Parameter calibration of anisotropic GTN model and forming limit for S600 aluminum alloy sheet

Abstract High strength aluminum alloy sheet has obvious anisotropic characteristics and negligible necking in plastic deformation, making its fracture judgment in forming process more difficult than other metals. Taking S600 aluminum alloy sheet as the research object, a coupling model of anisotropic yield criterion and micro-damage theory namely Yld2000-GTN model was established, and its VUMAT subroutine was embedded into ABAQUS software in this study. The proposed model can improve the accuracy of fracture prediction for high-strength aluminum alloy sheet during plastic deformation. Uniaxial tension test and shear test were used to adjust the anisotropic parameters in Yld2000-GTN model. Uniaxial tension test was also employed to adjust damage parameters in Yld2000-GTN model with a new proposed method named sectional type parameter identification method (STPIM) basing on response surface method (RSM) and objective function method (OFM). However, these damage parameters could not accurately simulate the Force-Stroke curves of other notched samples with the highest error up to 18.94%. To correct this error, the relationship between stress triaxiality and damage parameters was further investigated and used to modify damage parameters. Taking the modified parameters into simulation, the prediction error of Force-Stroke curve for all notched samples was reduced to less than 5%. Finally, the theoretical forming limit diagram (FLD) of S600 aluminum alloy sheet was established by the modified parameters, and its accuracy was verified by the bulging test with hemispherical punch.