Interaction between collinear asymmetric cracks

Abstract

Thin strips made of perspex and containing two collinear internal cracks of different length were subjected to tension. The thickness variation of the strips was depicted by the reflected-shadow method, in which a coherent monochromatic light beam, emitted from a helium-neon gas laser, was partly reflected from the rear surface of the specimen. The light rays emerging from the plate, which were twice refracted along the thickness and reflected on the rear surface of the plate, were retarded according to Favre's and Neumann's law. The retarded light rays were focused on a caustic surface which depicted the boundary between the constrained area surrounding the crack tip and the remainder of the plate. In this paper two asymmetric collinear internal cracks of different lengths were studied and the interaction between these cracks was evaluated by measuring the variation of the diameter and the distortion of the shape of the caustics for various ratios of crack lengths.