Vibration Fatigue Life Prediction Method Research Based On Stress Power Spectrum

The safety, comfort and reliability of the car have been the important indicators ofautomobile quality. Vibration fatigue as one of the important factors that affect theautomobile reliability and security has been favored by domestic and foreign scholars.Road excitation is transferred to the automobile body and its parts through the tires andsuspension structure, and it makes the car have been in the vibration environmentduring the process of driving. This excitation will result the vibration fatigue ofautomotive. Therefore, researching the automobile key components fatigue life underrandom vibration loading is of great significance.At present, the vibration fatigue research has achieved fruitful results. In terms oftime domain method, classic rain flow counting method has been proposed. In terms offrequency domain method, narrow band peak method and wide band amplitude methodhave been proposed. Every development of vibration fatigue is toward the direction ofmore convenient and more reliable. However, the same calculation precision as timedomain method can’t be achieved by using frequency domain method because of thecomplexity of the vibration fatigue study itself. Therefore, frequency domain vibrationfatigue life prediction is studied in this thesis from the vibration test and vibrationfatigue model aspects.The main research works of the thesis are listed as follows：(1) General scaling law based on the stress power spectrum density has beenintroduced. Accelerated factor mathematical model of vibration fatigue testing underthe narrow band random process is deduced by using equivalent stress to replace theactual stress and combining the material fatigue characteristic curve. Vibration fatigueaccelerated test factor mathematical model of CAE simulation under narrow bandrandom process is completed.(2) The mathematical model of the accelerated factor of vibration fatigue testunder the condition of broad band random process is deduced by combining withgeneral scaling law and classical frequency domain fatigue life prediction model——Dirlik broad band rain flow amplitude distribution model. Vibration fatigueaccelerated test factor mathematical model of CAE simulation under wide bandrandom process is completed.(3) The prediction model of fatigue life under non-Gaussian random process hasbeen established. First of all, the relationship between the amplitude probability density under non-Gaussian random process and Gaussian random process based onthe basis of Winterstein transfer function model is established. Then, fatigue lifeprediction model under non-Gaussian random process based on the Gaussianapproximation method is established. Finally, the polynomial response surface modelof non-Gaussian correction coefficient is established. The validation of non-Gaussiancorrection coefficient model based on CAE simulation is completed. The results meetthe engineering requirements.(4) Assuming that the rain flow amplitude probability density of random stressand rain flow mean probability density are independent of each other, the vibrationfatigue life prediction model considering the effect of mean stress is established bycombining with Goodman mean stress correction model. And the verification of thismodel is completed. The results show that the vibration fatigue life prediction modelconsidering the effect of mean stress can be more consistent with experiment results.