Shock Compression and Initiation of LX-10

LX-10 is a high energy density solid explosive consisting of 94.5% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 5.5% Viton A Binder pressed to 1.865 g/cm³ (98.4% of theoretical maximum density). In this paper the shock compression and initiation of chemical reaction in LX-10 by sustained shock pressures of 0.4 to 3 GPa are studied experimentally using embedded pressure and particle velocity gauges. The resulting pressure and particle velocity histories are evaluated theoretically using the ignition and growth reactive flow computer model of shock initiation and detonation. Manganin resistance and polyvinylidene fluoride (PVF₂) ferroelectric pressure gauges are both employed in the low pressure (0.4 – 0.7 GPa) shock compression experiments. Multiple manganin pressure and multiple electromagnetic foil particle velocity gauges measure the growth of reaction at various positions in LX-10 shocked to 1 – 3 GPa. The reactive flow modeling results imply that less than one percent of the LX-10 shocked to 0.4 – 0.7 GPa reacts in fifteen microseconds. For the higher pressure experiments, the ignition and growth model accurately calculates the pressure and/or particle velocity buildup in LX-10 as the reaction grows toward detonation. The LX-10 calculations are compared to those for the well-calibrated explosive PBX-9404, which contains 94% HMX and a reactive binder. Since it has the inert binder Viton A and better mechanical properties than PBX-9404, LX-10 is demonstrated to be significantly less reactive than PBX-9404 at these shock pressures. Therefore LX-10 is safer than PBX-9404 in many hazard and vulnerability scenarios to which solid explosives may be subjected.     

Approximate Method of Calculating Critical Shock Initiation conditions and run distance to detonation

An approximate model for pressure buildup behind the front of an initiating shock wave is developed. This model leads to the widely used P²t initiation criterion, but the pressure index is not limited to a value of two. Expressions for wave run time and distance to detonation are also obtained. The use of the model is illustrated using explosives widely discussed in the literature. It is shown that critical shock initiation and run distance to detonation can be rapidly estimated to good approximation over a wide range of shock conditions from the results of one or two relatively simple experiments. The calculational method may be useful for various applications.     

Investigation of shock detonation of TATB using proton radiography

The initiation of detonation of plasticized TATB by shock loading using an initiator pressure charge of an HMX based explosive was studied by radiography. In the experiments, the size of the initiator and the initial density of the TATB charge were varied. During initiation of TATB detonation, part of the material did not react, forming so-called dark zones. As the process goes on, the detonation wave bends around the dark zones, without initiating the material within them. The evolution of the area of dark zones was compared for samples of different initial density and initiators of different sizes. The characteristic boundaries and X−t diagrams of detonation front propagation under different loading conditions were constructed from images of the explosive process. Density distributions behind a divergent detonation wave front at different times were obtained and analyzed.     

PBX-9404和PBX-9502炸药拐角性能的数值模拟

借助于有限元动力学软件LS-DYNA,通过Mushroom试验模拟,研究了PBX-9404和PBX-9502的拐角性能.结果显示,在相同试验条件下,PBX-9502的出射角小于PBX-9404,PBx-9502具有明显的死区,表明PBx-9404的拐角性能优于PBx-9502.传爆药直径和炸药半球直径变化对表征炸药拐角...     

FOX-7和RDX基含铝炸药的冲击起爆特性

为研究FOX-7和RDX基含铝炸药的冲击起爆特性,对其进行了冲击波感度试验和冲击起爆试验,结合冲击波在铝隔板中的衰减特性,确定了FOX-7和RDX基含铝炸药的临界隔板值和临界起爆压力,并通过锰铜压阻传感器记录了起爆至稳定爆轰过程压力历程的变化。结果表明,以Φ40mm×50mm的JH-14为主发装药时,FOX-7和RDX基含铝炸药临界隔板值分别为37.51和34.51mm,对应的临界起爆压力为10.91和11.94GPa;起爆压力为11.58GPa时,FOX-7炸药的到爆轰距离为25.49~30.46mm,稳定爆轰后的爆轰压力为27.68GPa,爆轰速度为8 063m/s;起爆压力为14.18GPa时,RDX基含铝炸药的到爆轰距离为17.27~23.53mm,稳定爆轰后的爆轰压力为17.16GPa,爆轰速度为6 261m/s。     

Desensitization of pressed RDX/paraffin and HMX/paraffin compounds by multiple shock waves

Multiple shock initiation of detonation in pressed RDX/paraffin and HMX/paraffin compounds is studied. If the explosive is preshocked by a weak shock wave, the effect of desensitization is observed, which is detectable by two features. First, a weak reaction appears behind the second shock wave. Second, the run to detonation increases by 100% for pressed RDX. Experiments with the samples of pressed RDX show that the run to detonation in preloaded explosive can be estimated from the distance at which the second shock wave overtakes the first weak shock; the run to detonation expected for the second shock wave, from Pop-plot data.Novosibirsk. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 2, pp. 114–124, March–April, 1995.     

起爆方式对杆式弹丸成型和穿甲的影响

用LS—DYNA软件模拟了中心点起爆、平面起爆和环形起爆方式下所形成的爆轰波波阵面、压力场及杆式弹丸的外形和速度分布。结果表明,平面起爆和环形起爆方式下形成的爆轰波对药型罩的压垮角小而压垮速度大,最终所形成的高速杆式弹丸速度和长径比都优于中心点起爆。采用实验方法研究了中心点起爆、环形起爆和三点同时起爆以及不同起爆半径对高速杆式弹丸的速度和穿甲能力的影响。实验结果表明,环形起爆和三点起爆后的弹丸速度和穿甲深度明显优于中心点起爆,大环起爆优于小环起爆,但对弹丸形状和穿孔孔径影响不明显。     

Shock Initiation of the CL‐20‐Based Explosive C‐1 Measured with Embedded Electromagnetic Particle Velocity Gauges

Hexanitrohexaazaisowurtzitane (CL‐20) is a high‐energy material with high shock sensitivity. The evolution of shock into the detonation of CL‐20 deserves academic attention and research. An embedded electromagnetic particle velocity gauge was used to study the shock initiation of detonation in a pressed solid explosive formulation, C‐1, containing 94 wt‐% epsilon phase CL‐20 and 6 wt‐% fluororubber (FPM). In conventional experiments, the magnetic field was generated using a pair of electromagnets with a complex structure and operation. A new device was designed to solve complex problems. This device comprised NdFeB magnets, pole shoes and magnetic yokes; using this technique, a uniform magnetic field could be created. A series of shock initiation experiments on high‐explosive C‐1 was performed, and the explosive samples were initiated at different intensity input shocks by an explosive driven flyer plate. In situ magnetic particle velocity gauges were utilized to detail the growth from an input shock to detonation, and the attenuation of particle velocity in unreacted C‐1 was also obtained in low‐intensity shock initiation experiments. Hugoniot data for C‐1 in the form of shock velocity D vs. particle velocity Up were obtained. A simulation model for shock initiation of C‐1 was established, and the particle velocity data from several experiments were used to determine the parameters required for the unreacted equation of state and ignition and growth reactive flow model for C‐1. These coefficients were then applied in the calculation of the initial shock pressure−distance to detonation relationship (Pop‐plot) for the explosive. Based on the results of experiments and simulations, the shock sensitivity characteristic of C‐1 was described.     

Time Resolved Pressure Measurement of the Initiation in Gap Test Experiments

Time resolved measurement of shock pressures in high explosives is possible with inexpensive composite carbon resistors. These resistors are embedded plane to the surface of a Plexiglas slab fixed at the end of the explosive. This configuration was used with gap test experiments with a 10 g donor charge. No initiation delay is measured in Seismoplast I (plastic PETN) up to a gap height of 10 mm PMMA (Plexiglas) due to the time resolution of the measuring system. From 10 mm to 22.5 mm gap height distances for detonation development up to 25 mm are found. For even greater gap heights a shock wave with decreasing amplitude occurs. The detonation development can be explained by the measured structure of the shock waves. Behind a first shock front with nearly constant pressure a second front propagates with increasing pressure which at last catches up with the first and then the pressure increases further up to the Chapman-Jouguet pressure of 160 kbar. At a gap height of 25 mm a stationary shock wave configuration with amplitudes of 20 kbar and 30 kbar was observed.     

Numerical simulation of multi-layer flyer impact initiation of a certain PBX explosive

This paper addresses the problem of multi-layer flyer impact-induced initiation of a high-energy explosive PBX-1(based on 95 % TATB). The CREST reaction combustion model based on the time-step difference method is embedded in LS-DYNA, and the pressure history of PBX-1 in multiple impact initiation is numerically simulated. The strengths and weaknesses of the two models are analyzed by comparing the simulation results of the pressure-based IG model and the entropy-based CREST model in multiple impact initiation. The results show that the CREST model is significantly better than the IG model in the problem of multiple impact initiation of PBX-1, and it matches the experimental results better.     

Application of Crystal Lattice Disintegration Criteria to Compute Minimum Shock induced reactive conditions in solid explosives and inert materials

A threshold particle velocity criteria derived by E.R. Fitzgerald for the beginning of crystal lattice breakup and disintegration has been applied to shocked explosives and an inert material. In shocked explosives, reactions leading to detonation occur above a certain “threshold” magnitude. The computed crystal lattice breakup shock pressures compare rather well with observed experimental “threshold” shock pressures for six high explosives. The six explosives are: Comp-B3, Comp-B, TNT, PBX-9404, Tetryl, and H-6. In addition, the crystal lattice breakup criteria provides an explanation for the observed lowering of the detonation “threshold” shock pressure as the explosives are made more porous or less dense. Finally, the shock pressures, at which output from thermocouples embedded in shocked materials (PBX-9404 and Plexiglass) increases dramatically, compare favorably with predictions based on crystal lattice disintegration criteria. Consequently, it is tentatively concluded that crystal lattice breakup, or self-sustained phonon fission as Fitzgerald calls it, is responsible for the initiation of detonation in shocked explosives and enhanced thermocouple output in shocked materials. It is also postulated that the lattice breakup phenomena is also responsible for phase changes, increased chemical reactivity, and anomalous electrical activity which are observed in certain inert materials under relatively low level shock loading.     

Shock to Initiation Characters of Heated Explosives with Different Confinement

Heated explosives might undergo thermal expansion and/or phase transition, which affects their shock sensitivity. Therefore, investigating the effect of temperature on the shock initiation properties of explosives would provide valuable safety guidelines for their transportation and handling. In this study, an experimental detonation device that achieved homogeneous heating of the explosive test sample while avoiding unintended heat transfer to the donor was designed and constructed. The device allowed to perform flyer impact tests on PBXC10 at different temperatures and using different confinement conditions. The generated experimental pressure history curves were used to calculate the parameters of the I&G model and determine their relationships with the sample temperature. The fully parameterized I&G model enabled predicting the shock initiation properties of PBXC10 at temperatures where experimental data were unavailable. It was concluded that increased sample temperatures would lead to a shorter run distance to detonation, faster propagation of the detonation wave and enhanced shock sensitivity of the explosive. It was also demonstrated that unconfined PBXC10 exhibited significantly greater shock sensitivity compared to its partially and completely confined counterparts.     

Shock Initiation of PBX-9404 by electrically driven flyer plates

The shock initiation threshold of PBX-9404 has been studied over the pressure range 3.1 GPa-28 GPa with pulse lengths ranging from 0.007 μs-0.63 μs. The short-duration, high pressure pulses were produced by the impact of thin plastic flyer plates accelerated by electrically exploded metal foils. We performed the experiments on explosive pellets 25.4 mm in diameter with thicknesses of 6.0 mm, 10.1 mm and 19.1 mm. No dependence of the initiation threshold on pellet thickness was observed. The data are represented reasonably well by either the critical initiation energy or by the constant P²τ initiation criteria.     

Bubble detonation conditions

Initiation of bubble detonation in the system “inert liquid-explosive gas bubbles” by a detonation wave in a gas was studied experimentally. Compression-wave pressure profiles were determined as functions of the length of the initiation section and the initial pressure of the explosive gas mixture in it. It was shown that because of the effect of the explosive-gas volume between the diaphragm and the upper boundary of the bubble medium, the pressure in front of the initiating wave increased much more slowly than the initial pressure. The optimal length of the initiation section was found, and the critical (minimum) initiation pressure in it and at the shock-wave front were determined. It was found that for a fixed gas volume concentration in the bubble medium, the pressure in the initiation section increased insignificantly as the length of the section decreased. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 84–90, March–April, 2007.     

Bubble detonation as a self-sustained solitary wave with energy release

Previous experiments have shown that a bubble detonation wave is a resonant or self-sustained solitary wave in a bubble medium. Bubble detonation is modeled by a solitary wave with energy release in bubbles. The equation describing a solitary wave of small amplitude is shown to be an analog of nonlinear Boussinesq equation of the fourth order. A comparison of the solution obtained with averaged experimental pressure profiles shows that the analytical solution is suitable for describing bubble detonation waves with a finite pressure amplitude. In the model proposed, the time of action of solitary-wave compression on a separate bubble is several times the bubble oscillation period. This result agrees with experimental data and confirms the presence of a collective resonant effect in a bubble medium. Satisfactory agreement is obtained between experimental and theoretical data on the pressure profile and extent and velocity of bubble detonation waves. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 104–111, November–December, 2007.     

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.     

固体炸药冲击起爆研究

为了研究固体炸药冲击起爆特性,对JO-9159炸药进行了隔板冲击加载实验,用高速摄影方法记录炸药冲击起爆过程;用解析计算方法分析了有机玻璃隔板的临界厚度值;建立了炸药冲击起爆模型,对起爆过程进行了数值模拟,计算了炸药在冲击作用下的压力历史,分析了JO-9159炸药起爆压力阈值和爆轰成长距离。     

大板实验中TATB基炸药爆轰波的传播特征

为研究点起爆条件下TATB基炸药爆轰波传播特征,用双灵敏度激光速度干涉仪(VISAR)对TATB基炸药进行了大板实验研究,并用DYNA2D程序对实验进行了模拟计算.结果表明,大板实验中TATB基炸药爆轰波传播过程中的压力剖面具有"二维结构",且爆轰波传播方向由轴线方向逐渐向半径方向转变.实测铜飞片自由面的速度与计算值相吻合.     

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.     

Critical energy of bubble detonation wave initiation by a wire explosion

Initiation of bubble detonation by a short shock wave generated by exploding a wire located in a chemically active bubbled medium is studied experimentally. Critical energies of detonation initiation are determined for different volume fractions of bubbles. It is demonstrated that this method of initiation transforms the compression wave to a detonation wave at a length of ≈0.3 m. In the case of a wire explosion in a gas-liquid medium, the critical energy of bubble detonation initiation can be reduced by more than two orders of magnitude, as compared with initiation by a gas detonation wave.