Multi-scale damage mechanics method for predicting fatigue life of plain-braided C/SiC composites

In order to predict fatigue life of plain-braided C/SiC composites, a fiber bundle unit cell model and a braided unit cell model were established based on the meso-structure of two-dimensional braided C/SiC composites. First, different failure modes were considered and a progressive damage model of the two-dimensional braided C/SiC composite was established. Based on the results obtained by on-axis uniaxial tensile tests, the damage process of the unit cell model during off-axis tension was analyzed. In fatigue damage analysis, the uniaxial tensile fatigue experimental data of the plain-braided C/SiC composite standard specimen were used to fit the fatigue damage evolution equation of the fiber bundle. The fatigue damage results obtained by the model under uniaxial, biaxial, and shear loading were analyzed and fitted to obtain the equivalent stress equation and anisotropic macro-damage evolution equation. Finally, the life of the plain-braided C/SiC composite was estimated under random loading.