Shielding Effect in Fatigue Damage Process after Lateral Impact in CFRP Laminates.

Abstract

Fatigue tests were conducted on CFRP angle ply laminates with three-layered stacking sequence, which were damaged beforehand by means of a lateral impact using a free fall rod. Fatigue damage propagation process after the lateral impact consists of the extension of surface matrix crack inter-laminar delamination and damages at the edge of specimen. From a series of fatigue tests, it was found that there exists two extension mechanisms in surface matrix crack propagation. One is extension rates decreasing type with crack propagation, the other is almost constant rates type. In the former, it seems that the decrease in crack extension rates is due to the shielding effects, since small deflections in crack growth were observed on the specimen surface. In addition, from the SEM observation of fracture surfaces, it is shown that the out-of-order in fiber alignment and the fiber breakage were remarkable in the former, while in the latter, fibers were straightforward and few breakage was found. Based on the results, it is suggested that the shielding effects induced by the crack deflection and by the out-of-order in fiber alignment result in the decrease in extension rates of matrix crack.