In this study, impact and CAI (compressive after impact) tests, with varying impact energies, were conducted using quasi-isotropic laminates with different ply thicknesses (0.02, 0.12, 0.24mm). It consisted of a 0.02-mm-thick thin-ply prepreg sheet. The effects of ply thickness and impact energy on damage characteristics and CAI strength during impact were evaluated. Furthermore, specimens were meticulously inspected after impact using X-ray CT to investigate the effect of ply thickness on damage mode, especially the locations of matrix cracks and delamination in thickness direction. Results confirmed that fiber breakages became a predominant damage mode upon decreasing the ply thickness due to the constraining effect of neighboring layers, while most of the failures in thick-ply laminates, such as matrix cracks and delamination, were resin failure. Moreover, when the ply thickness was decreased, the CAI strength was lower than that in thick-ply laminates due to the propagation of fiber breakage in the thickness direction at a high impact energy. The CAI strength improved when the impact energy was below 5 J/mm.
