DEVELOPMENT OF ANISOTROPY DURING THE COLD-ROLLING OF ALUMINUM SHEET

Aluminium sheet of commercial purity was rolled to 11 different reductions corresponding to equivalent strains of up to 2.6. Samples machined from these sheets were then tested in uniaxial tension, plane strain tension and uniaxial compression. All of these exhibited "anomalous behaviour" (Lankford coefficient RBAR < 1 together with equibiaxial/uniaxial yield stress ratio, sigma-b/sigma-BAR(u) > 1) as well as a small amount of in-plane anisotropy. To describe these properties, a non-quadratic yield function is proposed, involving five independent parameters. Four of these are determined by assuming, to a first approximation, that the material anisotropy is four-fold symmetric. The fifth is introduced to describe the actual orthotropic behaviour of the sheet. It is then shown that the R(THETA) and sigma(THETA) functions derived from the criterion, as well as the associated yield surfaces, provide a reasonable description of the experimental data.