Influence of longitudinal magnetic field on coefficient ofultimate elongation of shaped charge jet
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摘要: 在分析纵向磁场能够增强聚能射流稳定性的基础上，根据聚能射流的运动方程以及聚能射流的塑性失稳条件，推导得到了聚能射流在纵向磁场中的极限拉伸系数计算公式，并计算了有、无磁场情况下极限拉伸系数的比值。通过两种炸高下的实验研究对理论模型进行了验证。结果表明：由于磁场的存在而引起的电磁力抑制了聚能射流颈缩的发展，进而延长了射流成型的惯性拉伸阶段，最终使聚能射流在磁场中的极限拉伸系数在一定程度上得到了增加；理论和实验所得结果吻合较好。运用所建立模型可以较准确地反映磁场对聚能射流极限拉伸系数的影响。Abstract: The coefficient of the ultimate elongation is one of significant parameters related with theoretical calculations of a shaped charge jet (SCJ). Based on the effect of a longitudinal magnetic field on the stress-strain of SCJ, and following the motion equation and the plastic instability condition, the formula of the coefficient of the ultimate elongation of a shaped charge inside the magnetic field was obtained and, using this formula, the ratio of the coefficient of the ultimate elongation was calculated respectively with and without the existence of a magnetic field. In addition, the theoretical model was verified through the experiments with two different standoffs. The results indicate that the electromagnetic force arising from the deformation of the SCJ due to the magnetic field that has penetrated into its material inhibits the development of the necking, and extends the stretching stage before the SCJ breaks up into particles, thus increasing the coefficient of the ultimate elongation. Predictions from the theoretical calculation are in good agreement with the data obtained from the experiments.
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图 3 起爆后30和50 μs的X射线照片
Figure 3. X-rays of shaped charge jet at 30 and 50 μs after initiation
图 7 炸高650 mm情况下聚能射流与磁场的耦合时序图
Figure 7. Sequence diagram of SCJ coupled with a magnetic fieldwith standoff of 650 mm
图 9 射流单元通过强磁体时在轴线上的磁感应强度
Figure 9. Magnetic induction intensities of element of SCJ passing through high field magnet
图 10 极限拉伸系数的比值随磁感应强度的变化
Figure 10. Change of ratio of coefficient ofultimate elongation with magnetic induction intensity
表 1 测量参数
Table 1. Measured parameters
单元 结构及连接特征 L/μH R/mΩ C/μF 电容器组 4台并联 - - 77.9 强磁体 矩形(2 mm×4 mm)截面铜导线双层并联 12 6.6 - 连接导线 截面为41.5 mm2的铜排 95 32.8 - 
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表 2 不同速度的射流单元进入和离开强磁体的相关参数
Table 2. Parameters of jet elements with different velocities entering and leaving high field magnet
h/mm v/(mm·μs-1) t1/μs t2/μs Δt/μs B/T 6.5 38.62 61.69 23.1 1.544 6 42.77 67.77 25.0 1.673 5 53.56 83.56 30.0 1.977 490 4 69.75 107.25 37.5 2.337 3 96.73 146.73 50.0 2.654 2 150.70 225.70 75.0 2.239 1 312.60 462.60 150.0 1.666 6 110.0 114.4 4.4 0.450 5 110.0 135.5 25.5 0.424 4.78 110.0 141.4 31.4 0.520 650 4 129.7 167.2 37.5 1.218 3 170.0 220.0 50.0 2.270 2 250.7 325.7 75.0 2.376 1 492.5 642.5 150.0 1.712
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表 3 理论计算与实验对比
Table 3. Comparison of theoretical calculation with experiments
h/mm B/T l/mm αexp αth εα/% 490 0 8.01 1 1 0 490 2.02 10.29 1.28 1.31 2.3 650 0 9.18 1 1 0 650 1.76 11.60 1.26 1.20 4.8
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