3.1 | CCF life
The valid CCF life results are listed in Figure 7(a). Among them, thirteen CCF life results come from the untreated blades and the other nine results come from the PSP treated blades. According to these test data, the σH-N curves of untreated and PSP treated blades are shown in Figure 7(b). There is a linear relationship between CCF life and vibration stress amplitudes. Furthermore, the least squares method is used to fit experimental data to get the fitting equations listed in Figure 7(b). It indicates that there is one threshold vibration stress with the value of 194.0MPa. When the vibration stresses are lower than the threshold value, the PSP treatment has a positive effect on the CCF life of blades. In contrast, the PSP treatment has a negative effect on the CCF life while the vibration stresses are above the threshold value.