Tough and stiff composites with simple building blocks

From bone to dentin to nacre, biomaterials are structurally advanced composites with superior toughness and significant stiffness, based on simple building blocks. Here, using a series of molecular mechanics models with bioinspired topologies, we propose design mechanisms rooted in the simplest mechanical interactions—perfectly brittle linear elastic—which are shown to be sufficient to achieve superior toughness at high stiffness in biological composites. In a two-phase composite system, we show that by adapting the elastic constitutive laws of the matrix phase and by tuning the interactions of the constituents we can realize materials with a large range of combinations of toughness and stiffness. Notably, this can be achieved without changing the fracture energy of the individual composite components. Through a systematic analysis and the development of a simple model, we unveil basic design principles that lead to fundamental insights into the mechanics of natural composites for applications in a range of engineering disciplines.