Strain energy based low cycle fatigue damage analysis in a plain C-Mn rail steel

Strain-controlled low cycle fatigue tests were performed on 60 kg/m 90-UTS plain C-Mn rail steel with fully pearlitic microstructure. Analysis of hysteresis loop shape and properties revealed that the steel deviated from the ideal Masing type material behaviour to a little extent. To evaluate the fatigue damage in rail steel, energy-based analytical approach proposed by Morrow based on Masing hypothesis was employed. The Morrow energy model resulted in reasonably good approximation of both average plastic strain energy and fatigue life in comparison to experimentally observed values. In addition to that the plastic strain energy density (ΔWp) was correlated to fatigue life (2Nf) through a simple power law and very well represented by Coffin-Mansion type relationship similar to conventional strain-life (Δεp - 2Nf) relationship. Finally, the concept of fatigue toughness, an energy parameter, was introduced to life prediction in rail steel which was proved to be a suitable and reliable alternative to strain-life approach in fatigue damage evaluation with high degree of accuracy.