Quasi-isentropic compression technique based on generalized wave impedance gradient flyer
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摘要:
基于变截面杆的波传播特性，设计了一种“针床型”广义波阻抗梯度飞片，即在圆薄片基座上密排叠加许多犹如针尖的小正四棱锥。采用LS-DYNA软件中SPH算法对广义波阻抗梯度飞片高速击靶过程进行了数值计算，结果显示：在飞片击靶过程中，每一个小正四棱锥台可以看作“点”式加载脉冲源，产生一系列具有缓慢上升前沿的近似球面波，球面波相互叠加得到具有缓慢上升前沿的平面加载波形，从而实现对靶板准等熵压缩加载。在数值计算中详细讨论了飞片击靶速度、飞片几何特征参数对准等熵压缩加载特性的影响规律，为广义波阻抗梯度飞片的设计与应用提供指导。基于数值计算结果，采用激光选区烧结金属增材制造技术，制备了一种广义阻抗梯度飞片样品，在一级气炮上进行击靶实验，实测了靶板自由面速度时程曲线，波形呈现了准等熵压缩加载特性，并与计算结果进行了对比，两者基本一致，从而验证了广义波阻抗梯度飞片结构设计的可行性以及数值计算结果的可靠性。
Abstract:Based on the wave propagation characteristics of variable cross-section rods, a generalized wave impedance gradient flyer, termed the " bed of nails” was designed. The process of the generalized wave impedance gradient flyer impacting the sample was simulated by using the SPH algorithm of the LS-DYNA software. The wave profiles display a smooth increase of velocity, with no indication of a shock jump. The physical mechanism of the quasi-isentropic compression generation is attributed to the interaction from a series of approximately spherical waves with slowly rising front. The influences of impact velocity and geometric parameters of the flyer on the ramp wave loading characteristics were discussed in detail, which provide some useful information for the design and application of the generalized wave impedance gradient flyer. Selective Laser Melting, and an additive manufacture technique, were used to manufacture the " bed of nails” flyer. The experiments were performed at the impact velocities of 348 m/s using the 57 mm gas gun. The measured free surface velocity profile agrees well with the simulation results.
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图 1 “针床形”广义波阻抗梯度飞片几何结构示意图
Figure 1. Schematic diagram of the “needle-bed” generalized wave impedance gradient flyer
图 2 波阻抗梯度飞片气炮实验的SPH单胞计算模型
Figure 2. SPH cell simulation model of impedance gradient flyer in gas gun experiments
图 3 靶板内不同时刻的应力波传播云图
Figure 3. Stress wave propagation contours in the specimen at different times
图 4 不同时刻飞片和靶板的塑性应变云图
Figure 4. Plastic strain contours in the flyer and specimen at different times
图 5 不同撞击速度下靶板自由面速度时程曲线
Figure 5. Free surface velocity profiles of specimen at different impact velocities
图 6 不同撞击速度下飞片变形的最终形态
Figure 6. Final deformation of the flyer at different impact velocities
图 8 自由面速度峰值与撞击速度比值随着撞击速度的变化曲线
Figure 8. Ratios between peak velocity and impact velocity vs. impact velocity
图 9 不同四棱锥台高条件下靶板自由面速度时程曲线对比
Figure 9. Comparison of the free surface velocity profiles for the specimen with different heights of the pyramid
图 11 不同锥角条件下靶板自由面速度时程曲线对比
Figure 11. Comparison of free surface velocity profiles for the pyramid specimen with different cone angles
图 12 压缩波上升沿时间和峰值速度随着正四棱锥台锥角的变化曲线
Figure 12. Compression wave front time and peak velocity vs. the cone angle of the pyramid
图 13 不同上底边宽度条件下靶板自由面速度时程曲线对比
Figure 13. Comparison of free surface velocity profiles for the specimen with different widths of the upper edge
图 14 广义波阻抗梯度飞片的3D几何模型和样品
Figure 14. 3D model and product of generalized wave impedance gradient flyer
图 16 实验与数值计算得到靶板自由面速度时程曲线对比
Figure 16. Experimental and numerical free surface velocities of the target
表 1 飞片和靶板材料本构和状态方程参数
Table 1. Flyer and target material parameters
E/GPa $\nu$ ρ/(kg·m−3) A/MPa B/MPa n c m $\mathop {\dot \varepsilon }\nolimits_0 $ Tm/K T0/K 210 0.3 7 830 792 510 0.26 0.014 1.03 1 1 800 293 
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