How super-tough gels break

TL;DR

This study visualizes the fracture process of tough double-network gels at high strains, revealing unique crack tip shapes and a new length-scale that scales with elastic energy, advancing understanding of large-strain fracture mechanics.

Contribution

It provides direct visualization and analysis of crack behavior in tough gels at high strains, introducing a new length-scale and linking it to elastic energy and crack velocity.

Findings

Crack tip shapes follow a $x\sim y^{1.6}$ power-law at high strains.

A new length-scale $\\ell$ scales with stored elastic energy.

DN gels exhibit brittle fracture behavior at large strains.

Abstract

Fracture of highly stretched materials challenges our view of how things break. We directly visualize rupture of tough double-network (DN) gels at >50\% strain. During fracture, crack tip shapes obey a $x\sim y^{1.6}$ power-law, in contrast to the parabolic profile observed in low-strain cracks. A new length-scale $\ell$ emerges from the power-law; we show that $\ell$ scales directly with the stored elastic energy, and diverges when the crack velocity approaches the shear wave speed. Our results show that DN gels undergo brittle fracture, and provide a testing ground for large-strain fracture mechanics.