PSI - Issue 19

Aaron Stenta et al. / Procedia Structural Integrity 19 (2019) 27–40 Author name / Structural Integrity Procedia 00 (2019) 000–000

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detected, it is always recommended that it be repaired. However, it is possible that an already initiated crack might not be detected if it were smaller than the minimum detectable crack size. For this reason, even if an inspection is performed and a crack is not detected, that doesn’t mean it’s not there. As a result, the optimal run time after the inspection is only 20 to 30 cycles to account for the possibly that an initiated crack might still be there but just wasn’t detected, because it was too small. After that, a second inspection may be performed, but that possibility is not allowed in this current network (it is allowed in more sophisticated networks that we have developed).

Fig. 7. Crack Growth Rate with Inspection and Repair Bayesian Decision Network.

On the other hand, if a crack was detected during the inspection, a repair is always recommended, along with a subsequent run time after the inspection of 190 to 200 cycles. Since the crack was found and repaired, the risk of failure goes back down to nearly zero at the start of the next run time interval in that case (assuming there are no other cracks that weren’t detected). Overall, the expected return per cycle for this improved decision strategy is about 645. Compare this to the expected return of 420 for the case where no inspections or repairs were permitted. Since the expected return is higher when an inspection is performed, that is the recommended strategy. Of course, there are many other scenarios that could be examined and considered with this network, but they are too many to consider here. The methods that we have developed using these networks allow for all possible cases to be explored and for optimal decisions strategies to be recommended. 4.3. Vibration Fatigue Application – High Cycle Fatigue The basis for the vibration fatigue life-cycle BDN presented here was recently published in Bifano (2018). In this effort, and over the past few years, a fitness-for-service assessment procedure has been developed to screen