Micro-mechanical properties of foamed polymer rehabilitation material: A molecular dynamics study

Abstract

The non-aqueous reactive foamed polyurethane is widely used in engineering. We have observed the micromorphology of the non-aqueous reactive foamed polyurethane by field emission scanning electron microscope. It is found that the pores are closed and the minimum pore wall thickness is only 63.5 nm. Therefore, we proposed a method to construct a microscopic model of the polyurethane closed pores with different densities. Combined with the change of non-affine displacement of atoms in the process of compression deformation, the influence mechanism of density and strain rate on the mechanical properties of polyurethane closed pores is studied from the microscopic scale, and compared with that of polyurethane elastomers. The results show that the yield strength of polyurethane closed pores increases with the increase of strain rate and density, and the yield strain of the pores is almost not affected by the density, but will increase with the increase of strain rate. The smaller the density, the greater the effect of strain rate on the polyurethane closed pores which is consistent with the experimental results. The polyurethane closed pores and elastomers will yield when the atoms whose non-affine displacement exceeds 1 Å accumulate to a certain extent. The increase of strain rate will make the number of atoms with non-affine displacement exceeding 1 Å less, so the pores will yield at higher strain. Under the same conditions, the yield stress and yield strain of polyurethane elastomers are significantly greater than that of polyurethane closed pores, and the average non-affine displacement of atoms in the pores is significantly greater than that of atoms in polyurethane elastomers, which indicates that more severe cavitation and chain slip phenomena will occur in the pores. The simulation results of this paper analyzed the mechanical properties of foamed polyurethane from a new perspective.