Fracture size effects in nanoscale materials: the case of graphene

TL;DR

This study investigates how the failure strength of nanoscale graphene sheets varies with size, disorder, temperature, and loading rate, combining molecular dynamics simulations with a generalized weakest-link theory.

Contribution

It introduces a generalized fracture size effect theory that accounts for rate and temperature dependence, validated by extensive simulations on graphene sheets.

Findings

Failure strength distribution depends on system size, disorder, temperature, and loading rate.

Theoretical model agrees quantitatively with molecular dynamics simulations.

Crossover between thermal/rate-dependent and disorder-dominated failure regimes explained.

Abstract

Nanoscale materials display enhanced strength and toughness but also larger fluctuations and more pronounced size effects with respect to their macroscopic counterparts. Here we study the system size-dependence of the failure strength distribution of a monolayer graphene sheet with a small concentration of vacancies by molecular dynamics simulations. We simulate sheets of varying size encompassing more than three decades and systematically study their deformation as a function of disorder, temperature and loading rate. We generalize the weakest-link theory of fracture size effects to rate and temperature dependent failure and find quantitative agreement with the simulations. Our numerical and theoretical results explain the crossover of the fracture strength distribution between a thermal and rate-dependent regime and a disorder-dominated regime described by extreme value theory.