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

TL;DR

This study uses atomistic simulations to explore how soft defects and loading geometry influence the brittle or ductile fracture behavior of glasses, revealing that both factors are crucial in determining toughness.

Contribution

It demonstrates that both soft defect abundance and loading geometry critically affect glass toughness, providing new insights into controlling fracture behavior.

Findings

Reducing cooling rate can induce brittle-to-ductile transition.

Poisson contraction influences whether glasses are brittle or ductile.

Constrained tension reveals the role of loading geometry in toughness variation.

Abstract

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' nonequilibrium mechanical disorder is quantified through $A_{\rm g}$, the dimensionless prefactor of the universal spectrum of nonphononic 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 $A_{\rm g}$, iso-$\!A_{\rm g}$ 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-$\!A_{\rm g}$ glasses feature similar toughness, and that varying $A_{\rm g}$ 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.