Distinguishing failure modes at the molecular level by examining heterogeneity in local structures and dynamics

Abstract: Brittle failure is ubiquitous in amorphous materials that are sufficiently cooled below their glass transition temperature, $T_g$. This catastrophic failure mode is limiting for amorphous materials in many applications, and many fundamental questions surrounding it remain poorly understood. Two challenges that prevent a more fundamental understanding of the transition between a ductile response at temperatures near $T_g$ to brittle failure at lower temperatures are i) a lack of computationally inexpensive molecular models that capture the failure modes observed in experiments and ii) the lack of quantitative metrics that can distinguish various failure mechanisms. In this work, we use molecular dynamics simulations to capture ductile-to-brittle transition in glass-forming short-chain polymer systems by using a modified Lennard-Jones potential to describe non-bonded interactions between the monomers. We characterized the effects of this new potential on macroscopic mechanical properties as well as microscopic structural and dynamical differences during deformation. Lastly, we present quantitative metrics that distinguish between different failure modes.