Basic Research On Measurement And Control Method Of Initial Residual Stress For Thick Aero-aluminum-alloy Plate

With the development of aviation manufacturing industry,high-performance aluminum alloy thick plate is widely used in the manufacture of aircraft large-scale integral structural parts because of its high corrosion resistance,high strength,high toughness and other characteristics.However,the increase of plate thickness not only makes it more difficult to control the mechanical properties of materials and reduce the residual stress,but also challenges the accurate measurement of the initial residual stress of the blank.In this paper,the aluminum alloy thick plate used in aviation is taken as the research object,and the formation mechanism of residual stress,measurement method,control means and the influence law of machining deformation are studied in depth.The main research work and results in this paper are as follows:(1)The research on the initial residual stress release and machining deformationThrough equaling the removal of materials to the release of residual stress,the residual stress remained in the aeronautical monolithic component were converted into the external force according to the static equilibrium conditions,the analysis model was deduced for machining deformation based on the small deformation theory.Because the overall consideration on position variation was done by the tension/compression of neutral surface,bending of neutral surface,and rotation of end surface,the superposition principle can be used to formulize the mechanical model of residual stress redistribution.(2)The research on the error analysis of stress measurement by crack compliance methodBased on the testing process of crack compliance method,the directionality of stress calculation error is analyzed by combining numerical simulation with cutting experiment.Research shows the results of the crack compliance method based on Legendre polynomials can show an incompletely symmetric stress distribution and the error decreases with oscillation along the cutting direction.The results show that the stress in the middle region of the plate compared with the edge region has higher accuracy and better stability.Finally,the mathematical model of relative error of stress-strain is established.It is pointed out that the error of stress calculation is related to the condition number of system matrix,and the higher the stress fitting order is,the higher the condition number is,the greater the error of stress calculation is.At the same time,the research shows that the condition number of the system can be changed by the primary transformation of the system,and then the accuracy of stress measurement can be changed.(3)The research on the test method of residual stress of aluminum thick plateBased on the theory of unit force method,the relationship model between residual stress and machining deformation is established.Based on the influence of stress release on machining deformation and the principle of unit force method,the analytical formula and finite element method of stress influence factor are constructed respectively.The results show that compared with the analytical method,the finite element method is simple and not limited by the part structure.Taking wedge-shaped parts as an example,the stress reverse model is established,and the influence of measurement error on calculation error is analyzed.Finally,aiming at reducing the error of stress calculation and the number of conditions,the flow of stress reverse calculation method is designed based on the influence of condition number on stress calculation,and the method is verified by an example.(4)The research on the formation mechanism and control method of quenching residual stressThe thermal-mechanical coupling finite element model of quenching process is established by ABAQUS software,and the correctness of the model is verified by an example.The mechanism of quenching residual stress is analyzed from temperature field and stress field respectively.It is found that convective heat transfer coefficient can have a great influence on quenching residual stress and cooling rate.In particular,the influence on the residual stress is mainly concentrated in the high temperature region,and the cooling process in the low temperature region will not have a substantial impact on the formation of the final residual stress.Therefore,a method is proposed to control the residual stress and cooling time by using the convective heat transfer coefficient.By this method,the contradiction between the residual stress and cooling time can be effectively balanced.