Influence of fatigue damage on the impact performance of toughened-interleave carbon fibre epoxy composite laminates

Abstract

The impact performance of mechanically fatigued carbon fibre-reinforced polymer (CFRP) composite laminates with and without thermoplastic toughening particles has been investigated through a joint experimental and numerical campaign. Prismatic carbon fibre/epoxy specimens with added toughening particles at the ply interfaces were mechanically fatigued with different load amplitudes leading to a loss in apparent stiffness of 10% to 15%. Following the fatigue loading, high resolution computed tomography (CT) has been performed, revealing varying degrees of delamination starting from the free edges along the length of the specimens. In addition, transverse matrix cracks are observed in all fatigued specimens regardless of the amount of delamination. The residual ballistic impact performance of the damaged specimens has been investigated in a dynamic three-point bending configuration at three different velocities, showing a significant detrimental effect of even barely visible initial delamination. In addition, post-mortem CT scans and detailed finite element simulations are used to gain further insight into the mechanisms by which the two types of initial damage affected the impact resistance of the laminates. Finally, repeating the same experiments on a similar CFRP system without discrete toughening particles showed that their inclusion significantly increased the impact resistance both with and without prior fatigue damage.