Experimental study on mixed mode fracture in unidirectional fiber reinforced composites

Fiber reinforced composites are applied broadly in aeronautic and astronautic fields as a structural material. But the investigation in dynamic fracture behavior of fiber reinforced composite stands in the breach for scientists due to a large number of aircraft disasters. In this paper, the mixed mode fracture problems in fiber reinforced composites under impact are studied. First, based on the theory of the reflective dynamic caustic method for mixed mode fracture, corresponding experiments are carried out to study the dynamic fracture behaviors of unidirectional fiber reinforced composites under two kinds load conditions. By recording and analyzing the shadow spot patterns during the crack propagation process carefully, the dynamic fracture toughness and crack growth velocity of fiber reinforced composites are obtained. Via the observation of the crack growth routes and fracture sections, we further reveal the fracture mechanism of unidirectional fiber reinforced composites. It concludes that opening mode still is the easier fracture type for the pre-crack initiation in fiber reinforced composites, while the interface between fibers and matrix becomes the fatal vulnerability during the crack propagation. ? 2009 SPIE.EI