Abstract
The ability of the complex hierarchical structure of nacre to withstand huge work of fracture beyond its constituent materials has generated much interest in its growth mechanism and biomimicry studies. However, the structural features directly involved in the robust mechanical properties have not been successfully identified or emulate in biomimetic materials. In the current article, we present the characterisation of a novel nanostructure framework in nacre of Perna canaliculus after chemical etching. The inner structure of the nacre platelet reveals a crystalline three-dimensional framework of orientated fibrous aragonite crystals, which shows that the hierarchical structure at the nano-scale level is much more complex than researchers previously thought. Fracture analysis shows that the fibrous aragonite framework remains largely intact, which indicates the strengthening nature of the elusive internal structure. The discovery of the nano-scale highly ordered structure could be the key to understanding the toughening mechanism in nacre and could serve as a guide to the future biomimetic design of nacre-like, high strength, tough, composite materials.
Highlights
Researchers have marvelled at nacre's complex hierarchical structure and its abilities to enhance the toughness of the brittle monolithic ceramic material
We present the characterisation of a novel nanostructure framework in nacre of Perna canaliculus after chemical etching
Fracture analysis shows that the fibrous aragonite framework remains largely intact, which indicates the strengthening nature of the elusive internal structure
Summary
Researchers have marvelled at nacre's complex hierarchical structure and its abilities to enhance the toughness of the brittle monolithic ceramic material. Structured biological materials have appeared to be a viable template in the enhancement of the mechanical properties of brittle ceramics, improvement in toughness without a sacrificial loss in strength is seldom observed. The hierarchical structure is vital as the structures at different scale levels interact with and complement one another, providing a synergetic improvement of the mechanical properties.[6] Many articles have reported biomimetics of nacre's brick-and-mortar structure;[7,8,9,10,11,12] in most cases only marginal improvements in toughness were achieved and often experienced a sacrificial reduction in strength of the ceramic constituent. Most researchers would agree that the magnitude of enhancement of mechanical properties in nacre is still unrivalled by any man-made ceramic composites and the structure–property behaviour of nacre is still not well-understood.[6,13,14] While one could argue that the low
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