PHYBAL ― Short-time calculation of Woehler curves for wheel steels

Mechanical stress-strain hysteresis, temperature and electrical resistance measurements were performed for the detailed characterisation of the fatigue behaviour of the railway wheel steel SAE 1050 and the quenched and tempered steel SAE 4140, both used in railway wheel sets. Stress-controlled load increase and constant amplitude tests were carried out at ambient temperature on servohydraulic testing systems, The applied measurement methods depend on deformation-induced changes of the microstructure in the bulk material and represent the actual fatigue state. On the basis of experimental fatigue data determined in one load increase test and two constant amplitude tests the fatigue life calculation method "PHYBAL" was developed. Woehler (S-N) curves calculated with "PHYBAL" on the basis of only three fatigue test measurements agree very well with conventional experimentally determined ones. The microstructural characterisation was done by scanning electron microscopy, allowing to interpret the measured physical data on the basis of microstructural details.