Influence of pore-size distributions and pore-wall mechanics on the mechanical behavior of cellular solids like aerogels

Abstract

The pore-size distributions play a critical role in the determination of the properties of nanoporous cellular materials like aerogels. In this paper, we propose a micromechanical model, and by further designing artificial normal pore-size distributions, we inspect their effect on the macroscopic stress-strain curves. We show that the location of the mean pore size as well as the broadness of the distribution strongly affects the overall macroscopic behavior. Moreover, we also show that by using different damage criteria within the proposed model, the elastic, inelastic, and brittle nature of the macroscopic material can be captured. The damage criteria are based on the different modes of deformation in the pore walls, namely, elastic buckling, irreversible bending and brittle collapse under compression, and combined bending and stretching under tension. The proposed model approach serves as a reverse engineering tool to develop cellular solids with desired mechanical properties.

Constitutive Modeling of the Densification Behavior in Open-Porous Cellular Solids

“…Considering the cell wall as an Euler-Bernoulli beam, the bending and stretching strain energy functions can be fundamentally expressed as [13]…”

“…The model was able to capture not only the nature of the stress-strain curve but could also predict the network failure with high accuracy. A generalized model to describe the mechanical behavior of open-porous cellular materials with elastic, ductile and brittle properties was very recently published in Rege et al [13], where the influence of the pore-size distributions in nanoporous materials, together with the mode of deformation in the pore walls, on the bulk mechanical properties was presented. However, while describing the compressive behavior, the model only captured the linear elastic regime and the subsequent pore collapse.…”

“…In all the above-mentioned studies, the shape of the cells was assumed to be constant through the structure. While the models proposed by Rege et al [8,[11][12][13] account for the variation in cell sizes, they also assumed an idealized cell shape. On the one hand Kraynik et al [15] established that the elastic response of such materials was insensitive to the variability in the cell sizes and shapes, while on the other hand, Rege et al [13] showed that the pore sizes play a significant role in dictating the mechanical properties of nanoporous cellular materials.…”

“…While the models proposed by Rege et al [8,[11][12][13] account for the variation in cell sizes, they also assumed an idealized cell shape. On the one hand Kraynik et al [15] established that the elastic response of such materials was insensitive to the variability in the cell sizes and shapes, while on the other hand, Rege et al [13] showed that the pore sizes play a significant role in dictating the mechanical properties of nanoporous cellular materials. To find a solution towards modeling such materials by accounting for the variability in the cell structure, an alternative approach is presented in the form of finite element methods [16][17][18].…”

“…However, in this paper, the focus is on numerical approaches and a reader interested in Voronoi-based methods, may refer to the references cited above. In this paper, the micromechanical model approach presented in [13] has been extended to capture the hardening in the compressive stress-strain curve during the densification of the material network.…”