Research On The Bauschinger Effect Of 2198 Al-Li Alloy Sheet

2198 Al-Li alloy has the advantages of low density,high strength and low crack growth rate.However,the severe springback after forming and strong anisotropy of 2198 Al-Li alloy sheet limit its application in the aerospace field.The mechanical behavior of the material depends on the strain path.In order to study the effect of simple strain path change on the mechanical behavior of 2198 Al-Li alloy sheet,Bauschinger Effect was tested by tensioncompression test and shear-reverse shear test.And an anisotropic constitutive model of 2198 Al-Li alloy sheet was established.The mechanical behaviors of 2198 Al-Li alloy sheet along RD,TD and 45° directions were tested by uniaxial tensile test.The results show that the strength of RD direction is slightly higher than that of TD direction.The strength of 45° direction is the lowest.Bauschinger Effect of 2198 Al-Li alloy sheet was tested by tensile-compression test.The results show that the Bauschinger Effect of 2198 Al-Li alloy is the highest along RD direction,followed by 45°direction,and the lowest in TD direction.The increase of pre-deformation will enhance the Bauschinger Effect.The shearing mechanical behaviors of 2198 Al-Li alloy sheet along RD,TD and 45°directions were tested.The results show that the shearing strength of 45° is the highest,and the shearing strength of TD direction is slightly higher than that of RD direction.2198 Al-Li alloy sheet was tested by shear-reverse shear test.The results show that Bauschinger Effect increases slightly in RD and TD directions with the increasing of pre-deformation.The increase in 45°direction is larger.The bigger the pre-deformation amount is in the same direction,the more obvious Bauschinger Effect is.The program of homogeneous anisotropic hardening（HAH）model of 2198 Al-Li alloy sheet was compiled by FORTRAN.The constitutive model is in good agreement with the experimental results,and can accurately describe Bauschinger Effect in the reverse loading.The yield circle gradually flattens in the opposite direction of loading when loading in the forward direction,while the yield circle gradually returns to its initial state near the current loading direction and flattens gradually in the opposite direction of the current loading direction during the forward loading.The displacement rate of yield circle under forward loading and reverse loading is faster in the initial stage,and then gradually slows down.