Fatigue Behavior And Structural Effects Of3-D Angle-interlock Woven Composites Undergoing Three-point Bending Cyclic Loading

The layer-to-layer three-dimensional (3-D) Angle-Interlock Woven Fabric (3DAWF) construction is composed of two types of yarn systems, i.e., warp and weft yarns. It presents a layer-to-layer angle-interlocking structure where the weft yarns are in almost straight way, as well as the undulated warp yarns are placed at an angle to the thickness direction of the material structure. The adjacent two undulated warp yarns in a single layer display a converse undulation form to ensure that two adjacent layers of non-crimp weft yarns be held together to form a stable and integrated woven construction. This structural feature imparts high strength, stiffness, inter-layer shear strength and large-area energy absorption capacity for the3DAWF reinforced composite, i.e.,3-D Angle-Interlock Woven Composite (3DAWC), which also make such type of composite have a wide potential in the field of structural engineering materials applications. Considering the performance of fatigue resistance for the composites is very important during the long-term use, especially in the design and applications of engineering structures such as aircrafts and vehicles. Conducting the research on the fatigue behavior of the3DAWC undergoing cyclic loading conditions is of critical importance. In this dissertation, the fatigue behavior, structural effects and damage mechanisms of the layer-to-layer3DAWC subjected to three-point bending cyclic loading are presented by both experimental and Finite Element Method (FEM).In the experimental, we have obtained the following contents:(1) the fatigue life (Stress levels vs. Numbers of cycles to failure, S-N) curve of the3DAWC samples for presenting the relationship between the fatigue resistance capacity and applied stress levels (60%-80%);(2) the curves of Stress vs. Deflection, Stiffness degradation and Deflection variation, for characterizing and analyzing the "three-stage" form cumulative fatigue damage evolution of the3DAWC under three-point bending cyclic loading;(3) the comparisons of ultimate damage modes of the3DAWC samples between the quasi-static three-point bending loading and three-point bending cyclic loading, for indicating the dominated role of the initiation and propagation of the cracks during the entire fatigue damage process of composites;(4) the comparisons of mechanical responses and damage modes between the3DAWC samples and the3-D Orthogonal Woven Composite (3DOWC) samples under both the quasi-static three-point bending loading and three-point bending cyclic loading conditions, for summarizing the structural characteristics and advantages of the3DAWC in resisting the three-point bending cyclic loading.In FEM model which takes the classic fatigue damage criteria into account, the main objectives are as follows:(1) to establish the micro-structural unit-cell model of the3DAWC under three-point bending cyclic loading;(2) to calculate the dynamic mechanical responses of the composite during fatigue loading;(3) to describe the structural effects and damage mechanisms of the layer-to-layer3DAWC subjected to three-point bending cyclic loading by the stress distribution, damage evolution of the yarns and resin, debonding initiation and propagation on the resin-yarns interface and critical regions of structural fatigue damage.This dissertation provides an effective method for the fatigue resistance structural designing of the3DAWC undergoing cyclic loading. Such an effect could be extended applied to the fatigue resistance structural design of the3D textile structural composites in the field of engineering structures such as aircrafts and vehicles.