Probabilistic Prediction Of Crack Growth Based On Creep Fatigue Damage Accumulation Mechanism

In this paper a deterministic creep/fatigue accumulation model from simple sequential and repetitive creep and fatigue crack growth mechanisms for creep-brittle materials is developed. In the model the maximum stress intensity factor and stress intensity factor range can be used to describe, respectively, the creep and fatigue crack growth behaviors. The probabilistic behavior of the combined creep-fatigue can be calculated by direct integration of a joint log-normal probability density function or other methods. The Monte Carlo simulation method is used in this paper to analyze the probabilistic behavior of the derived deterministic creep-fatigue model and to estimate the reliability of a creep-fatigue correlation as introduced by the uncertainties in both creep and fatigue lives. Predicted results from this new crack growth method are compared with the bi-linear creep-fatigue interaction models as adopted by ASME Code Case N-47 and API579/ASME FFS, and the results are discussed.