Comparison of elastic properties of low-density polymeric foams determined by ultrasonic wave propagation and quasi-static mechanical testing

The ability to predict the mechanical performance of materials without sample extraction is of great interest to manufacturers and end-users. The aim of this work was to examine the relationship between the quasi-static measurements (i.e. the typically reported elastic property) and the non-destructive in-line in-situ ultrasonic wave propagation-derived elastic moduli of porous polyurethane foams over a range of densities. It was found that the ratio of moduli was direction-dependent: a factor of 2 when the testing was perpendicular to the pore orientation and a factor of 1.7 when parallel to the pore rising direction. The deviation was explained by ruling mechanisms such as strain rate and amplitude, deviation from orthotropic theory and anisotropy, and degree of density which affected shear wave propagation. The correlations were in agreement with those reported for other porous materials. The quantification of this correlation is a practical tool for estimating elastic properties on heterogeneous, irregularly shaped samples not suitable for bulk testing, or for in-line rapid quality control of parts in production lines.