Stress intensity factors for near edge cracks by digital image analysis

Experimental stress intensity factors (SIFs) are evaluated for single, straight near edge cracks in a plate of finite width. The cracks are positioned at various angles and distances with respect to the edge of the plate. The far field stress is uniform tension parallel to the edge. Online digital image analysis procedures are used to extract photoelastic data from the whole field isochromatic fringe patterns. Two different techniques are used to obtain information on the near crack tip stress field: (1) Half fringe photoelasticity (HFP), which requires adjusting the load to keep the maximum fringe order less than 0.5 in the data extraction zone, and (2) Trace, a digital fringe sharpening procedure, which accurately produces traces of all half- and full-order fringes. The load is adjusted to yield multiple fringes in the field of data extraction. Experimental SIFs from HFP and Trace are compared to each other and to the numerical results that are determined by the boundary integral equation method. © 1987