Ratcheting Behavior of a Titanium-Stabilized Interstitial Free Steel

Engineering stress-control ratcheting behavior of a titanium-stabilized interstitial free steel has been studied under different combinations of mean stress and stress amplitude at a stress rate of 250 MPa s⁻¹. Tests have been done up to 29.80 pct true ratcheting strain evolution in the specimens at three maximum stress levels. It is observed that this amount of ratcheting strain is more than the uniform tensile strain at a strain rate of 10⁻³ s⁻¹ and evolves without showing tensile instability of the specimens. In the process of ratcheting strain evolution at constant maximum stresses, the effect of increasing stress amplitude is found to be more than that of increasing the mean stress component. Further, the constant maximum stress ratcheting test results reveal that the number of cycles (N) required for 29.80 pct. true ratcheting strain evolution exponentially increases with increase of stress ratio (R). Post-ratcheting tensile test results showing increase of strength and linear decrease in ductility with increasing R at different constant maximum stresses indicate that stress parameters used during ratcheting tests influence the size of the dislocation cell structure of the steel even with the same amount of ratcheting strain evolution. It is postulated that during ratcheting fatigue, damage becomes greater with the increase of R for any fixed amount of ratcheting strain evolution at constant maximum stress.