PSI - Issue 12

Venanzio Giannella et al. / Procedia Structural Integrity 12 (2018) 479–491 V. Giannella Structural Integrity Procedia 00 (2018) 000 – 000

490 12

For each step of crack advance, tractions on the new crack surface generated during the propagation are automatically added, as provided by the global FEM analysis of the uncracked model. The average crack advance per step is set up to 0.0015 in for the initial 5 steps and gradually increased up to 0.01 in for the last 5 steps. Results in terms of crack sizes vs. cycles are shown in Fig. 12 (the crack size definitions can be retrieved in Fig. 9c) in correspondence of two calculation strategies: “1LC” is the strategy currently adopted in GE-AVIO that does not consider the secondary cycles contribute, whereas the “2LC” takes into account the most relevant secondary cycle (in addition to the main cycle). As visible in Fig. 12, no appreciable differences come out, confirming the acceptability of the simplifications behind the 1LC approach. Figure 13 shows the DBEM model containing the considered final crack. Such model comprises 3435 quadratic elements.

Figure 13. (a) DBEM model with highlight of the final crack; (b) close-up of the remeshed area with tractions applied on crack face elements; (c) crack shape variation during the simulation with J-paths, for the J-integral evaluation, positioned along crack front.

5. Conclusions

A coupled FEM-DBEM procedure, based on the superposition principle applied to fracture mechanics, has been implemented to simulate a fatigue crack propagation on a GE-AVIO aeroengine turbine vane. Such an approach is fully automated and allows to predict SIFs along the crack front and then the CGRs and crack path with high accuracy. The initial crack has been inserted in the most fatigue critical point, as provided by an initial multiaxial fatigue analysis on the whole vane segment. Both the fatigue and fracture analyses takes into account a fatigue load spectrum made up with the main mission points of a realistic aircraft engine mission profile. A validation of the strategy followed by GE-AVIO, based on allowance for the only principal baseline cycle extracted by the rainflow approach, is provided.

References

Citarella, R., Cricrì, G., 2010. Comparison of DBEM and FEM Crack Path Predictions in a notched Shaft under Torsion. Engineering Fracture Mechanics 77, 1730-1749.