Studies of dynamic crack propagation and arrest in pressure vessel grade steels such as A533B and A36 indicate the development of unbroken ligaments behind the crack tip. The development of these unbroken ligaments suggests that the degree of singularity may be changed since the leading edge of the crack is no longer a well-defined line, and that examination of analysis methods may be needed.
In order to examine the influence of a diffused crack tip on the stress distribution around the crack tip and on crack behavior, a photoelastic model specimen was developed by bonding two halves of a crack-line-wedge-loaded (CLWL) specimen with a mica-impregnated adhesive. Under the application of load, interlamella debonding of the mica occurred. Islands of adhesive surrounded by the delaminated mica flakes simulated the unbroken ligaments.
The static and dynamic isochromatic fringe patterns surrounding a crack tip were photographed. Crack opening displacement measurements at two locations specified by ASTM Recommended Practice for R-Curve Determination (E 561-81) were made to assess the effective crack length. A comparison of the effective crack tip position with the isochromatic fringe patterns and fracture surface appearance was made.