Failure retardation in body armor

The protective structures that occur in biological systems are complex composite materials that display impressive mechanical properties, considering the weak properties of the individual constituents from which they are assembled. Body armors are hard materials designed to protect an animal from the fangs and claws of their predator. The usual engineering approach to biological materials has focused on treating them like synthetic composite materials designed to achieve higher strength and stiffness. Here, the authors propose that the basic evolutionary design of body armors and biological materials is related to the retardation of catastrophic failure through a variety of mechanisms, most of which directly relate to the absorption of energy during deformation. The authors subsequently reviewed and classified in a systemic way failure retardation mechanisms related to various types of body armor, including fish scales, fish dermal plates, osteoderms, mollusk shells and porcupine quills. These materials are compared with soft materials such as bacterial cellulose, jumbo squid mantles and actin microtubules that exhibit similar failure retardation characteristics. Through comparison of these failure analysis studies, the authors aim to develop a more nuanced understanding of the evolutionary design of the hierarchical structures observed in a variety of biological systems.