A MECHANISTIC APPROACH TO THE LIFE PREDICTION OF 316L STAINLESS-STEELUNDER COMBINED CREEP FATIGUE CYCLING/

In this work, the relaxation stress behaviour of a 316L stainless stee l cycled at high temperature has been analysed and a critical strain r ate, which marks the transition from a transgranular to an intergranul ar dominated damage regime, was obtained. This strain rate has been us ed to partition the relaxation strain into its transgranular and inter granular components. Coffin-Manson type relationships for both damage regimes have been derived and the corresponding intrinsic parameters, ductility and irreversibility damage coefficient, determined. PI cumul ative damage rule, resulting from equalling the sum of the transgranul ar and intergranular damages to unity, allows the calculation of the m aterial life under creep/fatigue conditions. These predicted values ha ve been tested against previously reported data obtained from the same material. It is shown that, irrespective of the imposed strain range, the duration of the hold period and the ratio between the transgranul ar and intergranular components of the damage, predicted and experimen tal lives are in close agreement. The points determined by the calcula ted transgranular and intergranular components of the overall damage f all closely along the failure locus as defined by the cumulative damag e rule.