Characterisation of crack tip fields under non-uniform fatigue loading

D. Nowell, M.E. Kartal, P.F.P. de Matos


The paper analyses previously reported work, which uses digital image correlation to measure
fatigue crack closure. As well as determining crack opening loads, the information on crack shape may be used
to estimate the stress intensity factor, as well as other parameters in more complex models of crack tip fields. A
number of specimens were subjected to single overload cycles, which produced a significant retardation in crack
growth rate. The method previously applied to the analysis of constant amplitude loading is here used to
analyse the single overload case. The stress intensity factor history is found to be very different in the two cases
and the consequences of this observation for analysis of fatigue crack propagation are discussed.

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