Fracture mode transition in expanding ring and cylindrical shell under electromagnetic and explosive loadings
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摘要: 考虑断面收缩率、局域断裂应变以及平均断裂应变，并基于电磁膨胀环、爆炸膨胀环(柱壳)实验平台，研究了高纯无氧铜(TU1)环及柱壳在高应变率载荷下的膨胀断裂行为。采用高速摄影技术拍摄柱壳外壁的膨胀断裂形貌演化过程，用于确定柱壳平均断裂应变；利用激光干涉测速技术获得样品径向膨胀速度历史，用于确定加载应变率；利用样品的全回收测量及微观表征，确定了无氧铜环、柱壳的局域断裂应变及断裂模式。实验表明，随着应变率的增加，TU1材料的平均断裂应变增加，断面的收缩程度加剧，并在应变率约为1.0×104 s-1附近会出现明显的断裂模式转变，断面收缩率出现量级上的跳跃，从100变化至约103，局域断裂应变呈现明显的分区现象。Abstract: In the present study, we designed the electromagnetic and explosive driving expanding ring/cylinder experiments and investigated the expanding fracture characteristics of oxygen-free high-conductivity copper (OFHC) in consideration of the conception of the reduction of area, the local fracture strain and the average fracture strain. We used a high speed camera to record the fracture process and obtain the fracture strain of the copper cylinder and the Doppler pins system (DPS) to obtain the radial velocity of the specimen in order to achieve the strain rate of the loading. We verified the local fracture strain and the fracture mode by analyzing the soft-recovered fragments of the expanding ring and the cylinder. Based on the experimental results, we found that the average fracture strain and the reduction of the area increases as does the strain rate. Moreover, the fracture mode transition may occur at the strain rate of about 1.0×104 s-1, and the reduction of the area may increase by an order of magnitude, i.e. from the order of 100 to that of 103, and the local fracture strain exhibits an obvious subarea.
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Key words:
- necking /
- fracture /
- expanding ring /
- high strain rate /
- fracture strain
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图 2 高纯无氧铜TU1环和柱壳样品实物图
Figure 2. Specimen of oxygen-free high-conductivity copper (TU1)
图 3 电磁膨胀环、爆炸膨胀环典型断面形貌
Figure 3. Fracture feature of expanding rings under electromagnetic and explosive loading
图 5 膨胀柱壳拉伸破片及断面微观表征图片
Figure 5. Fragments and microscopic fracture surface of expanding cylindrical shell
图 6 电磁膨胀环、爆炸膨胀环/柱壳中平均断裂应变与应变率的关系
Figure 6. Relationship between strain rate and average fracture strain in electromagnetic ring and explosive expanding ring/cylinder
图 8 爆炸与电磁加载下膨胀环、柱壳局域断裂应变与平均断裂应变
Figure 8. Local fracture strain and average fracture strain of explosive expanding ring/cylinder(EE-ring/EE-Cylinder) and electromagnetic ring (EM-ring)
表 1 电磁膨胀环、爆炸膨胀环(柱壳)实验数据
Table 1. Strain rate and fracture strain of experiments
实验号 样品 加载 ${\mathit{\dot \varepsilon }} $ /s-1 εf-average ψ εf-local 1 环 3.0 kV 2.8×103 0.155 - - 2 环 3.5 kV 4.6×103 0.224 78 4.36 3 环 4.0 kV 5.4×103 0.333 13 2.56 4 环 爆炸 5.8×103 0.130 4 1.39 5 柱壳 爆炸 8.6×103 0.267 2.5 0.92 6 柱壳 爆炸 12.0×103 0.465 ~500 6.21 
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表 2 不同应变率下M态TU1环碎裂数据[11]
Table 2. Fragmentations data of M state TU1 rings at varying strain rates
实验编号 R0/mm ε·/s-1 Nf $ {{\mathit{\bar L}}_{\rm{f}}}$/mm εf-average MR-01 21.1 3.50×103 3 51.0 0.143 MR-02 21.1 4.70×103 4 39.3 0.170 MR-03 21.1 5.04×103 7 23.1 0.199 MR-04 21.1 5.50×103 7 24.0 0.237 MR-05 21.1 6.05×103 9 21.6 0.388
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