The Research On Sheet Deformation Behavior Involving The Anisotropy And Thick Stress

The sheet forming has a long history,which plays a very important role in the manufacturing industry,and it cannot be replaced by many other processing technology.The deformation behavior of sheet metal is quite a complicated process,and the traditional processing modes are unable to adapt to the rapid development of forming process.To describe the complex deformation process of sheet metal,it is necessary to support a solid theory to guide the processing during the sheet metal forming process,thereby avoiding unnecessary losses.The material used for metal sheet is produced by rolling production and processing for many times.And some sheet has a visible anisotropy.When studying the forming properties of these sheets,the influence of sheet anisotropy on the choice of yield criteria needs to be considered.During the study of sheet metal forming process,the selection of yield criteria should be targeted,namely,different materials employ different yield criteria.For the applicable yielding criteria,they still need to be amended according to the specific materials.In addition,the sheet is in a complex stress state during the forming process,not in a simple plane stress state,but also by the stress in the thickness direction.Therefore,it is urgent to research the thickness stress in the deformation of the sheet in the study of the yield criterion and the forming limit.The research object is mainly titanium alloy.Through the one-way tensile test,forming the limit experiment,this thesis modifies yield criterion of describing the anisotropy in plane.This thesis obtains the basic mechanical properties of 4 titanium alloys with different thickness by experiment,and it carries out the simulation of finite element model,confirming that the thickness stress plays an important role in the process of sheet metal forming.A more reasonable constitutive model is established by fitting the data,and the applicability of constitutive model is verified by finite element simulation.From the experimental data,it is found that the titanium alloy has obvious anisotropy in the plane,and the anisotropy in the plane of the sheet is better described by modifying the Yld2000-2d yield criterion.The thick stress is introduced into the yield criterion.Basing on the improved yield criterion and M-K model,the forming limit is deduced theoretically.And the experimental results can verify that the theoretical deformation limit deduced when considering the thick stress is more consistent with the experiment.