Determination of creep crack growth threshold by experiments under elevated temperature with pre-stressed specimens

A novel test method is presented in this paper for determination of the creep crack growth threshold. In this method, a wedge is placed in the notch of a standard compact tension (CT) specimen with a pre-crack, which provides an evaluable stress fields characterized with stress intensity factor (K) at the crack tip. Then the specimen is kept in the test temperature for a certain time. The creep crack growth threshold of the material at a given temperature can be obtained by extrapolating the curves of the crack growth rate vs. K in the double logarithmic coordinates. Since it does not need mechanical testing machine and several specimens can be tested simultaneously, the proposed method is economical in both costs and time. Tests on a nickel-based powder metallurgy superalloy FGH97 are conducted using this method at 600°C, 650°C and 750°C, which indicate its feasibility.