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

微米级材料在力学性能和成形极限方面表现出与宏观材料不同的特点。为了建立合理的考虑尺度相关性和微观现象的本构模型，对铝箔的拉伸性能进行了研究。本工程取得的总体成果如下：1.拉伸试验方案：确定了拉伸试验试件的最佳形状。利用微伺服测试仪和有限元分析方法，对厚度约为10μm的电沉积铜箔的5种形状进行了分析，使其在规范长度内的有限区域内获得了均匀的变形。2.铜箔的厚度依赖关系：采用两种试验材料：电沉积铜箔和轧制铝箔。铜箔具有较高的变形抗力，但塑性下降。相反，在较薄的铝箔中，电阻和延展性都降低。这种差异可能源于铝箔的生产工艺，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产生影响。3.局部颈部拉伸：在本研究中，两种材料几乎没有观察到延性。这种延性的降低可能是由于试件形状上的尺度效应，使得局部颈缩而不是扩散颈缩，不同的机制作用于变形模式。因此，我们进一步研究了宏观材料参数与变形行为的相关性，从扩散颈缩到局部颈缩的分叉，以及材料厚度方向的各向异性。从这个角度出发，需要利用数值模拟技术来建立完整的材料试验方案。

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.