New insights into the indentation size effect in silicate glasses

When glasses resist permanent deformations, for applications such as a windshield or the cover of a touch-screen device, it is important to understand how they respond to inelastic energy dissipation processes. Many glasses exhibit the so-called Indentation Size Effect (ISE), where the indentation hardness is dependent on the maximum force exerted on the probe. In this study, we perform microindentation on silica and soda lime silicate glasses over a wide range of maximum forces and extract the Vickers hardness by the Oliver and Pharr method. The inelastic volume responsible for dissipating the inelastic energy is decomposed into densification and plastic flow, using surface topography and annealing. We show that the ISE is intimately linked to these mechanisms. Finally, we hypothesize the cause of the ISE is an increase in plasticity in a zone of material under the indenter probe experiencing reduced viscosity due to high strain rates and shear thinning.