Abstract
This paper shows that it is inappropriate to relate the angle between loading axis and shear-band (or fracture) plane in metallic glasses under uniaxial loading conditions to the coefficient of internal friction in the Mohr-Coulomb model. Shear bands in metallic glasses are a result of material instability (which can be predicted from constitutive parameters and loading conditions), but not a yield phenomenon. Specifically, the shear band directions depend on Poisson’s ratio, the ratios of three deviatoric principal stresses to Mises stress, the coefficient of internal friction, and the dilatancy factor. The last parameter describes whether the plastic flow is associative or non-associative. Theoretical predictions based on the classic Rudnicki-Rice model agree well with a compilation of observations in uniaxial mechanical tests. Furthermore, we identify three (two) regimes under the two-dimensional cylindrical (three-dimensional spherical) contact where different shear-band directions may occur. When using bonded interface technique to visualize the shear bands under the contact, it should be noted that the stress component normal to the bonded interface is released, resulting into the commonly observed semi-circular shear bands whose directions are predicted to follow the larger in-plane principal stress.
