Study On The Effect Of Rolling Correction Processes On The Fatigue Life Of Aerospace Structural Components

Due to its thin wall,large size,and weak rigidity,aluminum alloy aerospace structural parts are easily affected by factors such as blank stress,machining stress,cutting force and cutting heat during CNC machining,resulting in different degrees of machining distortion of the machined structural parts.Rolling correction is a correction method often used in the production process of aerospace structural parts.However,the rolling correction process is still based on practical application,and the understanding of the mechanism of rolling correction is still insufficient.In particular,the coupling mechanism between the original stress field of the workpiece and the rolling stress field is unclear,which limits the improvement of the stability of the rolling correction process.The microplastic deformation and residual stress introduced by rolling correction change the original physical and mechanical properties and internal stress state of the workpiece material,which affects the fatigue performance of aerospace structural parts.Therefore,this thesis takes the aluminum alloy 7050-T7451 as the research object.The research on the influence of rolling correction process on the fatigue life of aerospace structural parts was carried out.Firstly,the study on the effect of initial stress state on the double-sided rolling of aluminum alloy thin-walled parts was carried out.With the help of finite element analysis software ABAQUS,the finite element analysis models of T-shaped parts under different initial stress states(no initial stress,rough stress only,rough stress coupled with machining stress)were established.The macroscopic deformation of the workpiece under different initial stress states was studied,and the law of initial stress state on the deformation of thin-walled parts was obtained.The strain-stress field evolution mechanism in the rolling process was analyzed by taking the stress and strain data in the characteristic cross section and characteristic line as the research object.It is found that the workpiece surface is compressive stress in all three initial stress states,and reaches the maximum value at the secondary surface.Moreover,the blank stress and machining stress in the rolling direction lead to larger stress values in the full thickness range of the workpiece.In the vertical rolling direction,the initial stresses mainly cause the change of surface stresses,and the blank stresses lead to the decrease of surface compressive stress values,and the machining stresses lead to the increase of surface compressive stresses.Secondly,a study on the effect of bilateral rolling on the fatigue life of aluminum alloy thin-walled parts was carried out.By analyzing the surface characteristics of the thin-walled parts before and after rolling,the surface material was plastically deformed under the action of rolling,and a 200μm thick hardened layer was generated,and the surface roughness of the material was reduced from 1.181μm to 0.791μm,which was 33%.The S-N curves of the rolled specimens were obtained by conducting tensile-tensile fatigue tests with the aid of a fatigue testing machine.The results showed that the fatigue life of the rolled workpiece was improved at the same stress level.Comparing the fatigue fracture morphology at different stress levels,it was found that the fatigue crack source shifted from the surface to the subsurface and the average spacing of fatigue striations in the fatigue crack extension area was reduced after rolling compared with the unrolled workpiece.In combination with ABAQUS FEA software and FA-SAFE fatigue life analysis software,a collaborative simulation environment for rolling-fatigue analysis of thin-walled parts was established to open up the data transfer path in the process of rolling deformation correction and fatigue life prediction finite element simulation.Combined with the rolling fatigue test of thin-walled parts,the maximum error between the simulation value of rolling workpiece and test data is 12.1%,which verifies the correctness of the model.Finally,a study on the effect of rolling process on the fatigue life of typical aerospace structural parts was carried out.With the help of finite element simulation technology,a rolling-fatigue analysis model of aluminum alloy structural parts with three spacer frames was established.The effects of different load forms,roller indentation and rolling position on the fatigue life were analyzed.The results show that the fatigue life of the rolled workpiece is the highest under the compression-compression load and the lowest under the tension-compression load.In the case of a certain rolling position,the fatigue life of the workpiece gradually decreases with the increase of the roller indentation.In the case of a certain amount of roller indentation,the residual tensile stress above the rolling area is the highest when the rolling position is 2mm from the upper surface,and the fatigue life of the workpiece is the lowest at this time.The results of the study are of guiding significance to the development of rolling calibration process.