STABLE CRACK-GROWTH ALONG A BRITTLE DUCTILE INTERFACE - II - SMALL-SCALE YIELDING SOLUTIONS AND INTERFACIAL TOUGHNESS PREDICTIONS/

The problem bf a crack growing steadily and quasi-statically along a b rittle/ductile interface under plane strain, mixed mode, and small sca le yielding conditions is considered. The ductile material is assumed to be characterized by the J(2)-flow theory-of plasticity with linear strain hardening, while the brittle material is assumed to be linear e lastic. A displacement-based finite element method, exploiting the con vective nature of the problem; is utilized to solve the relevant bound ary value problem. In Part I of this work, the corresponding asymptoti c problem was solved. This paper addresses the full-field problem in o rder to validate the asymptotic solutions, and to explore the physical implications of the results. The numerical full-field results are fou nd to be in good agreement with the analytical asymptotic solutions. I n particular, the full-field results strongly Suggest that the stress fields in the vicinity of the crack tip are variable-separable of the power singular type; and also that the mode mix of the near-tip stress fields is, to a large extent, independent of the applied elastic;node mix; The amplitude (the plastic stress intensity factor) and the regi ons of validity of the asymptotic fields are estimated from the full-f ield results, and are observed to be strongly dependent on the, applie d mode mix. The-remote elastic loading fields appear to influence the near-tip fields, primarily, through the plastic stress intensity facto r. The present work also explores the suggestion made by Bose and Pont e Castafieda (1992) that the solutions to the small scale yielding pro blem may be used in the context of a standard crack growth criterion, requiring that continued growth take place. with a fixed near-tip crac k opening profile, to obtain theoretical predictions:for the dependenc e of interfacial toughness on the applied mode mix. Based on the numer ical results, predictions for mixed made toughness of the brittle/duct ile interface are reported. The results, which are in qualitative agre ement with available experimental data and also with some recent theor etical results, predict-a strong dependence of interfacial toughness o n mode mix, This suggests that ductility provides the main operating m echanism for explaining the dependence of interfacial toughness on-the mode mix of the applied loading fields, during steady crack growth. ( C) 1998 Elsevier Science Ltd. All rights reserved.