Prediction Of Forming Fracture Of Aluminum Alloy Sheet Based On Uncoupled Ductile Fracture Criterion

Lightweight is the main development direction of automobile technology,and the application of aluminum alloy is an important technical way to realize automobile lightweight.Fracture is one of the main defects in aluminium alloy sheet forming.The traditional method is not accurate enough to predict the location of fracture in the process of aluminium alloy sheet forming.The ductile fracture criterion of aluminium alloy sheet is deeply studied and applied to the prediction of forming fracture of automobile inner sheet.It has important engineering application value for perfecting the theory of predicting forming fracture of aluminium alloy sheet and improving the accuracy of predicting forming fracture of aluminium alloy sheet.The main research contents and conclusions are as follows:Six specimens of different shapes and sizes were designed and tested for Al6016-T4 sheet.The effects of anisotropy and different stress states on the mechanical properties and fracture behavior of Al6016-T4 sheet were studied.The results show that the tensile strength and yield strength of Al6016-T4 sheet have no obvious anisotropy in different orientations,but show obvious anisotropy in R value,of which the R value in 0 degree direction is the largest;the hardening coefficient and hardening index,fracture strain,maximum uniform strain and elongation of Al6016-T4 sheet show certain anisotropy in different orientations.The parameter calibration system of uncoupled ductile fracture criterion is developed based on MATLAB.The system can calibrate the parameters of uncoupled ductile fracture criterion accurately and quickly,and realize the comparison of different ductile fracture criteria in different spaces.For Al2024-T351 material,the system is applied to complete the parameter calibration.The fracture envelopes of ductile fracture criteria in different spaces are calibrated and drawn,and the applicable conditions of different ductile fracture criteria are analyzed.The results show that the hybrid method can more accurately determine the material parameters in the ductile fracture criterion.Within the stress triaxiality range(-1/3,1/3),only DF series fracture criterion and MMC fracture criterion can more accurately describe the variation of fracture equivalent plastic strain with stress triaxiality.Based on the experimental data,the selection of hardening model,yield criterion and parameter calibration were completed;the material parameters were determined by the hybrid method of experiment and finite element simulation,and the parameters of ductile fracture criterion were calibrated;Lou fracture criterion was applied to predict ductile fracture under different stress states,and the effects of different constitutive models on fracture prediction accuracy were studied.The results show that Swift-Voce hardening model has the highest prediction accuracy and can be used to predict the fracture of circular notched specimens R10 and R20 more accurately.Compared with the R-value calibration,the Hill48 yield criterion using the yield strength calibration has the highest prediction accuracy,and can accurately predict the fracture of the arc-notch specimen R5,R10 and the center-hole specimen.The finite element simulation of the forming process of the inner panel of the automobile was carried out.The ductile fracture criterion was applied to the prediction of part forming fracture by the user material subroutine of ABAQUS software.The influence of different yielding fracture prediction accuracy was compared.The results show that the DF2012 ductile fracture criterion can accurately predict the most rupture position of Al6016-T4 during forming;the Hill48 yield criterion of the two yield surface shapes predicts that the results are not much different,and the fractures at different positions can be predicted respectively.