Damage and Failure Mechanisms of Biological Materials

Abstract

Biological materials are generally lightweight composites made of a few weak universal building blocks and evolved through billions of years to provide a remarkable combination of mechanical properties. Besides structural integrity and durability, they show multiple functionalities, including self-healing capability. Although they are made of a limited palette of universal constituents, generally proteins and minerals, they are able to diversify in terms of structure and properties, within the same material and across different types. They self-assemble into intricate multiscale hierarchical structures, where it is possible to recognize recurring motifs, from fibrous to layered and gradient structures. Such motifs are common to different hierarchical levels, but also to different materials. The hierarchical architecture triggers specific deformation and toughening mechanisms at each length scale, resulting in a combination of mechanisms for the overall structures. In this chapter, we review the main deformation and failure modes of biological structural materials, also highlighting the structure-property relationship and length-scale dependence. We first describe the universal building blocks, then the common structural motifs, and finally the main toughening and damage mechanisms. As case studies, we choose three examples of biological structural materials, which can all be considered biominerals: bone, nacre, and diatoms. For each one we provide a structure-property-mechanism description.