Application of the dc potential drop technique in investigating crack initiation and propagation under sustained load in notched rupture tests

Abstract

Creep specimens of IN-X750 with U and V notch geometries have been tested at 700 °C under constant load. The do potential drop technique was employed to measure local deformation, detect crack initiation, and measure crack propagation rates in the notched specimens. Rupture of the U-notched bars and crack initiation in the V-notched bars were found to be controlled by creep deformation. The time to crack initiation and the rupture time can be predicted by using the Monkman-Grant relationship, which was shown to apply to localized crack initiation and multiaxial loading conditions. Sustained load crack growth rates were measured in the V-notched specimens. The dependence of the stage II crack growth rates on the stress intensity factor, the crack initiation, and rupture behavior of IN-X750 can be unified and interpreted with the continuous nucleation and constrained cavity growth model.