We performed a series of six plate impact experiments on polyimide and modeled them using new reactant and products equations of state combined with an Arrhenius rate model. The first experiment was diagnosed with embedded electromagnetic velocity gauges through which we directly observed attenuation of the lead shock to an approximately constant state over a propagation distance of roughly 4 mm. Simulated gauge profiles were in excellent qualitative agreement with experiment and suggested a sluggish chemical reaction that did not proceed to completion. The remaining five experiments were conducted in a transmission geometry and diagnosed velocimetrically at the sample/window interface. All five of these yielded profiles with a sharp shock followed by a more gradual approach to maximum interface velocity that was “rounded” to varying degree. These profiles proved difficult to interpret unambiguously due to the convolution of the reactive wave upon first shock with reflection of the lead wave and reshock or release by the window. Comparison with thermochemical calculations strongly suggests that the point of maximum interface velocity corresponds to the equilibrium reshock or release locus. We discuss the implications of this point for the practice of impedance matching based on the reflected Hugoniot of reactive materials such as polymers. The reactant and thermochemical products equations of state are developmental SESAME tables 97710 and 97720, respectively.

Observations of unit cell compression or decomposition during dynamic shock loading requires the implementation of a probe capable of penetrating an opaque and evolving sample at elevated pressures and temperatures. By pairing synchrotron generated high energy X-rays and gas gun driven plate impact, we were able to study the evolution of the structure in polytetrafluoroethylene (PTFE) at pressures spanning 1.84–52.9 GPa. Under the planar, one-dimensional, shockwave, the polymer was forced into an anisotropic conformation, in which the polymer chains assembled parallel to the shockwave. PTFE initially has a hexagonal crystal structure (Phase IV), once it was compressed above ~0.5 GPa it had a conformational change to the orthorhombic crystal structure (Phase III). The compression of the polymer chains was observed by X-ray diffraction, where the PTFE (110) peak shifted to higher q with increased pressure; polymer chain compression was still observed at 30.0 GPa. The highest pressure shot, at 52.9 GPa, above the reactants to products transition region, showed no new carbon species formation within the given time window and q -range. By following the orthorhombic lattice diffraction peak, we were able to calculate the Hugoniot loci of the crystalline and amorphous parts for each dynamic event (LA-UR-22-31436).

The chemical reaction zone (CRZ) of detonating explosives is defined by the leading, inert shock front, which compresses the explosive to the von Neumann (vN) spike condition on the unreacted Hugoniot, and the Chapman-Jouget (CJ) sonic locus condition, according to the Zel'dovich/von Neumann/Doering (ZND) one-dimensional theory of detonation. The CRZ is often measured using optical velocimetry techniques at a windowed interface; the window affects the reaction zone dynamics due to wave interactions from the interface. Fluoropolymer windows are attractive as they provide a near impedance match to most common explosives with initial densities 0 rho = 1.8-2.0 g/cm(3). Poly(chlorotrifluoroethylene-co-vinylidene fluoride) (Kel-F 800, Lot 30013) was purchased from 3M Inc., St. Paul, Minnesota. Small (150 mm 150 mm 50 mm) billets were prepared by compression molding the polymer at 90 degrees C and similar to 50,000 psi by Afton Plastics. This method resulted in a semi-transparent, golden-colored billet from which window samples were machined and polished to an optical clarity for experiments. To extend the window correction for Kel-F 800 (see D. M. Dattelbaum et al., Proceedings of the 15th International Detonation Symposium (2014)), a series of gas gun-driven plate impact experiments were performed using both VISAR (532 nm) and PDV (1550 nm) velocimetry methods to extend the window correction to a larger range of initial shock pressures and densities.

Using gas-gun-driven plate impact techniques, we have measured the Hugoniot of the filled silicone elastomer DC745U cooled to -60 degrees C. DC745U consists of approximately 62 weight% poly-dimethyl-siloxane rubber and 38 wt% silicon dioxide filler. At similar to -50 degrees C, the poly-dimethyl-siloxane rubber in DC745U crystallizes with similar to 40% crystallinity. This is accompanied by a density change from 1.31 g/cm(3) at 23 degrees C to 1.45 g/cm(3) at -60 degrees C. Below the crystallization transition temperature, a measurable increase in the shock velocity was observed. This is coincident with a decrease in compressibility due to crystallization of the polydimethylsiloxane repeat units. The linear Us up Hugoniot also significantly changes from U-S = 1.62 + 1.74u(p) mm/mu s at 23 degrees C to U-S = 2.00 +/- 0.05 + (2.06 +/- 0.06)u(p) mm/mu s at -60 degrees C. Cooling to -60 degrees C and the associated crystalline phase transition therefore results in considerable stiffening. This is the first time, to our knowledge, that a polymer crystallization transition has been shown to affect shockwave properties in this way.

We present gas-gun driven plate-impact shock initiation experiments on the explosive PBX 9502 (95 weight % triaminotrinitrobenzene, 5 weight % Kel-F800 binder) heated to 130 +/- 2 degrees C. PBX 9502 samples were heated using resistive elements, temperatures were monitored using embedded and surface mounted type-E thermocouples, and the shock to detonation transition was measured using embedded electromagnetic particle velocity gauges. Results indicate that PBX 9502 shock sensitivity at 130 degrees C is midway between shock sensitivity at 75 degrees C and 250 degrees C. For PBX 9502 heated to 130 degrees C, the "Pop-plot" or distance to detonation, x(D), vs. impact pressure, P, is log(10)(x(D)) = 2.79 +/- 0.12 - 2.16 +/- 0.12 log10(P). Within experimental error, measured initial particle velocities agree with those predicted by a new temperature dependent equation of state calibration for PBX 9502.

We examine shock, release and reshock into the tri-amino-tri-nitro-benzene (TATB) based explosive PBX 9502 (95% TATB, 5% Kel-F 800) from both an experimental and modeling point of view. The experiments are performed on the 2-stage light gas gun at Los Alamos National Laboratory and are composed of a multi-layered impactor impinging on PBX 9502 backed by a polymethylmethacrylate window. The objective is to initially shock the PBX 9502 in the 7 GPa range (too weak to start significant reaction), then allow a rarefaction fan to release the material to a lower pressure/temperature state. Following this release, a strong second shock will recompress the PBX. If the rarefaction fan releases the PBX to a very low pressure, the ensuing second shock can increase the entropy and temperature substantially more than in previous double-shock experiments without an intermediate release. Predictions from a variety of reactive burn models (AWSD, CREST, Augmented Ignition and Growth, SURF) demonstrate significantly different behaviors and thus the experiments are an excellent validation test of the models, and may suggest improvements for subsequent modeling efforts.

A novel gas loading system was designed for the specific application of remotely loading high purity gases into targets for gas-gun driven plate impact experiments. The high purity gases are loaded into well-defined target configurations to obtain Hugoniot states in the gas phase at greater than ambient pressures. The small volume of the gas samples is challenging, as slight changing in the ambient temperature result in measurable pressure changes. Therefore, the ability to load a gas gun target and continually monitor the sample pressure prior to firing provides the most stable and reliable target fielding approach. We present the design and evaluation of a gas loading system built for the LANL 50 mm bore two-stage light gas gun. Targets for the gun are made of 6061 Al or OFHC Cu, and assembled to form a gas containment cell with a volume of approximately 1.38 cc. The compatibility of materials was a major consideration in the design of the system, particularly for its use with corrosive gases. Piping and valves are stainless steel with wetted seals made from Kalrez® and Teflon®. Preliminary testing was completed to ensure proper flow rate and that the proper safety controls were in place. The system has been used to successfully load Ar, Kr, Xe, and anhydrous ammonia with purities of up to 99.999 percent. The design of the system and example data from the plate impact experiments will be shown.

We present gas-gun driven plate impact shock initiation experiments on the explosive PBX 9502 (95 weight percent triaminotrinitrobenzene, 5 weight percent Kel-F 800 binder) heated to similar to 76 degrees C. PBX 9502 samples were heated by flowing hot air through a sample mounting plate and surrounding coil. Temperatures were monitored using embedded and surface mounted type-E thermocouples. The shock to detonation transition was recorded using embedded electromagnetic particle velocity gauges. Results show increased shock sensitivity; time and distance to detonation onset vs. initial shock pressure are shorter than when the sample is initially at ambient temperature. Our results are consistent with those reported by Dallman and Wackerle: the "Pop-plot," or distance to detonation, x(D), vs. impact pressure, P, is log(10)(x(D)) = 3.41-2.47log(10)(P).

The shock response of solid polyurea and two polyurea aerogels were studied using gas-gun driven plate impact experiments. The materials reported on here are commercially available, brand named AIRLOY X103, and supplied by Aerogel Technologies, LLC. Polyurea Solid, with nominal density 1.13 g/cm(3), and two aerogels, with nominal densities of 0.20 and 0.35 g/cm(3), were studied. Most experiments were of the multi-slug type in which a sample of each density was mounted on an oxygen free high conductivity copper or 6061 aluminum baseplate. In these experiments, shock velocity was measured and other shock states calculated by the impedance matching technique. Peak particle velocity obtained in the 0.2 g/cm(3) aerogel was > 4.3 km/s, and peak pressure in the solid was > 29 GPa. A break in the data for the solid above particle velocities of 2.0 km/s (similar to 18 GPa) indicates a probable reaction with higher density products. A P-alpha model with Mie-Grueneisen form for the solid reasonably replicates the data.

We have developed a Light Detection and Ranging (LIDAR) diagnostic to track the position of a projectile inside of a gas gun launch tube in real-time. This capability permits the generation of precisely timed trigger pulses useful for triggering high-latency diagnostics such as a flash lamp-pumped laser. An initial feasibility test was performed using a 72 mm bore diameter single-stage gas gun routinely used for dynamic research at Los Alamos. A 655 nm pulsed diode laser operating at a pulse repetition rate of 100 kHz was used to interrogate the position of the moving projectile in real-time. The position of the projectile in the gun barrel was tracked over a distance of ~ 3 meters prior to impact. The position record showed that the projectile moved at a velocity of 489 m/s prior to impacting the target. This velocity was in good agreement with independent measurements of the projectile velocity by photon Doppler velocimetry and timing of the passage of the projectile through optical marker beams positioned at the muzzle of the gun. The time-to-amplitude conversion electronics used enable the LIDAR data to be processed in real-time to generate trigger pulses at preset separations between the projectile and target.

We present gas-gun driven plate impact shock initiation experiments on the explosive PBX 9502 (95 weight percent triaminotrinitrobenzene, 5 weight percent Kel-F 800 binder) cooled to liquid nitrogen temperature, 77K. PBX 9502 samples were cooled by flowing liquid nitrogen through a sample mounting plate and surrounding coil. Temperatures were monitored using embedded and surface mounted thermocouples. Reactive flow was measured with embedded electromagnetic particle velocity gauges. Wave profiles from the particle velocity gauges show that, even at 77K, shock initiation in PBX 9502 retains a heterogeneous or hot-spot character. The Pop-plot, or distance to detonation, xD, vs. impact pressure, P, is log10(xD) = 4.9 − 3.3log10(P).

Dilution of liquid explosives with "inert" solvents have been shown previously to affect a degradation in the detonation performance properties of the explosive, and result in a rapid increase in the critical diameter with increasing diluent. To date, the shock sensitivities of liquid explosive-diluent mixtures have not been measured. In this work, we describe the results of a series of gas gun-driven plate impact experiments on nitromethane (NM)-methanol (MeOH) solutions of several concentrations, using in situ electromagnetic gauging to measure the initial shock state (Hugoniot) of the mixture, as well as the overtake-time-to-detonation (Pop-plot). Surprisingly, the shock sensitivities did not fall off dramatically with increasing MeOH concentration. In fact, at some concentrations MeOH appears to sensitize NM, relative to neat NM.

A series of gas gun-driven plate impact experiments were performed on vacuum melt-cast Composition B to obtain new Hugoniot states and shock sensitivity (run-distance-to-detonation) information. The Comp B (ρ0 = 1.713 g/cm3) consisted of 59.5% RDX, 39.5% TNT, and 1% wax, with ~ 6.5% HMX in the RDX. The measured Hugoniot states were found to be consistent with earlier reports, with the compressibility on the shock adiabat softer than that of a 63% RDX material reported by Marsh.[4] The shock sensitivity was found to be more sensitive (shorter run distance to detonation at a given shock input condition) than earlier reports for Comp B-3 and a lower density (1.68-1.69 g/cm3) Comp B formulation. The reactive flow during the shock-to-detonation transition was marked by heterogeneous, hot spot-driven growth both in and behind the leading shock front.

We present an experimental investigation of the dynamics of rod impact on bare or uncovered PBX 9501 explosive. By weight, PBX 9501 contains 95% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, commonly known as HMX. The plastic binder is Estane combined with a nitro-plasticizer made of bis(2,2-dinitropropyl)acetal and bis(2,2-dinitropropyl)formal. Experiments were conducted using our single stage gas-gun, allowing us to get very repeatable impact velocities. A stainless steel rod attached to the front of the projectile impacted the explosive target. Impact occurred while the projectile was still in the barrel, allowing for accurate centering of the rod on the target. Seven channels of Photonic Doppler Velocimetry (PDV) were used to measure shock waveprofiles after transmission through the explosive. Velocimetry measurement points were located at different radii from the center of the rod, allowing us to capture the 2-D characteristics of the flow. Also, multiple sets or sequences of experiments were performed. Each set of experiments used a constant rod diameter, impact velocity and PDV probe locations: the thing that was varied from experiment to experiment was the thickness of the PBX 9501 explosive sample. In this way, we built up a detailed experimental record of the impact and reaction dynamics. All experiments discussed used a rod impact velocity near 0.744km/s resulting in an impact stress of ~ 4.5GPa. One series of experiments with 17mm diameter rods resulted in initiation with onset of detonation between 6 and 8mm into the explosive. Another series of experiments with 8.5mm diameter rods resulted in failure to detonate, reactions being quenched by rarefaction waves emanating from the edge of the rod.

A series of two-stage gus-gun driven plate impact experiments on PBX 9502 (95 wt.% tri-amino-trinitro-benzene, 5 wt.% Kel-F800 plastic binder) was completed in the 28-34 GPa pressure range. This is just above the Chapman-Jouguet state of ≈ 28 GPa. The experiments consisted of a thick oxygen free high conductivity copper (OFHC Cu) flyer plate impacting a PBX 9502 sample backed by a Lithium Fluoride (LiF) window. Photonic Doppler Velocimetry (PDV) was used to measure velocity histories (wave profiles) at the PBX 9502/LiF interface. Shock transit times and sample thicknesses were converted to shock velocities, Us. Particle velocities, up, were calculated by way of impedance matching. Lastly, the measured wave profiles were compared with numerical simulations of the experiments using the Wescott-Stewart-Davis reactive-burn model.

The equation of state (EOS) of polyurea aerogel (PUA) is examined through both single shock Hugoniot data as well as more recent multi-shock compression experiments performed on the LANL 2-stage gas gun. A simple conservative Lagrangian numerical scheme, utilizing total variation diminishing (TVD) interpolation and an approximate Riemann solver, will be presented as well as the methodology of calibration. It will been demonstrated that a p-alpha model based on a Mie-Gruneisen fitting form for the solid material can reasonably replicate multi-shock compression response at a variety of initial densities; such a methodology will be presented for a commercially available polyurea aerogel.

This study compares the shock initiation behavior of PBX 9502 pressed to less than nominal density (nominal density is 1.890 {+-} 0.005 g/cm{sup 3}) with PBX 9502 pressed to nominal density and then ''ratchet grown'' to low density. PBX 9502 is an insensitive plastic bonded explosive consisting of 95 weight % dry-aminated tri-amino-tri-nitro-benzene (TATB) and 5 weight % Kel-F 800 plastic binder. ''Ratchet growth'' - an irreversible increase in specific volume - occurs when an explosive based on TATB is temperature cycled. The design of our study is as follows: PBX 9502, all from the same lot, received the following four treatments. Samples in the first group were pressed to less than nominal density. These were not ratchet grown and used as a baseline. Samples in the second group were pressed to nominal density and then ratchet grown by temperature cycling 30 times between -54 C and +80 C. Samples in the final group were pressed to nominal density and cut into 100 mm by 25.4 mm diameter cylinders. During thermal cycling the cylinders were axially constrained by a 100 psi load. Samples for shock initiation experiments were cut perpendicular (disks) and parallel (slabs) to the axial load. The fourmore » sample groups can be summarized with the terms pressed low, ratchet grown/no load, axial load/disks, and axial load/slabs. All samples were shock initiated with nearly identical inputs in plate impact experiments carried out on a gas gun. Wave profiles were measured after propagation through 3, 4, 5, and 6 mm of explosive. Side by side comparison of wave profiles from different samples is used as a measure of relative sensitivity. All reduced density samples were more shock sensitive than nominal density PBX 9502. Differences in shock sensitivity between ratchet grown and pressed to low density PBX 9502 were small, but the low density pressings are slightly more sensitive than the ratchet grown samples.« less