How Supertough Gels Break*

Fracture of soft materials typically takes place at large stretches. This condition challenges our view of how things break, which is based on small-strain linear elasticity. In this talk, I will show how we directly visualized rupture of tough double-network gels at >50% strain. During fracture, crack tip shapes obey a x∼y^1.6 power law, in contrast to the parabolic profile observed in low-strain cracks. A new length scale emerges from the power law that scales directly with the stored elastic energy and diverges when the crack velocity approaches the shear wave speed. Our results show that double-network gels undergo brittle fracture and provide a testing ground for large-strain fracture mechanics.