Crack Extension and Propagation Under Plane Stress

Experiments are described that reveal the three-dimensional character of the plastic zone in front of notches and cracks in plates of an Fe-3Si steel and a plain carbon steel. These define the plane-stress regime as a function of applied stress and plate thickness. They also provide a rationale for the DM (dugdale - Muskhelishvili) model as a tentative elastic-plastic solution of a crack under plane stress. Refinements that offer a way of taking work hardening and rate - sensitive plastic deformation into account are described. In this way, unnotced tenile properties - the stress-strain curve and reduction in area - are used to calculate plastic-zone size, crack-tip displacements and strains, the crack - extension stress, and the fracture toughness, in accord with experiments. Finally, the approach is extended to ductile crack propagation and used to calculate the crack speed and the stress, strain, and strain rates imposed on material in advance of a moving crack.