Failure mechanisms of graphene under tension

TL;DR

This study uses density functional theory to uncover how pure graphene fails under tension, identifying a novel phonon instability and elastic failure as key mechanisms limiting its strength.

Contribution

It reveals a new soft-mode phonon instability as a failure mechanism in graphene, expanding understanding beyond traditional elastic failure.

Findings

Identification of a soft-mode phonon instability at the K1-mode

Graphene undergoes a phase transition towards benzene rings under tension

Elastic instability corresponds to maximum stress in stress-strain curve

Abstract

Recent experiments established pure graphene as the strongest material known to mankind, further invigorating the question of how graphene fails. Using density functional theory, we reveal the mechanisms of mechanical failure of pure graphene under a generic state of tension. One failure mechanism is a novel soft-mode phonon instability of the $K_1$-mode, whereby the graphene sheet undergoes a phase transition and is driven towards isolated benzene rings resulting in a reduction of strength. The other is the usual elastic instability corresponding to a maximum in the stress-strain curve. Our results indicate that finite wave vector soft modes can be the key factor in limiting the strength of monolayer materials.