Acceleration Evaluation Model of Metal/Gas Interface by Extra Electric Field Induced by Shock under Extreme Impacting Conditions
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摘要: 采用基于电子力场势函数的分子动力学方法，模拟了极端冲击压缩（22.50～78.75 km/s）下Li/H2界面的演化过程。计算结果表明，在极端冲击压缩条件下，激波压缩导致物质电离，由于电子和离子的扩散差异，激波附近出现电荷分离区，进而诱导出现附加电场。通过沿激波传播方向进行一维电荷统计和理论分析，发现在激波强度一定的情况下，随着激波的运动，电荷分离区的强度和宽度在整个过程中基本保持恒定，与激波强度正相关；进一步对电荷分布进行积分，得到由电荷分离引起的附加电场沿冲击波传播方向的变化。统计分析了附加电场影响下金属/气体界面附近金属侧物质产生的加速度随时间的变化，发现附加加速过程呈脉冲形态，满足Rayleigh模型。通过计算拟合，得到该模型的关键参数与初始冲击加载速度的关系，最终获得电离诱导附加电场引起界面金属侧物质附加加速度的经验计算公式。Abstract: The evolution processes of metal/gas (Li/H2) interface at extreme impacting conditions (22.50–78.75 km/s) were numerically studied by molecular dynamics (MD) method incorporated with the electron force field (eFF) model. It was found that the strong shock compression leads to ionization and the electron/ion separation is produced due to different diffusivities of ions and electrons. Then a strong extra electric field was established adjacent to shock font. Through 1D statistic along shock propagating direction from MD results and theoretical analysis, it was found that the electron/ion separation is moving with shock and the intensity and width of electron/ion separation zone are kept to be constant during shock propagating process and determined by shock strength. Further integrating the extra electric field and extra acceleration of metal material adjacent to the interface, the time histories of material acceleration were obtained. It was found that the extra material acceleration curves were in accordance with Rayleigh model. The key parameters were fitted based on computation results. Finally, an empirical extra acceleration evaluation model of metal material on Li/H2 interface under impact velocity range of 20–80 km/s was established.
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图 3 电荷密度分布一维模型以及电荷分离区宽度和强度的时间历程 (vp=22.50 km/s)
Figure 3. 1D model of charge density distribution and time histories of the width and intensity of the electron-ion separation zone for vp =22.50 km/s
图 2 vp=22.50 km/s时电荷密度分布一维统计及其随时间的变化
Figure 2. 1D statistic of charge density distribution for vp=22.50 km/s case and its patterns at different moments
图 4 一维附加电场和附加加速度(t=2.75 ps，vp=22.50 km/s)的eFF MD统计分析结果和基于1D电荷密度模型的计算结果对比
Figure 4. Comparison of 1D extra electric field and extra acceleration of materials between results of eFF MD statistics and 1D charge density model (t=2.75 ps of vp =22.50 km/s case)
图 5 不同冲击加载速度vp下界面金属侧物质附加加速度的变化历程
Figure 5. Acceleration time histories of material located at the metal side of the interface at different vp
图 6 Rayleigh模型的amax和τrise与vp的拟合关系
Figure 6. Fitted correlations of amax and τrise with vp in Rayleigh model
表 1 不同冲击加载速度下分离区的宽度和强度统计
Table 1. Statistics of the width and intensity of the electron-ion separation zone at different impact velocities
vp/(km·s–1) Width/nm Intensity/(108 C·m–3) 22.50 4.65 4.55 45.00 6.40 6.11 67.50 8.65 10.25 
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表 2 不同加载速度下Rayleigh模型的拟合参数
Table 2. The fitted parameters of Rayleigh model at different vp
vp/(km·s–1) amax/(1017 m·s–2) τrise/ps 22.50 1.7 0.50 33.75 1.9 0.38 45.00 3.5 0.30 56.25 5.3 0.24 67.50 7.5 0.20 78.75 12.0 0.17
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