Abstract: An equivalent homogenous model is presented for the compact tension (CT) specimen with different creep properties in the weld and base metals. Based on the proposed equivalent material model, the modified experimental C* integral estimation equations are derived for the CT specimens with a weld centre crack, a fusion line crack and an asymmetric crack, respectively. And then, finite element (FE) analyses for C* integral of welded CT specimens are performed by using the ABAQUS software. The C* parameters from FE simulation and the modified estimation equations are compared. Results indicated that an under-mismatched weld will increase the non-dimensional factor hw while an over-mismatched weld will decrease the hw value compared with the h0 factor of homogeneous CT specimens. It implicates that the current C* estimation equation in ASTM E1457 may underestimate C* for an under-mismatched weld but slightly overestimate it for an over-mismatched weld. Whether for under-mismatched weld (M<1) or for over-mismatched weld (M>1) considered herein, the predicted C* parameters from the presented formulae are very close to FE results and thus can be used to interpret the creep crack growth of weldments

Key words: C* parameter, CT specimen, Material mismatch, Weldseam Creep crack growth