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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3. The background of imitation modeling As was shown by Stepanov et al. (1985), Shlyannikov et al. (2001, 2014), Ilchenko et al. (2012) the main idea of imitation modeling consists in testing of specimens or imitation models, which are directly cut from investigated failure-critical components. Consequently the imitation model saves accumulated damages and outer surface state in critical zones under operating loading conditions. The main advantage of imitation modeling in certain cases is the replacement of costly and long-term tests of full-scale structures. The tests of such imitation models can solve a problem of determination of the components residual life. In some cases the imitation modeling is used for verification and calibration of the modern crack growth rate and life-time prediction models, because it is impossible to realize the complex stress-strain state (SSS) of real structural components, e.g. GTE compressor discs, on the standard specimens. Then it is allowed to design and manufacture the imitation models from the same structural material (titanium alloy, steel) and strictly according to manufacturer drawings. As a rule, imitation modeling is based on a combination of numerical and experimental studies. The basic principles of imitation modeling are the following:  First of all, the SSSs of critical zones both the real structural component and imitation model are the same. This principle of imitation modeling in application to the problems of assessing lifetime prediction consists in reproducing the conditions of a state in several critical areas of a structure and on an imitation model. Shlyannikov (2003) estimated the SSS in the control zone by the generalized parameters, such as elastic plastic stress and strain intensity:         2 2 2 2 2 2 6 2 1 zx yz xy xx zz zz yy yy xx e                    (1)         2 2 2 2 2 2 2                    (2) In this eq. (1-2)  e and ε e – equivalent stresses and strains, respectively.  Secondly, the loading conditions of imitation model correspond to operating loading profile: static, cyclic, random, program, dynamic, impact or other.  Thirdly, the crack initiation zone, crack path and crack inclination should coincide with what is observed in real structural component in service. Thus, the imitation modeling approach should reproduce the loading conditions, the processes of damage accumulation and growth and also fracture of real structural component. 4. Numerical analyses 4.1. Elastic-plastic stress fields in GTE compressor disk at room temperature According to principles of imitation modeling the first part of numerical calculations is concerned with SSS analysis of aircraft GTE high pressure compressor disk D-36 itself. The detailed numerical analysis of SSS of full size 3D finite element (FE) model of the compressor disk with blades under operation loading conditions was performed by Yarullin (2018). As it follow from these results, the equivalent stress peak mainly occurred close to the outer free surface of the slot key where a corner crack was likely to nucleate and start to grow due to the cyclic loading. The maximum value of the equivalent stress in this area is equal to σ e =1100MPa, which is higher than the yield strength of the titanium alloy VT3-1 at room temperature σ 0 = 1005 MPa. 2 3 3 zx yz xy xx zz zz yy yy xx e