Mechanical behaviour of fibre reinforced polymer composites is geared by the geometrical structure of the textile reinforcements. Consistent permeability, predictable impregnation and even distribution of resin are key factors in reaching targeted mechanical performance, whereas these parameters and others are functions of the geometrical composition. Hence numerous analytical geometrical models have been described in literature covering most of the conventional commonly used weave reinforcements. However, no current model can be broadly generalized to address, for instance, manufacturing deformation of fibres cross-section, periodic variability caused by stitching in 2.5D non-crimp stitched fabrics or arbitrary fibre orientation featuring some recently developed three-dimensional textiles reinforcements. Given that the latter structures can potentially provide more favourable mechanical behaviour in terms of bending stiffness, impact resistance and through-thickness properties, it is worthwhile attempting to adapt the available geometrical modelling concepts so as to address versatile structures. This review aims to trace the physical concepts used for modelling the geometrical structures of textile reinforcements at the mesoscale and compare applicability of various analytical and numerical models to types and geometrical dimensionality of woven textile structures.

A phenomenological study was carried out on laminated carbon fibre-reinforced polymer composites subjected to constant amplitude fatigue loading. Visualization of damage progression was performed using a high-resolution Skyscan micro-computed tomography unit which provided detailed information on propagation of initially occurring cracks throughout fatigue life at specific intervals. Quantitative analysis of image sequences of virtual cross-sections throughout the three orthogonal planes of the sample resulted in defining fatigue crack growth rates, da/dn for each plane, which was interpreted in terms of the three damage modes: opening (mode I), in-plane shear (mode II) and out-of-plane shear (mode III). By applying linear elastic fracture mechanics laws, strain energy release rates were calculated and then used in a cohesive zone model formulation to define model parameters. Considering a bi-linear triangular cohesive zone model curve, maximum traction and maximum separation were calculated for each of the three damage modes, differentiating between modes II and III in a novel manner.

A phenomenological experimental study was presented for understanding the effect of cyclic loading, generally experienced by typical modern aircraft structures during flight, on the propagation of micro-mesoscopic damage in carbon fibre reinforced composite laminates. Testing was carried out by employing ultra-high resolution SkyScan 1173 XRmicro computed tomography to identify and assess damage progression during fatigue testing. It provided qualitative as well as quantitative assessments of the damage in the composites which supported the analytical investigations. An in-house solution was developed for statistically analyzing the occurrence, frequency and geometry of cracks throughout the fatigue life. This methodology was used to process the data from scan for the purposes of visualizing damage initiation and propagation. I would never have been able to finish my dissertation without the blessing of God. I am grateful to the God for the good health and wellbeing. I am extremely grateful to my supervisor, Professor Jeremy Laliberté, for sharing expertise and sincere and valuable guidance. He was always available and willing to help, and had constantly led me to strive for excellence. He had seriously taken a personal interest in my success and building my confidence. I take this opportunity to express gratitude to my cosupervisor, Professor John Goldak, who gave me the opportunity to join the program. Many thanks as well to Professor Mike Munro for his help and support over years and to my dear supervisor late Professor Atef Fahim, may his soul rest in peace. Thanks to all my colleagues; Camille, Pedro, Sadeem, Taran and Alex, for their valuable help on my project. I wish to express my sincere thanks to Carleton University for the financial support, to the National Research Council in Ottawa and to the Science and Technology Centre at Carleton University for the specimens' preparations. Special thanks to the laboratory technologist, Steve Truttman, for helping with the fatigue testing. I am also indebted to my mother, Soheir. I really appreciate her consistent support and encouragement. Finally, words cannot express my gratitude, appreciation, dedication and love of my sons, Eyad and Youssef. They happily allowed me for long hours, which they deserved more, to work on my thesis. They encouraged and pushed me forward, never complained nor demanded the least of what I owe them. I admit so many debts to repay, but my sons' support goes beyond any intellectual loan. xv List of Appendices Appendix A Test Sample Specifications …………….….………....… Appendix B Material: DA 409U/G35 Unidirectional Carbon/Epoxy Prepreg …………………………………………….. Appendix C CLT calculations of Laminate Constants ………..…… Appendix D MATLAB Code for 3D Plotting of MicroCT scans …….. xvi Nomenclature List of Symbols Latin a Crack length CI Constant (normal mode) CII Constant (in-plane shear mode) CIII Constant (out-of-plane shear mode) EL Longitudinal modulus ET Transverse modulus E1, E2 Elastic Constants GLT Shear modulus Gn Fracture energy (normal mo...