Research On Life Analysis Method For Structure Vibration Fatigue

Many components usually undergo vibration loading, which are used in aircrafts, wind energy utilizations and automobiles. However, vibration fatigue is more complicated than general cycle fatigue. Up to now, little experimental work has been done for vibration fatigue, and many theoretical problems have not been solved completely. Thus the systematical study on the vibration fatigue life has not only the important significance, but also a practical value.A combined theoretical and experimental study method for vibration fatigue life prediction was used. The vibration fatigue life research was consisted of the research on fatigue life prediction methods and the effect factors in fatigue life. The fatigue S-N curve was used as computation basis of fatigue life prediction. The vibration fatigue test was provided the datas for experimental verification.Modal analysis test and vibration fatigue test were conducted on cantilever structure of LY12CZ aluminum alloy. Two types of notch specimens were used, one was U grooved and the other was circular grooved. Hammering method was used in modal analysis test. Three different fatigue loadings were used on vibration fatigue test of U grooved specimens, and two different fatigue loadings were used on vibration fatigue test of circular groove specimens.The all life model of fatigue S-N curve for metal materials was presented. The effect of frequency on fatigue life curve of metal materials has been analyzed. The all life model of fatigue S-N curve describes the relationship between cycle stress and fatigue life very well. The statistics and analysis of test results show that the S-N curve model and frequency effects are in good agreement with the experimental ones.The models of rainflow amplitude distribution for random process and the sample method for vibration fatigue life prediction in time domain were presented. An improved trigonometric series method for time domain simulation of random process was proposed to solve the time domain simulation of random process on non-uniform sampling in frequency domain. The sample method was proposed and used for vibration fatigue life prediction in time domain, which based on the improved trigonometric series method. The models of rainflow amplitude distribution for limited band white noise, unimodal resonance spectrum, bimodal stress spectrum and general broadband random process were proposed, and the experiential formulas of model parameters were given in this paper. New methods of vibration fatigue life prediction in frequency domain were developed. Several common frequency domain methods of vibration fatigue life prediction and our methods of vibration fatigue life prediction were examined with the test data. It is demonstrated that the proposed life prediction methods give better satisfactory results for all experimental samples.The effect of damping, stress concentration and mean stress on structure vibration fatigue life has been analyzed. The relationship formula between modal damping ratio and structure vibration fatigue life has been given. The stress concentration factor of root mean square has been defined in this paper. And the prediction method for vibration fatigue life of notch sample based on fatigue notch factor has been proposed. The model of rainflow mean distribution for random process was proposed. The prediction method for vibration fatigue life taken into account effect of mean stress was presented, and this method based on the assumption of mutually independent between rainflow amplitude and rainflow mean. The effect of damping and stress concentration on vibration fatigue life are examined with the results of modal analysis test and vibration fatigue test. The analyzed results show good agreement with experimental results.