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

为了满足人们对轻质、高品质、高附加值产品的需求，复合板越来越多地应用于汽车、家具、电子元器件等各种零件的冲压成形。由于复合板一般由2层或3层不同的材料组成，其塑性性能不同于单一板材的塑性性能。本文讨论了板材组合和复盖率对复合板加工硬化特性和成形极限的影响。首先，进行了单轴拉伸、单轴厚度压缩和平面应变压缩试验，以了解组成复合板的各金属板材的塑性性能。将Hill、Gotoh和Bassani各向异性屈服函数与实验结果进行了比较。其次，根据测得的各种材料的应力-应变曲线，对(Al-钢)和(Al-Cu)复合板的单轴压缩进行了上限分析。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率的变化规律。作为与复合板冲压成形相关的附加实验，进行了三层(铜-铝-铜，铝-铜-铝)管的拉深试验，阐明了拉深条件对各层厚度应变的影响。应进一步研究复合板的本构方程和评价其成形性的因素。还需要考虑各板材塑性各向异性的分析，以预测分层的开始，这是影响复合板变形行为的最重要因素之一。

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.