Fracture initiation in silicate glasses via a universal shear localization mechanism

Shear bands lie at the root of fracture initiation in bulk metallic glasses and amorphous polymers. For silicate glasses, in contrast, studies have largely emphasized permanent volumetric strain, commonly referred to as densification. Here we systematically investigate indentation-induced fracture in two distinct families of aluminoborosilicate glasses. The results demonstrate that plastic shear flow plays a decisive role in governing fracture initiation. In addition, molecular dynamics simulations reveal a pronounced composition dependence of softening associated with plastic shear flow, closely mirroring the experimentally observed propensity for strain localization. We conclude that silicate glasses conform to a universal pattern of rupture initiation governed by localization of shear-deformation, aligning with a broad range of amorphous materials, including bulk metallic glasses and glassy polymers.