Low-cycle fatigue life assessment for gas turbine engine disks under flight cycle conditions

We address the effects of the actual flight cycle on durability of gas turbine engine disks under low-cycle fatigue. An approach is proposed which improves reliability of life cycle prediction owing to schematization of flight cycle with a criterion for reaching the maximum intensity of total strain range. Contribution of subcycles to the cumulative damage is demonstrated. __________ Translated from Problemy Prochnosti, No. 1, pp. 129–133, January–February, 2009.     

Evaluation of the residual life of steam turbine rotors

The procedure of evaluation of residual life is applied to high-pressure and intermediate-pressure steam-turbine rotors. We consider the following mechanisms of crack initiation and growth: low-cycle thermal fatigue, high-cycle fatigue, and creep. To obtain conservative estimates, we use the worst possible characteristics of the materials. A detailed analysis of stress fields induced by centrifugal forces, steam pressure, rotational bending, and temperature is performed by the method finite-elements. As an example, the procedure is applied to the high-pressure rotor of Nikola Tesla power plant A, unit 3. Estimation of the residual service life of this rotor revealed some critical locations that should be subjected to more careful nondestructive inspection. The procedure is also applicable (without changes or with necessary modifications) to other components of power plants such as low-pressure rotors, steamlines, and casings. The entire procedure, including numerical analysis of nonstationary temperature and stress fields, was performed on a personal computer (PC 486).Published in Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 1, pp. 68–75, January–February, 1995.     

Criterial relationships for residual life assessment of materials

The paper gives the research findings which make it possible to construct an algorithm for the residual life assessment within the framework of a tensor approach to describing damage in a material under inelastic deformation. The authors propose explicit finite criterial relationships for the residual life assessment, which extend the known relationships to cover a wider range of loading processes.     

Creep life assessment method for online monitoring of steam turbine rotors

The principal objective of work was to develop fast and accurate method for online creep life monitoring of steam turbine rotors. For this purpose, a characteristic strain model of creep was investigated and validated using test data of 2%CrMoV rotor steel. The model was then used to determine creep damage functions which are introduced to compute creep damage at a constant temperature based on the Robinson time fraction rule. Finite element (FE) creep calculations of a turbine rotor were performed using the same creep model to obtain reference damage results for validating the proposed method. Comparisons of the results obtained using both methods showed a very good accuracy of the online creep damage predictions.     

Estimating working life for aircraft gas turbine engine disks at the stage of fatigue crack development. Part 1

Studies have been performed on the static and cyclic cracking resistance (failure ductility) of aircraft gas turbine disk materials at normal and elevated temperatures and at various frequencies and for various thicknesses. When the conditions of planar strain are violated for these materials and these geometrical dimensions, one can estimate the critical stress intensity coefficient K _Ic from the critical loading P _Q obtained on intersection of the 5% secant with the strain diagram.Deceased.Translated from Problemy Prochnosti, No. 11, p. 14–19, November, 1994.     

Estimating working life for aircraft gas turbine engine disks at the stage of fatigue crack development. Part 2

It is shown that the cyclic cracking resistance in turbine disk materials is substantially affected by temperature, frequency, loading-cycle shape, and specimen thickness. Formulas describing fatigue crack growth rates are considered and calculations are done on the periods needed for fatigue cracks to grow to critical sizes from stress concentrators at various temperatures. Deceased. Translated from Problemy Prochnosti, No. 12, pp. 3–15, December, 1994.     

Gas turbine blade service life assessment with account of fracture stage

The numerical simulation of creep, continuum fracture zone evolution and crack propagation in a gas turbine blade uner cyclic loading conditions have been performed using a semianalytic finite-element method. The blade basic life (before fracture zone appearance) and additional resource (concerned with fracture process) of a blade have been determined. __________ Translated from Problemy Prochnosti, No. 5, pp. 28–36, September–October, 2008.     

Analysis of fracture failure of fir-tree serrations of stage II turbine disks

This paper presents an analysis of fracture failure of fir-tree serrations in stage II turbine disks in a certain type of engine. On the basis of statistical analysis, basic fracture features and fracture mechanisms of stage II turbine disk serrations have been summarized. The reasons for the serration fracture failure are: (a) the first order bending resonance k=5 in the turbine blade occurring at the speed of 9700 rpm; (b) the unreasonable design of the five-serration structure, which causes each serration to bear non-uniform stresses; (c) the disk being made of the alloy GH2036 having a low fatigue resistance; (d) the high intergranular corrosion sensitivity of GH2036. Finally, measures, i.e. the change of the five-serration structure into a three-serration structure and the replacement of GH2036 with GH2132, have been given to prevent the fracture failures, and the application has indicated that these measures are effective.