In-foam additive manufacturing: Elastomeric cellular composites with tunable mechanics

Cellular materials are widely used for impact mitigation in various applications, such as helmets. They are studied under two broad categories of foams and (micro-)lattices with respectively stochastic and deterministic internal geometries. Here, we demonstrate for the first time that systematically modifying the internal structure of a stochastic foam by injecting thermosetting struts with deterministic geometry using a customized 3D printer results in markedly enhanced material properties, especially as related to mechanical energy absorption and dissipation. We refer to this method as In-Foam Additive Manufacturing (IFAM). The mechanics of the resulting foams with embedded struts are investigated experimentally to unravel the unique deformation mechanisms stemming from the interactions between struts and the foams. The design parameters of the resulting composite structure include strut spacing, diameter, and inclination angle. These parameters are examined via compressive mechanical testing, and they were compared with conventional state-of-the-art foams. The results show tunable performance and excellent energy absorption efficiency exceeding the neat foam by as much as nearly an order of magnitude. Our study demonstrates that this significant improvement is partly owed to the synergistic load bearing mechanisms in these cellular composite materials, leading to nearly 10x improvement in mechanics of the foams.