Study On Fatigue Property Of Crossbeam Under Torsion Condition Of Torsion Beam Rear Suspension

Torsion beam rear suspension is widely used in A-class cars.In recent years,with the extensive use of advanced high strength steel(AHSS)preforming + hydroforming,the overall property of torsion beam rear suspension has been greatly improved.However,the torsion beam rear suspension needs to absorb the excitation vibration during the driving process through the torsion of the crossbeam.Under the long-term and disordered excitation,the crossbeam inevitably becomes the high incidence area of fatigue failure,so the study on the fatigue property of the crossbeam is of great significance.Based on the torsion condition of the torsion beam rear suspension,the static analysis,fatigue analysis and life prediction of the crossbeam are carried out by using the finite element method,the relationship between the amplitude and life of the crossbeam condition is established,and the equivalent specimen is designed to verify the predicted life of the crossbeam high cycle fatigue simulation.The main research work of this paper is as follows:(1)Through cutting the typical section of the transition area,the thickness distribution characteristics of the variable section of the crossbeam are analyzed,and on this basis,the material flow characteristics in the direction of the section is studied.Through the analysis,the thickness reduction ratio and thickening ratio of the typical section of the transition section are all below 3%.The forming quality of the target corssbeam is evaluated by the thickness distribution index,and the forming reason of the thinning area in the forming process is explained by combining with the mechanical model.(2)The whole digital model of torsion beam suspension was established by reverse modeling and pre-processing of finite element software,and the mechanical test was carried out to obtain the property parameters of the beam material HZFB90 high strength steel.Based on the actual torsion load,the multi amplitude static analysis of the torsion beam rear suspension is carried out.The distribution characteristics and expansion rules of the dangerous area on the inner and outer surface of the corssbeam with the change of the working amplitude are mainly studied,and the actual stress state of the dangerous area on the inner and outer surface of the beam under the torsion load is analyzed,which provides the basis for the subsequent fatigue analysis and equivalent specimens.(3)Combined with the static analysis results and surface residual stress detection,the fatigue analysis of the torsion beam rear suspension was carried out.The difference of life prediction under uniaxial and biaxial method is compared,and the full amplitude condition is divided into high and low cycle fatigue.The maximum principal stress algorithm with Gerber correction and Brown Miller algorithm with morrow correction are used to calculate respectively,and the whole condition amplitude life prediction fitting equation of beam is established.(4)Through the design of the equivalent specimen,the high cycle fatigue life prediction of the crossbeam under the torsion condition is verified,and the feasibility of the equivalent specimen is verified from the stress state,the shape and the distribution of the residual stress on the inner surface.The forming die and special fixture of equivalent specimens for fatigue test are designed and manufactured.By comparing the stress-life fitting equation corresponding to high cycle fatigue calculated by crossbeam simulation and the stress-life fitting equation obtained by equivalent test,the life deviation under the same amplitude is kept within 25%.In this paper,a combination of finite element simulation and equivalent test is provided,which has practical significance and application value for the rapid verification of large-scale structural complex test.