A Study on Creep Rupture of Notched Sheet Specimens at Elevated Temperature

Abstract

From the results of the tensile creep rupture test on notched plate specimens of low carbon steel at 450°C, the following conclusions have been derived.(1) The level of equivalent stress at the notch bottom of the notched specimen under a fixed nominal stress is lower than that on the cross section of necked part of the unnotched specimen during the greater part of rupture life. The equivalent creep rate at the notch bottom of the notched specimen under a fixed nominal stress is also smaller than that of the unnotched specimen. Therefore, it is considered that the time for crack initiation in the notched specimen under a fixed nominal stress is longer than that in the unnotched specimen.(2) Both the level of hydrostatic stress at the notch bottom of the notched specimen under a fixed nominal stress and the rate of its increase with lapse of creep time are lower than those on the cross section of necked part of the unnotched specimen during the accelerating creep stage. Therefore, it is conjectured that the crack propagation rate of the notched specimen under a fixed nominal stress is lower than that of the unnotched specimen.(3) Rupture time versus minimum creep rate curve at the notch bottom of the notched specimen differs from that of the unnotched specimen. On the assumption that the crack initiation time versus minimum creep rate curve at the notch bottom of the notched specimen coincides with that of the unnotched specimen and creep rupture of the material occurs when the total length of cracks reaches to a limited length, it is considered that the time for crack initiation in the notched specimen is longer than that in the unnotched specimen. It is also conjectured that the crack propagation rate of the notched specimen is smaller than that of the unnotched specimen.