Three-dimensional effects in the determination of stress intensity factors by the method of caustics

A thorough investigation of the dependence of the stress-optical constants on the degree of triaxiality in the stress field is undertaken. This study is essential for the evaluation of stress intensity factors in crack problems by the method of caustics, since the state of stress around the crack tip, generally, is three-dimensional. Results showing the variation of the stress-optical constants around the crack tip are displayed. Based on these results a new methodology for the experimental evaluation of stress intensity factors by caustics is proposed. According to this methodology stress intensity factors can be determined even for the case when the initial curve of the caustic lies in the region where the state of stress is three-dimensional and cannot be approximated as plane stress or plane strain.