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Some energetic materials may explode at fairly low temperatures and the violence from thermal explosion may cause a significant damage. Thus it is important to understand the response of energetic materials to thermal insults for safe handling and storage of energetic materials. The One Dimensional Time to Explosion (ODTX) system at the Lawrence Livermore National Laboratory can measure times to explosion, lowest explosion temperatures, and determine kinetic parameters of energetic materials. Samples of different configurations can be tested in the system. The ODTX testing can also generate useful data for determining thermal explosion violence of energetic materials. We also performed detonation experiments of LX-10 in aluminum anvils to determine the detonation violence and validated the Zerilli Armstrong aluminum model. Results of the detonation experiments agreed well with the model prediction.

High-explosive (HE) material consists of large-sized grains with micron-sized embedded impurities and pores. Under various mechanical/thermal insults, these pores collapse generating hightemperature regions leading to ignition. A hydrodynamic study has been performed to investigate the mechanisms of pore collapse and hot spot initiation in TATB crystals, employing a multiphysics code, ALE3D, coupled to the chemistry module, Cheetah. This computational study includes reactive dynamics. Two-dimensional high-resolution large-scale meso-scale simulations have been performed. The parameter space is systematically studied by considering various shock strengths, pore diameters and multiple pore configurations. Preliminary 3-D simulations are undertaken to quantify the 3-D dynamics.

The two-phase model of Nigmatulin (Dynamics of Multiphase Media, 1991) is revisited and a second order Godunov solver is constructed for the corresponding Riemann problem using a seven wave structure. This model differs from the well established Baer-Nunziato model (International J. Multiphase Flow, Vol. 12, No. 6, 1986, pp. 861-889) in that it treats the solid phase as incompressible, and also accounts for thermal as well as elastic energies for the solid phase. Numerical results are presented for three classes of Riemann problems, demonstrating the accuracy of the method. The effect of inter-granular stress on the flow physics is investigated and it is shown that this term results in faster wave speeds for higher stresses. This study confirms that the Nigmatulin model can also be useful for the study of two-phase flows.

The role of dissipative effects, such as viscosity, in the ignition of high explosive pores is investigated using a coupled chemical, thermal, and hydrodynamic model. Chemical reactions are tracked with the Cheetah thermochemical code coupled to the ALE3D hydrodynamic code. We perform molecular dynamics simulations to determine the viscosity of liquid TATB. We also analyze shock wave experiments to obtain an estimate for the shock viscosity of TATB. Using the lower bound liquid-like viscosities, we find that the pore collapse is hydrodynamic in nature. Using the upper bound viscosity from shock wave experiments, we find that the pore collapse is closest to the viscous limit.

The reflection of a blast wave from a C4 charge detonated above a planar surface is simulated with our ALE3D code. We used a finely-resolved, fixed Eulerian 2-D mesh (167 μm per cell) to capture the detonation of the charge, the blast wave propagation in nitrogen, and its reflection from the surface. The thermodynamic properties of the detonation products and nitrogen were specified by the Cheetah code. A programmed-burn model was used to detonate the charge at a rate based on measured detonation velocities. Computed pressure histories are compared with pressures measured by Kistler 603B piezoelectric gauges at 7 ranges (GR = 0, 5.08, 10.16, 15.24, 20.32, 25.4, and 30.48 cm) along the reflecting surface. Computed and measured waveforms and positive-phase impulses were similar, except at close-in ranges (GR < 5 cm), which were dominated by jetting effects.

We will present results of an effort to improve the thermal/chemical/mechanical modeling of HMX based explosives like LX04 and LX10 for thermal cook‐off The original HMX model and analysis scheme were developed by Yoh et al. for use in the ALE3D modeling framework. The current results were built to remedy the deficiencies of that original model. We concentrated our efforts in four areas. The first area was addition of porosity to the chemical material model framework in ALE3D that is used to model the HMX explosive formulation. This is needed to handle the roughly 2% porosity in solid explosives. The second area was the improvement of the HMX reaction network, which included a reactive phase change model base on work by Henson et al. The third area required adding early decomposition gas species to the CHEETAH material database to develop more accurate equations of state for gaseous intermediates and products. Finally, it was necessary to improve the implicit mechanics module in ALE3D to more naturally handle the long time scales associated with thermal cook‐off The application of the resulting framework to the analysis of the Scaled Thermal Explosion (STEX) experiments will be discussed.

High‐explosive (HE) material consists of large‐sized grains with micron‐sized embedded impurities and pores. Under various mechanical/thermal insults, these pores collapse generating high‐temperature regions leading to ignition. A computational study has been performed to investigate the mechanisms of pore collapse and hot spot initiation in TATB crystals, employing the thermo‐hydrodynamics arbitrary‐Lagrange‐Eulerian code ALE3D. This initial study includes non‐reactive dynamics to isolate the thermal and hydrodynamical effects. Two‐dimensional high‐resolution large‐scale meso‐scale simulations have been undertaken. We study an axisymmetric configuration for pore radii ranging from 0.5 to 2 μm, with initial shock pressures in the range from 3 to 11 GPa. A Mie‐Gruneisen Equation of State (EOS) model is used for TATB, and includes a constant yield strength and shear modulus; while the air in the pore invokes a Livermore Equation of State (LEOS) model. The parameter space is systematically studied by considering various shock strengths, pore diameters and material properties. We find that thermal diffusion from the collapsed pores has an important effect in generating high‐temperature hot spots in the TATB. LLNL‐PROC‐415378

We present modeling results for the propagation of strong shock waves in metals. In particular, we use an arbitrary Lagrange Eulerian (ALE3D) code to model the propagation of strong pressure waves (P ∼ 300 to 400 kbars) generated with high explosives in contact with aluminum cylinders. The aluminum cylinders are assumed to be both flat‐topped and have large‐amplitude curved surfaces. We use 3D Lagrange mechanics. For the aluminum we use a rate‐independent Steinberg‐Guinan model, where the yield strength and shear modulus depend on pressure, density and temperature. The calculation of the melt temperature is based on the Lindermann law. At melt the yield strength and shear modulus is set to zero. The pressure is represented as a seven‐term polynomial as a function of density. For the HMX‐based high explosive, we use a JWL, with a program burn model that give the correct detonation velocity and C‐J pressure (P ∼ 390 kbars). For the case of the large‐amplitude curved surface, we discuss the evolving shock structure in terms of the early shock propagation experiments by Sakharov.

Knowledge of an effective interatomic potential function underlies any effort to predict or rationalize the properties of solids and liquids. The experiments we undertake are directed towards determination of equilibrium and dynamic properties of simple fluids at densities sufficiently high that traditional computational methods and semi‐empirical forms successful at ambient conditions may require reconsideration. In this paper we present high‐pressure and temperature experimental sound speed data on a simple fluid, methanol. Impulsive Stimulated Light Scattering (ISLS) conducted on diamond‐anvil cell (DAC) encapsulated samples offers an experimental approach to determine cross‐pair potential interactions through equation of state determinations. In addition the kinetics of structural relaxation in fluids can be studied. We compare our experimental results with our thermochemical computational model Cheetah. Experimentally grounded computational models provide a good basis to confidently understand the ch...

We model detonation waves for solid explosives, using 2‐D Arbitrary Lagrange Eulerian (ALE) hydrodynamics, with an equation of state (EOS) based on thermochemical equilibrium, coupled with simple kinetic rate laws for a few reactants. The EOS for the product species is based on an exponential‐6 potential model, whose parameters are fitted to a wide range of shock Hugoniot and static compression data. We show some results for the non‐ideal explosive, urea nitrate. Such a model is a powerful tool for studying such processes as initiation, and detonation wave propagation as a function of cylindrical radius.

We develop a model of chemical equilibrium mixtures containing the elements H, C, F. We show that the shock response of a wide variety of molecular and polymeric fluorocarbons can be modeled as a chemical equilibrium mixture of a small number of dissociation product molecules. HF is known to strongly associate in the supercritical fluid phase. We predict that such an association also occurs under shock conditions.

We have implemented a Wood-Kirkwood kinetic detonation model based on multi-species equations of state and multiple reaction rate laws. Finite rate laws are used for the slowest chemical reactions, while other reactions are given infinite rates and are kept in constant thermodynamic equilibrium. Within the context of WK theory, we study the chemical interaction between Al and HMX detonation products in non-ideal explosives. We develop a kinetic rate law for the combustion of Al in a condensed detonation that depends on the pressure and the detonation product gases. We use a Murnaghan form for the equation of state of the solid and liquid Al and Al2O3. We find that we can replicate experimental detonation velocities for HMX/Al composites to within a few percent for a wide range of aluminum content. We discuss the uncertainties in our model and the implications of our results on the modeling of other non-ideal explosives ???

The equilibrium thermochemical code CHEETAH V1.40 has been modified to detonate part of the explosive and binder. An Einstein thermal description of the unreacted constituents is used, and the Einstein temperature may be increased to reduce heat absorption. We study the effect of the reactivity and thermal transport on the detonation velocity. Hydroxy-terminated-polybutadiene binders have low energy and density and would degrade the detonation velocity if they burned. Runs with unburned binder are closer to the measured values. Aluminum and ammonium perchlorate are also largely unburned within the sonic reaction zone that determines the detonation velocity. All three materials appear not to fully absorb heat as well. The normal assumption of total reaction in a thermochemical code is clearly not true for these special cases, where the detonation velocities have widely different values for different combinations of processes.

A water-cooled beryllium target, capable of handling intense ion beams with power densities near 6 kw/cm2 is being developed and tested in conjunction with the high current tandem accelerator at MIT’s Laboratory for Accelerator Beam Applications (LABA). This target will be used to generate a high flux of neutrons via either the 9Be(p,n) or 9Be(d,n) reaction for use in Boron Neutron Capture Therapy (BNCT). Water cooling is provided by submerged jet flow impinging on the back surface of the target. Initial testing under low coolant flow rates indicates that the target temperature rise is linearly dependent on flow rate up to the point of critical heat flux. The critical heat flux is dependent on coolant velocity, nozzle diameter, and nozzle to target spacing. Design calculations will be compared with experimental measurements of target performance.

We summarize the stellar parameters which characterize the s‐process σN curve in the framework of models which produce an exponential distribution of exposures by periodic time‐dependent neutron irradiations. The optimum parameter space, defined by the best fit to the solar‐system σN curve, is distinctively different than the classical smooth monotonically decreasing curve. Constraints are placed on the s‐process environment. The needs for better neutron‐capture data in various mass regions are highlighted.

We summarize results from a detailed parameter study of the s‐process in models which produce an exponential distribution of exposures by sequential irradiations and dredge up in the stellar environment. The calculations are based on a complete network of measured and calculated neutron capture and beta‐decay rates as well as estimates for their temperature dependence. In the framework of these models we identify and systematically vary the astrophysical variables which affect the observed solar‐system σN (cross section times abundance) curve. Constraints are placed on the s‐process neutron exposure and flux as well as the temperatures, densities, neutron pulse shape and inter‐pulse period. The results also highlight important needs for better nuclear data in various mass regions.