The creep crack growth behavior in 3.5NiCrMoV steel had been investigated by using compact type tension specimen under constant $C_t$ and constant displacement rate conditions.
For constant $C_t$ tests, $C_t$ strongly rely on load line displacement rate adn is maintained with constant value under constant displacement rate condition. But $C^*$ usually increase with crack length though load is reduced in order to maintain constant $C_t$ value as crack extends.
Constant crack growth rate is held during crack growth of 1mm distance with constant $C_t$ value. At this constant $C_t$ regions, $à$ ~ $[C_t]^0.86$. While, at constant load region, $à$ $[C_t]^{0.92}$ and $à$ ~ [C^*]^0.60$
For constant displacement rate tests, crack growth rate increase and $à$ ~ [C^*]^0.50$ as the crack extends to the critical length. After this critical length, crack growth is essentially independent of crack length and $C_t$ is maintained with almost constant value.
Fully Coalesced Area(FCA) ahead of crack tip tend to increase as $C_t$ increase to the critical value (in this experiments, critical $C_t$=2000 [N/m.hr]). After the critical value, FCA tend to decrease as $C_t$ increase.
Contribution of steady state creep deformation for total displacement is changed as crack length increase. For the tertiary stage of crack growth test, the most of displacement is due to steady state creep, only small part is due to primary creep and other effects Test have to be interrupted in this tertiary stage to obtain high value of $C_t$. Therefore, this constant $C_t$ experiments are tested in the steady state creep regime.
