Research On Forming Limit Diagrams Under Different Loading Paths

The research on the theory of sheet metal plastic forming is of great significance to modern industrial production and manufacturing.It has been used in aerospace manufacturing,instrument manufacturing,automobile manufacturing,equipment manufacturing and other fields,with irreplaceable status.In the field of sheet metal forming,the forming limit is an important index for evaluating the forming performance of materials.It determines the maximum degree of deformation of the sheet during the deformation process,and provides a basis for manufacturing and product design.It has made great contributions in improving product quality and reducing production costs.Therefore,the research of forming limit has become an important direction in the field of plastic forming theory.In order to study the forming limit of materials,scientists have proposed the important concept of forming limit diagram(FLD).The forming limit diagram uses the minor strain as the abscissa and the principal strain as the ordinate,which is a curve composed of forming limit points under different loading paths.The forming limit diagram is very practical,it can intuitively distinguish the safe area and the failure area of the material,and can effectively avoid the fracture problem that occurs in the actual production process,which promotes the development of the sheet metal forming field.At present,the main methods to obtaining the forming limit diagrams are experimental method,theoretical calculation method and numerical simulation method.However,the anisotropy of the material,work hardening,and changes of the loading paths all have various influences on the forming limit.In the manufacturing process,the strain path of the material is often not linear.Obviously,the forming limit diagram under the linear path obtained by the standard experiment is not accurate to judge the material fracture in complex forming.Therefore,it is also necessary to conduct an in-depth study on the forming limit diagrams under complex strain paths to predict the material fracture more accurately.In this paper,the theoretical calculation method,experimental method and finite element simulation method are used to study the forming limit diagram under different loading paths.First,the uniaxial tensile tests were carried out on AZ31 B magnesium alloy to obtain mechanical performance data.Then the biaxial tensile tests of AZ31 B magnesium alloy was carried out with different load ratios.Based on the experimental data,the forming limit diagram was drawn and compared with the forming limit diagram obtained by the finite element simulation to verify the accuracy of the finite element simulation.Furthermore,the ABAQUS finite element software was used to study the forming limit of the cross-shaped specimen under a complex loading path,and the effect of pre-strain on the forming limit diagram was analyzed.Finally,the common yield criterion and instability criterion are realized through programming with the Visual C ++ software.Developed a convenient and fast software that can calculate and draw forming limit diagrams.Based on the Hill 48 yield criterion and M-K instability criterion,the software functions are verified.