Viscoelastic foam-filled lattice for high energy absorption

A new composite foam concept that involves infiltrating a polyurea-based foam through an open 3D lattice structure with 2 mm strut size is presented. The stress-strain characteristics, energy absorption, and cushioning efficiency are measured at quasi-static and dynamic strain rates using an Instron load frame and a drop tower facility, respectively. Results are compared with EPS72 (expanded polystyrene foam with a density of 72 kg/m3) and Poron320 (density of 320 kg/m3) foams that represent high performance benchmarks for foams that absorb impact energy through plastic crushing and rate-induced glass transition mechanisms, respectively. The composite foams absorb more impact energy in same section thickness, while keeping both the peak stress and impulse duration low compared to these benchmarks. Most importantly, the composite foams display stability at both low (0°C) and high temperatures (40°C) because of its extremely low Tg of − 50°C. Being viscoelastic, they recover fully within 30 s after each impact, without loss of any energy absorption capability. The underlying microstructural mechanisms for these superior impact properties are also discussed. These properties should allow these materials to have a wide range of military and civilian applications, especially in advance armors and protective body and headgear systems.