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.     

Experiments of Initiation of Covered,but Unconfined High Explosive Charges by means of shaped charge jets

Experiments on the initiation of high explosive charges in contact with a barrier or separated from it by a 15 mm air gap or a 2 mm acrylic glass layer have been performed utilising a simultaneous framing and streak camera. With increasing barrier thickness the shaped charge jet is increasingly consumed.     

Shock Initiation of Sheet Explosive

The shock sensitivity of a typical sheet explosive RDX-WAX (90:10) has been experimentally determined with gap test arrangement by measuring free surface velocity in different thicknesses of the barrier and shock and particle velocity of non-reactive shock wave in the sheet explosive with Pin Oscillography Technique. It has been found that a shock wave, generated by a point-initiated cylindrical explosive in contact with an aluminium barrier of diameter nearly twice the diameter of the charge, attenuates exponentially and a 6.5 mm thick sheet explosive, of density 1.28 g/cm³ and velocity of detonation 6.43 mm/μs, detonates with 50% probability by a shock wave of 11 kbar pressure in the explosive.     

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.     

Study on a System with a Neutral Barrier for High Explosives and a Zirconium‐Based Solid Incendiary

In the aim of defeating targets protected by fortification, it is necessary to develop systems that are able to create a leak in the fortification and destroy targets inside the fortification. A boat‐tailed hemispherical high explosive charge was designed to create the leak and an incendiary charge was prepared to burn the targets inside the fortification. A metallic neutral barrier was used to attenuate the back pressure generated by the front end hemispherical high explosive charge. In order to reduce the back blast, a boat‐tailed hemispherical charge with the composition cyclotrimethylene trinitramine and trinitrotoluene (RDX/TNT 60/40) was prepared. The blast pressure obtained from unconfined boat‐tailed high explosive charges using a linear pressure gauge brought to light that the pressure at the front end had a value of 2.3 MPa at 100 cm; and a value of 0.4 MPa at 75 cm distance at the rear end. A hemispherical boat tailed shaped charge with a mild steel liner of 1 mm thickness and 40 mm curvature radius was prepared. The incendiary composition comprised of finely divided metal powder dispersed in a polymer matrix consisting of 77 % zirconium and 20 % ester gum resin with 3 % polymeric binder (SBR, PIB). The incendiary composition was prepared and pelletized. Experiments for the design of the neutral barrier were conducted with the boat‐tailed hemispherical charge. A mild steel plate of 7.5 mm thickness was selected as neutral barrier. Static evaluation of the system against a hard target was carried out. It created a hole of 190 mm diameter in a reinforced concrete cement (RCC) target of 100 mm thickness. A neutral barrier of 7.5 mm thickness attenuates the back blast of the hemispherical boat‐tailed charge. Burning incendiary cinders were passed through this hole and dispersed at approx. 5 m distance. These cinders burnt for > 3 min with a temperature output of 1873 K.     

The Initiation of Covered Composition B by a Metal Jet

The initiation and build-up to detonation of Composition B covered by steel barrier plates and impacted by a shaped-charge jet has been studied. Two different barrier thicknesses were used representing strong and weak shock initiating systems. The results showed that, in both cases, a shock (designated the precursor shock) that travelled ahead of the penetrating jet and entered the explosive was roduced when the jet impacted the steel surface. The strong precursor shock from the thin barrier system produced initiation close to the explosive surface while for the weak precursor shock from the thick barrier system there was a long run to detonation (40 mm, 11 μs). In the latter case, close to the onset of detonation, a retonation was observed moving back through the previously shocked explosive which was expanding radially. These observations are used to discuss and explain some of the apparent anomalies in previously reported work. The effect of the precursor shock on the classical jet penetration theory was estimated.     

Initiation of a passive explosive charge through a target with gaps

Experimental data on the measurement of time of passive explosive initiation by an active charge through an inert target with air gaps are presented. Two types of gaps are considered: perpendicular to the passive charge (a slit in the inert target) and parallel to the surface of the passive charge (between the inert target and the passive explosive). In the case of gaps parallel to the surface of the passive explosive charge, two-wave loading of the passive explosive charge created by impacts of thin plates, which are located on the surface of the main target on the side facing the passive explosive charge, is studied. Experimental data are analyzed by numerical calculations with the EGAK software on a Eulerian grid, and the instant of initiation is determined by a criterial parameter F, which is proportional to the energy released in shear strains, when a shock wave passes through the passive explosive charge.     

INVESTIGATION OF IMPINGEMENT HEAT TRANSFER COEFFICIENT AT HIGH TEMPERATURES

ABSTRACT

Very little information exists for the impingement heat transfer coefficient at high temperatures. All available empirical correlations are mainly based on experiments conducted at relatively low impingement temperatures, and thus cannot describe the heat transfer characteristics of the impingement air at high temperatures with sufficient accuracy. A comprehensive study of the impingement heat transfer coefficient at high temperatures is carried out and presented in this paper. The aim of the study is to give a summary of the experimental results of the impingement heat transfer covering a large impingement air temperature range from 100 to 700°C. Heat transfer measurements were carried out on a laboratory-scale test rig. The main parts of the rig were a fan, a gas burner for air heating, a heavily insulated nozzle array with 300 × 500 mm impingement surface, a 40 mm thick and 300 × 500 mm sized aluminium plate for determination of heat transfer, and a data acquisition system. The heat transfer rate was determined from the heat-up rate of the aluminium plate due to the high temperature jet impingement.     

Manufacturing of Multiclads Using a Single Explosive Charge

A technique for the fabrication of several mono and/or bimetallic cladded plates using a single explosive charge has been developed at our laboratories. This technique enables the explosive welding of thin plates or foils which are otherwise produced by the rolling of thick explosively cladded plates. This paper describes the technique and lays down the theoretical basis for the determination of the process parameters. It is shown that up to four sheets of 0.5 mm thick stainless steel cladded to 2.0 mm mild steel could be produced using a single explosive charge. The technique was also used for the manufacturing of 8 sheets of 0.25 mm copper foil cladded to 0.5 mm mild steel plate.     

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.     

A study on air jet drying for water content reduction of sludge

An air jet drying system composed of a turbo blower, an air ejector and three stage cyclones is constructed to produce a dried powder through water content reduction of dewatered cake obtained from sludge treatment process. The air flow to be ventilated by the turbo blower forms a high speed flow field by passing through the air ejector and a circulative flow field by passing through the cyclones. Dewatered cake, 100 mm in size, is disintegrated by jet and collision through passing the air ejector and becomes fragmented with size no more than 2mm. These fragmented particles follow air flow and are dried as moisture is evaporated from particle surface. A powder composed of 1.6 mm spherical particles is produced from pilot scale equipment of 1 ton/hr under the conditions of air velocity, maximum flow rate and air temperature profile of 84 m/sec, 180 m³/min and 73-28 °C, respectively. The air dried powder with average water content of 49.8 wt% is recovered after drying the dewatered cake with water content of 83.3 wt% in a real operation, indicating 33.5 wt% decrease in water content. It is estimated that the power consumption of the air jet drying system requires 92 kWh/Ton to reduce the water content by 33.5 wt%, which is no more than a half against heat drying system to consume 164 kWh/ton.     

Dynamic Fragmentation and Blast from a Reactive Material Solid

Structural reactive material (SRM) is consolidated from a fine granular mixture of reactive materials towards the mixture theoretical maximum density with little porosity, thus bearing both high energy density and mechanical strength. A reactive hot spot concept was investigated for fine fragmentation of a SRM solid under explosive loading to augment air blast through rapid reaction of fine SRM fragments. In this concept, micro‐sized reactive materials were distributed in a fuel‐rich SRM solid, such as MoO₃ particles consolidated in a particulate aluminum base in 10Al+MoO₃. Intermetallic reactions of micro‐sized MoO₃ and nearby Al under explosive loading created heat and gas products to form microscale hot spots that initiated local fractures leading to fine fragments of the rest of Al. The SRM solid was made of a thick‐walled cylindrical casing, containing a high explosive in a detonation pressure range of 25–34 GPa with a casing‐to‐explosive mass ratio of 1.78. Experiments in a cylindrical chamber demonstrated the presence of a large amount of fine SRM fragments, whose reaction promptly after detonation significantly enhanced the primary and near field blast wave, as compared to the results from a baseline pure Al‐cased charge, thus indicating the feasibility of the concept.     

压装工艺对CL-20基炸药性能及聚能破甲威力的影响

利用常温成型和热压成型两种工艺制备了典型的CL-20基混合炸药装药,测试了其装药密度、密度均匀性、力学性能、爆速,计算了格尼系数。对Φ50mm标准聚能装药进行了破甲试验。验证了不同压装工艺条件下装填CL-20基炸药装药聚能射流对45号钢靶的侵彻深度和穿孔直径效果。结果表明,与常温成型CL-20基装药相比,热压成型工艺条件时装药的密度提高不小于1.46%,密度均匀性、爆速和格尼系数和破甲能力试验数据均有不同程度的提高,且Φ50mm标准聚能射流对45号钢靶的平均穿深从310mm提高至343mm,平均穿孔直径由18.0mm增至23.5mm。     

INVESTIGATION OF IMPINGEMENT HEAT TRANSFER COEFFICIENT AT HIGH TEMPERATURES

Very little information exists for the impingement heat transfer coefficient at high temperatures. All available empirical correlations are mainly based on experiments conducted at relatively low impingement temperatures, and thus cannot describe the heat transfer characteristics of the impingement air at high temperatures with sufficient accuracy. A comprehensive study of the impingement heat transfer coefficient at high temperatures is carried out and presented in this paper. The aim of the study is to give a summary of the experimental results of the impingement heat transfer covering a large impingement air temperature range from 100 to 700°C. Heat transfer measurements were carried out on a laboratory-scale test rig. The main parts of the rig were a fan, a gas burner for air heating, a heavily insulated nozzle array with 300 × 500 mm impingement surface, a 40 mm thick and 300 × 500 mm sized aluminium plate for determination of heat transfer, and a data acquisition system. The heat transfer rate was determined from the heat-up rate of the aluminium plate due to the high temperature jet impingement.     

Gold-thickness-dependent Schottky barrier height for charge transfer in metal-assisted chemical etching of silicon

Large-area, vertically aligned silicon nanowires with a uniform diameter along the height direction were fabricated by combining in situ-formed anodic aluminum oxide template and metal-assisted chemical etching. The etching rate of the Si catalyzed using a thick Au mesh is much faster than that catalyzed using a thin one, which is suggested to be induced by the charge transport process. The thick Au mesh in contact with the Si produces a low Au/Si Schottky barrier height, facilitating the injection of electronic holes from the Au to the Si, thus resulting in a high etching rate.     

Effect of Shock–Wave Loading Conditions on the Behavior of a PETN–Based Plastic Explosive

The paper reports results of investigation of the spallation and initiation of an explosive transformation in the plastic explosive formulation TP–83 under shock–wave loading. In the first case, specimens 20 mm thick were impacted by explosive driven steel plates 1.0 and 1.6 mm thick at velocities of 120—420 m/sec, and in the second case, the impact velocity was 430—580 m/sec. In addition, in the second case, specimens 5 mm thick were impacted by copper plates with a thickness of 0.10—0.28 mm accelerated to velocities of 590—1250 m/sec. The loading conditions were calculated in an elastoplastic formulation. The relationships between the loads leading to shock–induced spallation and explosive transformation of the explosive formulation are obtained and represented analytically.     

Flexible rGO-SnO2 supercapacitors converted from pastes containing SnCl2 liquid precursor using atmospheric-pressure plasma jet

Reduced graphene oxide (rGO)-SnO₂ nanocomposites are fabricated on carbon cloth from screen-printed pastes containing rGO nanoflakes and SnCl₂ liquid precursor by using a nitrogen atmospheric-pressure plasma jet (APPJ). RGO-SnO₂-coated carbon cloth is then used as the electrode of gel-electrolyte supercapacitors (SCs). Experiments conducted with various APPJ processing times suggest that the optimal APPJ processing time is 300 s. Cyclic voltammetry (CV) measurements indicate that 300-s APPJ processing results in the best areal capacitance of 97.53 mF/cm². The capacitance retention rate is ~85% after a 10,000-cycle CV test. Further, capacitance increases by 11% after a 1000-cycle bending test under a bending radius of 7.5 mm, possibly owing to the better electrolyte/electrode contact and decrease in the charge transport resistance after mechanical bending. This study also characterized APPJ-processed rGO-SnO₂ nanocomposites by scanning electron microscopy with energy dispersive spectroscopy, X-ray photoelectron spectroscopy, X-ray diffractometry, Raman spectroscopy, and water contact angle measurements.     

Study of the explosive behavior of highly confined cast PBXs submitted to bullet impact

Since many years, SNPE is trying to get a better understanding of the mechanisms which govern the bullet impact reactivity of highly confined eastable plastic bonded high explosives. In a first part, the different research thrust lines and the principal results are presented. In a second part are presented some results of bullet impact tests performed with instrumented small scale warheads which can be open after test without hazard. These small scale warheads are filled with disks of explosive and inert material. The presence of this inert material, which has the same mechanical properties that the explosive, allows to reduce the level of reaction and then, it is possible to:

• measure the stresses induced by the impact,
• localize the ignition points,
• assess the amount of damage,
• determine the amount of explosive having recated.

     

纳米CL-20炸药含能墨水的直写规律

针对MEMS引信中微传爆序列,基于直写技术,研究了由纳米CL-20炸药、黏结剂体系(包括黏结剂和溶剂)和其他添加剂组成的CL-20炸药墨水的直写特性,并制备了3种含能墨水。分析了直写压力、针头直径、直写高度和墨水黏度等因素对直写过程的影响规律。结果表明,随墨水黏度增大,直写线宽减小且减小幅度增大,但黏度过度偏大时,会影响直写线宽的均匀性,配方I在喷头高度为0.50mm和0.75mm时,以及配方III在喷头高度为0.75mm时,均出现了线宽不均的现象;配方II直写线宽稳定更适合直写装药。随着喷管压力的增大,CL-20油墨的打印线宽明显增加,且对于不同针头直径和不同配方墨水压力大小变化相同,线宽的增幅基本相同,当压力由100kPa增加到200kPa,线宽增大约2.5倍。随着喷头内径的增大,油墨的直写线宽明显增大,且线宽增加的幅度越来越大。随着喷头高度的增大,油墨的直写线宽减小。对于直写线宽大于1 285μm的墨水线条,固化后墨水表面均出现气泡,直写时应控制线宽,防止在直写过程中空气进入墨水。     

在撞击作用下炸药装药的底隙制作研究

通过各种底隙模拟实验,探讨了不同底隙在撞击作用下对炸药药柱产生点火起爆的敏感性,得出在模拟实验中比较理想的底隙制作方案。