Uniaxial Ratcheting Behavior of a Weather-Resistant Rail Steel: Effect of Mean Stress and Stress Amplitude

Uniaxial ratcheting behavior of a weather-resistant rail steel belonging to 60 kg/m 90-UTS variety was studied in true stress control mode with varying mean stress (σm) and stress amplitude (σa) at constant σa and σm, respectively. In all the loading conditions, the ratcheting strain (εr) increased almost monotonically and accumulation of ratcheting strain was found to increase at higher magnitude of σm or σa, perhaps due to the increase in remnant dislocation density in the substructure of the investigated steel. After the initial sharp fall in ratcheting strain rate with elapsed cycles in all the cases, a constant ratcheting rate was attained very soon; thereafter, the ratcheting strain kept on accumulating in the specimen at this constant rate till the failure of the specimen occurred. It was quite interesting to see that on increasing the mean stress level at a fixed stress amplitude, after the initial decrease, fatigue life of the steel improved marginally owing to the effect of mean stress-induced hardening. In absolute contrast, under the influence of stress amplitude at a fixed mean stress, fatigue life of the rail steel deteriorated gradually but to a significant extent. Finally, stress amplitude was found to have more severe effect than that offered by the mean stress in terms of` ratcheting strain accumulation and fatigue life of the investigated rail steel.