PSI - Issue 14

Vamsi Krishna Rentala et al. / Procedia Structural Integrity 14 (2019) 597–604 Vamsi Krishna Rentala et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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6

(a)

(b)

(c)

(d)

Fig. 1. POD curves using three approaches for multiple cracks at a site for FPI with (a) Type 1; (b) Modified Type 1;(c) Type 2; (d) ECI with Type 2 indicating a 90/95 values.

Table 2. a 90/95 values of FPI and ECI techniques using three approaches. NDT Technique a 90/95 , mm Type 1 Modified Type 1

Type 2

FPI ECI

1.52

1.59

2.38 1.12

3.1. Remnant life calculations using Deterministic Fracture Mechanics Approach

Table 3 shows the a 90/95 values and the corresponding remnant life in terms of fatigue cycles, engine operating hours and safe inspection intervals (SII) for FPI and ECI NDT techniques using all the three different POD approaches for multiple cracks at a site. From Table 3, it can be observed that ECI technique provides higher number of remaining fatigue cycles and remnant engine operating hours than FPI technique due to its higher sensitivity leading for lower a 90/95 . In addition, it can also be observed that lower a 90/95 values yields higher remnant life in the components. Further, the effect of a 90/95 values obtained from Type 1 and Type 2 approaches of FPI data on remaining fatigue cycles and engine operating hours can be clearly observed and the variation was found to be at least 50 %. Moreover, it is beneficial to have higher SII values for better usability and reduced down time of aircrafts or airframe structures (Koul et al. (1990)). In this study, it was observed that the SII values are also higher for lower a 90/95 values. Figure 2 shows the SII values corresponding to different a 90/95 values of both the NDT techniques. From Figure 2, it can be observed that the SII values decreases with increase in the a 90/95 values and follows almost a linear behavior. The SII values should be in the range between 4000 to 10000 hours (Koul et al.