Session J3: Detonation and Shock Induced Chemistry: Mechanical Properties and Shocked Liquids

High-rate experiments on a nitro\-cellulose/\allowbreak nitro\-glycerine propellant

The mechanical behaviour of a rubbery nitro\-cellulose/\allowbreak nitro\-glycerine double-base propellant was probed at a range of strain rates. The propellant was relatively soft, and inhomogeneous on the millimetre scale, presenting a few experimental difficulties. Techniques for overcoming these difficulties in split Hopkinson pressure bar and plate impact experiments are presented, along with the results of these experiments at a range of temperatures.   

Yield Stress Model for Molten Composition B-3

Composition B-3 (Comp B-3) is a melt-castable explosive composed of 60/40 wt{\%} RDX/TNT (hexahydro-1,3,5-trinitro-1,3,5-triazine/2,4,6-trinitrotoluene). During casting operations thermal conditions are controlled which along with the low melting point of TNT and the insensitivity of the mixture to external stimuli leading to safe use. Outside these standard operating conditions a more rigorous model of Comp B-3 rheological properties is necessary to model thermal transport as Comp B-3 evolves from quiescent solid through vaporization/decomposition upon heating. One particular rheological phenomena of interest is Bingham plasticity, where a material behaves as a quiescent solid unless a sufficient load is applied, resulting in fluid flow. In this study falling ball viscometer data is used to model the change in Bingham plastic yield stresses as a function of RDX particle volume fraction; a function of temperature. Results show the yield stress of Comp B-3 ($\tau_{\mathrm{y}})$ follows the expression $\tau_{y}=B\left( \phi -\phi_{c} \right)^{N}$, where $\Phi $ and $\Phi_{\mathrm{c}}$ are the volume fraction of RDX and a critical volume fraction, respectively and B and N are experimentally evaluated constants.   

Dynamic Shearing Resistance of Constituents of an Active Material Simulant.

Pressure-shear plate impact (PSPI) experiments have been conducted to provide an experimental foundation for developing constitutive models for the mechanical response of polymer-bonded sucrose (PBS) simulants of polymer-bonded explosives (PBXs). PSPI experiments on HTPB, an elastomer commonly used as a binder in PBXs, show a shearing resistance of 470 MPa at a pressure of 9.1 GPa and a shearing rate of 0.4x10$^{\mathrm{6}}$ s$^{\mathrm{-1}}$. At similar pressures and shearing rates, PSPI experiments on sucrose- a mechanical simulant for energetic crystals-show a shearing resistance of 510 MPa followed by pronounced strain softening. Preliminary modeling of the response has been done using a quasi-linear viscoelasticity model for HTPB.   

Numerical predictions of shock propagation through unreactive and reactive liquids with experimental validation

The objective of this work is to numerically analyze shock behavior as it propagates through compressed, unreactive and reactive liquid, such as liquid water and liquid nitromethane. Parameters, such as pressure and density, are analyzed using the Mie-Gruneisen EOS and each multi-material system is modeled using the ALE3D software. The motivation for this study is based on provided high-resolution, optical interferometer (PDV) and optical pyrometer measurements. In the experimental set-up, a liquid is placed between an Al 1100 plate and Pyrex BK-7 glass. A laser-driven Al 1100 flyer impacts the plate, causing the liquid to be highly compressed. The numerical model investigates the influence of the high pressure, shock-compressed behavior in each liquid, the energy transfer, and the wave impedance at the interface of each material in contact. The numerical results using ALE3D will be validated by experimental data. This work aims to provide further understanding of shock-compressed behavior and how the shock influences phase transition in each liquid.   

Comparison of shock-driven reactions in acrylonitrile and acetonitrile

Shock-driven reactions in simple molecules often occur with densification along the reaction coordinate. Acrylonitrile (CH$_{2}$-CH-CN) and acetonitrile (CH$_{3}$-CN) are two simple molecules that undergo shock-driven reaction on the principal Hugoniot. Using in situ embedded electromagnetic gauging techniques and the LANL large bore two-stage gas gun, a three-wave structure was observed in acrylonitrile indicating that at least two higher density species are formed. The reaction “cusp” or threshold was determined to be $\sim\!4.8$ GPa on the principal Hugoniot, and a series of experiments were performed above this condition to determine the state sensitivities of the reactions. The acceleration in reaction rate with shock input pressure (temperature) was found to be high, with a 5-fold increase in the rate over less than 2 GPa increase in shock input pressure. The global reaction rates were found to be similar to detonating high explosives. Time-resolved Raman spectroscopy was attempted to elucidate reaction species but it was found that the conditions became optically opaque even during the first wave. Acrylonitrile will be compared with acetonitrile, which despite having a similar chemical structure, has a higher reaction threshold. LA-UR-17-21553   

Detonation Velocity--Diameter Relation in Gelled Explosive with Inert Inclusions

The detonation velocity is measured in a gelled explosive that has been sensitized via the addition of glass microballoons (GMBs) and additionally diluted via the inclusion of large scale (300-700 micron) inert inclusions. The base explosive is nitromethane that has been gelled via the addition of poly(methyl methacrylate) and then sensitized via hot-spot inducing glass microballoons. Inert inclusions (e.g., glass, steel beads) are then added to the explosive to make a heterogeneous explosive with heterogeneities that are at a scale disparate from those of the microballoons. This system has the potential to be a synthetic explosive that can be tuned to have the properties of more complex commercial blasting agents. The velocity-diameter relation is studied using weak confinement (polyvinyl chloride) and time-of-arrival gages. The results are also used to further explore the phenomenon of anomalous scaling between axisymmetric charges (cylinders) and two-dimensional (slab) charges.