子弹侵彻靶板研究

为了有效打击地下目标，或是对此类问题的防护，高速弹丸对结构的侵彻毁伤研究越来越受到军事部门的关注，然而通过原型实验费时费力，因此本文在理论分析的基础上，采用ANSYS／LSDYNA软件对整个过程进行数值模拟，描述和动态显示问题的整个过程，可以节约实验投入．为提高弹丸侵彻效果提供参考。     

弹体撞击半无限金属靶极限侵彻深度分析

基于空腔膨胀理论和修正的流体动力学理论,提出了球形弹头弹体侵彻半无限金属靶深度的计算方法.进而根据侵彻极限状态得出的极限撞击速度,得到了极限侵彻深度计算公式,并与试验数据进行对比分析,验证了此种方法的实用性.     

炸高对侵彻效应影响试验和数值模拟研究

为了研究炸高因素对爆炸成型弹丸(EFP)成型性能及侵彻深度的影响,利用有限元软件LSDYNA,建立了球缺罩型聚能装药仿真计算模型。研究了十种不同炸高条件下,EFP着靶时性能参数和侵彻45#钢靶过程,并与该装药静破甲试验结果进行了对比分析。结果表明:试验与数值模拟结果较吻合,最大误差为10%,EFP装药的有利炸高与装药直径之比为3.9~4.4,最大破甲深度约为装药直径的0.92倍。     

EFP构型对其气动特性和侵彻性能影响分析EI北大核心CSCD

为综合分析爆炸成型弹丸(explosively formed projectile,EFP)的构型对其气动特性和侵彻性能的影响,实现兼具良好气动特性和侵彻性能的EFP设计。开展了EFP的成型和飞行试验,在试验验证数值有效性的基础上,基于任意拉格朗日欧拉(arbitrary Lagrange-Euler,ALE)算法分析了后翻型EFP的三种典型构型(实心杆状、小空腔状、大空腔状)的成型过程及气动特性,并进一步开展了三种构型EFP侵彻半无限厚45#钢的数值模拟。结果表明:EFP小空腔结构提高了其飞行稳定性;空腔的增大降低了EFP的存速能力,实心、小空腔、大空腔三种构型的EFP炸高在1000倍弹径(30 m)时平均速度降分别为158 m/s,172 m/s,210 m/s;随着EFP空腔的增大,靶板开坑形貌由漏斗状逐渐转为等直径状。从工程实践角度设计EFP构型时:对于近距离目标应选取实心型;对于远距离目标应选取小空腔型。     

不同倾角侵彻下半穿甲战斗部结构件受力仿真分析

利用有限元软件LS-DYNA建立了某型半穿甲弹战斗部模型,进行了在初始速度为300m/s,靶厚为34mm,倾角分别为0°、15°、30°、45°、60°条件下的侵彻数值模拟,对战斗部穿甲性能进行了研究,分析在侵彻过程中不同倾角对战斗部内部结构部件所受过载、应力及应力集中位置分布的影响。结果表明:小倾角侵彻时内部结构件所受最大应力随倾角的增大略有减小;大倾角侵彻时内部结构件所受最大应力随倾角的增大而增大,容易出现变形和失效,最终可能影响战斗部的整体功能。     

钝头弹高速斜侵彻中厚背水金属靶板的机理研究

为探讨高速钝头弹斜侵彻中厚背水金属靶板的机理,根据不同的受力状态及耗能机制,结合中厚背水靶板抗高速斜侵彻特点,通过厚度等效,将斜侵彻转化为相应的正侵彻。然后,将整个侵彻过程分为压缩镦粗、剪切压缩和剪切扰动三个阶段。基于三阶段侵彻机制,建立了钝头弹高速斜穿甲中厚背水金属靶板后的瞬时余速计算模型,并讨论了该计算模型的局限性。采用该模型计算了3.3 g立方体弹丸斜穿甲5 mm背水钢板后的瞬时余速,理论计算值与试验结果及相应的仿真计算值均吻合较好。由于该模型考虑了靶后水介质的动支撑作用及动能耗散等效应,在一定的适用范围内,能对钝头弹高速斜侵彻中厚背水金属靶板的瞬时余速进行合理地预测,具有一定的理论价值和工程应用价值。     

间隔介质对射流侵彻间隔靶影响的数值模拟

为了研究间隔介质对聚能射流侵彻间隔靶能力的影响,运用AUTODYN软件分别对射流侵彻水和空气介质间隔靶过程进行数值模拟。主要从侵彻过程中射流形态、间隔介质形态、射流头部速度三个方面出发,对模拟结果进行分析。首先与试验结果进行对比,验证了数值模拟分析的合理性和可靠性。然后通过分析数值模拟结果,得到射流头部速度随侵彻介质距离变化的拟合公式,并得出:射流头部速度在间隔靶水介质中衰减比空气介质中高17.6%,且金属射流速度愈低,相同距离水间隔介质对射流侵彻能力的衰减效果愈明显。     

管-杆伸出式弹芯垂直侵彻半无限靶机理研究

基于管-杆伸出式弹芯材料满足刚-塑性本构关系及该弹芯在侵彻过程中视为准定常运动等假设,通过分别对头部、管体、管与杆重合部及杆体等不同侵彻阶段的理论分析与推导,建立起该弹芯垂直侵彻半无限靶的简化模型。在1300 m/s~1500 m/s的速度范围内,对该弹芯进行了数值模拟与验证试验研究。通过对模型计算、数值模拟及试验结果之间的对比,表明简化模型及数值模拟方法的可靠性,得出了该弹芯垂直侵彻靶板所产生弹坑的形貌特征与形成机制,以及该弹芯在侵彻中的相对优势情况与侵彻深度随速度的变化规律。     

加筋靶板受到球形弹丸侵彻时的速度经验公式探讨

运用有限元模型仿真弹丸侵彻靶板的全过程，通过计算得到大量数据，然后在弹丸穿透平板时极限速度和剩余速度经验公式的基础上，来探讨弹丸穿透单筋板时的极限速度和剩余速度的经验公式。     

High velocity penetration of homogeneous, segmented and telescopic projectiles into alumina targets

Segmented and telescopic projectiles are designed to make efficient use of the higher impact velocities achievable with new acceleration techniques. This concept has been found to work against steel armour. In this study, we compare the penetration capability into an alumina target for these unconventional projectiles with that of a homogeneous projectile. The influence of segment separation distance and core-to-tube diameter ratio were simulated for the impact velocities 2.5, 3.0 and 3.5 km/s. The simulated final penetrations are compared to test results for one type of each of the homogeneous, segmented and telescopic projectiles at 2.5 and 3.0 km/s. Both simulations and tests show that the unconventional projectiles have better penetration capability than a homogeneous projectile with the same initial geometry.     

Numerical simulations of oblique-angle penetration by deformable projectiles into concrete targets

Numerical simulations of oblique-angle penetration by deformable projectiles into concrete targets are performed in this paper by using the three-dimensional finite element code LS-DYNA, into which a combined dynamic constitutive model which can simultaneously describe both the compressive and tensile damage of concrete is implemented. As a consequence, the ballistic trajectories and the depths of penetration under different oblique angles (from 10° to the ricochet angle) are obtained. Moreover, the damage distribution of concrete after oblique penetration is procured, which can really reflect the tensile and compressive damage of concrete. The numerical results for the depths of penetration are compared with experimental data obtained by previous authors and show good agreement.     

The influence of confinement on the penetration of ceramic targets by KE projectiles at 1.8 and 2.6 km/s

This paper presents the results of scale size experiments using a tungsten-alloy long-rod projectile fired against 97.5% Al₂O₃ ceramic targets at 1.8 and 2.6 km/s. Two targets were used, one having lateral steel confinement; the other without. The projectile overmatched the target, and residual projectile length and velocity were recorded using ballistic-syncro photography. Flash radiography was used during penetration of the unconfined target to obtain the penetration velocity. Manganin pressure gauges were also used to obtain additional data on the response of the ceramic target during penetration. Results from the eight experiments indicate that the confinement reduced the residual energy of the projectile at both impact velocities. Expressed in terms of the projectile impact energy, 55–56% was lost in the unconfined target at 2.6 km/s compared with 60% for the confined design. The same trend was found at 1.8 km/s with 68% and 72–73% for the unconfined and confined, respectively. Predictions using the QinetiQ GRIM2D hydrocode and a simplified form of the Johnson–Holmquist ceramic material model agreed well with the experiments for three out of the four test configurations. The predicted projectile erosion and retardation against the confined target at 1.8 km/s was excessively high. Analytical predictions using the Tate modified Bernoulli equation also gave reasonably accurate predictions for three of the tests, but values for the Tate target ‘strength’ extracted from experiments using a different target configuration were not accurate for the target design used in this paper.     

On the temperature dependence of the London penetration depth in a superconductor

In the framework of the electron-phonon theory of superconductivity [1], it is shown that the magnetic field penetration depth _L increases like a certain power of temperature atTT _c due to the low-lying excitations in the phonon spectrum. For the acoustic phonons with the density of states ² the penetration depth increases T ⁵. The origin of such a high power ofT is the same as that in the case of resistivity of the normal metal: the phonon corrections to the electromagnetic vertex should be taken into account, and major terms (T ³) cancel, the surviving ones having a higher power ofT. The possibility of linear and quadratic terms in _L(T) is discussed in a model of electrons interacting with two-level centers [2].     

空气夹层对含液结构在球形弹体侵彻作用下动态响应的影响

基于一维应力波理论对高强水中冲击波在不同介质间的传播进行分析,提出了2种防护含液结构的空气夹层形式,建立了数值仿真模型。在验证数值仿真方法的基础上,分析了含液结构在弹体侵彻过程中空穴演化、冲击波传播、空气夹层结构变形等的动态变化过程及弹体速度衰减规律,讨论了不同舱室结构在球形弹体侵彻作用下的冲击波特点和结构不同组成部分的能量转换关系,对比了不同弹速下前后板的塑性变形。研究结果表明:(1)在含液结构中添加空气夹层能有效降低含液结构前板和后板的冲量、能量和塑性变形;(2)空气夹层影响前后板变形的主要原因为阻抗失配和空气夹层变形引起的稀疏波及液体空化;(3)从整体看,双层间隔板结构衰减前后板变形能力优于方格夹层板结构,但随着弹速的增加,双层间隔夹层板的前后壁变形相互制约,2种结构对含液塑性变形的改变逐渐接近。     

基底厚度小于热渗透深度的石墨烯薄膜热声理论

基于热声效应,对基底厚度小于热渗透深度的石墨烯薄膜发声器进行理论和仿真研究。首先,利用石墨烯薄膜发声器的热功率平衡方程与气体中的热弹性耦合线性方程组推导出了石墨烯薄膜发声器的近/远场声压表达式。将理论计算结果与实验测试值进行对比,二者吻合良好,验证了理论模型的正确性。然后,利用仿真软件对石墨烯薄膜的近远场声压值进行了仿真计算,并将仿真值与理论值进行对比,二者有良好的一致性,验证了仿真计算方法的有效性。研究表明,石墨烯薄膜发声器的远声场为球面波,近声场近似为平面波。在远场低频段,声压级随输出声频率的增加而缓慢增大;在近场高频段,声压级几乎不受输出声频率的影响。研究结果为基底厚度小于热渗透深度情形下的热致发声器提供了理论计算和分析方法,对石墨烯薄膜声源器件的实验研究具有指导意义。     

线性聚能装药侵彻深度的影响因素

为了研究民用膨化硝铵炸药为主装药的线性聚能切割的工艺参数,采用实验研究和三维数值模拟(ANSYS/LS-DYNA)相结合的方法,对以膨化硝铵炸药为主装药的聚能射流侵彻钢靶板过程的特点和规律进行了研究。对比各工况数值模拟结果与实验结果表明,2种方法的侵彻深度吻合较好,验证了拉格朗日-欧拉(ALE)方法的有效性,说明可采用此方法模拟射流的形成和侵彻。研究结果表明,采用民用膨化硝铵炸药作为主装药用于线性聚能切割时,在实验给出的工况条件下,炸高为40 mm,药型罩厚度为1.0 mm,药型罩锥角为80°时,可获得最大侵彻深度。     

Shape effects in hypervelocity impact on semi-infinite metallic targets

In this study, an existing penetration equation, which was originally designed to give the penetration depth of spherical projectiles at hypervelocity into semi-infinite metallic targets, was modified to give the penetration depths of rotationally symmetric ellipsoid shaped projectiles into semi-infinite targets. To that purpose, a shape factor was defined in order to be able to describe the ellipsoid shape with a single number. The shape factor corresponds to the l/d ratio of rod- or disk-like projectiles. It was shown, that existing penetration equations can be modified to account for the shape of the projectile by introducing a single factor fⁿ. From the experimental and simulation data available in this study, N=0.45 was derived as a suitable exponent to describe the shape effect. In addition to the experiments numerical simulation was performed to enhance the data base and to show it's value for further investigations of the shape effect.     

Estimation of the depth of frost penetration in both uniform and layered soils in frost-affected regions

One of the most important factors affecting pavement performance is climate, including frost action and precipitation. The performance of pavements in frost-affected regions depends to a large degree on the depth of frost penetration. In this paper, a simple predictive tool is developed to calculate a new correction coefficient depending upon the thermal ratio and fusion parameter. The new correction coefficient can be used in follow-up calculations to estimate the depth of frost penetration for both uniform and layered soils in frost-affected regions to evaluate the performance of pavement. The results of the proposed method are found to be in excellent agreement with reported data in the literature with average absolute deviation being less than 0.8%. The predictive tool is simple, straightforward and can be readily implemented in any standard spreadsheet programme leading to accurate, smooth and non-oscillatory data points. The prime application of the method is as a quick-and-easy evaluation tool in conceptual development and scoping studies in which the depth of frost penetration for both uniform and layered soils in frost-affected regions is being considered. The method may also serve as a benchmark in numerical and rigorous simulation studies.     

Effects of anisotropy of the turbid media on the photon penetration depth

Biomedical applications of near infrared radiation (NIR) techniques (i.e. based on light wavelengths roughly between 400 and 1100?nm) require that a preliminary estimate of the tissue volume being investigated be found. One possible estimate is the depth to which a photon penetrates a tissue before eventually emerging at a separating plane at a given time. A simple model for this problem can be based on a lattice random walk and was initially analyzed when the associated optical coefficients are isotropic with respect to the geometrical configuration. Here we include the effects of anisotropy in the optical coefficients, finding that at long times the statistical properties of the depth of penetration can be accounted for by very simple scaling factors while at short times the anisotropy effects can be quite noticeable.