Cu-Ni-Al和Cu聚能射流侵彻后钢靶的毁伤特征

为了对比分析Cu-Ni-Al反应聚能射流和惰性Cu聚能射流对45钢靶的宏观侵彻特性和靶板的微观组织特征,分别进行了Cu-Ni-Al和Cu药型罩的侵彻实验,并利用光学显微镜、扫描电镜、能量色散光谱仪和Vickers显微硬度测量系统对回收钢靶进行表征。实验结果表明:Cu-Ni-Al反应射流对45钢的穿深与Cu射流相比明显降低,但其平均入口孔径提高了33.3%。两种聚能射流侵彻作用下钢靶中均存在残余射流区、白色区(马氏体和奥氏体的混合物)和变形区。与Cu射流相比,Cu-Ni-Al反应射流孔壁残余射流区的硬度值提高了34 MPa,孔壁尾部白色区的硬度值增加了95 MPa,其孔壁头部白色区的硬度值降低了28 MPa。两种聚能射流孔壁尾部白色区的硬度值均高于头部。研究结果可为评估反应材料药型罩聚能装药战斗部的毁伤效应提供一定的参考。     

杆式射流侵彻半无限靶的理论分析

 理论分析高速杆式射流侵彻半无限靶过程时,考虑速度梯度对聚能射流的影响,将射流进行分段计算,得到了射流拉伸后实际碰靶时的微元长度和直径变化。采用伯努利方程和静力学方法,通过对射流形状和速度分布作线性近似,理论分析了高速杆式射流侵彻半无限靶的过程,得到了靶体中的侵彻深度和侵彻孔径与射流长度、速度及直径之间的关系。将模拟结果与实验结果进行对比,结果表明理论分析结果与侵彻实验结果符合较好。     

大锥角聚能射流实验研究

 通过闪光X射线摄影技术，研究了两种大锥角射流的特性及其对钢靶的侵彻，并与小锥角射流进行了对比。研究结果表明：大锥角射流的头部速度较低，但直径和质量较大，在大炸高条件下对钢靶的侵彻孔深度浅，孔径大。     

冲击波影响下的聚能射流侵彻扩孔方程

 当聚能射流侵彻速度大于靶板声速时,由于冲击波的产生导致波阵面后材料的状态参数发生改变,影响聚能射流的侵彻扩孔过程,致使波阵面前后不能直接应用伯努利方程求解。在考虑侵彻过程中冲击波影响的基础上,对射流轴向侵彻和径向扩孔的力学特性进行了分析,并对冲击波的传播和衰减进行了假设,着重探讨侵彻速度大于靶板声速时冲击波的影响。针对侵彻速度大于和小于靶板声速两种情况,建立了相应的侵彻模型,提出了一个新的聚能射流侵彻扩孔方程。将该方程与Szendrei-Held模型进行了比较,结果表明,新模型更符合Held等人的实验数据,冲击波对轴向侵彻的影响远小于对径向扩孔的影响。     

射流侵彻陶瓷/橡胶/钢复合靶的数值仿真与实验研究

运用LS-DYNA动力学分析软件,对具有不同橡胶夹层厚度的陶瓷/橡胶/钢复合靶在30°和60°倾角下的射流侵彻情况进行了数值模拟。采用聚能装药基准弹,进行了剩余穿深实验,研究了射流侵彻陶瓷/橡胶/钢复合靶后射流速度、靶板变形和剩余穿深,分析了倾角和橡胶夹层厚度对复合靶抗射流侵彻性能的影响机理。结果表明:射流侵彻陶瓷/橡胶/钢复合靶的性能受倾角的影响很大,尤其是在大倾角下影响更为显著;橡胶夹层对射流侵彻性能有一定的影响,但其厚度的变化对射流侵彻性能的影响很小。     

增强后效复合药型罩结构的数值模拟

针对增强聚能射流的破甲后效问题,设计了等壁平顶锥形铜铝双层复合药型罩装药结构,采用冲击波物理显示欧拉动力学软件SPEED开展复合射流成型及对钢-铝间隔靶侵彻过程的数值模拟,分析内外双层药型罩高度比ε、药型罩锥角α等参数对复合射流成型和间隔靶侵彻性能的影响规律。研究结果表明:复合射流的头部速度随ε增大呈先减小后增加的趋势,在ε约为1/2时,可形成具有相近速度的铜铝同轴复合射流微元,利于铝射流微元与目标相互作用实现后效增强毁伤;且当α在50°~60°范围内时,复合射流中段为集中的铝射流微元,更利于侵彻后的爆炸或爆燃反应。对优化参数的复合药型罩结构数值模拟结果与文献公布的实验结果吻合较好。研究结果对增强后效聚能装药设计具有参考价值。     

射流侵彻陶瓷力学特性实验研究

 利用闪光X射线摄影技术观察了射流在氧化铝陶瓷靶中的侵彻过程。结果表明，射流在侵彻氧化铝陶瓷过程中，侵彻通道发生了一定程度的倒塌现象，致使后续射流断裂，部分断裂粒子扭曲、偏离侵彻方向，降低了射流侵彻能力。     

钛合金药型罩对纯铜及45钢靶的破甲特性

为了研究射流与靶板间的反应对其破甲性能的影响,选用钛合金药型罩分别对纯铜及45钢两种材质的靶板进行静破甲试验。研究结果表明:与钛合金反应不剧烈的纯铜靶板,静破甲试验后的破孔孔径较大,穿深较高;而与钛合金反应较为剧烈的45钢靶板,静破甲试验后的破孔孔径较小,穿深较低。对静破甲试验后纯铜靶板及45钢靶板进行了微观组织分析,研究了钛合金药型罩分别对纯铜靶板及45钢靶板的破甲特性及破甲机理,并探讨了射流与靶板间的反应对其破甲性能的影响。     

铝铜药型罩射流与侵彻数值模拟

为提高射流侵彻性能,根据聚能射流装置的射流形成特点,设计了爆炸复合铝铜金属体作为药型罩的聚能射流装置。此装置依据已有的锥角为42°的聚能装药紫铜药型罩改进而来。利用LS-DYNA软件中的MMALE多物质算法,对此装置的射流形成、侵彻金属靶体全过程进行数值模拟。在保持装药量不变的情况下,计算了当铝铜药型罩锥角分别为36°、38°、40°和42°时的射流形成及侵彻过程。结果表明:射流头部速度随着铝铜药型罩锥角的减小而增大;且锥角为38°时射流穿深最大。相比单纯金属铜药型罩情况,射流头部速度提高了13.2%,侵彻深度提高了14.5%。     

大法线角下射流的跳弹效应

国内外对大法线角下的射流侵彻问题缺乏系统研究。为此,对比分析了Tate模型、Rosenberg模型和可压缩流体力学模型3种跳弹模型,并对大法线角下射流侵彻装甲钢和铝靶进行了实验研究。理论分析表明,可压缩流体力学模型能更准确地预测跳弹角。实验结果显示:大法线角下射流的侵彻深度随法线角的增大而减小,射流的垂直侵彻深度仅为正侵彻深度的10%左右;射流头部速度为6 800m/s时,603装甲钢的跳弹角在6°~7°之间,铝的跳弹角在5°~6°之间。     

Collective behavior in a granular jet: emergence of a liquid with zero surface tension

We perform the analog to "water bell" experiments with granular jets. Rebounding from cylindrical targets, wide granular jets produce sheets or cones with shapes that mimic a zero-surface-tension liquid. The jets' particulate nature appears when the number of particles in the cross section is decreased: the emerging structures broaden, gradually disintegrating into diffuse sprays. The experiment has a counterpart in the behavior of quark-gluon plasmas generated by colliding heavy ions. There, a high collision density gives rise to collective behavior also described as a liquid.     

Penetration kinetics of a cumulative jet into brittle materials

The experimental results on the penetration of cumulative jets into brittle materials are analyzed to substantiate the assumption that continuous hydrodynamic penetration is violated. The penetration of a cumulative jet into a brittle material has a jumplike character and consists of hydrodynamic penetration, the collapse of the cavity, and secondary penetration into the collapsed material. For a continuous supply of a cumulative jet, this process is repeated at the penetration depth. The necessary conditions of the secondary penetration consist in a high strength of the brittle material and a high fracture rate, which should provide the spallation and collapse of the cavity walls. Jumplike penetration ends when a rarefaction wave passes to the zone of primary penetration.     

Collective penetration of cumulative jets into brittle materials

The group action of cumulative jets on a composite material made of corundum and glass-fiber reinforced plastic is studied. The obtained results show that the collective action of cumulative jets enhances the efficiency of resistance of a brittle material to high-speed penetration at certain geometric and time relations. These specific features manifest themselves under subsonic penetration conditions and support the mechanism of a radial action of a cavity in a high-strength brittle material on a penetrating cumulative jet.     

药型罩材料的晶粒度对射流性能的影响

 通过对紫铜药型罩的静破甲威力实验和脉冲X射线照像，研究了药型罩材料的晶粒度对射流性能的影响。研究结果表明，药型罩材料的晶粒度对射流动态延伸特性有重要影响。罩材料的晶粒细化可以增加有效连续射流的长度，推迟射流断裂的时间，提高静破甲威力水平。最后讨论了晶粒度对射流性能影响的机理。     

Mechanisms of manifestation of strength upon high-speed intrusion of metal jets into metals and brittle materials

Mechanisms of manifestation of strength upon penetration of cumulative jets into metals and brittle materials have been analyzed on the basis of studying the kinetics of intrusion. In contrast to intrusion into metals, which proceeds with a smooth variation in the velocity, the process of penetration of a cumulative jet into a brittle material is intermittent: the initial stationary intrusion stops and recommences after some time in an unstable form. The revealed features have been explained from the viewpoint of radial action of a cavern in a brittle material on a cumulative jet, when the primary intrusion of a jet causes radial convergence of fragments of cavern walls and the secondary penetration through the regions of interaction. The necessary conditions for the radial action are the high strength resistance and high destruction rate of brittle material is, providing the destruction and convergence of cavern walls. The collapse of the cavern and the secondary penetration terminate with the arrival of the unloading wave at the zone of primary intrusion.     

Analysis of the conditions for ultradeep penetration of powder particles into a metallic matrix

The critical conditions for ultradeep penetration of particles when a flux of high velocity particles interacts with a matrix material are examined from the standpoint of nonequilibrium thermodynamics. The problem of the change in entropy consistent with their deformation during loading is solved qualitatively for the example of aluminum and copper samples. It is shown that ultradeep penetration of particles is a system process of mass and energy transfer owing to a developed instability in the material caused by the shock-wave action of the particle flux. The degree of disequilibrium of the process is described by the dependence of the change in entropy on the deformation of the matrix material. It turns out that the ultradeep particle penetration process occurs only in a region lying beyond a bifurcation point. Zh. Tekh. Fiz. 68, 124–125 (July 1998)     

Nondeterministic approach to tree-based jet substructure

Jet substructure is typically studied using clustering algorithms, such as k(T), which arrange the jets' constituents into trees. Instead of considering a single tree per jet, we propose that multiple trees should be considered, weighted by an appropriate metric. Then each jet in each event produces a distribution for an observable, rather than a single value. Advantages of this approach include (1) observables have significantly increased statistical stability, and (2) new observables, such as the variance of the distribution, provide new handles for signal and background discrimination. For example, we find that employing a set of trees substantially reduces the observed fluctuations in the pruned mass distribution, enhancing the likelihood of new particle discovery for a given integrated luminosity. Furthermore, the resulting pruned mass distributions for (background) QCD jets are found to be substantially wider than that for (signal) jets with intrinsic mass scales, e.g., boosted W jets. A cut on this width yields a substantial enhancement in significance relative to a cut on the standard pruned jet mass alone. In particular the luminosity needed for a given significance requirement decreases by a factor of 2 relative to standard pruning.     

Effects of the penetration height of ethylene transverse jets on flame stabilization behavior in a Mach 2 supersonic crossflow

Effects of fuel jet penetration height on supersonic combustion behaviors were investigated experimentally in a supersonic combustion ramjet model combustor at a Mach speed of 2 and at a stagnation temperature of 1900 K. The jet-to-crossflow momentum flux ratio was varied to control the fuel-jet penetration height, using several injectors with different orifice diameters: 2, 3, and 4 mm. First, transverse nitrogen jets were observed to identify a relationship between the fuel jet penetration height and the momentum flux ratio by focusing Schlieren photography. Then, supersonic combustion behaviors of ethylene were investigated through combustion pressure measurements. Simultaneously, time-resolved images of CH* chemiluminescence and shadowgraphs were recorded with high-speed video cameras. Furthermore, a morphology of supersonic combustion modes was investigated for various equivalence ratios and fuel penetration heights in a two-dimensional latent space trained by the shared Gaussian process latent variable models (SGPLVM), considering CH* chemiluminescence images and the shock parameters. The results indicated that the penetration height of nitrogen jets was a function of the jet momentum flux ratio; this function was expressed by a fitting curve. Five typical combustion modes were identified based on time-resolved CH* chemiluminescence images, shadowgraphs, and pressure profiles. Even for a given equivalence ratio, different combustion modes were observed depending on the fuel penetration height. For an injection diameter of 3 and 4 mm, cavity shear-layer and jet-wake stabilized combustions were observed as the scram modes. On the other hand, although the cavity shear-layer and lifted-shear-layer stabilized combustions were observed, no jet-wake stabilized combustion was observed for an orifice diameter of 2 mm. Fuel penetration heights above the cavity aft wall were expected to affect the combustion behavior. Finally, a morphology of the supersonic combustion modes was clearly shown in the two-dimensional latent space of the SGPVLM.     

Penetration of long strikers under hydrodynamic conditions with allowance for the material compressibility

The influence of compressibility on the fast penetration of long metallic strikers into different barriers at interaction speeds of up to 10 km/s is investigated. The investigation is based on the hydrodynamic theory of penetration. Compressibility-related corrections to Lavrent’ev’s rate and depth of penetration, which were obtained in terms of the concept representing the penetration process as collisions of ideal incompressible liquid jets, are estimated. The variation of these corrections with the interaction speed under subsonic and supersonic conditions is analyzed. If the compressibilities of the striker and barrier materials differ radically, the penetration depth disagrees with that predicted by the hydrodynamic theory (assuming the incompressibility of the materials) by 10–15%.     

Quasi-radial wall jets as a new concept in boundary layer flow control

This work aims to introduce a novel concept of wall jets wherein the flow is radially injected into a medium through a sector of a cylinder, called quasi-radial (QR) wall jets. The results revealed that fluid dynamics of the QR wall jet flow differs from that of conventional wall jets. Indeed, lateral and normal propagations of a conventional three-dimensional wall jet are via shear stresses. While, lateral propagation of a QR wall jet is due to mean lateral component of the velocity field. Moreover, discharged Arrays of conventional three-dimensional wall jets in quiescent air lead to formation of a combined wall jet at large distant from the nozzles, while QR wall jet immediately spread in lateral direction, meet each other and merge together very quickly in a short distance downstream of the jet nozzles. Furthermore, in discharging the conventional jets into an external flow, there is no strong interaction between them as they are moving parallel. While, in QR wall jets the lateral components of the velocity field strongly interact with boundary layer of the external flow and create strong helical vortices acting as vortex generators.