Journal article

Bimaterial interface fracture: A discrete dislocation model

The influence of mode mixity on crack growth and failure at a metal/ceramic bimaterial interface is examined within the discrete dislocation (DD) plasticity framework. Plasticity occurs via the motion of dislocations embedded in a linearly elastic medium with physically based rules governing dislocation nucleation, motion and annihilation. The numerical procedure uses a new superposition technique, developed specifically to allow the efficient solution of DD problems containing elastic inhomogeneities. The existence of an interface crack in the unloaded configuration is assumed and the remote loading is given by the elastic bimaterial crack solution. in accordance with the small scale yielding assumption. A mode-independent cohesive zone law characterizes the interface ahead of the initial crack tip, with a small amount of viscous damping added to the interface constitutive description to avoid convergence problems. The model predicts crack growth with a resistance curve and an increasing fracture toughness with mode mixity, qualitatively similar to recent continuum plasticity calculations but much smaller in magnitude. The quantitative differences arise from the large opening stresses induced by dislocations which drives separation in cases where continuum plasticity can not. Crack tip blunting and shielding, the existence of preferential slip planes. localized regions of large deformation and competition between ductile and brittle fracture all emerge naturally from the boundary value problem solution and provide insight into the observed toughness trends. (C) 2004 Elsevier Ltd. All rights reserved.


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