Does a nucleated crack propagate?

Conditions for propagation or non-propagation of an incipient crack from stress concentrations such as notches, holes, etc., are evaluated using elastic-plastic fracture mechanics methods and the Kitagawa-Takahashi diagram, hence linking smooth specimen behavior to fracture mechanics. The analysis differs from all other previous models which are either empirically based or assume that short crack growth behavior differs from that of long cracks due to crack closure or lack of it. It is shown that the stress intensity factor of an incipient crack decreases and then increases as it moves away from the internal stress field of a notch. Crack propagation is ensured only when the minimum is equal to or greater than the unique fatigue threshold for crack growth. Otherwise non-propagation conditions prevail. Equations are developed to establish the conditions for the minimum stress required for continuous propagation of the originated crack. It is shown that by analyzing published results on notch-fatigue that specimen failure occurs only if the applied stresses exceed the minimum stress required for crack propagation. Otherwise crack arrest occurs resulting in non-propagating cracks. The analysis can be readily used to determine the conditions for failure of a notched specimen if the elastic stress concentration factor, kt, the notch-tip radius, ρ, and fatigue crack threshold, Kth, for the material are known. The analysis, in principle, is applicable to all subcritical crack growth processes.