Analysis On Vibration Fatigue Of Straddle-type Monorail Vehicle Carbody

The vibration fatigue damage is easily found in components of railway vehicles which are generally running in complex vibration environment.It will decrease the span life of these structures and even cause severe accident and economical loss if exposed to long-term vibration excitation.The comprehensive analysis method was carried out based on line test data to evaluate the vibration fatigue of a typical straddle-type monorail vehicle carbody.Firstly,the description of the comprehensive method was carried out.The comprehensive method is a vibration fatigue evaluation method which,in one hand,modifies the real part and imaginary part of the loads to take the load frequency characteristics and resonance into consideration,and in the other hand,retains the phase information of the time-domain loads that used to evaluate the vibration fatigue through an IFFT transform.Secondly,the loads sustained by the carbody were calculated based on the data measured by acceleration transducers and strain gage in line test.The vertical load of air spring was acquired through the dynamic model of air spring.The transverse and longitudinal loads of the center pivot were obtained with the FE analysis.The longitudinal load of the coupler was calculated by theoretical analysis.Thirdly,the FE modal was established,the modal analysis was accomplished with curb weight,and the critical time-domain and frequency-domain key point were obtained.While the response factors acquired by harmonic analysis were used to modify the load in frequency-domain,and the modified time-domain loads were then obtained by an IFFT transform in return.Moreover,the quasi-static factors acquired by the inertia relief method were multiplied with modified time-domain loads to obtain dynamic stress under single load.Thus the actual dynamic stresses of each key point were obtained by summing up single dynamic stress under all loads.Lastly,the vibration fatigue assessment of the carbody with multiaxial-stress and mean stress factors considered was carried out refer to the rainflow counting and the FKM reference,and a comparison between the results of the comprehensive method and the quasi-static method was accomplished.The results show that:the degrees of utilization of some frequency-domain key points are higher than that of some time-domain key points,that is,some more serious vibration fatigue of some frequency-domain key points are more likely to happen than that of some time-domain key points.This illustrates that the dangerous location and its level of the structure in frequency-domain could be easily found according to the vibration fatigue assessment with comprehensive method.Due to the little intersection between the frequency range that the main energy of the loads may concentrate and the resonance frequency range,a low vibration fatigue of the carbody would occur within these frequency characteristics.However,it may be higher when there are some more intersection between the frequency range that main energy of the loads may concentrate and the resonance frequency range,especially when the PSDs of the loads reach a higher value in the resonance frequency point.