Most of the assessment equations for C_t, which is a well-known fracture parameter characterizing creep and creep-fatigue crack growth rates, have limited applicability to constant load conditions. However, crack growth due to creep can also occur under varying load conditions when the load rate is slow enough such that accumulated creep deformation near the crack tip can't be neglected. An estimation equation of the C_t-parameter that can be applied to the case of slow load rising was derived by the authors and denoted as (C_t)_r.

In this paper, correlation between (C_t)_r at the end of the load-rising period and C_t at the beginning of the succeeding load hold period is shown. And a new C_t estimation equation that can be applied to the load hold period following a slow load rising period is derived using the relation between (C_t)_r and C_t. Finite element analyses of several cases with various load-rising conditions were performed. The results support accuracy of the proposed C_t estimation scheme. General applicability of the equation is also discussed.