Research On The Simulation Of Multi-axial Loading Fatigue Test Of The Driving Axle

The multi-axial loading fatigue test of motor vehicle axle is an important type of test in which the axle loading conditions experienced on the roads are realistically simulated,with which the product durability can be effectively verified and which plays an impotant role in the product developments.This paper focuses on research on how to simulate this type of the test.According to the principle of the multi-axial loading fatigue test of axle in which Schenck ITFC system is applied,a simulation method of the test is presented,in which the hardwares of the test system,such as servo-hydraulic system,axle,suspension,loading fixture,data measuring system,digital-analog signal converter,etc.,are replaced with the dynamic finite element model of the axle,with the basic algorithm of ITFC system being mainly followed.With the rear drive axle of a mini-vehicle as the object of research,the simulation of its multi-axial loading fatigue test is effectively achieved.One of the keys in implementing the simulation of the multi-axial loading fatigue test of the rear drive axle is to construct an accurate finite element model of the rear drive axle system.The rear drive axle and two leaf springs are contained in the rear drive axle finite element model constructed,with the objective of including the leaf springs in the model being providing the restraints to the rear drive axle.The finite element models of the rear drive axle and leaf springs are mainly constructed with the tetra elements.The tires are replaced with two loading rods whose finite element models are constructed with the shell elements and which are used to transfer the forces from the ground to the halfshafts.The accuracy of the finite element model is verified with a static calibration test.Accurately identifying the frequency response function of the finite element model of the rear drive axle system is one of the keys for an accurate simulation.The pseudo impulse signal is used as the input signals for frequency response function identification,with the frequency response function of high accuracy obtained.The MATLAB programs are compiled,which can be applied to perform the system frequency response function identification and calculate the dynamic input load signals for accurately reproducing the simulation target signals from the simulation target signals and system frequency response function.The vehicle run test for measuring the strain signals of the rear drive axle is performed on the Hainan proving ground,with the measured strain signals as the simulation target signals of the multi-axial loading fatigue test of the rear drive axle.The dynamic input load signals are calculated from the simulation target signals and system frequency response function.These dynamic input load signals are applied to the dynamic finite element model of the rear drive axle,with the achieved response signals or strain signals of the model are calculated with the modal transient dynamics analysis.Each achieved response signal is compared with the corresponding target signal,which indicates that their waveforms in time domain coincide very well,with the simulation errors being in the range of 0.3% and 11.61%.The empirical loading conditions for axle design check are applied to perform the static finite element analysis of the rear drive axle for seeking the dangerouse zones where the fatigue failures may occur earlier,with the elements in the zones used as the elements for outputing the response signals in the dynamic finite element models the rear drive axle.When the dynamic input load signals above are applied to the dynamic finite element model of the rear drive axle and the achieved response signals are calculated with the modal transient dynamics analysis,the stress signals of the elements of the model are output.A fatigue life prediction software based local stress-strain method is applied to process the stress signals,calculating the fatigue lives of the elements.The simulation model of the multi-axial loading fatigue test of the rear drive axle with the nonlinear damping characteristics of the shock absorber taken into account is constructed.The simulation performed with the model indicates that,as compared to the completely linear simulation model above,the simulation errors obtained with the simulation model with the nonlinear damping characteristics are significantly larger,the model calculation speed is much slower,with the nonlinear model less effective.