Bioinspired Design Criteria for Damage-Resistant Materials with Periodically Varying Microstructure

Many biological materials, such as bone, nacre, or certain deep‐sea glass sponges, have a hierarchical structure that makes them stiff, tough, and damage tolerant. Different structural features contributing to these exceptional properties have been identified, but a common motif of these materials, the periodic arrangement of structural components with strongly varying stiffness, has not gained sufficient attention. Here we show that the periodicity of the material properties is one of the dominant reasons for the high fracture resistance of these structures and their tolerance to short cracks. If the composite architecture fulfills certain design rules, which are derived in this paper, the stiff structure becomes fracture resistant and, most of all, flaw tolerant. This architectural criterion inspired from nature provides useful guidelines for the design of defect‐tolerant resistant man‐made materials. Inspired by the analysis of natural composites made of bio‐glass and protein, a criterion for the design of flaw‐tolerant and damage‐resistant multilayered materials is developed. The criterion proposes that the thickness of the layers should be chosen as a function of the stiffness and fracture properties of the two components in the multilayer. When the thickness of the stiff layer is small enough, cracks are arrested in the soft layer and cannot propagate further.