Anisotropic degradation mechanism on low-velocity impact of 3D braided composites after thermo-oxidative ageing

Anisotropic mechanical behaviors are the most prominent feature of 3D braided composites compared with homogeneous materials. This study reports anisotropic low-velocity impact behaviors of 3D braided carbon fiber/epoxy composites along in-plane (IP) and out-of-plane (OP) directions after thermo-oxidative ageing. The stress-strain responses, local strain and damage evolution were obtained. The stress distribution of each yarn and the interface damage propagation were analyzed with numerical analysis method. The retention rate of peak stress of 94.4% and elastic modulus of 91.45% along OP direction are greater than those along IP direction, which are 76.21% and 71.27% respectively. It reveals that the OP direction loading has a better performance on resistance ageing degradation than that in IP loading, and the stiffness degradation is more sensitive. There are X-shape shear damages along OP direction, and interior damages in surrounding area and yarn path along IP direction. Furthermore, the tight braided structure contributed to resisting degradation of mechanical properties along IP direction.