Internal pressure creep rupture tests of type 304 stainless steel cylindrical vessels containing an axial surface notch

The tendency of using plant structures in the temperature range, in which materials show the creep behavior, has increased especially in atomic energy field. In order to achieve this task, the method of designing high temperature structures has been developed, and in order to improve the reliability and economy of the structures, the studies on the progress of creep cracks and creep fatigue cracks, environmental effects and so on have been forwarded. The authors improved the measurement accuracy and measured the progress of cracks by electric resistance method, using the SUS 304 stainless steel cylindrical specimens with large diameter, each with an axial notch, and examined both aspects of the notch effect and the progress of cracks. They also studied on the formula for evaluating the axial notch effect, and attempted to apply an elastic stress intensifying factor to this problem. The test apparatus, the specimens and the shape of notches, the method of measuring the progress of cracks by electric resistance, the method and conditions of the test, and the test results are explained. As for the lowering of the creep strength of cylinders under internal pressure due to axial notches, the effects of the depth and length of the notches can be explained well with the flow stress equation. (Kako, I.)