The Deformation Properties of Clad Sheet Metals

Abstract

The techniques commonly used to produce clad sheet metals and the properties of these materials are reviewed. Experimental work is described for a range of two and three layer copper-steel composites produced by adhesive and roll bonding, the materials being processed to give a range of copper-steel thickness ratios. The tensile, plane strain compression, deep drawing and stretch forming properties of the composites were determined, the experimental results being compared with those calculated theoretically by means of the equal stress or equal strain hypothesis. The results showed that the stress-strain behaviour of the composites in both tension and compression; proof stress; ultimate tensile strength and the maximum punch loads for both deep drawing and stretch forming could be accurately predicted using the equal strain hypothesis. Properties such as uniform elongation and ‘R’ value could not be predicted with the same degree of accuracy; this being attributed to the accuracy with which these properties could be experimentally determined. The ‘n’ values for the composites could not be simply predicted by means of the equal strain hypothesis, but a relationship has been derived, and experimentally verified, to enable ‘n’ to be predicted from the stress-strain characteristics of the individual components. The stretch formability of the composites could not be predicted by the equal strain hypothesis because stretch formability was dependent upon the ductility of the component on the outermost surface during deformation. The existing theory for calculation of draw stress in the drawing of cylindrical flat bottomed cups has been modified so that the draw stress for composites may be calculated from the stress-strain characteristics of the individual components. The results from the modified theory have been shown to be as accurate as the results obtained for single metals calculated by the conventional theory.