Research On Random Fatigue Analysis Of The Vehicle Body Based On Pseudo-excitation Method

With the increasing speed of high-speed trains, the random vibration of the vehicle body which is caused by the random excitations, e.g. track irregularities, bow-net vibration and aerodynamic loads,, is increasing obviously. Consequently, the dynamic response and fatigue analysis are becoming more and more important for the vehicle design and safe operation. Limited by the low efficiency of the traditional CQC method, only the very simple rigid body dynamic models are included in the previous studies of vehicle body random vibration analysis, which obviously can not meet the needs for the precise vibration analysis. Pseudo excitation method (PEM) is a recently developed efficient algorithm for random vibration analysis. It is firstly applied in this paper to transform the complicated random vibration into a harmonic pseudo one; the harmonic response analysis module of general finite element software is then used to calculate the pseudo-responses of the vehicle body; finally the fatigue analyses of the hot points are carried out by using the existing fatigue theory. Three parts are consisted in this paper as follows.Firstly, the traditional time and frequency domain fatigue theory is introduced. In the latter theory, only the statistics of power spectrum density and probability density rather than the time domain response are required in the calculation, which makes it more applicable for random vibration fatigue analysis and the selection of probability density model of stress amplitude becomes the key problem. Several probability density models with different bandwidths are introduced in this part and the fatigue failure model and the treatment of stress concentration are also studied.Secondly, PEM for stationary random vibration analysis in real number field is established. Normally, the pseudo-excitation constructed by the traditional PEM is in the complex form which can not be directly applied into the harmonic response analysis module of general finite element software. To overcome this problem, a new form of PEM for harmonic response analysis subjected to stationary random excitation in real number field is derived, which makes the calculation of general finite element software available. In the calculation, the traveling wave effect is taken into account. This method is then justified by comparison with the traditional PEM by three examples, i.e. the random vibration analysis of two degrees of freedom system, plane truss structure and long-span cable-stayed bridge.Finally, based on the previous two parts, the random vibration and fatigue of the elastic vehicle body are analyzed. The Welch's method is applied to transform the time-domain load samples at the air-springs obtained from the experiment into load power spectrum densities and the proposed real number field PEM is then used to analyze the random vibration of the vehicle body excited by both the single source in phase and different phase loads. The stress power spectrum densities of the hot points are transformed into stress amplitude probability densities under three different probability density models and linear accumulative damage criterion is used to analyze fatigue damage of the hot points. The proposed method is then compared with the three-interval method and the results show that the calculated vehicle body of the high-speed train meets the fatigue resistance requirements.