True stress-controlled ratcheting behavior of 304LN stainless steel

Cyclic plastic deformation response of materials under asymmetric stress cycling is known as ratcheting. Combined effect of fatigue and permanent tensile strain accumulation results in early failure of materials during ratcheting. For this reason, ratcheting should be emphasized in the safety assessment and life estimation of engineering structures. Engineering and true stress-controlled ratcheting behavior of 304LN stainless steel has been carried out at room temperature. Effects of stress amplitude, mean stress, and their histories (i.e., step loading) on the ratcheting behavior are analyzed in this investigation. It is noticed that under true stress-controlled ratcheting experiments, ratcheting life increases in presence of mean stress, and hysteresis loop area and plastic strain energy decreases with the increasing mean stress. A comparison has also been drawn in between the true and engineering stress-controlled tests, and massive differences in ratcheting life and strain accumulation were found. Ratcheting strain accumulation ceases in descending step loading, is noticed in this work.