Non-destructive Residual Stress Analysis Inspection Method for Critical Engine Parts

There is a need for a non-destructive inspection technique and methodology for tracking low cycle fatigue (LCF) life in aircraft engine disks to safely extend useful like and reduce maintenance cost. Recognizing that cracks occur only after the surface residual stress is in tension, one can correlate the observed residual stress with accumulated cycles and crack appearance. By measuring the residual stress, parts may be safely considered for service beyond the current "Safe Life" arbitrary criteria, and disk sets of similar residual stress can be matched for fewer scheduled maintenance inspections. FMA's NDT methodology wold quantify the expected life prior to any observed cracking, and thus yield a more economical regimen; more conservative that "Retirement for Cause", but with similar large benefits. The proposed Phase I effort will establish an initial statistical disk population data base and analysis in order to demonstrate the feasibility of the methodology to determine the probability and time to crack initiation. This will be accomplished by measuring surface residual stress via X-ray diffraction.