An Approach for Fatigue Life Prediction

Abstract

Fatigue process is described as the nucleation and growth of cracks to final failure. These two stages are generally modeled with completely different methods with no quantitative relationships between them. A number of fitting parameters are needed to consider different effects. The current work is aimed at developing a robust approach to predicting fatigue life from crack initiation to final fracture. Fatigue damage is related to the stresses and strains. Both crack nucleation and crack growth are governed by the same fatigue damage mechanisms and a single fatigue damage criterion can model both stages. A basic rule is that any material point fails to form a fresh crack if the total accumulated fatigue damage reaches a limit. The approach consists of two steps. Elastic-plastic stress analysis is conducted to obtain the detailed stress-strain responses. A general fatigue criterion is used to predict both fatigue crack nucleation and growth. Notched specimens made of 1070 steel were experimentally tested from crack initiation until fracture. The approach was applied to predict the fatigue life of 1070 steel and the predicted fatigue lives were in excellent agreement with the experimental observations.