A method for monitoring crack growth during highcycle fatigue tests was demonstrated using acoustic emission (AE) monitoring. Windowing techniques were employed during the recording and interpreting of the AE data. The results provided linear relationships between AE events and amplitudes and crack lengths. The fatigue crack growth results from the AE data were in very good agreement with data measured using an optical microscope.
Fractographic observations of the crack and specimen surfaces showed that secondary cracks formed and linked to the main crack during intermediate stages of crack growth. The crack growth rate calculated from AE data reflected the formation of secondary cracks in this period.
Results are presented which show that it is possible to detect crack growth and crack presence in airframe components during flight. To accomplish this, a data acquisition system has been developed specifically for in-flight applications. It is shown that crack advance of less than 1 mm2 was readily detected during flight and the fracture-related acoustic emission signals unambiguously identified.
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