The influence of internal length scales on mechanical properties in natural nanocomposites: a comparative study on inner layers of seashells.

Natural materials exhibit outstanding properties compared to their single constituents because of their hierarchical alignment. Therefore, they can be used as a guide to enhance the properties of artificial nanocomposite materials, which eventually could excel compared to their biological counterparts. In this study, seashells of five species with different microstructures were compared by correlating the sizes and aspect ratios of the building blocks to their mechanical behavior. The analyzed nacreous seashells were Trochus maculatus, Haliotis rufescens and Pteria penguin; the non-nacreous seashells were Meretrix lusoria and Pecten maximus. The results were used to determine the optimal values for the shape, size and volume fraction of the structural elements with regards to hardness, Young's modulus and fracture toughness. Surprisingly, the aspect ratio of the mineral phase in all seashells investigated was found to be close to the optimal value for strength as predicted by theory.