Pulsed Laser Induced Decomposition of Energetic Polymers: Comparison of ultraviolet (355 nm) and infrared (9.3 μm) initiation

Irradiation of the energetic polymer GAP (glycidyl azido polymer) by a high power pulsed UV laser leads to its rapid decomposition. A large amount of solid and gaseous material is released, and in the presence of an inert gas, a shock wave develops. Comparison with an inert polymer indicates that the energy released by the exothermicity of the decomposition reaction contributes significantly to the shock formative energy. The energy released in the micro-explosion can be estimated from the analysis of the shock front propagation velocity. It is found that irradiation of polymers in which GAP is diluted by an inert polymer, may lead to a higher shock intensity than irradiation of neat GAP. Possible causes for this apparent inconsistency (which is not observed upon initiation by a pulsed infrared laser) are discussed.     

Detonation characteristics of emulsion explosives sensitized by MgH2

Preliminarily results on the reaction mechanism of detonation of composite emulsion explosives sensitized by MgH₂, which simultaneously plays the role of an energetic material, are presented. Compared to emulsion explosives sensitized by glass microspheres, emulsion explosives sensitized by magnesium hydride have a different reaction mechanism of detonation. The shock wave overpressure, specific impulse, shock wave energy, and bubble energy are all greatly increased with the use of MgH₂, and it is noticeable that the shock wave overpressure and shock wave energy increase by 17% and 24%, respectively. In addition, emulsion explosives sensitized by MgH₂ improve significantly in terms of detonation velocity and brisance. These emulsion explosives also meet safety requirements.     

An Analysis of the Influence of Detonator Parameters on the propagation of shock waves in an inert medium

The effect of mass, diameter and type of detonator on parameters of shock waves generated in plexiglas block is examined by experimental and theoretical means. The quantities connected with the shock wave, such as, the mean velocity of the shock wave front, the profile of mass velocity behind this front, and the mean velocity of free surface of the loaded block are measured. To perform an numerical analysis of the shock wave parameters mentioned above on type and size of detonator the problem is considered of acting of detonation products of an explosive charge on a block of inert material. In this goal, the active mass of charge is determined and, next, the model assumptions and mathematical formulation of the problem of penetration of pressure pulse into inert medium are presented. The results of computer simulation and experimental data are compared.     

复合杆式射流成型及威力性能的数值模拟及试验验证

为了阐明复合杆式射流的性能,设计了8种不同材料的复合球缺罩,包括聚乙烯/铜、铝/铜、钛/铜、铁/铜、铜/铜、钼/铜、钽/铜、钨/铜材料,并采用LS-DYNA软件对其杆式射流的成型过程进行三维数值模拟,分析了杆式射流威力性能,通过静破甲试验验证了数值模拟结果。结果表明,在保持内罩材料为紫铜的条件下,随着外罩材料密度的增大,射流整体速度减小,射流动能随外罩材料密度的增大而减小;在外罩为金属材料时,外罩材料冲击阻抗越大,内罩所受爆轰波透射压力越小,射流整体速度、射流动能随外罩冲击阻抗增大而减小;经对比发现,聚乙烯/铜复合杆式射流整体速度最高,动能最大,破甲威力较佳,铝/铜复合杆式射流次之。静破甲试验结果表明,聚乙烯/铜复合杆式射流对钢靶侵彻深度较铝/铜复合杆式射流有一定提高,与数值模拟结果一致。     

Computational simulation of cold spray process assisted by electrostatic force

The integrated model of compressible thermofluid, splat formation and coating formation for the cold spray process has been established. In-flight behavior of nano-micro particles and the interaction between the shock wave and the particles in a supersonic jet flow impinging onto the substrate and further effect of electrostatic force on the particle acceleration are clarified in detail by carrying out a real-time computational simulation. The optimal particle diameters for an impinging particle velocity exceeding critical velocity exist. Particles with the diameter of submicron interact with shock wave and particles are decelerated prior to the impact. However, the particles can be accelerated considerably by utilizing electrostatic forces even in the presence of unavoidable shock waves. Finally, based on the integrated model, the coating thickness in an electrostatic assisted cold spray process is evaluated.     

Dynamic response of a Li2O-Al2O3-SiO2 transparent glass-ceramic under shock compression

Li₂O-Al₂O₃-SiO₂ transparent glass-ceramics (LAS-TGCs) are promising candidates for transparent armour materials due to their excellent physical and mechanical capabilities. In this work, the dynamic behaviour of a LAS-TGC were further investigated using the planar impact technique and photon Doppler velocimetry. The shock stress, shock wave velocity, failure wave velocity and spall strength were obtained. In addition, the recompression signal, as a signature of failure waves, was observed to evolve into an oscillation signal as the impact stress decreases, indicating that the failure wave is gradually formed at a threshold. It has been noted that the failure wave velocity decreases with the increase in external loading and then turns upwards. The damage parameter of the LAS-TGC was assessed to be 0.410(5) under a shock stress of ~5.5 GPa, which is smaller than that of K9 glass. It is suggested that the LAS-TGC has better shock resistance than K9 glass.     

Jet Penetration of Surrogate Steel-Explosive Systems

Predicting the jet initiation of an explosive that is covered and in intimate contact with an inert material, is sensitive to the history of the jet in both the cover and the explosive. If the penetration velocity in the cover is subsonic, the acceptor explosive experiences complex wave structures that are significantly different from the case where the penetration velocity is supersonic. The pressure history in the explosive may cause prompt initiation, desensitization, or delayed initiation. We have used transparent polymethylmethacrylate (PMMA) as a surrogate for the explosive, allowing us to experimentally visualize the transition between the subsonic penetration behavior in a steel cover and the quasi-steady supersonic penetration behavior in the PMMA. The wave histories in PMMA downstream from two steel covers of different thicknesses have been measured by streak and image intensifier cameras and by flash radiography simultaneously. These were augmented with pressure gauges to measure the pressure history for one of the thicknesses. These experimental results and subsequent analysis show how initiation of an explosive acceptor can occur at various distances from the interface, depending on the thickness of the cover plate.     

Investigations on high enthalpy shock wave exposed graphitic carbon nanoparticles

The impact of high enthalpy shock wave on graphitic carbon nanoparticle (GCNP) films has been investigated and discussed in view of space and chemical engineering applications. The GCNP films were developed by using spray method and exposed to high enthalpy shock wave under an inert atmosphere. Upon shock wave treatment, two typical amendments such as weight loss in the deposited material and growth of second order nanostructures (SONs) have been observed. While increasing test gas pressure, the loss of material and density of SONs are gradually increased. Most of the shock wave induced SONs are highly crystalline and belong to the cubic diamond structure. Upon shock treatment as well as with increase of test gas pressure, a considerable improvement in the quality of GCNP films has been observed. Further, ablation of GCNPs exclusively on the top surface of the coatings and formation of hierarchical NPs (diamond NPs on GCNPs) has been observed.     

Shock and detonation waves generated by a wire explosion in liquids and bubbled media

Parameters of shock waves generated by a wire explosion in a gas, liquid, and inert or reactive bubbled media in a vertical shock tube are measured. Problems of shock wave velocity measurements in a liquid and inert bubbled medium are discussed. Experimental data are compared with theoretical estimates. Excitation of self-sustained detonation in a chemically active medium by a short shock wave induced by a wire explosion is studied.     

气流粉碎过程中激波的产生、影响及防止研究

分析了气流粉碎过程中激波产生的原因,采用数值计算方法,讨论了激波对气流磨中颗粒的冲击速度的影响,并提出了防止激波产生的措施。     

气流粉碎过程中激波的产生、影响及防止研究

分析了气流粉碎过程中激波产生的原因,采用数值计算方法,讨论了激波对气流磨中颗粒的冲击速度的影响,并提出了防止激波产生的措施。     

Experimental and Theoretical Investigation of Drying of Carrots in a Fluidized Bed with Energy Carrier

A pilot scale fluidized bed dryer with an inert energy carrier (steel, glass beads ranging from 2.7 to 6.5 mm) was used to investigate the drying of carrots. The effects of sample diameter, inert material type, inert material diameter, amount of inert material, air velocity, and temperature on the rate of drying were studied. A mathematical model was proposed for predicting the drying rate and temperature of drying material. It was found that presence of inert particles enhance the rate of drying. The results of this study also revealed that, although the rate of drying increases with decreasing sample diameter, increasing the inert material thermal conductivity, and increasing air temperature, but the inert material diameter and air velocity have no significant effects on the rate of drying. The independence of rate of drying on air velocity especially in well-fluidized systems indicates that external diffusion is not a controlling step in this process. Also the presence of inert materials causes the drying material to reach more rapidly to its final internal temperature.     

Experimental study on the effect of titanium hydride content on the detonation performance of emulsion explosives

In order to improve the explosion characteristics of emulsion explosives, titanium hydride was added to emulsion explosives to produce a new type of hydrogen storage emulsion explosives. Charges with different contents of titanium hydride were evaluated through underwater explosion experiments and detonation velocity tests. The tests on underwater explosion and detonation velocity reveal that compared to pure emulsion explosives, the detonation parameters of emulsion explosives containing titanium hydride showed a trend of first increasing and then decreasing. When the mass ratio of titanium hydride in the emulsion explosive is 1 % to 3 %, all detonation parameters have been improved to a certain extent. When the mass ratio of titanium hydride in the emulsion explosive is 3 % to 10 %, only part of the detonation parameters (specific impulse, specific shock energy, specific total energy and volume energy density) has been improved. The maximum increase of specific impulse, specific shock energy, specific total energy and volume energy density of emulsion explosive containing titanium hydride is 7.06 %, 8.95 %, 3.97 % and 8.22 %, respectively. Based on the analysis, it is evident that though powdered TiH₂ participates in the detonation reaction process of the emulsion explosive, the majority of TiH₂′s energy is released during the secondary reaction occurring after the detonation wave front. Therefore, the detonation performance of emulsion explosives can be effectively improved by adding a certain mass ratio of titanium hydride.     

Motion of a shaped-charge jet in a porous medium

The problem of the motion of a shaped-charge jet in a porous medium is equivalent to the problem of a blunt cylinder in a hypersonic flow whose velocity at infinity is equal to the jet velocity in the porous medium. The flow pattern of the medium is the same as in the case of propagation of a blast wave generated by a point explosion of a cylindrical charge. The approximate theory of a strong explosion is used to obtain the basic relations for the shock wave and the expanding cavity in the hypersonic flow of a porous medium around the blunt cylinder. A comparison with experiments on the motion of a copper shaped-charge jet in porous aluminum is performed. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 6, pp. 119–124, November–December 1999.     

超音速喷嘴激波粉碎效应研究

根据对颗粒穿过超音速喷嘴激波层动能变化率的分析,建立了气流磨喷嘴激波前后流动参数与颗粒尺寸和比表面积的变化关系,并且通过实验验证了激波强度、颗粒尺寸与粉碎效应的变化关系.研究表明,激波的产生降低了冲击粉碎强度,对提高综合粉碎效应不利.     

Assessment of crystallographic and electronic phase stability of shock wave loaded cubic cerium oxide nanoparticles

Rapid progress has been documented during the last couple of years in understanding the crystallographic structural features of a few functional materials that have been achieved under dynamic shock wave loaded conditions. In this context, we report the crystallographic and electronic phase stability of shock wave loaded Cerium oxide nano-crystalline (CeO₂ NPs) material and the results have been evaluated by X-ray diffraction (XRD), Raman spectroscopy and ultra-violet diffuse reflectance spectroscopy (UV-DRS). XRD and Raman spectroscopic results show that the title material doesn't undergo any crystallographic phase transitions. UV-DRS spectral results demonstrate that the Ce⁴⁺ ionic state is not affected by the impact of shock waves. The obtained FE-SEM micrographs provide the substantiation for the stability of the sample. Based on the observed results, the title material can be suggested for the making of medical glassware, spaceship windows and technological applications of coating.     

用于烃类裂解的新型激波反应器

新型的激波反应器可用于气相热解反应，具有许多优点。在反应器内，惰性载气和原料气预先分别被加热到一定程度，再超音速混合，依据激波原理使混和气体的温度瞬间上升到裂解温度，获得裂解产品。对乙烷裂解生成乙烯的模拟实验表明，乙烯收率比一般反应器得到的高２０％，能耗却降低１５％以上。     

Regimes of Unstable Expansion and Diffusion Combustion of a Hydrocarbon Fuel Jet

Results of an experimental study of hydrodynamics and diffusion combustion of hydrocarbon jets are presented. Various regimes of instability development both in the jet flame proper and inside the source of the fuel jet are considered. The experiments are performed for the case of subsonic gas jet expansion into the air from a long tube 3.2 mm in diameter in the range of Reynolds numbers from 200 to 13 500. The fuel is the propane–butane mixture in experiments with a cold jet (without combustion) and pure propane or propane mixed with an inert dilutant (CO₂ or He) for the jet flame. The mean velocity and velocity fluctuations in the near field of the jet without combustion are measured. Among four possible regimes of cold jet expansion (dissipative, laminar, transitional, and turbulent), three last regimes are investigated. The Hilbert visualization of the reacting flow is performed. The temperature profiles in the near field of the jet are measured by a Pt/Pt–Rh thermocouple. An attached laminar flame is observed in the transitional regime of propane jet expansion from the tube. In the case of combustion of C₃H₈ mixtures with CO₂ or with He in the range of Reynolds numbers from 1900 to 3500, the transitional regime is detected in the lifted flame. Turbulent spots formed in the tube in the transitional regime exert a significant effect on the flame front position: they can either initiate a transition to a turbulent flame or lead to its laminarization.     

Modeling of dynamic compression of porous iron

A relation closing the model of a porous medium, which is based on the Maxwell representation of the irreversible strain mechanism, has been obtained. This model takes into account the effect of grain (particle) size on dynamic compression. To specify the model, use is made of the experimental data on uniform compression of specimen of porous iron. The shock adiabats have been calculated. The obtained results are compared with the data of independent experiments. The evolution of compression pulses of finite duration which propagate over a porous half-space is analyzed. The grain size is shown to affect the shock wave processes in a porous medium. It has been established that it is possible to estimate the stress (pressure) in a decaying shock wave by the known mass velocity and shock adiabat.Lavrent'ev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 4, pp. 124–133, July–August, 1994.     

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.