PSI - Issue 7

E. Vacchieri et al. / Procedia Structural Integrity 7 (2017) 182–189

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E. Vacchieri et al. / Structural Integrity Procedia 00 (2017) 000–000

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Fig. 2. Creep-fatigue lifing procedure applied to case study FE simulation.

Fig. 3. Comparison between calculated life maps and field feedback for a daily cycling blade after service.

The e ff ect of the metallic coating has been evaluated through a correction factor calculated in the basis of TMF test results for coated samples, Vacchieri (2017), and applied to the locations where the service conditions are critical for the used metallic coating.

3.3. Statistical Analysis of Field Feedback

Weibull statistics have been used to support the creep-fatigue life prediction methodology and to exploit field feedback data. The statistical analysis has been applied to two of the critical locations identified by the lifing procedure, i.e. the fillet radii on the pressure side (green circle) and on the suction side (yellow circle) in Fig.3. The considered data comes from 20 engines that operated in a wide range of service profile, from base load to daily cycling. Survivability or reliability level according to Summers-Smith (1989) has been estimated following Eq. 4. S k = 1 − ( i − 0 . 3 n + 0 . 4 ) (4) where i is the number of blades with at least a crack of size k , n is the number of individual components in a set (in this case 80). Although the appearance time of the crack on the last blade of the whole set cannot be known, it can be assumed to have occurred shortly before the maintenance interval. In Fig. 4 the cumulative distribution for the crack of minimum length l is reported for both considered critical locations of the blade.