Fatigur Life Analysis And Test Of Engine Mount Under Vibration Load

Engine mount is an important component to isolate engine vibration and road surface excitation.It is subject to reciprocating inertia force and torque under its working condition.Therefore,fatigue failure is its main failure mode.It is important to accurately predict the fatigue life of an engine mount,which can ensure both driving safety and service reliability of automobile.Based on stress power spectral density,in this thesis,the Dirlik method is used to study the fatigue life of the engine mount.Firstly,a thin plate sample is taken as the research object,and the fatigue life analysis is carried out by using the Dirlik method.According to the transfer function method,the maximum stress part of the thin plate under an excitation signal is analyzed to obtain the stress power spectral density at this position,and the test verification is conducted.The bandwidth coefficient is calculated,and the Dirlik life prediction method is determined to predict the life in frequency domain.Furthermore,to study the amplitude of power spectral density on the life result,the wavelet packet is used to extract the characteristic parameters in time-frequency domain and the main frequency bands that affect life.The life prediction is carried out.The time-domain method is used to conduct the life prediction based on load time signal measured by tests.Accuracies of the Dirlik method and wavelet packet analysis are verified.Secondly,the life prediction method of thin plate is applied to the engine mount for analyzing the fatigue life under vibration load.Under the multiple excitation signals,the stress power spectral density at the stress dangerous part of the engine mount is analyzed to predict the fatigue life in frequency domain.The wavelet packet analysis method is used to decompose the load signal to extract the kurtosis and skewness coefficients.A normalized frequency bands are used to determine the main frequency band that affects lifetime.Thus the lifetime of the engine mount is predicted.Finally,a bench test of the engine mount is performed.The lifetime failure location and damage results are obtained and compared with the results of Dirlik’s method and wavelet packet analysis.The results show that the failure points in simulation of the engine mount are in agreement with those of the test,and are located at the top of the rubber near the middle position.The predicted life of the Dirlik method is 22.85% different from the test result,compared to the difference of 8.81% from the wavelet packet analysis.Thus,the wavelet packet analysis with higher prediction accuracy is a more effective method for lifetime prediction of engine mount.This thesis aims to study a novel fatigue life analysis method of engine mount,and the conclusions obtained can be extended to predict the life of other automotive components,which has theoretical value and guiding significance.