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.     

Parametric Influences on the Sensitivity of Exploding Foil Initiators

Analyses of firings by the up‐and‐down method were employed to gain a better understanding of the influences of foil bridge width, foil thickness, flyer thickness, and barrel length on the sensitivity of exploding foil initiators. Characterization was performed via the mean threshold voltage. The results showed that the mean threshold voltage of exploding foil initiators was reduced by 16 % when the foil bridge width was reduced from 0.4 mm to 0.3 mm, which means that a reduced foil bridge width could decrease the mean threshold voltage of exploding foil initiators as suggested by theoretical analysis. The mean threshold voltage of exploding foil initiators was reduced by 20 % as the flyer thickness was decreased from 50 μm to 25 μm, which could be an efficient way to improve the sensitivity of exploding foil initiators. The flyer accelerated to over 90 % maximum velocity after flying 0.15 mm in a fine barrel, which revealed that exceeding a barrel length of 0.15 mm has little effect on the performance of exploding foil initiators.     

Compacted Modified Propellant Blocks as Traveling Charge in the Hybrid Shot Scheme

The burning of compacted modified propellant charges applied as a traveling charge in the hybrid shot scheme was studied. The block charges were manufactured by pressing fine propellant grains coated by a thin film of polyvinyl butyral. A stick from several pressed pellets was insulated over its lateral surface by a thin layer of silicon paste, glued to the back of the projectile and inserted into the barrel of the 23‐mm smooth‐bore laboratory gun. The loose‐packed accelerator charge was placed in the breech. Combustion was initiated by an igniter plug placed between the traveling and breech charges. A set of piezo‐quartz gauges placed in the breech and along the barrel, as well as a frame‐target device were used for recording characteristics of the firings. It is shown that blocks of this type, applied as the traveling charge, provide a stable burning process resulting in high ballistic performance. The block traveling charge preserves its integrity in the course of its motion along the barrel, and burning envelopes its total mass when pressure in the breach passes the maximum value. The descending portion of the pressure diagram demonstrates appreciable transformation, with convex or secondary hump sections. The shape of spatial pressure profiles behind the moving projectile is also transformed, and the pressure at the projectile butt end may be higher than the pressure in the breech. Compared to the conventional charges at the same maximum pressures the muzzle velocity increment attains 340 m s⁻¹ (or 23 %) for a light 35‐g projectile and 200 m s⁻¹ (or 19 %) for a heavy 104‐g projectile.     

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.     

Preparation and Performances of Castable HTPB/CL‐20 Booster Explosives

HTPB/CL‐20 castable booster explosives were prepared successfully by a cast‐cured process. Scanning electron microscope (SEM) and the charge density test were employed to characterize the molding effect of HTPB/CL‐20 explosives. The propagation reliability, detonation velocity, mechanical sensitivity, thermal decomposition characteristics and thermal stability of the HTPB/CL‐20 explosives were also measured and analyzed. The results show that, when CL‐20 content is less than 91 wt.‐%, the charges with better molding effect were obtained easily. The critical diameter of HTPB/CL‐20 explosives is less than 1 mm, which exhibits good propagation reliability. When the density of HTPB/CL‐20 charge with 91 wt.‐% CL‐20 is 1.73 g cm⁻³, its detonation velocity can reach 8273 m s⁻¹. Moreover, this kind of explosives has low mechanical sensitivity and good thermal stability.     

小飞片起爆系统加速膛参数的确定

对小飞片起爆系统中的关键部件之一-加速膛的主要参数进行了分析确定，其中包括加速膛的材料、长度以及直径的尺寸选择，为保证整个系统具有好的工作效果提供理论依据。     

Reaction Zones in Ultrafine TATB

We have measured the particle velocity of aluminum foils placed between ultrafine TATB and lithium fluoride, where the TATB thicknesses are varied between 0 and 8 mm. Resolution is about ±2 ns. The reaction zones are determined from the data, with 0.3 mm being the average. We suggest a 1‐D analytical approach based on the idea that the initiating flyer must put in some minimum amount of energy over one reaction zone length. The energy is calculated three ways: flyer input, reaction zone to be filled and the P²τ initiation energy. Code calculations show the reaction zones rapidly growing in the region dominated by the flyer followed by a slow increase as the detonation takes hold.     

Atomic oxygen resistant coating from poly(tetramethyldisilylene‐co‐styrene)

A polydisilahydrocarbon, namely, poly(tetramethyldisilylene‐co‐styrene), synthesized from dimethyldichlorosilane and styrene in 1 : 0.5 mol ratio under dechlorination conditions was evaluated as an atomic oxygen (AO) resistant coating for polyimide film and C‐polyimide composite. Exposure of the polymer coating on a quartz plate to an AO fluence of 2.1 × 10²¹ atoms/cm² resulted in practically no mass loss, indicating the AO resistance of the polymer. Ten percent solution of the polymer in toluene was applied on aluminized Kapton® polyimide film (125 μm thick) to obtain a coating thickness of ～ 5 μm on the unaluminized surface. In a similar way, the coating was applied on a C‐polyimide composite. The coated and uncoated samples of Kapton® film and C‐polyimide composite were exposed to AO in a plasma barrel system. The uncoated aluminized Kapton® film (125 μm) lost 6.35 mg/cm² when exposed to AO fluence of 1.6 × 10²¹ atoms/cm² whereas the corresponding coated film lost only 0.14 mg/cm² even after exposure to AO fluence of 2.1 × 10²¹ atoms/cm². In the case of the C‐polyimide composite, the uncoated sample lost 63.64 mg/cm² on exposure to AO fluence of 1.8 × 10²¹ atoms/cm² whereas the coated one lost only 0.21 mg/cm² even after exposure to AO fluence of 2.1 × 10²¹ atoms/cm². SEM studies suggest that the coating offers good protection to the substrates. Formation of cracks on some portions of the coating was noticed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2368–2375, 2004     

Determination of Solvent Contamination and Characterization of Ultrafine HNS Particles after Solvent Recrystallization

Solvent–antisolvent recrystallization employed for size reduction of HNS has been described and the effect of various parameters such as stirring rate, effect of antisolvent type, antisolvent temperature, ultrasonication, etc. was investigated. Purified HNS, produced by hot solvent recrystallization of production grade crude HNS, of mean particle size ∼95 μm was used for preparation of ultrafine particles of HNS. Solvent contamination in terms of residual solvent was determined by ¹H NMR and GC‐MS analysis. In addition, ultrafine HNS has been characterized for purity (HPLC, ¹H NMR), particle size and shape (PSA and SEM), specific surface area (BET analysis), thermal behavior (TGA, DSC), sensitivity (impact, friction), etc. The results have been compared with C‐HNS. UF‐HNS was >99% pure with mean particle size <1 μm. SEM showed submicrometer size rods like particles of HNS as the final material.     

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.     

Quantifying intermediate‐frequency heterogeneities of SOFC electrodes using X‐ray computed tomography

The electrodes in solid oxide fuel cells (SOFCs) consist of three phases interconnected in three dimensions. The volume needed to describe quantitatively such microstructures depends on several lengths scales, which are functions of materials properties and fabrication methods. This work focuses on quantifying the volume needed to represent “intermediate frequency” heterogeneities in electrodes of a commercial SOFC using X‐ray computed tomography (CT) over two different length scales. Electrode volumes of 150 μm × 150 μm × 9 μm were extracted from a synchrotron‐based micro‐CT data set, with 1³ μm³ voxels. 13.6 μm × 19.8 μm × 19.4 μm of the cathode and 26.3 μm × 24.8 μm × 15.7 μm of the anode were extracted from laboratory nano‐CT data sets, both with 65³ nm³ voxels. After comparing the variation across sub‐regions for the grayscale values from the micro‐CT, and for the phase fractions and triple phase boundary densities from the nano‐CT, it was found that the sub‐region length scales needed to yield statistically similar average values were an order of magnitude larger than those expected to capture the “high frequency” heterogeneity related to the discrete nature of the three phases in electrodes. The challenge of quantifying such electrodes using available experimental methods is discussed.     

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。     

Velocity profiling inside a ram extruder using magnetic resonance (MR) techniques

The extrusion of soft-solid materials is an important industrial process. Magnetic resonance imaging (MRI) has been used to acquire in situ velocity profiles during the ram extrusion of two opaque materials representative of those often extruded in industry; a mixture of 5 cSt poly-dimethylsiloxane (PDMS) added to a commercial soap (Dove^TM) (a soft solid), and a stiff biscuit dough (a paste). Radial velocity profiles have been acquired in both the axial and radial directions at different positions within the barrel (25 mm diameter) and die land, during extrusion through two 8 mm diameter cylindrical dies (length 8 and 16 mm), and through a multi-holed die. At a height of 24 mm above the die entrance, both materials exhibit plug flow with pure slip at the barrel wall. Nearer to the die, the flow has converged towards the centre of the barrel and static zones are observed at the barrel walls. The shape of the velocity profiles was found to be independent of ram speed (0.6-1.2 mm/s), and die length. The shape of the velocity profiles is material dependent, with greater shear effects evident in the biscuit dough and compression effects evident in the soap material.     

High Brightness 2.2–12 μm Mid‐Infrared Supercontinuum Generation in a Nontoxic Chalcogenide Step‐Index Fiber

An environment friendly nonlinear chalcogenide glass fiber with a Ge‐Sb‐Se core and a Ge‐Se cladding is fabricated for bright broadband mid‐infrared (MIR) supercontinuum (SC) generation. The fabricated Ge‐Sb‐Se/Ge‐Se fiber with a core diameter of 6 μm shows zero group velocity dispersion at ~4.2 μm and ~7.3 μm. By pumping the fiber with a length of 11 cm at 4.485 μm with 330 fs pulses, we achieve a SC covering the 2.2–12 μm spectral range and with an output average power of ~17 mW. This bright broadband SC source is promising for high‐resolution MIR spectroscopy.     

Fabrication of Titanium Bipolar Plates by Rubber Forming Process and Evaluation Characteristics of TiN coated Titanium Bipolar Plates

In this study, the rubber forming process is used to fabricate a micro‐channel titanium plate for a PEM fuel cell. The micro‐channel plate is fabricated using a 200 ton hydraulic press, and various parameters (punch speed, press pressure, rubber thickness, rubber hardness) are investigated in order to evaluate the formability. TiN films are deposited by reactive DC magnetron sputtering (DCMS) with an electromagnetic field system (EMFS). For the uncoated titanium and TiN‐coated titanium substrates, the hardness, surface roughness, and corrosion resistance are estimated by nano‐indentation and electrochemical methods, respectively. The improved corrosion resistance of the TiN films can be attributed to the densification of the film caused by enhancement of nitrification with increasing high reactive nitrogen radicals. The uncoated titanium and TiN‐coated titanium bipolar plates are combined with a unit cell for a performance test, and respective current densities of 0.396 and 0.888 A cm⁻² at 0.6 V are obtained.     

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).     

Preparation and properties of thermally conductive photosensitive polyimide/boron nitride nanocomposites

A new thermally conductive photoresist was developed. It was based on a dispersion of boron nitride (BN) nanoflakes in a negative‐tone photosensitive polyimide (PSPI) precursor. 3‐Mercaptopropionic acid was used as the surfactant to modify the BN nanoflake surface for the dispersion of BN nanoflakes in the polymer. The thermal conductivity of the composite films increased with increasing BN fraction. The thermal conductivity of the PSPI/BN nanocomposite was up to 0.47 W m⁻¹ K⁻¹ for a mixture containing 30 wt % nanosized BN filler in the polyimide matrix. Patterns with a resolution of 30 μm were obtained from the PSPI/BN nanocomposites. The PSPI/BN nanocomposites had excellent thermal properties. Their glass‐transition temperatures were above 360°C, and the thermal decomposition temperatures were over 460°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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.     

Facile fabrication of polyimide foam sheets with millimeter thickness: Processing,morphology, and properties

A series of polyimide foam sheets (PIFSs) with thickness of 0.5 mm using 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), 3,4′‐oxydianiline (3,4′‐ODA), and polyaryl polymethylene isocyanate (PAPI) as main materials were first fabricated by liquid foaming and compression molding technology. The effects of different PAPI contents and 3,4′‐ODA contents on the structures and properties of PIFSs were investigated. The results indicated that PIFSs exhibited a structure that front surface displayed closed cells made of damaged cell walls and membranes, while internal cells were open, and elliptic vacancies were flatted in the thickness direction from the cross section. The average cellular diameter increased with increasing PAPI loading. In addition, the introduction of 3,4′‐ODA increased the average cell size of PIFSs. Further, PIFSs had density of 0.087–0.239 g/cm³, elongation at break of 3.75–8.01% and tensile toughness of 3.46 × 10^?2?13.87 × 10^?2 J/cm³. Notably, they exhibited higher tensile strength of 1.89–5.42 MPa and lower thermal conductivity of 14.727–19.25 mW/m ?K at 24°C, compared to the polyimide foams reported earlier. The sound absorption coefficients (α) of samples with different PAPI contents increased and then decreased with increasing PAPI content. At low frequencies, a certain content of 3,4′‐ ODA allowed an improvement of the acoustical behavior of PIFSs, and the α increased and then decreased with increasing density. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39881.     

单螺杆FDM线材挤出机机筒结构分析与优化设计

对机筒的加热器位置、机筒长度和机筒内径等影响单螺杆FDM线材挤出机挤出成型的机筒结构因素进行了分析,以压力梯度、出口平均温度和流场平均温度为试验指标,基于ANSYS Workbench软件进行正交试验和极差分析,得到最优因素组合。并在试压工况、正常工况、极限工况和极限冷态工况等4种工况下,对采用最优因素组合设计的机筒进行了热力耦合试验验证。试验结果表明:当机筒的加热器位置43 mm、机筒长度270 mm、机筒内径15 mm时,单螺杆FDM线材挤出机出丝顺利,效率较高且安全可靠。