Microscopic mechanism of shear-band formation in amorphous solids

Determine the microscopic mechanism responsible for the formation of shear bands in amorphous solids such as glasses, explicitly identifying the particle-scale origins that lead to localized plastic flow in materials lacking crystalline order and dislocations.

Background

Shear bands are narrow regions of localized plastic flow that play a central role in the mechanical response of amorphous solids. Unlike crystals, which possess dislocations as identifiable carriers of plasticity, amorphous materials lack a periodic lattice, making it difficult to define topological defects and predict where and how shear bands form. Prior work suggested connections to soft spots, Eshelby inclusions, and, more recently, to topological defects in displacement fields.

This paper provides numerical evidence in 2D ultrastable glasses that shear bands coincide with aligned chains of topological defects (vortex–antivortex pairs with alternating charge). While these results advance understanding, the authors explicitly note the longstanding status of the formation mechanism as an open question, motivating further clarification and generalization across systems and conditions.