Correlation between Poisson ratio and Mohr–Coulomb coefficient in metallic glasses

Yielding in metallic glasses is often described in terms of the Mohr–Coulomb criterion, τ + μσ ≥ τ0. It suggests that a material yields when a combination of shear (τ) and normal stresses (σ), linked through the friction coefficient (μ), reaches the critical shear stress (τ0). In this paper, an increase of the friction coefficient for increasing Poisson ratio is foreseen, if the elastic limit observed under uniaxial (tensile or compressive) and shear stresses remain constant. Experimental values of Young and shear moduli and Poisson ratio of metallic glasses have been collected from the literature. Compressive and tensile yield stresses have been also collected and elastic limits have been calculated. The elastic limit observed under compressive stress decreases with increasing Poisson ratio and it appears similar for metallic glasses based on the same metals. The values of the friction coefficient for metallic glasses have been obtained from the fracture angle observed under uniaxial stress (compressive or tensile) and from the ratio between compressive and tensile strength. Experimental data of the friction coefficient appear rather scattered and a clear trend as a function of Poisson ratio cannot be outlined. The increase of toughness of metallic glasses with increasing Poisson ratio has been ascribed to the corresponding reduction of the compressive elastic limit.