GS0221-344 Fundamental Concepts for Diagraming/Formulating Fatigue Strength of Notched Materials : Hypothesis of Cyclically Plastic Adaptation and Yield-Zone-Based Criterion on Size Effects

Abstract

Two fundamental concepts for diagraming and formulating fatigue strength of notched materials are described; the hypothesis of cyclically plastic adaptation and the yield-zone-based criterion on size effect. Each concept is independently and has a quite different base. The former describes cyclic stress behavior at a fatigue slip band and is concreted as an equivalent cyclic stress ratio reflecting mean stress effect. The latter is formulated by normalizing a yield zone growth curve and ranked as a kind of a ductile failure rule combining with stress distribution. Based on such conceptions, the fatigue strength of the notched and un-notched specimen can be linked completely analytically. It is noted that, by utilizing formulae in plasticity on beams and torsion bars, the yield-zone-based criterion on size effect explains analytically and numerically the size effect of the un-notched specimen itself.