Keywords: dynamic, residual stresses, rolling contact, fatigue crack initiation, crack propagation, rail defects, maintenance.

A new numerical tool based on an original approach is developed for studying the fatigue phenomena of initiation and propagation, that are induced by repeated rolling, or rolling-sliding contacts between wheel and rail. Cracks initiate and propagate in the rail head in a complex varying multiaxial stress regime arising from Hertzian or non Hertzian contacts generating three-dimensioanl residual stress patterns. This paper presents the main steps of such a global approach devoted to the modelling of defects induced in the rails by the traffic. Special attention is paid to some of the principal difficulties met and to the proposed solutions. Examples of applications for the prediction of initiation as well as propagation of some defects are presented. It is shown that numerical simulations predict very well the locus of crack initiation as well as its propagation in the rail. This approach presents at least two main originalities: the first originality resides in its global character and the second one in the use of a special and original numerical methods for the evaluation of the initial states, the overloads and the elastoplastic state under service loading as well as the use of a new concept based on a "structural Paris' Law".

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