Measurement of Stress Intensity Factor under Mixed-Mode Loading by the Method of Caustics

Abstract

As one of optical methods, the method of caustics is useful for determining the stress intensity factor. In this paper, the method of caustics was applied to the specimens with an oblique crack. The results obtained are summarized as follows: (1) The method of caustics is a useful technique to determine the stress intensity factors K_I and K_II separately under mixed-mode loading. (2) The existing theory used for measurement of this method is effective only when the initial curve radius r₀ is larger than the minimum initial curve radius r₀^min determined in this study. It is recognized that the value of r₀^min decreases as the ratio of K_II to K_I increases. (3) The 3-D stress field exists in the vicinity of crack tip, while the state of stress is nearly planestrain deformation in the case of mode I loading. In the case of mixed-mode loading, the state of stress is approximately plane-stress deformation as the ratio of K_II to K_I increases. (4) A correction is proposed to obtain the values of K from caustic images in the case of r₀<r₀^min.