Study of mixed mode stress intensity factor using the experimental method of transmitted caustics

Abstract

<p>A convenient, new experimental technique for estimating both mode I and mode II stress intensity factors using the method of caustics is described and demonstrated;The use of transmitted caustics was thought to have limited potential and for this reason and others, the method was almost forgotten. One of the problems with the transmitted caustic was that the information gained seemed to be limited (since there was no inner caustic). But now with available least square techniques, which has been modified to be used with transmitted caustics, transmitted caustics can be used to solve many different mixed mode fracture problems;In this study, as one of the first steps in bringing up the almost forgotten method of transmitted caustics, stress intensity factors were determined using this method. Twelve sets of specimens with double edge cracks were examined. The models for this experiment were from a thin plate of transparent material, plexiglas. Two edge cracks were machined into one of the long edges of the plate 9.5 in long, 1.8 in wide, and 1/8 in thick. The straight cracks were positioned perpendicular to the edge of the plate with various lengths and distances with respect to each other. The models were subjected to a uniaxial tension. The caustic curves were photographed with a 35-mm camera, at different loading conditions, during the test. Measurement of the photographs gave caustic dimensions as a function of applied load. Different cases of interaction between two edge cracks have been studied. The results compared well with experimental method of reflected caustics and a numerical method. The reliability of the method of transmitted caustic is established.</p>