Research And Application Of 7075 Aluminum Alloy Damage Model

The increasingly stringent automobile fuel economy and greenhouse gas emission standards have forced automobile manufacturers to use lightweight materials to improve fuel consumption and reduce vehicle emissions.Because of its excellent specific strength,bending stiffness,corrosion resistance and reusability,7000 series aluminum alloy has attracted people’s attention as a substitute for some high strength steel.However,the flowability of 7000 series aluminum alloy sheet is poor in the room temperature forming process,which is prone to fracture,springback and other defects.The hot forming process of aluminum alloy can improve the sheet forming performance.In the process of high temperature forming and room temperature collision of 7000series aluminum alloy,accurate prediction of damage and failure has become a key issue in the development of automobile parts.Taking 7075 aluminum alloy as the research object,the GISSMO damage model is introduced into the finite element simulation of formability and collision performance to study the damage behavior in hot stamping and automobile parts collision.In order to characterize the deformation behavior of 7075 aluminum alloy under hot stamping conditions,hot tensile tests were carried out at 300°C～450°C,0.01s^-1～1s^-1strain rate on Gleeble1500 thermal simulation machine.The experimental results show that under the same strain rate,the yield stress,tensile stress and strain hardening exponent n of 7075 aluminum alloy decrease with the increase of temperature.At the same temperature,the flow stress increases with the increase of strain rate.The high temperature flow stress curve of 7075 aluminum alloy was fitted by Hockett-Sherby model.The anisotropy coefficient of 7075 aluminum alloy was obtained by tensile test in different rolling directions,and the parameters of Barlet＿YLD＿2000 anisotropy model were calculated.In order to explore the material damage behavior of 7075aluminum alloy in hot stamping process,based on GISSMO damage model,the tensile samples with different stress triaxiality were designed.The parameters of high temperature GISSMO model were obtained by combining experiment and finite element simulation,and the mesh dependence analysis was carried out.U-shaped parts with different forming states were prepared by using molybdenum disulfide lubricant and without lubricant.The Barlet＿YLD＿2000 constitutive model combined with the high temperature GISSMO damage model was applied to the finite element simulation of 7075 aluminum alloy hot stamping to realize the accurate prediction of the damage behavior of the sheet metal in the high temperature forming process.In order to explore the damage behavior of 7075 aluminum alloy parts at room temperature,specimens with different stress triaxialities were designed for quasi-static tensile tests.According to the results of smooth specimens and 0°shear specimens,the‘Ling flow stress model’was used to establish the flow stress extrapolation part.The strain of samples was measured by DIC optical measurement technology,and the parameters of GISSMO model at room temperature were obtained by experimental-finite element simulation hybrid method.The accuracy of GISSMO model under high stress triaxiality was verified by the Nakajima test.The three-point bending experiment was carried out on the door strengthening beam made of 7075-T6 aluminum alloy plate.The results show that the material model of‘Von Mises+Gissmo’combination can well predict the three-point bending force-displacement curve and the folding morphology of the parts of the door strengthening beam.