Initiation Of Explosives Research Articles

An Analytical Study for Explosive Grain Initiation

The most common form of solidification of metals is heterogeneous nucleation, in which the particles, regardless of whether they are endogenous or exogenous, nucleate the primary crystal phase, becoming solid crystal particles and, subsequently, initiating into grains during solidification. Explosive grain initiation has been proposed recently for these particles, which have significant nucleation undercooling, in which once nucleation happens, a certain number of solid particles can initiate into grains simultaneously, resulting in recalescence. This is a different form of grain initiation and has high potential for more significant grain refinement in casting alloys. In this work, an analytical model is designed to describe explosive grain initiation, based on which the criteria for the three different grain initiation forms, explosive grain initiation (EGI), hybrid grain initiation (HGI), and progressive grain initiation (PGI), are derived. These criteria are employed to develop a grain initiation map for the Mg-Al alloy system inoculated with nucleant particles having a log-normal size distribution. This work can not only help us to understand the effect of each condition, such as the cooling rate and the solute concentration, on grain initiation behaviors, but also predict the grain size for alloy systems with relatively impotent nucleant particles during solidification.

The Effects of Material‐Filled Voids on Detonation Wave Shape in Rubberized RDX Explosives

AbstractThe sensitivity of explosives is affected by inhomogeneities within the material. This is evident in the increased shock sensitivity of explosives with slightly lower densities resulting from an increased number of hotspots. The influence of hotspots on explosive initiation has been well studied; however, few studies have been conducted on the effect of intermediate‐sized voids (0.1–10 mm) on a propagating detonation wave. Cylindrical voids filled with air have been studied for diameters ranging from 0.3 mm to 0.8 mm for both 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane (HMX) and 1,3,5‐trinitro‐1,3,5‐triazinane (RDX)‐based rubberized explosives. Continuing the investigation into single cylindrical voids, this study examined the effects of 0.5 mm diameter voids filled with different inert cylindrical metals on the detonation wave shape for an RDX‐based rubberized explosive. The metals selected for experiments were 1066 aluminum, brass, copper, and tungsten. The propagation of the detonation wave was captured using a digital streak camera. Experimental results showed that the extent of detonation wave shaping was closely tied to the density differential between the bulk explosive and metal insert. Forty‐four different filler materials, including non‐metals, were simulated using a hydrodynamic code to further analyze material inclusion effects. The main factors hypothesized to be of interest were bulk sound speed, shock impedance, and filler material density. We found that the local detonation delay could be correlated fairly well to a ratio of bulk sound speed and density. Understanding the influence of material inclusions on detonation performance and wave shape allows for tailoring of detonations.

An Integrated Experimental and Modeling Approach for Assessing High-Temperature Decomposition Kinetics of Explosives.

We present a new integrated experimental and modeling effort that assesses the intrinsic sensitivity of energetic materials based on their reaction rates. The High Explosive Initiation Time (HEIT) experiment has been developed to provide a rapid assessment of the high-temperature reaction kinetics for the chemical decomposition of explosive materials. This effort is supported theoretically by quantum molecular dynamics (QMD) simulations that depict how different explosives can have vastly different adiabatic induction times at the same temperature. In this work, the ranking of explosive initiation properties between the HEIT experiment and QMD simulations is identical for six different energetic materials, even though they contain a variety of functional groups. We have also determined that the Arrhenius kinetics obtained by QMD simulations for homogeneous explosions connect remarkably well with those obtained from much longer duration one-dimensional time-to-explosion (ODTX) measurements. Kinetic Monte Carlo simulations have been developed to model the coupled heat transport and chemistry of the HEIT experiment to explicitly connect the experimental results with the Arrhenius rates for homogeneous explosions. These results confirm that ignition in the HEIT experiment is heterogeneous, where reactions start at the needle wall and propagate inward at a rate controlled by the thermal diffusivity and energy release. Overall, this work provides the first cohesive experimental and first-principles modeling effort to assess reaction kinetics of explosive chemical decomposition in the subshock regime and will be useful in predictive models needed for safety assessments.

Simulation of Exploding Foil Initiator Flyers Driving Detonation

Abstract Flyers are the key components that determine the detonation ability of Exploding Foil Initiators (EFI). The incident attitude and velocity of the flyer are the decisive factors affecting the initiation of explosives. This work utilizes a new simulation method to simulate the impact detonation process of flyers. Here we simulate the process of flyers being cut and accelerated, impacting explosives and explosives being detonated. It is possible to obtain the orientation and dynamic velocity changes of the flyer during its motion and the propagation process of detonation waves in explosives. The results provide detailed flyer morphology during the operation of the EFI and pressure changes in explosives. The results indicate that during the formation process of 10 μm and 20 μm flyers, the flip will occur. Additionally, 20 μm and 25 μm flyers can detonate HNS-IV, while 10 μm and 30 μm flyers can not detonate HNS-IV.

Shock-induced nanoscale pore collapse and hotspot in cyclotetramethylene tetranitramine (HMX)

Pore collapse induced hotspot formation is a key mechanism for initiating detonation of shocked high explosives. Accurate continuum models that faithfully capture the pore collapse dynamics and resulting hotspot temperatures for multiscale initiation of high explosive are still lacking. Here, an atomistically informed dislocation plasticity model is developed for cyclotetramethylene tetranitramine (HMX), which includes nonlinear thermoelasticity, pressure-dependent and temperature-dependent dislocation motion and homogeneous dislocation nucleation, and new melting criteria. Nanoscale pore collapse simulations based on the proposed model could well reproduce the pore collapse transition from a strength-dominated regime to a hydrodynamic regime observed in molecular dynamics results. During the pore collapse transition, dislocation motion and dislocation generation induced plasticity is decoupled and evaluated. It indicates that the homogeneous dislocation nucleation suppresses the dislocation motion. Through linkage analysis of dislocation physical quantity histories of tracer particles, this work clarifies the interplay between physical dependences and dislocation mechanisms on pore collapse behaviors for the first time. The results reveal that the transition of pore collapse regime emerges from the strong pressure-dependent homogeneous dislocation nucleation. In addition, the pore collapse responses and energy localizations of the proposed model are further compared with different strength models to prove the importance of pressure dependence and homogeneous dislocation nucleation on pore collapse behaviors. Based on the simulations of pore collapse, the potential heat sources are quantified to provide a physical understanding of hotspot formation mechanisms. The present work demonstrates a key step in multiscale modeling of high explosive initiation in that atomistic simulation results are directly used to guide and refine the mesoscale model of energetic crystal used in the continuum.

Preparation and Decomposition of Spherical CL-20 Composites with Enhanced Laser Absorbance and Decreased Mechanical Sensitivity.

Direct initiation of secondary explosives by a semiconductor laser is highly demanded, but it is challenging to exclude the use of sensitive primers. Most laser-sensitive energetic materials are usually mechanically sensitive. In order to reduce the mechanical sensitivity (MS) of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) while improving laser absorbance in the near-infrared band, spherical CL-20 composites (SCCs) embedded with nano aluminum (Al) powder and graphene-based catalyst (GO-CHZ-Co) were prepared by a spray drying method. These SCCs have been characterized comprehensively in terms of their morphologies, particle size distribution, laser absorbance, thermal decomposition behaviors, MS, and laser ignition properties. Results show that the maximum critical impact energy of SCCs was 3.8 J, which is 2.8 J higher than that of pristine ε-CL-20. The critical friction load was increased by at most 108 N compared to pristine CL-20. The absorbance has also been significantly increased up to almost 70% in the wavelength between 400 and 1400 nm, where the peak absorption is located in the region of 800-900 nm. In addition, the initial decomposition temperature (Ti) of SCCs is lower than that of pure CL-20, especially in the presence of GO-CHZ-Co. The apparent activation energy (Ea) for the decomposition of SCCs was largely dependent on the particle size of Al. Preliminary ignition tests indicate that the SCCs can be ignited successfully by a small-power laser.

An updated technique to obtain explosive kinetics data on microsecond timescales.

There are few techniques available for chemists to obtain time-to-explosion data with known temperature inputs at the early stages of the design and synthesis of new explosives. In the 1960s, a technique was developed to rapidly heat milligram-quantities of confined explosives to ∼1000K on microsecond timescales. Wenograd [Trans. Faraday Soc. 57, 1612 (1961)] loaded explosives inside stainless steel hypodermic needles, connected them to a fireset and rapidly discharged a capacitor through the steel. He obtained the temperature by measuring the needle resistance in a Wheatstone bridge arrangement and the time to explosion from a needle rupture. However, owing to the narrow-gauge needles used in the original research, the experiment was only possible with melt-castable explosives; it was never replicated, and modern diagnostics are now available with advances beyond the 1960s. Here, we report the development of the High Explosives Initiation Time (HEIT) test, which utilizes a 250J pulsed power system to heat the needles. This work extends the Wenograd approach by using optical diagnostics, computational modeling, and advanced techniques to measure needle resistance and needle rupture. Preliminary rate information for pentaerythritol tetranitrate (PETN) will be presented.

Modelowanie numeryczne jako narzędzie do badania wybuchów wodoru

Currently, the burning of fossil fuels in industry or for transportation has a major negative impact on the environment. Most countries are concerned with environmental security and pollution regulation, motivating researchers around the world to find alternative solutions. An alternative solution may be the large-scale use of hydrogen. Applications of hydrogen in industry or for transportation face challenging conditions. Among other things, we are talking about pressures of up to 1000 bar, extreme temperatures starting from -253 °C (for liquefied hydrogen) and up to 650 °C - 950 °C (in the case of solid oxide electrolytic cells), as well as the imminent risk of explosion. This is because H2 has an extremely low ignition energy, with much wider flammability limits compared to other fuels such as methane or propane. Hydrogen is a highly reactive and explosive gas. Therefore, explosion protection is essential for all processes involving the use of hydrogen in one form or another. The same principles that are applied to natural gas can be applied. Hydrogen behaves similarly to methane in terms of explosion risk, meaning in principle that explosion protection works similarly for both gases. However, there are still many unknowns regarding the phenomenon of initiation and propagation of explosions caused by air-hydrogen mixtures. Taking into account the multiple aspects related to security techniques that must be taken into account for the use of hydrogen in industry or for transport, the current paper focuses on aspects with regard to the use of modern numerical modelling tools for increasing the occupational health and safety level in technological processes endangered by the occurrence of explosive atmospheres generated by air-hydrogen mixtures. It presents a review on the main research activities to be carried out within a the H2Model research project implemented between 2023 – 2026, project which focuses on numerical modelling on the ignition and propagation of explosions caused by air-hydrogen mixtures.

Influence and comparison of cylindrical engineered defects on detonation waveshape in a rubberized RDX explosive

AbstractInhomogeneities within explosives affect the sensitivity and detonation waveshape of energetic materials. The influence of voids on explosive initiation has been well documented; however, the effects that voids between 0.1 mm and 10 mm have on a propagating detonation wave remains largely unexplored. The effect of single cylindrical voids on detonation waveshape and re‐initiation was examined here using manufactured voids in a rubberized 1,3,5‐trinitro‐1,3,5‐triazinane (RDX) explosive. Two streak imaging techniques were fielded to investigate void influence. For the first, back‐surface streak imaging, the location of the void on the samples was changed and the resulting change in detonation waveshape at the downstream breakout was captured using a streak camera in cut‐back experiments. The results from this experiment showed the effects of an initial jet form for short cut‐back distances and as shock propagation progressed, the jet formation was absorbed by the unaffected portions of the wave front. The second method, top‐surface streak imaging, was used to investigate the re‐initiation/downstream propagation of the detonation front and the detonation velocity of the rubberized explosive. These experiments were compared to similar experimental results from machined voids in PBX 9501, an 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane (HMX)‐based explosive, to investigate the interaction of a detonation wave with a 0.5 mm void for different explosives. The experiments were also compared to simulations using a multi‐dimensional and multi‐material hydrodynamic code. These results showed the influence that small features can have on detonation waveshaping and how explosive properties play a key role in that interaction.

Simulation Study of Crack Extension in Concrete Blast Walls Under Blast Impacts

To study the crack propagation law of concrete blast wall (CBW) under explosion impact, this paper uses ANSYS/LS-DYNA finite element software to numerically simulate the crack growth law under the influence of different explosion loads and explosion distances. The results show that: after the explosion, the change of composite velocity of each measuring point on the wall at a certain distance from the explosion point is mainly divided into three stages: explosive initiation stage, the composite velocity and acceleration of each measuring point are zero; In the accelerated crack growth stage, the acceleration of each measuring point reaches the peak value; At the stage of uniform crack growth, the crack will no longer accelerate its diffusion. When the explosion distance is fixed, the explosion load is positively correlated with the number of radial cracks; When the explosion load is small, there are only inconspicuous circumferential cracks in the center of the wall. When TNT equivalent is 15g, 25g, and 30g, CBW circumferential cracks increase and mainly concentrate in the center, and gradually expand outward to the boundary in the form of concentric circles. At the same time, when the explosion load is constant, the explosion distance is negatively related to the number of cracks, mainly radial cracks, while circumferential cracks are always distributed in the center of the wall. In the range of simulated explosion distance, the cracks only appear at the boundary and gradually change from square to round with the increase of explosion distance, and the crack area decreases. The research results can provide a theoretical basis for avoiding such accidents and a powerful reference for accident investigators to determine the location and intensity of explosion sources.

Experimental and Numerical Investigation of Dynamic Damage and Load Transfer of PBX Substitute Material under Low Velocity Impact.

The accidental initiation of explosives under mechanical loads has caused numerous catastrophic events. Therefore, the dynamic damage behavior of confined polymer-bonded explosives (PBXs) must be assessed to improve their practical applicability. In this study, polymer-bonded sugar (PBS) materials were prepared using a novel agglomerate to develop a PBX substitute material with enhanced experimental safety. The mechanical properties of the PBS shell were evaluated using a dynamic compression test, which revealed that the compression response of the shell was affected by the strain rate. A low-velocity impact experiment was performed to investigate the dynamic damage and load transfer characteristics of the PBX substitute. A constitutive model was developed to characterize the mechanical response of PBS subjected to high strain rates, and implementing this model in ABAQUS ensured successful prediction of the damage evolution process associated with PBS. Simulation results indicated that the PBS specimen was primarily damaged around its center while sliding friction was dominant near the center during pressure application. Notably, different stress states result in distinct crack growth velocity histories along the axial direction, with the damage ratio progressively decreasing toward regions closer to the impact surface.

ERA5‐Based Significant Tornado Environments in Canada Between 1980 and 2020

AbstractThis study uses ERA5 close‐proximity soundings and associated convective parameters to characterize significant tornadic storm (F/EF2+) environments between 1980 and 2020 in parts of Canada. It is shown that ERA5 convective parameters are suitable to represent observed parameters, based on radiosonde comparisons. Results indicate that the eastern Canadian Prairies have nearly double the lifted condensation level with higher level of free convection compared to eastern Canada (southern Ontario/Quebec). Eastern Canada has more a humid boundary layer and free troposphere that can lead to warmer cold pools, favoring tornadogenesis. Central Canada (Manitoba) has the largest mixed‐layer (ML) convective available potential energy (CAPE) mainly due to a combination of regional differences in low level moisture and steeper mid‐level lapse rates in western Canada. Central continental U.S. and Canadian regions appear to have the highest (most negative) convective inhibition, leading to more explosive initiation. Mean bulk wind shear and storm relative helicity (SRH) increases from west to east, with eastern regions being significantly larger. The supercell composite and significant tornado parameters are generally less than U.S. magnitudes, particularly in western Canada, and would require recalibration for more practical use in Canada. Overall, western Canada significant tornadic storms are associated with more low‐level looping hodographs and dominated by thermodynamic influences compared to larger wind influences in eastern regions. This is likely due to more spring, late summer, and autumn events that typically have well‐developed synoptic systems (stronger wind shear) with overall less buoyant energy in eastern regions.

Demonstrating resonant ultrasound spectroscopy as a viable technique to characterize thermally conditioned high explosive materials

We present results of resonant ultrasound spectroscopy (RUS) measurements applied to granular high explosive materials at different bulk pressing densities and degree of thermal conditioning. The material chosen in this study is a ubiquitously used explosive material known as pentaerythritol tetranitrate (PETN), which is used commercially in civil and defense applications both as a binderized plastic bonded explosive material and an unbinderized neat material. However, changes in granular PETN bulk elastic properties due to thermal conditioning, which could have implications for better understanding environmental aging-related effects, have not been well studied even though it is believed that elasticity may play an important role in explosive material initiation mechanisms. Furthermore, monitoring elastic property changes in granular explosive pressings has not yet been demonstrated using RUS, which is an appealing non-destructive characterization tool that requires only dry point contact with the explosive material. To this end, we report the first study using RUS to quantify the elastic properties of binderized and neat PETN pressings as well as to quantify changes in elastic properties as a function of both thermal conditioning and bulk pressing density. Elastic stiffness coefficients, sometimes more commonly referred to as elastic constants, calculated from the RUS measurements on the different PETN-based materials show a significant increase for the post-conditioned samples compared to the pre-conditioned samples. This trend of increasing elastic properties with thermal conditioning was consistent for different density pressings, different thermal exposure conditions, and even different neat PETN pressings of differing average crystal sizes and/or specific surface areas.

Numerical study on detonation initiation by multiple hot spots

Detonation initiation is important not only for the development of advanced detonation engines and but also for the control of accidental explosion. There are mainly two types of detonation initiation, i.e., direct initiation and indirect initiation. This work focuses on direct detonation initiation which has a short initiation distance but requires large amount of energy deposition. Specially, we investigate the reduction in the critical initiation energy through replacing the single hot spot by multiple hot spots. The transient detonation initiation process in a stoichiometric H2/O2/Ar mixture is examined through two-dimensional simulations considering detailed chemistry. It is found that under the same initiation energy, detonation initiation fails for a single large hot spot while successful detonation initiation can be achieved by employing six small hot spots. The collisions among adjacent transverse detonation waves induce new local explosions, which play a pivotal role in detonation initiation. To further assess the impact of wave collision, we change the hot spot energy used in the multiple hot spot configuration. For relatively low initiation energy, the blast wave quickly decays and decouples with the reaction zone. Consequently, the collision among transverse shock waves cannot induce new local explosion and detonation initiation fails. Increasing the initiation energy can enhance the blast wave and is favorable to the formation of local explosion, facilitating the rapid detonation initiation. Furthermore, the influence of hot spot number on detonation initiation is assessed. Interestingly the hot spot number is found to have non-monotonic effect on detonation initiation. Splitting a single hot spot into multiple hot spots enhances detonation initiation since the wave collision helps to induce local explosion. However, as the hot spot number increases, the energy of each hot spot is decreased and becomes excessively dispersed, which results in relatively weak blast wave and thereby weak wave interaction. Consequently, local explosion cannot be triggered and detonation initiation fails for relatively large hot spot numbers. This study provides insights on promoting detonation initiation through multiple hot spots.

Effect of priming and explosive initiation location on pull in hard rock underground mine

Effect of priming and explosive initiation location on pull in hard rock underground mine

Gas-dynamic processes and causes of accidents at mines

Geodynamic phenomena that occur during the exploitation of a coal-bearing massif lead to human casualties, reduce the speed of penetration, and significantly complicate the operation of the mine.The article analyzes existing views on geodynamic processes occurring within mining fields located in coal-bearing formations. A safe technology for identifying potential outburst locations during coal mining is characterized. The technology has been tested during prospecting and environmental studies within the mining workings at active mines and abandoned mining fields. The results of profile and planar investigations in he areas exhibiting geodynamic outbursts in coal deposits and mines are presented.When sampling subsoil air using the technology of structural-thermo-atmospheric-hydrogeochemical research (STAHGS), which is carried out on the surface of the earth in profile and planar versions, the authors came to the conclusion about the possibility of predicting fault zones of increased permeability and zones of low fluid permeability. The first affect the rate of destruction of rocks under pressure, and in the second case, the possibility of gas emissions into the mine, which can be accompanied by an explosion and fire. Such zones are dangerous, because the most destructive events occur in places of collision. Early identification of places of geodynamic stress of rocks, fault zones of increased permeability, accumulation of gases – all this will allow to make a decision in advance about changing the conditions of conducting mining operations and degassing of the coal massif.In addition, the authors draw attention to hydrogen gas as one of the causes of initiation of explosions and fires during underground mining operations in mines, which is not taken into account at the current stage of safety control of mining operations. The possible cause of a hydrogen explosion is not taken into account in coal mine accidents. The appearance of hydrogen and helium in coal samples taken from the mine may indicate the deformation of the massif, which leads to the opening of cracks and the outflow of gas from deeper horizons. And then an increase in the concentration of hydrogen, not methane, creates the conditions for explosions and fires.

Initiation of PETN and HNS-IV Explosives by Laser Driven Al Flyer Plate

Initiation experiment of Pentaerythritol Tetranitrate (PETN) and Hexanitrostilbene IV(HNS-IV) explosives by laser driven flyer plate is conducted. By using an optimum selection of 5μm Al flyer and φ0.5×0.3 metal barrel, the explosive samples of about 1μm mean grain size and 90% theoretical maximum density(TMD) in a metal case are detonated successfully. The PETN has a much lower critical firing laser energy than HNS-IV, which is in accordance with the electrical slapper exploding practices. The much lower critical firing laser energy of the explosives makes it possible for safe transmission of laser by a fiber optic line with the core diameter no more than 600μm, and in turn makes it possible for the use of optical detonation technique in multipoint synchronous initiation of warheads.

System modeling and simulation of flyer acceleration and explosive detonation in exploding foil initiator

In this theoretical study on an exploding foil initiator (EFI), the sequential events in an EFI system were numerically modeled and investigated from metallic bridge burst by ohmic heating and flyer acceleration by plasma expansion to explosive detonation by high-speed flyer impact. The EFI system modeling employed mass, momentum, and energy conservation coupled with the resistance–inductance–capacitance circuit equation of the initiation circuit and plasma property calculations of highly dense metallic plasma as well as a semi-empirical detonation model. The aim was to predict transient bridge behavior, flyer velocity, and detonation initiation threshold. Through comparisons and verifications with measured data from several existing EFI firing tests, the present system model was shown to predict bridge burst and flyer velocity very well. The numerical results indicated two different thresholds of charging voltage for flyer creation out of plastic film and impact detonation of explosive charge to be quite consistent with the measurements. The system behaviors in three different ranges of charging voltage were discussed in terms of discrete nature of this high-voltage explosive charge initiator.

Influence of explosion distance on the dynamic mechanical response of underground fortification

Many key military targets have been moved underground to improve the battlefield survivability. To study the influence of explosion distance on the dynamic mechanical response of underground fortification, the full-time numerical simulation is conducted based on the CDEM numerical method. First, four numerical simulations corresponding to different explosion distances are conducted. Then, the displacement characteristic of underground fortification and rock mass is analyzed. Finally, the fracture characteristic of underground fortification and rock mass is analyzed. The numerical results show that the damage degree of underground fortification and rock mass weakens with the increase of explosion distance. When the distance increases from 5 m to 20 m, the volume of rock entering the underground fortification decreases from 24.78 m3 to 0 m3. The time-history curve of crack ratio has the four-stage characteristic, and it increases rapidly during the explosion initiation process. As the explosion distance increases, the top concrete wall mainly undergoes tensile fracture.

Intergranular Hotspots: A Molecular Dynamics Study on the Influence of Compressive and Shear Work

Numerous crystal- and microstructural-level mechanisms are at play in the formation of hotspots, which are known to govern high explosives initiation behavior. Most of these mechanisms, including pore collapse, interfacial friction, and shear banding, involve both compressive and shear work done within the material and have thus far remained difficult to separate. We assess hotspots formed at shocked crystal–crystal interfaces using quasi-1D molecular dynamics simulations that isolate effects due to compression and shear. Two high explosive materials are considered (TATB and PETN) that exhibit distinctly different levels of molecular conformational flexibility and crystal packing anisotropy. Temperature and intramolecular strain energy localization in the hotspot are assessed through parametric variation of the crystal orientation and two velocity components that respectively modulate compression and shear work. The resulting hotspots are found to be highly localized to a region within 5–20 nm of the crystal–crystal interface. Compressive work plays a considerably larger role in localizing temperature and intramolecular strain energy for both materials and all crystal orientations considered. Shear induces a moderate increase in energy localization relative to unsheared cases only for relatively weak compressive shock pressures of approximately 10 GPa. These results help isolate and rank the relative importance of hotspot generation mechanisms and are anticipated to guide the treatment of crystal–crystal interfaces in coarse-grained models of polycrystalline high-explosive materials.