Effect of residual stresses on the onset of yielding in a Zr-based metallic glass

Indentation experiments were performed on as-cast and elastically-bent-and-constrained Zr-based metallic glass samples to investigate the effect of strain rate and residual stresses on the onset of yielding in the material. The critical shear stress for the onset of yielding in the as-cast sample was found to be insensitive to the applied strain rate. By contrast, in the elastically-stressed sample, the maximum contact pressure from the Hertzian stress field at the onset of yielding was found to largely decrease under tensile residual stress, but only slightly increase under compressive residual stress. Despite the different residual stresses, the effective shear stress, i.e. the superimposition of residual and Hertzian stress fields, for the onset of yielding in the Zr-based metallic glass was essentially a constant. The constancy of the effective stress for the onset of yielding was discussed in light of a critical excess volume associated with the atomic structure upon loading. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.