Crack growth on the basal plane in single crystal zinc: experiments and computations

Abstract

Crack propagation on the basal planes in zinc was examined by means of in situ fracture testing of pre-cracked single crystals, with specific attention paid to the fracture mechanism. During quasistatic loading, crack propagation occurred in short bursts of dynamic crack extension followed by periods of arrests, the latter accompanied by plastic deformation and blunting of the crack-tip. In situ observations confirmed nucleation and propagation of microcracks on parallel basal planes and plastic deformation and failure of the linking ligaments. Pre-existing twins in the crack path serve as potent crack arrestors. The crystallographic orientation of the crack growth direction on the basal plane was found to influence both the fracture load as well as the deformation at the crack-tip, producing fracture surfaces of noticeably different appearances. Finite element analysis incorporating crystal plasticity was used to identify dominant slip systems and the stress distribution around the crack-tip in plane stress and plane strain. The computational results are helpful in rationalizing the experimental observations including the mechanism of crack propagation, the orientation dependence of crack-tip plasticity and the fracture surface morphology.

Keywords:

• basal cleavage
• crack growth
• single crystal
• zinc
• experiments
• computation
• crystal plasticity
• anisotropy

Acknowledgments

This work is supported primarily by the MRSEC Program (Micro- and Nano Mechanics of Materials; Brown University) of the National Science Foundation under award DMR-0520651. We acknowledge Y.J. Wei for providing the user subroutine for crystal plasticity calculations used in this effort, and thank A.F. Bower, W.A. Curtin and Y.J. Wei for many helpful discussions.