Jones-Wilkins-Lee Unreacted and Reaction Product Equations of State for Overdriven Detonations in Octogen- and Triaminotrinitrobenzene-Based Plastic-Bonded Explosives.

The Jones-Wilkins-Lee (JWL) equation of state (EOS) is used to calculate expansion of detonation reaction products from the chemical equilibrium Chapman-Jouguet (C-J) state to large volumes. Overdriven detonation waves with shock pressures higher than C-J are created by high-velocity impacts or converging detonation waves. Reflection from high-impedance materials, multiple shock impacts, and Mach stem wave interactions creates similar pressures. When overdriven states were first measured experimentally, the original reaction product JWL EOSs predicted excess compression. This problem was resolved by modifying the JWL EOS to produce less compression at high pressures while still correctly calculating expansion from the C-J state. Zeldovich-von Neumann-Doring (ZND) reactive flow models, which include the measured reaction zone momentum, explained experimental observations that lower C-J pressures are required to smoothly connect the C-J state to overdriven states on the product Hugoniot curve. Experimental data on overdriven detonation waves for two octogen (HMX)-based plastic-bonded explosives (PBXs), PBX 9501 and PBX 9404, and for two triaminotrinitrobenzene (TATB)-based PBXs, LX-17 and PBX 9502, are compared to various JWL reaction product EOSs, including ones generated by the CHEETAH chemical equilibrium code. Excellent agreement is obtained using JWL EOSs for overdriven shock pressures and densities up to 130 GPa and 3.8 g/cm3 for both HMX- and TATB-based PBXs.

Ultrafast detonation of hydrazoic acid (HN3).

The fastest self-sustained chemical reactions in nature occur during detonation of energetic materials where reactions are thought to occur on nanosecond or longer time scales in carbon-containing materials. Here we perform the first atomistic simulation of an azide energetic material, HN3, from the beginning to the end of the chemical evolution and find that the time scale for complete decomposition is a mere 10 ps, orders of magnitude shorter than that of secondary explosives and approaching the fundamental limiting time scale for chemistry; i.e., vibrational time scale. We study several consequences of the short time scale including a state of vibrational disequilibrium induced by the fast transformations.

Corner turning and shock desensitization experiments plus numerical modeling of detonation waves in the triaminotrinitrobenzene based explosive LX-17.

Five new experiments are reported that tested both detonation wave corner turning and shock desensitization properties of the triaminotrinitrobenzene (TATB) based plastic bonded explosive (PBX) LX-17. These experiments used small pentaerythritol tetranitrate (PETN) charges to initiate hemispherical ultrafine TATB (UF TATB) boosters, which then initiated LX-17 hemispherical detonations. The UF TATB boosters were placed under steel shadow plates embedded in the LX-17 cylindrical charges, which were covered by thin aluminum plates. The LX-17 detonation waves propagated outward until they reached the aluminum plates, which were instrumented with photonic Doppler velocimetry probes to measure their axial free surface velocities. X-ray radiographs and framing camera images were taken at various times. The LX-17 detonations propagated around the two corners of the steel shadow plates and into thin LX-17 layers placed between the steel and the top aluminum plates. The detonation waves were met there by weak diverging shocks that propagated through the steel plates and imparted 1-2 GPa pressures to these unreacted LX-17 layers. These weak shock waves compressed and desensitized the unreacted LX-17, resulting in failures of the LX-17 detonation waves. The hydrodynamics of double corner turning and shock desensitization in the five experiments were modeled in two dimensions using the Ignition and Growth LX-17 detonation reactive flow model. The calculated arrival times and axial free surface velocity histories of the top aluminum plates were in excellent agreement with the experimental measurements.

Analysis of simulation technique for steady shock waves in materials with analytical equations of state.

We calculate and analyze a thermodynamic limit of a multiscale molecular dynamics based scheme that we have developed previously for simulating shock waves. We validate and characterize the performance of the former scheme for several simple cases. Using model equations of state for chemical reactions and kinetics in a gas and a condensed phase explosive, we show that detonation wave profiles computed using the computational scheme are in good agreement with the steady state wave profiles of hydrodynamic direct numerical simulations. We also characterize the stability of the technique when applied to detonation waves and describe a technique for determining the detonation shock speed.