An Extreme Toughening Mechanism for Soft Materials

TL;DR

This paper introduces a new mechanism and scaling law explaining the extreme toughness of soft materials, emphasizing the role of near-crack dissipation alongside bulk hysteric dissipation, supported by experiments and theory.

Contribution

It proposes a novel toughening mechanism for soft materials that accounts for near-crack dissipation, extending understanding beyond bulk hysteresis effects.

Findings

Near-crack dissipation significantly enhances toughness.

The new scaling law applies to various soft materials.

Bulk hysteresis alone underestimates toughness enhancement.

Abstract

Soft yet tough materials are ubiquitous in nature and everyday life. The ratio between fracture toughness and intrinsic fracture energy of a soft material defines its toughness enhancement. Soft materials' toughness enhancement has been long attributed to their bulk stress-stretch hysteresis induced by dissipation mechanisms such as Mullins effect and viscoelasticity. With a combination of experiments and theory, here we show that the bulk dissipation mechanisms significantly underestimate the toughness enhancement of soft tough materials. We propose a new mechanism and scaling law to account for the extreme toughening of diverse soft materials. We show that the toughness enhancement of soft materials relies on both bulk hysteric dissipation, and near-crack dissipation due to mechanisms such as polymer-chain entanglement. Unlike the bulk hysteric dissipation, the near-crack dissipation does not necessarily induce large stress-stretch hysteresis of the bulk material. The extreme toughening mechanism can be universally applied to various soft tough materials, ranging from double-network hydrogels, interpenetrating-network hydrogels, entangled-network hydrogels and slide-ring hydrogels, to unfilled and filled rubbers.