Issue 35

G. Dhondt et alii, Frattura ed Integrità Strutturale, 35 (2016) 108-113; DOI: 10.3221/IGF-ESIS.35.13 111 20-node reduced integration hexahedral mesh with collapsed quarter point elements was generated, whereas the remaining domain was automatically meshed with quadratic (10-node) tetrahedral elements. Figure 4 : Mesh of the engine blade. Figure 5 : Mesh at the crack tip. In a subsequent calculation the eigenmodes of the blade were determined. The first eigenmode, which is a bending mode (Fig. 6) was, taking fictitious experimental data in to account, judged most critical. This mode was appended to the full power loading point. The crack length versus the number of cycles for the original LCF mission and the LCF-mission augmented by the HCF-mode is shown in Fig. 7. The superimposed HCF vibration clearly decreased the life of the blade substantially. The shape of the crack, however, did not change. This is illustrated in Figs. 8a and 8b. Although the crack in Fig. 8b is somewhat more rough, the overall shape is the same. This was to be expected since both the centrifugal force and the bending mode lead to a predominantly mode-I loading of the initial crack. This, however, may be different for other missions and vibrational modes. Taking the HCF-cycle on its own revealed that no HCF crack propagation takes place, i.e. all equivalent K-values along the crack front in each iteration are below threshold.