STEADY-STATE CRACK-GROWTH AND WORK OF FRACTURE FOR SOLIDS CHARACTERIZED BY STRAIN GRADIENT PLASTICITY

Mode I steady-stale crack growth is analysed under plane strain condit ions in small scare yielding. The elastic-plastic solid is characteriz ed by a generalization of J(2) flow theory which accounts for the infl uence of the gradients of plastic strains on hardening. The constituti ve model involves one new parameter, a material length l, specifying t he scale of nonuniform deformation at which hardening elevation owing to strain gradients becomes important. Gradients of plastic strain at a sharp crack tip result in a substantial increase in tractions ahead of the tip. This has important consequences for crack growth in materi als that fail by decohesion or cleavage at the atomic scale. The new c onstitutive law is used in conjunction with a model which represents t he fracture process by an embedded traction-separation relation applie d on the plane ahead of the crack tip. The ratio of the macroscopic wo rk of fracture to the work of the fracture process is calculated as a function of the parameters characterizing the fracture process and the solid, with particular emphasis on the role of l. (C) 1997 Elsevier S cience Ltd.