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Study of a flight monitor for jet engine disk cracks using the critical length criterion of fracture mechanicsA disk crack detector is discussed which is intended to operate while in flight. The crack detector monitors the disk rim for radial surface cracks emanating from the blade root interface. An eddy current type sensor with a remotely located capacitance-resistance bridge and signal analyzer is able to detect reliably a simulated crack 1/8 in. long. The sensor was tested at rim velocities of 600 fps and at 1000 F. Fracture mechanics is used to calculate the critical crack length. Knowledge of the crack growth rate permits the calculation of the number of stress cycles remaining for the detected crack to grow to critical size. A plot is presented of the remaining life as a function of the critical crack length and the operating stress. It is shown that for a disk of Inconel 718 a through-the-thickness crack operating under a rim stress of 50 kpsi has a critical length of 0.7-in. and a remaining life of 130 flights.
Document ID
19740045554
Acquisition Source
Legacy CDMS
Document Type
Conference Proceedings
Authors
Barranger, J. P.
(NASA Lewis Research Center Cleveland, Ohio, United States)
Date Acquired
August 7, 2013
Publication Date
January 1, 1974
Subject Category
Instrumentation And Photography
Meeting Information
Meeting: Symposium on Instrumentation for airbreathing propulsion
Location: Monterey, CA
Start Date: September 19, 1972
End Date: September 21, 1972
Accession Number
74A28304
Distribution Limits
Public
Copyright
Other

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