Configurational forces explain echelon cracks in soft materials

TL;DR

This paper introduces a configurational mechanics framework to analyze echelon crack patterns in soft materials, revealing complex facet interactions and coalescence effects that influence fracture morphology under mixed-mode loading.

Contribution

It applies the Configurational Force Method within finite-element simulations to elucidate the physical mechanisms behind echelon cracks in soft materials, advancing understanding beyond traditional linear elastic fracture mechanics.

Findings

Configurational forces determine crack propagation direction and magnitude.

Tilted facets significantly influence fracture morphology.

Facet coalescence affects crack front evolution.

Abstract

Soft fracture in highly deformable solids involves both geometric and constitutive nonlinearities, necessitating advanced theoretical and computational frameworks for its accurate understanding. Tensile fractures subjected to mixed-mode loading deviate from their original planar shape, resulting in echelon crack patterns. When out-of-plane shear is superimposed, a crack front segments into an array of tilted facets. The physical interpretation of echelon cracks is only marginally understood, and it is customarily based on rather limited approaches based on Linear Elastic Fracture Mechanics. Here we investigate mixed-mode I + III fracture within the framework of configurational mechanics. Using the Configurational Force Method, implemented as a post-processing algorithm in a finite-element-based simulation, we compute the configurational forces acting at the crack tip of model fracture geometries prior to propagation. Configurational forces characterize both the magnitude and direction of propagation for maximal energy release rate. Our results reveal the complex interactions between tilted facets and their critical role in shaping the fracture morphology. We also examine the effects of facet coalescence-driven by the growth of the parent crack-where neighboring facets merge into a unified crack front. These findings provide new insights into fracture processes in soft, quasi-brittle materials under mixed-mode loading.