CONTACT DEFECTS INITIATION IN RAILROAD WHEELS – EXPERIENCE, EXPERIMENTS AND MODELLING Radim Halama a,* , Rostislav Fajkoš b , Petr Matušek b , Petra Bábková c , František Fojtík a , Leo Václavek a a Department of Mechanics of Materials, VŠB-Technical University of Ostrava, Ostrava, 17.listopadu 15, 708 33, Czech Republic b Bonatrans Group, Bohumín, Revoluční 1234, 735 94, Czech Republic c Centre of Advanced Innovative Technologies, VŠB-Technical University of Ostrava, Ostrava, 17.listopadu 15, 708 33, Czech Republic * Corresponding author: tel. +420597321288, fax. +420596916490, radim.halama@vsb.cz ABSTRACT Main results of comprehensive research of rolling contact defects initiation are presented in this contribution. Description of own experimental study has been preceded by practical experience of a wheelset producer. A line rolling /sliding contact case with creepage of 0,75% was investigated using a unique test machine. The rail disc was made from Class C steel grade while the wheel disc from R7T steel grade. Unlike the standard twin-disc test, the diameter of the rail disc was 2.6 times bigger than the diameter of the wheel disc. Development of contact cracks and accumulation of shear strain for the wheel material R7T during rolling contact loading were namely evaluated. On the basis of test conditions, simulation by FEM was performed. As the result, very good prediction of shear strain accumulation was achieved using the AbdelKarim-Ohno cyclic plasticity model. The proposed computational strategy can be used for fatigue life prediction till initiation of a crack caused by low-cycle fatigue or by ratcheting failure. Keywords: rolling contact fatigue, ratcheting, crack initiation, low-cycle fatigue 1 INTRODUCTION Similarly as in the classical fatigue of materials, three stages can also be found in rolling contact fatigue (RCF) of the Wheel/Rail system, namely microcracks nucleation, crack initiation and crack growth. However, there are many differences between the classical multiaxial fatigue and the rolling contact fatigue (RCF) [1]. There are many research models for life prediction in the area of rolling contact fatigue [2]. Nevertheless, empirical approach has been the most frequently used approach in practise so far. In the empirical approach, Wear. 2011, vol. 271, issue 1-2, p. 174-185. Elsevier http://dx.doi.org/10.1016/j.wear.2010.10.053