Shock Sensitivity of Pressed RDX‐Based Plastic Bonded Explosives under Short‐Duration and High‐Pressure Impact Tests

The shock sensitivities of plastic bonded explosives were studied with a thin flyer impact test by using two types of pressed RDX. The thin flyer, driven by an electrically exploding plasma, exerts a short‐duration, high‐pressure pulse to the samples to trigger a shock‐to‐detonation process. It was found that the duration and magnitude of the incident shock strongly influence the dominant mode of hot‐spot formation, promoting a fast pore collapsing mechanism while suppressing other slower shear or friction mechanisms, as proposed by Chakravarty et al. [1]. The pressed PBX based on reduced sensitivity RDX had higher shock threshold pressure, compared to the pressed PBX based on commercial RDX. The difference was observed even with a certain portion of external extragranular defects. It is postulated that the internal crystal defects are more efficient than the external porosity in terms of the rapid reaction of hot spots.     

塑料黏结炸药JH-94和JO-96的热安全性

借助不同升温速率（β）下,PBX-JH-94和PBX-JO-96的非等温DSC曲线的onset温度（Te）和峰温（Tp）,Kissinger法和Ozawa法求得的热分解反应的表观活化能（EK和EO）和指前因子（AK）,标准方法GJB 772A-97-406．1,401．2和409．1确定的比热容（Cp）、密度（ρ）和热导率（λ）以及分解热（Qd,取爆热之半）数据,用Zhang-Hu-Xie-Li公式、Smith方程和Wang-Du公式求得了PBX-JH-94和PBX-JO-96在β→0时的Te和Tp值（Te0和Tp0）、热爆炸临界温度（Tb）、绝热至爆时间（tTIad）、厚度之半和半径为0．05m的无限长平板和无限长圆柱及球状PBX-JH-94和PBX-JO-96被373K环境包围的热感度概率密度函数S（T）与温度（T）的关系曲线、S（T）-（T）曲线峰值温度（Ts（T）max）及热安全度（SD）和热爆炸临界环境温度（Tacr）。结果表明,无限长平板和无限长圆柱PBX-JO-96的热安全性优于PBX-JH-94,绝热分解至爆炸的加速趋势为后者小于前者。     

The Effect of Pressing Parameters on the Mechanical Properties of Plastic Bonded Explosives

Quasi‐static, uniaxial mechanical properties were measured for a series of PBX 9501 parts that were compacted using a permutation of various pressing parameters. Results were analyzed in terms of specimen density as well as pressing parameters. These data led to a second set of tests where PBX 9501 parts were compacted using various dwell times and temperatures, all other pressing parameters being held constant. Quasi‐static tensile data for these parts indicated that for the given range of parameters and specimen densities, the compaction temperature has a larger effect on the mechanical properties than does the dwell time. Moreover, for the range of parameters used, higher compaction temperatures and lower dwell times gave the compacted part more strength and toughness. Desired mechanical characteristics may be achieved by the appropriate selection of pressing conditions.     

Energetic Materials: Crystallization,Characterization and Insensitive Plastic Bonded Explosives

The product quality of energetic materials is predominantly determined by the crystallization process applied to produce these materials. It has been demonstrated in the past that the higher the product quality of the solid energetic ingredients, the less sensitive a plastic bonded explosive containing these energetic materials becomes. The application of submicron or nanometric energetic materials is generally considered to further decrease the sensitiveness of explosives. In order to assess the product quality of energetic materials, a range of analytical techniques is available. Recent attempts within the Reduced‐sensitivity RDX Round Robin (R4) have provided the EM community a better insight into these analytical techniques and in some cases a correlation between product quality and shock initiation of plastic bonded explosives containing (RS‐)RDX was identified, which would provide a possibility to discriminate between conventional and reduced sensitivity grades.     

Effect of Different Polymeric Matrices on Some Properties of Plastic Bonded Explosives

Matrices based on polyisobutylene (PIB), polymethyl‐methacrylate (PA), Viton A 200, Dyneon FT 2481 (Fluorel), and polydimethyl‐siloxane binders were studied as desensitizers. A series of plastic explosives (PBXs) were prepared, based on four different nitramines, namely RDX (1,3,5‐trinitro‐1,3,5‐triazinane), β‐HMX (β‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane), BCHMX (cis‐1,3,4,6‐tetranitro‐octahydroimidazo‐[4,5‐d]imidazole) and ε‐HNIW (ε‐2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane, ε‐CL‐20), bonded by the matrices mentioned. For comparison, pentaerythritol tetranitrate and certain commercial explosives based on it, Semtex 1A, Semtex 10 and Sprängdeg m/46, were used. Detonation velocities, sensitivities to impact and friction, and peak temperatures of thermal decomposition by differential thermal analysis technique (DTA) for all the explosives studied were determined. Heat of detonation was calculated by means of a thermodynamic calculation program (EXPLO 5 code). Fluoroelastomers have a neutral to positive effect on the thermal stability of nitramines and they have a significant effect on decreasing the friction sensitivity. However, their anti‐impact efficiency is the lowest in this study although they have a positive effect on performance of the corresponding PBXs. PA and PIB matrices markedly decrease thermal stability of nitramines, the anti‐impact influences of PIB‐binders are better than those of PA‐binders, while PA‐binders have a higher anti‐friction effect and slightly less negative influence on the performance of the PBXs in comparison with PIB mixtures. The polydimethyl‐siloxane matrix has a neutral effect on thermal stability of the nitramines studied, it has an influence on the volume thermochemistry of detonation comparable with that of fluoroelastomers although it does not provide comparable performance, and its corresponding PBXs have optimum sensitivity parameters.     

The Effect of Shear Strain on Texture in Pressed Plastic Bonded Explosives

The insensitive explosive PBX 9502 contains 95 wt‐% of TATB crystals and a plastic bonding agent (Kel‐F). The TATB crystals have plate‐like morphology, similar to that of graphite or boron nitride. We have used X‐ray diffraction to measure the preferred orientation (texture) of the TATB crystals in parts fabricated by pressing PBX 9502 powder. Independently, we have used finite‐element calculations to derive the direction and magnitude of the shear imposed during the consolidation of this composite material. Based on our results, we propose that the texture develops because the applied shear causes the TATB crystals to rotate such that their (002) basal planes are parallel to shear planes. The texture predicted by this model agrees qualitatively with that measured at various locations within the PBX 9502 compact. Further validation of this model is obtained by the measurement of the thermal expansion coefficient of PBX 9502, which is highly anisotropic.     

高聚物黏结炸药的冲塞试验研究

用冲塞试验评价大药量装药在撞击、剪切、绝热加热等综合作用条件下的安全性.用火药加速装置对试件加速,并通过高速摄像机拍摄炸药试验件跌落撞靶、点火等试验过程,利用冲击波压力传感器测试冲击波超压表征炸药试验件的反应程度.结果表明,PBX-1炸药在撞靶速度高达37.6 m/s时没有发生反应,且PBX-2炸药在撞靶速度为27.7 m/s时发生了爆燃反应,在撞击速度低于25.5 m/s时未发生反应,说明PBX-2炸药的冲塞试验撞击感度高于PBX-1炸药.     

On the Certification of Bonded Repairs to Primary Composite Aircraft Components

Airworthiness certification is required when bonded repairs are made to primary composite structure in situations where damage has reduced or has the potential to reduce residual strength to below the design ultimate strength. Generally, certification of bonded primary structure poses many difficulties. As most repairs are one-off events meeting these certification requirements is especially challenging since demonstration by testing will generally not be possible or cost-effective. This paper discusses options for addressing the two key issues relating to certification: (a) how to validate initial and enduring bond strength of adhesive bonds, mainly given the inability of conventional non-destructive inspection to provide this assurance and (b) how to develop acceptable generic design allowables for bonded repairs which represent actual failure modes – especially for cyclic loading, since validation by testing of simulated repairs will generally be infeasible. It is concluded that proof testing of bonded repair coupons is a promising approach for validating bond strength and fatigue testing of representative bond joint specimen can provide generic allowables for patch design. For hidden structure or very high value repairs structural health monitoring of repairs based on a strain-transfer approach offers considerable promise.     

Shock compressibility and shock-induced phase transitions of C60 fullerite

Shock compressibility of C₆₀ fullerite and sound velocities in shock-compressed fullerite were experimentally studied at the pressures range up to 50 GPa. In our experiments, we used polycrystalline C₆₀ specimens with a density of 1.64 g/cc. The Hugoniot of C₆₀ fullerite had a set of peculiarities, which may be attributed to a series of polymorphic phase transitions. The jump of sound velocity in shocked C₆₀ at pressure 9 GPa indicates the formation of a rather hard carbon phase. It is possible to assume that it is a polymerized C₆₀ phase. In the region of pressures 9–25 GPa, destruction of this phase and formation of a graphite-like carbon occurs. With further growth of shock pressure, phase transition of the graphite-like carbon to a diamond-like phase is observed with a transition onset pressure 25 GPa. If shock pressures are higher than 33 GPa, Hugoniot of C₆₀ fullerite is determined by the thermodynamic properties of the diamond-like phase.     

Dynamic Compressive Properties of Polymer Bonded Explosives under Confining Pressure

Passively confined dynamic impact experiments on PBX1314 specimens are performed by employing aluminum jackets with split Hopkinson pressure bar. The axial and radial stress history curves are measured in the experiments, and the characterizations of the behavior of PBX1314 under dynamic multi‐axial loads are studied. A constitutive relation is developed for modeling the dynamic mechanical responses of PBX1314 by using the Boltzmann superposition principle with a Prony series representation. The material parameters of PBX1314 can be obtained by fitting the modulus master curve. Detailed finite element simulations of the passively confined tests are carried out to evaluate the measure accuracy of the device to the material mechanical behavior. The correctness of the constitutive relation is verified by comparison the finite element simulations with the experiments. Good agreements are obtained.     

玻璃钢材料的胶接

通过对单一成型法所得玻璃钢制品的简单性和实际使用时的复杂性之间的矛盾进行分析，并结合玻璃钢材料及成型特点，对玻璃钢材料的胶接进行了重新定义；对玻璃钢胶接的优缺点、接头形式和设计原则、接头强度计算、胶接工艺、接头破坏形式和原因，以及对胶接强度的影响因素，诸如：胶粘剂选择、基体材料、表面处理等，做了详细阐述。最后，还根据胶接的工作实践所得，给出了一些实用性较强的经验数据。相信本文对生产实践具有较强的指导作用。     

Migration of Plasticizer between Bonded Propellant Interfaces

Plasticizer migration across bonded propellant interfaces during cure has been shown to have a measurable effect on propellant properties compared to each propellant by itself. This shows that the curing period is significant to the migration phenomenon. The plasticizer migration has been shown to have a direct influence on tensile strength for short aging periods up to the point the plasticizer reaches equilibrium. The tensile data for short aging periods have been shown to follow an empirical equation connecting the physical characteristics of plasticizer migration with increasing propellant tensile strength. The diffusion coefficient has been evaluated on the basis of this relation from a plot of σ versus t^1/2 and was in good agreement with the diffusion coefficient from the plasticizer content data.     

Characteristics of the Insensitive Pressed Plastic Bonded Explosive,DXD-59

The technical objective of this investigation is to develop an explosive formulation that will maintain operational performance but is less sensitive to initiation by unplanned stimuli. The pressed, plastic bonded explosive composition, DXD-59 is composed of HMX, HyTemp acrylate binder and plasticizer. Results from initial characterization and large scale gap test indicate that DXD-59 exhibits relatively insensitive behavior with high detonation velocity. Susan test results are also reported in this paper.     

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.     

Aspects of the Tribology of the Plastic Bonded Explosive LX‐04

The dynamic coefficient of friction, μ_d, of the plastic bonded explosive (PBX) LX‐04 was measured on stainless steel, aluminum, Teflon and the explosive itself as a function of temperature between ambient and 135 °C at a rotational speed of 0.0025 rad/s⁻¹. An optical profilometer was used to analyze surface roughness. LX‐04 is a composite of the explosive 1,3,5,7‐tetranitroazacyclooctane (HMX) and Viton A in an 85/15 weight ratio. For LX‐04 on stainless steel, μ_d decreased from 0.38 at ambient to 0.18 at 95 °C, then was nearly constant to about 125 °C, where the coefficient began to increase again. The opposite behavior was observed for aluminum. Against Teflon μ_d was nearly constant from ambient to 65 °C at 0.43, and then decreased to 0.17 from 100 °C to 135 °C. Against LX‐04 itself the coefficient of friction averaged 0.64 at temperatures between 35 °C and 95 °C, but tended to increase during the measurement, probably due to adhesion of the Viton to itself. Above 95 °C the coefficient dropped off and became nearly constant again at 0.16 up to 135 °C. Measurements on stainless steel with the mock explosive RM‐04‐BR, a composite of cyanuric acid and Viton A, and with the same weight ratio as the actual explosive, compared reasonably well with the explosive itself.     

粘结剂增强对TATB基PBX力学性能的影响

采用熔融共混法制备了氟聚合物/增强剂复合粘结剂体系,考察了增强剂含量对复合粘结剂体系性能的影响。动态力学分析(DMA)结果显示,增强剂的玻璃化转变温度大大高于氟聚合物,复合粘结剂体系的储能模量随增强剂含量的增加而增加。随着增强剂含量增加,复合粘结剂体系的拉伸强度明显增加。采用水悬浮法制备了TATB基高聚物粘结炸药(PBX),探讨了粘结剂增强对其力学性能的影响。实验结果表明,随着增强剂含量增加,TATB基PBX的力学性能显著提高。当复合粘结剂体系中增强剂含量为20%时,PBX的力学性能最佳:20℃和60℃下压缩强度为32.15 MPa和20.00 MPa,60℃下劈裂强度为2.84 MPa。     

Afterburn Ignition Delay and Shock Augmentation in Fuel Rich Solid Explosives

We present experimental and computational results that explain some aspects of measured energy release in explosions of unconfined trinitrotoluene [TNT, C₆H₂(NO₂)₃CH₃], and an aluminum‐containing explosive formulation, and show how this energy release can influence shock wave velocities in air. In our interpretation, energy release is divided into early, middle, and late time regimes. An explanation is provided for the interdependence of the time regimes and their influence on the rate at which energy (detonation/explosion and afterburn) is released. We use a merging of the thermodynamic and chemical kinetic processes that predicts how chemical kinetics may determine the time delay of the afterburn of combustible gases produced by the initial detonation/explosion/fast reaction. The thermodynamic computer code CHEETAH is used to predict gaseous and solid products of early time energy release, and a chemical kinetic reaction mechanism (CHEMKIN format) is used to describe the subsequent afterburn of the gas phase products in air. Results of these calculations are compared with field measurements of unconfined explosions of 2 kg charge weights of TNT and an aluminum‐containing explosive formulation.     

Diffusion of Moisture in Adhesively Bonded Joints

In this article, diffusion of moisture in adhesively bonded composite joints is discussed and analysed experimentally, analytically and numerically. The experimental studies concentrate on moisture diffusion in adhesive films and in unidirectional and multidirectional composite substrates exposed to two different conditioning environments, namely 45°C/85% RH and 90°C/97% RH for the absorption studies and 90°C/ambient for the desorption studies. The coefficients of diffusion are determined from the water uptake plots. The analytical solutions for diffusion in joints with impermeable adherends are based on the classical theory of diffusion and are used to derive equations in two-dimensions for different adhesive fillet shapes, namely radiused fillet, triangular fillet and rectangular fillet. In the finite element analysis, the diffusion of moisture from the composite substrates into lap-strap joints is also taken into account. Both unidirectional and multidirectional composites are considered, as well as two different fillet shapes, i.e., rectangular and triangular fillet. A comparison between the results obtained using FEA and those obtained using the analytical solution is made. Finally, fatigue test data for lap-strap joints aged and tested in different environments is presented and a tentative link between fatigue threshold and water concentration at the site of failure initiation is made, indicating a semi-empirical method of predicting the strength of joints subjected to moisture-induced degradation.     

Study of Plastic Explosives based on Attractive Cyclic Nitramines Part I. Detonation Characteristics of Explosives with PIB Binder

Four plastic explosives based on energetic nitramines and a non‐energetic binder were prepared and studied. The nitramines were RDX (1,3,5‐trinitro‐1,3,5‐triazine), HMX (1,3,5,7‐tetranitro‐1,3,5,7‐tetrazine), BCHMX (cis‐1,3,4,6‐tetranitro‐octahydroimidazo‐[4,5‐d]imidazole) and HNIW (ε‐2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane, ε‐CL‐20). The binder was in all cases polyisobutylene (PIB) as in the standard composition C‐4. These powerful plastic explosives were compared to standard PETN‐based commercially available explosives Semtex 1A and Sprängdeg m/46. The detonation velocities were experimentally measured and compared to the ones calculated by the Kamlet–Jacobs method, CHEETAH and EXPLO5 Codes. The experimental detonation velocities as well as the calculated detonation parameters decrease in the following order: HNIW‐PIB>HMX‐PIB≥BCHMX‐PIB>RDX‐PIB>Sprändeg m/46≥Semtex 1A. Urizar coefficients for the various binders were calculated from experimental data.     

混合炸药对温度渐变环境的适应性研究

研究了几种混合炸药在经历了温度渐变试验（又称高低温循环试验）后的尺寸、质量、力学性能的变化，以及外观和内部结构的改变，分析了环境因素的影响程度及作用机理。建立了混合炸药对温度渐变环境的适应性试验方法，评价了混合炸药对温度渐变环境的适应能力。为混合炸药的配方设计、生产、运输和贮存提供指导性依据和评价标准。