Recording caustic images by phase-shifting digital holography

Phase-shifting digital holography is applied to record the caustics of a stationary crack at arbitrary distances. The stress intensity factors of the crack are measured from the reconstructed images of the caustics. The measurement results show that the stress intensity factors are almost constant in the region where the initial curve radius, i.e., distance from the crack tip, is greater than half the specimen thickness. In addition, the stress intensity factors decrease in a three-dimensional stress field. These results correspond to those by Rosakis and Ravi-Chandar. This confirms that this method is applicable to measure the stress intensity factor of cracks.