13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Creep-fatigue interaction model for crack growth of nickel-based superalloys with high temperature dwell time Hongqin Yang 1,*, Rui Bao2, Jiazhen Zhang1 1 Beijing Aeronautical Science & Technology Research Institute of COMAC, Beijing 100083, PR China 2 Institute of Solid Mechanics, Beihang University (BUAA), Beijing 100191, PR China * Corresponding author: yanghongqin@comac.cc Abstract A three-term crack growth model was developed by adding a creep-fatigue interaction term to the traditional linear superposition law. It is based on the hypothesis that the maximal creep-fatigue interaction occurs when creep and fatigue crack growth rates are comparable. Thereby a novel exponential form of interaction intensity factor was proposed. In order to verify the model, the creep-fatigue crack growth behaviour of a nickel-based powder metallurgy superalloy (FGH97) was experimentally investigated. Creep-fatigue crack growth rates were obtained at 750 °C with various dwell times. Comparison of the crack growth rates between fitted and measured values at 0s, 90s, 450s and 1500s dwell times show great agreement. Encouragingly, excellent predictive ability of the model was verified by the experiment at 25s dwell time. Furthermore, to test the applicability of the interaction law on other materials, experimental data of two additional superalloys from references, namely Alloy 718 and Hastelloy® X, were used to fit the model. The results are also satisfactory. Keywords Crack growth rate modelling, high temperature, dwell time, nickel-based superalloys 1. Introduction As for the quantitative description of creep-fatigue crack growth rate, several models have been developed. Tong et al. [1] proposed single term models, in which creep damage is taken into account by modifying the coefficient of the basic fatigue model. Other researchers [2] have used an alternative approach. They assumed that creep-fatigue behaviour is governed by competing mechanisms of creep and fatigue crack growth, and whichever gives a higher growth rate dominates the entire crack growth process. A more universal model is based on simple linear superposition of creep crack growth and fatigue crack growth [3]. However, such methods tend to overlook the effect of creep-fatigue interaction, which cannot be ignored by many materials. For this reason, a three term model considering the interaction effect separately was referred in [4], expressed in the form of linear superposition of fatigue crack growth rate, creep crack growth rate and their interactions. However, the quantitative relationship between the creep-fatigue interaction and the loading condition for certain materials is still an open question. The work of Grover and Saxena [5] indicated that the intensity of the creep-fatigue interaction is directly related to the relative sizes of the creep zone and cyclic plastic zone. Recently, the authors [6] presented an exponential formed interaction intensity factor to help describing the interaction effect. The accuracy of the model proposed was experimentally confirmed by a nickel-based superalloy FGH97. The study presented here is a continuation of that work and applicability of the model on other materials was verified. 2. Creep-fatigue interaction model
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