Study On Simulation And Experiment Of Forming Limit Diagram Of 22MnB5 Steel Sheet At Warm Temperature

With the rapid development of the automotive industry and the intensification of the global energy crisis,the demand of the energy saving and environmental protection of the automotive industry has greatly increased.High strength steel has high tensile strength,which can ensure the safety while reducing the body weight.However,compared with ordinary steel,high strength steel has poor plasticity and low forming limit at ambient temperature which may cause the emergence of fracture.The forming ability and deformation resistance of high strength steel can be improved by heating method.In addition,the forming limit is a very important parameter to characterize the forming properties in the stamping process,so it is of great significance to master the forming limit of high strength steel for making a scientific and reasonable forming process.As a result,the FLD of 22MnB5 was investigated during the temperature range of warm forming based on the theory of ductile fracture damage with the method of combining experimental study with finite element simulation analysis in this article.The main contents and conclusions are as follows:(1)Through the uniaxial tensile test,the mechanical behavior of high strength steel is studied.The boundary condition of extreme state is determined and the rheological stress curve is drawn.It is found that the increase of temperature has a certain degree of improvement on the stamping performance of the sheet material,the specimen is a cup–and-cone-shaped which belongs to the typical ductile fracture.(2)Using the Fortran language,the finite element model of uniaxial tensile test was embedded with four common ductile damage criteria via user subroutine and the ductile damage with respect to the four ductile criteria was calculated at different temperatures.The ductile damage value control method is used as the rupture basis for numerical simulation of bulge test,and the forming limit diagram at different temperatures is calculated.It was founded that the higher the temperature is,the more huge the critical damage value is,the greater the forming limit is.(3)The bulging test mold that can be heated was designed,and bulging test at 100? and 200? was performed to evaluate the reliability of the ductile fracture model.The results showed that the accuracy of the ductile fracture model based on the Cockroft and Latham criterion is not high except for a few tension-compression strain points.The Brozzo criterion,Ayada criterion and Rice and Tracey criterion predicted that the ultimate strain points of the tension-compression region are basically consistent and the precision of the prediction is higher.But for the tension-tension state,the results of the above three fracture criteria are all very different from those of the test.The trend of the curve is opposite and it failed to predict the limit point of the tension-tension area accurately.