Effects Of Residual Stress On Creep Damage And Fracture In Notched CT Specimens

In this work, the effects of residual stress on creep damage and creep fracture are investigated by numerical analyses. Different residual stress fields ahead of notches are introduced by pre-compressing notched CT specimens of a Cr-Mo-V steel at room temperature, and then creep at 566℃. Two cases of residual stress alone and residual stress combined with primary load are analyzed, including creep strain, the creep damage, creep crack initiation (CCI) time and the creep crack growth (CCG) rate due to residual stress relaxation. The effects of primary load level, residual stress and material creep ductility on CCI time are mainly analyzed. The main conclusions obtained are as follows:(1)The results show that for the case with residual stress alone, larger residual stress relaxation occurs at initial creep stage, and the creep strain and damage are accumulated ahead of notches during the residual stress relaxation. The CCI time increases with increasing the failure strain of material, and after the failure strain is larger than a critical value, the creep initiation due to the residual stress relaxation alone may be avoided.(2)For the case of residual stress combined with primary load, the residual stress also promotes creep damage and crack initiation. It is found that the effects of residual stress on CCI time are related to the failure strains of material and primary load levels. With increasing the failure strain, the reduction magnitude in the CCI time due to the residual stress relaxation increases to a maximum value, and then decreases slightly. The reduction magnitude in the CCI time due to the residual stress relaxation decreases with increasing primary load level. These results are analyzed by the change in residual stress relaxation time in the materials with different failure strain and at different primary loads.(3) For the case of residual stress relaxation alone, the CCG length increases with increasing the residual stress level. For the case of residual stress combined with primary load, the residual stress relaxation promotes creep crack growth significantly during frist 250 hours, later the CCG is mainly controlled by the primary load level.