PSI - Issue 18

V.N. Shlyannikov et al. / Procedia Structural Integrity 18 (2019) 322–329 Author name / Structural Integrity Procedia 00 (2019) 000–000

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4.2. Development of imitation models geometries The next part of numerical analyses is concerned with development of imitation models geometries. As it has been mentioned above, the compressor disk and blade dovetail type attachment is most common crack initiation area. As was shown by Shaniavski (2003) the cracks in compressor disk can occur in any slot fillets of keys with the same probability. Thus, we can consider the geometry of one dovetail type attachment as an imitation model. The two geometries of imitation models were developed. The first imitation model was supposed to be used on standard test machines with simple uniaxial loading (Fig. 2a). It is well known that during aircraft engine operation, rotating disks are frequently subject to biaxial or multiaxial loading conditions. Shlyannikov and Zakharov (2017) had sound experimental evidence that the fatigue crack growth rate is strongly influenced by the biaxial loading conditions. However, the state of stresses in the 3D full-size compressor disc obtained from FE calculation was found to be biaxial, that is, the structure in the slot of key region is subjected to both radial and tangential (or hoop) stresses. Stress biaxiality ratio  =  rr /   is a function of the current value of the disk radius r and varied from  = 0.47 at r 0 =190mm to  =0.33 at r 1 =160mm. Therefore, the second imitation model (Fig.2,b) should more accurately reproduce the conditions of biaxial loading of the critical zone of the disk and blade attachment. When developing the configuration of imitation models, the following requirements were formulated. Each of the models needs to fully reproduce the key slot geometry of the disk and blade dovetail type attachment in the compressor disk and tension load is applied by means of special designed loading fixture.

Loading fixture

Imitation model II

Imitation model I

a)

b)

Fig. 2. Uniaxial tension (a) and biaxial (b) loading conditions for imitation models I and II, respectively.

In order to perform numerical calculations, the main mechanical properties listed in Table 1 were used. Iteratively, it was found that uniaxial tension load of P y =40 kN should be applied to the imitation model I, while the imitation model II needs to be loaded with forces along two axes of P x =19 kN and P y =38 kN. In this case the maximum value of the equivalent stress around the slot key area is approximately equal to σ e =1100MPa, which coincides with maximum value of stress in full-size compressor disc. To compare the parameter distributions along the key slot on the free surface of the disk, as well as along the disc rim in the horizontal direction (Fig.3a), it is convenient to introduce the dimensionless coordinates in the following form:   l l d 2  , b s t  where l and s are current coordinates, t is rim thickness, d is slot depth. In such representation of numerical results, we will use variables l and b ranging from 0 to 1. Fig. 3 presents a comparison of the stress component distributions on the free surface of the key slot and along the thickness direction