Low velocity impact and compression after impact tests on thin carbon/epoxy laminates

The results of drop-weight impact tests and compression after impact (CAI) tests on carbon/epoxy laminates are presented. The experiments were carried out on specimens of two different geometries (rectangular and circular), according to two ASTM standards. Laminates of small thickness, thus prone to buckling under compression, were considered. Two different quasi-isotropic stacking sequences, obtained by cutting the specimens in two perpendicular directions, were also tested for each geometry, in order to study the influence of both these factors on the impact and post-impact response. In impact tests different dynamic behaviour, energy absorption and material damage were observed between coupons of different geometry; in the case of rectangular coupons, stacking sequence also affected the results. The behaviour of laminates under compression was always characterized by global buckling due to the small thickness. Different deformed shapes of the buckled specimens were observed, depending on geometry and lay-up, also by means of strain measurements. Finite element analysis was helpful in the interpretation of strain recordings in different positions of the laminates. Impact-induced damage did not affect the compressive behaviour and strength in every case, depending on the extent of delamination and the global buckling mode. In some cases the pre-existing damage was able to change the buckling mode and to lower the critical load as well as the ultimate compressive load.