Nanoscale deformation mechanics reveal resilience in nacre of Pinna nobilis shell

Jiseok Gim,Yuchi Cui,Stephan E Wolf,Amit Misra,Robert Hovden,Noah Schnitzer,Frédéric Marin,Dorrit E Jacob,Sébastien Motreuil,Laura M Otter

doi:10.1038/s41467-019-12743-z

Abstract

The combination of soft nanoscale organic components with inorganic nanograins hierarchically designed by natural organisms results in highly ductile structural materials that can withstand mechanical impact and exhibit high resilience on the macro- and nano-scale. Our investigation of nacre deformation reveals the underlying nanomechanics that govern the structural resilience and absorption of mechanical energy. Using high-resolution scanning/transmission electron microscopy (S/TEM) combined with in situ indentation, we observe nanoscale recovery of heavily deformed nacre that restores its mechanical strength on external stimuli up to 80% of its yield strength. Under compression, nacre undergoes deformation of nanograins and non-destructive locking across organic interfaces such that adjacent inorganic tablets structurally join. The locked tablets respond to strain as a continuous material, yet the organic boundaries between them still restrict crack propagation. Remarkably, the completely locked interface recovers its original morphology without any noticeable deformation after compressive contact stresses as large as 1.2 GPa.

Highlights

The combination of soft nanoscale organic components with inorganic nanograins hierarchically designed by natural organisms results in highly ductile structural materials that can withstand mechanical impact and exhibit high resilience on the macro- and nano-scale
Li et al observed the plastic deformation of aragonite surfaces under tensile load at the nanometer level using atomic force microscopy[18,21]
Direct observation is required to disambiguate the mechanism of nanomechanical deformation of nacre; most knowledge of the biomineral toughening process is assembled from microscale tribology[8,12,15,16], tensile[5,12,15,19,20,22,39], or compression[14,19,40] testing on bulk specimens

Summary

Introduction

The combination of soft nanoscale organic components with inorganic nanograins hierarchically designed by natural organisms results in highly ductile structural materials that can withstand mechanical impact and exhibit high resilience on the macro- and nano-scale. Nature has optimized high-performance materials with unrivaled strength, toughness, and resilience using three-dimensional (3D) hierarchical architectures that traverse the atomic, nano-, micro-, to macro-scale with precision that human technology is yet to achieve[4]. Wegst et al.[9] have suggested that crack bridging and the resulting “pull-out” of mineral bricks is associated with controlled, yet limited, sliding of the aragonite layers over each other and is aided by visco-plastic energy dissipation in the organic layer. Understanding nanomechanical responses across the 3D hierarchical architectures is critical to understanding how the individual nacre components work together to create properties greater than the sum of their parts (i.e., far exceeding the rule of mixtures[9])

Methods

Results

Conclusion