Mechanical performance of solid and sheet network-based stochastic interpenetrating phase composite materials

Nature-inspired architected materials premise effective property combinations that are well beyond the limits of classical engineering materials. The current study expands the concept of architected, interpenetrating phase composites (IPC) with regular periodic inner phase reinforcements to the realm of stochastic designs. Schoen's Wrapped Package minimal surface (IWP) is used as base reinforcement phase structure, while implicit functions are employed for the creation of stochastic solid and sheet topologies. The study is performed for various reinforcement volume fractions as low as 20 and up to 40%, using a resin-based 3D printer for the specimen fabrication. The strong directional dependence of the uniaxial properties of regular IWP-based designs is highlighted, while their linear and nonlinear material attributes are compared with the ones of stochastic architectures. It is shown that stochastic, sheet-based single phase and IPC material architectures can yield comparable effective mechanical properties or outperform the energy absorption capacity of regular designs at low volume fraction reinforcements. The stochasticity of the strain fields is experimentally verified through digital image correlation (DIC), associating the arising failure modes with the regular or stochastic nature of the inner reinforcement phase. Moreover, functionally graded stochastic architectures are engineered and characterized, establishing a fundamental control of the deformation and resulting stress-strain response along a desired material direction. The high-performing effective material attributes, combined with the directional independence premised by the stochasticity of the IPC metamaterial architectures constitute objectives beyond the performance limits of regular cellular materials, opening new frontiers in the design of advanced structural applications.