Slowly Propagating Cracks Emanating from the Corners of Inclusions in Composite Materials

The problem of propagation of a crack from the corners of an orthogonal inclusion in a composite was considered in this paper by using a plane-stress bi-phase model. The specimen was made from an orthogonal metallic strip penetrating into an elastic orthogonal matrix made of plexiglas, and it was submitted to a uniform stress pulse applied at the extremity of the strip. The experimental method used in the tests was the optical method of transmitted caustics together with a high-speed camera arrangement. The successsive photographs taken during the propagation of the cracks con tained all the necessary quantities for evaluating the stress intensity factors K _I and K _II at the propagating-crack tips and the propagation velocities. This experimental arrangement has the advantage of creating slowly propagating cracks convenient for the study of dynamic phenomena in composites. The results of the tests were presented in diagrams and interesting conclusions for the behavior of slowly propagating cracks were derived.