Experimental determination of the high-temperature crack growth behavior of incoloy 800H

Crack growth and the crack growth rate can be determined continuously by using the single-specimen partial unloading compliance technique, modified for high-temperature tests, or a direct-current potential drop technique with similar accuracy for temperatures up to 800 degrees C and test durations from a few hours up to several months. The possibilities and limitations of the experimental setup are discussed. The increasing influence of time-dependent processes with increasing test temperature is shown on the basis of J-integral versus crack growth resistance curves (J-R curves), determined in short-time tests in the temperature range from room temperature to 800 degrees C. Creep deformation and creep crack growth are significant for this alloy at temperatures higher than about 600 degrees C. An evaluation in terms of J-R curves represents the limiting case of negligible time-dependent effects, and therefore it is only meaningful for relatively high loading with relatively high deforma tion rates. This is demonstrated for high temperature crack growth experiments with different loading rates. For these cases the evaluation of short - time tests (less than one day) in terms of the C-integral for steady-state creep conditions is consistent with results of long-time creep tests at 800 degrees C.