Mechanical Characterisation of Composite Materials with 3D Woven
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Mechanical characterisation of composite materials with 3D woven reinforcement architectures Winifred O Obande, BEng Submitted in fulfilment of the requirements for the Degree of Master of Engineering. Department of Mechanical, Aeronautical and Biomedical Engineering Supervisor: Dr. Walter F. Stanley Submitted to the University of Limerick, November 2016 DECLARATION I hereby declare that this project is entirely my own work, in my own words, and that all sources used in researching it are fully acknowledged and all quotations properly identified. It has not been submitted, in whole or in part, by me or another person, for the purpose of obtaining any other credit / grade. Winifred Obande __________________________________ School of Engineering, University of Limerick. November 2016 ABSTRACT The use of traditional two-dimensional (2D) fibre preforms can be associated with poor out- of-plane and interlaminar mechanical performance, particularly in response to impact loads. Such preforms comprise multiple plies which necessitate labour-intensive ply cutting and assembly steps. 3D woven textiles, due to the incorporation of through-thickness yarns, have been found to exhibit superior out-of-plane mechanical properties whilst simultaneously reducing ply-assembly time and cost (single-piece preform construction). Their delamination resistance and damage tolerance have been extensively investigated over the last number of years; however, there is a paucity of published work on their in- plane and out-of-plane mechanical properties when compared to their 2D counterparts. Thus, this research details a comprehensive mechanical characterisation of an orthogonal 3D woven composite in comparison with a suitable 2D laminate. Composite panels have been manufactured with Henkel’s Loctite BZ9130 benzoxazine resin by means of the EADS- patented vacuum assisted process (VAP®). In-plane compressive performance, impact damage resistance, damage tolerance, and out-of-plane tensile behaviour have been evaluated for both reinforcement architectures. Coupons were subjected to an energy level of 6 Joules per millimetre of laminate thickness by means of a drop-weight impact tower. Damage resistance was quantified as a function of impact damage area using penetrant-enhanced x-radiography (PEXR). Combined loading compression (CLC) tests were performed to complement compression after impact (CAI) testing which was conducted to evaluate the materials’ damage tolerance. Furthermore, out-of-plane tensile (OPT) testing has been performed on cruciform coupons using a novel test method. The experimental data revealed a 7.5% higher compressive strength for the 2D material, which was expected due to the presence of crimp and yarn misalignments within the 3D woven material. In contrast, the 3D material performed better than the 2D laminate for all other tests with 13% lower damage area, 15.5% higher residual compressive strength and 36.8% higher mean out-of-plane tensile strength. It can thus be concluded that the incorporation of through-thickness yarn components can lead to significant improvements in damage resistance and tolerance by arresting the growth of delamination and limiting the growth of localised damage. Furthermore, when loaded in the out-of-plane direction, as with the OPT test configuration, much of the load is borne by the z-binder bundles rather than the much weaker fibre-matrix interface (as is the case with 2D laminates), and consequently, the OPT strengths are higher in the 3D woven composites. Limitations of this test method have been identified and recommendations for further development are presented in the concluding remarks. ACKNOWLEDGEMENTS I would like to express sincere gratitude to my supervisor Dr. Walter Stanley for the opportunity of studying under his supervision and for being a trusted source of knowledge and guidance; I am truly grateful beyond words for his encouragement and support in all aspects of the project, especially in the final days of writing. To the Irish Centre for Composites Research (IComp), for allowing me to complete this project in parallel with core research projects. I would especially like to thank Dr. Terry McGrail, Dr. Ioannis Manolakis, Dr. Dipa Roy and Dr. Peter Hammond for their support throughout the project. I would like to acknowledge Henkel AG & Co. KGaA and Axis Composites Belfast for supplying the materials used in this study. To the Faculty of Science and Engineering for facilitating my Masters project. A special thanks to Adrian McEvoy for always being on-hand to aid in testing and his invaluable help, support and advice throughout the project. Also, thanks to the staff of the MABE workshop, particularly Joseph Leen, Paddy Kelly and Ken Harris without whom much of the project would not have been possible. I would like to dedicate this thesis to God, to my father Damian and mother Theresa and my nephews, Jake and Jamie, without whom this would not have been possible. TABLE OF CONTENTS 1 Introduction .................................................................................................................. 1 1.1 Carbon Fibre Reinforced Polymer (CFRP) Composites ............................................. 1 1.2 Autoclave Manufacturing Processes ........................................................................ 3 1.3 Liquid Resin Infusion for OOA Manufacturing.......................................................... 4 1.3.1 Resin Transfer Moulding (RTM) ........................................................................ 5 1.3.2 Vacuum Assisted Resin Transfer Moulding (VaRTM) ........................................ 6 1.3.3 Vacuum Assisted Process ................................................................................. 7 1.4 Reinforcement Materials ...................................................................................... 10 1.4.1 Textiles as Materials for OOA Manufacturing ................................................. 11 1.4.2 Resins for Advanced Applications ................................................................... 13 1.4.3 Research Objectives ....................................................................................... 14 2 Literature Review ........................................................................................................ 17 2.1 3D Weaves as Reinforcement Materials for Advanced Composites ....................... 19 2.2 Mechanical Behaviour of Textile Composites ........................................................ 22 2.2.1 Compressive Properties of Undamaged Composite Materials ........................ 22 2.2.2 Impact Damage Resistance & Damage Tolerance ........................................... 23 2.2.3 Characterisation of Out-of-Plane Mechanical Properties ................................ 32 2.2.4 Summary ....................................................................................................... 35 3 Materials and Manufacturing Methods ....................................................................... 37 3.1 Overview of Materials ........................................................................................... 37 3.2 3D Woven Preform Production Process ................................................................ 37 3.3 Panel Fabrication .................................................................................................. 40 4 Experimental Methods ................................................................................................ 45 4.1 Mechanical Characterisation ................................................................................. 45 4.1.1 Compression Testing ...................................................................................... 45 4.1.2 Drop-weight Impact Testing ........................................................................... 46 4.1.3 Compression after Impact Testing .................................................................. 50 4.1.4 Out-of-Plane Tension Tests ............................................................................ 51 5 Results and Discussions ............................................................................................... 55 5.1 Compression Testing ............................................................................................. 55 5.2 Drop-Weight Impact Testing ................................................................................. 60 5.3 Compression after Impact Testing ......................................................................... 63 5.4 Out-of-Plane Tensile Testing ................................................................................. 66 6 Conclusions and Recommendations for Future Work .................................................. 75 6.1 Conclusions ........................................................................................................... 75 6.2 Recommendations for Future Work ...................................................................... 76 7 REFERENCES ................................................................................................................ 78 TABLE OF FIGURES Figure 1-1: Roll of preimpregnated carbon fibre .................................................................... 3 Figure 1-2: RTM process schematic ....................................................................................... 5 Figure 1-3: Schematic of a conventional VaRTM set-up ......................................................... 7 Figure 1-4: Cross-sectional micrograph showing