Constraint effects on ductile fracture processes near a notch tip under mixed-mode loading

In this work, the effect of constraint on ductile fracture process of micro void growth and coalescence near a notch tip in a ductile material under mo de I and mixed mode loading (involving modes I and II) is investigated. To this end, two sets of finite element simulations are carried out under two- dimensional plane strain conditions. In the first set, a modified boundary layer formulation is employed in which the mixed mode elastic K-T field is prescribed as remote boundary conditions. Several analyses are carried out corresponding to different values of T-stress and remote elastic mode-mixit y. Next, ductile four point bend specimens subjected to mode I and mixed mo de loading are considered. In both sets of simulations, the interaction bet ween a notch tip and a pre-nucleated hole ahead of it is modelled. The back ground material is represented by the Gurson constitutive model and micro-v oid nucleation at uniformly distributed small scale particles is also taken into account. The accumulation of matrix plastic strain and porosity in th e ligament between the notch tip and the hole as well as the growth of the hole are studied. Finally, the effect of crack tip constraint on the relati onship between the fracture toughness and mode mixity is examined. (C) 1998 Elsevier Science Ltd. All rights reserved.