Effect of Relative Density on the Dynamic Impact Behaviors of Closed-Cell Foam

Dynamic behaviors of closed-cell foam are investigated with cell-based finite element models based on the 3D Voronoi technique. The typical deformation feature of cellular structures under high-velocity impact is layer by layer collapse, like a shock wave propagating in the specimen. The one-dimensional velocity distribution of the structure is calculated to characterize the propagation of shock front and thus the shock wave speed is determined quantitatively. It is found that the shock wave speed has intense dependence on the impact velocity for a specific relative density. The difference between the shock wave speed and the impact velocity is asymptotic to a constant as the impact velocity increases. This constant can be therefore regarded as a dynamic material parameter. The influence of relative density on this dynamic material parameter is investigated. The results show that the shock wave speed at a specific impact velocity increases with the increase of the relative density of cellular structure in a certain extent. An expression of the shock wave speed with respect to the impact velocity and relative density is obtained. The dynamic strain hardening parameter is lower than that in the quasi-static one, which indicates different mechanisms of the deformation under high-velocity and quasi-static loadings.