Crack growth at low ?K’s and the Frost-Dugdale law

This paper examines the fatigue crack growth histories, at low ?K’s, of a range of test specimens and service loaded components and concludes that, as a first approximation, there is a linear relationship between the log of the crack length or depth and the service history (number of load cycles). We also show that, for the cases studied, that the log linear method can give a better prediction of experimental data than a conventional crack growth model.