Wear 258 (2005) 973–980 An integrated approach to rolling contact sub-surface fatigue assessment of railway wheels A. Bernasconi ∗ , P. Davoli, M. Filippini, S. Foletti Dipartimento di Meccanica, Politecnico di Milano, Via La Masa, 34 I-20156 Milano, Italy Received 13 June 2003; received in revised form 28 November 2003; accepted 1 March 2004 Abstract A rolling contact fatigue assessment procedure for railway wheels is presented. The method aims to define the time required for the nucleation of sub-surface cracks in the wheel rim under different service conditions. The approach combines fatigue damage evaluation with dynamic loads simulation, by the application of multiaxial fatigue criteria to the contact stress histories. Material fatigue properties were obtained from both uniaxial tension–compression and reversed torsion stress conditions on specimens directly extracted from wheels. To validate the multiaxial model, non-proportional combined torsion and pulsating tests were also performed. © 2004 Elsevier B.V. All rights reserved. Keywords: Rolling contact fatigue; Sub-surface nucleation; Multiaxial fatigue; Testing 1. Introduction The total life assessment of railway wheels needs to take into account all the different damaging events that are typical to these components [1,2]. Among these, fatigue and wear play a major role, particularly because of the large contact forces observed in high speed trains as a consequence of the track–wheel dynamic interaction. Fatigue cracks can be detected near the tread surface, where they may nucleate by a plastic strain accumulation mechanism, i.e. ratchetting, and then propagate in a zone highly affected by both plastic strain (similar to the “sea of plasticity” reported by Smith in the case of rails [3]) and by wear, which represents a competing damaging event that may remove the material where cracks nucleated, but also mod- ify the contact geometry. Thus contact stresses may increase because of the modified dynamic behaviour of the wheel and the bad contact geometry. Cracks may also nucleate under the tread surface, at depths on an order of magnitude of several millimetres, where the material can be assumed to behave elastically, as long as the ∗ Corresponding author. Tel.: +39 02 2399 8222; fax: +39 02 2399 8202. E-mail address: andrea.bernasconi@polimi.it (A. Bernasconi). strain state evolves to elastic shakedown conditions. In this region crack nucleation may be accelerated by the presence of inclusions [4]. Nevertheless, to be assessed on the basis of multiaxial fatigue criteria and elastic stress calculations, the material has to be assumed as a defect-free material. This limitation is partly compensated by allowing for the presence of defects and inclusions in the specimens used for the iden- tifications of the material parameters of the fatigue model. The assessment method presented in this paper is based on a multiaxial fatigue criterion and relies on material param- eters identified in tests performed on specimens which have been extracted from wheels. Moreover, as it is recognised that any multiaxial model should also be validated on multiaxial tests which have been performed under stresses which repli- cate as accurately as possible the typical stress–time histories experienced in rolling contact fatigue problems, multiaxial fatigue tests were also performed. 2. Sub-surface fatigue assessment procedure A numerical procedure based on simulated dynamic loads has been developed, which allows for the calculation and summation of sub-surface fatigue damage. 0043-1648/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2004.03.044