抄録
This paper describes a method of predicting low-cycle fatigue life in long-term hold-time tests at elevated temperatures. In order to develop a proper life prediction method under creep-fatigue conditions, especially for the case of long hold-time, the correlation between the static creep rupture data and the low-cycle fatigue data in hold-time tests was examined. The specimens used were an unnotched and three round notched ones of austenitic stainless steels of SUS 304 and SUS 316 having elastic stress concentration factors of 2.6, 4.2 and 6.0. Zero-to-tension low-cycle fatigue tests were carried out by four modified creep machines at 873K using trapezoidal stress waves with 10, 30, 60, and 1440min hold-time. Static creep tests were also carried out on those specimens.
Two fracture regions were found to exist in the failure cycles-test frequency plot: one is the cycle-time dependent fracture region where the elastic stress cocnentration reduces the low-cycle fatigue life and the other is the pure time dependent fracture region where it does not. A new prediction method of fatigue life of the unnotched and the notched specimens in low-cycle tests with various hold times from the static creep rupture time and low-cycle fatigue life data obtained in no hold-time and comparatively short hold-time tests was proposed.
