Size selection of crack front defects: Multiple fracture-plane interactions and intrinsic lengthscales

TL;DR

This study investigates how multiple crack interactions in 3D brittle materials lead to stable out-of-plane fracture structures, revealing intrinsic lengthscales that depend on material properties and crack velocity.

Contribution

It introduces a new understanding of crack front defect size selection through experiments on hydrogels, linking out-of-plane crack structures to intrinsic lengthscales.

Findings

Maximum crack separation distance $h_{max}$ varies linearly with elastic and dissipation lengthscales.

Intrinsic lengthscales depend on crack velocity, fracture energy, and shear modulus.

Experimental evidence of stable out-of-plane crack structures in brittle hydrogels.

Abstract

Material failure is mediated by the propagation of cracks, which in realistic 3D materials typically involve multiple coexisting fracture planes. Multiple fracture-plane interactions create poorly understood out-of-plane crack structures, such as step defects on tensile fracture surfaces. Steps form once a slowly moving, distorted crack front segments into disconnected overlapping fracture planes separated by a stabilizing distance $h_{\rm max}$. Our experiments on numerous brittle hydrogels reveal that $h_{\rm max}$ varies linearly with both a nonlinear elastic length $\Gamma(v)/\mu$ and a dissipation length $\xi$. Here, $\Gamma(v)$ is the measured crack velocity $v$-dependent fracture energy and $\mu$ is the shear modulus. These intrinsic lengthscales point the way to a fundamental understanding of multiple-crack interactions in 3D that lead to the formation of stable out-of-plane fracture structures.