An angle of attack-based derailment criterion for wheel flange climbing

A three-dimensional equilibrium model of a wheelset is created that takes the geometrical contact and non-linear creep force between the wheel and rail into account. This model can thus be used to study derailment conditions during flange climbing. To ensure the validity of Nadal’s criterion at small and negative angles of attack, the effects of the angle of attack and friction coefficient on an “equivalent friction coefficient”, which is defined as the ratio of the lateral creep force to the normal force, are studied. Using the results of the wheelset equilibrium equation, two curve-fitted formulas for the equivalent friction coefficient are generated in terms of the angle of attack and friction coefficient using, respectively, the Shen–Hedrick–Elkins creep theory and FASTSIM approach. A derailment criterion is proposed based on the curve-fitted equivalent friction coefficients, which takes the angle of attack, friction coefficient and contact angle into consideration. The effectiveness of the proposed criterion is verified through numerical comparisons with wheelset equilibrium equations for different contact angles and friction coefficients, and through experimental comparisons with scaled tests made by Japanese National Railways and full-scale field testing at the Transportation Technology Center, Inc.