Mechanical response of AZ31B magnesium alloy: Experimental characterization and material modeling considering proportional loading at room temperature

Tension and compression experiments have been performed to characterize the mechanical response of 1.57 mm AZ31B-O sheet at room temperature. Five different sheet orientations were used to characterize the in-plane anisotropy under tensile loading conditions while cubic samples consisting of adhesively-bonded layers of sheet samples were used for compression testing along four sheet directions. During uniaxial tensile testing, the axial and transverse strain components were measured using two independent extensometers. A digital image correlation system was used to measure the strain components during compression testing. Both instantaneous and cumulative r-values were measured as they evolved with plastic strain. A strong, evolving asymmetry is observed. An evolving anisotropic/asymmetric continuum-based material model based on a Cazacu-Plunkett-Barlat (CPB)-type yield function is proposed to fit the material behavior as a continuous function of plastic strain. Considerable improvement in the representation of the material behavior is achieved as the number of stress transformations used in the CPB yield surface formulation is increased. To capture the evolution of the envelope of the subsequent yield surfaces, the anisotropy and asymmetry parameters are replaced with functions expressed in terms of plastic strain. The evolution parameters are found by minimizing the difference between the model predictions and the experiments at discrete plastic strain levels, using gradient search methods. A strain rate-independent elastic-plastic material model incorporating the evolving envelope of subsequent yield surface formulation has been developed and implemented within a commercial finite element package. The model reproduces the experiments initially used for fitting. The predictions of the developed material model are compared with the measured load-displacement and strain distributions from a three-point bending experiment. Improvement in the prediction of strain and forming forces is observed compared to the previously available non-evolving material models.