Investigation On Yield Criteria For Engineering Application

With the rapid development of science and technology,the forming process of sheet metal is more complicated,and the loading state is no longer singular,which puts forward higher requirements for accurately predicting the plastic deformation behavior of sheet metal.The yield criterion and the hardening model are the theoretical basis for studying the plastic forming problem of sheet metal,which has attracted the attention of scholars.At present,due to the limitation of its own functional form or the neglect of some practical factors,the yield criterion and strengthening model,which are convenient for practical engineering application,have low accuracy in describing the plastic deformation behavior during sheet metal forming.Therefore,it is of great theoretical significance and engineering practical value to study the yield strengthening behavior of sheet metal under complex loading,establish a mechanical model that can accurately characterize the plastic deformation behavior of sheet metal,and realize the accurate analysis of sheet metal plastic forming problem by embedding it into the finite element software.Through theoretical research,experimental verification and finite element analysis,a yield criterion and hardening model which is convenient for practical engineering application are established.Based on the idea of follow-up strengthen,the Hill'48 yield criterion,which is widely used in practical engineering,is piecewise processed,that is,the new yield criterion is established by the correction function.Based on the strict mathematical derivation,the parameter solution method of the new yield criterion,the proof of the convexity and the proof of the overall smooth continuity of the piecewise yield function are obtained.Compared with the original Hill'48 yield criterion,the new yield criterion compensates for the original yield criterion's defect of attend to one thing and lose another in the parameter solving process,and solves the problem of the "abnormal"phenomenon in the application of the original yield criterion.Based on the assumption that the hydrostatic stress does not change the plastic deformation of the material,the Yld2000-2d yield criterion,which can accurately predict the anisotropic mechanical behavior of the sheet under the plane stress,is improved and extended to the three-dimensional stress space,which is recorded as"Yld2000-3d" yield criterion.The UMAT subroutine based on return mapping Algorithm was programmed to embed "Yld2000-3d" yield criterion into the finite element software,ABAQUS.Taking the 57540 aluminum alloy plate as an example,based on Yld2000-2d yield criterion and "Yld2000-3d" yield criterion,two dimensional stress shell elements and three dimensional stress solid elements were used to simulate the three-point bending test respectively,and the simulation results were compared with the test results.The results show that compared with Yld2000-2d plane stress yield criterion,the improved "Yld2000-3d" 3d stress yield criterion can more accurately predict three-point bending springback of sheet metal.Taking full account of the multidimensionality of the generalized Bauschinger effect,a new method for describing the subsequent yield behavior of the sheet metal with openness,high precision and convenient engineering application is proposed.The method can select the applicable yield criterion according to the actual engineering needs,and solve the parameters of yield criterion under different strain conditions dynamically by establishing the influence pattern of the mechanical properties in one direction on the mechanical properties in other directions during the deformation process,so as to obtain the subsequent yield trajectory of the sheet.Combined with the,Yld2000-3d"yield criterion,the accuracy of the proposed new method was verified by taking 5754-M aluminum alloy as an example.The results show that the proposed new method can accurately predict the subsequent yield trajectory of the sheet.