Nanoscale deformation mechanics reveal resilience in nacre of Pinna nobilis shell

TL;DR

This study uncovers how nacre's nanoscale structure enables it to recover from deformation and maintain resilience, combining organic-inorganic interactions with nanograin mechanics.

Contribution

It reveals the nanomechanical mechanisms behind nacre's resilience, including nanoscale recovery and locking of inorganic tablets under high stress.

Findings

Nacre can recover up to 80% of its yield strength after deformation.

Nacre's inorganic tablets lock and recover without damage under high compression.

Organic interfaces restrict crack propagation while allowing structural recovery.

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.