In this article, the effects of ply thickness on the impact damage mechanisms in CFRP laminates are discussed based on the experimental observations. Quasi-isotropic CFRP laminates were manufactured using 38 mm thick thin-ply prepregs. Impact damage inside the laminates was evaluated by using ultrasonic scanning and sectional fractography. Compression after impact strength was also evaluated. Thin-ply laminates showed 23% higher strength than standard-ply laminates. Transverse cracks decreased drastically in thin-ply laminates, and localized delamination was largely extended. Based on the discussions in our previous study and the literature, the specific ply thickness without drastic crack propagation appears to be less than or equal to 40 mm. Therefore, the thin laminates showed few and localized transverse cracks and delamination was largely propagated in the midplane.
In order to examine the effect of ply thickness on the crack initiation and propagation in the 90 layer in [0 /90 n /0 ] laminates, we conducted numerical simulations using two-dimensional mesoscopic numerical models. We found that the stress increase in the thin layer with 40 mm thickness was restricted in the vicinity of the adjacent layers, leading to restriction of crack penetration through the 90 layer. In addition, we confirmed the effect of stiffness of adjacent layers. In the case where the 90 layer was sandwiched between 45 layers, which had lower stiffness than the 0 layers, crack propagation in the 90 layer was faster than that observed with the 0 adjacent layers. Thus, the crack propagation behavior in the 90 layer was significantly influenced by the change in the stiffness caused by the orientation angle of the adjacent layers.
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