Scale Dependence of Mechanical Properties and Forming Limit in Thin Plates and Foils

微米尺度材料在力学性能和成形极限方面表现出与宏观尺度材料不同的一面。为了建立考虑尺度依赖性和微观现象的合理本构模型，对箔片的拉伸性能进行了研究。通过该项目获得的总体成果如下：1。拉伸试验设定：确定拉伸试样的最佳形状。利用微伺服试验装置和有限元分析，对厚度约为10 μm的电沉积铜箔进行了5种形状的测试，在量规长度范围内的有限域内获得了均匀的变形。箔的厚度依赖性：采用两种测试材料；电沉积铜箔和轧制铝箔。铜箔具有较高的抗变形能力，但延展性降低。相反，薄铝箔的电阻和延展性都降低。这种差异可能源于铝箔的生产过程，在铜中的沉积过程不提供任何先前的变形，而塑性变形对轧制铝箔的后续拉伸有影响。局部颈部张力：本研究中几乎没有观察到两种材料的延展性。这种延性下降可能是由于试件形状的尺度效应导致的，形成局部颈部而不是扩散颈部，不同的机制对变形模式起作用。因此，我们进一步研究了宏观材料参数与变形行为、从扩散颈到局部颈的分岔以及材料在厚度方向上的各向异性之间的相关性。从这一角度出发，需要利用数值模拟技术建立综合材料试验方案。

Micron scale materials reveal different aspect from macro-scale materials in view of their mechanical properties and forming limit. In order to establish a rational constitutive model taking account of the scale dependence and microscopic phenomena, tensile properties of foils are examined. Overall results obtained through the project are as follows :1.Settine of tensile tests :The optimal shape of tensile test specimen is established. Using a micro-servo testing apparatus and the finite element analysis, five kinds of shapes are examined for electrodeposited copper foils with the thickness of about 10 μm, such that uniform deformation can be obtained for a finite domain within the gauge length.2.Thickness dependence of foils:Two kinds of test materials are employed; electrodeposited copper foils and rolled aluminum foils. The copper foils show high deformation resistance while the ductility decreases. In contrast both the resistance and the ductility decrease in thinner aluminum foils. This difference may arise from the production process of the foils in the way that the deposition process in copper does not provide any prior deformation while the plastic deformation has an influence on the subsequent stretching in the rolled aluminum foils.3.Localized neck in tension :Almost no ductile property is observed for both materials in this study. This diminish in ductility may arise from the scale effect in the shape of specimen, so that localized neck is furnished rather than diffusive neck, and the different mechanism acts on the deformation mode.It follows that we further examine the correlation between the macroscopic material parameters and the deformation behavior, the bifurcation from diffuse neck to localized neck, and the material anisotropy in thickness direction. From this point of view, it is desired to establish the integrated material test scheme by use of numerical simulation technique.