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 ( a i) 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 a i 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.