PSI - Issue 13

R.R. Yarullin et al. / Procedia Structural Integrity 13 (2018) 902–907 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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3. Numerical study 3.1. Elastic-plastic stress fields in GTE compressor disk

The first part of numerical calculations is concerned with stress-strain state analysis of compressor disk. ANSYS finite element (FE) code (2012) is used in mechanical analysis. Twenty nodal solid brick elements with quadratic interpolation were used to mesh the 3D FE model configuration, which is a segment of the compressor disk including blades. At the side surfaces of the compressor disk segment cyclic symmetry conditions were applied. The 3D FE model of aircraft GTE high pressure compressor disk D-36 are presented on Fig. 2a, 2b.

σ e =828MPa

a)

b) c) Fig. 2. FE model and equivalent stress distribution for the compressor disk with blades.

The numerical analysis of stress state of full-size 3D FE model of the compressor disk with blades was performed under operation loading conditions. In operation compressor disk and blades are subjected to centrifugal loading caused by rotation of the turbine rotor. In this model all contact surfaces between disk and blades use a surface-to surface formulation. This is because accurate results are required. Bending moment induced by air pressure was neglected as well as the value of bending stresses represent only 0.15% of the stress caused by centrifugal loading. In order to perform numerical calculations, the main mechanical properties determined by testing at high temperature and listed in Table 1 were used. The elastic-plastic material behavior is described by bilinear kinematic hardening model. Fig. 2c shows the total stress state of compressor disk and the equivalent stress distribution at the critical region. As it follows from these results maximum equivalent stresses are localized in slot fillets under the blades near the disk outer surface. The von Mises peak stress in this area is equal to σ e =828MPa, which is higher than the yield strength of the titanium alloy VT3-1 σ 0 = 753 MPa. Accordingly, plastic zones availability along with the cyclic loading leads to damage accumulation and its growth in compressor disk and blade «dovetail type» attachment. 3.2. Stress-strain state of GTE compressor disk with operation damages The second part of numerical study is concerned with stress-strain state analysis of GTE compressor disk with operation damages. As was shown by Shaniavski (2003), the critical size of growing crack in this type of compressor disks is approximately 9 mm on the disk outer surface and crack aspect ratio varied from 0.2 to 0.6. Further, the growing crack intersects full thickness of the compressor disk and rupture of disk rim is occurred. In all of these failures, crack propagation started from part-trough quarter- circular corner surface flows. The crack tip shape, varied from quarter-circular to quarter-elliptical, is considered at present study. The crack sizes are presented on Fig. 3b, 3c. In this figure a is crack depth and c is crack length. The details of the crack initiation zone are presented on Fig. 3a. Once the location of the crack and the size of the crack are identified, the region around the crack needs to be meshed appropriately to accurately calculate elastic-plastic fracture resistance parameters. In general this means more accurate results, but higher solution costs. To solve this problem, the submodeling technology is employed for detailed analysis of stress-strain state in the crack tip vicinity. Special requirements of Shlyannikov et al. (2016a) have been met to form the FE mesh of compressor disk with quarter-elliptical cracks. Typical FE meshes for the compressor disk with quarter-elliptical crack are illustrated in Fig. 4a, 4b.