# Toughening in a nacre-like soft-hard layered structure due to weak nonlinearity in the soft layer

## TL;DR

This paper demonstrates that weak nonlinearity in the soft layers of nacre-like structures significantly enhances toughness by redistributing stress, providing insights for designing tough bio-inspired composites.

## Contribution

It introduces an analytical and numerical model showing how weak nonlinearity in soft layers improves toughness in layered structures, a novel mechanism for bio-inspired material design.

## Key findings

- Weak nonlinearity redistributes stress at crack tips.
- Enhanced toughness observed due to nonlinear soft layers.
- Model provides a design principle for tough composites.

## Abstract

Recently, it has been found experimentally that hydrated nacre exhibits a nonlinear mechanical response. While mechanical nonlinearity has been shown to be important in other biological structures, such as spider webs, the implications of mechanical nonlinearity in nacre have not been explored. Here, we show that the nonlinear mechanical response of nacre can be reproduced by an analytical model, which reflects a nacre-like layered structure, consisting of linear-elastic hard sheets glued together by weakly nonlinear-elastic soft sheets. We develop scaling analysis on this analytical model, and perform numerical simulations using a lattice model, which is a discrete counterpart of the analytical model. Unexpectedly, we find the weak nonlinearity in the soft component significantly contributes to enhancing toughness by redistributing the stress at a crack tip over a wider area. Beyond demonstrating a mechanism that explains the unusual properties of biological nacre, this study points to a general design principle for constructing tough composites using weak nonlinearity, and is useful as a guiding principle to develop artificial layered structures mimicking nacre.