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.
Bibliographical noteP. F.P. de Matos would like to gratefully acknowledge the support of the Portuguese Fundação para a Ciência e a Tecnologia (FCT) for providing a D.Phil. scholarship (reference SFRH/BD/12989/2003, financed by POSI).
- Digital image correlation
- Displacement measurement
- Crack-tip fields
- Elastic-plastic fatigue crack