Fatigue crack growth from simulated flight cycles involving superimposed vibrations

The fatigue crack growth in response to vibrations, to load combinations wh ich reproduce the transition from one flight stage to the next, and to simu lated flight cycles, has been monitored in Ti-6Al-4V cross-rolled plate hav ing the microstructure and properties of the skin of a wide chord fan blade . The underload which preceded the take-off loading reduced the threshold v alue for crack growth, but the overloads associated with subsequent transit ions in the flight cycle did not. The crack growth retardation associated w ith the transition from take-off to climb, and from climb to cruise, was ge nerally described by the Wheeler model, using Wheeler exponents in the rang e 4.5-8.5. A model for predicting the fatigue crack growth rates during rep eated flight cycles suggested that the crack growth during climb was better represented by higher values of the Wheeler exponent. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.