Influence of uniaxial ratchetting on low cycle fatigue behviour of SA 333 Gr. 6 C-Mn steel

Ratchetting behaviour and its influence on the subsequent low cycle fatigue behaviour of a plain carbon steel (SA 333 Gr. 6) has been evaluated. Uniaxial stress controlled ratchetting experiments have been carried out at various combinations of mean stress and stress amplitudes. It is noted that the ratchetting strain increased with increasing mean stress and stress amplitude. Maximum strain accumulation was observed for the highest value of the peak stress, irrespective of the stress ratio. Further, post ratchetting-low cycle fatigue (LCF) tests have been carried out and compared with non-ratchetted base LCF behaviour. The comparison showed that the fatigue life decreased in proportion to the accumulated ratchetting strain. This indicates that accumulation of significant ratchetting strain can be detrimental to the fatigue life and must be avoided. Mean stress induced due to pre-ratchetting is found to be responsible for the decrease in LCF fatigue life.