The development of new steel grades for railways application, with the aim of reducing Total Life Cycle Cost, is nowadays an important target for every wheelsets producer. It has been proved that wheel-rail contact conditions always occur in 'elastic-plastic' regime. Localized plastic deformation, frequently caused by cyclic loading (shakedown - ratchetting), is of substantial importance, as it is associated with fatigue cracking. Consequently, Monotonic Yield Strength cannot longer be regarded as the only guide parameter. Also plastic deformation behavior of the material has to be in fact considered, not only in Monotonic conditions, but also in Cyclic conditions. In this paper, a simplified criterion is proposed to estimate and compare RCF materials resistance, in Monotonic and Cyclic conditions. It is based in part on traditional parameters and in part on other parameters not considered by railways standards. Common pearlitic steel grades, new conception bainitic steel grades and optimized pearlitic steel grades, with delayed transformation phase, have been tested. The behavior of all materials tested, with strain based approach to fatigue at R=-1, shows a cyclic softening, contrarily to expectations due to UTS/YS ratio evaluations. This points out the potential inconstistency of using only Monotonic properties to predict Cyclic strains. There are materials that soften more than others and this has to be taken into account during materials selection and RCF designing. In order to summarize the criterion, a diagram is proposed, which could represent a map in materials choice, taking into account both the cyclic yield strength and ductility. Tests are, presently, in progress in order to further validate the criterion with a greater number of data.
Mechanical behaviour of materials for railways solid wheels: A simplified criterion to estimate and compare RCF resistance
2003
9 Seiten, 12 Bilder, 4 Quellen
Conference paper
English
Eisenbahnrad , Eisenbahnschiene , Rollkontakt , Ermüdung , Produktentwicklung , plastische Verformung , Wechsellast (mechanisch) , Bruchmechanik , Berechnung , mechanischer Widerstand , perlitischer Stahl , bainitischer Stahl , mechanische Entfestigung , Werkstoffauswahl , Schaubild , Lebenszykluskosten
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