Line-spring finite element for fully plastic crack growth—II. Surface-cracked plates and pipes

Abstract

Crack-tip opening angle (CTOA) is generally considered as the most operable fracture descriptor for fully plastic, quasi-steady, extensive crack extension. In Part I, based on the CTOA crack growth criterion, a line-spring finite element model was presented to resolve through-thickness crack growth in plane strain single-edge-cracked specimens and surface-cracked plate/shell structures under fully plastic loading. With constraint-dependent CTOA and some supplemental kinematic relations given, the line-spring model ultimately monitors crack extension from the history of generalized displacements. The model was implemented in the implicit ABAQUS finite element code (1993b) in a user-defined element form. Following the plane strain parametric studies in Part I, we further apply the line-spring model to the problems of surface-cracked plates and pipes in Part II here. Effects of material hardening, configuration and location of the surface crack on the histories of penetration-displacement/pressure are examined in a remotely-stretched plate and a pressurized cylindrical vessel. As the most plausible exercise of a stable crack propagation leading to leak-before-break failure, a circumferentially cracked pipe subject to pure bending is selected. Evolution of CTOA along the crack-front and surface crack enlargement pattern are examined for each case. Experimentally-observed CTOA values for the remotely-stretched plate are interpreted in light of the model prediction.