Nanothermite/RDX‐Based Miniature Device for Impact Ignition of High Explosives

A miniature rocket device integrating nanothermite and RDX is presented for shock initiation of high explosive application. This Ø 2.5 mm device consists in several assembled and screwed parts: a pyroMEMS chip with a Al/CuO multilayers on it to ignite within less than 100 μs a few milligrams of nanothermite, which reacts violently and ignites within 150 μs a RDX charge compacted in the closed combustion chamber. The gases generated by the RDX combustion rapidly expand, cut and propel a Ø 2.5 mm by 1 mm thick stainless steel flyer in the barrel. After the presentation of the rocket design, fabrication and assembly, by measuring the pressure‐time evolution in the chamber we demonstrate the advantage to ignite the RDX with Al/Bi₂O₃ nanothermite to optimize the pressure impulse. We show that the stainless steel flyer of 40 mg is properly cut and propelled at velocities calculated from 665 to 1083 m s⁻¹ as a function of the RDX extent of compaction and ignition charge. As expected, the average flyer velocity increases with the mass of loaded RDX and flyer's shear thickness. We finally prove that the impact of the flyer can initiate directly in detonation a RDX explosive, which is very promising to remove primary explosives in detonator.     

Comparison of Polyvinylidene Fluoride (PVDF) Gauge Shock Pressure Measurements with Numerical Shock Code Calculations

Polyvinylidene fluoride (PVDF) thin film pressure gauges are capable of measuring dynamic shock pressures of at least 25 GPa with nanosecond time resolution for impact-loading conditions. The performance and lifetime of PVDF gauges impacted by a detonator flyer were investigated. The pressure history in the gauge was varied by varying the flyer travel distance and the thickness of the gauge backer, which determined the delay time for reflected shocks. The measured pressure histories were compared with the results of shock code calculations. Agreement between the measured and calculated histories was good for times less than 1.5 µs after impact. Even small details in the measured signal could be explained by the propagation of shock and rarefaction waves and their interactions with each other and material boundaries. The results give confidence that the gauges yield accurate, dynamic data for 1 µs to 1.5 µs after impact.     

Measurement of Shock Initiation Threshold of HNAB by flyer plate impact

The shock initiation threshold of HNAB (Hexanitroazobenzene) explosive has been measured using pressure pulses generated by flyer plate impact. The flyer plates were accelerated by an electrically exploded metallic foil (electric gun) up to velocity of 2.5 mm/m̈s generating impact pressures, P, up to 7.3 GPa lasting between τ = 40 ns to 210 ns, where τ is the duration of the impact. One dimensional semi-empirical model was developed to describe the exploding foil process. We found a good agreement between the semi-empirical model and the experimental data. It was found that as the pressure duration gets longer, the initiation threshold curve swings away from the P²τ= constant. For long (200 ns) pulses, the initiation criterion becomes one of a constant pressure. This constant threshold pressure is 2.9 GPa at 1.6 g/cm³ (grain size is 5 m̈m). The effect of the explosive density and grain size on initiation threshold can be explained by hot spots and porous explosive concept. A critical energy for initiation threshold of 12 J/cm² was derived from our measurements (with flyer thickness 76 m̈m and grain size 5 m̈m).     

冲击载荷下JH-14C传爆药的动态响应实验研究

采用分离式Hopkinson压杆技术对JH-14C传爆药在不同应变率冲击过载作用下的动态响应特性进行研究,观察该传爆药的宏观破坏形式并对回收试样细观损伤模式进行扫描电镜(SEM)观测,获得相应的应力-应变曲线。结果表明,该传爆药的应力-应变曲线呈现明显的应变率效应,失效应力随应变率的增加而增加,失效应变基本保持不变。     

用电磁粒子速度计实验研究一种TATB基钝感炸药的冲击响应

针对一种新的TATB基钝感炸药(Tx),应用组合式电磁粒子速度计(EMV)测试技术,测量了炸药直接加载、增加有机玻璃隔板以及炸药驱动飞片3种加载状态下炸药内部的粒子速度历程和冲击波轨迹。根据测试结果,分析了不同加载压力下炸药的冲击响应过程。结果表明,炸药直接加载时,加载压力最高,Tx钝感炸药很快达到爆轰状态,到爆轰距离约为1.5mm;在增加有机玻璃隔板、加载压力为14.2GPa时,与直接加载时炸药粒子速度一致,Tx钝感炸药的到爆轰距离明显增加,约为5mm;在炸药驱动飞片、加载压力为9.5GPa时,Tx钝感炸药的粒子速度逐渐降低,存在一定钝化现象,到爆轰距离达到20mm以上。     

Estimating impact breakup and initiation parameters of condensed explosives

The existence of two critical states of an explosive material associated with the weakening of a layer of explosive and the excitation of an explosion is examined qualitatively on the basis of the general concepts of mechanical deformation and destruction of a thin layer of viscoplastic explosive material under impact and the resulting dissipative and chemical heat release. The critical conditions, i.e., the impact energy and the pressure created by it in the material, for destruction and initiation of the explosive material are estimated. The results are used to explain experimental data on the dependence of the initiation parameters on the thickness of a layer of explosive material which are of practical interest for analyzing tests of the sensitivity of explosive systems to mechanical interactions. Translated fromFizika Goreniya i Vzyva, Vol. 35, No. 2, pp. 88–95, March–April 1999.     

超临界流体反溶剂法制备超细HMX传爆药

为了克服超细炸药在常规包覆过程中易团聚的缺点,采用超临界流体反溶剂法( SAS)制备了以亚微米HMX为主体炸药的超细传爆药,探讨了工艺条件对亚微米HMX包覆效果的影响.结果表明,影响亚微米HMX包覆效果的主要因素有初始浓度、系统温度、系统压力、平均压力升高速率和平均压力下降速率.在加入20 mL的乙酸乙酯、系统压力9....     

改性铵油炸药连续爆速实验研究

采用连续速度探针研究改性铵油炸药在不同起爆条件下爆速和爆轰成长的连续变化.在起爆条件分别为雷管/160g起爆药柱、雷管/160g起爆药柱/有机玻璃隔板和仅采用雷管时,改性铵油炸药在稳定爆轰阶段的稳定爆速分别为4569m/s、4496m/、4559m/s,爆轰成长距离分别为3.5、7.3和20cm,爆轰成长时间分别为0.01、0.025和0.06ms.结果表明,在相同的装药约束条件下,起爆能量越大,改性铵油炸药爆轰成长时间和爆轰成长距离越短,即越容易发展为稳定爆轰.     

The Initiation Threshold Sensitivity of HNS Explosive as a Function of its Grain Size

The initiation threshold sensitivity of HNS versus explosive grain size has been measured, using an electric gun, with two flyer thicknesses. The initiation threshold, (kinetic energy of flyer plate), versus explosive grain size shows that the threshold curve increases dramatically at grain size over 5.4 m̈m (for flyer thickness 76.2 m̈m at explosive density 1.6 g/cm³). Minimum critical energies were calculated to be 12.15 ± 0.5 J/cm² and less than 7.0 J/cm², for flyer thicknesses 76.2 m̈m and 20.0 m̈m, respectively.     

Laser Initiation of Non‐Primary Explosive Detonators

Aiming to solve the problems caused by primary explosives in traditional detonators, a new kind of non‐primary explosive detonator based on the principle of flying plate detonator is invented. However, in some special circumstances, such as high temperature, strong radiation, strong magnetic field, overload, high‐pressure conditions, the non‐primary explosive detonator cannot work well because of the defects of its usual used initiating method like electric hot wire initiating devices, electric exploding bridge wire initiator, and initiating by a shock‐conducting tube. In this context, initiation by low energy laser is applied to non‐primary explosive detonator. After this combination, the non‐primary explosive detonator performs well in resisting high temperature, high pressure, overload, and electric interference.     

Electrothermal analysis as a tool for Designing Electric Detonator Firing Circuits

The use of modified forms of the Rosenthal electrothermal equation to aid in the design of a capacitor discharge firing circuit for a specific detonator is described. The electrothermal parameters C_p and γ, representing the heat capacity of the bridge and the heat loss factor, respectively, were calculated from previously obtained firing data for the detonator. These calculations provided input to the design of a firing circuit utilizing electrolytic capacitors, which have a large value of electrical capacity but also a non-negligible internal resistance. Calculations were performed which (1) revealed the degrading effect on detonator initiation caused by too large a value of internal resistance, and (2) permitted selection of a particular capacitor that would allow reliable functioning of the detonator with initiation times of about 230 μs. The circuit was designed utilizing this capacitor, and in the experimental evaluation of the circuit the measured initiation times were compared with the calculated values. Good agreement between the two was documented, and the conclusion was reached that the detonator functioned reliably. The merits of the electrothermal analysis and the assumptions utilized therein relative to a vigorous heat transfer/reaction kinetics modeling of the flow of energy from the bridge into the explosive flash charge are discussed in detail.     

双向聚能预裂爆破切割器的研制与应用

为解决普通线性聚能切割器所用炸药等问题不能满足工程中预裂和光面爆破的要求,研究了一种双向聚能预裂爆破切割器,采用廉价的低爆速工业炸药为主装炸药,以两条高爆速炸药条带动主装炸药爆轰,使主装炸药产生聚能爆轰波,利用聚能爆轰波和聚能装药的双重聚能效果产生强烈的聚能气体或金属射流。依据这种设计思想制造出以工业炸药为主体的双向聚能预裂爆破切割器,可用于预裂、光面爆破与岩石切割等。现场试验表明,双向聚能预裂爆破切割器使用方便,爆破效果显著。     

Particle Size Modification of Thermally Stable Secondary Explosives for IM Applications

As well as improving the survivability of weapons and platforms, insensitive munitions (IM) reduce both casualty rates and mission losses. Their use also leads to improved safety during storage and transportation. For a munition to fulfil IM criteria, each of its energetic sub‐sections must be IM compliant. The initiator and explosive train are the most critical of these sub‐systems as their safety and reliability are of paramount importance if the weapon is to be suitable for service use, yet they are generally the most difficult part of a weapon to protect from inadvertent initiation. As part of an ongoing study into initiation methods suitable for use in IM systems, an investigation into the behaviour of energetic materials when impacted by laser‐driven flyers was performed. Laser‐based detonators exhibit increased safety characteristics over conventional initiation methods as they can be based on insensitive secondary explosives rather than sensitive primary explosives. Also, they are less susceptible to accidental initiation due to an external hazard threat. Single pulses from a high‐powered Q‐switched Nd:YAG laser were used to launch flyers from substrate‐backed aluminium films to velocities up to 6 km s⁻¹ across a short stand‐off to impact explosive targets. Several novel energetic materials have been selected for investigation as potential candidates for inclusion within flyer‐based initiation systems and explosive train applications. The materials are of interest due to their increased thermal stability and power output over conventional explosives currently in service. Attempts were made to increase the flyer responsiveness of the materials by tuning their particle size using ultrasound. The effect of particle size on the initiation threshold energy was investigated for three materials.     

Acceleration Profile of a Flat Flyer Driven by Detonation Isentrope

In the design of explosive devices, understanding of the behavior of explosively propelled matter is one of the important steps to optimize the performance of the device. In a typical flat, metallic flyer and explosives charge system, the flyer reaches its maximum velocity after a certain degree of expansion of the detonation gas. During this expansion, the flyer is deformed in an arced‐shape by the incoming rarefaction from nearby surfaces. In this work, an acceleration/deformation profile of an explosively propelled flat, metallic plate was studied based on the isentropic expansion of detonation gas and subsequent rarefaction intrusion to the center of the flyer. In order to properly describe the arced deformation of the flyer, a rather simplified new term of the pressure release ratio behind the flyer η is introduced based on the expansion of the detonation isentrope behind the flyer. A theoretical model was built to predict the behavior of an explosively driven flyer and the rarefaction intrusion into the center of the explosives charge. The results are compared to a hydrocode simulation and exhibit favorable agreement in a limited application.     

Flying Plate Detonator

Design and function of an all-secondary explosive low-voltage electric detonator will be described. Results of the threshold values of current, voltage, energy will be presented together with the re-sponse times, the initiation capability gainst boosters of tetryl and the results of a few safety tests.     

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.     

膨化硝酸铵的感度特征研究

膨化硝酸铵是近年来得到广泛使用的工业炸药氧化剂，本文对其撞击感度，摩擦感度，爆发点，火焰感度，静电火花感度等危险感度进行了测定，并对膨化硝酸铵进行了PSC实验，以及对雷管感度及冲击波感等实用感度进行了测定，研究表明，同普通硝酸铵相比，膨化硝酸铵具有较低的危险感度及良好的实用感度。     

On the Use of Composite Charges to Determine Insensitive Explosive Material Properties at the Laboratory Scale

Laboratory‐scale air‐blast experiments an gram‐range composite explosive charges are presented. The composite charges consist of a spherical booster charge surrounded by a concentric, spherical “candidate material” shell charge. By way of composite charge explosive characterization, the candidate explosive material is able to be characterized through the “removal” of the known booster effects. Using peak shock wave pressures, a method is developed to remove the booster effects from the composite charge’s signature to yield the sole effects of the candidate explosive material, permitting its characterization. Air‐blast explosive tests are conducted using digital high‐speed shadowgraph visualization to measure the resulting shock wave radial position as a function of time. Booster and composite charge data are converted to Mach number versus shock wave radius profiles and subsequently to peak shock wave pressure versus shock wave radius profiles for characterization of the shell material. Explosives tested include: PETN, RDX, HMX, and Alliant Bullseye® SP.     

Flyer Plate Motion by Thin Sheet of Explosive

Acceleration of a metal plate by explosive energy at low value of charge to metal mass ratio has been studied by employing a new theoretical model based on uniform pressure and density of detonation products behind the flyer plate. Theoretical velocities of flyer plates have been compared with those measured by radiographic technique and found in good agreement. Comparing the relations for plate velocity, obtained from the present model and earlier Gurney model at low C/M values, an analytical expression for Gurney energy has been obtained in terms of detonation velocity of the explosive and adiabatic exponent of the detonation products.     

A Miniature Device for Shock Initiation of Hexanitrostilbene by High‐Speed Flyer

A miniature device for shock initiation of the hexanitrostilbene (HNS) through micro‐charge detonation‐driven flyer was fabricated. This device consisted of the substrate, micro‐charge, flyer, and barrel. Four types of flyer (titanium of 28 μm, aluminum of 22 μm, copper of 22 μm and polyimide (PI) of 55 μm in thickness) were studied and the effect of micro‐charge thickness, diameter, and barrel length were investigated by measuring the average flyer velocities using polyvinylidene fluoride (PVDF) films. The results show that the titanium flyer is more proper for such initiation device compared to aluminum, copper, and polyimide flyer. The average velocity of the flyer increased with the thickness of micro‐charge and the increment was larger when the thickness increases from 0.3 mm to 0.4 mm than when the thickness increases from 0.4 mm to 0.6 mm. The flyer velocity significantly increased with the increase in the diameter of micro‐charge until a plateau appeared at 0.8 mm. The flyer velocity increased first and then decreased sharply with the increase in barrel length. The average velocity for a 28 μm thick titanium flyer was measured to be as high as 2468 m s⁻¹ when the thickness, micro‐charge diameter and the length of barrel were 0.6 mm, 0.8 mm and 659 μm, respectively. The HNS‐IV explosive with density 1.57 g cm⁻³ was initiated by this miniature device.