Research Papers: Gas Turbines: Structures and Dynamics

Nonlocal Cyclic Life Prediction for Gas Turbine Components With Sharply Notched Geometries

[+] Author and Article Information
Roland Mücke, Holger Kiewel

 Alstom, Brown Boveri Strasse 7, 5401 Baden, Switzerland

J. Eng. Gas Turbines Power 130(1), 012506 (Jan 09, 2008) (8 pages) doi:10.1115/1.2747642 History: Received April 27, 2007; Revised May 07, 2007; Published January 09, 2008

The safe and efficient operation of modern heavy duty gas turbines requires a reliable prediction of fatigue behavior of turbine components. Fatigue damage is located in areas where cyclic stress and strain amplitudes are highest. Thus, geometrical notches associated with stress/strain concentrations and stress/strain gradients appear to be the most important sites for fatigue crack initiation. The paper addresses a nonlocal concept for cyclic life prediction of notched components. Contrary to various local approaches in the field, the proposed method explicitly accounts for stress and strain gradients associated with notches arising from grooves, cooling holes, fillets, and other design features with stress raising effect. As a result, empirical analytical expressions for considering either strain or stress gradients for cyclic life prediction are obtained. The method has been developed from cyclic test data on smooth and notched specimens made of a ferritic 1.5CrNiMo rotor steel. The analytical formulations obtained have then been applied to test data on the nickel base superalloy MAR-M247 CC showing a good agreement between prediction and measurement. Moreover, the proposed nonlocal lifing concept has been validated by component tests on turbine blade firtrees. The predicted number of cycles to failure correlates well with the experimental results showing the applicability of the proposed method to complex engineering designs.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Strain distribution in notched and smooth specimens

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Figure 2

Example of notched specimen

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Figure 3

Principle of potential drop monitoring

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Figure 4

Example of potential drop measurements

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Figure 5

The electrostatic field problem

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Figure 6

Boundary conditions for electrostatic field calculations

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Figure 7

Example of potential drop calibration curves

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Figure 8

LCF crack shape after heat tinting

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Figure 9

Strain-based approach for cyclic life assessment at notches

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Figure 10

Cycles to crack initiation versus global strain amplitudes

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Figure 11

Cycles to crack initiation versus local strain amplitudes

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Figure 12

Linear fit of local strain amplitudes and strain gradients

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Figure 13

Comparison of raw data and prediction for the 1.5%CrNiMo rotor steel

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Figure 14

Comparison of raw data and prediction for MAR-M247 CC

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Figure 15

Component test setup with strain gauges and potential drop probes

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Figure 16

FEA model of the component test setup

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Figure 17

Effect of friction coefficient on maximum principal stress distribution in the notch

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Figure 18

Examples for the distribution of the electric potential for a crack on one lobe

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Figure 19

Examples for potential drop calibration curves

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Figure 20

Results of component test

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Figure 21

Contact faces after testing



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