Crack front instabilities under mixed mode loading in three dimensions

TL;DR

This paper investigates how crack fronts evolve under mixed mode loading in three dimensions using a phase field model, revealing relaxation to a mode I dominated state and the influence of initial conditions on front fragmentation.

Contribution

It introduces a 3D phase field model to study crack front evolution under mixed mode loading and explores the effects of initial conditions on front stability.

Findings

Crack fronts relax to a mode I dominated geometry without fragmentation.

Irregular initial cracks can cause front fragmentation at lower mode mixity ratios.

The model aligns with experimental observations in gels.

Abstract

The evolution of a crack front under mixed mode loading (I+III) is studied using a phase field model in 3 dimensions with no stress boundary conditions. As previously observed experimentally in gels, there is a relaxation toward a geometry where $K_{III}=0$ without any front fragmentation even for high values of the initial mode mixity $K_{III}/K_{I}$. The effects of the initial condition is studied and it is shown that irregularities in the initial slit can lead to front fragmentation for smaller values of the ratio $K_{III}/K_{I}$ as is observed in experiments.