Damage-tolerance-based life prediction of aeroengine compressor discs: I. A deterministic fracture mechanics approach

This paper reports the results of a demonstration programme carried out to determine the influence of the sensitivity and reliability of non-destructive inspection (NDI) techniques on the damage-tolerance-based life assessment of aeroengine compressor discs. The programme was carried out on AM-355 compressor discs of an aeroengine. The safe inspection intervals (SII) for the disc are calculated using deterministic fracture mechanics (DFM) principles and different initial crack length (ai) selection criteria. These calculations involve the use of the NDI data, finite-element analysis and the experimental fatigue crack growth rate (FCGR) data generated on compact tension specimens machined from safe-life-expired discs. The results demonstrate that a sensitive eddy current and the ultrasonic leaky surface wave NDI techniques yield the largest SII values when the longest crack missed and the detectable crack sizes at 90% probability of detection (POD) and 90/95 POD are substituted for the ai values in the DFM calculations. In all cases, however, the SII values are too short for the damage-tolerance-based life cycle management procedure to be cost effective.Peer reviewed: YesNRC publication: Ye