Experimental investigation on single and repeated flexible impact response and residual strength of composite foam sandwich structures

Composite foam sandwich structures are widely employed in aerospace and other advanced engineering fields due to excellent mechanical properties. During manufacturing and service, composite foam sandwich structures are inevitably subjected to various impacts, including flexible and repeated impacts, which introduce complex damage and severely threaten structural integrity and service life. This study presents an experimental investigation into the response of CFRP/PMI foam sandwich panels subjected to single and repeated flexible impacts. The impact response, energy absorption efficiency, and interlaminar damage evolution (characterized via C-scan) were analyzed under varying impact energies and numbers of impacts. The residual compressive strength after impact was further investigated through compression-after-impact (CAI) tests on impacted and inspected foam sandwich panels. Residual strength values and failure modes of the panels were obtained under different impact energies and numbers of impacts. In addition, correlations between single-impact energy and repeated impacts at equivalent damage levels were established. The results indicate that a limited number of repeated low-energy impacts resulted in damage comparable to that from a moderate-energy single impact, while a greater number of such repeated impacts produced damage equivalent to a high-energy single impact.