The Modified Rate Approach Method to Evaluate Fatigue Life Under Synchronously Changing Temperature and Strain Rate in Elevated Temperature Water

Abstract

The fatigue life of steel in elevated temperature water is strongly affected by the composition of the environmental water, temperature and strain rate. The effects of these parameters on fatigue life reduction have been investigated experimentally in these years. One problem to be discussed is the fact that the previous experiments which leaded main conclusions on the environmental effects were generally executed by keeping a set of experimental parameters constant. In the transient condition in an actual plant, however, such parameters as temperature and strain rate are not constant. In order to evaluate fatigue damage in an actual plant on the basis of experimental results under constant temperature and constant strain rate conditions, the modified rate approach method was developed. The method can be applicable to changing temperature condition and strain rate condition separately. In the present study, an additional model is proposed with considering that both temperature and strain rate change simultaneously in an actual plant. The applicability of this method is discussed and verified experimentally. The fatigue lives predicted by this method are scattered within the factor of 2 or 3 bands against test results even when several parameters changed synchronously.