Kevin S. Vandersall

On the low pressure shock initiation of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine based plastic bonded explosives

In large explosive and propellant charges, relatively low shock pressures on the order of 1–2 GPa impacting large volumes and lasting tens of microseconds can cause shock initiation of detonation. The pressure buildup process requires several centimeters of shock propagation before shock to detonation transition occurs. In this paper, experimentally measured run distances to detonation for lower input shock pressures are shown to be much longer than predicted by extrapolation of high shock pressure data. Run distance to detonation and embedded manganin gauge pressure histories are measured using large diameter charges of six octahydro-1,3,5,7–tetranitro-1,3,5,7-tetrazocine (HMX) based plastic bonded explosives (PBX’s): PBX 9404; LX-04; LX-07; LX-10; PBX 9501; and EDC37. The embedded gauge records show that the lower shock pressures create fewer and less energetic “hot spot” reaction sites, which consume the surrounding explosive particles at reduced reaction rates and cause longer distances to detonation....

Time-resolved measurements of the shock-compression response of Mo+2Si elemental powder mixtures

The shock-compression response of Mo+2Si elemental powder mixtures was investigated using instrumented experiments in the velocity range of 500 m/s to 1 km/s. The experiments employed polyvinyl difluoride stress gauges placed at the front and rear surfaces of the powder mixtures to determine the crush strength, densification history, and shock-induced reaction initiation characteristics. Experiments performed on ∼58% dense Mo+2Si powder mixtures at input stresses less than 4 GPa showed characteristics of powder densification and dispersed propagated wave stress profiles with rise time >∼40 ns. At input stress between 4 and 6 GPa, the powder mixtures showed a shock-compression response following the Hugoniot of the solid-density mixture. In the stress regime of 6–7 GPa, shock-induced melting of silicon was observed, which appears to inhibit a shock-induced chemical reaction on the time scale of the time-resolved measurements. The results of the present work on Mo-Si, taken in conjunction with prior work on...

Isentropic compression of cyclotetramethylene tetranitramine (HMX) single crystals to 50GPa

Single crystals of cyclotetramethylene tetranitramine (HMX) were isentropically compressed perpendicular to (010) and (011) faces at the Sandia Z-Machine. A 50GPa ramped magnetic pressure load of about 200ns rise time loaded four specimens of each orientation. HMX specimens were from 300–600μm thick. Velocity histories at the rear of each crystal were measured by Doppler velocimetry. Although a phase change in HMX at 27GPa has been proposed based upon isothermal data, no evidence of this change is seen in our analyses between 5 and 50GPa along the isentrope. Previous isentropic loading experiments on HMX had not shown evidence of a phase change either, but those experiments were complicated by the use of NaCl interferometer windows that have a phase change near the pressure of interest. The experiments described in this paper employed LiF interferometer windows that are known to be absent phase changes in the regime of application. Accurate determination of isentropic compressibility for HMX was not possi...

Shock initiation experiments with ignition and growth modeling on low density HMX

Shock initiation experiments on low density (~1.2 and ~1.6 g/cm3) HMX were performed to obtain in-situ pressure gauge data, characterize the run-distance-to-detonation behavior, and provide a basis for Ignition and Growth reactive flow modeling. A 101 mm diameter gas gun was utilized to initiate the explosive charges with manganin piezoresistive pressure gauge packages placed between packed layers (~1.2 g/cm3) or sample disks pressed to low density (~1.6 g/cm3). The measured shock sensitivity of the ~1.2 g/cm3 HMX was similar to that previously measured by Sheffield et al. and the ~1.6 g/cm3 HMX was measured to be much less shock sensitive. Ignition and Growth model parameters were utilized that yielded good agreement with the experimental data at both initial densities.

Shock Sensitivity of LX-04 Containing Delta Phase HMX at Elevated Temperatures

LX‐04 is a widely used HMX‐based plastic bonded explosive, which contains 85 weight % HMX and 15 weight % Viton binder. The sensitivity of LX‐04 to a single stimulus such as heat, impact, and shock has been previously studied. However, hazard scenarios can involve multiple stimuli, such as heating to temperatures close to thermal explosion conditions followed by fragment impact, producing a shock in the hot explosive. The sensitivity of HMX at elevated temperatures is further complicated by the beta to delta solid‐state phase transition, which occurs at approximately 165°C. This paper presents the results of shock initiation experiments conducted with LX‐04 preheated to 190°C, as well as density measurements and small scale safety test results of the δ phase HMX at room temperature. This work shows that LX‐04 at 190°C is more shock sensitive than LX‐04 at 150°C or 170°C due to the volume increase during the β to δ solid phase transition, which creates more hot spots, and the faster growth of reaction duri...

Investigation of Steven Impact Test Using a Transportation Hook Projectile with Gauged Experiments and 3D Modeling

The Steven Impact Test and associated modeling offer valuable practical predictions for evaluating numerous safety scenarios involving low velocity impact of energetic materials by different projectile geometries. One such scenario is the impact of energetic material by a transportation hook during shipping, which offers complexity because of the irregular hook projectile shape. Experiments were performed using gauged Steven Test targets with PBX9404 impacted by a transportation hook projectile to compliment previous non‐gauged experiments that established an impact threshold of approximately 69 m/s. Modeling of these experiments was performed with LS‐DYNA code using an Ignition and Growth reaction criteria with a friction term. Comparison of the experiment to the model shows reasonable agreement with some details requiring more attention. The experimental results (including carbon resistor gauge records), model calculations, and a discussion of the dominant reaction mechanisms in light of comparisons bet...

Threshold Studies of Heated HMX-Based Energetic Material Targets Using the Steven Impact Test

Impact tests performed at low velocity on heated energetic material samples are of interest when considering the situation of energetic materials involved in a fire. To determine heated reaction thresholds, Steven Test targets containing PBX 9404 or LX‐04 samples heated to the range of 150–170°C were impacted at velocities up to 150 m/s by two different projectile head geometries. Comparing these measured thresholds to ambient temperature thresholds revealed that the heated LX‐04 thresholds were considerably higher than ambient, whereas the heated PBX 9404 thresholds were only slightly higher than the ambient temperature thresholds. The violence of reaction level of the PBX 9404 was considerably higher than that of the LX‐04 as measured with four overpressure gauges. The varying results in these samples with different HMX/binder configurations indicate that friction plays a dominant role in reaction ignition during impact. This work outlines the experimental details, compares the thresholds and violence l...

SHOCK INITIATION EXPERIMENTS ON PBX9501 EXPLOSIVE AT 150?C FOR IGNITION AND GROWTH MODELING

Shock initiation experiments on the explosive PBX9501 (95% HMX, 2.5% estane, and 2.5% nitroplasticizer by weight) were performed at 150°C to obtain in‐situ pressure gauge data and Ignition and Growth modeling parameters. A 101 mm diameter propellant driven gas gun was utilized to initiate the PBX9501 explosive with manganin piezoresistive pressure gauge packages placed between sample slices. The run‐distance‐to‐detonation points on the Pop‐plot for these experiments showed agreement with previously published data and Ignition and Growth modeling parameters were obtained with a good fit to the experimental data. This parameter set will allow accurate code predictions to be calculated for safety scenarios involving PBX9501 explosives at temperatures close to 150°C.

Pressure Wave Measurements Resulting from Thermal Cook‐Off of the HMX Based High Explosive LX‐04

Experiments that investigate thermal and nearby explosion scenarios are needed to provide essential data to models for accurate predictions. A porous LX‐04 (85/15 wt% HMX/Viton) sample was heated in a heavily confined donor charge until it thermally exploded. The reaction accelerated a steel cover plate across a 10 cm gap into a preheated gauged acceptor cylinder (near its theoretical maximum density) of LX‐04. The carbon resistor gauges in the acceptor measured the resulting multi‐dimensional ramp wave as it propagated through the pre‐heated LX‐04. Detonation of the LX‐04 acceptor does not occur. Results are compared to similar experiments with acceptors at room temperature.

Carbon Resistor Pressure Gauge Calibration at Low Stresses

The 470 Ohm carbon resistor gauge has been used in the stress range up to 4–5 GPa for highly heterogeneous materials and/or divergent flow experiments. The attractiveness of the gauge is its rugged nature, simple construction, low cost, reproducibility, and survivability in dynamic events. Gauge drawbacks are the long time response to pressure equilibration and gauge resistance hysteresis. In the regime below 0.4 GPa, gauge calibration has been extrapolated. Because of the need for calibration data within this low stress regime, calibration experiments were performed using a split‐Hopkinson bar, drop tower apparatus, and gas pressure chamber. Since the performance of the gauge at elevated temperatures is a concern, the change in resistance due to heating at atmospheric pressure was also investigated. Details of the various calibration arrangements and the results are discussed and compared to a calibration curve fit to previously published calibration data.