Fatigue Life Prediction Of Three-dimensional And Four-directional Braided Composites

As more significance has been laid on lightweight and high-strength in the development of aerospace and war industries,fiber-reinforced composites have gradually drawn greater attention and begun to be widely used.Three-dimensional braided composites can form along the three directions of length,width and thickness an overall network structure which is not liable to stratification,creating superior structural integrity.However,due to the complexity of its structure,the fatigue properties of three-dimensional braided composites are still relatively small.In this thesis,the preform of three-dimensional and four-directional braided composites was fabricated by RTM to obtain the tensile test specimens,which underwent a static tensile test and tensile fatigue test at different stress levels.The strength data of the material were obtained by the static tensile test.The fatigue life of the material at different stress levels is obtained by the tensile-tensile fatigue test and its failure mechanism was analyzed.The unit cell model of three-dimensional and four-directional braided composites with an octagonal fiber cross section was established.Using the ABAQUS finite element analysis software,the progressive damage analysis program was developed to study the damage process of three-dimensional four-direction braided composites under static tension.The tensile strength and failure modes were in good agreement with the experimental results,which verified the accuracy of the unit cell model in the thesis.Based on the fatigue residual stiffness and strength model of unidirectional composites,the fatigue life prediction model of three-dimensional and four-directional braided composites was created by combining the fatigue failure criteria and performance damping method of component materials.The fatigue life prediction and progressive damage analysis program was developed by using the ABAQUS finite element software UMAT to simulate the fatigue life and damage propagation process of three-dimensional and four-directional braided composites under fatigue loading.