Evaluating Mohr-Coulomb yield criterion for plastic flow in model metallic glasses
M Vargonen and LP Huang and YF Shi, JOURNAL OF NON-CRYSTALLINE SOLIDS, 358, 3488-3494 (2012).
The yielding of metallic glasses (MGs) is generally considered to be dependent on pressure or normal stress, which is usually described by the Mohr-Coulomb yield criterion. Experimentally, the orientation of the shear band angle or fracture angles in MG is roughly 40 degrees to 42 degrees in uniaxial compression and 50 degrees to 59 degrees in uniaxial tension, both with respect to the loading direction. However, the amounts of deviation from the maximum shear stress direction (45 degrees) under uniaxial tension and compression are quite different, which seems to be inconsistent with the Mohr-Coulomb yield criterion. Here we carried out molecular dynamics simulations to study the incipient plasticity of model Dzugutov glasses subjected to various uniaxial and biaxial stress states. The yield points are defined as the sharp rise of the population of atoms participating in non-affine deformations, in addition to the traditional offset method. The yield surfaces thus created agree well with the Mohr-Coulomb yield criterion. Furthermore, the orientations of the embryonic shear bands (instead of the fully-grown shear bands, or fracture planes) are measured, which also follow predictions based on the Mohr-Coulomb criterion. Our simulation results call for orientational measurement of incipient shear bands in experiments to critically examine the Mohr-Coulomb yield criterion in MG systems. (c) 2012 Elsevier B.V. All rights reserved.
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