Dynamic crack growth at a ductile-brittle interface

Abstract

In recent years, there has been increasing technological application of multi-phase materials like composites, cermets and polycrystalline alloys. These materials fail, most commonly, by debonding of the constituent phases along the interfaces. Hence, understanding the mechanics of interface debonding is crucial for the efficient and reliable use of these materials. In this thesis, an interface fracture mechanics approach has been adopted for studying dynamic debonding along a ductile-brittle interface. The ductile material is taken to obey an incremental theory of plasticity with linear isotropic strain hardening, while the brittle substrate is assumed to exhibit isotropic linear elasticity. Firstly, the asymptotic fields associated with dynamic interfacial crack growth under plane strain and anti-plane strain conditions are derived. The asymptotic fields are assumed to be variable-separable in polar coordinates r and 0 centered at the moving crack tip and to be of the type r% where 5 is the singularity exponent. The effect of the bi-material parameters like mismatch in elastic stiffness, strain hardening of the ductile phase, etc. and crack speed on the near-tip fields is investigated. Secondly, a full-field finite element analysis of dynamic anti-plane strain crack growth under small-scale yielding conditions is performed. The results of the finite element computations and the corresponding asymptotic analysis are compared to validate and to establish the range of dominance of the asymptotic solution. Further, theoretical predictions are made of the variation of the Mode III dynamic fracture toughness with crack velocity for interface crack growth. The influence of the bi-material parameters on the above variation is examined.