[论文解读] Non-isentropic layers in matter behind shock and ramp compression waves

K. V. Khishchenko, Alexander E. Mayer|arXiv (Cornell University)|Jul 31, 2014

High-pressure geophysics and materials参考文献 30被引用 3

一句话总结

本研究调查了在金属的冲击和斜坡加载过程中，界面附近形成的非等熵层——即熵升高或降低的区域，伴随相应的温度偏差。基于位错塑性模型和数值模拟，研究发现：在撞击和斜坡加载下会形成高熵层，而在斜坡加载或阻抗不同的材料界面处则形成低熵层，这些现象会影响表面现象（如熔化和辐射测温测量）。

ABSTRACT

According to the ideal fluid dynamics approach, the temperature and entropy values of a medium undergo a jump increase in the shock front as well as on contact interface between different materials after the shock wave propagation, but remain constant behind the shock front out of the contact interface. In the real condensed matter, the shock fronts and transition regions near the interfaces have finite thicknesses; therefore, the temperature field is disturbed around the interfaces. In this work, such disturbances are numerically analyzed for the problems of formation of the steady shock wave at impact and ramp loading of metals, reflection of the steady shock wave from a free surface, and the shock wave passing through the interface between two different materials. Theoretical analysis and computations show that the non-isentropic layers (the high-entropy ones with the increased temperature and the low-entropy ones with the decreased temperature) arise near the interfaces in the above problems of shock and ramp loading. The impact produces the high-entropy layer; while the ramp loading can result in the both high- and low-entropy layers. At the shock wave passing through the interface, the high-entropy layer is formed in the lower-impedance material and the low-entropy in the higher-impedance one. These high- and low-entropy layers should be taken into account in simulations of shock-wave processes in thin targets or in other cases where surface effects are important. For example, melting can take place in the high-entropy layer on the interface between colliding plates at shock intensities lower than the bulk melting threshold; also the temperature perturbations near the studied surface can affect the result of pyrometric measurements. A mathematical model with accounting for the dislocation plasticity is described here as well as the appropriate numerical scheme is proposed.

研究动机与目标

• 分析在冲击和斜坡加载下真实凝聚态物质界面附近的温度和熵扰动，超越理想流体动力学假设。
• 研究由于有限冲击波前厚度和材料界面效应导致的非等熵层（熵升高或降低的区域）的形成机制。
• 建立一个结合位错塑性的数学模型，以准确模拟冲击波过程中这些热学和熵异常现象。
• 评估这些非等熵层对表面现象（如熔化和薄靶或界面主导系统中的辐射测温测量）的影响。

提出的方法

• 使用基于位错塑性的模型，对金属在撞击和斜坡加载下稳态冲击波形成的数值分析。
• 模拟冲击波从自由表面的反射以及穿过双材料界面的透射，以研究界面引起的熵变。
• 应用有限差分数值格式求解控制方程，考虑过渡区中熵和温度的演化。
• 将位错塑性纳入热-机械模型，以捕捉界面附近的非平衡效应。
• 利用计算建模解析有限厚度冲击波前和熵与温度偏离等熵行为的过渡区。
• 分析界面附近的熵和温度分布，识别不同加载条件下形成的高熵和低熵层。

实验结果

研究问题

• RQ1 在金属的冲击和斜坡加载过程中，界面附近会形成何种类型的非等熵层（高熵或低熵）？
• RQ2 加载类型（撞击与斜坡）如何影响高熵和低熵层的形成？
• RQ3 材料阻抗对比在决定双材料界面处熵异常的位置和性质方面起什么作用？
• RQ4 这些非等熵层在多大程度上影响熔化或辐射测温测量等表面现象？
• RQ5 如何有效建模位错塑性，以捕捉冲击压缩材料中熵和温度的偏离？

主要发现

• 在撞击加载下，由于压缩区域温度和熵升高，界面附近形成高熵层。
• 斜坡加载可依据材料特性和加载历史产生高熵层或低熵层。
• 在双材料界面处，冲击波透射时，低阻抗材料中形成高熵层，而高阻抗材料中形成低熵层。
• 这些非等熵层可导致在低于体材料熔化阈值的冲击强度下发生熔化，尤其在薄靶中更为显著。
• 界面附近的温度扰动可能显著影响辐射测温测量，若未加以校正，将引入误差。
• 所提出的位错塑性模型和数值格式能成功捕捉冲击压缩材料中的非等熵行为，并实现真实的热-机械演化。