PSI - Issue 12

Venanzio Giannella et al. / Procedia Structural Integrity 12 (2018) 404–415 V. Giannella/ Structural Integrity Procedia 00 (2018) 000 – 000

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K th K c K eff Threshold value for K Critical value for K Effective value for K Paris’ law exponent W Strain energy density Γ υ Poisson’ ratio ρ Mass density n

Closed contour around crack tip

2. FEM analyses

2.1. FEM modelling

The global FEM model is representative of one quarter of a compressor disk, comprising nine blades (Fig. 1a). All the parts are made of a two-phase titanium alloy, with the main mechanical and fatigue properties listed in Tab. 1. The loading boundary condition consists only of the centrifugal force, with a rotational speed of 925 rad/s, applied to the whole domain. The kinematic boundary conditions consist of normal constraints, applied on the two orthogonal disk cut surfaces, in addition to axial constraints again applied on the two disk cut surfaces and on some blade surfaces (to prevent their rigid body motion; Fig. 1d). These boundary conditions allow the model to deform freely in the radial direction due to the centrifugal forces. A second level of submodelling has been performed (Fig. 1b) in order to gain accuracy (by further mesh refinement) in the volume surrounding the interface between blade roots and disk slots; such interface (Fig. 1c) is modelled with nonlinear contact conditions with allowance for friction (f=0.3).

Figure 1. (a) FEM model, (b) FEM submodel and (c) close-up on the crack insertion point (red dot) in the slot fillet; (d) boundary conditions applied on the two disk cut surfaces and on the Z+ surfaces of the blades.