Effects of component size, geometry, microstructure and aging on the embrittling behavior of creep crack growth correlated by the Q∗ parameter

The driving force for creep crack growth is dominated by local elastic–plastic stress in the creep damage zone around a crack tip, temperature and microstructure. In previous work, C∗, Ct, load line displacement rate dδ/dt and Q∗ parameters have been proposed as formulations of creep crack growth rate (CCGR). Furthermore, using parameters mentioned above, the construction of the algorithm of predictive law for creep crack growth life is necessary for life assessment procedures. The aim of this paper is to identify the effects of component size, geometry, microstructure, aging and weldment on the embrittling behavior of creep crack growth and incorporate these effects in a predictive law, using the Q∗ parameter. It was found that for specimen size (width and thickness) and of material softening due to aging the values of the activation energy were the same whereas for grain size change and structural brittleness, which affected crack tip multi-axial stress state the values for the activation energy for CCGR differ.