On the Construction of the Diagram of Growth Rates for a Fatigue Macrocrack

We consider some problems encountered in constructing the diagrams of growth rates for fatigue macrocracks. It is shown that, in the subthreshold part of the diagram and at the beginning of its Paris part, the minimum increments of crack length Δa specifying reliable values of the crack growth rate are determined by a linear (structural) parameter d* of the material. Therefore, it is necessary to fix increments of crack length according to the condition Δa ≈ d*.