Modeling of temperature influence on the fatigue crack growth behavior of superalloys

Fatigue crack growth (FCG) rate is an important material parameter in structure safety and reliability assessment. As temperature T has remarkable effects on FCG behaviors of superalloys, it is in urgent need to establish an accurate FCG model which can predict FCG rates of superalloys at different temperatures. This work aims to model the temperature influence on FCG rate for superalloys. Firstly, systematic FCG experiments of a Ni-base superalloy at different temperatures are conducted to obtain the experimental data. Test results show that the FCG rate increases significantly with increase of temperature. Then, based on the observed linear relationship between the ratio of FCG rate to T and the stress intensity factor (SIF) range ΔK, an empirical FCG model called temperature exponential model, in which there are four material parameters C1, C2, C3 and C4, is built up by means of fitting approach. Two different methods, which are based on the FCG rates data and Paris model parameters respectively, are developed to acquire the four material parameters. At last, the temperature exponential model is validated against a variety of superalloys, proving its high accuracy and wide applicability.