Quantitative fractography of fatigue and an illustrative case study

Abstract Quantitative fractography (QF) may be used for measuring service- and test-induced fatigue crack growth (FCG) in metallic components and structures. The QF compares progression and striation markings on fatigue fracture surfaces with known occurrences in the components' load histories. This paper concisely surveys fatigue-related QF, followed by a case study for a crack in a component from a maritime patrol aircraft. The case study illustrates how a FCG versus time history can be estimated. This was achieved using (i) knowledge of when the crack was detected, (ii) a reconstruction of the aircraft usage history from counting accelerometer (g-meter) data, (iii) an exponential FCG model of how cracking could have progressed, and (iv) QF of progression markings. Comparison of the reconstructed usage data and the QF information showed that the model provided a useful correlation.

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