Abstract
The creep-fatigue crack growth problem remains challenging since materials exhibit different linear and nonlinear behaviors depending on the environmental and loading conditions. In this paper, we systematically carried out a series of creep-fatigue crack growth experiments to evaluate the influence from temperature, stress ratio, and dwell time for the nickel-based superalloy GH4720Li. A transition from coupled fatigue-dominated fracture to creep-dominated fracture was observed with the increase of dwell time at 600 °C, while only the creep-dominated fracture existed at 700 °C, regardless of the dwell time. A concise binomial crack growth model was constructed on the basis of existing phenomenal models, where the linear terms are included to express the behavior under pure creep loading, and the nonlinear terms were introduced to represent the behavior near the fracture toughness and during the creep-fatigue interaction. Through the model implementation and validation of the proposed model, the correlation coefficient is higher than 0.9 on ten out of twelve sets of experimental data, revealing the accuracy of the proposed model. This work contributes to an enrichment of creep-fatigue crack growth data in the typical nickel-based superalloy at elevated temperatures and could be referable in the modeling for damage tolerance assessment of turbine disks.
Highlights
Crack growth assessment on load-bearing components serving at elevated temperatures, e.g., the fracture-critical component turbine disk in an aeroengine, is one of the most crucial contents to ensure the structural integrity [1,2,3]
This paper presents a comprehensive summary on existing creep-fatigue crack growth models and could be referred for a proper choice of analysis models during damage tolerance assessment
A concise binomial model for creep-fatigue crack growth is constructed on the basis on existing models, where the linear and nonlinear behaviors at different environmental and loading conditions are elaborated
Summary
Crack growth assessment on load-bearing components serving at elevated temperatures, e.g., the fracture-critical component turbine disk in an aeroengine, is one of the most crucial contents to ensure the structural integrity [1,2,3]. Existing studies [4,10,11] revealed that the creep-fatigue crack growth (CFCG) behavior is significantly affected by temperature, applied stress, dwell time, and their conjoined effects. Due to the complex conjoined effects from high temperature, dwell time, and micro-mechanism of fracture, there are no universally accepted rules or analytical models for describing the creep-fatigue crack growth rates at high temperatures. Surface at the initial stage presents both creep and fatigue characteristics, where the dimples and striation platforms are marked in red and yellow, respectively It transit to the pure fatigue fracture at the midterm stage and the later stage. As the temperature increases to 700 °C, all the fracture surfaces exhibit typical creep-dominated dimples, re6- of 16 gardless of the dwell time, which means the creep damage acts as the principal motivation for the crack growth.
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