BRITTLE-INTERGRANULAR FAILURE IN 2D MICROSTRUCTURES - EXPERIMENTS ANDCOMPUTER-SIMULATIONS

Brittle intergranular fracture (BIF) is a common mode of failure for m onolithic ceramics and intermetallics, as well as for some refractory metals and metals exposed to environmental corrosion, stress corrosion cracking or high temperature creep. As interest in applications for t hese materials grows, research programs have been developed to charact erize and predict their fracture behavior. In order to experimentally quantify the effects of microstructure on local BIF, systems which hav e a minimum number of variables which influence fracture must be used. Evaluation of materials with two dimensional (2D) microstructures can considerably reduce the complexity of the system. In addition, provid ing a biaxial stress state in the 2D microstructure ensures that all b oundaries experience exclusively Mode I loading prior to failure. Biax ial elastic loading of this simplified microstructure allows the calcu lation of (a) local stress and strain fields (and their concentrations ) prior to failure, as well as (b) prediction of grain boundary streng th criteria, and (c) prediction of intergranular crack paths. This can be achieved by conducting computer simulations of the experimentally observed fracture phenomena in polycrystalline specimens having a give n texture and microgeometry. These simulations use high resolution fin ite-difference grids below the crystal scale, and involve the derivati on of a spring-network model for arbitrary in-plane crystal anisotropy . Since the grain boundary strength criterion is easily controllable i n such simulations, it can be inferred by a comparison with actual exp erimental results. The latter is complemented by results on fracture o f materials with very weak grain boundaries, thus providing a clear pe rspective on evolution of the failure process for varying degrees of e mbrittlement. Copyright (C) 1996 Acta Metallurgica Inc.