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Aiming at the fracture of the bracket of sanding nozzle of CRH5 EMU bogie, the fatigue strength analysis and modal analysis of the bracket were conducted according to En13749 and BS7608 standards, and the track excitation during the vehicle running was thoroughly analyzed. The cause leading to the fracture of the bracket was found and the bracket was redesigned.

With the development of high-speed train and the increase of the speed, some non-sustaining components of the bogie are affected by the wheel-rail excitation and the fatigue fractures thus often occur. Fatigue failure is not only related to the amplitude of vibration, but also associated with the vibration frequency. Once, cracks appear on the bracket of sanding nozzle of CRH5 EMU bogie after for 1,200,000 kilometers operation. Aiming at this fatigue fracture, the fatigue strength analysis and modal analysis of the bracket structure were conducted in this paper. Based on the modal theory, the natural vibration modes and track excitation were combined to be analyzed. The cause of the fatigue crack was found, which provided a basis for the improvement of subsequent structural design.

A sander is mounted on the side sill end of the CRH5 EMU bogie, as shown in Figures 1(a)-(b). The sanding device is fixed on the side sill by bolts, and the nozzle bracket is connected to the sander; the baffle is fixed on the end of the side beam; the baffle, the nozzle bracket, the heating box and the nozzle are connected by bolts.

The cracks occurred at the welding end of the rib plate, as shown in

In the finite element analysis, the sander was discretized by shell elements. The bolts connection was modeled using the bond constraints. The model totally consisted of 19,862 elements and 17,313 nodes. The hose and the bolts were ignored in the model. The joint of components and sander structure is considered as fixed constraint and the FEM model is shown in

The sander is mounted on the end of bogie side beam, which would undertake complex loading condition in the process of train’s running. In addition, the sander will vibrate under the excitation of trail-wheel interaction due to its complex structure. Therefore, modal analysis on the whole sander system should be carried out, thereby the natural frequency range and the main vibration modes of the sander structure can be understood clearly so as to find the critical weak links sensitive to stress and the cause of cracks, providing the basis for structural improvement.

The results of modal analysis of the whole sander are shown in

The whole sander is installed on the end of the bracket frame. According to the En13749 [

When the vehicle is running, the wheel-rail interaction produces an excitation on the vehicle system. According to the test data [

rence, it is the reflection of wheel’s ellipticity; 6.5 m is the length of track plate, so the frequency is caused by the forced vibration of track slab. In consideration of the wheel diameter 890 mm, when the train runs at a speed of 200 km/h, the corresponding excitation frequency is 40 Hz, 20 Hz and 8.55 Hz respectively; when the train is running at a speed of 250 km/h, the excitation frequency is 49.6 Hz, 24.8 Hz and 10.68 Hz respectively.

So, no matter whether the train runs at 200 km/h or 250 km/h, the wheel-rail excitation frequencies are all close to the natural frequencies of the sand. The wheel-rail excitation is a kind of forced vibration input, assuming the displacement of the bracket is

where

structural damping to critical damping, namely,

Suppose train’s running speed is 200 km/h, means

coefficient

under the excitation of this frequency, the stress will be 2.89 times as much as the normal value in stiffened plate.

At the same time, the vibration acceleration is the two-order derivative of displacement,

According to the BS7608 standard in [^{7}, the stress range is 40 Mpa, as shown in

It can be seen from the above analysis that the wheel-rail excitation frequency is close to the first-order natural frequency of sander. When the train is running, the first-order mode can be easily excited, resulting in abnormal vibration on the nozzle bracket and making the stress at the end of the internal welding rib plate exceed the fatigue limit. Based on this, we optimized the design of the sanding nozzle structure, aiming to increase the first-order natural frequency of the nozzle seat, or trying to avoid the stress concentration at the rib plate welding end of nozzle bracket inner side. The improved structure is shown in

This paper used a method combining dynamic analysis with fatigue strength to conduct an in-depth study on the bogie sanding nozzle bracket structure, which took into account the intrinsic vibration mode of structure and rail

track excitation, then the reason that caused fatigue damage on the sanding nozzle bracket was found. On the basis of above analyses, the nozzle bracket structure was redesigned. The fatigue strength design method based on structural modal analysis has important theoretical significance and engineering value for the structural design of non-sustaining bogie components.