Fundamental Concepts for Diagraming/Formulating Fatigue Strength of the Notched and Un-notched Specimen

(Methodology for Considering Material- and Size-Dependence of Notch Effect and Its Perspective)

Abstract

A study for diagraming and formulating fatigue strength of notched and un-notched specimens has been developed. As a result, two fundamental and important concepts have been proposed; a hypothesis of cyclic plastic adaptation and a size effect criterion based on a normalized yield zone growth curve. From the former concept, an equivalent cyclic stress ratio is derived as a primary parameter correlating a cyclic stress condition of the notched specimen with that of the un-notched specimen, and a fatigue strength diagram is formulated for a large-sized notch and un-notch type specimen. From the latter, a secondary parameter quantifying concretely the size effect is derived and inserted in the equation of the fatigue strength diagram. In the present paper, a principle and methodology, and a perspective of the approach are discussed with reviewing the outline of the study.