Frank Garcia

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....

Embedded Electromagnetic Gauge Measurements and Modeling of Shock Initiation in the TATB Based Explosives LX‐17 and PBX 9502

We have completed a series of shock initiation experiments on PBX 9502 (95 weight % dry aminated TATB explosive, 5 weight % Kel‐F 800 binder) and LX‐17 (92.% wet aminated TATB, 7.5 % Kel‐F 800). These experiments were performed on the gas/gas two stage gun at Los Alamos. Samples were prepared with ten or eleven embedded electromagnetic particle velocity gauges to measure the evolution of the wave leading up to a detonation. Additionally, one to three shock tracker gauges were used to track the position of the shock front with time and determine the point where detonation was achieved. Wave profiles indicate little delay between formation of hot‐spots in the shock front and release of hot‐spot energy. In other words, a great deal of the buildup occurs in the shock front, rather than behind it. Run distances and times to detonation as a function of initial pressure are consistent with published data. The Ignition and Growth model with published parameters for LX‐17 replicate the data very well.

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...

Shock sensitivity of LX-04 at elevated temperatures

Hazard scenarios can involve multiple stimuli, such as heating followed by fragment impact (shock). The shock response of LX-04 (85 weight % HMX and 15 weight % Viton binder) preheated to temperatures near 170C is studied in a 10.2 cm bore diameter gas gun using embedded manganin pressure gauges. The pressure histories at various depths in the LX-04 targets and the run distances to detonation at several input shock pressures are measured and compared to those obtained in ambient temperature LX-04. The hot LX-04 is significantly more shock sensitive than ambient LX-04. Ignition and Growth reactive flow models are developed for ambient and hot LX-04 to allow predictions of impact scenarios that can not be tested directly.

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...

Measurement of Low Level Explosives Reaction in Gauged Multi-Dimensional Steven Impact Tests

The Steven Test was developed to determine relative impact sensitivity of metal encased solid high explosives and also be amenable to two‐dimensional modeling. Low level reaction thresholds occur at impact velocities below those required for shock initiation. To assist in understanding this test, multi‐dimensional gauge techniques utilizing carbon foil and carbon resistor gauges were used to measure pressure and event times. Carbon resistor gauges indicated late time low level reactions 200–540 μs after projectile impact, creating 0.39–2.00 kb peak shocks centered in PBX 9501 explosives discs and a 0.60 kb peak shock in a LX‐04 disk. Steven Test modeling results, based on ignition and growth criteria, are presented for two PBX 9501 scenarios: one with projectile impact velocity just under threshold (51 m/s) and one with projectile impact velocity just over threshold (55 m/s). Modeling results are presented and compared to experimental data.

Manganin Gauge and Reactive Flow Modeling Study of the Shock Initiation of PBX 9501

A series of 101mm diameter gas gun experiments was fired using manganin pressure gauges embedded in the HMX‐based explosive PBX 9501 at initial temperatures of 20°C and 50°C. Flyer plate impact velocities were chosen to produce impact pressure levels in PBX 9501 at which the growth of explosive reaction preceding detonation was measured on most of the gauges and detonation pressure profiles were recorded on some of the gauges placed deepest into the explosive targets. All measured pressure histories for initial temperatures of 25°C and 50°C were essentially identical. Measured run distances to detonation at three input shock pressures agreed with previous results. An existing Ignition and Growth reactive flow computer model for shock initiation and detonation of PBX 9501, which was developed based on LANL embedded particle velocity gauge data, was tested on these pressure gauge results. The agreement was excellent, indicating that the embedded pressure and particle velocity gauge techniques yielded consistent results.

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.

The Isentrope of Unreacted LX‐04 to 170 kbar

We present new data on the unreacted approximate isentrope of the HMX-based explosive LX-04, measured to 170 kbar, using newly developed long pulse isentropic compression techniques at the Sandia National Laboratories Z Machine facility. This study extends in pressure by 70% the previous state of the art on unreacted LX-04 using this technique. This isentrope will give the unreacted Hugoniot from thermodynamic relations using a Gruneisen equation of state model. The unreacted Hugoniot of LX-04 is important in understanding the structure of the reaction front in the detonating explosive. We find that a Hugoniot given by U{sub s}= 2950 m/s + 1.69 u{sub p} yields for an isentrope a curve which fits our LX-04 ICE data well.