Quantifying Densification versus Shear Flow during Glass Nanoindentation via Atomic-Scale Descriptors

Plastic deformation in glasses under sharp contact loading can occur through distinct mechanisms, ranging from volumetric densification to shear flow. While molecular dynamics simulations provide detailed atomic-scale information, a transferable framework to quantitatively compare these mechanisms across chemically distinct glasses is still lacking.In this work, we introduce a set of atomic-scale descriptors to quantify densification and shear flow during nanoindentation, derived from local irreversible deformation fields obtained from molecular dynamics simulations. The analysis combines volumetric and deviatoric strain components, atomic-scale densification, and the non-affine displacement measure D2min​, with particular emphasis on the residual deformation after unloading to isolate plastic effects.The proposed approach is applied to vitreous SiO2​, a sodium silicate, albite, anorthite glasses and the Cu64​Zr36 metallic glass, spanning densification-dominated, shear-dominated, and mixed deformation behaviours. We show that strain-based descriptors alone are insufficient to uniquely discriminate these mechanisms. To address this limitation, we introduce an end-member-based Densification–Shear Fraction (DSF), constructed from residual densification and non-affine rearrangement intensity. The DSF provides a continuous and physically grounded quantification of the relative contribution of densification and shear flow. This framework establishes a unified and transferable atomic-scale description of nanoindentation-induced plasticity, applicable to chemically diverse glassy systems.