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.