The Common Rail Damages

Rail is one of the most important bearing parts of railway system. The traction and braking of trains are realized by the friction between wheels and rail. Therefore, a good rail condition is the prerequisite to ensure the safe and smooth running of trains. However, due to the alternating contact stresses, the rail material often suffers from wear or fatigue damage. As shown in Figure 1, the main types of rail damage include: fatigue crack, peeling, corrugation wear, crushing and rail side wear, which account for more than 80% of all rail damages. With the increase of train running speed and axle load, the rail fatigue and wear problems become increasingly serious, which causes the demands for rail grinding technologies sharply increased.

1. Rolling contact fatigue crack. Rolling contact fatigue crack is one of the most common damage forms of high-speed railway rail [1], as shown in Figure 2. Generally, the cracks will not extend all the way down, but extends to the rail surface in an arc to form rail peeling appearance, as shown in Figure 2 The top surface of the rail is depressed due to the peeling, and the impact stress is formed when the train wheels pass, which aggravates the vibration and noise. In some case, the branch cracks in the peeling pit may expand below the rail and lead to rail fracture, which may cause the major safety accidents [2].

2. Rail corrugation wear. Rail corrugation wear refers to the phenomenon of periodic uneven worn surface on the rail within a certain longitudinal range [3, 4], as shown in Figure 3. The corrugation wear will increase the vibration and noise of the train, affect the ride comfort, and reduce the fatigue life of locomotive and vehicle parts. According to the wavelength of corrugation wear, it is divided into short-wave (wavelength 25~80 mm) and long-wave (wavelength greater than 100 mm) corrugation. The main causes of corrugation include dynamic and non-dynamic theories. The dynamic theory believes that wheel-rail system vibration leads to the corrugation, including self-excited vibration, resonance and feedback vibration [5]. Non-dynamic theory that the formation of corrugation is mainly related to rail materials and smelting process, etc.; and even if the wheel-rail interforce is constant, the rail will also occur corrugation due to its uneven plastic flow [6,7].

3. Rail crushing. Rail crushing is the phenomenon that the rail top material appears plastic deformation and the rail tread becomes flattened, which is commonly observed on the rails in the curved section of heavy-duty railway [8], as shown in Figure 4. Rail crushing changes the shape of the rail head, the wheel-rail contacting force is changed, which will aggravate the running vibration and noise. In addition, rail crushing is often accompanied by stripping or fatigue crack damages. Stability limit is often used as a criterion to judge whether crushing damage occurs in rail, and increasing yield limit of materials can prevent or slow down this type of damage.

4. Rail side wear. Rail side wear is the main damage form of rail with small radius curves [9], as shown in Figure 5. In Chinese railway, 98% of the small radius curve rail is scrapped because of the excessive side wear. When the locomotive and vehicle enter the curve section, the train moves forward due to inertia, but the track forces the train body to turn. In this case, the wheels will impact the rail and the serious side wear will occur. Especially, when the centrifugal force and centripetal force of the train are unbalanced, the load of the inner and outer rail will be biased, which greatly aggravates the side wear [10, 11]. It is widely believed that the rail side wear shortens the service life of rail, and the change of rail profile makes the wheel/rail interaction worse, affecting the stability of train passing the curve.

Fig. 1 Fatigue cracks.        

Fig. 2 Rail peeling.

Fig. 3 Rail corrugation wear. 

Fig. 4 Rail crushing.

Fig. 5 Rail side wear.

References

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