Experimental study of wave effects in the explosive loading of steel plates and shells

The shock stage in the behavior of explosively loaded steel plates and cylindrical shells was studied experimentally. A three-wave structure of the shock front was observed for both plane and cylindrical samples. The split-off strength of the shell and plate materials was determined. For both loading schemes, the split-off was shown to not occur for the samples with a thickness of 1 mm. The decay of the pressure amplitude in the first shock wave was found to be appreciably stronger for the cylindrical samples than for the plane samples.     

A study of the effects of mass transfer under quasi-spherical loading of a composite spherical sample

Metallography and electron probe microanalysis were used to study the structure of a composite ball, 60 mm in diameter, subjected to quasi-spherical shock-wave loading. The sample consisted of spherical steel and brass shells and a brass cylinder at the center. Converging shock waves were generated by a spherical HE charge, which was initiated at several points uniformly distributed over its external surface. The pressures at the surface and center of the sample were ～40 and ～100 GPa, respectively. Brass and steel were observed to penetrate into the narrow channels of the joints between the halves of the shells and into the compact material. The depths of penetration into the joints and compact material were 3.2 and 0.3 mm, respectively. Mass transfer occurred along the radius from the surface to the center of the sample and in the opposite direction. The mass transfer effects revealed are of hydrodynamic nature.     

Shock wave propagation in gases under subatmospheric pressure

In the present paper the results of the experiments on the shock wave dynamics under subatmospheric pressure in neutral gases are presented. The characteristics of spherical and plane configuration shock wave excitation and propagation are studied in the pressure region 1 torr<p<760 torr. It is shown that whenp=3 torr it is still possible to fix successfully the shock wave appearance and propagation in various neutral gases. The pressure dependence of the shock wave propagation velocity and amplitude is determined experimentally. It is shown that when the pressure decreases the shock wave amplitude decreases and an increase of the Mach number takes place. In the case of plane shock wave the Mach number reaches the valueM=5.2 under the pressurep=3 torr.     

二氧化硅气凝胶的防爆震性能及机理研究

利用聚偏二氟乙烯压电传感器研究了爆炸加载下冲击波在二氧化硅气凝胶中的传播特性,并对冲击波在二氧化硅气凝胶和泡沫铝中的传播特性进行了比较.结果表明:在二氧化硅气凝胶中冲击波的强度随传播距离的增加呈现指数衰减的趋势.冲击波在二氧化硅气凝胶中衰减比在泡沫铝中衰减明显.由于二氧化硅气凝胶内部特殊的纳米多孔网状结构,导致冲击波在二氧化硅气凝胶中的衰减效果较好.冲击波在二氧化硅气凝胶中的传播速度极低,因此冲击波在二氧化硅气凝胶中传播时卸载波的追赶卸载效应非常明显,这又进一步促进了冲击波的衰减.     

Nonstationary processes in a Cerenkov VHF generator with dielectric loading

The dynamics of nonstationary processes in a VHF generator loaded with a dielectric and excited by a high current relativistic electron beam is investigated by means of the numerical solution of the self-consistent set of Maxwell-Vlasov equations. The results are compared with the linear theory of a stationary generator. The case of a beam current above the critical value, when a virtual cathode is formed in the drift space, is also included.     

窗口声阻抗对锆相变动力学的影响

基于磁驱动加载装置CQ-4开展了锆的斜波压缩相变实验,研究了锆样品后表面窗口声阻抗对相变波形的影响.实验结果显示,锆后表面为较低声阻抗窗口(自由面和LiF窗口)时,相变起始对应的特征粒子速度约331.0 m/s,而高阻抗蓝宝石窗口时,特征粒子速度约301.9 m/s,特征速度对应的压力从约9.14 GPa下降到8.27 GPa.相变对应的速度特征拐点是与多种因素相关的实验信息,因此它对应的压力并不是材料属性参数相变压力.结合基于热力学Helmholtz自由能的多相状态方程和非平衡相变动力学方程开展了锆的相变动力学数值模拟研究,相变弛豫时间为30 ns,计算结果与三种情况的实验结果符合良好,可以较好地模拟斜波压缩下锆的弹塑性转变、相变等物理过程.在压力-比容和温度-压力热力学平面,相变前锆的准等熵线与冲击绝热线差异很小,相变后准等熵线都位于冲击绝热线下方,随着压力的增加准等熵线和冲击绝线偏差越来越大,温度-压力平面中在20 GPa时相差约100 K.相变开始后,由于相变引起比容的间断,导致锆的拉氏声速迅速下降约7%,相变完成后拉氏声速恢复到体波声速.     

爆轰加载下弹塑性固体Richtmyer-Meshkov流动的扰动增长规律

研究了冲击波加载弹塑性材料扰动自由面的动力学演化过程,分析了高能炸药爆轰驱动时初始扰动与材料性质对扰动增长的影响.研究结果表明:初始扰动的振幅与波长之比越高,扰动越易增长,强度越高的材料扰动增长幅度越小;扰动增长被抑制时,尖钉的最大振幅与增长速度无量纲数之间存在线性近似关系,进一步理论分析表明尖钉的振幅增长因子与加载压力、初始扰动形态和材料强度有关,该理论关系作为扰动增长规律的线性近似在一定范围内适用于多种金属材料.     

Electrical and radiative processes in ball lightning

Summary The observational parameters of ball lightning are given, together with an analysis of electrical processes during the origin and evolution of ball lightning. It is suggested that ball lightning formation takes place in a unipolar plasma with a high concentration of charged particles. According to the analysis such a plasma is formed as a results of electric breakdown of atmospheric air between a dust cloud and a hard surface. A comparison is made between observational ball lightning as a light source, a black body and a flame. It is shown that the luminosity of ball lightning is created by separated hot regions with a temperature of about 2000 K. Excited atoms or molecules in these regions are found in thermodynamical equilibrium with air. The waves of ball lightning luminosity spread along separated threads of the active substance of ball lightning, with some 10²⋎10⁴ threads being involved in this process. The luminisity of many points is perceived as a volume radiation of ball lightning.

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Riassunto Si danno i parametri d’osservazione del ball lightning insieme ad un’analisi di processi elettrici durante la sua origine e evoluzione. Si suggerisce che la sua formazione avvenga in un plasma unipolare con alta concentrazione di particelle cariche. Secondo l’analisi tale plasma si forma in quanto risultato di una scarica disruttiva di aria atmosferica tra una nuvola di polvere e una superficie dura. Si fa un confronto tra il ball lightning osservato come fonte di luce, un corpo nero e una fiamma. Si mostra che la luminosità del ball lightning si crea da regioni calde separate con una temperatura di circa 2000 K. Si trova che atomi eccitati o molecole in queste regioni sono in equilibrio termodinamico con l’aria. Le onde di luminosità del ball lightning si diffondono lungo fili separati della sostanza attiva del ball lightning con circa (10²⋎10⁴) fili coinvolti in tale processo. La luminosità di molti punti è percepita come radiazione di volume del ball lightning.

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Резюме Приводятся наблюдаемые параметры шаровой молнии. Анализируются электрические процессы при образовании и эволюции шаровой молнии. Предполагается, что шаровая молния образуется в униполярной плазме с высокой концентрадией заряженных частиц. Согласно проведенному анализу, такая плазма образуется в резяльтате электрического пробоя атмосферного воздуха между рылевым облаком и твердой поверхностью. Проводится сравнение наблюдаемой шаровой молнии, как источника света, света, с черным телом и с пламенем. Показывается, что излучение шаровой молнии обрззуется отдельными горячими областями с температурой около 2000 К. Отмечается, что возбужденые атомы или молекулы в этих областях находятся в термодинамическом равновесии с воздухом. Волны илучения шаровой молнии распространяются вдоль отдельных нитей активного вещества шаровой молнии, причем в процессе участвует порядка 10²⋎10⁴ нитей. Светимость большого числа точек воспринимается как объем излучения шаровой молнии.

     

Shock wave structure in a two-components gas mixture

Summary The nonlinear differential equations describing the problem of shock wave structure in a two-component gas mixture are reduced to a system of two coupled nonlinear differential equations. This system is solved numerically using the finite-difference method. It is found that the relative shock wave thickness of the mixture increases with the increase of the ratio between the viscosity coefficients when the ratio between the mass fractions is constant. It is also shown that the relative shock wave thickness of the mixture decreases with the increase of the ratio between the mass fractions when the ratio between the viscosity coefficients is constant.

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Riassunto Si riducono le equazioni differenziali non lineari che descrivono il problema della struttura dell’ onda d’urto in una miscela di gas a 2 componenti a un sistema di due equazioni differenziali accoppiate non lineari. Questo sistema si risolve numericamente usando il metodo delle differenze finite. Si trova che il relativo spessore dell’onda d’urto della miscela aumenta con l’aumento del rapporto tra i coefficienti di viscosità, quando il rapporto tra le frazioni di massa è costante. Si mostra anche che lo spessore relativo dell’onda d’urto della miscela diminuisce con l’aumento del rapporto tra le frazioni della massa, quando il rapporto tra i coefficienti di viscosità è costante.

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Резюме Нелинейные дифференциальные уравнения, описывающие проблему структуры ударной в двух-компоентной газовой смеси, сводятся к системе двух связанных нелинейыых дифференциальных уравнений. Получается, что относительная толщина ударной волны в смеси увеличвается с увеличением отношения между коэффиыентами вязкоти, когда отнощение между массовыми доями остается постоянным. Также показывается. что относительная толщина ударной волны уменьшается с увеличением отношения между массовыми долями. когда отношение между коэффициентами вязкости остается постоянным.

     

Aspects of the reflexion and free wave properties of a composite panel under fluid loading

The response of a composite panel to external forcing, with inclusion of fluid loading effects, is considered. Of the two strata comprising the composite panel one, backed by a vacuum, is of the conventional thin elastic plate or membrane kind, while the other, in contact with the fluid, is more like an elastic solid and may suffer significant compression. The behaviour of the acoustic field close to grazing incidence is examined, this behaviour being determined by that of the plane wave reflexion coefficient. In the absence of the upper stratum it is well known that the reflexion coefficient has the value ?1 around grazing incidence, so that direct and reflected fields from an external source cancel and preclude the propagation of a genuine acoustic field over the surface (a situation known in optics as the “Lloyd's mirror” effect). It is shown that, at any given frequency, an impedance for the upper stratum can be prescribed which will lead to the value +1 for the grazing incidence reflexion coefficient, and will thus obviate the severe power loss which would otherwise occur in directions close to the surface. Next the free subsonic surface waves which can exist in the coupled three-part (two-layer panel plus fluid) system are examined. It is shown analytically that, if the upper layer has low impedance controlled by stiffness forces, a new surface wave can exist in the system. This wave essentially involves the stiffness of the upper layer and the mass of the fluid, and has a wavenumber much higher than that of the surface wave in a single conventional panel. It is also shown from numerical studies that two subsonic surface waves will exist over quite a wide range of parameters, though not necessarily with the wide wavenumber separation of the low impedance case. A discussion is given of the possible importance of the high wavenumber mode in the case of excitation by high wavenumber boundary layer turbulence, and of the significance of two free subsonic surface wave modes in calculations of energy transmission over composite panels of the kind modelled here.     

Deformation processes in tungsten carbide powder ground in a ball mill

Electron diffraction microscopy and x-ray structural analysis are used to study the evolution of particle size and defect structure in tungsten carbide powder during deformation by grinding in a ball mill. Correlations are obtained between grinding time, particle size, and defect structure parameters (scalar dislocation density and azimuthal component of the full disorientation angle).Structural Engineering Institute, Institute of Strength Physics and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 62–67, May, 1992.     

Dynamic and fractal properties of SP-28 steel under high-speed loading conditions

Using an interferometric method to record the velocity of the free surface of a target subjected to two-dimensional shock loading, it is shown experimentally that the decrease in the compression pulse amplitude is due to the nonstationary nature of mesoscale processes — the amplitude decrease is progressively larger for higher rates of change of the variance of the mesoparticle velocity. It is shown theoretically that the loading rate influences the spallation strength of a material in a planar collision only if the variance of the particle velocity is nonzero. A fractal analysis of the spallation surfaces of steel samples is performed by quantitative fractography methods. An expression relating the fractal dimension of the spallation fracture surface and the variance of the mesoparticle velocity is derived. For typical values of the load pulse parameters for which back-side spallation occurs the fractal dimension agrees satisfactorily with the fractal dimensions for triadic Koch islands. Zh. Tekh. Fiz. 68, 43–49 (October 1998)     

Dislocation structure of plastic relaxation waves in polycrystals and alloys under intense shock wave loading

The influence of the structure factors (sizes of grains and precipitates) on the dislocation structure formed in polycrystals and alloys behind the shock wave front (elastic precursor) has been theoretically discussed in terms of the dislocation kinetic relationships and kinetic equation for the dislocation density. The critical conditions of the transition from the cellular dislocation structure to a uniform dislocation distribution have been formulated. These conditions are used to determine the dependences of the critical pressure, above which the dislocation distribution becomes uniform, on the grain size and precipitate volume density.     

Dislocation nonlinearity and nonlinear wave processes in polycrystals with dislocations

Based on the modification of the linear part of the Granato–Lücke dislocation theory of absorption, the equation of state of polycrystalline solids with dissipative and reactive nonlinearity has been derived. The nonlinear effects of the interaction and self-action of longitudinal elastic waves in such media have been theoretically studied.