Volume change versus pressure is expressed through an equation of state (EOS) such as the well-known Mie-Gruneisen equation. Equation of state is an essential requirement to be defined for numerical simulation of high rate events such as impact. All EOSs have some coefficients which are identified by experiment and are usually considered constant and strain rate independent. In this study, the effect of strain rate on the coefficients of Mie-Gruneisen equation is obtained for polyethylene by experiment and numerical simulation. The low and high strain rate compression tests are conducted using Instron testing machine and Hopkinson bar, respectively. The load-displacement and load-volume change curves are obtained from the experiments. The strain rate dependent constants of Mie-Gruneisen equation of state are obtained through a combined experimental/numerical/optimization technique. The compression test is simulated using Ls-dyna hydrocode. The results show that the coefficient γ is not affected by strain rate but the coefficients C and S₁ are severely strain rate dependent. The latter varies with strain rate in a linear fashion and the former varies cubically with strain rate.

体积变化与压力之间的关系通过状态方程（EOS）表示，例如众所周知的Mie-Gruneisen方程。状态方程是定义高速率事件（例如冲击）的数值模拟的基本要求。所有EOS都有一些通过实验确定的系数，通常被认为是常数且与应变率无关。在本研究中，通过实验和数值模拟，得出了应变速率对聚乙烯的Mie-Gruneisen方程系数的影响。低应变率和高应变率压缩测试分别使用Instron测试机和Hopkinson棒进行。从实验中获得了载荷-位移和载荷-体积变化曲线。Mie-Gruneisen状态方程的应变速率相关常数是通过组合实验/数值/优化技术获得的。使用Ls-dyna液压码模拟压缩测试。结果表明，系数γ不受应变率的影响，但系数C和S₁严重依赖应变率。后者随应变率线性变化，而前者随应变率立方变化。