Theoretical and experimental study of forming-limit strain of half-hard AA1100 aluminium alloy sheet

The forming-limit diagram (FLD) of a half-hard aluminium alloy (AA1100-H24) sheet was obtained theoretically for linear strain paths using two different approaches: phenomenological theory and crystal plasticity theory. For both approaches, the Marciniak-Kuczynski model was applied to the computation of the FLD. The Yld2000-2d yield function was used for the phenomenological analysis and a full-constraint Taylor-type model was adopted for the crystal plasticity analysis. The experimental FLD was also obtained through the Marciniak in-plane stretching test. The theoretical predictability of the FLD was assessed by comparing the predicted FLDs with the experimental FLD. The comparison demonstrated that the phenomenological theory could duplicate the experimental FLD on the left-hand side of the diagram but could not do so over the entire range on the right-hand side up to the equibiaxial stretching. The same was true when the Yld2000-2d yield function was determined based on numerically evaluated anisotropic properties instead of measured values. It was also shown that the crystal plasticity theory predicted higher forming-limit strains on the left-hand side and markedly lower limit strains on the right-hand side than the experimental strains except for the equibiaxial stretching.