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特点。为了建立一个合理的本构模型，考虑尺度依赖性和微观现象，箔的拉伸性能进行了研究。通过本课题的研究，取得了以下主要成果：1.拉伸试验的确定：确定了拉伸试样的最佳形状。利用微型伺服测试装置和有限元分析，对厚度约为10 μm的电沉积铜箔进行了五种形状的测试，使其在标距内的有限区域内获得均匀变形。2.箔的厚度依赖性：采用了两种测试材料：电沉积铜箔和轧制铝箔。铜箔表现出高的变形抗力，但延展性降低。相比之下，在较薄的铝箔中，电阻和延展性都降低。这种差异可能来自箔的生产过程中的方式，在铜的沉积过程中不提供任何先前的变形，而塑性变形的影响，在随后的拉伸轧制铝箔。3.局部颈部拉伸：几乎没有韧性性能观察到这两种材料在这项研究中。这可能是由于试样形状的尺度效应导致局部颈缩而不是扩散颈缩，不同的机制作用于变形模式，进而研究了宏观材料参数与变形行为的相关性、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。从这个角度来看，需要利用数值模拟技术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.