Research On Constitutive Model And Ductile Fracture Criterion Of AA5052 At High Work Piece Speed

In the automotive industry,improving vehicle fuel economy has always been an important challenge,and lightweight technology is one of the main means to solve this problem.In the field of automotive lightweight,an important way to achieve this is to apply lightweight materials such as aluminum alloys to automotive bodies.Aluminum alloy is an ideal material to realize lightweight due to its high strength-to-weight ratio.However,the plasticity of aluminium is lower than the conventional mild steel,and it is easy to appear wrinkle,fracture,local neck shrinkage and other defects in the traditional forming process.In recent years,high energy rate and high rate forming have attracted wide attention,including electromagnetic,electro-hydraulic and explosive forming.Under the high velocity of deformation,the aluminum alloy shows a better elongation and formability than the quasi-static condition.However,at present,the dynamic constitutive relationship and fracture failure criterion of aluminum alloy at high velocity were less studied,which was not conducive to the application of aluminum alloy in the process of high speed forming.Therefore,it is of great significance to accurately obtain the fracture law of aluminum alloy sheet at high speed,which is very important to guide the material selection,structure design and optimization of workpiece.The main research contents of this paper are as follows:Firstly,the corresponding test of AA5052 aluminum alloy was conducted.Using the DIC(Digital Image Correlation)method,the uniaxial tensile study of AA5052 aluminum alloy notch parts under different strain rates was carried out,and the stressstrain curves and fracture strain under different stress triaxiality were obtained,which can provide experimental basis for the establishment of the dynamic constitutive relation and the fracture failure criterion of AA5052 aluminum alloy,and enrich the material properties database of AA5052 aluminum alloy.Secondly,the true stress-strain curve under large strain range was obtained by DIC method,which was used to determine the strain hardening effect of AA5052 aluminum alloy.Then the strain rate effect in Johnson-Cook constitutive relationship and the influence of strain rate in the constitutive relationship of AA5052 aluminum alloy was determined.By fitting the experimental data,the dynamic constitutive relationship of AA5052 aluminum alloy at room temperature was established.Thirdly,the ductile fracture criterion of AA5052 aluminum alloy is putforword.Based on the Lou ductile fracture criterion,the corresponding fracture model parameters were fitted according to the fracture limit strain of different stress triaxiality and Lord Angle under quasi-static condition,and the strain rate correction term was added considering the influence of different strain rates on fracture limit.Thus,the ductile fracture model of AA5052 aluminum alloy considering the strain rate effect at room temperature was established.Finally,the experiment and simulation of electromagnetic forming was conducted to verify the accuracy of the ductile fracture model.Using the LS-DYNA finite element analysis software,the numerical model of electromagnetic forming was carried out,and the proposed dynamic constitutive model and fracture failure model were added to predict the failure of materials at high speed.The results of good comparison between experiment and simulation show the accuracy of simulation and fracture model.