Directional dependence of fracture in copper/sapphire bicrystal

Two cracks that propagate along the interface of a copper/sapphire bicrystal in opposing directions exhibit a directionally dependent fracture behavior. Rice, Suo and Wang, using the Rice-Thomson model, suggested that the phenomenon could be explained on the basis of crack tip dislocation nucleation concepts. We show that the experimentally observed orientation of directional dependence is opposite that of the prediction. Further, it is shown that Beltz and Wang, who had previously reported the experimentally observed orientation to be in accord with predictions, incorrectly measured the orientation. The crack opening displacement profile of the two cracks, as measured interferometrically and via AFM, is shown to exhibit a directional dependence. The results of finite element simulations of the specimen offer an explanation for the directional dependence of fracture on the basis of the continuum crack tip fields. (C) 2000 Acta Metallurgica Inc. Published by Elsevier. Science Ltd. All rights reserved.