Effect of Stacking Sequence on Fatigue Damage Process in CFRP Laminates after Lateral Impact.

Abstract

A series of tensile and fatigue tests were conducted on CFRP angle ply laminate specimens with different atacking sequence, i. e. three-layered, five-layered and seven-layered laminates, which were damaged from lateral impact by a free fall rod. The extension of surface cracks and the development of delaminations were observed by using a replicating method and a scanning acoustic microscope (SAM), respectively. In all stacking sequences under fatigue loading, the crack growth process consisted of several stages, and crack growth rates gradually decreased. In three-layered specimen, a single crack was nucleated in the opposite layer to the surface which was given lateral impact. After the crack tips attained to the edge of specimen, inter laminar delamination began to extend. On the other hand, several cracks were observed in the five-layered and seven-layered specimen. In addition to the extension of cracks in the surface layer introduced by impact load, several new matrix cracks initiated at the edge of specimen. Crack growth was followed by the development of interlaminar delamination. The delamination in each stacking sequence developed along the preceding matrix cracks, and the effect of the preceding matrix cracks in the middle layer was notable in threelayered specimen. In five-layered specimen, the delaminations in the failured specimen was not influenced by the matrix cracks in the middle layer, but were affected by the cracks emanating from the free edge in the outer layer.