Energetic Material Detonation Characterization: A Laboratory‐Scale Approach

A novel energetic‐material detonation and air‐blast characterization technique is proposed through the use of a laboratory‐scale‐based modified “aquarium test.” A streak camera is used to record the radial shock wave expansion rate at the energetic material air interface of spherical laboratory‐scale (i.e., gram‐range) charges detonated in air. A linear regression fit is applied to the measured streak record data. Using this in conjunction with the conservation laws, material Hugoniots, and two empirically established relationships, a procedure is developed to determine fundamental detonation properties (pressure, velocity, particle velocity, and density) and air shock wave properties (pressure, velocity, particle velocity, and density) at the energetic material air interface. The experimentally determined properties are in good agreement with published values. The theory’s applicability is extended using historical experimental test data due to the limited number of experiments able to be performed. Predicted detonation wave and air shock wave properties are in good agreement for a multitude of energetics across various atmospheric conditions.     

Optical Measurement of Peak Air Shock Pressures Following Explosions

High speed video and streak camera imaging are used to measure peak pressures for explosions of spherical charges of the high explosive C‐4 (92 % trimethylenetrinitramine, C₃H₆N₆O₆). The technique measures the velocity of the air shock produced by the detonation of the explosive charges, converts this velocity to a Mach number, and uses the Mach number to determine a peak shock pressure. Peak pressure measurements are reported from a few millimeters to approximately one meter from the charge surface. Optical peak pressure measurements are compared to peak pressures measured using piezoelectric pressure transducers, and to peak pressure measurements estimated using the blast computer code CONWEP. A discussion of accuracy of peak pressures determined optically is provided.     

壳体约束强度对温压炸药空中爆炸性能的影响

为评估壳体约束强度对温压炸药爆炸性能的影响,对不同壳体约束强度下的固体温压炸药进行野外静爆试验,用AUTODYN软件对该过程进行数值模拟,并与试验结果进行对比。结果表明,相同装药条件下,裸装药爆炸冲击波参数值、冲击波衰减速率和后燃峰压力值大于带壳装药;铝壳体装药爆炸冲击波参数值、冲击波衰减速率和后燃峰压力值较钢壳体装药高;数值模拟得到的冲击波曲线形态、峰值及冲量与试验结果吻合较好,且裸装药爆炸冲击波的后燃峰到达时间较带壳装药早,铝壳体装药爆炸冲击波的后燃峰到达时间较钢壳体早;初始冲击波超压值受壳厚影响较大,壳体的存在使冲击波的传播滞后。     

Shock Profiles Along a Specimen

The observation of shock waves in a block of plexiglass caused by a detonating high explosive charge shows the influence of air-gaps and cover-plates which are attached head on. The shock wave for high explosive charges without any cover plate gives a high maximum pressure which decays quickly. The detonating high explosive charge which is covered with a two millimeter thick disc of copper shows a shock wave which is constant over a certain time. An air-gap between the high explosive charge and the measuring plexiglass block always gives a weak shockwave at the beginning. In the case of an uncovered high explosive charge the expansion of the high explosive products gives a relatively smooth increasing blast or shock wave, and in the case of a covered high explosive charge a strong shock resulting from the following impact of the flying plate.     

Quantitative Schlieren Measurement of Explosively‐Driven Shock Wave Density,Temperature, and Pressure Profiles

Shock waves produced from the detonation of laboratory‐scale explosive charges are characterized using high‐speed, quantitative schlieren imaging. This imaging allows the refractive index gradient field to be measured and converted to a density field using an Abel deconvolution. The density field is used in conjunction with simultaneous piezoelectric pressure measurements to determine the shock wave temperature decay profile. Alternatively, the shock wave pressure decay profile can be estimated by assuming the shape of the temperature decay. Results are presented for two explosive sources. The results demonstrate the ability to measure both temperature and pressure decay profiles optically for spherical shock waves that have detached from the driving explosion product gases.     

Development of a Structure for Blast Wave Mitigation

The internal structure of a blast containment container has been developed and examined by experiments involving the explosion of a high explosive. A steel pipe was selected as an effective structure for blast mitigation, because it dramatically reduces the blast wave in the radial direction near the explosion source. To also reduce the blast wave in the axial direction, two types of model structures consisting of a steel pipe as the main part were examined by both high‐speed photography and pressure measurements of the blast waves. A 0.34‐scale internal structure was constructed by combining these structures. To induce a powerful mitigation effect, the internal structure was filled with a shock‐absorbing material. The peak pressures of C4 explosions in free air were obtained on the basis of the published blast wave data for TNT explosions in free air using an equivalent weight of 1.37. The peak pressures of the blast waves from the structures for all cases were compared with the blast wave data for C4 explosions in free air to estimate the blast mitigation effect. As a result it was estimated that the internal structure not only eliminates the blast pressure in the radial direction but also reduces the blast wave in the axial direction by 36 %. By combining the effects of the internal structure and the shock‐absorbing material, the structure can reduce the peak pressure by 75 %.     

Shaped Charge Jet Initiation on Explosive Charges equipped with barriers made up of various materials

This paper describes initiation tests on cast TNT/RDX (35/65) explosive charges applying shaped charge jets with test set-ups on which the HE charge was arranged either in contact to a 50-mm thick barrier or after a 100-mm thick barrier in a 15-mm air gap. A variety of materials was attached to the barrier's rear side which, on one band, resulted in a varying shock wave attenuation and also in different bulging effects that are responsible for the differences in the initiation mechanisms observed on the two test arrangements. Materials with a lower density also provide, due to a less precompression of the IIM charge used on the arrangement “test charge in contact”, shorter buildup distances than materials with a higher density. An exception to this is a high ductile material such as e.g. steel. The build-up distances, however, remain constant when arranging the explosive charge with an air gap. This backs up the hypothesis that most of all, bulging of the target is responsible for the sensitivity reduction observed on the test HE charges in contact with the barrier.     

Impulse Plug Measurements of Blast Reflected Impulse at Close Range

A series of blast tests is described in which blast impulse is measured by an impulse plug technique for spherical explosive charges. In this approach the reflected blast impulse delivered to a hardened bullet‐shaped steel plug is determined from a measurement of the plug terminal momentum. Plug velocity is measured by a high‐speed, high‐resolution video camera operating at 20,000 frames per second. Spherical C4 charges are studied for varying charge weight and charge‐to‐plug standoff distance. Tested standoffs include the demanding near‐field blast zone within which pressure measurement by transducer is extremely difficult or impossible. Results are compared with previous studies made using transducer and impulse plug methods for both C4 and Pentolite charges. The present data for half‐pound C4 charges are in good agreement with much earlier impulse plug data for spherical Pentolite in the near‐field region, however, differences of up to 26 % are noted with more recent transducer measurements for C4 just beyond the near‐field zone. Test results are also compared with hydro‐code simulations of the plug response.     

Semi‐Closed Investigations of New Aluminized Thermobaric and Enhanced Blast Composites

The investigations of new aluminum‐enriched RDX‐based composites belonging to the thermobaric and enhanced blast explosive formulations were undertaken. In a semi‐closed bunker, the blast wave and the thermal characteristics of pressed and layered charges made from the composites are determined. The study includes the blast wave history registrations as well as the determination of the overpressure peaks and the specific impulses of the incident blast wave. The total impulses have been estimated for a period of 60 ms. Since the composites are supposed to be volumetric, the explosion light outputs and the fireball temperatures were also investigated. The results obtained for the composite charges were compared with the blast performances and fireball temperatures of TNT and phlegmatized RDX charges of the same mass. Also differences between the pressed and the layered composite charges prepared from the same composites were observed and explained. The effect of the aluminum particle size was checked. Discussion of the results and conclusions about the aluminum combustions during the explosions of such charges were presented.     

Effect of Scale and Confinement on Gap Tests for Liquid Explosives

The factors influencing initiation of detonation in gap tests for liquid explosives are investigated experimentally. A calibrated donor charge (nitromethane) and PMMA attenuator disk arrangement are used to transmit shocks of known strength (2–10 GPa) into a test explosive of nitromethane sensitized with 5% diethylenetriamine. The test explosive is contained in capsules of different wall materials (PVC, Teflon, aluminum), and the dimensions of the charges vary from 25 mm to 100 mm in diameter. For the small‐scale charges, the presence of the confining wall of the test capsule is seen to have a pronounced effect on the detonation initiation. Certain wall materials (PVC, Teflon) exhibit a multi‐valued critical gap thickness, meaning that a weaker shock may result in initiation while a stronger shock does not. The effect of the wall materials could not be correlated with their acoustic or shock impedance, and the only way to eliminate these effects was to make the diameter of the test charge larger than the donor charge. When the size of the donor charge was increased, the critical pressure required for initiation decreased. These results could be correlated to “ideal” shock initiation experiments that use flyer plates as shock sources assuming that lateral rarefactions quench detonation initiation if they reach the central axis of the charge before the onset of detonation is complete.     

薄环形装药起爆技术研究

设计和压制了一种薄型起爆药片及环形药柱,并对其隔爆和起爆能力、可靠性和同步性进行了测试研究。采用环形装药起爆可以有效地提高聚能装药的威力,而且其威力随着环形装药直径的增加而增加。研究结果对于传爆序列的可靠性和起爆技术的研究有重要的参考价值,可用于聚能装药的起爆,提高其作战能力。     

The Influence of Additives on Pressure and Momentum of the Air Shock from detonating charges

The air blast effect produced by high explosives with additives of various types and quantities was studied. To this end, air shock intensities and pressure profiles were recorded at certain distances from an unconfined charge. Among those additives which by their reaction with the gaseous products of the detonated explosive theoretically should increase the energy potential, aluminum and zirconium exhibit a positive effect while other substances such as boron react too slowly for strengthening the blast effect. An addition of aluminum (32 weight%) causes the shock wave pressure to increase by about 15% and the momentum by 30% as compared with the pure explosive.     

基于顶盖举起试验的炸药内爆炸性能评估

为了评估炸药在密闭/半密闭结构内的爆炸性能,通过自建的顶盖举起试验装置对5种典型炸药装药进行了内爆炸试验,利用冲击波超压和顶盖的举起位移评估了其内爆炸威力。结果表明,冲击波超压高的炸药,内爆炸性能不一定好,炸药的空中爆炸性能与内爆炸性能具有显著的差异;顶盖举起最大位移与炸药的非同步自氧化燃烧热具有线性关系,关系式为xmax=17.717ΔHas-5.322,相关系数R2=0.991 7;内爆类炸药应具有高燃烧热、高非同步自氧化燃烧热和适中的爆速。     

Ignition and Growth Modeling of LX‐17 Hockey Puck Experiments

Detonating solid plastic bonded explosives (PBX) formulated with the insensitive molecule triaminotrinitrobenzene (TATB) exhibit measurable reaction zone lengths, curved shock fronts, and regions of failing chemical reaction at abrupt changes in the charge geometry. A recent set of “hockey puck” experiments measured the breakout times of diverging detonation waves at ambient temperature LX‐17 (92.5% TATB plus 7.5% Kel‐F binder) and the breakout times at the lower surfaces of 15 mm thick LX‐17 discs placed below the detonator‐booster plane. The LX‐17 detonation waves in these discs grow outward from the initial wave leaving regions of unreacted or partially reacted TATB in the corners of these charges. This new experimental data is accurately simulated for the first time using the Ignition and Growth reactive flow model for LX‐17, which is normalized to detonation reaction zone, failure diameter and diverging detonation data. A pressure‐cubed dependence for the main growth of reaction rate yields excellent agreement with experiment, while a pressure‐squared rate diverges too quickly and a pressure‐quadrupled rate diverges too slowly into the LX‐17 below the booster equatorial plane.     

Determination of Critical Conditions for Detonation Initiation in a Finite Volume by a Converging Shock Wave

Direct initiation of spherical and cylindrical detonation in a stoichiometric hydrogen–air mixture under normal conditions by a collapsing low-pressure region (cavity) in a space bounded by a rigid shell is considered. The study of the flow with allowance for the actual mechanism of chemical reactions was performed using the finite-difference method based on the Godunov scheme, with a moving computational grid and explicit capturing of the leading shock wave and contact surface. It is established that, for a fixed pressure in the collapsing region and for its radius equal to or exceeding the known critical radius for an unbounded space, there exists a minimum (critical) shell radius, on exceeding which a detonation wave emerges in the flow field under study. In the case of spherical symmetry, the excess internal energy of the spherical layer between the shell and the low-pressure region to be spent on initiation of detonation burning attains a minimum value that far exceeds the critical energy for detonation initiation by a TNT charge in an unbounded space. Key words: discontinuity decay, hydrogen–air mixture, detonation, shock wave, critical initiation energy.     

壳体厚度和爆炸深度对水下爆炸冲击波的影响

根据Cole水下爆炸冲击波经验公式和C-J爆轰理论,用AUTODYN软件对带壳小药量装药水下爆炸进行数值模拟,计算了不同壳体厚度的TNT水下爆炸冲击波压力峰值,得到带壳装药水下爆炸冲击波峰值压力的拟合公式,分析了冲击波随装药壳厚与半径比以及爆炸深度的变化规律.结果表明,带壳装药水下爆炸的冲击波峰值压力随壳厚与装药半径比...     

低附带毁伤弹药爆炸威力的理论分析与试验研究

为适应现代反恐作战的需求,提出了一种新型低附带毁伤弹药,根据爆炸力学相关理论建立了杀伤元抛撒速度与复合材料外壳、装药三者之间的关系模型.通过静爆试验,利用压力传感器测试出3种不同装药爆炸后的超压曲线.结果表明,从压力曲线来看复合材料外壳装药与纯炸药、发泡塑料外壳装药爆炸产生的冲击波超压曲线不同,正压作用时间长.最后得出,与传统杀爆弹相比低附带毁伤弹的杀伤区域较小,而在较小的杀伤区域内杀伤效应更强.     

Preparation and Properties of An Insensitive Booster Explosive Based on LLM‐105

A new insensitive booster explosive based on 2,6‐diamino‐3,5‐dinitropyrazing‐1‐oxide (LLM‐105) was prepared by a solvent‐slurry process with ethylene propylene diene monomer (EPDM) as binder. SEM (scanning electron microscopy) was employed to characterize the morphology and particle size of LLM‐105 and molding powder. The mechanical sensitivity, thermal sensitivity, shock wave sensitivity, and detonation velocity of the LLM‐105/EPDM booster were also measured and analyzed. The results show that both mechanical sensitivity and thermal sensitivity of LLM‐105/EPDM are much lower than that of conventional boosters, such as PBXN‐5 and A5. Its shock wave sensitivity is also lower than that of PBXN‐5 and PBXN‐7. When the density of charge is 95 % TMD, its theoretical and measured detonation velocities are 7858 m s⁻¹ and 7640 m s⁻¹, respectively. These combined properties suggested that LLM‐105/EPDM can be used as an insensitive booster.     

Detonation Failure Characterization of Homemade Explosives

Typically characterizing home made explosives (HMEs) requires many large scale experiments, which is prohibitive given the large number of materials in use. A small scale experiment was developed to characterize HMEs such as ammonium nitrate‐fuel oil mixtures. A microwave interferometer is applied to small scale confined transient experiments, yielding time resolved characterization of a failing detonation that is initiated with an ideal explosive booster charge. Experiments were performed with ammonium nitrate and two fuel compositions (diesel fuel and mineral oil). It was observed that the failure dynamics were influenced by factors such as the chemical composition, confiner thickness, and applied shock wave strength. Thin steel walled confiners with 0.71 mm wall thickness experienced detonation failure and decoupling of the shock wave from the reaction zone. Confiners with a wall thickness of 34.9 mm showed a decrease in propagation speed and a steady reactive wave was achieved. Varying the applied shock strength by using an attenuator showed corresponding changes in the initial overdriven reactive wave velocity in the HMEs. The distance to detonation failure was also shown to depend on the attenuator length when thin wall confinement was used. This experimental method is shown to be repeatable and can be performed with little required material (about 2 g). The data obtained could be useful to model development and validation, as well as quantifying detonability of materials.     

Discussion of the Experimental Findings from the initiation of covered,but unconfined high explosive charges with shaped charge jets

The results of experiments on the initiation of covered, but unconfined high explosive charges with shaped charge jets from Chick and Hatt, which have been diagnosed by the flash X-ray technique, as well as the author's own experiments in which the build-up distances and the run-up times have been recorded by means of a rotating-mirror camera in the framing and streak modes, are analyzed and explained in detail in this paper. Build-up distances and run-up times versus the residual jet velocity, or versus the dynamic pressure, are in fairly good agreement, despite the somewhat different shaped charges and acceptor charges that have been used in the two approaches. The greater initiability of an acceptor charge behind a barrier, but with an air gap between, is attributed less to a precursor shock that desensitizes the high explosive charge which is in contact with a barrier, but rather to the higher velocity of the free shaped charge jet and, particularly, to the area loading on a high explosive charge with an air gap in front.