The influence of material mismatch an the evaluation of time-dependent fracture mechanics parameters

The influence of material mismatch on the stress field of uniaxial specimen s and the time-dependent fracture mechanics parameters is studied in the pr esent work. The applicability of the conventional C* equation based on the load line displacement is re-examined by using the finite element method. I t is found that under the extensive creep condition the C* value of hard we ld/soft parent metal specimen can be significantly higher than that of a si ngle weld metal specimen, and the material mismatch has little influence on C(t) in small scale creep in the studied cases. It is proposed that the C* formula based on the load line displacement recommended by ASTM E1457 need s to be modified to interpret the CCG behaviour of welded specimens. Candid ate modification factors have been proposed. (C) 1999 Elsevier Science Ltd. All rights reserved.