Characterization of Reversible Tablet Sliding in Nacre from Haliotis rufescens (Red Abalone)

Abstract

Nacre or “Mother of Pearl” is a biogenic material that has garnered a lot of attention as its hierarchal architecture of calcite-based materials imparts extraordinary mechanical performance compared to its monolithic form. Nacre is a micro-laminate composite composed of layers of organic matrix and calcium carbonate tablets (aragonite). The tablets are polygonal in shape and approximately 400–500 nm thick. They are organized in irregularly stacked columns that overlap each other, often described as stacks of coins randomly overlapping each other. Each tablet is covered in nano-scale asperities that help lock the tablets together. The Nacre architecture has been well studied the past decade or so to ascertain the mechanistic origins of its extraordinary performance. One of the important aspects of its behavior involves tablets sliding relative to one another. This sliding has been well characterized by various mechanical methods, mostly involving tensile and indentation-based methods. A clear assentation of the developed models suggests that this tablet sliding should be reversible to a degree. However, reversible sliding has only been observed in a few instances and not studied systematically. This work reports on a method that was adept at observing wide-scale reversible tablet sliding. A systematic study this phenomenon was performed enabled by the precise deformation control it offered. The results determined a threshold strain whereby the deformation from tablet sliding became permanent, suggesting the failure of the organic matrix’s recovery ability.