The Ct parameter has been proposed for characterizing creep crack growth rate in the small scale to extensive creep regimes. In this paper, creep crack growth data from compact specimens ranging in widths from 50.8 to 254 mm and in thickness from 63.5 to 6.3 mm are analyzed to evaluate the Ct parameter. A second objective is to use the load-line deflection rate data obtained during these tests to evaluate the expressions used for estimating Ct in components. These expressions use creep deformation data obtained from uniaxial specimens for estimating Ct.
The analysis of the above data clearly shows that Ct may be used to characterize creep crack growth rate data over a wide range of deformation conditions. For 12.7-mm thick specimens, Ct failed to characterize the creep crack growth rate during the first 1 mm of crack extension. It is further shown that the expressions used for estimating Ct in components are reasonably accurate in the small scale creep region but are not accurate in the extensive creep region. The measured values of load-line deflection rates in the extensive creep region lay between the predicted values based on the assumptions of plane stress and plane strain.