The competitive role of wear and RCF: Full scale experimental assessment of artificial and natural defects in railway wheel treads

Abstract

Assessments of the severity of wheels tread defects under rolling contact fatigue conditions are in general very uncertain when based on theoretical concepts supported only by small scale material characterization and without the possibility of a full scale validation. In real service conditions, the tread surface and subsurface defects are subject to a number of variable mechanical loading conditions given by the combination of vertical and lateral loads and wheelset steering. The present paper describes some interesting experiences from recent RCF tests performed by Lucchini RS on its full scale roller rig (named “BU300”) on two very high speed railway wheelsets coming from revenue trafic. The test rig was used in order to reproduce running conditions very near to normal service conditions. A concept for test acceleration was applied: the ratio curve distance/straight distance was increased, since curves are more critical to RCF compared to straight running. Firstly, the scope of the test was to monitor the behavior of defects in order to evaluate the impact on the safe integrity and to reduce RCF damage by considering two different steel grades: ER8 (EN13262) and Superlos® developed by LucchiniRS. Secondly the results of the tests provided interesting information regarding rate of crack propagation.Depending on the crack depth from the tread surface and the wear rate obtained, an important basis for describing the competitive role of RCF and wear is offered. In addition some considerations on preventive wheel reprofiling (skimming) strategies are proposed that can reduce RCF impact on wheel life. The accumulated results are also valuable since they can be used as a basis for the validation of RCF models. Finally this work confirms the ability of the roller rig to reproduce equivalent service running conditions that can generate RCF cracks similar to those found in service.