抄録
A hypothesis of fatigue plastic adaptation is proposed as a basic concept on strength of fatigue macrocrack initiation. The hypothesis represents that plastic deformation, which is caused in a surface layer by slip bands inherent in fatigue, is equal to maximum elastic deformation in a pertinent location and the deformation is generated in a surface layer of an unnotched specimen and at a notch root of a notched one. Parallel multi-bar models are devised based on the hypothesis in order to simulate cyclic stress behaviors in a surface layer and at a notch root, respectively. Consequently, an equivalent stress ratio R_<EQ> is derived from consideration of mechanical behaviors in the models as a stress parameter for correspondence between fatigue macrocrack initiation strength in unnotched and notched specimens. The parameter R_<EQ> is applied to published experimental data on notched plates and notched round bars as well as authors' fatigue test data on round bars, and the correspondence between notched and un-notched specimen fatigue data is investigated. As a result, availability of the parameter of the equivalent stress ratio R_<EQ> is proved.
