Investigation of creep-fatigue crack growth of G115 steel using a novel damage model

The flexible operation of power-plant structures could cause creep-fatigue crack propagation, which is a major concern for design and maintenance. Therefore, this study investigated the crack propagation in G115 steel under isothermal creep-fatigue loading by using a novel damage model. Creep and fatigue damage were determined by the exhaustion of the creep ductility and the total plastic strain energy during the crack growth process, respectively. The crack propagation behavior was simulated by the finite element method, and the calculated data were compared with experimental results, which demonstrated the high precision of this model. The calculated damage values at the crack tip were analyzed, and the creep damage (cavities) around the main crack under 60 and 600 s hold times were observed based on X-ray micro-computed tomography. The cavity density for the test with 600 s of holding was obviously larger than that for the 60 s dwell test, with the former showing more significant creep damage. Calculations of compact tension specimens with different hold times, specimen thicknesses, and crack lengths were further conducted and analyzed. The results revealed that increasing the hold times, specimen thicknesses, and crack lengths increased the cyclic crack growth rate.