TATB-based Explosives Research Articles

Micromechanical models and experiments for diffractive elastic constants of TATB-based polymer-bonded explosives

TATB-based polymer-bonded explosives (PBXs) exhibit intricate internal stress distributions due to crystal anisotropy. When diffraction techniques are employed to measure these internal residual stresses, it is critical to identify the discrepancy between the diffraction elastic constants (DEC) of particular crystal planes of a TATB-based PBX and the macroscopic elastic constant of the PBX. This study introduced various micromechanical models to describe the mechanical behavior of TATB-based PBXs, as well as assessing their accuracy in predicting the elastic properties of the PBXs and calculating the DECs of different crystal planes. Using in situ tensile experiments, this study obtained accurate DECs of the crystal plane of TATB-based PBXs and revised the residual stress measurements of the PBXs. The comparison between experimental results indicates that the two-phase and double-inclusion micromechanical models proposed in this study exhibit higher precision in predicting both the quasi-static mechanical properties of the PBXs and the DECs of the crystal plane. Furthermore, the DECs of the PBXs with high volume fractions of TATB are close to those of pure TATB crystals. Based on the established double-inclusion model, it can be inferred that the DECs of different crystal planes vary as a function of the TATB volume fraction. This study lays the foundation for profound analyses of the mechanical characteristics of TATB-based PBXs using diffraction techniques.

The role of detonation condensates on the performance of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) detonation

Thermochemical models of detonation are widely used to estimate energy delivery, but they are based on the assumption that the carbon-rich condensates (soot) formed during detonation are very similar to bulk carbon. We present an analytic equation of state (EOS) based on experimental detonation data for soot formed during the detonation of triaminotrinitrobenzene (TATB)-based high explosives. X-ray photoelectron spectra of several detonation soots are used to determine the elemental nitrogen abundance, with surprisingly high values for TATB. The proposed TATB soot EOS is highly compressible at low pressures and shares some features of glassy carbon, exhibiting graphite- and diamond-like behavior as a function of pressure. We demonstrate the influence of formed soot on detonation performance, including a lowering of the detonation velocity at typical charge densities, and a more compressive product Hugoniot at overdriven conditions. The soot model improves the accuracy of thermochemical calculations for TATB-based explosives across a wide range of states. Detonation velocity predictions for HMX (cyclotetramethylene-tetranitramine)-TATB blends with 80% or more TATB content, as well predictions for 1,3-diamino-2,4,6-trinitrobenzene (DATB) and 3-nitro-1,2,4-triazol-5-one (NTO), which share some features with TATB, are also improved.

Quasistatic mechanical behavior of HMX- and TATB-based plastic-bonded explosives

Data on the macroscopic quasistatic mechanical behavior of pressed HMX- and TATB-based plastic-bonded explosives (PBXs) are listed in this paper. This review shows that (1) few characterizations are available for TATB-based PBXs. This gap is filled in this paper. An extensive database is detailed for the CEA M2 explosive composition. The HMX and TATB database then enables selection of the deformation mechanisms to be considered: viscoelasticity, damage-induced anisotropy and its effectivity (i.e.: whether or not the damage is influenced by the loading direction), plasticity with kinematic and isotropic hardenings, pressure and temperature dependencies and asymmetric failure threshold. The review also shows that (2) HMX- and TATB-based materials share close elastic and ultimate properties when the compositions (binders, solid volume fractions) and the mechanical behavior of the two crystals differ. The constitutive laws proposed in the literature are reiterated. In our opinion, a universal law could be proposed in the near future, each material being considered by its own set of parameters. The objective of this paper is to draw up the guidelines for model improvement.

Shock Hugoniot measurements of single-crystal 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) compressed to 83 GPa

We present laser-driven shock Hugoniot measurements of single-crystal (SC) 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) between 15 and 83 GPa, spanning pressures below and well above the Chapman–Jouguet pressure of ∼28 GPa for TATB formulations (TATB grains mixed with plastic binders at 5–10 wt. %). The new SC data are generally ∼3% more compressible than previously published data on neat and formulated TATB measured in gas-gun and explosive-driven experiments. An exception is at compressions in the density of ∼1.5 (∼30–40 GPa), where our new SC data exhibit significantly lower pressures than previous results on overdriven TATB formulations, suggesting that our SC samples remain largely unreacted below 35 GPa over the short nanosecond-time scales inherent to our laser-driven experiments. These novel equation-of-state measurements are a critical step toward understanding TATB in its most fundamental form and improving predictive modeling of TATB-based explosives.

Numerical analysis of response of a fuze to cook-off

ABSTRACTA fuze may be exposed to extreme thermal environments during its life cycle, such as high temperature resulting from burning of leaked fuel, or accidental deflagration (or explosion) of shells. It is essential to study the response of fuzes under cook-off conditions to reduce possible economic loss and casualties. Cook-off tests are an important experimental method to test and evaluate the thermal sensitivity of shells and fuzes at present, and extensive research has been done on the subject. However, it is not economical to conduct many experiments in the early stage of product development due to high cost and risk. Herein, numerical simulations are conducted to analyze the response of a fuze to cook-off. Thermal-decomposition models for HMX- and TATB-based polymer-bonded explosives proposed by Tarver are applied in the numerical models. In addition, the influence of various factors on simulation results, such as heating rate, package of the fuze, type of high explosives within the fuze is analyzed quantitatively. The law is summarized and can be used for future development of similar products.

Thermal–mechanical analysis for confined HMX-based polymer-bonded explosives

It is known that the reaction rate of the thermal decomposition of polymer-bonded explosives exposed to cook-off has a certain relation with temperature, confining pressure and some other factors, which were verified by many experiments. Temperature-dominated thermal-decomposition models were developed for various high explosives and applied to study their decomposition process, such as HMX- and TATB-based polymer-bonded explosives. These models have reasonable accuracy. For example, the multistep thermal-decomposition model of PBX 9501 (which consists of 95% HMX, 2.5% Estane and 2.5% BDNPA/F) proposed by Tarver considers decomposition of both HMX and polymer binders. The temperature-dominated thermal-decomposition model only applies to preignition thermal decomposition. After ignition occurs, the dominant mechanism of the reaction transforms to deflagration and subsequent explosion, where the effect of pressure can no longer be neglected. Furthermore, the time scale of deflagration and explosion (millisecond or microsecond) differs significantly from the time scale of slow thermal decomposition (hours or minutes). The numerical model of postignition phenomenon (deflagration and final explosion) is still under investigation and is far from maturity. The predicted violence scale resulting from thermal explosion does not agree with experiment very well. An alternative method is to conduct a thermal–mechanical analysis for preignition stage, which takes advantage of a developed temperature-dominated thermal-decomposition model, and to analyze the stress caused by quasi-static thermal expansion. Herein, a thermal–mechanical analysis is implemented for a one-dimensional time-to-explosion experiment (ODTX) and a scaled thermal explosion experiment (STEX) with HMX-based polymer-bonded explosives inside using the finite element method. Then, the finite element model is applied to investigate the thermal decomposition of PBX 9501 inside an explosive device exposed to cook-off. The regions that have maximum temperature, maximum hydrostatic pressure and maximum von Mises stress are identified based on simulation results, which can benefit future improvement of the explosive device.

Correlation of electrical conductivity in the detonation of condensed explosives with their carbon content

This paper presents the comparative analysis of the results of more than fifty experiments on measuring the electrical conductivity of detonation products of RDX, HMX, PETN, TNT, and TATB-based explosives. It is revealed that there is a correlation between the electrical conductivity and the mass fraction of carbon both in the chemical spike and at the Chapman–Jouguet point.

Self-consistent modeling of the influence of texture on thermal expansion in polycrystalline TATB

This paper presents a modeling approach for simulating the anisotropic thermal expansion of polycrystalline (1,3,5-triamino-2,4,6-trinitrobenzene) TATB-based explosives which utilizes microstructural information including the porosity, crystal aspect ratio and processing-induced texture. A self-consistent homogenization procedure is used to relate the macroscopic thermoelastic response to the constitutive behavior of single-crystal TATB. The model includes a representation of the grain aspect ratio, porosity and, crystallographic texture attributed to the consolidation process. A quantitative model is proposed for describing the evolution of the preferred orientation of basal planes in TATB during consolidation and an algorithm constructed for developing a discrete representation of the associated orientation distribution function. Analytical and numerical solutions using this model are shown to produce textures consistent with previous measurements and characterization for isostatically and uniaxially ‘die-pressed’ specimens.Predicted thermal strain versus temperature results for textured specimens are shown to be in agreement with corresponding experimental measurements. Results from these simulations are used to identify qualitative trends. Key conclusions from this work include the following. Both porosity and grain aspect ratio have an influence on the thermal expansion of polycrystal TATB, considering realistic material variability. The preferred orientation of the single-crystal TATB [0 0 1] poles within a polycrystal gives rise to pronounced anisotropy of the macroscopic thermal expansion. The extent of this preferred orientation depends on the magnitude of the deformation and, consequently, is expected to vary spatially throughout manufactured components much like the porosity. The modeling approach presented here has utility toward bringing spatially variable microstructural features into macroscale system engineering models.

CREST modelling of PBX 9502 corner turning experiments at different initial temperatures

Corner turning is an important problem in regard to detonation wave propagation in TATB-based explosives. Experimentally, a sudden change in the direction of the propagating wave, such as turning a sharp corner, can result in dead-zones being left behind in the corner turn region, with the observed behaviour being particularly sensitive to the initial temperature of the explosive. In this paper, the entropy-dependent CREST reactive burn model is used to simulate corner turning experiments on the TATB-based explosive PBX 9502. Calculated results of double cylinder tests at three different initial temperatures (−54°C, ~23°C, and 75°C), and a "hockey puck" experiment at ambient temperature, are compared to the corresponding test measurements. The results show that the model is able to: (i) calculate persistent dead-zones in PBX 9502 without recourse to any shock desensitisation treatment, and (ii) predict changes in corner turning behaviour with initial temperature using one set of coefficients.

Effects of crystal quality and preferred orientation on the irreversible growth of compact TATB cylindrical explosives

Three kinds of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) cylinders compacted with TATB raw materials, recrystallized near-spherical and platy TATB crystals are compared to investigate the effects of crystal quality and preferred orientation on their irreversible growth. The results show that the higher the crystal quality, the lower the irreversible volume growth. The compacted cylinders of raw material TATB, with the poorest crystal quality, possess more irreversible growth than those with recrystallized high quality TATB crystals. Irreversible growth of TATB cylinders are also affected by crystal preferred orientation. With the same crystal quality, crystal preferred orientation leads to anisotropic irreversible dimension growth, but has no effect on the volume expansion of TATB cylinders. By changing the crystal quality and preferred orientation, the deformation problem of TATB-based PBX explosives may be restricted.

Thermal expansion of TATB-based explosives from 300 to 566 K

We report thermal expansion measurements and coefficient of thermal expansion (CTE) for LX-17-1 (92.5 wt.% 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), 7.5 wt.% Kel-F 800) from 300 to 558 K. Samples uniaxially-compressed at 300 K show an axial CTE of (2.7+0.42 T)×10 −6 K −1 and a radial CTE of (48+0.16 T)×10 −6 K −1; the different axial and radial CTE indicate a small degree of alignment of the TATB molecules under uniaxial compression. LX-17-1 that was pressed in a die heated to 375 K showed additional growth in the 350–400 K temperature range during heating; apparently residual strain is produced in the heated Kel-F during pressing and is released when the material is reheated and the Kel-F softens. We observed irreversible “ratchet” growth from temperature cycling, and also found that LX-17-1 continues to expand when held at 524–558 K for periods of 4–5 h. Self-heating during thermal soak at 546–566 K indicated exothermic thermal decomposition.

Effect of confinement and thermal cycling on the shock initiation of LX-17

The shock initiation of the insensitive high explosive LX-17, which contains 92.5% triaminotrinitrobenzene (TATB) and 7.5% Kel-F binder, was studied under two simulated accident conditions: initially confined charges were heated to 250°C and shocked; and unconfined charges were thermally cycled between 25° and 250°C and shocked. Previous research on unconfined TATB-based explosives heated to 250°C revealed increased shock sensitivity. This increase was attributed to both the increased porosity caused by the unsymmetrical thermal expansion of TATB, which resulted in more hot spot ignition sites, and the faster growth of hot spot reactions due to the increased surrounding temperature. In this study, aluminum confinement was used to decrease the thermal expansion of LX-17. The shock sensitivity of confined LX-17 at 250°C was observed to be less than that of unconfined charges at 250°C but greater than that of unconfined, ambient temperature LX-17. The thermal cycling results showed that the LX-17 heated to 250°C and then shocked at 25°C was more sensitive than pristine LX-17, because irreversible growth had produced more ignition sites. LX-17 held at 250°C for an hour or fired at 250°C after two thermal cycles did not appear to be significantly more shock sensitive than LX-17 heated to 250°C and shocked immediately. Therefore it is unlikely that TATB is thermally decomposing into less stable intermediate species at 250°C. The Ignition and Growth reactive flow model for shock initiation of LX-17 was normalized to these experimental results to provide a predictive capability for other accident scenarios that cannot be tested directly.