Experimental study of the influence of thickness and ply-stacking sequence on the compression after impact strength of carbon fibre reinforced epoxy laminates

Composite structures are particularly vulnerable to impact which drastically reduces their residual strength [1-3]. In this work, the influence of laminate thickness, ply-stacking sequence and scaling technique on the impact damage tolerance of CFRP laminates is investigated by means of compression after impact (CAI) tests. Drop-weight impact tests were carried out to determine impact response of the different composite laminates. CAI tests were performed in a non-standard CAI device in order to obtain the compression residual strength. In addition, open-hole compression (OHC) tests were performed for comparative purposes. Ultrasonic C-scanning and cross-sections of CAI samples were examined to assess failure mechanisms of the different configurations. It was observed that damage tolerance decreases as impact energy increases. In addition, thicker laminates show higher CAI strength due to higher bending stiffness. Furthermore, angle-ply laminates depict better performance in terms of damage tolerance. Finally, the results obtained demonstrate that introducing ply blocking had a negative effect on the damage resistance but, conversely, an improvement of the CAI strength.