An Experimental Investigation of Deformation and Fracture of Nacre–Mother of Pearl |
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Authors: | F Barthelat H D Espinosa |
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Institution: | (1) Department of Mechanical Engineering, McGill University, Montreal, Quebec, H3A 2K6, Canada;(2) Department of Mechanical Engineering, Northwestern University, Evanston, IL 60208-3111, USA |
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Abstract: | Nacre, also known as mother-of-pearl, is a hard biological composite found in the inside layer of many shells such as oyster
or abalone. It is composed of microscopic ceramic tablets arranged in layers and tightly stacked to form a three-dimensional
brick wall structure, where the mortar is a thin layer of biopolymers (20–30 nm). Although mostly made of a brittle ceramic,
the structure of nacre is so well designed that its toughness is several order of magnitudes larger that the ceramic it is
made of. How the microstructure of nacre controls its mechanical performance has been the focus of numerous studies over the
past two decades, because such understanding may inspire novel composite designs though biomimetics. This paper presents in
detail uniaxial tension experiment performed on miniature nacre specimens. Large inelastic deformations were observed in hydrated
condition, which were explained by sliding of the tablets on one another and progressive locking generated by their microscopic
waviness. Fracture experiments were also performed, and for the first time the full crack resistance curve was established
for nacre. A rising resistance curve is an indication of the robustness and damage tolerance of that material. These measurements
are then discussed and correlated with toughening extrinsic mechanisms operating at the microscale. Moreover, specific features
of the microstructure and their relevance to associated toughening mechanisms were identified. These features and mechanisms,
critical to the robustness of the shell, were finely tuned over millions of years of evolution. Hence, they are expected to
serve as a basis to establish guidelines for the design of novel man-made composites. |
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Keywords: | Biological material Biocomposite Tensile strength Fracture Toughening mechanisms |
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