Variations of constraint and plastic zone size in surface-cracked plates under tension or bending loads

Elastic-plastic finite element analyses of surface-cracked plates are performed using the commercial finite element code ANSYS. Various crack geometries are analyzed under tension and bending loads. A constraint factor dependent on the location along the perimeter of the surface crack, similar to the global constraint factor defined by Newman, is presented. This newly defined constraint factor is the averaged normal stress to flow stress ratio acting on a line originating on and perpendicular to the crack front at a prescribed location and terminating at the perimeter of the plastic zone on the crack plane. The plastic zone shape and size around the three-dimensional crack front determined from the finite element analyses are also presented. The analyses indicate that the maximum plastic zone size occurs beneath the free surface (2° < Φ < 5°). Geometry and applied loading parameters are considered in equations relating them to constraint along the crack front.