Prediction Of Springback Of Aluminum Alloy Sheet Under Changing Strain Paths

In recent years,aluminum alloy and other light metal materials have been widely used in aerospace,automobile,medicine and other important fields because of their high specific strength and good stability.These materials generally have higher strength than ordinary metal materials.High strength will make the larger springback more obvious during the plastic forming process of the metal sheet.As one of the main defects during sheet metal plastic forming,the springback phenomenon seriously affects the quality and production efficiency of sheet metal products.How to control and prevent springback effectively has been a hot and difficult research point in the field of metal plastic forming.Therefore,it is necessary to predict the springback of the product in the process of forming,so as to compensate for the mold to make its parts meet the needs of production.The springback of sheet metal is mainly affected by two factors:Young’s modulus and final stress state before unloading.The damage propagation,inelastic recovery behavior and hardening mechanism of the material will affect the above two factors with the change of the loading path of the sheet metal,thus affecting the springback of the material.In order to improve the accuracy of springback prediction,a more practical material theoretical model must be used as the research basis.In the process of plastic deformation of metal materials after reaching the yield point,there are not only isotropic hardening and kinematic hardening,but also distortional hardening due to plastic deformation induced anisotropy,which has an effect on the ultimate stress state.Therefore,the selection of the hardening law of the simulation process has an important impact on the accuracy of the final simulation results.The evolution of subsequent yield surfaces determines the evolution of stress-strain in the hardening process of metal materials.At the same time,the evolution of subsequent yield surfaces is very sensitive to the strain history and damage propagation.Due to the different loading paths,the stress states in the final springback stage are also different.Only by fully understanding the loading and unloading process of metal materials and accurately describing the subsequent yield surfaces of materials can the high precision prediction of springback be realized.Based on a fully coupled damage model considering plastic deformation induced anisotropy,the springback phenomena of AA7055 aluminum alloy under complex strain paths is discussed in this paper.The main research contents are as follows:In this paper,the springback phenomenon of sheet metal materials were studied through the experimental and FEA methodologies.In the experiment,AA7055 aluminum alloy sheet are chosen as the research objective.In order to simulate the stamping process of sheet metal,the springback angle of the specimen under different loading paths can be obtained and the springback process can be discussed by using the method of combining pre-stretching test and three-point bending tests.The influence of different strain degree on Young’s modulus of materials was studied by cyclic loading of loading-unloading test.In the simulation,the plastic deformation induced anisotropy and fully coupled ductile damage were both considered in the proposed fully coupled damage model.The given constitutive model was also implemented into Abaqus through the user material subroutine Umat/Vumat,and the springback under variable strain paths was simulated by the method of combining explicit step and implicit step.By comparing the experimental and numerical results,the effects of hardening distribution,inelastic recovery behavior,damage and plastic deformation induced anisotropy on the springback of sheet metal under complex loading paths were discussed.