The variation of the fatigue crack propagation data for nodular cast iron in the literature is investigated. Crack closure is identified as one of the main causes of these variations. Fatigue crack propagation results for ferritic nodular cast iron with simultaneous measurements of crack closure are presented. It is shown that improved material characterization is obtained if closure is considered. The transferability of crack growth data to realistic three dimensional surface cracks is investigated. Crack closure levels are measured during these tests so that closure-free data could be used in the crack growth analysis. It is shown that the predicted crack growth rate was a factor of two larger than the measured. A simple modeling technique, in which the fatigue process is regarded as subsequent crack retardation and intermediate propagation, is proposed. The model indicates that the retardation of the crack caused by the nodules is small for a long, propagating crack. However, the influence for the long crack in the threshold regime remains uncertain.
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