On the impact damage resistance and tolerance improvement of hybrid CFRP/Kevlar sandwich composites

Abstract

This work presents an experimental demonstration of the significant improvement in the damage resistance of carbon fiber reinforced polymer (CFRP) Kevlar sandwich composite laminates under impact and compression after impact loads. A core of Kevlar plies was sandwiched between two face sheets of CFRP, representing two-third the global laminate thickness. Hand lay-up and vacuum bagging were used to manufacture the sandwich composite structure. Tests of low velocity impact and compression after impact (CAI) were performed to characterize the damage resistance. The different damage modes and their sequence during low velocity impact were visualized using microcomputed tomography. The results showed different damage levels in CFRP/Kevlar core laminates at low and high impact energies. At low impact energy, 10 J, few matrix cracks and delaminations were the main damage modes inside CFRP/Kevlar core laminate, however, extensive delamination, matrix cracks and fiber cut at the lower part of the laminate were appeared inside the fully CFRP laminate. At high impact energy, 70 J, fiber cut was observed inside the whole CFPR laminate, however, for CFRP/Kevlar core laminate, the lower CFRP face sheets did not suffer from any kind of damage. This allowed CFRP/Kevlar core laminate to sustain large load after the load drop occurred when the maximum load capacity of the laminate is reached. Moreover, it allowed CFRP/Kevlar core laminate to sustain larger compressive load during CAI tests resulting in improved residual CAI strength. Owing to the low density of Kevlar fibers and lower damage level during impact (better damage resistance), CFRP/Kevlar core laminate showed up to 51% larger specific CAI strength than CFRP laminate (better damage tolerance).