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Results for “plastic-bonded explosives”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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27 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Subsurface spectroscopy of heterogeneous materials using optical wavefront shaping

Plastic-bonded explosives and propellants consist of energetic molecular crystals embedded in a polymer matrix that also includes additives, such as taggants, plasticizers, grit, antioxidants, etc. Furthermore, this heterogeneous composition renders these materials optically opaque, limiting optical characterization techniques (e.g., Raman spectroscopy) to probing chemical reactions at the sur-face. However, many reactions of interest are believed to occur inside the material where current optical techniques can not probe. To address this challenge, we have developed a new optical technique that utilizes feedback assisted wavefront shaping (using spatial light modulators) to focus probe light inside a heterogeneous material, such that we can perform subsurface spectroscopy. Recently, we demonstrated this technique by monitoring subsurface photodegradation and thermal degradation of Eu-doped molecular crystals using both fluorescence and Raman spectroscopy. Based off these successes we are now looking into improvements to this technique to allow for greater time resolution, including replacing our spatial light modulators with fast digital mirror devices, using ns optical phase conjugation, and self-healing optical beams.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Comparing the shock sensitivity of insensitive energetic materials

We present a tabletop method to study the shock sensitivity of plastic-bonded explosives that are considered shock insensitive using high dynamic range optical emission spectroscopy with laser-launched km/s flyer plate impacts (2, 3, and 4 km/s), which measures the spectral radiance (the emission spectrum vs a calibrated intensity standard) every 0.8 ns in the nanosecond and microsecond regimes. The explosives were TATB (1,3,5 trinitro, 2,4,6 triamino benzene), FOX-7 (1,1-diamino-2,2-dinitroethylene), LLM-105 (2,6-diamino-3,5-dinitropyrazine-1-oxide), and NTO (nitrotriazolone), all with 20% Sylgard 182 binder. Time resolving emission from shocked explosives produces a unique fingerprint at each shock pressure, and the emission temporal profile can be used to understand each material's shock response and the underlying mechanisms within the framework of the well-known shock ignition and growth models. Ignition was characterized by the emission intensity during nanosecond hot spot ignition. The growth process, which occurs after the shock has unloaded, was characterized by the time derivative of microsecond emission intensity. Singular-value decomposition was used to determine a characteristic spectral radiance over the entire time range, and this radiance was fit to a graybody model to determine a characteristic temperature Tc. Even though these insensitive explosives have similar shock sensitivities, our method can clearly distinguish their shock response. FOX-7 and NTO were the most sensitive, with FOX-7 having the greatest shock ignition sensitivity, growth rate, and Tc. LLM-105 was much less sensitive than FOX-7 and NTO, and TATB consistently showed the lowest sensitivity by any measure.

Akhtar, Meysam (ORCID:0000000243897837)↗
DOE OSTI2022

Shock ignition and deflagration growth in plastic-bonded TATB (1, 3, 5-trinitro-2, 4, 6-triaminobenzene) microstructures

TATB (1,3,5-triamino-2,4,6-trinitrobenzene) plastic-bonded explosives (PBX) were shocked with laser-launched flyer plates. The spectral radiance of the emitted light from a small portion of the microstructure (a “microenvironment”) containing a small number of TATB particles with an estimated mass of 150 ng was measured every 0.8 ns from 1 ns to 200 μs and was analyzed to give radiance and time-dependent graybody temperatures. By fabricating an array with 186 PBX charges, we could obtain ≥15 shots at each of 12 velocities between 1.8 and 4.7 km/s. We found that every microenvironment generated a unique radiance fingerprint. Some of these microenvironments were much more reactive than average. The radiance has two peaks around 20 ns and 5 μs, associated with shock ignition and deflagration growth. In our interpretation, the shock creates an ensemble of hot spots of various sizes and temperatures. Of those hot spots that ignite, only a small portion, at about 2200 K, was large enough and hot enough to survive long enough (>100 ns) to ignite individual TATB particles, leading to deflagration. Integrating various time intervals of the radiance can quantify the strength of the shock–PBX interaction, and the decay and growth of the hot spot ensemble and the deflagration.

Akhtar, Meysam (ORCID:0000000243897837)↗
DOE OSTI2021

Gel Permeation Chromatography Methods for Stockpile Relevant PBXs

In order to accurately characterize chemical changes to the binder in plastic-bonded explosives (PBXs) it is important to develop new gel permeation chromatography (GPC) methodologies as well as update previous methods. Herein we present new and updated GPC methodology for Viton A, Kraton G, and Oxy 461. The methods developed were specifically designed for Malvern OMNISEC with a Mixed C column, but minor modifications could be made to these methods to make applicable to other instrumentation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Time-Temperature-Stress Superposition of PBX 9502 Compressive Creep Data for Lifetime Predictions

The plastic-bonded explosive (PBX) 9502 is a viscoelastic, high-solids loaded polymer bound composite comprised of 95 weight% (wt%) TATB explosive crystals and 5 wt% FK-800 polymer binder. The uniaxial quasi-static mechanical properties have been studied and characterized extensively over 25+ years, including creep. Creep is the strain evolution over time as a result of an asymmetric load typically at temperatures above ambient. Creep measurements to failure can take excessively long periods of time depending on various factors including applied stress, temperature, and loading rate that render a single test to failure impossible. Using the principles of time-temperature-stress superposition (TTSSP), short-term creep tests at various applied stresses and temperatures can be used for long-term creep predictions. The TTSSP model shifts short-term test data using two factors, one for temperature and stress, creating a master curve at a reference test condition. The master curve can be shifted to predict the creep response at any desired test condition. PBX 9502 compression specimens were tested at three temperatures and various applied stresses. This work discusses the TTSSP analysis of PBX 9502 compressive creep data to create a single comprehensive master curve.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effect of PBX Prill Size on the Compressive Properties of PBX 9502

Plastic-Bonded Explosive (PBX) prills are agglomerates a few millimeters in diameter composed of High Explosive crystals non-uniformly distributed in and surrounded by a polymer binder. When pressed at elevated temperatures at or above the binder melt temperature the polymer flows to uniformly coat the HE crystals to create a well-consolidated compaction. In reality it does so imperfectly, such that x-ray tomographic scans often look like a collection of prills mashed together. It is speculated that the larger the prill, the more non-uniform the binder distribution, but this has never been proven. Even if that were not so, the larger the prill the farther binder must flow toward the middle to homogenize during pressing. Thus, the degree of homogenization depends in part on prill size. The degree to which binder flows during pressing in turn affects the void distribution within pressed charges, which one suspects will affect shock sensitivity and material strength. In this paper we explore, for ~30 PBX 9502 formulation batches using the same TATB powder lot, how prill size effects the compressive mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Multiscale investigation of the microstructural mechanisms driving ratchet growth in PBX 9502

The high explosive PBX 9502 undergoes irreversible expansion during thermal cycling (“ratchet growth”). Recent innovations in thermomechanical modeling via homogenization strategies are beginning to incorporate mesoscale information such as grain size, total porosity, and spatial distribution of voids and cracks. To generate a complete experimental data set to challenge and inform these models, PBX 9502 pellets were thermally cycled, cross-sectioned using ion polishing, and imaged in high resolution with scanning electron microscopy. Ratchet growth was found to drive expansion through microcracking. Microcracks were affected by agglomeration of crystals within the PBX. Virgin material showed greater ratchet growth than recycled material.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Extrusion‐Spheronization of Energetic Materials

The prevailing method to produce plastic‐bonded explosive (PBX) molding powder, or “prills”, is a complex, multiphase, and bespoke process that was developed by the high explosives (HEs) manufacturing industry several decades ago. This work demonstrates the utility of a simpler, widely‐used mechanical process—extrusion‐spheronization—to produce PBX prills. We begin by detailing precautions taken to enable safe remote operation of extrusion‐spheronization equipment with HE. We then perform a study investigating the effect of lacquer solvent composition on the particle packing, pressed density, and compressive strength properties of a 95 wt.% TATB/5 wt.% polymer binder formulation akin to PBX 9502. It was found that increased composition of low vapor pressure solvents caused prolonged retention of the solvent, resulting in tackier materials that would agglomerate and form larger prills. The larger prills also led to lower poured density and tapped density of HE prills and compressive strength of pressed PBX articles. The samples prepared with a 75% propyl acetate/25% butyl acetate lacquer solvent composition exhibited the highest compressive strength. However, it is believed that the prill packing and compressive strength properties are primarily driven by the prill size rather than the chemical composition of the lacquer itself. Extrusion‐spheronization remains a promising method to reliably and repeatably produce HE prills that is less sensitive to feedstock or process variation than traditional methods.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Shock initiation and hot spots in plastic-bonded 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)

TATB (1,3,5-triamino-2,4,6-trinitrobenzene) is a powerful explosive whose dynamical behavior is difficult to study because TATB is so insensitive to initiation by shock waves. We used a tabletop microscope equipped with 0–4.5 km/s laser-launched flyer plates to study shock initiation of TATB, which was fabricated in the form of an array of hundreds of plastic-bonded explosive minicharges (X-TATB = 80% TATB + 20% Sylgard 182 polymer). The 4 ns shocks from the flyer plates were not effective in initiating TATB, but we also developed a two-layer array where flyers first initiated a plastic-bonded PETN (pentaerythritol tetranitrate) charge (X-PETN = 80% PETN + 20% Sylgard), which drove an initiating 25 ns shock into the X-TATB. Thermal emission from shocked X-TATB was used to measure time-dependent temperature profiles with a resolution of 2 ns and to produce high-speed (5 ns) videos. In X-TATB, flyer plates produced 2500–3500 K hot spots and combustion at 2500 K. With X-PETN initiators, X-TATB had 3500–4000 K hot spots and a powerful volume explosion lasting a few nanoseconds. Prospects for producing TATB detonations on a tabletop are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗