Superior damage tolerance of fish skins

TL;DR

This study reveals that fish skins are highly ductile, damage tolerant, and exhibit strain-stiffening behavior, inspiring the development of advanced artificial skins for soft robotics.

Contribution

It provides the first detailed mechanical characterization of fish skins and models their collagen network to explain their exceptional damage tolerance.

Findings

Fish skins have rupture strains of 30-40% and strengths of 10-15 MPa.

Stretching reduces stress concentrations near flaws, enhancing damage tolerance.

The collagen network model explains strain-stiffening and flaw insensitivity.

Abstract

Skin is the largest organ of many animals. Its protective function against hostile environments and predatorial attack makes high mechanical strength a vital characteristic. Here, we measured the mechanical properties of bass fish skins and found that fish skins are highly ductile with a rupture strain of up to 30-40% and a rupture strength of 10-15 MPa. The fish skins exhibit a strain-stiffening behavior. Stretching can effectively eliminate the stress concentrations near the pre-existing holes and edge notches, suggesting that the skins are highly damage tolerant. Our measurement determined a flaw-insensitivity length of several millimeters, which exceeds that of most engineering materials. The strain-stiffening and damage tolerance of fish skins are explained by an agent-based model of collagen network in which the load-bearing collagen microfibers assembled from nanofibrils undergo straightening and reorientation upon stretching. Our study inspires development of artificial skins that are thin, flexible, but highly fracture-resistant and widely applicable in soft robots.