Reversible Tablet Sliding and Strain-Limited Deformation in Nacre: In-Situ Observations and Threshold Determination

Abstract Background Nacre, or mother-of-pearl, is renowned for its exceptional toughness and energy-dissipating capabilities, attributed to its hierarchical structure of overlapping aragonite tablets bonded by a compliant biopolymer matrix. While tablet sliding has long been proposed as a key toughening mechanism, the reversibility of such sliding under mechanical loading and its strain-dependent behavior remain poorly quantified. Objective This study aims to investigate the formation and recovery of dilation bands in nacre, regions where tablet assemblies slide and separate during deformation. The work seeks to determine the strain threshold for reversible deformation and provide new insights into how nacre’s energy dissipation mechanisms operate. Methods Nacre beams were prepared from Haliotis rufescens shells and subjected to both ex-situ and in-situ three-point bending tests, the latter within a scanning electron microscope (SEM). High-magnification imaging was employed to monitor tablet gap formation and closure at incremental deflection stages. Tablet gap widths and their propagation depth were quantified as a function of applied strain using image analysis techniques. Results Localized dilation bands that formed near the tensile surface under applied bending do so under plane stress conditions. This deformation mechanism redistributes the applied stress locally, effectively reducing stress concentrations and suppressing crack initiation. This work presents direct evidence of large-scale recovery of tablet sliding in nacre, which, to our knowledge, has not been reported before. Furthermore, a critical threshold strain of ~ 0.0062 was identified, beyond which residual tablet gaps remained after unloading, marking the onset of irreversible deformation. Conclusions The findings provide two key insights into nacre’s intrinsic mechanisms for mechanical energy dissipation and enhanced damage tolerance. They offer new understanding and design benchmarks for the development of engineered composites aiming to replicate nacre’s exceptional combination of toughness and recoverability.