Investigation on the forming limits of 5754-O aluminum alloy sheet with the numerical Marciniak–Kuczynski approach

The aim of this work was to study the formability of 5754-O aluminum alloy sheet through utilizing the finite element M–K approach. The uniaxial tensile test and the Nakajima test were performed respectively for determining the mechanical properties and the forming limit strain pairs. The finite element M–K approach considering the Swift model, the Yld2000-2d yield function and the groove orientation was developed through utilizing software Abaqus. The predicted forming limit curve (FLC) agreed well with the Nakajima test results. Furthermore, the limit strains with the consideration of pre-strain under uniaxial tensile condition were experimentally determined, and numerically predicted by the original M–K approach. The numerical limit strains under different pre-strain paths and pre-major strains showed that the M–K approach could only predict partial FLC when the effective strain caused by the pre-strain was larger than the one at plane strain state. This phenomenon was interpreted by the evolution of the stress state in the groove of the M–K theory, i.e., the change of the strain path in loading process resulted in the stress state rotation, and consequently made the ratio of major strain increment in the groove to that out the groove increase when the stress state in the groove approached the stress state at plane strain state.