Propagation Properties of Shock Waves in Polyurethane Foam based on Atomistic Simulations

Porous materials are widely used in the field of protection because of their excellent energy absorption characteristics. In this work, a series of polyurethane microscopic models are established and the effect of porosity on the shock waves is studied with classical molecular dynamics simulations. Firstly, shock Hugoniot relations for different porosities are obtained, which compare well with the experimental data. The pores collapse and form local stress wave, which results in the complex multi-wave structure of the shock wave. The microstructure analysis shows that the local stress increases and the local velocity decreases gradually during the process of pore collapse to complete compaction. Finally, it leads to stress relaxation and velocity homogenization. The shock stress peaks can be fitted with two exponential functions, and the amplitude of attenuation coefficient decreases with the increase of density. Besides, the pore collapse under shock or non-shock are discussed by the entropy increase rate of the system. The energy is dissipated mainly through the multiple interactions of the waves under shock. The energy is dissipated mainly by the friction between atoms under non-shock.