โ Scribed by Jeffrey W Kysar
No coin nor oath required. For personal study only.
AbstractรTwo 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 RiceยฑThomson 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 proยฎle of the two cracks, as measured interferometrically and via AFM, is shown to exhibit a directional dependence. The results of ยฎnite element simulations of the specimen oer an explanation for the directional dependence of fracture on the basis of the continuum crack tip ยฎelds.
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Shock recovery experiments have been conducted to assess the role of shock stress and orientation dependence on substructure evolution and deformation twinning of a [1 0 0]/ยฝ0 1 1 copper bicrystal. Transmission electron microscopy of the post-shock specimens revealed that well-defined dislocation ce