Session T2: Energetic and Reactive Materials X: Simulations

Ignition and Growth Reactive Flow Modeling of Shock Initiation of PBX 9502 at -55$^{\circ}$C and -196$^{\circ}$C

Recently Gustavsen et al.[1] and Hollowell et al.[2] published two stage gas gun embedded particle velocity gauge experiments on PBX 9502 (95{\%}TATB, 5{\%} Kel-F800) cooled to -55$^{\circ}$C and -196$^{\circ}$C, respectively. At -196$^{\circ}$C, PBX 9502 was shown to be much less shock sensitive than at -55$^{\circ}$C, but it did transition to detonation. Previous Ignition and Growth model parameters for shock initiation of PBX 9502 at -55$^{\circ}$C are modified based on the new data, and new parameters for -196$^{\circ}$C PBX 9502 are created to accurately simulate the measured particle velocity histories and run distances to detonation versus shock pressures.\\[4pt] [1] R. Gustavsen, et al., J. Appl. Phys. \textbf{112}, 074909 (2012).\\[0pt] [2] B. Hollowell, et al., Journal of Physics: Conference Series \textbf{500} (2014)182014.   

Determination of Detonation Wave Boundary Angles via Direct Numerical Simulations Using CREST

A key input parameter to Detonation Shock Dynamics models is the angle that the propagating detonation wave makes with the charge edge. This is commonly referred to as the boundary angle, and is a property of the explosive/confiner material combination. Such angles can be determined: (i) experimentally from measured detonation wave-shapes, (ii) theoretically, or (iii) via direct numerical simulations using a reactive burn model. Of these approaches: (i) is costly, (ii) breaks down for certain configurations, while (iii) requires a well validated model. In this paper, the CREST reactive burn model, which has previously been successful in modelling a wide range of explosive phenomena, is used to simulate recent Detonation Confinement Sandwich Tests conducted at LANL using the insensitve high explosive PBX 9502. Simulated detonation wave-shapes in PBX 9502 for a number of different confiner materials and combinations closely match those recorded from the experiments. Boundary angles were subsequently extracted from the simulated results via a wave-shape analysis toolkit. The results shown demonstrate the potential usefulness of CREST in determining detonation wave boundary angles for a range of explosive/confiner material combinations.   

Modelling IHE Main Charge Initiation Trains based on HMX and TATB based Booster Charges

There is always a requirement to reduce the size of initiation trains. However, as the size is reduced the performance characteristics may be compromised. To enable compact and robust initiation trains to be designed requires a detailed science-based understanding of the processes (for example, growth to detonation) which determine the performance characteristics. A numerical modelling study has been performed to understand the designs of initiation trains comprising flyer plate detonator, booster charge and an IHE main charge. The effect of the flyer plate diameter on the distance required to establish uniformly diverging detonation waves in HMX and TATB based booster charges has been studied. Numerical simulations have also examined the effect of the relative sizes of the booster and IHE main charge on the distance required for a stable detonation front to be established in the main charge for both HMX and TATB based booster charges. The implications of the numerical simulations are discussed in terms of the design of initiation trains for IHE main charge systems.   

Multi-dimensional hydrodynamic simulations aimed at characterizing heavily aluminized RDX

An accurate and reliable prediction of reactive flow is a challenging task for an energetic material subjected to an external shock impact. The present study aims at simulating the shock induced detonation of heavily aluminized RDX which contains 35\% of aluminum. A series of gap tests with the longitudinal simulations involving gap substances are conducted to understand the inherent initiation process that depends on the shock propagation through multi-material domain and the high strain dynamics of nearby confinement materials. A pressure chamber test is used to validate the blast wave calculation of the sample charge, and a full 3-D hydrodynamic simulation is performed to predict fragmentation of an explosively loaded steel casing. The paper provides an elaborate description of how a heavily aluminized RDX is characterized in terms of its thermo-chemical response and multi-material interaction with inert confinement materials.   

Mesoscale thermal-mechanical analysis of shocked induced granular explosives and polymer-bonded explosives

The thermal-mechanical response of HMX-based granular explosives (GXs) and polymer-bonded explosives (PBXs) with variable number of crystals from 10 to 100 under impact loading is investigated with finite element software ABAQUS. A series of three dimensional mesoscale calculations are carried out with the crystal plasticity constitutive model for HMX crystals that accounts for nonlinear elasticity and crystalline plasticity and the viscoelastic model for the polymer binder. To make the analysis comparable, the morphology and the size of HMX crystals are kept the same for both GXs and PBXs. In order to quantify the effect of polymer binder under different strain rate, the calculation models are impacted with initial boundary velocities from 10 to 100 m/s. The results shows that the average pressure of PBXs is approximately 50\% higher than GXs and that the localized stress and temperature is highly increased with the polymer binder, which indicates the crystal anisotropy as well as the polymer binder plays an important role in influencing the stress and thermal response of HMX crystals. The thermal-mechanical response analyzed here is essential to predict the formation of hot spot and the ignition of explosives.   

Modeling shock responses of plastic bonded explosives using material point method

Shock responses of plastic bonded explosives are modeled using material point method as implemented in the Uintah Computational Framework. The two-dimensional geometrical model was established based on the micrograph of PBX9501. Shock loading for this explosive was performed by a piston moving at a constant velocity. Simulation results indicate that under shock loading there forms some stress localizations on the grain boundary of HMX explosive. These stress localizations lead to some serious plastic deformation. Simultaneously, the plastic strain energy transforms to thermal energy, causing the temperature to rise rapidly and form some hot spots on grain boundary areas. There are also some micro cracks appear at early time of the shock loading. But after some time these cracks begin to close, forming a few hot spots. The influence of shock strength on the responses of explosive was also investigated by increasing the piston velocity. And the results show that with increasing shock strength, the distribution of plastic strain and temperature does not have significant change, but their values increase obviously. Namely, the higher the shock strength is, the higher the hot spot temperature will be.