The mechanics of energy dissipation in a three-dimensional graphene foam with macroporous architecture

The three-dimensional porous architecture of graphene foam combines extraordinary mechanical properties of graphene with a unique structural organization to produce a strong, lightweight material. In this study, mechanisms for energy dissipation in graphene foam are investigated by localized nano-scale dynamic mechanical testing. Mechanical response of the material subjected to cyclic loading-unloading is captured as loss tangent (tan δ), characterizing the energy dissipation. Indentation tips with different geometries and dimensions (from 100 nm to 100 μm) are employed, which translate into variable stress-states with mechanical stresses ranging from a few kilo-Pascals to a few giga-Pascals. Formation of dynamic ripples, flattening of intrinsic corrugations, kink band formation, inter-layer van der Waals spring-like action, and membrane vibration are proposed as the key energy dissipation mechanisms in graphene foam. The relative contribution of these mechanisms towards energy dissipation is compared and quantified, with tan δ values varying from about 0.1 to 0.45. The energy dissipation behavior of the material is found to be highly stable, as the loss tangent values are retained for as high as 50,000 cycles. The fundamental understanding of intrinsic mechanics will enable engineering of impact-tolerable foam structure with desirable and predictable mechanical performance.