Deconvolution of the elastic properties of bivalve shell nanocomposites from direct measurement and finite element analy
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Deconvolution of the elastic properties of bivalve shell nanocomposites from direct measurement and finite element analysis Matthias O’Toole-Howes1, Ruth Ingleby1, Melanie Mertesdorf1, James Dean2, Wei Li2, Michael A. Carpenter1,a), Elizabeth M. Harper1 1
Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, U.K. Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS, U.K. a) Address all correspondence to this author. e-mail: [email protected] 2
Received: 7 January 2019; accepted: 15 April 2019
A new protocol has been devised for determining elastic properties of natural biocomposites in the form of bivalve shells under wet and dry conditions. Four-point bending on shell slices of Mytilus edulis, Ensis siliqua, and Pecten maximus give generally lower and more reliable values of Young’s modulus, E, than those in the literature from three-point bending, due to the more even distribution of strain. Finite element analysis of the prismatic microstructure of Pinna nobilis, obtained by X-ray tomography, shows that values of E 20 GPa can be understood in terms of the real microstructure containing a small proportion of organic matrix phase with E 1 GPa and a dominant proportion of calcite with E 90 GPa. Higher values of E obtained by nanoindentation give results which are biased toward the properties of the carbonate phase rather than of the biocomposite as a whole.
Introduction Nanocomposites that mimic nature have been increasingly studied in the past two decades due to advances in the fields of nanoscience and nanoengineering. Biocomposites, such as nacre, bone, sponge spicules, and fish scales, consist of a softer phase that normally provides energy dissipation, toughness, and flexibility, and a harder phase that provides stiffness [e.g., Refs. 1, 2, 3, 4, 5, 6, and 7]. Their unique combinations of properties make them suitable for a variety of adaptations such as structural support, protection, and absorption of impact energy. Within this broader context, bivalve Mollusca are important aquatic organisms ranging from freshwater through marine to hypersaline habitats, and from shallow to deep seas. They have a long evolutionary history, first appearing in the Lower Cambrian, and they show considerable taxonomic and adaptive diversity [8]. Bivalves have been popular targets for understanding biomineralization and, in the field of biomimetics, bivalve shell formation has been studied with potential applications such as bone implants, where biological compatibility and strength are two key characteristics [9, 10, 11].
ª Materials Research Society 2019
Bivalve shells consist of a hard calcium carbonate phase within a soft organic matrix. Microstructures with aragonite include nacre, prisms, crossed-lamellar, complex crossedlamellar, and homogeneous. Calcitic microstructures include prismatic and foliated [8]. Different taxa employ different microstructural arrangements that are clearly under strong genetic control [8, 12, 13]. In the early days of mechanical te
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