High explosives (HE) are normally sensitive to heat, impact, and other external variables. Insensitive high explosives (IHE) have been developed to significantly improve the safety and reliability of weapon systems in case of an accident or an encounter under a hostile environment.

The overall goal of the HE group is to provide the predictive material models and physical data to address such a situation. It requires a fundamental understanding of the initiation and detonation processes based on the underlying physics and chemistry. Our approach is (1) to identify physical sources of insensitivity; (2) to address them by quantum chemical calculations, atomic simulations, and thermochemical calculations; and (3) to provide reliable IHE equations of state (EOS) and constitutive relations for hydro-performance and safety predictions. Our effort consists of molecular, grain scale and continuum level studies. The molecular-level studies employ the statistical mechanics and intermolecular potentials to provide EOS of reactive mixtures. The continuum-level studies use the resulting EOS data in hydrodynamics codes to describe the material flow based on the conservation laws of mass, momentum, and energy. The grain-scale dynamics effort introduces more detailed heterogeneous effects from HE grains, plastic binder, and voids in the continuum models, with additional refinement derived from the molecular modeling effort. Specifically, molecular models of the carbon kinetics are used to address the energy release rates in continuum simulations of the detonation wave.

Quantum chemistry and molecular dynamics calculations of the energy and conversion rates of carbon clusters are used to improve the molecular model of carbon kinetics. First-principles calculations of energetic materials and detonation products are used to uncover the new physics and improve the potentials of detonation products in the thermochemical code CHEQ. The CHEQ code is used to create an EOS table that includes a consistent set of transport coefficients for the grain-scale dynamics. All these models are being implemented to provide improved predictions of the performance, safety, and reliability of the high explosives in the weapons stockpile.