Experimental verification of anisotropic constitutive models under tension-tension and tension-compression stress states

Constitutive model is vitally important to finite element simulation which determines the accuracy and reliability of predicting material yield and plastic flow behaviors. Due to lack of accurate and sufficient experimental data for the tension-compression (T-C) stress state, the anisotropic constitutive model can only be calibrated with tension-tension (T-T) data and its accuracy cannot be thoroughly verified under the complete stress states, including T-T and T-C stress states. To address the limitation, a novel controllable biaxial loading test device was developed to conduct systematic experiment and determine sufficient data. Using such a device, arbitrary stress paths can be applied to thin-walled tubes under T-T and T-C stress states. Subsequently, the yield and plastic flow behavior of anisotropic AA6061-O tubes were analyzed through the measured stress and strain data. These were then used to verify the accuracy of common anisotropic constitutive models including Hill48, Barlat-Lian, and Yld2000-2d, those are extensively implemented in commercial finite element software, under the complete stress states. It is indicated that the yield behavior exhibited anisotropy in the complete stress states, but the yield characteristics differ for the T-T and T-C stress states. The plastic flow behavior exhibits isotropic characteristics in the T-C stress state, while anisotropic in the T-T stress state. These common anisotropic constitutive models can accurately describe yield and plastic flow behavior in either T-T or T-C stress state only. None of the models are able to provide accurate predictions of the plastic deformation behavior both in the T-T and T-C stress states simultaneously.