Fatigue behaviour of rail steel - A comparison between strain and stress controlled loading

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Fatigue behaviour of rail steel - A comparison between strain and stress controlled loading

Ahlström, J. / Karlsson, B.

Strain and stress controlled testings have been performed on a common rail quality. For the strain controlled tests, total strain amplitudes of 0.4, 0.6 and 1.0% were used. Two tests were run at each strain amplitude level. The stress controlled tests were performed at stress amplitudes corresponding to the stabilized values found in strain controlled tests. The results are first presented individually and are then combined and compared. The material tested was cut out from virgin rail of steel quality UIC 900A. The chemical composition of the actual rail and microstructures from the transverse and longitudinal cross sections are characterised. The micrographs are taken at a depth of 6 mm below the running surface. The microstructure is fully pearlitic. After investigating the low cycle fatigue behaviour and comparing the results of strain and stress controlled testing following conclusions are drawn: 1. Softening takes place during the initial part of the life time. This is most evident at low strain amplitudes corresponding to the largest number of cycles to failure 2. When comparing strain and stress controlled tests, the number of cycles to failure is very similar in both cases provided the strain and stress amplitudes are selected correspondingly at the same level of stabilised stress-strain amplitude. 3. For precise evaluation of strain and stress controlled tests, there is a need to take strain rate effects into account. In the present investigations such corrections are discussed but could be neglected with good approximation.