HOLD TIME CRACK-GROWTH ANALYSIS AT ELEVATED-TEMPERATURES

Integral parameters J* and ($) over cap J are used to predict crack growth under R(c) = O strain cycling with hold time at the maximum strain. Both nominally elastic and nominally plastic strain levels are investigated. Test data are obtained for single edge notch specimens of Alloy 718 at 593 and 649 degrees C with and without hold time. The da/dN - Delta J* or Delta ($) over cap J data for strain cycling without hold time, and the da/dt - J* or ($) over cap J data for the time-dependent crack growth under static control conditions obtained previously are used to predict the crack growth rate under strain cycling with hold time. The superposition method in which the predicted crack growth rates under strain cycling and under constant strain are directly added to obtain the total crack growth rate is found to be satisfactory only at low applied strain ranges. A modified superposition method suitable for both low and high applied strain ranges is proposed.