Experimental evaluation of stress field around crack tip by caustic method

Abstract

The caustic method is an optical technique which is useful to determine stress intensity factor values. In this paper, the caustics method was applied to specimens which have an oblique crack, various thicknesses and an open notch to investigate the stress field around the crack tip. The results are summarized as follows: 1. The caustic method is a useful technique to determine the stress intensity factor values of the specimens which have an oblique crack or various thickness and an open notch. 2. The conventional theory of measurement concerning this method is effective when the initial curve r 0 is larger than the minimum initial curve r 0 min which was obtained in this study. It is observed that the values of r 0 min decrease as the ratio of K II to K I increases under mixed-mode loading, the one increases with an increase of thickness and notch opening angle. 3. The 3D stress field exists in the vicinity of crack tip; however, the stress state is nearly plane strain deformation in the case of mode I loading. In the case of mixed-mode loading, the stress state approximates to plane stress deformation as the ratio of K II to K I increases. 4. A method based on the distribution of the three-dimensional (3D) stress field is proposed to expediently yield the values of K I using the caustic method in the case of r 0< r 0 min.