Polymer-based, 3D printed, Syntactic Foams Maintain Modulus and Energy Dissipation Under Cyclic Loading due to Shell Buckling and Elastic Recovery

Additive manufacturing has magnified capabilities for on-demand fabrication of bio-inspired materials possessing complex architectures across broad length scales, leading to systems that are simultaneously stiff, tough, and lightweight. We recently developed a two-step digital light processing (DLP)-based 3D printing approach that involves an initial photopolymerization step followed by the thermal expansion of embedded microspheres, which allows additively manufactured closed-cell composite polymer foams with variable porosity and tunable mechanics. Here, we report thermomechanical characterization of the constituents (i.e., polymer matrix and shell of microspheres) which led to an improvement in material processing and facilitated the detailed mechanical analysis of the compressive behaviors of the composite foams. Effects of foaming on the stress-strain response, Poisson’s ratio, and energy dissipation were investigated using uniaxial compression. The foams show remarkable fatigue tolerance under cyclic loading at large deformation, maintaining superior energy dissipation capabilities and modulus. Electron microscopy of mechanically deformed materials via suggests that their resilience can be attributed to shell bucking and elastic recovery of the polymeric microsphere.