Effect of microscopic deformation mechanisms on the dynamic response of soft cellular materials

Abstract

Cellular materials show progressive or uniform collapse during impact loading depending on their microstructural and material properties. It is generally agreed that a complex interplay among microinertia, microbuckling and microbending of the cell walls of these materials plays an important role in determining their macroscopic stress-strain response. However, an evaluation of the dependency of the overall deformation behavior on these parameters requires sophisticated modeling approach due to extremely fast and complex wave propagation events occurring during dynamic deformation. We have developed a transient finite element based computational framework that can examine the contribution of each of these effects on the deformation history of this class of materials. An in-depth parametric study for different loading, microstuctural and material parameters has been undertaken in this study. Our significant finding is that at high strain rate, shorter pulse rise times lead to higher microinertial stress enhancement due to an increase in apparent microbuckling strength. A variation of cell size shows insignificant effect of microinertia and microbuckling at initial stage but localization can be found at later stage of deformation due to increasing microbuckling and microbending activities. Deformation localization occurs in lower Young's modulus specimens due to lower buckling and bending strength of the cell walls. A significant inertial stress enhancement can be noticed in the specimens with higher bulk density of the constituent material leading to increased microbuckling activities resulting in localized collapse at the impact end.