Mechanical Behavior Characterization of Knitted Textiles A Thesis Submitted to the Faculty of Drexel University by Mustafa Oncul in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering December 2017 © Copyright 2017 Mustafa Oncul. All Rights Reserved. ii In the Name of Allah, the Entirely Merciful, the Especially Merciful iii TABLE OF CONTENTS LIST OF TABLES .......................................................................................................... v LIST OF FIGURES ........................................................................................................ vi ABSTRACT .................................................................................................................... x CHAPTER 1: INTRODUCTION ................................................................................... 1 1.1 An Overview ............................................................................................................. 1 1.1.1 Knitted Textiles .................................................................................................. 3 1.2 Testing and Characterization of Textiles .................................................................. 7 1.3 Nonlinear Mechanics of Knitted Textiles ................................................................. 9 1.4 Thesis Structure ....................................................................................................... 12 CHAPTER 2: BACKGROUND AND STATE-OF-THE-ART IN MECHANICAL BEHAVIOR CHARACTERIZATION AND TESTING OF KNITTED TEXTILES . 14 2.1 Bulk Measurements ................................................................................................. 14 2.2 Local Level Measurements ..................................................................................... 18 2.3 Textile Testing Standards ........................................................................................ 22 2.4 Three-dimensional Geometry Extraction ................................................................ 25 2.5 Modeling ................................................................................................................. 26 CHAPTER 3: THESIS OBJECTIVE AND APPROACH ............................................ 31 3.1 Research Motivation ............................................................................................... 31 3.2 Hypothesis and Objective ........................................................................................ 33 3.3 Proposed Approach ................................................................................................. 34 CHAPTER 4: EXPERIMENTAL SETUP AND PROCEDURE ................................. 37 4.1 Manufacturing of Specimens .................................................................................. 37 4.2 Mechanical Testing Setups ...................................................................................... 41 4.2.1 Micro-scale ....................................................................................................... 42 4.2.2 Lab-scale........................................................................................................... 43 4.3 Strain and Apparent Stiffness Calculations ............................................................. 45 4.3.1 Strain Calculation ............................................................................................. 45 4.3.2 Apparent Stiffness Calculation ......................................................................... 46 4.4 Speckle Pattern Creation for Digital Image Correlation ......................................... 47 4.5 Image Acquisition Setup ......................................................................................... 50 iv CHAPTER 5: MECHANICAL BEHAVIOR CHARACTERIZATION OF KNITTED TEXTILES .................................................................................................................... 52 5.1 Global Measurements .............................................................................................. 52 5.1.1 Deformation ...................................................................................................... 52 5.1.2 Anisotropy ........................................................................................................ 55 5.1.3 Cyclic Loading ................................................................................................. 61 5.1.3 Stress Relaxation .............................................................................................. 63 5.2 Local Measurements ............................................................................................... 65 5.2.1 Yarn-level measurement results ....................................................................... 69 5.3 Correlation of Global and Local Measurements ..................................................... 72 CHAPTER 6: 3D GEOMETRY EXTRACTION ......................................................... 77 6.1 Material Geometry Characterization ....................................................................... 77 6.2 Data Extraction and Connection to Modeling ......................................................... 78 CHAPTER 7: CONCLUDING REMARKS AND FUTURE PROSPECTS ................ 82 LIST OF REFERENCES .............................................................................................. 83 v LIST OF TABLES Table 1: Deformation mechanisms of fabrics: a) Knitted, b) Woven, c) Nonwoven [14] ......................................................................................................................................... 8 Table 2: Measurement types and ASTM Standards ...................................................... 23 Table 3: Geometrical parameters and gauges of the manufactured specimens ............. 39 Table 4: GATAN load stage characteristics .................................................................. 42 Table 5: Mark-10 tensile tester characteristics .............................................................. 44 Table 6: Average speckle length values ........................................................................ 50 Table 7: Facet field characteristics ................................................................................ 51 Table 8: Average apparent stiffness values (N/mm) ..................................................... 58 Table 9: Areas of the load-strain curves ........................................................................ 62 vi LIST OF FIGURES Figure 1: Common textile structures: a) Knitted, b) Woven, c) Nonwoven, and d) Braided [2, 3] ................................................................................................................... 2 Figure 2: Various knitting patterns: a) Plain weft knit (Single Jersey), b) Rib knit, c) Plain warp knit, d) Single Tuck stitch F, e) Single Tuck stitch G, f) Interlock E, g) Full tricot, h) three-needle queens cord, i) Three-needle sharkskin [4-6] .............................. 3 Figure 3: Schematic representation of the hierarchical knit architecture; a) knitted loop, b) knit patterns, c) grid pattern, d) restructured grid [11] ............................................... 4 Figure 4: a) plain weft knit, b) weft knitting process, c) warp knit, d) warp knitting process [4, 5] ................................................................................................................... 5 Figure 5: The mechanism of a latch needle; a) running, b) clearing, c) feeding, d) loop pulling, e) knock over [8] ................................................................................................ 6 Figure 6: Some of the textile testing and characterization methods [1] .......................... 9 Figure 7: Load-displacement curves for woven and knitted fabrics [16]...................... 10 Figure 8: Structure of the thesis .................................................................................... 13 Figure 9: Macro-level deformation modes: a) transverse compression, b) in-plane tension, c) in-plane shear, d) out-of-plane bending [16] ............................................... 14 Figure 10: (a) Structure of the co-woven-knitted fabric, (b) Tension stress-strain and (c) tear displacement-load curves, along various directions ............................................... 16 Figure 11: Tensile test setup with non-crimp fabric structure....................................... 17 Figure 12: Stress-strain curves of the spacer fabrics: a) not glued, and b) glued to platens surfaces ............................................................................................................. 18 Figure 13: Micro-level deformation modes: a) inter-yarn slip, b) inter-yarn shear, c) yarn bending, d) yarn buckling, e) intra-yarn slip (inter-fiber friction), f) yarn stretching, g) yarn compression, h) yarn twist [16] ....................................................... 19 Figure 14: Displacement fields; a) at macroscale, b) at mesoscale (within the yarn) ... 21 Figure 15: a) Test apparatus; tensile tester and image acquisition, b) Displacement field within a woven yarn with 1.92 mm warp width and 2.21 mm weft width ................... 21 Figure 16: Picture frame test: (a) ‘Small Square’ setup in the reference state (ROI and subset window is indicated), (b) Fabric deformation for the ‘Small Square’ setup, (c) Fabric deformation for the ‘Large Cross’ setup ............................................................ 22 Figure 17: a)