Effects of impactor geometry and multiple impacts on low-velocity impact response and residual compressive strength of fiber-reinforced composite laminates

Fiber-reinforced composite panels used in aerospace applications often experience low-velocity impacts (LVI) during service and maintenance by objects of various shapes, sizes, and masses, which can significantly reduce the panel's residual compressive strength. This study provides a detailed numerical and experimental analysis of LVI and compression after impact (CAI) failure mechanisms of laminates impacted by different impactor sizes and masses, along with damage accumulation during multiple impacts, and presents an effective approach for modeling progressive damage in composite laminates. The experiments were conducted using three hemispherical impactors with diameters of 6.35 mm (sharp), 25.4 mm (standard), and 96 mm (blunt), at impact energy levels of 30 J and 75 J, corresponding to barely and clearly visible impact damage (BVID and CVID). Quasi-isotropic IM7/977-3 composite specimens, sized 254 mm x 304.8 mm, were used to better represent large composite panels and study a wider range of impact scenarios. A finite element modeling methodology was developed based on the integrated enhanced LaRC05 failure criteria and the cohesive zone modeling technique to predict various composite failure modes, such as fiber breakage, pull-out, kinking, crushing, and splitting, as well as matrix cracking and delamination. The LaRC05 fiber tensile failure criterion was revised based on experimental data, improving the accuracy of the model at higher impact energies. At the same energy level, the sharp impactor caused more concentrated and severe damage, leading to lower CAI strength. The blunt impactor caused less surface damage but similar internal delamination and CAI strength compared to the standard impactor.