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Plane-strain elastic-plastic crack-tip fields at a constant J and various elastic T-stress levels were obtained in a modified boundary layer (MBL) formulation similar to that of Betegón and Hancock but with a slightly different power law hardening stress-strain law. The analyses were based upon small geometry change formulation and deformation theory plasticity. To verify the two-parameter characterization of elastic-plastic crack-tip fields, three-dimensional (3-D) elastic-plastic finite element (FE) analyses were performed on plates with deep (a/t = 0.60) and shallow (a/t = 0.15) semielliptical surface cracks under both remote tension and bending. Here t is the plate thickness and a is the maximum penetration of the crack through the plate thickness. In topological planes perpendicular to the semielliptical crack fronts, the crack-opening stress fields, normalized by the local J, were compared with the plane-strain MBL predictions based upon the local J and T. In all four cases studied, better than 94% agreement between the 3-D FE solutions and the plane-strain solutions was obtained for loads up to general yielding. This remarkable agreement held throughout all crack-front locations where the stress fields could be resolved accurately. Given the vastly different distributions of J, T, and crack-opening stress profiles along the collective set of respective crack fronts, the elastic T-stress appears to be a tractable, predictive parameter in quantifying elastic-plastic crack-front stress constraint.
crack-tip constraint, T, -stress, two-parameter characterization, J, -dominance, surface-cracked plates, three-dimensional finite element analysis
Senior research engineer, Edison Welding Institute, Columbus, OH