Title: The conch shell as a model for tougher composites

Authors: D.M. Williamson, W.G. Proud

Addresses: SMF Group, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK. ' SMF Group, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK

Abstract: The conch shell is 95% by volume CaCO₃ (chalk), yet its toughness is 10³ times greater than that of monolithic CaCO₃. In this review paper we look at how this increase in toughness is achieved and what lessons can be learnt for designing new tough composites. Essentially, we find that the CaCO₃ is finely divided into single crystals whose relevant dimensions are below the Griffith flaw size for the anticipated stresses; thus upon failure intergranular cracking dominates. Furthermore, failure is encouraged to proceed in a controlled way, which frustrates crack growth and maximises crack surface area. This strategy of maximising damage can only be successful in combination with self-healing properties. Examples are given of synthetic analogues, so-called biomimetic materials.

Keywords: nacre; Griffith flaw; self-healing composites; biomimetics; lightweight armour; body armour; conch shells; toughness increase; CaCO3; failure; intergranular cracking; biomimetic materials; calcium carbonate; chalk.

DOI: 10.1504/IJMATEI.2011.039506

International Journal of Materials Engineering Innovation, 2011 Vol.2 No.2, pp.149 - 164

Published online: 26 Mar 2015 *

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