The conch shell as a model for tougher composites

摘要

The conch shell is 95% by volume CaCO_3 (chalk), yet its toughness is 10~3 times greater than that of monolithic CaCC>_3. 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 CaCO_3 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.