Abstract
Fatigue fracture behavior in two types of laminate specimen ([0_4/90_8/0_4] and [90_4/0_8/90_4]) with a hole in the middle was investigated under cyclic tensile loading. Two parameters were examined and evaluated: an equivalent stiffness and a dissipated energy calculated from hysteresis loop area in one cycle loading. Fatigue damages of specimen surface and around a hole were observed using replicated method and a scanning acoustic microscope (SAM) respectively. Four stages of fatigue damage process were recognized; (I) matrix cracks appeared around a hole and propagated in longitudinal and transverse directions, which led to steep reduction of the equivalent stiffness. (II) inter laminar delamination at 0/90 inter-ply occurred at the initiation sites of matrix cracks, and grew to the edge of the specimen. This brought on increasing area of hysteresis loop and reduction of stiffiiess. (III) inter laminar delamination took place fully in the transverse direction followed by further extension in the longitudinal direction. (IV) when the propagation of inter laminar delamination grew to the gage points of the displacement meter, fatigue loading was sustained by 0 degree layer, i.e.,0 degree fiber.
