Abstract
Equations expressing fatigue strength diagrams of notched materials have to explain both of material dependence and notch size dependence of notch effects. From such a viewpoint, two concepts have been introduced into the study. The first is the hypothesis of cyclic plastic adaptation that reflects mechanical behavior/property peculiar to persistent slip bands and the parameter of an equivalent cyclic stress ratio that is derived from the hypothesis and can correlate the fatigue strength diagrams of the notches of a large size very satisfactorily. The second idea is the inclusion of some notch size factors in the equation of the fatigue strength diagram in order to take a size effect into consideration. The concrete forms of these size factors are determined based on the distribution of the fatigue strength σ_<w1> and σ_<w2> that are drawn on the notch behavior map. At the beginning, the notch size factors are determined by trial and error, empirically rather than analytically, though they are done based on a systematic way to some extent. However, the subsequent research has proved that the notch size factors can be determined directly as numerical expressions based on a notch root yield zone model, which is extended from Dugdale Model. In the present paper, the process of determination of the notch size factors is described as a main subject.
