(1)
where a is crack length; BN is the net thickness; W is the width; σ0 is the yield strength of material (in this paper, σ0 =311 MPa is used). Among the test cases, the specimen 1 having the highest load ratio would be the creep-dominant case and the specimen 5 having the shortest hold time would be the fatigue-dominant case. For the specimen 3, the creep and fatigue effect would be comparable. These three creep-fatigue crack growth tests cases will be analysed in this paper. Test results for the crack length versus number of cycles are shown in Fig. 2(a) and for load line displacement versus number of cycles in Fig. 2(b).