Impact and Post-Impact Compression Buckling Behavior of Symmetrical Foam-Filled Hat-Stiffened Panels

This study investigates the mechanical behavior and failure mechanisms of SFHCPs under low-velocity impact and compression after impact (CAI) conditions. Symmetric foam-filled hat-stiffened composite panels (SFHCPs) are widely used in critical load-bearing structures such as vessels and aircraft due to their high strength-to-weight ratio and integrated stiffener design. However, due to the material’s high sensitivity to impact, it is necessary to conduct a systematic evaluation of its application reliability. By integrating experimental testing and numerical simulation, the buckling modes characterized by symmetry and envelope number were adopted as key performance indicators. The integration of an optical buckling measurement method with iterative finite element model (FEM) updates significantly enhances model accuracy and computational efficiency. Experimental results indicate that for specimens impacted at the mid-section of the stiffener the residual compressive strength drops sharply from 106 kN to 40.6 kN (a reduction of 61.7%), with the buckling mode changing from a symmetric four-wave pattern in the undamaged state to localized buckling in the impact region, leading to brittle failure. The integration of FPP data improved the accuracy of the FEM, highlighting the critical influence of the symmetry of the buckling mode in optimizing impact-resistant composite structures.