Effect of microstructure closed-pore content on the mechanical properties of flexible polyurethane foam

Poroelastic models are constructed based on a set of physical parameters known as the Biot's parameters (for isotropic materials these are comprised of 5 non-acoustical parameters and 4 mechanical parameters). These macroscopic properties are inter-correlated and dependent on the microstructure of the foam. Therefore, to optimize vibroacoustic behavior, the correlation between foam microstructure and macroscopic properties is needed. In this study, the effect of closed windows content (known as reticulation rate), cell size, and relative density on the mechanical properties of polyurethane (PU) foam are numerically studied using an isotropic, tetrakaidecahedral unit cell. Then, an existing analytical model that correlates unit cell microstructure properties (thickness and length of struts) of fully reticulated foams to their mechanical properties is extended numerically. The membrane thickness is considered to be thinner at the center and larger at the edge of the window. The ratio of membrane thickness to strut thickness is either considered to be fixed or variable. Results show that the Young's modulus and Poisson's ratio of unit cells with smaller cells size, when relative density is fixed, are more affected by closed window content.