Photoelastic investigation on the crack-arrest capability of a hole

Dynamic photoelasticity employing a 16-spark gap Cranz-Schardin camera system was used to determine certain conditions leading to fracture arrest by a circular hole ahead of a propagating crack. Photoelastic models of 3/8×10×10-in. Homalite-100 plates with a 1/2-in. edge crack were loaded in a fixed-grip configuration and crack arrest was made possible by central holes of 1/2, 1/4, and 0.15-in. diameters. In one test of a uniformly loaded plate with a central hole of 0.15-in. diameter, the propagating crack continued through this hole. Changes in dynamic-stress-intensity factors, as the crack tip approaches the hole, as well as changes in the dynamic-stress-concentration factors at the far side of the hole were studied, and these results were compared with the corresponding static results determined by finite-element analysis. This comparison shows that the static analysis can be used to qualitatively assess the arrest capability of the hole using the maximum static-stress concept or the proposed concept of strain energy released as the crack penetrates the hole.