Investigation On Anisotropic Yield Behavior Of 5A90 Al-Li Alloy Sheet And Modification Of Yield Criterion

In recent years,with the gradual improvement of people's environmental awareness,the continuous promotion of sustainable development concepts and the pursuit of lightweight construction materials,Al-Li alloys has been widely used in the aerospace industry and the manufacture of cutting-edge weapons,thanks to its low density,high specific strength,high specific rigidity,excellent corrosion resistance.However,compared with conventional aluminum alloy materials,Al-Li alloy sheets have different obvious anisotropy,which limits their industrial applications to some extent.In order to scientifically and rationally use Al-Li alloy materials,it is necessary to systematically study the anisotropic yield behavior and modify the yield criterion.To this end,taking the 5A90 Al-Li alloy sheet as example,the anisotropic yield behavior of the material was studied through theoretical analysis,numerical simulation and experiments in this work.(1)Firstly,based on the DIC strain measurement system,unxial tensile tests were conducted on 5A90 aluminum-lithium alloy sheets in five directions(0°,22.5°,45°,67.5°,90°)at a speed of 3 mm/min at room temperature,and the plastic rheological behavior and determine the anisotropic r value were studied,and draw the theoretical yield loci under different anisotropic yield criteria(Hil148,Hosford,Barlat89,Yld2000-2d).(2)The cross tensile specimens were designed according to ISO 16842:2014 standard.At room temperature,the cross biaxial tensile machine was used to test the specimens at a speed of 3 mm/min in the main direction under different loading ratios(2:4,3:4,4:4,4:3,4:2).The test yield points of the 5A90 Al-Li alloy sheet were obtained,and the test yield loci of the first quadrant of the 5A90 Al-Li alloy in stress space were draw.(3)Unixial tensile tests and cross biaxial tensile tests under warm(150?)condition were tested to obtain stress-strain curves and yield points,and analyzed the effect of temperature on the yield loci of the material.(4)Based on the Hil148 yield criterion,the yield criterion applicable to 5A90 Al-Li alloy sheet at room temperature was modified.(5)The stress-strain relationship of modified yield criterion were verified by Drucker's postulate and the principle of plastic strain work,The modified yield criterion was written into a VUMAT subroutine,The forming limit of the 5A90 Al-Li alloy sheet was simulated to obtain the forming limit diagram,and the modified yield criterion was verified.