Some comments on surface cracks in rails

The present work considers the problem of whether a shallow angle surface crack on a rail may propagate either parallel or perpendicular to the surface. After referring to a classification of crack‐like defects, a distinct surface crack with a typical length of 1 mm and more, inclined to the surface by an angle of approx. 30°, is introduced. Then various strain and stress states are discussed (eigenstress, residual and load stress state) which may control the crack growth. Stress intensity factor equations are provided for the internal and load stress states. In particular, the deformation process due to a single pass (overrolling) by a wheel is investigated. Recommendations are presented on how to relate the stress intensity factor ranges to the actual deformation process. For a typical loading condition, the positive part of the mode I stress intensity factor range is near to the effective threshold value of a rail steel. The influence of the material and its strength on the crack propagation behaviour is discussed qualitatively.