Secondary High Explosives Research Articles

Review of modern military insensitive high explosives

In the last twenty years, high energetic materials have changed significantly. Several factors have influenced the development of these materials, which include new operational requirements such as insensitive ammunition (IM), as well as factors in the availability of new materials and new production techniques, safety assessment, and modeling. All this enables more efficient use of materials and a more detailed understanding of the processes involved in the application of new technologies. This work presents new insensitive secondary high explosives such as TATB, FOX-7, GUDN, NTO, and others that are in different stages of development. A review of these explosives is given and their stability, reliability, and specific application are described. Energy materials are known to be chemical compounds or mixtures that contain significant amounts of energy and it has been shown that successful design of new energetic materials with customized performance properties and increased stability is possible. The properties of new insensitive energetic materials must be further researched and improved before they can be used in new or existing systems. Insensitive ammunition testing is a vital component of many national IM programs. The international community has established requirements for testing the insensitivity of materials and developed six unique tests based on testing the response of the material to the effects of heat, impact, or shock.

Professor Dr. Thomas M. Klapötke

Professor Dr. Thomas M. Klapötke

Recent Advances in the Synthesis of High Explosive Materials

This review discusses the recent advances in the syntheses of high explosive energetic materials. Syntheses of some relevant modern primary explosives and secondary high explosives, and the sensitivities and properties of these molecules are provided. In addition to the synthesis of such materials, processing improvement and formulating aspects using these ingredients, where applicable, are discussed in detail.

Validated model-based simulation tool for design optimization of exploding foil initiators

Exploding foil initiators (EFIs) are highly suitable for use in inline fuze trains containing only secondary high explosives, mainly due to their insensitivity with respect to electromagnetic disturbances or mechanical stress, their precisely controllable fire characteristics and compact size. During EFI operation various multi-physical phenomena occur, such as high-volt switching, foil explosion, generation and acceleration of the flyer plate, as well as shock wave initiation of the explosive by flyer plate impact. In this work all the physical processes, including their coupling, are modelled using multi-physical models that neither employ complex finite elements computations nor experimentally determined fitting parameters. Implemented in a simulation tool, the complete EFI behaviour is covered, from firing (switching) to explosive initiation. Complementary experiments with test structures are conducted, analysing the electrical behaviour and the resulting flyer velocities of different EFI designs. Comparison with these experiments demonstrates the consistency of the simulations and sufficient accuracy. The validated simulation tool is used to determine all-fire/no-fire criteria, to improve geometries and materials and to analyse parasitic influences in the firing circuit. The paper shows that this model-based approach can be used to assess high reliability and safety either for existing or when developing new EFIs.

Complex Microwave Permittivity of Secondary High Explosives

AbstractWe aim to understand how microwaves interact with high explosives by studying the complex permittivity from 1–18 GHz of HMX, RDX, TNT, TATB, PETN, Octol, Comp B, 95 % RDX/5 % Viton A (PBX‐RDX), PBX 9404, PBXN‐5, PBXN‐7, PBXW‐14, PBX 9501, and PBX 9502. The combination of a resonant cavity perturbation technique for determining the room‐temperature complex dielectric constant at discrete frequencies and a wide band open circuit method (1–18 GHz) provides an accurate, broadband measurement that describes the dielectric properties in the frequency range of interest. While the values of the real and imaginary permittivity components did not vary significantly as a function of frequency, we found the real part of the permittivity to be highly dependent on relatively small changes in the material density. We used dielectric mixing theory, specifically the linear‐law approximation, to compare the predicted values based on the dielectric properties of individual components with those of the resulting formulation measured experimentally for a select number of samples; the prediction agrees well within the observed variability of the experimentally measured values.

Electromagnetically induced localized ignition in secondary high explosives: Experiments and numerical verification

In order to more fully understand the factors that influence the thermal “hot-spot” initiation of high explosives, we have chosen a model system for study that uses the internal and localized dissipation of long wavelength electromagnetic energy (microwaves). High purity organic crystals generally interact weakly with microwave energy. Therefore, the addition of electromagnetically absorbing inclusions of silicon carbide provides a tractable system for the study of hot-spot ignition phenomena. Previously, we developed a simple analytic model that illuminates the important physical factors. In this work, we verify the relationships of the analytic model using a series of experiments and a numerical model.

Influence of the initial gas pressure on the detonation limits and parameters of low-density secondary explosives in an inert porous medium

This paper reports the results of an experimental study of the detonation of low-density (3–40 mg/cm3) secondary high explosives (HEs) in evacuated and gas-filled inert porous media. A convective-jet mechanism of detonation propagation was found to occur under all conditions studied. The effects of the type of HE and initial gas pressure on the critical density of the HE and detonation parameters were elucidated. It is shown that, in the presence of air, detonation can occur at a lower volume-averaged density of the HE than in the case of the evacuated media and there are two limits (minimal and maximal) for the initial gas pressure. As the volume-averaged density HE decreases, the limits approach each other and, for a certain critical density of the HE, detonation exists only at one value of the initial pressure.

Electromagnetically induced localized ignition in secondary high explosives

A model for electromagnetically induced hot spots is developed from the well-established theories of dielectric mixtures, microwave absorption, heat transfer, and thermal ignition. This mathematical model is used to elucidate the interplay among these theories for a microwave heated system of secondary high explosive within which isolated electromagnetically lossy spheres are randomly distributed. Results are shown in this article for the specific case of pentaerythritol tetranitrate with embedded spheres of varying diameter and conductivity illuminated by a uniform time harmonic electromagnetic field of 1, 8, and 15 GHz. It is shown that for a given frequency and electric field strength internal to a particle embedded in a secondary high explosive, there exists a range of values for the particle’s diameter and conductivity for which electromagnetically induced hot-spot ignition of the high explosive is possible. By providing an accurate estimate for the range of necessary geometric and electrical properties of the system, this idealized model can be used to guide potentially complex and otherwise less tractable computational and experimental studies of microwave-induced hot spots. We found that the condition of relatively large particles, with semiconductorlike conductivity, exposed to the highest possible frequency is most favorable for hot-spot ignition.

Radiation-induced decomposition of explosives under extreme conditions

We present high-pressure and high temperature studies of the synchrotron radiation-induced decomposition of powder secondary high explosives pentaerythritol tetranitrate (PETN) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) using white beam synchrotron radiation at the 16 BM-B and 16 BM-D sectors of the HP-CAT beamline at the Advanced Photon Source. The radiation-induced decomposition rate TATB showed dramatic slowing with pressure up to 26.6 GPa (the highest pressure studied), implying a positive activation volume of the activated complex. The decomposition rate of PETN varied little with pressure up to 15.7 GPa (the highest pressure studied). Diffraction line intensities were measured as a function of time using energy-dispersive methods. By measuring the decomposition rate as a function of pressure and temperature, kinetic and other constants associated with the decomposition reactions were extracted.

Quantification of reaction violence and combustion enthalpy of plastic bonded explosive 9501 under strong confinement

The confinement experienced by an explosive during thermal self-initiation can substantially affect performance in terms of deflagration–to–detonation characteristics and explosion/detonation violence. To this end, we have developed an experiment to quantitatively observe enthalpy change and reaction violence in thermally initiated plastic bonded explosive (PBX) 9501. Traditionally, researchers attempt to quantify violence using terminal observations of fragment size, fragment velocity, and through subjective observations. In the work presented here, the explosive was loaded into a heated gun assembly where we subjected a 300 mg charge to a cook-off schedule and a range of static and inertial confinements. Static confinement was controlled using rupture disks calibrated at 34.5 and 138 MPa. The use of 3.15 and 6.3 g projectile masses provided a variation in inertial confinement. This was a regime of strong confinement; a significant fraction of the explosive energy was required to rupture the disk, and the projectile mass was large compared to the charge mass. The state variables pressure and volume were measured in the breech. From these data, we quantified both the reaction enthalpy change and energy release rate of the explosive on a microsecond time scale using a thermodynamic analyisis. We used these values to unambiguously quantify explosion violence as a function of confinement at a fixed cook-off schedule of 190 C for 1 h. P2τ, a measure of critical shock energy required for shock ignition of an adjacent explosive was also computed. We found variations in this confinement regime to have a weak effect on enthalpy change, power, violence and shock energy. Violence was approximately 100 times lower than detonating trinitrotoluene, but the measured shock energy approached the critical shock energy for initiating secondary high explosives.

Preexplosion Phenomena in Prompt Initiation of Secondary Explosives (Review)

This paper reviews experimental studies of preexplosion phenomena during shock‐wave and laser initiation of secondary high explosives (HEs). The main research results are discussed from the viewpoint of similarity and difference between the processes occurring in these methods of initiation. Approaches to developing research into the phenomena in question are proposed.

Cutting and Machining Energetic Materials with a Femtosecond Laser

AbstractA femtosecond (fs) laser has been used as a tool for solving many problems involving access, machining, disassembly, inspection and avoidance of undesirable hazardous waste streams in systems containing energetic materials. Because of the unique properties of the interaction of ultrashort laser pulses with matter, the femtosecond laser can be used to safely cut these energetic materials in a precise manner without creating an unacceptable waste stream. Many types of secondary high explosives (HE) and propellants have been cut with the laser for a variety of applications ranging from disassembly of aging conventional weapons (demilitarization), inspection of energetic components of aging systems to creating unique shapes of HE for purposes of initiation and detonation physics studies. Hundreds of samples of energetic materials have been cut with the fs laser without ignition and, in most cases, without changing the surface morphology of the cut surfaces. The laser has also been useful in cutting nonenergetic components in close proximity to energetic materials.

Detonation of a thin explosive layer in evacuated tubes

Detenation of thin layers of dispersed primary and secondary high explosives (HE) on the outer surface of glass and plastic tubes 0.6–3 mm in diameter was examined at an initial air pressure inside the tube of 0.1 MPa to 30 Pa. It is shown that, under these conditions, the air practically does not influence the detonation velocity, which for secondary explosives (PETN, RDX, and HMX), is lower than or approximately equal to the Chapman-Jouguet detonation velocityD CJ for a homogeneous mixture of the same substances. Experiments with a primary HE (lead azide) revealed regimes with a wave velocity higher thanD CJ and a varying reaction zone pattern. When tubes containing a layer of a secondary HE were filled with an explosive gas mixture, waves of a hybrid detonation with a velocity both higher and lower than that in the evacuated tubes was observed. In tubes with diameter 2–3 mm, detonation proceeded in a spinning regime over the entire range of the initial pressure and at a velocity higher thanD CJ. It is concluded that in the evacuated tubes with a thin HE layer on the walls, ignition is transferred by the stream of hot detonation products moving at the head of the detonation wave.

Industrial explosives - a brief history of their development and use

In this article we provide a brief overview of chemical explosives history, from primitive Chinese bamboo rockets to the 17th century introduction of black powder in mining to the powerful and economical blasting agents which now support the mining and construction industries. Explosive behavior is traced to the very same combustion reactions that drive more familiar power sources, but running millions of times faster. The physical basis for the extraordinary reaction rate of explosives is outlined. The four major classes of chemical explosives (low, or deflagrating explosives, primary and secondary high explosives, and blasting agents) are illustrated by examples. The main features of explosive initiation systems are described, including the careful sequencing required in modern industrial blasting. The recent development of economical and super - safe blasting agents is traced to accidental ammonium nitrate explosions, such as the one that devastated Texas City in 1947. Finally, the principal uses of industrial explosives in mining, quarrying and construction are described.

The burning of secondary high explosives under high pressure up to 1000 kg/cm2

1. The effect of high pressures on the burning of secondary high explosives has been investigated. 2. An empirical equation for the relation between the burning velocity and pressure over the range from 1–900 cm2 has been obtained. 3. Burning in the gas evidently proceeds over the burning surface and in the pores of the charge with different velocities, the difference depending on the external pressure.