Research On Fatigue Life Analysis And Fatigue Load Spectrum Compilation Method Of Steering Knuckle Of An Electric Car

In order to improve the mileage of electric car,it needs to be further lightweight.Aluminum alloy parts are more and more used in electric cars.However,while the electric car is lightweight,it is necessary to verify the fatigue durability of its parts.On the premise that the current automobile development iteration is getting faster and faster,it has become an urgent demand for the automobile industry to accurately and quickly predict the fatigue life of the lightweight parts of the electric car.With the continuous development of automobile test technology and simulation technology,in the automobile development cycle,the combination of vehicle test field durability road test and virtual simulation,and then compared with the fatigue durability bench test of key parts for durability analysis and verification can effectively improve the prediction accuracy of fatigue life and shorten the development cycle of the whole vehicle.Taking the lightweight aluminum alloy steering knuckle of an electric car as the research object,based on the road spectrum signals collected in the automobile test field,combined with the key technologies such as multi-body dynamics,virtual iteration,load decomposition,finite element,fatigue damage,fatigue durability bench test and load spectrum compilation,this paper systematically studies the fatigue life prediction,verification and load spectrum compilation method of aluminum alloy steering knuckle of electric car.The vehicle multi-body dynamics model is the basis of load virtual iteration and load decomposition.In order to improve the accuracy of the multi-body dynamics model,the reasonable modeling method of each subsystem of an electric vehicle is analyzed and selected.Based on the real vehicle data,the subsystem models of front and rear suspension,stabilizer bar,body and steering system are established,and the multi-body dynamics model assembly of the whole vehicle is carried out.The accuracy of the vehicle multi-body dynamics model is verified by the actual vehicle state parameters.In order to ensure the accuracy of the road spectrum signal in the subsequent load virtual iteration and load decomposition simulation,the effectiveness confirmation,abnormal signal removal,filtering and resampling of the collected road spectrum signal are carried out.In order to improve the simulation accuracy,the load loading method driven by the vertical displacement of the wheel center and the other five component forces of the wheel center is used to obtain the fatigue analysis load spectrum of the steering knuckle attachment point.In order to obtain the vertical displacement of the wheel center,the load virtual iteration technology is adopted,and the measured road spectrum signal dominated by the six component force of the wheel center is used as the response signal to reverse the vertical displacement of the wheel center.Then,the multi-body dynamic model of the whole vehicle is driven by the vertical displacement of the wheel center and the other five components of the wheel center.Through the load decomposition method,the fatigue analysis load spectrum of the steering knuckle attachment point is extracted.Based on the three-dimensional model,the finite element model of aluminum alloy steering knuckle of electric car is established,the inertia release analysis is carried out,and the stress distribution diagram of steering knuckle under unit load is obtained.Based on the fatigue load spectrum of the steering knuckle,the finite element analysis results and the S-N curve of the material,the fatigue life prediction analysis of the steering knuckle is carried out,and the dangerous areas and points of the fatigue failure of the steering knuckle are obtained.It is concluded that the fatigue life of steering knuckle meets the relevant provisions of national motor vehicles.In order to further verify the correctness of the fatigue life prediction method of the steering knuckle based on the finite element analysis results,the contribution of each direction of the loading point of the steering knuckle to the structural fatigue damage is analyzed,the steering knuckle Fatigue Bench test scheme is formulated,and the Fatigue Bench Test of the aluminum alloy steering knuckle is carried out.The fatigue fracture phenomenon of the steering knuckle does not appear within the number of basic cycles,indicating that the fatigue life of the steering knuckle meets the provisions of relevant standards,The validity of the fatigue life prediction results of steering knuckle is verified.The fatigue crack and fracture of the steering knuckle appear when the number of test cycles is terminated.Under the loading scheme of the number of test cycles,the fatigue life prediction simulation of the steering knuckle is carried out.By comparing the results of the test and simulation,the correctness of the steering knuckle fatigue analysis method based on the results of finite element analysis is verified.In order to improve the efficiency of Fatigue Bench Test for vehicle and its components,the acceleration method of load spectrum has been studied and applied more and more.In this study,the fatigue load spectrum compilation method for accelerated test is studied for vehicle Fatigue Bench test.By analyzing the advantages and disadvantages of various methods for compiling fatigue load spectra,the time-domain damage editing method is selected to accelerate the processing of the measured spectrum.The comparison between the original load spectrum and acceleration load spectrum in rain flow counting,step-through counting,power spectrum density,impact response spectrum,statistical characteristics and fatigue analysis results verifies that the acceleration load spectrum has a certain accuracy and significantly reduces the loading time.