Some Studies of the Influence of Localized and Gross Plasticity on the Monotonic and Cyclic Concentration Factors

Abstract

Abstract The variation in monotonic and cyclic concentration factors (namely, Kt, Kε, Kσ) due to localized and gross plasticity is presented and discussed for two alloys of contrasting stress-strain behavior, an aluminum alloy 2024 T351 and a mild steel SAE 1015. Thin plates with circular and elliptical holes made of these alloys were subjected to monotonic and cyclic straining in a servo controlled testing machine. Predominant in the monotonic behavior of the concentration factors is the rapid increase in strain concentration factor in notched mild steel plates, attributed to the unrestrained plastic flow (Lüders deformation) characteristic of this material. Such behavior is compared to the response of the continuously strain hardening aluminum alloy when subjected to a similar nominal strain history. The dominant feature of the cyclic behavior is the variation in the notch strains as influenced by the overall hardening or softening phenomenon which accompanies cyclic plastic deformation. With the aid of these results, the accuracy of the Neuber rule is checked and restrictions to its application in fatigue life predictions of notched members using smooth specimen data are presented.