Modeling of Size Effect on Tensile Flow Stress of Sheet Metal in Microforming
Modeling of Size Effect on Tensile Flow Stress of Sheet Metal in Microforming
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DOI：
10.1115/1.3039520
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发表时间：
2009-02
影响因子：
4
通讯作者：
Daw-Kwei Leu
中科院分区：
文献类型：
--
作者：
Daw-Kwei Leu
本文考虑了微成形中简单拉伸变形行为的尺寸效应，提出了一个简单的板料拉伸流动应力模型。实验结果表明，流动应力的测量可以表示为双曲线函数tanh（T/D），这是一个函数的T/D（板厚/晶粒尺寸）。预测的流变应力与已发表的实验结果吻合得很好。值得注意的是，对于给定的TID，具有较小晶粒的试样具有较低的归一化流动应力。由于宏观尺度试样的材料性质不属于微观尺度，临界条件（T/D）c。基于“影响区”模型、位错堆积理论和Hall-Fetch关系，提出了区分拉伸流变应力的宏观尺度和微观尺度的新概念。预测的（T/D）c的分布与实验发现的（T/D）c随晶粒尺寸的增加而减小相似。取向依赖因子β对（T/D）c敏感。因此，有必要进一步研究取向相关因子β，以获得更精确的（T/D）c，从而更好地评估和理解微成形中金属板料的拉伸流动应力。
This investigation considers the size effect on the deformation behavior of simple tension in microforming and thus proposes a simple model of the tensile flow stress of sheet metal. Experimental results reveal that the measure of the flow stress can be represented as a hyperbolic function tanh(T/D), which is a function of T/D (sheet thickness/grain size). The predicted flow stress agrees very well with the published experiment. Notably, a specimen with smaller grains has lower normalized flow stress for a given TID. Since the material properties of the macroscale specimen do not pertain to the microscale, a critical condition (T/D) c . that distinguishes the macroscale from the microscale in the tensile flow stress is subsequently proposed, based on the "affected zone" model, the pile-up theory of dislocations, and the Hall-Fetch relation. The distribution of the predicted (T/D) c is similar to the experimental finding that the (T/D) c decreases as the grain size increases. However, the orientation-dependent factor β is sensitive to (T/D) c . Hence, further study of the orientation-dependent factor β is necessary to obtain a more accurate (T/D) c and, thus, to evaluate and understand better the tensile flow stress of sheet metal in microforming.