表面加工塑性层对金属柱壳剪切带自组织单旋起始的影响
EFFECT OF SURFACE PROCESSING PLASTIC LAYER ON SELF-ORGANIZED SINGLE ROTATION INITIATION OF SHEAR BANDS IN METAL CYLINDRICAL SHELL
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摘要: 在外爆加载金属柱壳高速坍塌过程中, 发生塑性变形失稳形成的剪切带具有高度的自组织特征, 甚至出现剪切带排列的单旋现象—剪切带在顺时针和逆时针两个方向呈现一个方向占优的现象. 柱壳在坍塌时, 最大剪切应力位于柱壳内表面, 剪切带的形核及扩展行为受内表面材料介观状态的影响显著. 本文通过选材和控制柱壳加工工艺, 获得了内表面具有不同厚度塑性层的20钢柱壳, 采用厚壁圆筒实验技术, 研究了表面加工塑性层对金属柱壳绝热剪切带自组织单旋现象起始的影响规律及其物理机制. 研究结果表明, 金属柱壳内表面加工塑性层显著改变了试样剪切带的起始条件, 沿顺时针或逆时针方向排列的剪切带形核数量在总剪切带数量中所占比例取决于表面加工塑性层的厚度和晶粒取向, 具有单一晶粒拉伸方向的较厚塑性层样品更容易形成单向螺旋剪切带结构. 在相同变形条件下, 随着塑性层厚度增加, 剪切带平均形核速率和扩展速率增大, 剪切带平均间距减小. 结果可为理解金属柱壳在高速塌陷过程中绝热剪切带占优取向现象提供有价值的参考.Abstract: In the process of high-speed collapse of metal cylindrical shell loaded by external explosion, the shear band formed by plastic shear instability has high self-organization characteristics, and even forms a single direction spiral pattern - shear bands are dominant in clockwise or counterclockwise direction. When the cylindrical shell collapses, the maximum shear stress is located on the inner surface of the cylindrical shell. The nucleation and propagation behaviors of the shear band are significantly affected by the mesoscopic state of the material on the inner surface. In this paper, AISI 1020 steel cylindrical shells with plastic layers of different thickness on the inner surface are obtained by selecting materials and controlling the cylindrical shell processing technology. The effect of surface processing plastic layer on the initiation of self-organized single rotation phenomenon of adiabatic shear band of metal cylindrical shell and its physical mechanism are studied by using thick-walled cylinder experiment. The experimental results show that the processed plastic layer on the inner surface of the metal cylindrical shell significantly changes the initial conditions of the shear band. Shear bands are nucleated and distributed in the clockwise and counterclockwise direction. The proportion of clockwise or counterclockwise shear bands in the total shear bands is dependent on the thickness and grain stretching direction of the plastic layer in samples. The results indicate that the thicker plastic layer with a single grain stretching direction is easier to form a single direction spiral structure of shear bands, either clockwise or counterclockwise. In addition, samples with a thick layer have a higher nucleation rate, a smaller spacing and a higher propagation velocity of shear bands, in comparison with those of a thin layer at the same effective strain. The results can provide a valuable reference for understanding the dominant orientation of adiabatic shear bands in the process of high-speed collapse of metal cylindrical shell.