Influence of a cushion on dynamic expansion and fracture of an explosively-driven metallic cylinder
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摘要: 采用多普勒光纤探针测速技术（Doppler pins system，DPS，又称全光纤位移干涉测速技术）和高速摄影技术，研究装配垫片对金属柱壳膨胀断裂的影响，获得了有无垫片对应柱壳外表面位置的速度曲线和垫片对柱壳膨胀断裂影响明显的高速摄影图像。实验结果表明：与无垫片区域相比，垫片区域的柱壳外表面经历了先凸起后内凹的过程，导致垫片对应柱壳的径向运动位移发生反复错位，最终低于无垫片区域约0.34 mm，该位移差可能导致柱壳发生径向剪切断裂；实验结果还表明，在垫片与间隙交界处两侧（沿垫片方向约7.5°、沿间隙方向约9°）处各增加了一条裂纹，该断裂模式既不同于环向拉伸断裂，也不同于45°的剪切断裂，而是由垫片/间隙边界产生的两束稀疏应力波传到柱壳外表面引起的扰动影响所致，这个新的断裂模式与柱壳材料的动态力学性能密切相关。数值模拟结果表明，装配垫片对柱壳断裂机制影响不仅包含该处附加的质量效应，还应考虑炸药通过垫片后作用在柱壳上的冲击加载幅值变化、冲击加载时序与其他部位不同步的差异，以及垫片/间隙交界处引起的表面波传播对柱壳断裂模式的后续发展行为的影响。Abstract: The influence of assembly cushions on the fracture of an expanding metal cylindrical shell was studied. The velocity of the outer surface of the shell with or without a cushion in it was measured by a Doppler pins system (DPS) array, and images with the obvious influence of an inner cushion on the fracture of the shell were recorded by the high-speed photography. Compared with the area without the cushion, the outer surface of the cylindrical shell in the cushion area experienced a process of first convex and then concave movement, which made the radial displacement of the surface repeatedly misplace, leading to a final displacement of 0.34 mm lower. This displacement difference may lead to the radial shear fracture of the cylindrical shell. Besides, in the experiment, a crack appeared on both sides of the cushion/gap interface (7.5° deviation on the cushion side and 9° deviation on the gap side). These cracks were resulted from the disturbance of two sparse stress waves, which were generated from the cushion/gap interface and then transmitted to the outer surface of the cylindrical shell. The fracture mode is different from both circumferential tensile fracture and shear fracture along 45° direction. This new fracture mode is closely related to the dynamic mechanical properties of the cylindrical shell’s material. Further numerical simulation analysis shows that the influence of the assembly cushion on the fracture mechanism of the cylindrical shell includes three aspects: firstly, the additional mass effect; secondly, the amplitude change of the explosive impact loading after it passing through the cushion, and the asynchronous difference of the impact loading sequence with other parts; and thirdly, the influence of the propagation of surface waves, which originate from the interface between the cushion and the gap, on the subsequent development behavior of the cylindrical fracture mode .
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Key words:
- expansion /
- fracture /
- DPS array /
- high-speed photography /
- cushion /
- metallic cylinder
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图 1 柱壳实验装置及测点布局
Figure 1. The cylindrical shell experimental device and its measuring point layout
图 2 速度测量和高速摄影的现场布局
Figure 2. Field layout of velocity measurement and high-speed photography
图 4 点起爆柱状炸药驱动柱壳运动的示意图
Figure 4. The diagram of cylindrical shell movement driven by point-initiated cylindrical explosive
图 5 有无垫片时柱壳膨胀速度和位移差曲线
Figure 5. Expansion velocity and displacement difference curves of the cylindrical shell with or without a cushion
图 6 垫片对柱壳膨胀断裂的影响
Figure 6. Influence of cushion on cylindrical shell expansion fracture
图 7 垫片对柱壳膨胀断裂爆轰产物的影响
Figure 7. Influence of cushion on detonation products of cylindrical shell expansion fracture
图 9 轴对称计算模型和柱壳内外表面的冲击压力曲线
Figure 9. Axisymmetric calculation model and impact pressure curves on the inner and outer surfaces of the cylindrical shell
图 10 平面应变计算模型、垫片变形和柱壳外表面速度曲线
Figure 10. Plane strain calculation model, cushion deformation and velocity curves of cylindrical shell outer surface
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