Four-Parameter Universal Equation of State

Based on the fact that the Lagrangian bulk moduli of many materials can be expressed as a second order expansion with respect to pressure, a four-parameter equation of state has been proposed which, in comparison with the three-parameter equation of state, can be applied to a wider pressure range and has higher fitting accuracy and good extrapolation behavior.The parameters in the equation are dependent on the first, second and third order derivatives, hence, by using the derivative relations of the Hugoniot and isentropic equations, one can verify if the dynamic high-pressure experimental data match the static high-pressure experimental data.The equation describes shock, isentropic and isothermal compression states in a unified form, is suitable for a variety of materials in a wide pressure range, and therefore can be considered as a universal equation of state.Being simple and easy to operate, our equation overcomes the weakness of conventional four-parameter equations of state which are of no practical use due to their complicated structure, lengthy formula, and high correlation between parameters.