The effect of low-energy impact damage on the stiffness of composite materials

The structural performance of carbon fiber reinforced polymer (CFRP) composites is significantly influenced by low-energy impact events, which may lead to progressive stiffness degradation. In the initial stage of this study, the mechanical response of CFRP specimens to single low-energy impacts was examined, with stiffness evaluated via four-point bending tests. The findings indicated that isolated impact-induced damage, even in the presence of large-area defects, does not substantially affect the material’s stiffness. In contrast, the second phase revealed that repeated impacts of varying energy levels, generating defects at different through-thickness locations, result in damage accumulation and a marked reduction in structural stiffness. These results highlight the critical importance of considering the complete damage history and support the necessity for advanced non-destructive testing (NDT) techniques in the accurate assessment of the residual mechanical integrity of composite structures.