Low-parametric equation of state for graphite describing solid and porous samples under shock and unloading waves

This study is aimed to obtain the parameters of the graphite equation of state represented as the Mie-Grüneisen equation of state. Graphite with metals and the porous graphite are considered as simple thermodynamically equilibrium mixtures. The equilibrium state is determined by the conditions of equal pressure, temperature, and velocity of the components in the mixture. Thus, the motion of the multicomponent medium can be described as the motion of a continuum with a special equation of state that takes into account the properties of the mixture components and their concentration, which significantly reduces the number of equations. For the Grüneisen parameter, a logarithmic dependence on density is used, which adequately describes the variation in the Grüneisen parameter for both normal and anomalous behavior of shock adiabats.
The increasing scope of the equation of state is a result of comparing experimental data with calculations for the following: 1) shock-wave loading of porous materials to cover the range of higher temperatures; 2) double compression of the samples to cover the range of increased densities; 3) isentropic expansion of samples to cover the range of low densities; and 4) sound velocities, which characterize the compressibility of matter, slope of the Poisson adiabat on the shock adiabat, and propagation velocity of the weak shock waves and unloading waves through the compressed matter.
The comprehensive analysis confirms that the proposed model of the equation of state for graphite is applicable to practical applications.