YIELD LOCI OF ANISOTROPIC ALUMINUM SHEETS

AA8014 aluminium sheets were tested in uniaxial, equibiaxial (bulge test) and plane-strain tension at an almost constant strain rate of 2 x 10(-3) s(-1). The results were compared with predictions at different levels of strain, based on macroscopic and crystallographic theories of yielding. While most of the previous investigations compare the results at a strain level of 0.10, the present comparison was made in early stages of the deformation, which might be considered as the real yielding strain of the material. It was concluded that, at the high strain levels Hosford's method, which is a modification of Hill's ''old'' criterion, gives a proper fit to the experimental data. However, at the lower strain levels the experimental results were very close to the crystallographic loci.