LEFM is agnostic to geometrical nonlinearities arising at atomistic crack tips

TL;DR

This paper investigates the applicability of linear elastic fracture mechanics (LEFM) at the atomic scale, revealing that lattice discreteness causes deviations from LEFM predictions due to geometrical nonlinearities, not nonlinear elastic response.

Contribution

The study demonstrates that atomic lattice discreteness leads to deviations from LEFM, emphasizing the role of geometrical nonlinearities in crack tip behavior at the atomic scale.

Findings

Deviations from LEFM are caused by lattice discreteness.

Crack advance depends on the collective region, not just the crack tip bond.

Crack behavior cannot be fully predicted by properties of individual bonds.

Abstract

Various fields such as mechanical engineering, materials science, etc., have seen a widespread use of linear elastic fracture mechanics (LEFM) at the continuum scale. LEFM is also routinely applied to the atomic scale. However, its applicability at this scale remains less well studied, with most studies focusing on non-linear elastic effects. Using a harmonic (snapping spring) nearest-neighbor potential which provides the closest match to LEFM on a discrete lattice, we show that the discrete nature of an atomic lattice leads to deviations from the LEFM displacement field during energy minimization. We propose that these deviations can be ascribed to geometrical nonlinearities since the material does not have a nonlinear elastic response prior to bond breaking. We demonstrate that crack advance and the critical stress intensity factor in an incremental loading scenario is governed by the collectively loaded region, and can not be determined analytically from the properties (max. elongation, max. sustained force, etc.) of the stressed crack tip bond alone.