winding angle [47].

Polar Fibres are wound pole to pole where the fibres constrained by bosses on each pole of the component.

Polar winding

Helical winding

Hoop winding Figure 2.23 Three basic winding patterns

Multi-Axis Winding Machines

Six axis winding mechanisms have been developed by various companies like Magnum Venus Plastech, McClean Anderson. Likewise a 6-axis winding robot ‘Kuka’ developed by a French company MF Tech, incorporates 8-axis motion [48].

Axial Fibre Placement

As axial (0°) fibre placement has been a limitation of filament winding machine, so additional parts are used for this purpose. A pair of pin wheels is used by Rousseau et al. [49] to produce unidirectional structures. The schematic is shown in Figure 2.24.

Teflon coated mandrel End-cap Pin Ring

Figure 2.24 Pin wheels for placing unidirectional fibre using filament winding [49]

An equipment called ‘L-O-T-U-S’ was developed in Brigham Young University, which has a spinning wheel with 4-axes of motion control and it is capable of filament winding of various shapes that resembles the letters itself [50].

Figure 2.25 First prototype of LOTUS [51]

2.6.4 Braiding The mechanical complexity of the preforming techniques, the cost and adoptability of the machines for various fibre architectures, the modelling for predicting properties and post impact behaviour of the composites are the main hindrances to the commercialisation of textile composites on a larger scale. 3D textile braiding has been found versatile amongst the textile preforming techniques. A wide range of near-net shaped complex structures offers higher out-of-plane properties, greater delamination resistance, and diverse inter-twining patterns, and these are the characteristic features of the techniques which make it more attractive for researchers.

Braiding has been considered to be less adaptable than weaving for technical textiles as textile composites. Previously braids were roughly meant for ropes, hoses etc. However,

43 over the last 50 years, braiding has been realised to have great potential in the preforming of textile composites in a versatile mode with greater flexibility in the shapes, forms, architectures and mechanical properties. Braiding may be categorized as 2D or 3D.

The 2D braiding machines are either vertical or horizontal according to orientation of the track plate. The simplest braid can be produced by using 3 counter rotating bobbins mounted on the carriers e.g. soutache set-up [52]; the largest 2-D braiding machine commercially available has 800 carriers [53]. Braids with 0° fibre are called as tri-axial structures and those without the 0° fibre are termed as biaxial structure as shown in Figure 2.26.

Fig 2.26 Biaxial and tri-axial braids [54]

There are two basic principles of fabricating 3D braids.

1. Horn-gear braiding principle 2. Cartesian braiding principle

The chief distinction between the two is the yarn carrier displacement method [1, 55]. In case of Horn-gear the yarn carriers follow sinusoidal path along the circular track in a maypole inter-twining pattern. Whereas, in the case of Cartesian braiding sets of the yarn carriers move along the track in rows and columns perpendicular to each other. Horngear braiding is faster compared to Cartesian type braiding [1].

2.6.4.1 Horngear Braiding Horngear braiding works at the pattern of maypole dance. A simple braiding machine as shown in Figure 2.27 comprises a braiding bed with two sets of yarn carriers. These sets

44 of yarn carriers move in sinusoidal waves in opposite directions to each other along the circular track plate as shown in Figure 2.28b. The drive to the yarn carriers comes from horngears beneath the track plate, which are intermeshed with one another. An arrangement of horngear with yarn carrier demonstrating the mechanism of horngear braiding is shown in Figure 2.28a. A mandrel may or may not be used through the centre of the machine. Axial yarns passing through the centre of the horngears may also be incorporated in the braid.

Figure 2.27 Horngear braiding machines [56]

Figure 2.28 (a) Horn gear with yarn carrier arrangement [54]; (b) track plate showing the carrier path [57]

Horngear braiding is faster compared to Cartesian type braiding. Though the braiding beds may be circular or rectangular, the number of yarns being used (both axial and braider) are limited resulting in inadequate shapes and sizes of the preforms [1].

To overcome the major shortcomings of braided preforms, a number of attempts have been made including AYPEX, Interlock twiner [58], 2-Step [30], 3D Solid [59], and Cartesian [32]. Out of these, the 3D solid braiding and Cartesian braiding seem to be the most leading techniques.

Advancements in braiding technology have exploited the architectural benefits of braided reinforcements. In the last couple of decades the use of braided reinforcements for large structural preforms has been increased significantly. Until recent past, filament winding, automated tape layup, and fibre placement have been the known techniques used for the manufacture of large, composite aerospace structures where as braiding has not been considered as capable to produce mega-structures. In 2000 [60], after successful designing of a series of large braiders, A&P Technology constructed a mega- braider named as Mantis as shown in Figure 2.29. This braider is claimed to reduce setup time and some added benefits like integral hoop winding. This rapid growth is very likely to lead to new generation of braiding machinery concepts for large composite structures.

Braiding yarns

Large Mandrel

Figure 2.29 Mega-braider for up to 100 inches diameter and 15 feet long mandrels

FJ Cimprich et al in 1981 [61] constructed a braiding machine for the manufacture of braided hoses. The machine comprised at least two braiding beds where the rear deck is connected to the front deck. A demonstration with three decks is shown in Figure 2.30. The concept is a good example of over stacked multi-layer braided elements.

Figure 2.30 A side view of three deck braiding set-up

Brookstein et al in 1994 [62] devised a method of braiding solid structures using the conventional horngear braiding principle with a modified configuration of the bobbin carrier track in accordance with the structure to be produced. The main feature of the invention is to impart layer-to-layer interlocking of the solid braided structure a shown in Figure 2.31. The layer-to-layer interlocking of the braid is more or less similar to stitched multilayer woven fabric. The invention also claims the capability to produce various shapes of the braided structures like I-beams and hollow circular braided structures as shown in Figure 2.32. The yarn carriers follow serpentine path along the track designed for a particular shape to be braided. As the yarn carriers move along their defined track, they interlace with yarn carriers of the adjacent track by shifting onto that track and then after a certain length reverse to their own track. Another feature of the invention is the use of linear yarns inter-braided by moving packages.

Figure 2.31 Demonstration of two inter-locked layers with cross over points

Figure 2.32 Configuration of the braiding bed for an I-beam

Brookstein et al 1996 [63] presented another extended version of braiding layer-to-layer interlocked braided structures. The yarn carriers follow sinusoidal path along the track designed in a circular configuration. The invention consists of a number of sinusoidal yarn paths. The drive comes through horngear to the yarn carriers whereas the horngears are driven by electric or pneumatic drive via driving shaft. As the yarn carriers move along their defined track, they interlace with yarn carriers of the adjacent track by shifting onto that track and then after a certain length reverse to their own track. Another feature of the invention is the use of linear yarns inter-braided by moving packages. The invention claims the capability to produce shapes of the braided structures with hollow, circular or irregular cross sections. Figure 2.33 shows the front view of the apparatus with drives in the corners and a horngear braiding track for two adjacent layers with a cross over point.

Figure 2.33 Apparatus and braiding track for two layers with a cross over point

Yasu Akiyama et al, in 1995 [64] developed a braiding method, using horngear braiding track and consisting of moving yarn carriers along a plurality of braiding regions in such a way that all these regions are connected with one track. The braid so produced may be cords or strands or even various shapes depending upon the configuration of the regions on the track as shown in Figure 2.34. The inventor claimed specifically the formation of H-shape braided structures as shown in Figure 2.35.

Figure 2.34 (a) Configuration for a circular braid with another layer inter- connected in the core (b) A circular solid braid

Figure 2.35 Braiding bed configured in two regions for an I-beam shaped structure

2.6.4.2 3D Solid The 3D rotary system of braiding as shown in Figure 2.36 is capable of fabricating net shape braided preforms with better adaptability for various configurations of yarn interlacements. The method permits each yarn bobbin to move or remain in position independently on the base plate. Horngears and gripping forks are the key parts of the system to translate the drive to the yarn carriers. Through this selectively controlled mechanism for machine operation, the technique has the potential to develop a range of

49 braids with different shapes and cross sections. Axial yarns can also be added to the structure [65].

Braid point

Braiding Bed

Figure 2.36 3D Solid braid configuration [59] & 3D solid braiding machine [60]

Makato Tsuzuki in 1991 [61] devised an apparatus for making three-dimensional solid braids. The apparatus comprises a plurality of a large number of rotors disposed in rows and columns. The rotors are holding yarn carriers in such a way that two rotors are responsible for holding a particular yarn carrier in combination where one rotor is to move the yarn carrier while the other is to guide it along with. The yarn carrier is, thus moved along a predetermined track path between rows and columns. It is important to know that at a time one rotor may hold more than one yarn carrier as each rotor has a provision for four yarn carriers around its circumference. A demonstration of rotors and yarn carriers movement is shown in Figure 2.37. The unique feature of the invention is the movement of a large number of carriers on their respective predetermined path independently. By repeating the cycle of movement a 3D solid structure is braided in a variety of shapes depending upon the configuration of the travelling surface and programming the movement of each individual yarn carrier by controlling the motion of rotors and propellers. The machine is potentially capable of producing I-beam, T-beams, circular objects and double layered 3D structures with channels through. Figure 2.38 shows circular and rectangular braiding bed configurations.

Figure 2.37 A demonstration of rotors and yarn carriers movement

Figure 2.38 Circular and rectangular braiding bed configurations

Mungalov et al. [68], in 2002, developed a 3D braiding machine for producing complex shaped 3D braided structures. These braided structures are seamless, integral and unitary that may even be of variable cross sections along the axis of the braid. A variety of shapes have been claimed by the inventor, such as T and J-stiffeners, I-beam and box-beam structures, tubular and circular cross sectional structures and engine valves. The method includes a set of axial straight yarns interlaced with another set of braiding yarns. The machine consists of at least one module that comprises of at least two horngear, two carrier drivers and a rotary gripping fork. A computerised control system for a predetermined pattern to be achieved is used for the carrier movement through the horngears and gripping forks. The machine layout, mechanism and braiding bed configurations are shown in Figures 2.39~ 2.41.

Figure 2.39 Mungalov’s 3D braiding machine

Figure 2.40 Featured machine parts of Mungalov’s 3D braiding

Figure 2.41 Braiding bed configurations for different shapes

In collaboration between the Advanced Fibrous Materials Laboratory (AFML) of University of British Columbia, Vancouver (Canada) and the Institut für Textiltechnik (ITA) of RWTH Aachen University, Aachen (Germany), F. Schreiber, K. Theelen, E.S. Sudhoff, H.Y. Lee, F.K. Ko, T. Gries developed a novel and unique hexagonal braiding machine.

According to the authors, the new braiding mechanism is capable of fabricating complex shaped two-dimensional and three-dimensional composite structures. The braiding process is based on a hexagonal principle and the authors expect it to be a new family of complex fibre architectures especially for medical applications [27, 69]. The 1st generation of the 3D-hexagonal braiding machine is claimed to be capable of handling micro filaments and manufacturing complex shaped three-dimensional braided structures. The 2nd generation of this braiding machine is introduced with an additional feature that two carriers can take position between two cams and thus the number of carriers can be increased significantly. Snapshot view of the braiding bed and yarn carrier arrangement of 1st and 2nd generation machines are shown in Figures 2.42 and 2.43.

Figure 2.42 1st generation hexagonal braiding machine with single carrier position

Figure 2.43 2nd generation hexagonal braiding machine with two carrier positions

The concept claims to produce braiding patterns for solid and multilayer 3-D braided structures with various shapes in comparison to common 3-D rotary braiding machines. Chief advantages of this work could be the possibilities in preform production for lightweight and medical applications. Figure 2.44 shows various braid patterns for 3D solid round and triangle structures with yarn groups.

Figure 2.44 Braid pattern for 3D solid round and triangle structures showing yarn groups In another study, Alexander Bogdanovich and Dmitri Mungalov [70] explained their own concept of a novel 3-D rotary braiding process and shown certain advantages over other 3-D rotary braiding machines. Particularly they emphasized a novel type carrier switch mechanism that makes possible the interchanging of two yarn carriers simultaneously between adjacent horngears. Minimizing of the ratio of the machine bedplate size to the product cross-section size and the flexibility to manufacture variable cross-section preforms are the major advantages of the mechanism. Figure 2.45 is top view of horngears showing the switching mechanism of yarn carriers.

Figure 2.45 The yarn carrier switch mechanism

2.6.4.3 Cartesian Braiding Cartesian braided composites are known for excellent shear resistance, quasi isotropic elastic behaviour, low stiffness and strength and high Poisson effect. The poor characteristics are supposed to be because of lack of axial yarns [1].

In Cartesian braiding, yarn carriers are displaced along a linear track on the planer braiding bed through a certain distance both along x-axis and y-axis alternately. The resultant trajectory of the yarn carriers is in the form of a zigzag route. In general, 4-step Cartesian motion is in small steps. However, in case of 2-step braiding, the braiding yarn carriers travel across the width of the braiding structure diagonally but in straight line along the same two axes perpendicular to each other.

2.6.4.3.1 Two-Step Cartesian Braiding 2-step braided composites comprise of axial yarns intertwined by braider yarns [4]. An array of axial yarns are arranged on the machine bed and a fewer number of braiding yarns arranged at the periphery entangle the axial yarns. Axial yarns give a specific shape to the article being produced [30].

2-step braided composites show higher stiffness and axial strength with improved out of plane properties. These characteristics are attributed to axial yarns intertwined by braider yarns [4].

In 1988, McConnell at el [30] devised an apparatus for manufacturing complex shaped 3D braided structures. The machine as shown in Figure 2.46, comprises an array of axial yarns arranged on a rectangular machine bed with a fewer number of braiding yarns. The axial yarns give a specific shape to the article being produced.

Figure 2.46 2-step Braiding machine developed by Ronald F McConnell et al.

The braiding yarns are arranged at the periphery, which pass in-between the axial yarns across the structure in a 2-step Cartesian fashion. The braiding yarns pass across the axial yarns first along one diagonal direction and then along a direction perpendicular to the first, every time reversing to a point outside the array. At a time all the braiding yarns are situated at the peripheral points. Paths followed by yarn carriers on 2-step braiding bed are shown in Figure 2.47.

Figure 2.47 Two-step braiding bed with carrier paths [30]

The inventor claimed the capability of the machine to braid various structures including I-beams, T-beams, hollow structures, and structures with varying cross section along its length. Furthermore McConnell at el claimed to mould the articles in a curved shape

56 and also made use of rubber rods instead of a few axial yarns to be removed afterwards so as to create structural voids.

In 1990, Du et al [71] developed a braiding machine capable of preforming a diversity of braiding tasks. The machine is composed of interchangeable track units and it employs one or more self propelled bobbin carriers following the track. The self propelled bobbin carriers are energised by means of electrical arrangements established on the bed and the bobbins. The power supply points are provided beneath the braiding bed. A number of axial yarns are arranged in a specific order so as to produce a particular shaped article. The braiding yarns are doing the job of interlacing the entire structure. The machine and tack plate are shown in Figures 2.48 and 2.49.

Figure 2.48 Braiding machine developed by Du et al.

Figure 2.49 Track plates of the machine

2.6.4.3.2 Four-Step Cartesian Braiding Cartesian braiding machines can braid preforms with compact size, which are more economical and architecturally flexible. The preforming of thick and complex shapes, near-net shapes and delamination resistant structures are the distinguishing features of

Cartesian braiding [1]. Composites reinforced with 4-step braids exhibit outstanding shear strength and quasi-isotropic properties on account of their symmetric interlaced architecture [4]. The braided composites with axial yarns possess better tensile, compressive and flexural properties. The lower compression properties of 4-step Cartesian braid owe to waviness in the braiding yarns [72]. A schematic of 4-step Cartesian braiding is shown in Figure 2.50.

Braided preform

Braiding yarns

Yarn carriers

Machine bed

Figure 2.50 Cartesian braiding arrangement

The Cartesian braiding process comprises four distinct steps of yarn carrier movement in rows and columns which is reflected in Figure 2.51. The alternate row (or columns) are moved a predefined distance respective to one another along the horizontal (or vertical) direction where as in the next step the columns (or rows) are moved a prescribed distance respective to one another along vertical (or horizontal) direction. The subsequent two steps are just reverse shifting of the row and columns respectively. All the four steps constitute a complete machine cycle, which repeats continuously as the machine keeps running.

Figure 2.51 Cartesian braiding process [1]

Using a simulation of 1x1 4-step Cartesian braiding, T.D. Koster and T.W. Chou [4] established that the yarns follow the same path as traced by yarns in the 2-step braider.

A general braiding machine consists of five main parts namely: machine bed, actuating system, take up motion and compaction system, yarn carriers and a control panel. The braid is formed at a set distance from the machine bed either on top of the machine, in case of a vertical braiding machine, or horizontally on one side of the machine, in case of a horizontal braiding machine. Mechanical actuating systems are old fashioned, and the pneumatic actuating systems, being programmable, seem more appealing.

The braid to bed ratio is still a question to be fully exploited as it limits the braids cross sectional dimension greatly. Though some attempts [12] are made, it is wiser to consider the optimization of the length and size of the cross section.

The take-up followed by compaction, performed after every machine cycle, plays a vital role in determining the pitch length and hence the fibre orientation angle within the braid. So the degree of compaction decides the orientation angle which is held by the cohesive frictional forces and interlacing of the fibre.

Pattern of Braiding

A braid pattern refers to the shifting distance of row and columns alternately. If both rows and columns are moved a distance equal to one position, the pattern so fabricated will be 1x1. A variety of patterns can be adopted as per requirements of the architecture and the end properties to be induced e.g. 2x1, 1x2, 2x2.

Multi-Step Braiding Machine

The braiding machine cycle may be prolonged to more than four steps to complete one set of operations that repeats. Such a machine comprising of many steps in one cycle is termed as a multi-step braiding machine.

A prototype of a multi-step braiding machine developed by T.D. Koster and T.W. Chou [4] has a capacity of holding 240 yarn carriers and 207 axial yarns. The machine is capable of manufacturing 2-step, 4-step and innovative braids, hence proving that 2-step braiding and 4-step braiding are special cases of multi-step braiding. The prototype machine with an eight step machine cycle is shown in Figure 2.52.

Figure 2.52 A prototype of multi-step braider with Eight-step 1×1 braid cycle [4]

A variety of yarn architectures, hybrids, shapes and forms are expected to be produced using Cartesian braiding machine subject to the establishment of the multi-step machine cycle, independent movement of rows and columns, and non-braider yarn insertion.

In 1969, Bluck et al [73] demonstrated a continuous high speed bias weaving and braiding machine with optional longitudinal yarns as shown in Figure 2.53. The inventors claim roughly a 90o sweep of the yarn orientation from perpendicular to parallel to the axis of the preform. The individual yarns pass through separate segments, termed as guide member, which can move both in horizontal and vertical axis of the machine bed. The guide members are propelled through an old fashioned cam operated actuating system driven by a single rotary drive. The guide members return to their starting point by reversing on the same path they followed to repeat the operation and so on. Hence, the articles so formed will have a certain pattern of architectures.

Figure 2.53 Cartesian braiding machine developed by Bluck et al.

A range of bias woven and braided preforms including I-beams, double skin structures interlinked in various types of linking, and double skin panels provided with cylindrical longitudinal tubular passages, are claimed to be produced.

In 1982, Florentine [32] devised an apparatus for weaving 3D articles. The machine, shown in Figure 2.54, comprises an array of cubical yarn carriers arranged on a rectangular machine bed.

Figure 2.54 Cartesian braiding machine developed by Florentine

The yarn carriers hold yarn spools for preform fabrication. The rows and columns are operated through solenoid controlled actuating systems being operated alternately by energizing the desired set of actuators. Unlike Raymond, the yarn supply does not pass through the machine bed; rather the spools are mounted onto the yarn carriers directly on the machine bed. The cubical blocks are further supported to hold themselves strong by means of magnets situated in their sides, with adjacent blocks contain magnets of opposite poles as shown in Figure 2.55. Figure 2.56 shows zigzag path followed by the blocks as a result of row and column movements.

Figure 2.55 Cartesian braiding blocks with magnets and bobbin on the top

Figure 2.56 Yarn carrier paths on Florentine rectangular braiding bed

Florentine also presented a modified braiding bed in circular form as shown in Figure 2.57. It consists of a number of yarn carriers arranged in concentric circles with clearly defined radially extending rows of yarn carriers. It is capable of producing hollow structures.

Figure 2.57 Yarn carrier trajectory on Florentine circular braiding bed

K.L. Krauland in 1989 [74] developed a simple Cartesian braider with an addition of intermediate self supporting elements that guide the braiding yarns. A floating braiding carriers’ creel is provided on the bottom with a similar configuration in accordance with the self supporting elements. It is imperative that movement of both the braiding creel and the self supporting elements is synchronous. Figures 2.58 and 2.59 depict the concept.

Figure 2.58 A schematic arrangement of row and columns on the braiding bed

Figure 2.59 an array of self supporting elements and floating creel

Toshihide Sekido et al in 1990 [75] devised a machine for weaving three dimensional article based on Cartesian braiding principle. The concept is mainly derived from those of Florentine and Bluck apparatus. The inventor has presented two versions of the concept. Both are similar with regards to the main central arrangement of the Cartesian braiding bed in the form of an array of yarn guides arranged in rows and columns. In the first version, the yarns pass through the yarn guides and are held by take up means on both sides under controlled tension. As the apparatus works, the structure is braided on both sides. In second case, the yarn packages are mounted on one side of the braiding bed and the yarns pass through the guide members and are taken up from the other side of the bed. As the machine braids an article, intertwining of yarns occur on both sides. So a limited length of article is feasible to be braided. A braiding bed and both the versions of the machine are shown in Figures 2.60~ 2.62.

Figure 2.60 A Cartesian braiding bed with yarn carrier trajectory on it

Figure 2.61 Set-up-A with take-up on both side and braiding bed between them

Figure 2.62 Set-up-B with creel on one side and take-up on the other

In 1993, Farley and Huey [76] reported that all of the previously designed Cartesian methods were restricted to the braiding patterns in relation to the mechanical complexity.

They proposed two processes based on the following four requirements:

 A completely general braiding machine capable of moving any yarn carrier from one position to any other on the bed.  Practicable control and construction of large sized beds.  To achieve a large number of axial and braider yarns.  To minimise the overall size and the cost.

The first process termed as “Farley braider” is composed of an array of rotors that can oscillate in 90o steps. At a time they all are aligned along one axis (e.g. x-axis) when they are propelled by way of a gear train controlled electronically. These segments are then rearranged perpendicular to the previous alignment and moved again. An entire braiding program is executed and the switching of the segmented elements is controlled by computer programming. A prototype of the machine is shown in Figure 2.63.

Figure 2.63 Prototype braider showing some basic components by Farley et al.

The second process is called as “shuttle plate braider”. The machine surface holds an array of stationary square blocks, with separating lines between them along both axes. The yarn carriers are moved in the desired direction by controlling them with a flat plate beneath these blocks. The plates beneath can move any of the carriers by engaging it in a particular direction. The braider has an electrical control on both the power and control systems. A sequence of motions, as an example, is shown in Figure 2.64.

(a) Both shuttles at rest.

(b) Right shuttle energized, plunger down.

(c) Shuttle plate shifted, shuttle carried to the right. Figure 2.64 Schematic representation of shuttle plate braider operation

The controlled action is a simple switching command to the actuators and is directly transmitted to the carriers. Hence, the braider grid size is claimed to be of no relation with the number of controlled devices.

Both the shuttle plate and Farley braider are capable of shifting a yarn carrier from any point to any other desired position on the bed. The authors claim this specification to be achieved for the first time. Both the braiders transmit the power to the yarn carriers through the braiding surface. The shuttle plate braider is mechanically simple and easy in its control, whereas the Farley braider is better in speed over the shuttle plate.

In 1994, Huey [77] demonstrated an apparatus for braiding based on the shuttle plate braider principle. The details are more or less the same as briefed in the Farley and Huey [76] research paper published in 1993.

Samir A. Nayfeh et al in 2006 [78] designed bias weaving machine comprising a number of bias yarn carriers that can move along the rows perpendicular to the weaving direction. The bias yarn carriers are mounted on vertical block that can rise up and lower down as configured to weave a particular pattern. It includes warp yarns disposed among the bias yarn carriers and serve for shed formation. The invention incorporates a shuttle for fill insertion perpendicular to the downstream direction. Interesting aspect of the invention is that it has combined two basic principles of textile preforming; weaving and Cartesian braiding. The bias yarn carriers operate in Cartesian manner whereas the warps and shuttle works according to simple weaving process. A compaction is ensured by providing a comb that can extend up to a certain distance. The concept is depicted in Figure 2.65

Figure 2.65 Schematic representation of Nayfeh bias weaving operation

2.6.4.3.3 Circular Braiding Machine In 1988, Brown [79] devised a braiding machine comprising a number of rings noticeably of the same size and diameter positioned alongside each other such that they are aligned in an axial manner. All the rings have a common axis about which they can move relative to one another. A number of yarn carriers are mounted in rows onto the rings which move a predetermined distance axially from ring to ring. The yarn carriers are supported from the sides at an angular distance of 90o.

The adjoining rings are rotated in opposite directions to each other and the adjacent rows of yarn carriers are displaced from one ring to the next but mutually in opposite directions. The degree of rotation of the rings and the extent of displacement of the carriers depend upon the pattern to be designed. These movements result in intertwining the yarns to form a braid on the same principle as that of the rectangular type of row and column braiders. The machine side and front views are shown in Figure 2.66 whereas the discrete element of the machine is shown in Figure 2.67.

Figure 2.66 Front & Side elevational views of circular braiding machine by Brown

The scope of the invention allows for the modification of the embodiments e.g. the rings may be made of discrete elements that replace the axial tracks as shown in figure. The idea for actuating the yarn carriers is the same as that in rectangular row and column braiders. However the rings may be rotated using suitable means.

Figure 2.67 Discrete elements of the ring for the fibre carrier on Brown’s machine

In 1990, Culp et al. [80] put forth a modified version of the circular braiding machine developed by Brown in 1988. The main distinguishing feature of the machine was the replacement of the ring members with flexible elements or belts. The yarn carrier members move through the slots provided in the belts. The accuracy of the movement of yarn carriers and alignment of the belts is monitored by sensors mounted on each belt. After the belts have been shifted and have attained a new position accurately, the yarn carriers are displaced through the belt slots in accordance with the predetermined distance. The scope of the invention permits the use of flexible chains comprising links and pins instead of flexible elements also. Some of these modified belts are shown in Figure 2.68.

Figure 2.68 Side views of portions of the modified belts

Kadir Bilisik and Mansour H. Mohamed [81] studied the feasibility of development of multiaxial 3D flat and circular preform architectures, which describes the characteristics of the circular preform and the way of preforming. The machine developed for making such preforms has already been patented by Bilisik in 2000 [82]. The Multiaxis 3D circular preform comprises five sets of yarns as +/– bias, axial, circumferential and radial yarns. Axial yarns arranged in circular rows are stationary. Circumferential fibres are positioned on concentric rings between each adjacent axial fibre row. Bias (+/–) yarns are positioned on both surfaces of the preform. The circumferential yarns are placed by rotating the rings. Radial yarns are placed between each axial row by way of special needles that move inwards and outwards alternately after every rotation of the rings, hence locking all the circumferential and bias yarns together. Figure 2.69 shows the machine and Figure 2.70 presents a multi-axial 3D circular preform along with an interlacement unit.

Take up

Multiaxis 3D circular woven Beat up preform Radial yarn Circumferential yarn

Circumferential

Radial carrier carrier

+/- Bias yarns Carrier bed

Axial yarn Guide plate

Bobbin plate Axial bobbins

Figure 2.69 Circular preforming machine

Radial yarn

Axial yarn

Circumferential + Bias yarns yarn

- Bias yarns

Figure 2.70 A multi-axial 3D circular preform and an interlacement unit.

As is a continuation of the principle Cartesian braiding machines, Ivsan [83] invented a braiding machine in which the fibre carriers were positioned equidistant from the braiding point as shown in Figure 2.71. The invention consists of a number of fibre carriers arranged on concentric quadratic surface. The fibre carriers are placed in specially designed channels or grooves of their respective quadratic surface, from where they can be moved to the adjacent one as per fibre architecture to be produced. A provision for the stuffer fibres to be incorporated is made sure in the mechanism.

Figure 2.71 An isometric view of the mechanism with equidistant fibre carriers

Hurst et al. [84], in 1992, invented a braiding machine with a different but very interesting concept. The machine consists of an annular rotor and fibre carriers as shown in Figure 2.72. The rotor has been provided with a number of slots along its periphery. The fibre carriers are mounted on the rotor such so they can slide smoothly on the rotor with the help of an assembly of gears and rack. Both the rotor and fibre carriers are made to rotate about the same central axis with the same speed but in opposite directions. The first spool of fibre is mounted on the rotor by means of a support fixed to the rotor between two consecutive slots. The second spool is mounted on the fibre carrier assembly. The yarn drawn from the first spool passes through a pivotal arm mounted on the rotor. The pivotal arm is responsible for positioning the yarn in the slots and then lifting it out as the fibre carrier assembly along with the second spool passes under the first yarn. Such an interchanging pattern of the yarns results in the intertwining of the yarn hence forming a braided structure. Both the yarns are taken to the centre of the machine where a mandrel or wire or alike is extending along the central axis.

Figure 2.72 Braiding machine developed by Micheal J. Hurst et al.

At Auburn a new braiding technology was developed to produce true tri-axial braids as they named it on account of the axial yarn’s interlacement with the helical braiding yarns. It is a rotary braider that incorporates axial yarns, and the two sets of oppositely rotating braiding yarns interlace with axial yarns, but not with each other. The axial yarns in these structures have crimp due to interlacement contrary to the conventional triaxial braid where the axial yarns are straight without crimp between braided yarns [87]. A snapshot photograph is shown in Figure 2.73.

Figure 2.73 True Tri-axial Braiding Machine John T Klein and et al in 1999 [85] developed a tri-axial circular braided fabric with axial stability. Such tri-axial braids are different from the conventional 2D tri-axial braids formed on horngear 2D braiding machines. Contrary to those braids, here in these

73 braids the two bias sets of yarns are not interlacing with each other. Whereas the axial yarns are interlacing with two layers of the bias yarns such that it goes over and under these sets of yarns alternately. However the mechanism and modifications to the braiding machine have not been disclosed. This invention addresses the interlocking of layers of bias yarns in a way that axial yarn is interlaced with only one layer of bias yarns but not the both layers and only axial yarns are serving for axial and binding purpose. Figure 2.74 weave architecture of the braids and a circular braided element.

Figure 2.74 Axially stable tri-axial tubular fabric and its interlacement pattern

W Scherzinger’s [86] circular braiding machine is a modified version of Hurst’s circular braider. The main difference lies in the mechanism for interlacing the fibres coming from the second set of spools. It makes use of a crank arm rotating at a preset rate so as to pass the rotation set of spools. As the crank arm rotates, another lever connected to it oscillates up and down in a slot with a fibre guide on top of the lever. Hence the fibre is lifted and lowered alternately as the first set of spools moves along the rotating track and thus the two sets of fibres are interlaced with each other forming s braided structure in the centre. An overview of the machine is shown in Figure 2.75.

Figure 2.75 Front view of the machine with inner rotating spools and outer interlacing spools

2.7 Critical Review & Conclusion After a thorough survey of the literature a number of key points and conclusions have been derived. It is quite obvious that textile composites have attained a significant position in the realm of advanced composite materials and high performance applications. The chief advantages of textile composites over other composites using isotropic reinforcements are their high strength-to-weight ratio, near-net shaped complex preforms, enhanced mechanical, flexural and torsional properties, better in- plane and out of plane properties, improved impact resistance, damage tolerance and resistance to delamination. Textile composites especially those reinforced with 3D textile preforms have been realised in the aerospace industry, marine, automobiles, biomedical and civil engineering as a dependable competitor. However, from a manufacturing point of view the research work on this subject is still insufficient and the testing database is limited.

The mechanical complexity of the preforming techniques, cost, adaptability of the machines for various fibre architectures, modelling for predicting properties and post impact behaviour of the composites are the main impeding factors for textile composites to be commercialised on a larger scale. 3D textile braiding has been found to be the most versatile of the textile preforming techniques. A wide range of near-net shaped complex structures, higher out-of- plane properties, greater delamination resistance, and diverse inter-twining patterns are the characteristic features of the techniques which make it more attractive for researchers.

An insight into the literature reveals that multi-axial 3D textile preforms are ranked above all textile preforms for high performance applications; however the choice of the preform chiefly depends upon the application.

Despite all these distinguishing features and characteristics, textile preforms have to be investigated for their structure-process-properties relationship. That is why a lot of research is aimed at devising new methods and processes to develop more and more compatible structures with various fibre architectures to optimise their properties.

3D woven preforms and their manufacturing methods have been a success to greater extent; however near-net shaping and complex manufacturing structures are still a distant milestone. Biased yarn placement has not yet been successfully exploited.

Filament winding has achieved a distinguished position in fibre deposition around large size structure and parts. As the fibres are placed in the form of layers which are simply cross-wound in successive layers, the structure may disintegrate under high pressure and loading. Moreover the technology is capable to insert neither axial yarn nor binders, compromising their tensile and impact properties.

The potential of 3D horngear, 2-step, 4-step, multi-step and circular braiding is comprehended. The 4-step Cartesian circular braiding technique has been a focal point during this study on account of its capability for multi-axial preforming and pertaining to future work.

Over-braided preforms developed by 2D circular braiding machines may be bi-axial or tri-axial and can be produced up to many layers of thickness. But these machines are unable to insert perpendicular yarn along the z-axis that can bind the layers together. The absence of binder yarns decreases the resistance to delamination and damage propagation once the damage starts.

3D solid braiding has been a successful step towards near-net and complex shape preforming. Whereas 3D braids, due to the absence of through-the-thickness yarn, suffer from shear, poisson effect and poor out-of-plane properties.

3D circular braiding has been attempted by several methods with distinctive specifications suitable for certain application. Generally these methods do not include through-the-thickness yarns in the braids leaving a certain aspect of the structure deficient.

In general all methods of braid preforming are facing certain challenges including aspect ratio i.e. braid-to-bed ratio, limited numbers of yarn carriers that constrains the braid cross section, limited length of yarn on spools that restricts the length of the braid element, mechanical complexity that is necessarily accompanied by many associated problems and draw backs, and its adoptability for various sizes and braid patterns.

3 CHAPTER 3 CONCEPTUAL DESIGN OF 3D

NOVEL MACHINE

3.1 Preliminary Concepts The final design of 3D novel textile machine has eventually been presented after a thorough exercise of various concepts one after the other for designing of a 3D textile manufacturing machine. These concepts have been demonstrated and modifications to the ideas have been presented and introduced into the final design of the machine. Each of these concepts has been evaluated for its advantages and shortcomings. The principle, working, key features and limitations of each of them have been briefly described in the following narration.

3.1.1 Concept-1: Cartesian Braiding with Continuous Supply of Yarn from a Creel A flat bed braiding machine working on row and column principal is presented with a continuous supply of yarn from a single package of yarn in the form of a beam or a set of beams. The apparatus comprises a braiding bed, comber board, beam/ set of beams, take-up mechanism, an automated compaction arrangement, braid locking set-up and a tension compensation system as shown in Figure 3.1.

Figure 3.1 Isometric view of the braiding machine presented in concept-1

3.1.1.1 Cartesian Braiding Bed A self supported braiding bed with a number of block units is designed as shown in Figure 3.2. The block units have through holes in their centre. All the yarns drawn from the beam pass through their respective blocks. The braiding bed is made considerably small in dimension in accordance with the braided structure cross section, minimizing the braid to bed ratio to a greater extent. The manoeuvring of row and columns displacement is more or less similar in its arrangement to the existing Cartesian braiding beds using any of the appropriate actuating systems. However, for a programmable braiding bed, pneumatic actuators are more suitable.

Pneumatic actuators

Braiding bed

Bobbin carriers

Figure 3.2 Cartesian braiding bed with pneumatic actuators

Instead of a plurality of yarn bobbins mounted on the braiding bed itself, a common single supply of yarn in the form of a sheet is introduced for yarn delivery that may not necessarily be parallel. The idea is to reduce the space occupied by a large number of individual bobbins by collecting the required number of yarns onto a large spool or a beam or even a set of beams. The beam may either be driven positively or negatively whichever is preferable as per requirement of the conditions under which it will be operated.

A comber board is being used that serves for positioning the yarns straight between the braiding bed and beam. The comber board ensures to avoid yarn entanglements and restricts it at a certain distance from the beam. Hence overlapping of yarns may not reach the surface of beam and cause fibre damage by rubbing and friction. The comber board may be designed according to the braid structure to be produced for keeping the yarns straight as possible. It can be made in rectangular, square, or any other required shape as shown in Figure 3.3.

Figure 3.3 Comber boards in rectangular and square shapes

3.1.1.2 Braid Locking Set-Up An additional arrangement is provided for locking the braided yarns within the braid structure after certain steps of the machine. A shuttle type yarn insertion system is provided in front of the braiding bed. Once the locking yarn has been passed through the braiding yarns, the Cartesian braiding pattern of intertwining is reversed, therefore, releasing the entanglements which occurred behind the braiding bed. The yarn withdrawn from the bobbin in the shuttle is interlaced with the braid structure. The locking yarns restrict the braid from opening on its reversal. The number of locking yarns may be more than one for an improved grip on the braided structure. Furthermore locking yarns may be inserted along two axes, both perpendicular to each other as well as to the axis of braiding.

Taking up of the newly braided preform away from the braid point is the same as in the existing braiding systems. A metallic comb with adjustable prongs is proposed for compacting the braided structure after the predetermined steps of the machine.

3.1.1.3 A Hand Operated Prototype A hand operated prototype of the concept was developed to observe the method and its workability. Figures 3.4 and 3.5 of the demonstrator show schematic view of the mechanism and its arrangement, and a set-up of self-supporting 4-step Cartesian vertical bed for braiding the minimum number of yarns.

Braiding Single spool bed yarn supply

Comber board

Figure 3.4 A schematic view of the prototype

Column

Braiding Row bed

Figure 3.5 A 4-step vertical Cartesian braiding bed

3.1.1.4 Advantages  The method provides a continuous supply of yarn for longer length braided preforms.  It eliminates the use of individual yarn bobbins and yarn carriers, hence minimizing the braiding bed size to the least possible dimension that would result in decreased braid to bed ratio.  It introduces the concept of binder yarn that serves as locking yarn.  Space occupied is less than that covered by present machines.  Increased number of yarns may be used by this concept for braiding which is not possible with individual bobbins. So braided preforms with large cross sections are possible to be manufactured.

 Longer length of yarns on the beam(s) leads to reduce stops and bobbin changing time.  Loading and set-up time for the beam(s) is much smaller than that required for large number of bobbins.  The system offers increased production rate.

3.1.1.5 Limitations  Beam winding is an additional process, though it is a replacement of bobbins winding.  Beam winding needs better skill and care for smooth winding with uniform length and tension.  Limited architectures will be possible because of the reversal of the braid pattern after a small number of steps to avoid increased entanglement.

3.1.2 Concept-2: Cartesian Braiding with a Mini-Braiding Bed This concept deals with the braid to bed ratio by decreasing the braid angle to the minimum possible value. It is made possible by using a mini-braiding bed next to the braiding creel.

Braided structure

Mini braiding bed

Braiding yarns

Yarn carriers Base braiding

bed Figure 3.6 Line diagram of Cartesian braiding machine with a mini-braiding bed

The mini-braiding bed serves for inter-twining the braiding yarns. However, the creel is made to follow the same row and column movement as the mini-braiding bed so as to avoid yarn entanglement behind the mini braiding bed. Line diagram of the machine is shown in Figure 3.6. The mini-braiding bed comprises an array of self supporting square blocks in required shapes as shown in Figure 3.7. The whole assembly of the blocks is supported in a framework by supporting means in the centre of the machine at an appropriate position. These blocks have holes through their centres for yarn passage. The same blocks may serve for axial, semi-axial and braiding yarns depending upon the fibre architecture to be developed as shown in Figure 3.8a,b. However, these blocks have been profiled in specific shapes in order to hold one another. Figure 3.8c shows spacer block designed for filling the spaces in-between the yarn carrier blocks. This arrangement allows the machine to feed the yarn supply to the braiding point at a very small angle to the braid dimensions. Pulling apart because of yarn orientations and stresses remain behind the mini bed and their impact does not affect the braid element.

Axial yarn carrier Braiding yarns

Spacer Braiding bed

Braiding yarn carrier

Figure 3.7 Self supporting mini-braiding bed with axial and braiding yarns

(a) (b) (c)

Figure 3.8 (a) Braiding yarn Carrier (b) Axial Yarn Carrier (c) Spacer

Pneumatic actuators are used for the row and column movements based on the 4-step Cartesian principal. Any of the smooth intermittent linear take up can be used at a predetermined rate.

Preferably the machine can be erected vertically with the creel bed at the bottom position and the take-up at the top of the entire assembly.

3.1.3 Concept-3: Cartesian Braiding Machine Inter-twining Braiding, Axial & Semi-Axial Yarns This concept basically deals with the yarn inter-twining patterns involving three different types of yarns with least focus on the machine mechanics. These sets of yarns are axial, semi-axial and braiding yarns.

3.1.3.1 Axial Yarns The axial yarns run through the centre of the block that remains stationary during the machine cycle, hence leaving the yarn in a set position. The position and number of these blocks for axial yarns are defined by the pattern to be braided. A plurality of axial yarns can be used on these specific points.

3.1.3.2 Braiding Yarns The braiding yarns simply work for braiding and locking the axial yarns into the predetermined braid architecture. The braiding yarns follow a specific path on self supported braiding bed according to the braid configuration. The braiding yarns may be further divided into different groups depending upon the path being followed by these groups; hence more than one yarn paths for particular braid architecture are possible. Thus the braiding yarns are laid along multiple axes across the entire cross section of the braid structure.

3.1.3.3 Semi-Axial Yarns The semi-axial yarns are displaced between two fixed points through oscillating movement of the bobbin carriers. It resembles the shedding motion in conventional weaving machines but only for a selective number of yarns. During this shifting of yarns, the braiding yarns pass across by locking them in a preset pattern of braid. This results in yarns orientation which seems similar to normal braiding yarns but have different braiding angle and do not run across the entire cross section of the braid. So these yarns assume a vertically zigzag posture along the length of the braid element.

The concept is equally applicable to both the machines with two beds (mini braiding bed and a creel bed) and the machine with yarn replenishment motion. The braiding bed

86 under the said arrangement of axial yarn, semi-axial yarns and braiding yarns marked with “S”, “B” and “A” respectively is shown in Figure 3.9.

Figure 3.9 Cartesian braiding machine with 3 Sets of yarns

Pneumatic actuators are used for the row and column movements alternately based on the 4-step Cartesian principal. Any of the smooth intermittent linear take-up methods can be used at a predetermined rate for various shapes accordingly.

3.2 Modifications in Concepts It was found, in the course of literature review, that both solid and tubular 3D structures have not been possible to be produced on conventional 2D braiding machines. Secondly, to mould a flat braiding bed into a circular braiding bed is not beyond the scope of the concept but in turn it give you an opportunity to manufacture structures which are three dimensional (thick layered) as well as circular. Hence attention was diverted to mould the flat Cartesian braiding bed into circular Cartesian braiding bed to produce circular 3D structures, and that to combine all of the above features of individual concepts in one for the development of a 3D textile preforming machine.

3.2.1 First modification: Cartesian Circular Braiding Machine incorporating Braiding, Axial & Binder Yarns The idea was quite feasible within the scope of the project entitled as development of multi-axial textile preforms. Though the circular braiding and weaving are already in the field, the proposed concept offers an easy approach to develop 3D circular structures with enhanced mechanical properties. It can also incorporate axial/ stationary yarns along with the Cartesian braiding yarns. Moreover a distinguishing feature of the process is to incorporate binder yarns that serve as through-the-thickness (orthogonal) yarns in the braided structures which have not been introduced before. These binder yarns act as locking yarns for the braiding yarns especially at the time of manufacturing and help to avoid slippage of the tow on the curved parts of the mandrel e.g. pressure cylinders. CAD drawings for the said concept were made in succession with the previous work.

The said concept consisted of a plurality of especially designed rings arranged side by side giving a shape of merely a hollow cylinder. A number of grooves, basically of two types, were made on the inner side/face of each ring; one for holding the braiding bobbins and the other to provide channel for the transverse bobbins to pass through. Initially twelve (12) positions were set for the braiding bobbins; however the number may vary depending upon the size of the bobbins, ring diameter and space required for the transverse bobbins. An external gear cut and a support cover plate were designed. The external gear is provided to drive the rings from a motor and the support is to fix the rings in position such that the rings can freely move inside the cover plate on ball bearings. The braiding bobbins are mounted on the inner side of the rings in hanging position towards centre of the respective rings. The bobbins are actually fitted to a shuttle like block placed inside the groove and provided with bearings. A segmented piece of the ring with a braiding bobbin is shown in Figure 3.10.

Toothed curvature to be meshed with driving gear

Shuttle to Binder yarn carry Binder Bobbin Channel for yarn Bobbin the shuttle to pass through Figure 3.10 Segmented piece of the ring with braiding bobbin

Working of the machine is purely Cartesian based such that the rotation of the rings serve as displacement of the bobbins in column and shifting of the bobbins from one ring to the adjacent ring serves for displacement of the bobbins in row. All the adjacent rings are driven in counter directions to one another. Displacement of the braiding bobbins in rows is repeated on back and forth positions alternately after every rotation of the rings. As a result, intertwining of the braiding yarns is performed. The transverse bobbins stay in the parking rings while the rings are in operation. Once the rings have completed one step of their motion, the transverse bobbins are propelled from one side of the rings to the other side passing freely through the channels provided in the rings which are aligned while the rings are stationary. Movement of both transverse and braiding bobbins commence simultaneously. Pneumatic actuators are used for pushing the bobbins. The actuators are mounted on circular plates on both ends of the machine. An individual ring with bobbins and an array of rings arranged side by side are shown in Figure 3.11.

Braiding rings

Binder yarn Bobbins Figure 3.11 Single ring & an array of rings arranged side by side

As far axial yarns, an arrangement of an external circular creel is made around the aforementioned rings. This is a stationary creel of rings holding yarn packages. The yarns coming from these packages pass through the spaces between the braiding rings. The structure so produced in the form of solid, hollow or over-mandrel is withdrawn away from the centre of the machine by means of an appropriate take up system provided on one side of the machine as shown in Figure 3.12. Take up shown in the figure is just a symbolic presentation of the drive.

Supporting rings for Axial yarn supply pneumatic actuators Taking-up arrangement Braiding rings

Parking rings

Figure 3.12 Circular Braiding Machine based on Cartesian principle incorporating Braiding, Axial & Semi-Axial

3.2.2 Second modification: Circular Braiding cum Winding Machine for Multi-Layer Multi-axial Textile Preforms Incorporating Braiding, Axial & Binder Yarns The aforementioned concept has been presented as a principle idea for the development of 3D circular structures. However, considering the time restrictions, capability of the workshop to develop/design such part with specific profile and accuracy and/or their availability in the market, some inevitable modification were made to the proposed design of the concept.

First of all, the number of braiding rings were decided to be reduced to the minimal number as two (2) instead of four (4). Secondly, the shifting of the braiding bobbins was decided to be eliminated in the first version of the concept. As a result the machine would behave more like a winding rather than a braiding. Consequently the parking rings for the stay of the braiding bobbins were decided to be removed as there is no shifting of the braiding bobbins. However the transverse bobbins yet needed to pass across the rings for binding the structure and there should be a support for the transverse bobbins on both sides of the rings. This requirement was fulfilled by providing pneumatic grippers for holding the bobbins. Whereas these pneumatic grippers are mounted onto pneumatic actuators and the pneumatic actuators carry them from one side of the rings to the other. Diameter of the rings was reduced to minimize the size of the machine. This could be possible by positioning the braiding bobbins on the lateral sides of the rings as the braiding bobbins are no more shifting from one ring to the other, or by using bobbins of small diameter with a bit large thickness. These bobbins are mounted on to small shafts that pass through the threaded hole in the rings. So purposefully modified rings were designed as shown in Figure 3.13 which were available in the market.

Alternative support Holes for side for hanging way spindles bobbins

Figure 3.13 Modified ring

A central well-built support is required as a main frame of the machine on which the rings can be mounted. Two different designs for frame; a solid one and with aluminium profile, were proposed as shown in Figure 3.14. The one made with aluminium profile frame is light in weight, economical, easily portable and can quickly be assembled or dismantled.

Alternate support frames

Braiding Rings

Figure 3.14 A solid & an aluminium Central support frames for holding the rings

An important part of the machine is a set of central guide plates which direct all the yarns towards centre of the machine and then to the mandrel as shown in Figure 3.15. These plates are positioned vertically aligned and parallel to each other in the centre of the machine between the two rings.

Braiding rings Braiding bobbins

Central guide plates

Figure 3.15 Central guide plates as positioned between the rings

3.2.2.1 Bobbin Transfer System Bobbin transfer system is the heart of the concept. It is carried out with a uniqe rapier- cum-shuttle system which makes use of bobbin holder for carrying the binder yarn bobbin across the rings. Essentially a miniature shuttle has been specially designed for this purpose. The concept design makes use of two sets of pneumatic actuators complementary to each other. Pneumatic actuators are positioned aligned initially at outer most points. One set of pneumatic actuators that serve as donor is carrying the binder yarn bobbins. The other set of pneumatic actuators are the receivers. As the machine works, the pneumatic actuators move forward towards the centre of the machine. As they approach each other the binder yarn bobbins are transferred from donor to receiver pneumatic actuators. A line diagram indicating both the positions of the pneumatic actuators during bobbin transfer motion is shown in Figure 3.16.

Central support frame Pneumatic actuators at out most position Braiding rings

Pneumatic actuators meeting at centre

Figure 3.16 Bobbin transfer system

During the course of machine design, an alternative to the individual pneumatic actuators was designed in the form of an assembly and all the bobbins are mounted on the assembly. The assembly is moved by a single actuator as shown in Figure 3.17.

Figure 3.17 An assembly with bobbins mounted on it

The design of transverse bobbin with or without casing was a critical aspect of the concept for the machine design. The key features to bring about were the size of the bobbin (with or without casing), length of yarn on the bobbins, weight of the bobbin, shape formation in accordance with the pneumatic grippers functioning and tension compensation while slackening of yarn. The idea to use yarn bobbins as small as possible led to investigate the sewing machine yarn bobbins which could serve the object perfectly and could easily be available in the market. But the casing of the existing bobbins was not suitable for the purpose. Hence casing/covering of the bobbin was designed. Bobbins with casing were designed on two basic principles; one for external three jaws pneumatic grippers as shown in Figure 3.18, the other for internal pneumatic gripper as shown in Figure 3.19.

Casing cover Binder bobbin

Casing for Binder bobbin Spindle

Compression spring Casing cover

Casing butt

Yarn Tensioner

Figure 3.18 Casing of transverse bobbin for external gripper

Casing of the bobbin for external grippers is a simple small boat like shuttle with a round cut in the thickness direction having a peg in the centre for the bobbin to be mounted onto it. A lid with a compression spring to exert pressure on the bobbin against free rotation is placed over it to close the casing. A yarn compensator lever, which can either be positioned inside the casing or outside, is provided to take up yarn slack.

Hollow sleeved flanges Yarn guide Binder yarn bobbin

Compression springs

Binder yarn bobbin

Bellow gripper Bellow gripper

Hollow sleeved flanges

Figure 3.19 Specially designed transverse bobbin for internal gripper

Gripper’s outer Hollow sleeved Gripper’s body sleeve/ collar flange

Figure 3.20 Internal gripper with Sleeve

The second type of bobbin with bobbin holder is designed such that a narrow shaft is passed through the bobbin barrel so as the bobbin can freely rotate over it. Two hollow cylindrical shafts with larger diameter as compared to the narrow central shaft but in accordance with the internal grippers are mounted on the extreme ends of the narrow

shaft. The internal pneumatic bellow gripper is shown in Figure 3.21.

Gripper’s body

Expandable band Threaded screw to fix

Figure 3.21 Pneumatic internal gripper

The internal pneumatic bellow gripper enters the hollow cylindrical shafts on approaching the bobbin during the machine operation. One of the gripper serves as donor and the other as receiver at one time and vice versa in the next phase of the operation cycle. A yarn guide in the form of a lever with a hole on the top is mounted on the hollow shaft. A similar sort of lever is designed beneath it which serves as yarn compensator to take up yarn slack. Both the levers can rotate freely. Normally they remain align for smooth yarn passage under tension, however during yarn slack they move apart angularly from each other by means of a expansion/compression spring placed between them.

3.2.3 Final Modification A few more modifications were made to give a final shape to the design. Instead of using two sets of pneumatic actuators on both sides of the rings in the centre, one set of pneumatic actuators was eliminated. However the receiving bellow grippers were attached to the solid machine frame, and only one set of pneumatic actuators is approaching the other side and then returns to its initial/ start position.

Setting up of an axial yarn creel for mounting the axial yarn bobbins is another addition to the design for incorporating the axial yarns into the structures to be produced. The axial yarn creel is positioned in the centre between the two rings and the axial yarn bobbins are mounted onto it such that the bobbins are held between the two circular cut plates through their slits in them such as the yarn from the bobbins are directed straight to the centre of the machine without any inclination. The creel is made such that a plurality of the axial yarn bobbins can be used depending upon the diameter of the

98 braiding/ winding rings, the number of pneumatic actuators being used and the position where the axial yarns are to be placed. The creel is formed in a very simple way by using metal plate cut into circular shape with a big hole in the centre and then a slit in the plate. Again the plate is made into three pieces for ease while making it and fixing to the machine frame. Two such similar plates are made and then they are positioned parallel to each other with a distance depending upon the thickness of the axial yarn bobbins to be held between them. The creel is fixed to the machine frame by way of a set of four simple support clamps.

3.3 Conclusion

The concepts presented in this chapter have the potential to be implemented in their individual from, but off course with different scope and capabilities. However these concepts have been investigated as means for the main goal of designing a novel concept derived from these ideas. These concepts have been discussed mainly from their principles view point. The first concept is about continuous supply of yarn for longer length braided preform by using beam as yarn supply. Importantly this concept gave the idea to introduce binder yarn that serves as locking yarn. The second concept of self supporting mini braiding bed is an interesting idea coupled with another bed as creel. The noticeable point here is the use of the spacer block which diverted the attention to use semi-axial yarns instead of leaving free space among the braiding and axial yarn block. The third concept identifies the possibility of incorporating three sets of yarns; braiding, axial and semi-axial. The semi-axial yarns may be treated as binder yarns but interlacing only with neighbouring layers of braiding yarns. This idea also indicates the likelihood of inserting binder yarns. The main derivation out of these concepts happened to be the inclusion of binder yarn. Insertion of binder yarn particularly through-the-thickness creates the possibility of laying the yarn along the z- axis. When it comes to braiding there is no such precedence both in 3D and 2D over- braided multi-layer structures. Moreover, the compromise of the multi-layered over- braided circular structures on delamination and damage propagation has been another inspiration for developing such structure that can overcome these issues. Hence the idea of inserting through-the-thickness binder yarn seemed to be very appealing for this purpose. This became the motive to design a circular braiding machine with through- the-thickness binder yarns.

The modification to the concept is the next step toward the final design of the concept. The first modification deals specifically with circular braiding principle based on Cartesian rather than rectangular braiding systems. The second modification has been brought to minimise the mechanical complexity by eliminating the transfer of bobbins from one ring to the other ring. The other important feature of the concept is the method of transferring the binder yarn bobbins from one side of the rings to the other side by means of a specially designed shuttle-cum-rapier mechanism. This unique method of

100 transferring the bobbin is considered as distinguishing feature of the concept for machine development. The prospective attributes of the machine to be developed based on this concept have been anticipated as follow.

o The machine based on this concept can produce 3D circular structures. o The structure so produced will be composed of three sets of yarns: braiding yarns, axial yarn and binder yarns. o The machine will produce multi-layered structures. o The multi-layers of the structure will be locked by means of binder yarns in through-the-thickness pattern. o Binding of multi-layer braided structure during preforming is a distinguishing feature of the proposed concept. o Braiding, axial and binder yarns can be introduced simultaneously.

101

4 CHAPTER 4 DEVELOPMENT OF THE

NOVEL 3D TEXTILE PREFORMING MACHINE

The development of the novel 3D textile preforming machine has been a major objective of this project. Once the concept has been presented, it needed to prove the practicable implementation of the concept by developing a machine to demonstrate it. Hence a fully automated Novel 3D braiding machine capable of producing multi-axial tubular structures has been successfully developed. The machine is designed with least mechanical complexity. The functioning of the machine has been programmed in a very simple mode. The motions of the machine have been synchronised in a well planned manner. The working of the machine is so clear that the preform is fabricated neat and clean without any obstacle and entanglement of the yarns among themselves or with the machine parts.

The machine is based on a novel concept and is unique in its working and fabricating the preform. The chief distinction is the shuttle-cum-rapier yarn insertion system for the placement of the binder yarns. This system is derived from the concept of rapier weft insertion and shuttle weft insertion systems. Although it is a combination of the two yet it is different from both of them.

Another distinctive component of the machine is a miniature shuttle which is a complementary part of the binder yarn insertion system. The miniature shuttle is a purpose built small size shuttle designed according to the requirement of the concept and it holds a binder yarn bobbin. The miniature shuttle is carried by means of the shuttle-cum-rapier system for binder yarn insertion.

The binder yarn insertion system along with the miniature shuttle is explained in the later part of the chapter.

Insertion of axial yarn is another significant attribute of the machine. An axial yarn assembly is designed such that the yarn placement has been made convenient and smooth.

102

Braiding rings

Pneumatic actuator Mandrel

Take up clamp

Take up drive

Main frame

Control panel

Figure 4.1 a full view of the machine

The machine can produce multi-axial textile preforms such that it incorporates braiding, axial and binder yarns simultaneously. The structures developed on novel 3D machine consists of two sets of braided yarns forming cross-wound layers, one set of interlocking yarns that serves as binder yarns and one set of axial yarns laying straight at 0o parallel to the braiding axis. The axial yarns are sandwiched between the braiding layers whereas the binder yarns are positioned through-the thickness of the structure. The number of braided layers depends upon the braiding rings being used in the machine.

103

The developed machine currently comprises two rings which can be multiplied up to a required number.

4.1 Construction of the Machine The major components of the machine include two braiding rings that hold braiding bobbins, four pneumatic actuators, eight internal grippers, a linear take up drive, three stepper motors; two for the braiding rings and one for the take-up drive, a control panel and user interface. The main frame of the machine is holding various parts together giving an integrated shape to the machine. It is designed such as to constitute the preforming area of the machine on top of the frame and to provide space for locating the control panel underneath.

4.1.1 Braiding Rings The braiding rings are positioned side by side and vertically aligned towards one end of the machine. The braiding yarn bobbins are mounted on to small spindles on the outer sides of the rings. The number of rings determines the number of braiding layers to be preformed. Multiple numbers of rings can be used commensurate with the workable space available in the machine for preforming a multi-layered structure. Secondly the stroke length of the pneumatic actuator also limits the number of rings to be used. The braiding rings with 512mm diameter are suitable for holding 4 to 12 braiding bobbins each. The rings are fixed to the main frame by means of bevel wheel and are driven by electric motors through pinion gears. Each ring is held in three bevelled wheels equally spaced from one another at an angle of 120o. These bevelled wheels are fastened to support plates fixed to the main frame of the machine.

104

Braiding bobbins

Braiding rings

Axial bobbins

Axial yarn Mandrel assembly

Guide rings

Figure 4.2 Main braiding area of the machine

Small spindles (40mm long) are fixed to the outer sides of the rings for holding the braiding bobbins. The bobbins are mounted on to the spindles and secured with the help of compression springs and screw nuts. Special jumbo size bobbins have been used as braiding yarn to accommodate enough length and occupy less space whereas for binder and axial yarns standard size sewing bobbins have been used.

105

Braiding Ring

Braiding bobbin Braiding yarn

Figure 4.3 Braiding bobbin attached to the ring

4.1.2 Pneumatic Actuators A set of four (4) pneumatic actuators is used for transferring the binder yarn bobbin from one side of the rings to the other side. The pneumatic actuator specifications have been decided in accordance to the space occupied by the braiding rings and the length of the miniature shuttle. A stroke length of 200mm of the pneumatic actuator is selected to cover this distance occupied by rings and leaving a safe margin left on both sides of the rings.

106

Pneumatic actuators

Braiding rings

Guide rings

Figure 4.4 A view of the machine showing pneumatic actuators

4.1.3 Pneumatic Internal Grippers Four sets of two pneumatic internal bellow grippers each are used and both the internal bellow grippers of each set are working complementary with each other. One internal bellow gripper of each of these sets is mounted onto the leading end of the pneumatic actuators, and the second internal bellow gripper is attached to the main frame of the machine. In other words, there are two set of the internal bellow grippers; those mounted onto the pneumatic actuators and those attached to the main frame. The internal bellow grippers which are attached to the pneumatic actuators move along the pneumatic actuators as the pneumatic actuators extend across the rings and retreat. The internal bellow grippers which are fixed to the main frame are stationary.

107

Expandable band Fastening screw Pneumatic internal gripper

Body Gripper outside Compressed air supply sleeve

b a Figure 4.5 Pneumatic bellow gripper (a) without sleeve (b) with sleeve

Gripper outside sleeve

Fastening screw

Figure 4.6 Bellow gripper’s outer sleeve

The internal bellow gripper enters the cylindrical flange of the miniature shuttle and the expandable band of the internal bellow gripper grip the flange internally to hold the miniature shuttle. The internal bellow grippers are assisted by means of cylindrical sleeves mounted on top of them as shown in Figure 4.5 and 4.6. The purpose of these sleeves is to align the approaching miniature shuttle with the internal bellow gripper if there is any misalignment or vibration.

4.1.4 Miniature Shuttle A specially designed miniature shuttle is introduced which can carry the binder yarn bobbins to transfer from one side of the rings to the other side with the help of pneumatic actuators. The specially designed miniature shuttle is made in three pieces; a central 20mm long shaft of 5mm diameter, two 16mm long hollow sleeve like

108 cylindrical flanges with 11mm outer diameter and 9mm inner diameter. The cylindrical flanges are fitted to the central shaft through the threaded holes on the rear sides of the flanges. A U-shaped guide plate with a hole through it and a ceramic guide in it is used. This guide is used to keep the yarn straight as it unwinds from the bobbin. The bobbin is mounted on the shaft such as that it is surrounded in the centre by the U-shaped guide which is also mounted on the same shaft. On both sides of the bobbin compression springs are used to offer friction as the bobbin unwinds in order to keep the yarn under appropriate tension. The hollow flanges make provision for the pneumatic internal bellow grippers to enter the shaft and grip from inside. The outer edges of the cylindrical flanges are tapered slightly so as they enter the sleeves of the bellow grippers smoothly and may not encountered with each other due to any vibration or misalignment. A miniature shuttle with yarn bobbin is shown in Figure 4.7.

Yarn Ceramic yarn guide U-shaped guide leaf Cylindrical flanges Tapered end of Cylindrical flanges Bobbin

Figure 4.7 Miniature shuttle

109

4.1.5 Axial Yarn Supply An axial yarn assembly serves as a creel to hold multiple numbers of axial yarn bobbins to supply yarn for axial placement in the preform. The assembly is in the form of two circular cut plates which are held side by side at a distance in accordance to the thickness of the axial yarn bobbins. The axial yarn bobbins are held between the two circular cut plates of the assembly. The assembly is located in the centre between the braiding rings to deliver the axial yarn straight between the braiding layers without any inclination. The creel is made such that a slit is cut along the entire circumference of the plates to provide enough space for using multiple number of bobbins. Setting up of such an assembly is a unique method of incorporating axial yarn in the preform being produced.

Standard size sewing bobbins are used for axial yarn supply. Though smaller in size, the axial yarn bobbins accommodate enough length as the axial yarn is lying straight in the preform. Likewise the axial yarn bobbins, the binder yarn bobbins are also smaller in size. Though the binder yarn is placed through-the-thickness, enough length can be accommodated on the bobbin as the binder yarn is finer compared to the braiding yarn

Bobbin rings Axial yarn assembly

Axial yarn bobbins

Figure 4.8 Axial yarn assembly Bobbin

In the middle of the braiding rings two guide rings of 150mm diameter are positioned side by side with a gap of 10mm between them. These rings are used to guide and direct

110 the yarns coming from the braiding bobbins and the binder yarn bobbins towards the centre of the winding rings. These rings serve to reduce the conversion length by bringing the yarns closer to the mandrel.

The take-up unit is positioned parallel to the central axis of the machine such that a take-up clamp appears right in the line of the braiding axis. The take-up clamp is erected vertically on a platform of the drive that moves along the length of drive. The clamp is made such as to hold mandrels with diameter up to one inch with the help of three equally spaced plastic blocks sitting in grooves and can move inward to hold mandrels even with small diameter in the centre.

Configuration is done through Festo Configuration Tool (FCT) [99]. The machine settings for different operations are made in FCT, and then downloaded to the EMMST drivers in the control panel. The machine motions and working is controlled by way of a computer program CoDeSys V2.3. Compressed air supply to various components it regulated through air control valves in a range of 5bar~7bar.

4.2 Bobbin Transfer Mechanism The bobbin transfer mechanism is the heart of the concept. It involves the key components of the machine namely miniature shuttle, bellow grippers, pneumatic actuators and the associated parts with these components.

All the four pneumatic actuators come into operation simultaneously and extend to a distance of 200mm and retract. The motion is activated by a supply of compressed air at a pressure of 5~7bars from a portable compressor. The pneumatic actuators operation cycle is repeated time and again after a predetermined dwell period allowing the rings to rotate during this period of time. Moreover the pneumatic actuators stay for a small period of time before retracting providing sufficient time to the bellow grippers to perform their action.

The machine makes use of eight bellow grippers such that one set of four bellow grippers is mounted onto the pneumatic actuators, whereas the other set of four bellow grippers is fixed to the machine frame. All the four bellow grippers in each set work together simultaneously, however the two sets operate alternately. Function of each and

111 every bellow gripper is the same and their bands expand to grip the bobbins internally for a certain period of time and then release after a predefined period of time.

A set of four miniature shuttles is used in the machine. The miniature shuttles are loaded with the binder yarn bobbins and are mounted onto the pneumatic actuators. The yarn from each bobbin is withdrawn and directed to the mandrel through the guide rings.

Figure 4.9 is a brief demonstration for the mechanism of bobbin transfer from one side to the other. It show two main positions of the miniature shuttles; one in the grip of the pneumatic actuators whilst the actuators are at their original position and the second when the shuttles are held by the bellow grippers fitted to the machine frame across the rings. It also indicates the binder yarn trajectory in both cases.

112

Braiding rings

Mandrel

Miniature shuttle Pneumatic actuators

Bellow grippers fixed to main frame

Figure 4.9 Bobbin transfer arrangement

Images for the same mechanism have been taken while the machine was working as shown in Figure 4.10.

113

Miniature shuttle Bellow gripper

Pneumatic actuator at original position

Pneumatic actuator at extended position

Figure 4.10 Machine view showing pneumatic actuators

In order to elaborate the mechanism thoroughly, the process is explained step by step with the help of line diagrams as shown in Figure 4.11. In every step of the figure, there are two bellow grippers on the extreme side and a miniature shuttle in the centre. The circles on the tip of the grippers are representing the expandable bands of the grippers. The colour of the circles (black/ white) indicates the state of the band (expanded/ unexpanded). It is marked as black when the band is expanded and it has gripped the shuttle, and is marked as white when the band is unexpanded and it has released the shuttle.

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Bellow gripper Miniature shuttle

B A

Unexpanded Expanded

band band

A approaches B A

Bobbin B A transfer from A to B

A retracts B A leaving the bobbins

A approaches B A B again

Bobbin transfer B A

from B to A

A retracts again along B A with bobbins

Figure 4.11 Bobbin transfer mechanism

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As the machine is switched on and the air supply is released, the bellow grippers of the pneumatic actuators expand. As a result the miniature shuttles mounted onto the pneumatic actuators are held firm internally by means of the bellow grippers.

The miniature shuttle and the bellow grippers are situated such that the expandable band of the bellow gripper is inside the sleeve of the miniature shuttle and the sleeve of the miniature shuttle itself is inside the outer sleeve of the bellow gripper as shown in Figure 4.12.

Bobbin flange (sleeve) Outer sleeve of gripper

Gripper

Figure 4.12 Miniature shuttle in bellow gripper

The rings will take one quarter rotation and stop. Once the rings have stopped, the pneumatic actuators along with the miniature shuttle extend across the rings and approach the other set of bellow grippers fitted to the machine frame. The flange of the miniature shuttle would enter the outer sleeve of the bellow gripper. The receiver bellow gripper will expand now to hold the miniature shuttle and the donor bellow grippers will release it. Once the miniature shuttle is released from one gripper and held by the other, the pneumatic actuator will retract to its original position. The ring will take another quarter of rotation locking the binder yarn in the structure. The pneumatic actuator will again extend up to the miniature shuttle still held by the bellow gripper on the other side and the bellow gripper mounted on the pneumatic actuator will enter the sleeve of the miniature shuttle and the sleeve of miniature shuttle itself will enter the outer sleeve of the bellow gripper. Once the grippers and the shuttle are positioned, the gripper will expand to hold the shuttle and the other gripper will release the shuttle afterwards. Now the shuttle is in the grip of the gripper of the pneumatic actuator. The actuator will now

116 retract along with the shuttle such that the binder yarn will be locking the braided structure. The rings will again rotate another quarter. In this way the machine goes on working and this cycle is repeated again and again. The binder yarn moves from to layer to underneath the bottom layer and then from underneath the inner layer to the outer surface of the outer most layer locking the structure through-the-thickness.

This system is termed as shuttle-cum-rapier insertion system. It is a combination of shuttle and rapier weft insertion system, but different from both of them. The principle difference from shuttle insertion system is that the shuttle is carried by means of a solid support in case of shuttle-cum-rapier system unlike shuttle insertion system where the shuttle is fired and then it moves under inertia without any solid grip. The main difference from rapier insertion system is that the yarn insertion is continuous from the bobbin in shuttle making a loop in case of shuttle-cum-rapier system unlike shuttle insertion system where the yarn is cut after every cycle of the rapier.

In case of shuttle weft insertion system, the bobbin for yarn supply is placed inside the shuttle. The shuttle is pushed with the help of a lever to pass through the open shed across the width of the fabric. As the shuttle runs on the race-board through the shed, the yarn is released from the bobbin inside the shuttle. As the shuttle reaches the other side of the fabric being woven, a continuous length of yarn is laid in the shed making a loop at the left hand side selvedge of the fabric from where it entered the shed. Once the shuttle arrives at the right hand side of the machine, it is pushed again in the backward direction to pass through the open shed for the next pick insertion. This time it makes a loop at the right hand side selvedge of the fabric. This process goes on along the formation of the fabric without cutting the yarn from the bobbin. Various steps of the process are shown in Figure 4.13. The important point in this system is that the yarn coming from the shuttle is not cut for every single pick. Whereas in case of rapier system the yarn is cut from the bobbin on completion of every pick and it is held again for the next pick.

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Shuttle at LHS

Shuttle fired while passing through shed

Shuttle reached RHS Shuttle

Shuttle returns through the shed to LHS

Shuttle ready for next pick

Figure 4.13 Shuttle weft insertion system

In case of rapier weft insertion system, the yarn is taken from a stationary yarn supply system including yarn package and an accumulator positioned on one side of the machine. As the rapier move forward, it withdraws the yarn already held in its head from the yarn supply. The rapier passes across the width of the fabric through the open shed. On the other side of the fabric the yarn is held from the grip of the rapier head. The rapier after leaving the leading end of the yarn retracts to its original position. Once

118 it comes out of the shed, it holds the yarn again which is cut near the left hand side selvedge of the fabric. Different steps of the process are shown in Figure 4.14. The notable point here is that the yarn is cut after every pick insertion contrary to the shuttle weft insertion system.

Rapier at LHS Guide outside the shed Accumulator Yarn package

Rapier approaches the yarn from bobbin on RHS

Rapier retracts to LHS along with yarn

Figure 4.14 Rapier insertion system

4.3 Braiding Yarn Placement The braiding yarn bobbins are mounted on to the braiding rings with the help of spindles on the outer sides of the rings. The number of bobbins depends upon the space provision for the pneumatic actuator to pass through between two consecutive braiding

119 yarns while manufacturing. A maximum of 24 bobbins; 12 bobbins on each ring have been used. However, the number of rings determines the number of braiding layers to be preformed.

Both the rings are driven in opposite directions through pinion gears. For every rotation the rings move one quarter resulting in the braiding yarn placement in a cross-wound pattern. After one quarter rotation the binder yarn bobbin is shifted from one side of the rings to the other. The rings rotate again another quarter and the braiding yarns are further spiralled around the mandrel. Again shifting of the binder yarn bobbin takes place but this back to its original position. The rings have moved 180o i.e. half rotation so far and completed one repeat of the braid pattern. So in one full rotation of the rings using four bobbins each, two repeats of the weave pattern are preformed. For different number of bobbins the degree of rotation of the rings will be altered. The degree of rotation decreases by increasing the number of bobbins.

A sequence of rotation of the rings have been demonstrated in a 2D diagram with a slight change by showing one ring inside the other ring due to the drawing limitation as shown in Figure 4.15. Four bobbins on each ring have been shown and are marked with different colours to identify their movements.

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Figure 4.15 Rings’ rotations in four steps

4.4 Process Layout of the Machine Operations The whole process of the machine is quite simple. Once the miniature shuttle is gripped by bellow grippers mounted onto pneumatic actuators, the rings rotate 90o simultaneously but in opposite directions. Then the pneumatic actuators extend from one side of the rings to the other side. The pneumatic actuators deliver the miniature shuttle to the grippers fixed to the machine frame and returns to their original position. The rings would rotate again and the take-up assembly moves a pre-set distance. The pneumatic actuators extend to take the miniature shuttle from the gripper fixed to the main frame and retract. This cycle is repeated again and again and the braid is fabricated. The complete process of machine operations is summed up in a flow chart diagram as shown in Figure4.16.

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Switch on Open the air

supply power Homing

Bellow Grippers A Grip the miniature bobbin

Rings rotate one quarter

Pneumatic Actuators Extend

Bellow Grippers B Catch the miniature bobbin

Bellow Grippers A Release miniature bobbin

Pneumatic Actuators Retract

Take-up Drive Moves

Rings rotate one quarter

Pneumatic Actuators Extend again

Bellow Grippers A Grip miniature bobbin

Bellow Grippers B Release miniature bobbin

Take-up Drive Moves

Figure 4.16 Process layout

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4.5 Conclusion The development of 3D novel braiding machine is deemed to be a step forward in the preforming techniques. The machine has been elaborated initially from construction view point along with the key features of the main components of the machine. Then the principle mechanisms have been discussed with the distinguishing characteristics. The machine is based on a novel concept of preforming. A new method of transferring the binder yarn bobbins has been introduced which is termed as “shuttle-cum-rapier system”. A miniature shuttle has been introduced as a key component of this system. This system is quite smart and different from rapier insertion system and shuttle insertion systems. Moreover in this system the miniature shuttle serves to insert the binder yarn through circular structures. The associated components such as pneumatic internal grippers and pneumatic actuators play vital role to execute the functioning of the shuttle-cum-rapier system.

Axial yarn insertion has been introduced by constructing an axial yarn assembly. The assembly serves as creel, holding a number of bobbins to deliver yarn into the braiding area while preforming. The development of the new systems has made it possible for the machine to incorporate braiding yarns along with axial yarns with a distinction of inserting through-the-thickness yarns along the z-axis.

The bobbin transfer process has been described with ample details. The process layout of the machine operation is well defined in the end of the chapter.

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5 CHAPTER 5 DEVELOPMENT OF MULTI-

AXIAL BRAIDED PREFORMS

5.1 Prospective Fibre Architectures A wide range of fibre architectures is possible within the scope of the machine. The machine has the capacity / potential to develop circular structures with uniform diameter as well as structures with various shapes and varying diameters. Both hollow structures and over mandrel structures can be produced. Some simple and preliminary structures that can be produced on this machine are shown in Figure 5.1. These are over-mandrel structures using two rings of the machine, each carrying four bobbins. One set of four bobbins is coloured as green and the other as blue for the first two structures. Both structures are double layer wounded and distinctly interlocked by binder yarns resulting in stitched multi-layer structures.

Binder yarns (Black Binder yarn Outer wound & white) layer (Green)

Cross wound layers Inner wound (Green & Blue) layer (Blue)

Figure 5.1 CAD models of double layered fibre architecture

Figure 5.2 shows a CAD model for another multi-layered (four-layer) structure. These examples are shown only for the sake of illustration. The number of layers can be increased by increasing the number of rings. Layered laminated circular structures can also be developed. Furthermore axial yarns can be incorporated to enhance tensile properties of the structures.

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4 Cross wound Binder yarns Binder yarns layers

Axial yarns

Figure 5.2 CAD models of fibre architecture

The basic attribute of all of these structures is the through-the-thickness binding of the structures, which is the main theme of the concept.

The structures can be braided at various braid angles, within a range of 10o to 80o. Multi-layered structures can be produced where the number of layers depends upon the space provision for mounting the number of rings required onto the machine. Figures 5.3-5.5 show a few more architectures modelled to demonstrate the capacity of the machine within the scope of the concept.

Braided carbon yarn

Axial carbon yarn

Binder yarn

Figure 5.3 Cross wound preform with axial yarns

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Braided carbon yarn

3 layers of axial yarn

Binder glass yarn

Figure 5.4 Multi-layered preform using different fibres in different layers

Binder yarn

Braided carbon yarn

Axial carbon yarn

Figure 5.5 A sample in which braiding layers are not cross-wound

On the developed machine six (6) rings can reasonably be used in the present set-up. However with a slight modification by changing the braiding bobbins position from the lateral sides of the rings to the inside hanging position towards the centres of the rings, the number of rings can further be increased. At present two (2) rings are used, hence double layered structures can be produced.

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5.2 Development of Multi-Axial Textile Preforms In order to produce a standard structure on this machine, the procedure below was followed starting with preparation for sample development.

5.2.1 Preparation Mandrel In the case of regular circular structures, a mandrel made from a round bar was used for the structure to be made upon. The mandrel can be made from any material that suits the after processing such as vacuum bagging, resin infusion, thermal curing at 140o (max up to 150o) and can withstand its shape. The mandrel should be hard enough to remove the samples from it after processing. Usually metals such as stainless steel or aluminium are used. As the structures are circular in shape and are needed to be removed afterwards, it is difficult to remove the samples only by pulling them from the mandrel. Usually the samples would grip the mandrel after consolidation. Therefore, various ways were attempted for its removal including tapering the mandrel before sample development and freezing the mandrel along with the sample.

Tapering

The ASTM standards [87] have stated guidelines for tapering a mandrel. It states that the acceptable amount for taper is 0.0005 mm in diameter between the two ends of the mandrel per 1 mm length of the mandrel. So a 1 metre long mandrel can have a maximum of 0.5 mm tapering. This amount of tapering will not affect the test results and facilitate the removal of the samples from the mandrel.

Winding of bobbins

Large size bobbins have been used for braiding to accommodate a considerable longer length enough for braiding a number of samples. Whereas for axial and binder yarns regular sewing bobbins have been used as they consume a much smaller length compared to braiding bobbins. In addition the binder yarn is kept very fine to serve the objective of binding primarily. Figure 5.6 shows both of the bobbins used for developing the preforms.

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38 mm

20 mm

Figure 5.6 braiding bobbin with 38mm diameter & regular size binder yarn bobbin with 14mm diameter

Winding of carbon fibre on large braiding bobbins is carried out on a conventional auto- winder or using a manually operated winder under tension. The tension is set according to the unwinding tension at the time of braiding on the machine. It should be more than the tension at the time of braiding so that the upper coil of unwinding tow may not submerge into the underlying coils, which may lead to fibre damage, intense fibre entanglement and ultimately stopping the bobbin from unwinding. An arrangement for winding on a simple winder is shown in Figure 5.7.

Winder 12 k carbon tow

Winder head

Braiding bobbin Figure 5.7 Winding set-up, a simple winder and braiding bobbin

Winding of the binder and axial tow on small bobbins can be carried out on sewing machines, conventional auto-winder or manually. Again the tension will be the key factor to be careful about.

A certain number of braiding bobbins are mounted onto the rings according to the required structure and fibre architectures. For a regular structure four bobbins on each

128 ring will be mounted and then the axial yarn bobbins are mounted on the axial yarn creel. The number of axial yarn bobbins can be 4, 8 or 12 or even more. The binder yarn bobbins are loaded in the miniature bobbin holder.

5.2.2 Tensions Adjustment Tensions of all the three sets of yarns are set in accordance with each other and it is a critical issue as this has to be done manually. Braiding yarn tensions are set higher than those of binder yarns and axial yarns. The axial yarn tensions do not matter much in relation to structure formation as they lay straight and are drawn in between the layers with least friction. However the tension of the axial yarns is kept similar to that of binder yarns. It is critical to ensure that the winding tension of braiding bobbins is greater than the unwinding tensions. Otherwise the outer coils of wound yarn will be embedded into the inner layers while unwinding the yarns from the bobbins resulting in excessive fibre damage and ultimately result in fibre entanglement. Table 5.1 shows a workable range of tensions for a good structure to be produced.

Table 5.1 Proposed yarn tensions

Yarn tensions Unwinding tensions Winding tension Compactness Braiding Binder Axial of braiding yarn yarns yarns yarns Fairly compact structures 900g 700g 300g 150g Very compact structures 1500g 1100g 500g 300g

Tension optimisation is an extremely important aspect of the machine. During manufacturing of the samples on 3D novel textile machines, it was found that to set tensions of all the three set of yarns (braiding, axial and binder) with respect to one another with the least tension for braiding the sample in proper shape, has been a great challenge particularly for increased number of yarns. If the tensions are not optimised, the structure will either be loose or over tensioned. If the binder yarns tension is higher than that of braiding yarns, the structure will have gaps at every intersection of binder yarn. If the braiding yarns tension is higher than that of binder yarns, the structure will be such that the binder yarns will be pulled by the braiding yarns resulting in the binder

129 yarns to follow a knit loop like path (as in knitting structures) rather than a proper orthogonal loop (forming a U shape).

Another issue as a component of the above point is the non-uniformity of the yarn tension among themselves within a group of yarns such as braiding yarns, binder yarns and axial yarns. It has been found that the tension within a group of yarn vary from yarn to yarn.

The reasons for both of the above points are the same. It includes that the machine does not have a mechanical arrangement for pre-set tensions. Compression springs are being used to impart tension to the yarns. Each individual yarn has a cut piece of the compression spring and is adjusted manually. Thus the resulted tension in each and yarn is may vary.

Both the rings are positioned such that they are aligned with each other and their quarterly located reference points where the bobbins are mounted should be aligned vertically and horizontally. The pneumatic actuators are at the outermost retracted position whereas the take-up head is at the front most position near the preforming point. As the machine is switched on, it starts preforming the braided structure with programmable architecture.

5.3 Validation of the Weave Architecture A trial run of the machine was conducted to verify it as in working order and to analyse the weave architecture. Eight bobbins (four on each ring) for braiding yarn (Carbon fibre) and four binder yarns (Glass fibre) were used to produce a sleeve over a large mandrel (2.5” diameter) in order to analyse the structure clearly. Figure 5.8 shows two cases; one with spaced yarn placement and the other comparatively closer yarn placement by changing the take-up rate. The two cross-wound carbon layers interlocked by the glass binder yarn can clearly be distinguished, hence verifying the concept.

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Outer Wound Layer

Binder Yarn

Inner Wound Layer

Figure 5.8 Interlocked braided structure with different spacing of braid

5.4 Initial Trials to Develop Preforms A number of trials have been conducted to develop the braided preforms in order to achieve the structures in reasonably good shape and form. In a few attempts the desired shape and form of the structure has been achieved. From these trials it has also been learnt that how do various parameters of the machine work for different settings and what are the major considerations while preforming a structure. Some of these sample developed in the initial trials have been shown in Figures 5.9~5.14 with gradual improvements in the fibre architecture. All of these samples have been produced using eight (8) braiding yarns of 6K Carbon fibre, four (4) binder yarns of 6K Carbon fibre and four (4) axial yarns of 300 Tex Glass.

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SAMPLE–1

Figure 5.9 Sample-1 of the braided structure

 Lot of fibre damage  Binder yarn path not straight  Binder yarn lying straight rather than interlocking  Binder and axial yarns are not clearly visible  Irregular surface

SAMPLE–2

Figure 5.10 Sample-2 of the braided structure

 Comparatively less fibre damage  Binder yarns are not at appropriate position  Binder yarn are still lying straighter though slightly bent.  Binder and axial yarns are now clearly visible  Axial yarns are almost straight

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 Non uniform distribution of fibres

SAMPLE – 3

Figure 5.11 Sample-3 of the braided structure

 Least fibre damage  Some of the binder yarns not equidistant  Binder yarn have some bend  Binder and axial yarns are clearly visible  Axial yarns are straight  Better coils but non-uniform distribution/ spacing of coils

SAMPLE – 4

Figure 5.12 Sample-4 of the braided structure

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 More neat sample with least fibre damage  One of the binder yarns not straight  Axial yarns are straight  Better coils comparatively with uniform spacing

SAMPLE-5

Figure 5.13 Sample-5 of the braided structure

 Composed of 6K Carbon braider yarns, 6K Carbon binder yarns and 300 Tex Glass yarns.  Cleaner sample with least fibre damage  Binder yarns are better bent showing interlocking  Axial yarns are straight  Approximately equidistant coil spacing

SAMPLE-6

Figure 5.14 Sample-6 of the braided structure

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From this exercise it has been derived that yarn tension play key role while preforming the structures. It is utmost important to optimise the tensions of braiding yarns and binder yarns with respect to each other. If any of these tensions is higher than a certain limit, it will pull the other set of yarn giving the preform a deformed shape along with excessive fibre damage. Lesser the tensions are, more loose and fluffy the structure will be. Therefore, tensions of both sets of yarns should be appropriate and in good agreement with each other. An example of preform braided with uniform tension in good shape is shown in Figure 5.15.

Figure 5.15 A 30cm long uniform braided structure

5.5 Preform with Various Structure Compactness Once a uniform structure was achieved, trials had been conducted to develop the braided preforms by applying different settings of take-up in order to achieve closely packed structures. Close packing mainly depends upon the take-up rate. Increase in take-up speed results in placement of braiding yarns at wider distance. Alternatively, by increasing the number of braiding yarns the spaces between the yarns are reduced and a compact structure can be produced. Mandrel diameter also plays a defining role in yarn packing and braid angle as well. The samples in Figure 5.16-5.24 have been developed by changing various parameters.

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Sample-1a

Figure 5.16 Sample-1a

 Cross wound  90o Rotation  Take up 0.75mm  Braider - 6 K Carbon  Binder - 300 Tex Glass  Axial - 6K Carbon  No. of braiding yarns = 4+4  No. of binder yarns = 4  No. of axial yarns = 4

Sample-1b

Figure 5.17 Sample-1b

 Cross wound  90o Rotation  Take up 0.5mm  Braider - 6 K Carbon  Binder - 300 Tex Glass

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 Axial - 6K Carbon  No. of braiding yarns = 4+4  No. of binder yarns = 4  No. of axial yarns = 4

Sample-2a

Figure 5.18 Sample-2a

 Cross wound  90o Rotation  Take up 2mm  Braider - 12 K Carbon  Binder - 300 Tex Glass  Axial - 6K Carbon  No. of braiding yarns = 4+4  No. of binder yarns = 4  No. of axial yarns = 4

Sample-2b

Figure 5.19 Sample-2b

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 Cross wound  90o Rotation  Take up 0.75mm  Braider - 12 K Carbon  Binder - 300 Tex Glass  Axial - 12K Carbon  No. of braiding yarns = 4+4  No. of binder yarns = 4  No. of axial yarns = 4

Sample-3

Figure 5.20 Sample-3

 Cross wound  90o Rotation  Take up 2 mm  Braider - 12 K Carbon  Binder - 300 Tex Glass  Axial - 12K Carbon  No. of braiding yarns = 8+8  No. of binder yarns = 4  No. of axial yarns = 8

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Sample-4a

Figure 5.21 Sample-4a

 Cross wound  90o Rotation  Take up 4 mm  Braider - 12 K Carbon  Binder - 300 Tex Glass  Axial - 12K Carbon  No. of braiding yarns = 12+12  No. of binder yarns = 4  No. of axial yarns = 12

Sample-4b

Figure 5.22 Sample-4b

 Cross wound  90o Rotation  Take up 3 mm  Braider - 12 K Carbon  Binder - 300 Tex Glass

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 Axial - 12K Carbon  No. of braiding yarns = 12+12  No. of binder yarns = 4  No. of axial yarns = 12

Sample-4c

Figure 5.23 Sample-4c

 Cross wound  90o Rotation  Take up 2 mm  Braider - 12 K Carbon  Binder - 300 Tex Glass  Axial - 12K Carbon  No. of braiding yarns = 12+12  No. of binder yarns = 4  No. of axial yarns = 12

Sample-5 (Special Case with 180o +90o rotation)

Figure 5.24 Sample-5

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 Cross wound  90o + 180o Rotation  Take up 6mm  Braider - 12 K Carbon  Binder - 300 Tex Glass  Axial - 6K Carbon

5.6 Braided Yarn Placement at ±45o Various samples have been developed using mandrels with different diameters and different number of braiding yarns in order to place the braiding yarns at ±45o. It was found that the smaller the diameter of the mandrel, the smaller the braid angle. Also greater the number of braiding yarns, smaller the braid angle. Figure 5.25 shows samples braided at different angles on mandrels with different diameters.

Figure 5.25 Preforms braided at ±60o and ±45o

5.7 Sample Development for Tomography Samples have been produced for imaging through X-ray tomography. Tomographic images can be better viewed with a good contrast of density of the materials being used. For this reason glass fibre has been used as braiding yarn and a paper mandrel has been used for the development of such samples as shown in Figure 5.26.

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Glass braiding yarn

Carbon Preform axial Braided on yarn mandrel

Figure 5.26 Sample developed for tomography

Samples produced using glass fibres for imaging through X-ray tomography are shown in Figures 5.27~5.29.

Sample-1

Figure 5.27 Sample-1

 Cross wound  90o Rotation  Take up 6 mm  Braider - 600 Tex Glass

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 Binder - 300 Tex Glass  Axial - 12K Carbon  No. of braiding yarns = 8+8  No. of binder yarns = 4  No. of axial yarns = 8  Tube diameter = 30 mm

Sample-2

Figure 5.28 Sample-2

 Cross wound  90o Rotation  Take up 4 mm  Braider - 600 Tex Glass  Binder - 300 Tex Glass  Axial - 12K Carbon  No. of braiding yarns = 8+8  No. of binder yarns = 4  No. of axial yarns = 8  Tube diameter = 30 mm

Sample-3

Figure 5.29 Sample-3

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 Cross wound  90o Rotation  Take up 2 mm  Braider - 600 Tex Glass  Binder - 300 Tex Glass  Axial - 12K Carbon  No. of braiding yarns = 8+8  No. of binder yarns = 4  No. of axial yarns = 8  Tube diameter = 30 mm

5.8 Weave Topology of Novel Braided Preform Various weave patterns are possible to be preformed by the developed machine such as regular braids, square braids and many others. These weave designs can be produced by using different number of braiding yarns and keeping the ring’s degree of rotation same or by changing the degree of rotation of the rings whilst maintaining the same the number of braiding yarns.

The primary difference between the weave patterns of the braided preforms developed on the novel 3D braiding machine from those produced on a 2D circular braiding machine is the presence of binder yarn. The second difference is that the weave patterns of the braided preforms developed on the novel 3D braiding machine are in square shape unlike those produced on a 2D circular braiding machine, which may be square or rectangular. Two different weave designs are compared in Table 5.2 showing 1/1 and 2/2 interlacement patterns both for braided preforms developed on the novel 3D braiding machine and those produced on a 2D circular braiding machine.

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Table 5.2 Weave patterns of different preforms

Weave patterns of Weave patterns of Novel 3D 2D circular braiding braiding with binder yarn Square Square

B Regular Regular

5.9 Conclusion From the detailed description of preform development it is clearly evident that the machine developed on the proposed concept is capable of producing a wide range of samples. The primary goal has been the development of the anticipated preforms to validate the concept. These preforms have successfully been developed and can be compared with CAD models of the preforms within the capacity of the novel 3D braiding machine. In addition CAD models of the preform which need multiple numbers of rings can also be produced in the same manner.

Once the concept was verified by sample development, it was further investigated for closely packed preforms. It is found that the lower the take-up rate, the closer the braiding yarn placement and hence a more compact preform structure. Moreover, smaller the diameter of the mandrel, the more compact the structure will be.

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On the basis of the trial and error method, an estimation has been established for yarn tensions to develop preforms in good shape with appropriate compactness. Tensions of braiding and binder yarns have been found very vital with respect to each other. Lower tensions result in soft preforming whereas higher tensions give compactness to the preform.

Braid compactness relates with the number of braiding yarn, mandrel diameter and the take-up rate. This has been found by developing various samples by changing the take- up speed. Also the change in number of braiding yarn resulted in a change in packing. Whereas by reducing the mandrel diameter the yarn packing increases and smaller angles can be achieved. Hence a braid can be placed at ±45o angle using a mandrel with 8mm diameter and sixteen (16) braiding yarns.

Different weave designs are possible to be braided with different braid patterns of preforms. These weave patterns are different from those produced on a 2D circular braiding machine as the interlacement is achieved by way of binder yarns.

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6 CHAPTER 6 GEOMETRICAL ANALYSIS OF

BRAIDED STRUCTURES USING COMPUTED

TOMOGRAPHY

6.1 Computed Tomography (CT) Computed Tomography (CT) has been initially used in biomedical field [88]. It is a non- destructive technique to get geometrical information about the internal structure of an object. Different researchers have employed computed tomography for the study of the geometry, damage and voids of the composite materials [89, 90].

The process of CT involves collecting a large set of projections of a sample as it is rotated through 3600. In the present study, the braided samples were scanned on a Zeiss- Versa 520 system at the Henry Mosley X-ray Imaging Facility in The University of Manchester.

Scanning was performed with a voltage of 50 kV and a power of 4w. The number of projections was set to 1600. The volume was reconstructed at full resolution with a voxel size of 17.85 μm along the x, y and z directions.

Image analysis was performed using Avizo 9 software. Each volume was cropped and a non-local means filter was applied to reduce noise in each data set.

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Figure 6.1 Sample mounted on the Zeiss-Versa 520 system during CT acquisition

Braid angle Braid axis Ɵ

Figure 6.2 3D structure of the braid showing braid angle and braid axis

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Figure 6.3 Axial yarn extracted from 3D novel braided structure

Yarn crowns

Figure 6.4 Binder yarn extracted from 3D novel braided structure

The 2D braided fabric samples and 3D novel braided preforms developed on the new machine were scanned and analysed using computed tomography (CT). Figure 6.2 represents the 3D structure of the 2D braided preform showing only braided yarns obtained by using the volume rendering method in the Avizo software while Figure 6.3 represents segmented tows of the axial yarn extracted from the 3D novel braided preforms using segmentation method in Avizo software. In segmentation technique, the glass yarns were selected by using the magic wand at a threshold value corresponding to glass fibre and then 3D surface was generated by using surface generation method in the same software. Figure 6.4 represents the extracted binder yarn from the 3D novel braided preforms again by using volume rendering technique. It can be seen from Figure 6.3 that a slight crimp has been inserted into the axial yarn which was supposed to be straight due to its linear path. Figure 6.4 for the binder yarn shows higher crimp in the yarn and the crimp pattern has been affected by the non-uniformity among the braided yarns’ tension. The crowns of the binder yarn are clearing visible from the tomographic image as can be seen in Figure 6.4.

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The detail of the samples which were scanned by CT is described below.

1-Braided Sample Developed on Novel 3D Braiding Machine

Material of braided yarns 600 tex E- glass yarn

12-k carbon yarn

Material of axial yarns 12-k carbon yarn

Material of binder yarns 300 tex E- glass yarn

Interlacement angle of braided yarns 80о

Intersections/cm 1.5

No of braided yarns

Glass yarns 08

Carbon yarns 08

No of axial yarns 08

No of binder yarns 04

Diameter of the tube 30 mm

Glass braided yarns

Carbon axial yarns

Glass binder yarns

Figure 6.5 Cross-sectional views of the CT image

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Glass binders

Figure 6.6 3-D reconstruction of the braided sample

A contrast of the two colours among the braiding yarns has been used by fabricating carbon fibres and glass fibres in equal proportions in order to see the braiding pattern with clear visibility. As a result the braid pattern and the braided yarn placement can easily be distinguished along with the binder yarn interlocking through-the-thickness. The structure seems to be well packed at an angle of 80o.

In the transverse cross section (Figure 6.5 left) of the sample the glass fibres can be isolated, however in the longitudinal cross section the glass fibres are getting confused with binder yarns making it difficult to be differentiated.

2- 2D Braided Sample

Material of braided yarns 600 tex E- glass yarn

Material of axial yarns 12-k carbon yarn

Interlacement angle of braided yarns 80о

Intersections/cm 4.6

No of braided yarns 12

No of axial yarns 12

Diameter of the tube 30 mm

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Axial yarn between two braid yarns at interlacing point

Figure 6.7 Cross-sectional views of the sample

Sample No. 2 and 3 have been developed on 2D braiding machine. The weave pattern for both of the sample is the same with only difference of braiding angle.

Sample 2 is braided at an angle of 80о whereas sample 3 is developed at 65о. The advantage of the smaller angle is that the yarns in the preform are more prominent than those braided at higher angle. Moreover the axial yarns are quite visible in the sample braided at lower angle as can be seen in Figure 6.9.

The cross section of the sample 2 reflects the proper intersections between the braiding yarns whereas the axial yarns have been sandwiched between them.

There are two distinct positions; one where the axial yarns are clearly interlaced between the braiding yarns and the other where the axial yarns are running free along the length of the braided preform. Both the points can be identified from the transverse cross section. The longitudinal cross section is a cut sliced image from the 3D structure showing the braiding pattern.

3- 2D Braided Sample

Material of braided yarns 600 tex E- glass yarn

Material of axial yarns 12-k carbon yarn

Interlacement angle of braided yarns 65о

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Intersections/cm 3

No of braided yarns 12

No of axial yarns 12

Diameter of tube 30 mm

Braid glass yarn Axial carbon yarn between braid glass yarns

Figure 6.8 Cross-sectional views of the sample

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Braided yarns

Axial yarns

Figure 6.9 3-D reconstruction of the braided sample

4- Braided Sample Developed on Novel 3D Braiding Machine

Material of braided yarns 600 tex E- glass yarn

Material of axial yarns 12-k carbon yarn

Material of binder yarns 300 tex E- glass yarn

Interlacement angle of braided yarns 85о

Intersections/cm 2

No of braided yarns 16

No of axial yarns 08

No of binder yarns 04

Diameter of the tube 30 mm

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Glass braid yarns

Figure 6.10 Transverse cross-sectional views of the sample

Axial carbon yarn between two white braided glass yarns

Figure 6.11 Longitudinal cross-sectional views of the sample

Sample 4 has been developed on novel 3D braidng machine using glass fibres both for braiding and binder yarns and carbon fibres for axial yarns to observe the yarn trajectory of the axial yarns in order to comprehend the crimp of these yarns. The axial yarn is clearly identified in the longitudinal cross section of the sample as shown in Figure 6.11 and it seems to be fairly straight, though a fractional amount of crimp has been calculated in them.

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5- Braided Sample Developed on Novel 3D Braiding Machine

Material of braided yarns 12-k carbon yarn

Material of axial yarns 12-k carbon yarns

Material of binder yarns 300 tex E- glass yarn

Interlacement angle of braided yarns 80

Intersections/cm 2.2

No of braided yarns 24

No of axial yarns 08

No of binder yarns 04

Diameter of tube 22 mm

Carbon braided yarn

Glass binder yarn

Carbon axial yarn

Figure 6.12 3-D reconstruction of the 3D novel braided structure

Sample 5 has been produced by using carbon fibres for both brading and axial yarns whereas glass fibre for binder yarn in order to highlight the binder yarns and their

156 trajectory within the the braid a shown in Figure 6.12. In the following Figures 16.3a and 6.13b the binder yarns have been isolated by using volume rendering and segmentation techniques repectively in the Avizo 9 software.

Figure 6.13a Binder yarns in the 3D novel braided structure

Figure 6.13b Binder yarns in the 3D novel braided structure

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6- Braided Sample Developed on Novel 3D Braiding Machine

Material of braided yarns 600 tex glass yarn

Material of axial yarns 12-k carbon yarns

Material of binder yarns 300 tex E- glass yarn

Interlacement angle of braided yarns 70

Intersections/cm 1.5

No of braided yarns 16

No of axial yarns 08

No of binder yarns 04

Diameter of tube 30 mm

Figure 6.14 Cross-sectional views of the 3D novel braided structure

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Pulled out braided yarn by binder yarn

Figure 6.15 3-D reconstruction of the 3D novel braided structure

Sample 6 has been developed with lesser density by yarn placement at an angle of 70o compared to sample 4 with braid angle of 85o. It has been observed that some of the braiding yarns at certain points have been pulled off by binder yarns; which most likely is due to the tension variation among the braiding yarns.

The crimp % of the axial and binder yarn of the 3D novel braided preform has been calculated by measuring crimped yarn length and extended yarn length and applying the following relation.

(1)

Where

C % = Crimp of yarn taken as percentage

Lo = Original yarn length (extended yarn length)

Lc = Crimped yarn length

The crimp in the axial yarns of the 3D novel braided preforms was expected to be the least approaching zero level due to the fact that the axial yarn is simply placed between the two cross wound layers of the structure like a sandwich without any interlacement

159 with the cross wound layers. However a fractional amount of crimp as 0.3 % has been observed in the axial yarns.

The crimp value in the binder yarns of the 3D novel braided preforms has been calculated 6 % which is higher as it was expected due to the yarn being placed through- the-thickness of the structure.

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6.2 Mechanical Testing In the previous literature, different researchers have studied the mechanical performance of biaxial and tri-axial braided fabrics and also have compared the braided and the woven fabric test results [94-101]. In the present work, a preliminary testing has been done for compression and tensile loading of the 3D novel braided structure and compared with the test results of 2D braided fabrics developed on the horngear braiding machine. The details of the material, methodology and test results are present here. 2D braided fabrics are represented as B and 3D novel braided fabrics as NB in this discussion.

6.2.1 Composite Forming Once the Novel braided preforms and the 2D braided preforms are produced over mandrel, they are infused with resin epoxy by vacuum bag infusion technique (Figure 6.16). The resin is allowed to flow through the reinforcement under vacuum to wet out the preform completely. The infused samples are then cured using 2-step curing cycle; first at 80o for two hours and then at 140o for eight hours as shown in Figure 6.17. After curing the samples are cleaned and taken off the mandrel. The composite tubes are then cut into defined length according to the standards of the test to be conducted.

Figure 6.16 Vacuum Bagging & Resin Infusion for composite forming

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Curing Cycle Curve 160

140

120

C) o 100

Temperature ( Temperature 40

0 0 1 2 3 4 5 6 7 8 9 10 11 12 Time (Hours)

Figure 6.17 Curing cycle for resin infused carbon composite

6.2.2 Compression Testing

6.2.2.1 Material The specifications of the samples used for the compression loading are given in the following tables.

Table 6.1 Specifications of the material

2D Braided Samples Novel Braided Samples Braiding yarn material 12 K Carbon 12 K Carbon Axial yarn material 12 K Carbon 12 K Carbon Binder yarn material ------300 Tex Glass Braid angle 45o 45o No. of Braiding yarns 24 24 No. of Axial yarns 12 12 No. of Binder yarns ------4

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Table 6.2 The dimensions of the samples

Outer diameter Wall thickness Gauge length

(mm) (mm) (mm) 2D Braided Samples 13.30 1.35 30.00 Novel Braided Samples 12.70 1.15 30.00

6.2.2.2 Methodology An Instron 5569 testing machine with a load cell of 50kN was used for the compression testing of the braided composite samples. During the compression of the braided samples, two compression plates were used for compressing the sample as shown in Figure 6.18, the diameter of the upper and lower plates was 50cm2. During the compression, the upper crosshead was moved downwards at a constant speed of 1mm/min until the failure of the samples. Before starting to do the compression tests, a compliance curve was taken and adjusted to the compression test results to calibrate the compliances due to machine.

Load Cell

Top plate Sample

Bottom plate

Figure 6.18 Instron 5569 testing machine set-up for compression

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6.2.2.3 Results and Discussion The 2D braided samples and samples developed on 3D novel braiding machine were tested for the compression strength up till failure point. Figure 6.19 is showing a sample during compression as it has been damaged at failure.

Damage due to compression

Figure 6.19 Damaged sample at failure after compression loading

The compression stress results are plotted against compression strain results and are represented in Figure 6.20. It can be seen from Figure 6.20 that the compression strength at break is much higher for the Novel braided sample compared to 2D braided samples; it is almost more than double. The higher strength at break values of Novel braided samples may be due the closely packed yarn placement without crimp as they are not interlacing with each other hence leaving negligible spacing among them. Whereas the 2D braided sample may have lower strength at break values due to the fact of have interlaced braided yarns with crimp and small gaps at each intersection which allow the yarns to adjust while being loaded under compression.

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Figure 6.20 Compressive stress vs Compressive strain

In addition to stress strain graph, the modulus of the braided structures was also calculated and is presented in Figure 6.21. The moduli of the Novel braided samples were higher comparative to 2D braided samples which might be due to the binder yarns in the Novel braided samples that act as through-the-thickness reinforcement along the z-axis. The average modulus of Novel braided samples is 14.2GPa whereas that of 2D braided samples is 8.7GPa.

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Figure 6.21 Compression modulus of Novel braided samples & 2D braided samples

6.2.3 Tensile Testing

6.2.3.1 Material Table 6.3 Specifications of the material

Table 6.4 The dimensions of the samples

Outer diameter Wall thickness Gauge length

(mm) (mm) (mm) 2D Braided Samples 13.30 1.35 50.00 Novel Braided Samples 12.70 1.15 50.00

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6.2.3.2 Methodology An Instron 5569 testing machine with a load cell of 50 kN was used for the tensile testing of the braided composite samples. During the tensile loading of the braided samples, the samples were clamped in-between specially designed clamps as shown in Figure 6.22 and then were gripped between the upper and lower jaws of the Instron machine. During the tensile loading of the samples upper cross-head was moved upwnwards at a speed of 1 mm/min. Before starting to do the tensile testing, a compliance curve was taken to calibrate the minor compliances due to machine stroke.

Braided sample

Figure 6.22 Sample clamped in Instron machine

Figure 6.23 Fixture for clamping the braided composite tubes

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6.2.3.3 Results and Discussion 2D braided samples and samples developed on 3D novel braiding machine were also tested for the tensile strength. Figure 6.24 shows the damage occurred at failure of the sample as a result of tensile loading.

Damage due to tensile loading

Figure 6.24 Fracture in the sample during tensile loading

The tensile stress and strain results were obtained during the testing and are plotted against each other which are presented in Figure 6.25. The tensile strength at break of the Novel braided samples is higher compared to that of 2D braided samples. The possible reasons could be the crimp in braided yarns of 2D braided samples which results in reduction of the strength compared to Novel braided samples which have closely packed yarn layers with minimal crimp or even no crimp. However the presence of binder yarns may reduce the strength of the Novel braided samples to a very small extent as the ratio of the binder yarns to the braiding yarns is 1:6 as can be seen in the table 6.3. Another aspect of the stress-strain graph is that the Novel braided samples exhibit smooth curves which show that they are taking load to strain with uniform elongation until a sudden break at failure. However the 2D braided samples exhibit jumbled curves with fluctuating rise and fall of stress against strain. It might be due to the locking and relaxing of the interlaced braiding yarns as the samples are subjected to loading hence gaining and loosing strength respectively.

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Figure 6.25 Tensile stress vs Tensile strain

The tensile modulus calculated for the tensile testing results are graphically presented in the Figure 6.24, which shows higher values of modulus for the Novel braided samples compared to those of 2D braided samples. The possible reasons may be the presence of nearly straight axial yarn in Novel braided samples whereas the axial yarns in 2D braided samples get slightly higher crimp on account of being interlaced between the two sets of braiding yarns hence resulting in lower modulus values. The average modulus of the Novel braided samples is 15.5GPa and that of the 2D braided samples is 10.4.

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Figure 6.26 Tensile modulus of Novel braided samples & 2D braided samples

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6.3 Conclusion It has been found in the CT results that binder yarn have higher crimp % while axial yarn of the 3D structure has very less crimp. Also it has been noticed that tow pull out occurs due to binder yarn in 3D novel structure. In mechanical test results of 2D braided and 3D novel braided structure, the compression and tensile modulus and strength of 3D novel braided structures are higher than those of 2D braided structure which might be due to the presence of crimped braiding yarn in 2D braided structure as it has been observed by previous researchers that high crimp reduces both compression and tensile modulus of the woven structure. Additionally, the slight crimps in axial yarns in 2D braided structure also contribute to the reduction in strength and stiffness. Though the presence of binder yarns in Novel braided structures should be the reason for decreasing the tensile and compression strength but they are not playing a major role in this regards probably being very small in number.

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7 CHAPTER 7 CONCLUSION AND FUTURE

WORK

7.1 Conclusion The research was aimed to develop a novel 3D textile preforming machine and this has resulted in the successful construction of an automated machine to develop multi-axial 3D textile circular preforms. After considering a number of useful ideas eventually the research has been narrowed down to focus on the development of a circular braiding machine that is capable of incorporating braiding yarns along with axial yarns and the novel insertion of through-the-thickness yarns along the z-axis. Then the idea was further modified to make it possible for the concept to develop multi-layered circular structures with through-the-thickness yarns along the z-axis to serve as binder yarns which interlock all the layers together. The z-axis yarn is similar to that used in 3D through-the-thickness woven preforms developed by various methods. In short the main distinguishing feature of the concept has been the introduction of through-the-thickness binder yarns along the z-axis; this has not been previously possible in either 3D circular braided structures or 2D circular over-wrapped layered structures.

Insertion of binder yarns has been achieved by introducing a smart bobbin transferring mechanism. The key element of this development is the miniature shuttle and its associated handling mechanism. The use of internal pneumatic grippers complementary with a pneumatic actuator has made it possible to transfer the bobbin across the braiding area and to return it, thus resulting in the placement of z-axis yarns in the structure.

Once the machine had been developed, the 3D braided preforms could be produced. The development of various samples and their fibre architectures was analysed through tomographic images and these have verified the concept and its potential for braiding a wide range of fibre architectures within the scope of the concept. Preliminary mechanical tests have been conducted to observe the trend and behaviour of the multi- axial textile preforms by comparing with similar braided structures produced on a horngear braiding machine. The tensile test results of the multi-axial preforms showed good agreement with those of the braided structure produced on the horngear braiding

172 machine. Whereas the compression test results seemed to be slightly better than those of the braided structure, probably on account of the z-axis yarns in the structure of the multi-axial preforms.

This research work has been concluded here whilst opening a new window in preforming technology. This development requires further research in this area to exploit its potential for future prospects.

7.2 Future Work First and foremost, a new version of the machine should be constructed. This should be done mainly by increasing the number of rings, along with some necessary modifications to the machine parts. The number of rings may be increased commensurate with the workable space available in the machine to be constructed, length of take-up drive, and the size of the pneumatic (or electronic) actuators for transferring the miniature shuttles of binder yarn bobbins. It will also depend upon the required number of layers in the structures to be produced.

The development of this new version will expand the scope of the machine from developing double-layered structures to multi-layered structures.

Tension optimisation has a vital role in preforming a the braids in acceptable shape as the tension variations cause deformation of the preform structure resulting into a non- uniform preforms. While manufacturing the samples on 3D novel textile machine, it was found that setting the yarn tensions of all the three set of yarns uniform with respect to one another has been a challenging task. The structure of the braid will either be loose or over tensioned in case the yarn tensions are not properly optimised. The tension variation exists between the different sets of yarn as well as within the same set of yarn. In case of higher tension in binder yarns, the structure will be pulled out with small gaps between intersections of the binder yarn. Whereas in case of higher braiding yarn tensions, the structure will be such that the binder yarns will be compelled to follow a knit loop like trajectory instead of a proper through-the-thickness loop.

Another issue as a component of the above point is the non-uniformity of the yarn tensions among themselves within a group of yarns such as braiding yarns, binder yarns

173 and axial yarns. It has been found that the tensions within a group of yarn vary from yarn to yarn.

The reasons for both of the above points are the same; the machine does not have a mechanical arrangement for pre-setting yarn tensions. Compression springs are being used to impart tension to the yarns. Every single yarn has its tension controlled by a cut piece of compression spring and each is adjusted manually. Thus the resulting tension in each and every yarn may not be the same.

Mechanical testing to evaluate the out-of-plane properties is an important task yet to be done with full range of tests including impact testing, bending tests, a transverse compression test, and a torsion test. This would be an extensive job for future researchers.

Modelling can be another key area of research to predict the behaviour and response of the structures produced by the novel 3D textile machine.

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Appendix

Programming

FCT (Festo Configuration Tool) images have been shown for setting various parameters to develop samples. The first six images are showing overall configuration of the machine.

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The following image is displaying the motion settings for braiding ring R1.

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The following image is displaying the motion settings for braiding ring R2.

The following image is displaying the settings for take-up motion.

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The following images are the screenshots of the CoDeSys V2.3 programming software by Festo.

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