Shear Banding in a Contact Problem between Metallic Glasses

The case of a frictionless contact between a spherical body and a flat metallic glass is studied using a mesoscopic description of plasticity combined with a semi-analytical description of the elastic deformation in a contact geometry (code ISAAC). Plasticity is described by irreversible strain rearrangements in the maximum deviatoric strain direction, above some random strain threshold. In the absence of adhesion or friction, the plastic deformation is initiated below the surface. To represent the singularities due to adhesion, initial rearrangements are forced at the boundary of the contact. Then, the structural disorder is introduced in two different levels: either in the local strain thresholds for plasticity or in the residual plastic strains. It is shown that the spatial organization of plastic rearrangements is not universal, but it is very dependent on the choice of disorder and external loading conditions. Spatial curved shear bands may appear below the contact but only for a very specific set of parameters, especially those characterizing the random thresholds compared to externally induced strain gradients.