Experimental identification of yield surface of Al–Cu bimetallic sheet

Abstract

Design of structures made form metal layered composite with a gradient variation of physical properties requires knowledge of their behaviour in the small of elasto-plastic strain. The aim of the research was the experimental investigation of these behaviours. Preliminary tests were carried out on standard flat specimens made from aluminium-copper layered composite, which was obtained by rolling process. Each component (layer) in the state before connecting into a composite was tested independently. The test specimens were cut from metal sheets in different directions (in the range 0–90°). The primary strength tests showed a large anisotropy of mechanical properties. Further studies, in the main part, were associated with the investigations of evolution of yield surfaces for Al–Cu bimetal and components in the range of strains from proportional limit to 0.3%. The investigations were realised by monotonic tensile tests of mini specimens, which were cut out in different directions from the large-size specimens and put to the initial deformation 0.75% in the direction of rolling. The method gave possibility to realising tests in the plane stress state and build for aluminium, copper and Al–Cu bimetal experimental yield surfaces. Evolution of yield surface with increasing levels of plastic deformation was studied. Analysis of their shape showed that aluminium, copper and Al–Cu bimetal had isotropic hardening. It was shown that the law of mixtures applied to the determination of the yield surface of Al–Cu bimetal was applicable only in a short range of elasto-plastic deformation (0.05–0.2%) and for specimens cut at an angle 0–45° from the large-size specimen.