Work-hardening Characteristics and Forming Limit of Clad Sheet Metals.

近年来，为了获得重量轻、质量高、附加值高的产品，复合板越来越多地用于汽车、家具、电子零件等各种零件的冲压成形。由于复合板通常由两层或三层不同的材料组成，其塑性性能与单层板不同，本文讨论了复合板材料组合和复合率对复合板加工硬化特性和成形极限的影响。首先，进行单向拉伸、单向厚度压缩和平面应变压缩试验，以了解组成复合板的每个金属板的塑性特性。将Hill、Gotoh和Bassani三种各向异性屈服函数与实验结果进行了比较。其次，根据上述实验测得的铝-钢复合板和铝-铜复合板的应力-应变曲线，对两种材料的单轴压缩上限进行了分析。在此基础上，预测了复合板的应力-应变曲线、屈服轨迹和成形极限随复合比的变化规律，并作为复合板冲压成形的补充实验，对三层复合板进行了变薄拉深试验（Cu-Al-Cu，Al-Cu-Al）并阐明了变薄条件对各层厚度应变的影响。本构方程和影响复合板成形性能的因素。考虑到每个金属板的塑性各向异性的分析也是必要的，以预测分层的开始，分层是影响包覆金属板的变形行为的最重要的因素之一。

For recent demands to obtain products with light weight, high quality and high aded value, clad sheet metals are increasingly used in the press forming of various parts such as car, furniture and electronic components. Since a clad sheet is generally composed of 2 or 3 layers of different materials, the plastic properties are different from those of a single sheet.In the present investigation, the effects of the combination of sheet materials and tha clad ratio on the work-hardening characteristics and forming limit of a clad sheet are discussed. First of all, uniaxial tension, uniaxial compression through thickness and plane strain compression tests are carried out to know the plastic properties of each sheet metal composing a clad sheet. The Hill, Gotoh and Bassani anisotropic yield functions are compared with the experimental results.Secondly, an upper bound analysis of the uniaxial compression of (Al-steel) and (Al-Cu) clad sheets is made based on the stress-strain curves of each material measured above. From this analysis, it has been predicted how the stres-strain curve, yield locus and forming limit of the clad sheet metal change with the clad ratio.As an additional experiment related to the press forming of clad sheet, ironing of 3-layer (Cu-Al-Cu, Al-Cu-Al) tubes is carried out and the effects of ironing conditions on the thickness strain of each layer are clarified.Further investigations should be made of the constitutive equation and the factors for estimating formability of clad sheet metals. An analysis taking into consideration the plastic anisotropy of each sheet metal is also necessary to predict the onset of de-lamination which is one of the most important factors affecting the deformation behaviour of the clad sheet metal.