Ignition and Growth Modeling of Shock Initiation of Different Particle Size Formulations of PBXC03 Explosive

The change in shock sensitivity of explosives having various explosive grain sizes is discussed. Along with other parameters, explosive grain size is one of the key parameters controlling the macroscopic behavior of shocked pressed explosives. Ignition and growth reactive flow modeling is performed for the shock initiation experiments carried out by using the in situ manganin piezoresistive pressure gauge technique to investigate the influences of the octahydro-1,3,5,7–tetranitro-1,3,5,7-tetrazocine (HMX) particle size on the shock initiation and the subsequent detonation growth process for the three explosive formulations of pressed PBXC03 (87% HMX, 7% 1,3,5-trichloro-2,4,6-trinitrobenzene (TATB), 6% Viton by weight). All of the formulation studied had the same density but different explosive grain sizes. A set of ignition and growth parameters was obtained for all three formulations. Only the coefficient G₁ of the first growth term in the reaction rate equation was varied with the grain size; all other parameters were kept the same for all formulations. It was found that G₁ decreases almost linearly with HMX particle size for PBXC03. However, the equation of state (EOS) for solid explosive had to be adjusted to fit the experimental data. Both experimental and numerical simulation results show that the shock sensitivity of PBXC03 decreases with increasing HMX particle size for the sustained pressure pulses (around 4 GPa) as obtained in the experiment. This result is in accordance with the results reported elsewhere in literature. For future work, a better approach may be to find standard solid Grüneisen EOS and product Jones-Wilkins-Lee (JWL) EOS for each formulation for the best fit to the experimental data.     

GAP/CL-20-Based Compound Explosive: A New Booster Formulation Used in a Small-Sized Initiation Network

With ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and glycidyl azide polymer (GAP) as the solid filler and binder, respectively, GAP/CL-20-based compound explosives were designed and prepared. Using micro injection charge technology, the compound explosives were packed into small grooves to explore their application in a small-sized initiation network. The detonation reliability, detonation velocity, mechanical sensitivity, shock sensitivity, and brisance of the explosive were measured and analyzed. The results show that when the solid content of CL-20 is 82 wt%, the explosive charged in the groove has a smooth surface from a macroscopic view. From a microscopic view, a coarse surface is bonded with many CL-20 particles by GAP binder. The GAP/CL-20-based explosive charge successfully generates detonation waves in a groove larger than 0.6 mm × 0.6 mm. When the charge density in the groove is 1.68 g·cm^?3 (90% theoretical maximum density), the detonation velocity reaches 7,290 m·s^?1. Moreover, this kind of explosive is characterized by low impact and shock sensitivity.     

Shock initiation of TATB/FEFO formulations

Abstract

The shock initiation properties of transferable insensitive explosive (TIE) formulations based on the solid high explosive, triaminotrinitrobenzene (TATB), and the liquid explosive, bis(2-fluoro-2,2-dinitroethyl) formal (FEFO), are measured by wedge test, embedded particle velocity gauge and embedded manganin pressure gauge techniques and calculated using the Ignition and Growth reactive flow model. These extrudable formulations are demonstrated to be slightly more shock sensitive than the TATB/inert binder explosive, LX-17. However, the TIE formulations are much less sensitive than HMX-based explosives and still qualify as insensitive explosives in safety and hazard tests. The wedge tests showed a very steep dependence of run distance to detonation on the input shock pressure. Embedded gauge and reactive flow modeling results imply that shock initiation begins when a small amount of the solid TATB decomposes rapidly enough to heat the surrounding FEFO to decomposition temperature. The FEFO then reacts rapidly, raising the pressure and temperature sufficiently to cause surface decomposition of the TATB particles at rates comparable to those measured in other TATB-based explosives. An Ignition and Growth reactive flow model for TIE based on these assumptions yields reasonable agreement with the experimental shock initiation data.     

Numerical modeling of the effect of temperature and particle size on shock initiation properties of HMX and TATB

Abstract

The three-dimensional Eulerian reactive hydrodynamic code 3DE has been used to investigate the effects of particle size (and the remaining void or hole size) and of initial temperature on the shock initiation of heterogeneous explosive charges of HMX and TATB.

Shocks interacting with HMX and TATB containing various hole sizes have been modeled. The void fraction was held at 0.5% while the spherical hole sizes were varied from 5.0- to 0.00005 mm radius. The shock pressure was also varied.

As the hole size in TATB was varied from 5.0 to 0.5 mm, the explosive became more sensitive to shock. Decreasing the hole size to 0.0005 mm resulted in failure of the shock wave to build toward a propagating detonation. This is similar to the results previously reported for TNT.

HMX became more sensitive to shock as the hole size was varied from 0.5 to 0.005 mm. The hole size had to be decreased to 0.0005 mm before the explosive became less shock sensitive. Smaller hole sizes (0.00005 mm) resulted in failure of the shock wave to build to detonation.

At the same density, the most shock-sensitive explosive is the one with particle sizes between coarse and fine material. The shock sensitivity of HMX continues to increase with decreasing hole sizes for hole sizes where TNT or TATB fail.

The shock sensitivity of TATB, TNT, and HMX increases with initial temperature. TATB at 250°C is as shock-sensitive as HMX at 25°C. This is in agreement with experimental observations. The shock sensitivity of HMX is less dependent on temperature than TATB or TNT.     

Shock Initiation Characteristics of an Aluminized DNAN/RDX Melt-Cast Explosive

Shock sensitivity is one of the key parameters for newly developed, 2,4-dinitroanisole (DNAN)-based, melt-cast explosives. For this paper, a series of shock initiation experiments were conducted using a one-dimensional Lagrangian system with a manganin piezoresistive pressure gauge technique to evaluate the shock sensitivity of an aluminized DNAN/cyclotrimethylenetrinitramine (RDX) melt-cast explosive. This study fully investigated the effects of particle size distributions in both RDX and aluminum, as well as the RDX’s crystal quality on the shock sensitivity of the aluminized DNAN/RDX melt-cast explosive. Ultimately, the shock sensitivity of the aluminized DNAN/RDX melt-cast explosives increases when the particle size decreases in both RDX and aluminum. Additionally, shock sensitivity increases when the RDX’s crystal quality decreases. In order to simulate these effects, an Ignition and Growth (I&G) reactive flow model was calibrated. This calibrated I&G model was able to predict the shock initiation characteristics of the aluminized DNAN/RDX melt-cast explosive.     

基于HMX/HNS组合的双层装药射孔弹实验研究

为研究石油射孔弹装药对药型罩爆轰驱动的聚能射流形态和参数,提出一种高性能双层装药射孔弹,通过少量的高爆速辅助炸药改变原主炸药的从起爆端依次传爆的顺序,部分主炸药被几乎同时激发,增大主炸药对药型罩作用的压跨角,提高了原低爆速主炸药的能量利用率。设计3种类型的双层装药射孔弹,由2种炸药组成:一种为爆速高的HMX辅助炸药,一种为爆速较低的HNS主炸药。初步实验验证,装填HMX/HNS炸药的双层装药射孔弹钢靶平均穿深最大提高23.5%,混凝土靶平均穿深最大提高19.6%。基于HMX/HNS组合的双层装药射孔弹模拟计算和实验结果,研究了HMX/RDX组合的双层装药射孔弹在3种类型上的表现,其射流的速度和动能相对于原RDX炸药射孔弹提高较小,实验钢靶、混凝土靶平均穿深最大提高分别只有9.1%、11%。对比HMX/HNS组合与HMX/RDX组合可知,双层装药的射孔弹性能同辅助炸药与主炸药爆速差有重要的关系。     

Reaction Buildup of PBX Explosives JOB-9003 under Different Initiation Pressures

Aluminum-based embedded multiple electromagnetic particle velocity gauge technique has been developed in order to measure the shock initiation behavior of JOB-9003 explosives. In addition, another gauge element called a shock tracker has been used to monitor the progress of the shock front as a function of time, thus providing a position-time trajectory of the wave front as it moves through the explosive sample. The data are used to determine the position and time for shock to detonation transition. All the experimental results show that: the rising-up time of Al-based electromagnetic particle velocity gauge was very fast and less than 20 ns; the reaction buildup velocity profiles and the position-time for shock to detonation transition of HMX-based PBX explosive JOB-9003 with 1–8 mm depth from the origin of impact plane under different initiation pressures are obtained with high accuracy.     

Shock sensitivity of blasting explosive cartridges

Abstract

The undersand variable gap–initiator test was applied to most Japanese blasting explosive cartridges and found useful as the sensitivity test for the cartridges. The recent Japanese watergel and emulsion explosives were shown to be more shock–sensitive than previous ones. The blast noise in the undersand explosion was shown to decrease when the depth of sand cover the cartridge was increased. For 100g of explosive, a sand layer 20cm deep was effective in reducing the blast noise, when the depth of the sand layer was increased, there was no additional effect. All blasting explosives excluding Kuro Carlit were not ignited by a small gas flame. A cartridge of 100g Kuro Carlit was ignited undersand but did not show the phenomenon of deflagration to detonation     

Empirical estimate of detonation parameters in condensed explosives

Abstract

Based on the available data base on the detonation parameters of existing explosives, an observation was made that by proper normalization with the dynamic pressure - ρ_oD² the Chapman-Jouguet states of all explosives converge to a single generic point in the pressure-specific volume plane. With the exception of very few explosives, this point in P-V plane has a variance of less than 1 %. The pressure-particle velocity (P-Up) plot of all Chapman-Jouguet states revealed a simple quadratic relationship between P and Up which, together with the nondimensional identities of the generic point, led to a simple relationship between the initial density (ρ_o) of an explosive and its detonation velocity (D).

Thus, having the values of ρ_o and D of any explosive, one can easily estimate all of its detonation parameters (P_CJ, U_CJ, V_CJ, and Γ_CJ) with an accuracy of less than 3%. However, if the detonation velocity is also not known, it too can be estimated quite accurately, increasing the margin of uncertainty to about 10%.     

Microstructure effects on the detonation velocity of a heterogeneous high-explosive

ABSTRACT

Although numerous methods exist for the theoretical calculation of detonation parameters of explosives, few thermodynamic-hydrodynamic-based theoretical codes take into account particle size. The basis for their computational analysis is primarily focused on the equation of state of the detonation products, heat of formation, and density of the explosive composition. This study utilized regression analysis to model the relationship between the microstructure characteristics and detonation velocity of a heterogeneous high-explosive composition containing cyclotrimethylene-trinitrmaine (RDX). The principal characteristics examined were the average particle size of RDX, amount of HMX impurity within the RDX particles, method of RDX manufacture, and compositional density. Statistical analysis demonstrated the relevancy of the microstructure influence on the detonation velocity of the developed experimental compositions of 73 wt. % solids and 27 wt. % polyurethane binder. An equation is developed that accurately predicts detonation velocity based on average particle size, density, and manufacturing process for RDX. The model underscores the significance of the relationship between the average particle size and detonation velocity. Compositions containing smaller average particle sizes of RDX generate higher detonation velocities. A 100 micron increase in the average particle size was shown to decrease detonation velocity by 161 m/s for the monomodal polyurethane compositions used in this study. The relevance of using statistical models for selecting characteristics that result in optimum explosive performance is addressed.     

A novel method for prediction of the critical diameter of solid pure and composite high explosives to assess their explosion safety in an industrial setting

ABSTRACT

For the explosion safety assessment in an industrial setting, the knowledge of critical diameter of high explosives provides important information on the sensitivity and conditions whereby detonations are likely to occur. The critical diameter or failure diameter is the minimum diameter of a cylindrical charge of high explosive which sustains a high order steady-state detonation. Available predictive methods require complex models, which are based on complicated variables such as the shock adiabat, and the generalized kinetic characteristic of decomposition of a high-explosive charge under shock-wave compression. For the first time, this paper describes a novel simple method for assessment of the critical diameter of pure and composite CHNO high explosives. The new model is based on the contribution of the number of nitrogen and oxygen atoms as well as some conditions, which are based on shock sensitivity, impact sensitivity and the negative values for core critical diameter of the desired explosives under certain situations. Experimental data of 42 high explosives have been used to derive and test the new model. The predicted critical diameters for building the model (29 explosives) and the test set (13 explosives), under the unconfined condition of these explosives, have the values of root-mean-square deviation (RMSD) of 5.14 and 3.96 mm, respectively.     

Modelling of the underwater shock sensitivity of polyurethane FOAM / PETN explosives

Abstract

The underwater shock sensitivity of a Polyurethane Foam / PETN explosive system was investigated using the Forest Fire model. Pop plots for the explosive were determined by conducting calibrated gap tests. Wedge tests were used but proved extremely difficult to control due to the inhomogeneity of the explosive, its low detonation performance and its high sensitivity. Numerical modelling of calibrated gap tests and underwater gap sensitivity experiments yielded results very close to the experimental ones indicating that the technique is applicable to the low density - low impact pressure regimes.     

Reaction Characteristic for Various Scale Explosive under Mild Impact

This work presents a varying trend of impact ignition threshold denoted by minimum impact velocity to trigger an ignition when the scale of the explosive changes. The effects of explosive scale factors on impact-induced reaction degree were investigated using Steven tests and numerical simulation for polymer-bonded explosive-C03 (a cyclotetramethylene tetranitramine [HMX]-based explosive) impacted by projectiles of various velocities. Two scale factors—that is, axial thickness and radius—were studied through various scale samples including Φ98 mm × 13 mm, Φ98 mm × 39 mm, Φ140 mm × 13 mm, and Φ140 mm × 39 mm. The velocities of projectiles and the impact and ignition processes were analyzed using a high-speed camera. The pressure histories were measured by embedded manganin pressure gauges and poly vinylidene fluoride stress gauges. The reaction overpressures of the explosive were obtained by blast pressure gauges to evaluate the reaction degree. The effects of explosive scale factor on reaction degree and characteristics under mild impact were summarized. In a certain range (larger than the diameter of the impact projectile), different sample diameters do not influence the velocity threshold, but the thickness of the samples does; that is, the velocity threshold increases with the thickness of the sample. The study also indicates that the ignition and explosion in Steven tests are mainly triggered by the overlapping of direct impact and reflected stress waves. Our numerical simulations results of pressure and ignition times are consistent with the experimental data. The obtained knowledge can be used to evaluate the safety of different scale HMX-based explosives under accidental impact or falls.     

Composition Choice and Formulation of Three HMX-Based Research Explosives

The composition and formulation for three research explosives having similarities to military explosives are described. The primary energetic ingredient in each is cyclotetramethylene-tetranitramine (HMX), whose particle size is limited to a range of 125–210 μm to reduce variations in shock reactivity and performance. The binder in each explosive is hydroxy-terminated polybutadiene (HTPB). The first composition contains only these two components. Aluminum with a nominal particle size of 5 μm is incorporated into the second composition. The third composition contains ammonium perchlorate (AP) with a nominal particle size of 200 μm in addition to the aluminum. The explosives are designed with features to allow for comparisons in shock reactivity and performance and to elucidate the roles of HMX, Al, and AP.     

Thermal Behaviors and Their Correlations of Mg(BH4)2-Contained Explosives

In order to explore the effect of metal hydride on energetic materials’ thermal behaviors and their correlations, we studied the heats of combustion and detonation of RDX, TNT, and Mg(BH₄)₂-containing explosives both theoretically and experimentally. The results showed that Mg(BH₄)₂ can significantly improve the energy of explosive. As the mass fraction of Mg(BH₄)₂ increases, the combustion heat of composite explosives increases gradually, while the combustion efficiency decreases. When its mass fraction is about 30%, the theoretical heats of detonation of RDX/Mg(BH₄)₂ and TNT/Mg(BH₄)₂ reach maximum, which are 7418.47 and 7032.46 kJ/kg, respectively. When we compared the errors between calculation and experimental values, we found that L-C method is more accurate in calculating oxygen-enriched and oxygen-balanced explosives, and that minimum free energy method is more suitable for seriously negative oxygen-balanced explosive. For single explosive, there are three kinds of relationships between heat of combustion and detonation according to the oxygen balance. For Mg(BH₄)₂-containing explosives, the relationship is in accordance with Boltzmann function.     

The influence of temperature on the detonation velocity of selected emulsion explosives

ABSTRACT

Many years of research on more effective and safer explosives led to the development of emulsion explosives. They are the second most commonly used group of explosives in the world, primarily due to the fact that they are a good alternative to ANFO explosives or dynamites. Their key advantage in underground applications is the lower content of toxic fumes in the detonation products. Emulsions are also characterized by high detonation velocity, high water resistance, low value of critical diameter and mechanical loading capacity. Multiple factors related to the applied mining method influence the detonation parameters of emulsion explosives. One such parameter is the time between the loading of the explosive into the blast hole and firing, which in the case of underground copper mines in Poland can even last up to 48 hours. This becomes a particularly significant issue due to the increasing depth of mining in Polish copper mines and the high virgin temperature of rock mass at these depths. Experiences related to the use of explosives and their efficiency under such conditions confirm the intuitive thesis that high ambient temperature has a negative impact on the explosives’ effectiveness. In this regard, research concerning the influence of temperature on the detonation velocity of selected emulsion explosives was carried out, including bulk and packaged explosives. The tests were performed for different conditioning temperatures, which are all locally observed in Polish copper mines. The obtained results confirmed the significant influence of temperature on the velocity of detonation of the considered explosives.     

Explosion Power and Pressure Desensitization Resisting Property of Emulsion Explosives Sensitized by MgH2

Due to low detonation power and pressure desensitization problems that traditional emulsion explosives encounter in utilization, a hydrogen-based emulsion explosives was devised. This type of emulsion explosives is sensitized by hydrogen-containing material MgH₂, and MgH₂ plays a double role as a sensitizer and an energetic material in emulsion explosives. Underwater explosion experiments and shock wave desensitization experiments show that an MgH₂ emulsion explosives has excellent detonation characteristics and is resistant to pressure desensitization. The pressure desensitization–resistant mechanism of MgH₂ emulsion explosives was investigated using scanning electron microscopy.     

Jet initiation and penetration of explosives

Abstract

The two-dimensional Eulerian hydrodynamic code 2DE, with the shock initiation of heterogeneous explosive burn model called Forest Fire, is used to model numerically the interaction of jets of steel, copper, tantalum, aluminum, and water with steel, water, and explosive targets.

The calculated and experimental critical condition for propagating detonation may be described by the Held V² d expression (jet velocity squared times the jet diameter). In PBX 9502, jets initiate an overdriven detonation smaller than the critical diameter, which either fails or enlarges to greater than the critical diameter while the overdriven detonation decays to the C-J state. In PBX 9404, the jet initiates a detonation that propagates only if it is maintained by the jet for an interval sufficient to establish a stable curved detonation front.

The calculated penetration velocities into explosives, initiated by a low-velocity jet, are significantly less than for non-reactive solids of the same density. The detonation products near the jet tip have a pressure higher than that of nonreactive explosives, and thus slow the jet penetration. At high jet velocities, the calculated penetration velocities are similar for reactive and inert targets.     

Study of continuous velocity probe method for the determination of the detonation pressure of commercial explosives

ABSTRACT

A novel velocity probe, which permits recording the continuous velocities of detonations and shock waves, has been developed based on the transition of operation principle from ionization to pressure-conduction. Using the new probe and the impedance matching method, a series of measuring devices were set up to obtain the shock wave velocities in different inert materials, i.e., water, Plexiglas and paraffin wax. Two test types of powder ammonium nitrate/fuel oil (ANFO), exposed on the ground and tamped in the blast hole, were performed, from which we calculated their detonation pressures, with a density of approximately 0.86 g·cm^?3, ranged from 3.52 GPa to 3.65 GPa, and the adiabatic exponents from 2.24 to 2.30. The results show that the present velocity probe-based method can be used to determine the detonation pressure of commercial explosives conveniently and reliably, which is an important supplement for the testing techniques of explosive performance.     

Preparation and thermal properties study of HNIW/FOX-7 based high energy polymer bonded explosive (PBX) with low vulnerability to thermal stimulations

ABSTRACT

For modern munitions, high energy explosives are expected to reduce vulnerability and improve safety. In this study, based on the formulation of PAX-11 (94 wt% HNIW, 2.4 wt% CAB, 3.6 wt% BDNPA/F), FOX-7 is used as a portion replacement for HNIW to decrease vulnerability. To further decrease mechanical sensitivities and prevent static electricity, 0.5 wt% graphite is added to the surface of PBXs. A series of HNIW/FOX-7 based polymer bonded explosives (PBXs) with different formulations are prepared and mechanical sensitivities, thermal stabilities, detonation velocities, and slow cook-offs are studied to evaluate the energy and hazard of these PBXs. Additionally, finite element numerical simulations are utilized to study the transient temperature distributions, ignition time and ignition locations of the PBX cylinders during slow cook-off. Based on the results of this study, we obtain a high energetic low vulnerable PBX formulation (54 wt% HNIW, 40 wt% FOX-7, 2.4 wt% CAB, 3.6 wt% BDNPA/F, 0.5 wt% additional graphite) that balances energy and vulnerability. This formulation passes the slow cook-off test and detonation velocity reaches 8776 m·s^?1, which can be used in the warhead of the high explosive anti-tank cartridge.