Random 3D-printed isotropic composites with high volume fraction of pore-like polydisperse inclusions and near-optimal elastic stiffness

Abstract

Abstract Highly porous materials with random closed-cell architecture combine isotropy with high stiffness. Yet in practice, the complexity of their manufacturing limits the experimental exploration of these materials, for which studies of the elastic response remain to date mainly theoretical. In this study, we measure experimentally the elastic moduli of random closed-cell porous-like composites fabricated by 3D-printing. These materials contain a high volume fraction (up to 82 vol pct) of non-overlapping, polydisperse void-like spherical inclusions, which are randomly dispersed in a homogeneous polymer matrix. We first generate the virtual microstructures of these materials using a random sequential adsorption (RSA) algorithm, and then use numerical homogenization to compute the size of the material representative volume element (RVE). The latter is used to assemble the test samples, whereby the void-like inclusions are 3D-printed using a gel-like polymer with mechanical properties that are in high contrast with those of the base polymer thus behaving mechanically as pores. Experiments reveal that the proposed isotropic random closed-cell porous materials have bulk and shear moduli that lie very close to the theoretical Hashin-Shtrikman upper bounds for an isotropic porous solid.