The effect of crack orientation on the fracture properties of composite materials

The fracture properties of a composite material reinforced with discontinuous fibers depend on how the fibers are oriented with respect to the crack plane. If the fibers are randomly oriented, their fracture contribution is independent of the crack orientation. In the more usual case, fibers possess a biased-orientation distribution, and fracture properties such as fiber pull-out energy or fiber crack bridging do depend on the crack orientation. Simple methods are given for finding These methods are demonstrated for the pull-out energy of poorly bonded fibers. The results clearly show the variation of pull-out energy with crack orientation. The proposed methods are presented as an "enabling technology", and are sufficiently general to permit application to other fracture properties.