Brittle‑to‑ductile transitions in glasses: Roles of soft defects and loading geometry

Understanding the fracture toughness of glasses is of prime importance for

science and technology. We study it here using extensive atomistic simulations in

which the interaction potential, glass transition cooling rate, and loading geometry

are systematically varied, mimicking a broad range of experimentally accessible

properties. Glasses’ non-equilibrium mechanical disorder is quantified through

Ag, the dimensionless prefactor of the universal spectrum of non-phononic

excitations, which measures the abundance of soft glassy defects that affect

plastic deformability. We show that while a brittle-to-ductile transition might be

induced by reducing the cooling rate, leading to a reduction in Ag , iso-Ag glasses

are either brittle or ductile depending on the degree of Poisson contraction under

unconstrained uniaxial tension. Eliminating Poisson contraction using constrained

tension reveals that iso-Ag glasses feature similar toughness, and that varying

Ag under these conditions results in significant toughness variation. Our results

highlight the roles played by both soft defects and loading geometry (which

affects the activation of defects) in the toughness of glasses.

See manuscript at: https://link.springer.com/article/10.1557/s43577-021-00171-8