An assessment of the C* and KI parameters for predicting creep crack growth in a Ni-based superalloy (Waspaloy) at 700℃

摘要

The results of experimental creep crack growthtests, using compact tension specimens, made from a Ni-basedsuperalloy (Waspaloy) at 700℃ are presented. Theexperimental results indicate that the creep crackgrowth rate data for the Ni-base superalloy Waspaloy,at 700℃, can be correlated using the C* parameter,calculated from load-line displacement rates. Themode-I stress intensity factor, KI, does not appearto be capable of correlation the data except at highcreep crack propagation rates. Analytical solutionsindicate that creep crack growth was occurring undertransient creep conditions in the experiments.Finite element (FE) simulations were performed inwhich the experimentally determined crack growthversus time results were imposed. The good agreementbetween the resulting FE solutions for load-linedisplacements and corresponding C* values with theexperimental results show that the FE simulation wassuccessful. The FE simulation revealed that the creepzone increases as the crack growth and a transientstate of creep occurs in the vicinity of the advancingcrack tip. An apparent correlation between the crackgrowth rates and the C* parameter has been shown. Thisinformation is helpful in assessing the likelyusefulness of the C* and KI parameters for predictingcreep crack growth in more general situations.