Theoretical Research And Numerical Simulation Of Forming Limit Line For Zirconium Alloy Sheet

Zirconium alloys are widely applied in the field of nuclear industry and aerospace due to its excellent nuclear properties,mechanical properties and corrosion resistance.It is of great significance to study the stamping properties of Zirconium alloy sheet.Forming limit diagram(FLD)is an important tool to judge the form ability of sheet metal,and can be used to predict the problems of sheet metal in the forming process.In fact,the method through experiment to obtain FLD is expensive and time-consuming.So the paper chose the Zr-Sn-Fe metal plate as research object,which is of the thickness of 0.46 mm,using the method of theoretical derivation and finite element simulation to acquire the FLD of the zirconium alloy,and analyzes its influence factors and applications and so on.Firstly,this paper is based on the theoretical knowledge of theory of plasticity,including an isotropic yield criterion,flow rule and hardening criterion and so on.Then,based on the Hill79 yield criterion,using the Swift diffuse instability theory and Hill localized instability theory to deduce the limit strain formula.Similarly,according to the M-K groove theory,the corresponding program is compiled by MATLAB,so as to get the ultimate strain under different stress paths.The FLD of Zr-4 alloy is obtained by introducing the mechanical property parameters into different theoretical model,which are obtained by uniaxial tensile test.And this paper makes a comparative analysis of the different curves,and studies the influence of relevant parameters on forming limit line.Secondly,in the DYNAFORM software,the finite element simulation is used to simulate the bulging test,and change the strain paths to obtain the FLD of the sheet.Moreover,using maximal male modulus force criterion and criterion of strain path transformation as instability criterion to obtain the ultimate strain of board material under different strain paths.Then this paper compares and analyzes the result of the finite element simulation and theoretical prediction,which show that the right half of FLD obtained by Swift-Hill instability theory is very different from the simulation result,and overall height is lower.However,the result obtained by using M-K groove theory is not so different from the simulation,but the left half is bigger than the simulation,the right half is less than the simulation results.Finally,the influence of friction coefficient,virtual stamping speed and edgeforce is discussed by means of finite element simulation.It is known from the simulation that the friction condition has a great influence on the FLD of the zirconium alloy.With the increase of the friction coefficient,the height of forming limit line is gradually decreasing,and the friction coefficient is more significant in the double pull zone.When the friction coefficient is 0.125,the virtual punching speed is2000mm/s and the edge force is 20 KN,the result of finite element simulation is reasonable.In addition,during the simulated stamping process of the box-shaped part,the FLD obtained by the finite element simulation is used as the fracture criterion of the DYNAFORM software.And compared with the experimental results,the simulation results are reliable.In this paper,through theoretical and finite element method to predict the forming limit diagram zirconium alloy sheet with a thickness of 0.46 mm,which can be used to predict the forming limit of other types of zirconium alloy.