Finite element analyses of rolling contact fatigue crack initiation in railheads

A finite element (FE) tool was developed for the analysis of rolling contact fatigue crack initiation in railheads. An elastic-plastic non-linear kinematic hardening material model is included in the tool, which can model decaying ratcheting rate. The FE tool was applied to rails used in commuter train traffic at a Swedish test site. Two rolling contact conditions were compared, with respect to fatigue crack initiation, by modelling the contact loads differently. The two conditions were newly manufactured rails (Hertzian distribution) and rails that have been in service for 16 months (non-Hertzian distribution). A strategy proposed for fatigue analysis comprises a critical plane approach used together with a multiaxial fatigue model; a damage accumulation rule is also proposed that takes into account low-cycle fatigue and ratcheting damage mechanisms. Together with a two-dimensional FE analysis of a twin disc test, the fatigue evaluation strategy was validated by a set of twin disc data with good agreement. A fatigue analysis of the results from the FE tool show good agreement with observations and measurements made at the Swedish test site with respect to position for fatigue crack initiation, angle of the crack plane and the calculated number of wheel passages to initiation of head checks. Agreement was particularly good for the Hertzian distribution.