Rolling Contact Fatigue of Railway Wheels Towards Tread Life Prediction through Numerical Modelling Considering Material Imperfections, Probabilistic Loading and Operational Data

Doctoral thesis, 2000

Higher train speeds and increased axle loads have led to larger forces acting on the railway wheels. Also, efforts are presently being made to straighten existing tracks, to design new tracks with larger curve radii and to optimize bogie designs. This evolution tends to shift the major cause of wheel rim damage from wear to fatigue due to the different physics of these two phenomena. In contrast to the slow deterioration through wear, fatigue sometimes causes abrupt fractures where a part of the wheel tread breaks off. Such failures may cause damage to rails and sleepers and to train suspensions and bearings and, in rare cases, serious derailments. The failures may be very costly in terms of operational delays and human injuries. Thus, an understanding of the underlying physical mechanisms and a search for means of prevention of fatigue of railway wheels have become research subjects of great importance. The approach in this thesis is twofold: Fatigue failures of wheels in operation are investigated, causes of the failures are identified and possible countermeasures are discussed Fatigue initiation in railway wheels is studied theoretically including computer analyses of stress and strain and of the resulting impact on fatigue The above studies concern forged wheels and are supported by experimental tests. Rolling contact fatigue of railway wheels involves a number of complicating factors normally not encountered in the 'classical' fatigue analysis. Factors studied in some depth in this thesis include multiaxial loading statistical effects material anisotropy material defects Among the concrete results obtained are parametric influences of load magnitudes and contact geometries on fatigue life, and also estimations of the influence of material defects and of the stochastic nature of the loads. A new material composition is proposed and tested.