Meeting Abstract

S7.9  Tuesday, Jan. 6  Structure and Properties of Mineralized Tissues: The Deformation and Fracture of Nacre from Mollusc Shells BARTHELAT, Francois; McGill University francois.barthelat@mcgill.ca

For millions of years natural organisms have been incorporating minerals for structural purposes, mainly to achieve the stiffness required for mechanical support (bones), cutting and crushing aliments (teeth) or protection against predators (seashells). The individual components of these mineralized tissues are relatively weak, yet complex hierarchical microstructures provide them with remarkable mechanical performances and unique combinations of stiffness, hardness and toughness. A good example of such material is nacre, the material of pearls found in mollusc shells. Nacre contains 95% of the brittle mineral aragonite, which comes in the form of microscopic polygonal tablets tightly stacked to form a three dimensional brick wall. A small fraction (5%) of organic materials is found at the interfaces and bonds the tablets together, while enabling them to slide on one another under mechanical stresses. This unique mechanism makes nacre 3,000 times tougher than aragonite, a degree of improvement currently not matched by any manmade composite material. Using combinations of small-scale mechanical experiments and modeling we have discovered a key microscopic feature responsible for the spreading of tablet sliding over large volumes. The mechanical energy dissipated in this process explains the tremendous toughness of Red Abalone nacre. Nacre from Pearl Oyster has is slightly different microstructure, and recent experiments on this material have revealed an even greater toughness with patterns of deformation and fracture never observed before. Understanding nacres with different structures across different species is expected to yield new insights into the design and optimization rules underlying its construction. This will in turn guide the development of novel biomimetic materials with superior properties.