Determination of the JWL Coefficients of the Hexomax Explosive

Abstract

The replacement of plastrite by Hexomax leads to determinate and validate the equation of state parameters of the detonation products, in the goal to make performances numerical calculations of this energetic material. The Chapman- Jouguet state is calculated using two ways, firstly from simulations with the thermo-chemical code named SIAME developed by the CEA for the French DGA and conventional defense applications, secondly from an approach based on empirical relations available in the literature. The hypothesis of a mean value for the polytropic coefficient in the ambient state of detonation products and also for exponential decreasing members coefficients of JWL equation allows to reach to other parameters according the strength to respect the detonation CJ state. Inside SIAME, these coefficients are obtained by minimization of the JWL equation isentropic form of the detonation products CJ expansion. Used in a hydrodynamical calculation code (OURANOS, LS-DYNA), JWL parameters allow to compare the numerical simulation results to experimental results of the cylinder test. The correlation is very good with parameters from the thermo-chemical simulation. The empirical method looks like a FREM (« Fast Running Engineer Model ») leading to a good approximative solution of JWL parameters when the necessary enthalpy of formation for the thermo-chemical simulation is not available. The JWL parameters are used afterwards to evaluate the Hexomax blast effects for aerial detonation.