Prediction of probability distribution of fatigue life of 15MnVN steel notched elements under variable-amplitude loading

Abstract

Attempts are made to develop procedures for predicting the probability distribution of the fatigue life of notched elements of a high-strength low-alloy steel, 15MnVN steel, under variable-amplitude loading (VAL). First, expressions for the fatigue life of 15MnVN steel with given survivabilities are obtained by fitting the test data of the fatigue life with corresponding survivabilities. Then procedures are outlined for predicting the probability distribution of the fatigue life of notched elements of 15MnVN steel, which has a non-continuous strain hardening characteristic, under VAL, based on the assumption that Miner's rule and the expression with given survivability could be directly used to predict the fatigue life with corresponding survivability under VAL. The predicted probability distribution of the fatigue life of 15MnVN steel notched elements under VAL follows a log-normal distribution and is checked by testing notched specimens under two types of block loading. The procedures mentioned above are of general applicability in predicting the probability distribution of the fatigue life of notched elements of metals with non-continuous strain-hardening characteristic. A criterion is also tentatively proposed for omitting small loads in the load spectrum in life prediction under VAL.