NTSB ACCIDENT INVESTIGATIONS INVOLVING FATIGUE FRACTURES INITIATING FROM SUBSURFACE DEFECTS

The U. S. National Transportation Safety Board has investigated accidents involving fatigue fractures that initiated at subsurface anomalies including (1) a fatigue fracture that initiated from a ceramic inclusion in a turbocharger turbine wheel from a Piper PA-46-350P airplane which contributed to a forced landing, (2) a fatigue fracture of a railcar axle that initiated from a casting void that resulted in a derailment and crude oil explosion, and (3) a fatigue fracture of a high-pressure turbine stage 2 disk on a Boeing 767-300 airplane that initiated from a discrete dirty white spot and resulted in an uncontained engine failure, engine fire, and aborted takeoff. Processes used by the NTSB Materials Laboratory to analyze the fracture mechanisms and characterize the initiating defects will be discussed.
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