Strain rate and loading mode effects on impact response and damage evolution of pierced C/C composites: experiment and numerical simulation

Fine-woven needled C/C composites typically served in thermal structural components under high-load impact, where their service environment involved complex dynamic loads. In this study, the effects of strain rate and loading mode on impact performance and damage evolution mechanisms were investigated by combining experimental and finite element methods. Results showed that the impact performance of the composites demonstrated significant strain rate dependence and anisotropy. The X-impact strength and modulus increased moderately with strain rate, which was attributed to the dense in-plane yarn. In contrast, the Z-impact exhibited a more prominent strain rate strengthening effect: at low strain rates, its performance was limited by interfacial microcracks; while at high strain rates, the straight Z-yarns enabled rapid stress transmission, leading to Z-impact performance surpassing that of the X-impact. Strain rate and loading direction jointly influenced the damage evolution. For X-impact, damage initiated at in-plane yarn intersections and accelerated with increasing strain rate. For Z-impact, interfacial microcracks were dominant at low strain rates, whereas Z-yarn failure and shear damage became the main modes at high strain rates. The revealed strain rate dependence and anisotropy of impact performance, and the proposed finite element method provided theoretical guidance for the service application of C/C composites.