4. RESULTS
4.1 Load-Load Line Displacement Results
The creep-fatigue crack growth tests of Grade 91 at 600oC were simulated using the FE analysis method described in Section 3.1 with the material models given in Sections 3.2 and 3.3.
The simulated load-line displacement results are compared with the experimental data in Fig. 6. It shows that, regardless of the cyclic hardening model used, all FE analysis results are very close and are overall in good agreement with experimental data. It shows that deformation behavior of Grade 91 at 600oC under creep-fatigue loading can be well simulated, provided appropriate creep strain model is chosen. The reason is that creep deformation is more dominant than plastic deformation in all cases; creep deformation occurs globally but the plastic deformation is concentrated only near the crack tip (this will be presented in Section 4.2). In the subsequent sub-sections, the combined hardening model by Saad et al. [48] which is closest to experimental result shown in Fig. 5 is used as representative model for FE analysis among the three hardening models, and only the results using the combined hardening model by Saad et al. [48] will be presented.