Elastic Field Surrounding a Rapidly Tearing Crack

The transient elastic stress field surrounding a rapidly tearing crack in a single-edged notch (SEN) specimen is analyzed by dynamic photoelasticity using a 16-spark gap Cranz-Schardin camera system. The 1.6-mm-thick annealed polycarbonate SEN specimens produced rapidly tearing cracks with approximately 11-mm-long necked regions which were modeled as Dugdale strip yield zones. In addition, the wake of the residual compressive stress along the rapidly tearing crack was modeled statically by a single force parallel to the crack and acting close to the physical crack tip. Theoretical isochromatics generated by this residual-stress-corrected, propagating Dugdale model of a rapidly tearing crack agreed reasonably well with those obtained experimentally by dynamic photoelasticity.

The experimental analysis showed that the length of Dugdale strip yield zone remained essentially constant through much of the rapid tearing. The crakc-tip opening angle also remained constant, while the crack-mouth opening displacement increased during the terminal stage of crack propagation.