The initiation of local rolling contact fatigue on railway wheels: An experimental study

•Initiation of local RCF from indentations is confirmed on a twin-disc test rig.•Indentations over ~0.2 mm deep can lead to LRCF on the tested discs of Φ 60 mm.•Plastic flow at an indentation is crucial to the initiation of cracks and LRCF.•A critical indentation depth applicable in practice needs further studies. Twin-disc tests have been conducted to study the initiation of local rolling contact fatigue (LRCF) observed on high-speed railway wheels. The tested wheel and rail discs, being about 60 mm in diameter, are extracted from ER8 wheel tires and U71MnG rail heads, respectively. Since indentations have been identified as the main cause of LRCF in practice, artificial defects are applied on the contact surfaces of wheel discs before tests using three different methods, namely, the Vickers hardness tester, electric discharge machining (EDM) and indenting of M10 tap tips (TT). Test results have shown that significant cracks and LRCF can indeed initiate under fully lubricated conditions at TT indentations deeper than approximately 0.15 mm and 0.2 mm, respectively, but not at Vickers indentations or EDM defects. Larger plastic flow and sharper geometries at relatively deep TT indentations, the influencing depth of the normal contact load and the detachment of wear debris should be the dominating factors, based on which a mechanism is proposed for the initiation of LRCF. Care should be taken, when applying the above thresholds into practice, to take into account the scale effect of the test rig, and dry load cycles and various types of indentations present in the field.