Crack Tip Relaxation Governs Onset of Fracture Instability

TL;DR

This paper introduces a new atomic-level explanation for the onset of fracture instability in dynamic cracks, linking atomic bond relaxation to the effective elastic modulus that predicts critical crack speeds.

Contribution

It reveals that broken-bond relaxation at the crack tip explains the effective elastic modulus used in predicting fracture instability, bridging atomic-scale processes with continuum mechanics.

Findings

Broken-bond relaxation explains the effective elastic modulus.

The model predicts critical crack speeds accurately.

Atomic picture links microscopic processes to macroscopic fracture behavior.

Abstract

A dynamic crack will travel in a straight path up to a material-dependent critical speed beyond which its path becomes erratic. Predicting this critical speed and discovering the origin of this instability are two outstanding problems in fracture mechanics. We recently discovered a simple scaling model based on an effective elastic modulus that gives successful predictions for this critical speed by transforming the nonlinear crack dynamics problem into a linear elasticity representation. We now show that a simple atomic picture based on broken-bond relaxation at the dynamic crack tip provides an explanation for the origin of the effective elastic modulus.