Bending Fatigue Behaviors Of Four-step3D Braided Composite T-beam

The four-step braiding technology can manufacture complex structural component with near-set-shape feature which can meet the safety requriements of aerospace engineering and automotive industry etc. As a common stucture part, T-beam always be sustained to cyclic bending loading during service life which makes it great vaule for experimental characterization of its bending fatigue behavior.This project reports the three-point bending fatigue behaviors of four-step3D braided composite T-beam. The fatigue life, stiffness degradation of T-beam under three-point cyclic bend loading is explored. The effects of stress level on T-beam fatigue failure mode are discussed by comparing the damage morphologies under different stress levels.The main investigations equivalent to the following:1. Four-step braiding of3D braided T-beam preformsThe T-beam preforms were fabricated by four-step braiding technique whose integrated microstructures could avoid the defect between web and flange, enhance the interlaminar shear strength and improve the strength along the thickness.2. VARTMThe vacuum assisted resin transfer molding techique (VARTM) was employed to manufacture the3D braided composite T-beam which could reach the requirements of T-beam composites perfectly. The web and flange of T-beam composites must be vertically, uniform thickness, smooth appearance, good infiltration degree of resin and less bubbles are also required. 3. The quasi-static three-point bending test and finite element method (FEM) of3D braided T-beam composites.The quasi-static three-point bending test was experimented on the MTS810.23tester, from which the ultimate bending stiffness could be obtained. Then the FEM of quasi-static bending test conducted by the interaction between ABAQUS and VUMAT written in FORTRAN. FEM results show that the centre area of web where sustains tension load endures the largest stress during the test.4. Three-point bending fatigue testThe three-point bending fatigue test also conducted on the MTS810.23systems. The stress levels used in fatigue tests were obtained from the ultimate bending stiffness of T-beam. Fatigue limit of T-beam is50%stress level on the basis of test data. Three stages could be found from the stiffness degradation curves of T-beam. The fatigue failure modes of T-beam are matrix cracks, debonding between fiber-matrix interface and fiber breakage, comparing the damage morphologies of T-beam under different stress levels.