13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- creep followed by fatigue loading (C+F), and found that the creep-fatigue damage in the cases of CF and F+C was larger than unity, while that was smaller than unity at C+F. Luo [9] carried out a statistical analysis on the mechanical parameters of GH4133B superalloy at room temperature, and found that the three-parameter Weibull distribution was fit for the reliability assessment of this superalloy. Padula II [10] investigated the effect of grain size on high frequency fatigue crack propagation of nickel-based superalloys at various stress ratios. The results indicated that there is no effect of frequency on the fatigue behavior at ambient temperature. The threshold stress intensity for fatigue crack propagation decreases with decreasing grain size and with increasing stress ratio. In this paper, the fatigue damage and fracture tests of GH4133B superalloy used in turbine disk of earo-engine are carried out at room temperature. The fatigue limit is measured for smooth samples at various stress amplitudes, and the fatigue crack growth rates are detected for standard compact tension samples under different stress ratios. A modified Chaboche model is applied to predict the accumulated damage of smooth samples of GH4133B superalloy at symmetrical cycle loading, and a Paris formula considering threshold stress intensity factor range is deduced to describe the fatigue crack growth behavior. The fracture surface morphologies of standard compact tension samples of GH4133B superalloy are investigated using scanning electron microscope, and the crack growth equations and loads are derived using the inverse deducing method. 2. Material and samples The material used in this research is a nickel-based GH4133B superalloy with following chemical composition in % weight: C 0.06, Cr 19~22, Al 0.75~1.15, Ti 2.5~3.0, Fe 1.5, Nb 1.3~1.7, Mg 0.001~0.01, Zr 0.01~0.1, B 0.01, Ce 0.01, Mn 0.35, Si 0.65, P 0.015, S 0.007, Cu 0.07, Bi 0.0001, Sn 0.0012, Sb 0.0025, Pb 0.001, As 0.0025, and the balance nickel. The superalloy samples are machined from a turbine disk. The heat treatment process is as follows: 1080±10ºC, 8 hours, air cooling with 750ºC±10ºC, 16 hours air cooling. The samples for fatigue damage tests are machined in rod shape, as shown in Fig. 1. The samples for fatigue crack growth tests are machined in the shape of standard compact tension sample, as shown in Fig. 2. Figure 1. Dimensions of smooth sample (unit: mm) Figure 2. Dimensions of standard compact tension sample (unit: mm)
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