Zbornik radova Koridor 10 - Kirilo Savić

3rd International Scientific and Professional Conference
CORRIDOR 10 - a sustainable way of integrations
FIGURE 7. Typical appearance (left) and severe stage of squat (right) development on running
surface (railway line Podgorica - Bar, 2012)
FIGURE 8. Typical belgrospi pattern on running surface (railway line Podgorica - Bar, 2012)
FIGURE 9. Severe stage of shell development
Rolling contact fatigue cracks are initiated by the high shear stresses that can develop at the wheel/rail
contact region when such stresses exceed the allowable limits for the rail steel. A number of factors
can influence the high shear stresses, including:
The nominal, dynamic and impact wheel loadings (Figure 10), and the factors that influence
wheel loadings (rail cant, track geometry, rail and wheel vertical irregularities, bogie
characteristics, etc.
The radii of the wheels and rails at their contact area (Figure 11).
The radius of the wheels (smaller radius results in higher stress).
The traction/creep forces: as the traction level increases, the maximum stress also increases
and its location moves closer to the wheel/rail contact surface (Figure 12).
It is evident that at the lower values of traction coefficient (T/N up to about 0.2) the maximum shear
stresses are obtained at some depth from the rail contact surface, which corresponds to the region in
which shelling develops (Figure 12). Higher axle loads increase the normal forces N and may reduce
the T/N values, which in turn would enhance sub-surface crack initiation (Figure 9).
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