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Research Papers: Gas Turbines: Manufacturing, Materials, and Metallurgy

Mitigation of Fretting Fatigue Damage in Blade and Disk Pressure Faces With Low Plasticity Burnishing

[+] Author and Article Information
Paul S. Prevéy

 Lambda Technologies, 3929 Virginia Avenue, Cincinnati, OH 45227pprevey@lambdatechs.com

N. Jayaraman

 Lambda Technologies, 3929 Virginia Avenue, Cincinnati, OH 45227njayaraman@lambdatechs.com

Ravi A. Ravindranath

 Propulsion and Power, NAVAIR, 22195 Elmer Road, Patuxent River, MD 20670-1534ravi.ravindranath@navy.mil

Michael Shepard

 WPAFB AFRL/MLLMN, 2230 10th Street, WPAFB, OH 45433-7817michael.shepard@wpafb.af.mil

J. Eng. Gas Turbines Power 132(8), 082105 (May 20, 2010) (8 pages) doi:10.1115/1.2943154 History: Received January 14, 2008; Revised February 05, 2008; Published May 20, 2010; Online May 20, 2010

Low plasticity burnishing (LPB) is now established as a surface enhancement technology capable of introducing through-thickness compressive residual stresses in the edges of gas turbine engine blades and vanes to mitigate foreign object damage (FOD). The “fatigue design diagram” (FDD) method has been described and demonstrated to determine the depth and magnitude of compression required to achieve the optimum high cycle fatigue strength, and to mitigate a given depth of damage characterized by the fatigue stress concentration factor, kf. LPB surface treatment technology and the FDD method have been combined to successfully mitigate a wide variety of surface damage ranging from FOD to corrosion pits in titanium and steel gas turbine engine compressor and fan components. LPB mitigation of fretting-induced damage in Ti–6Al–4V in laboratory samples has now been extended to fan and compressor components. LPB tooling technology recently developed to allow the processing of the pressure faces of fan and compressor blade dovetails and mating disk slots is described. Fretting-induced microcracks that form at the pressure face edge of bedding on both the blade dovetail and the dovetail disk slots in Ti-6-4 compressor components can now be arrested by the introduction of deep stable compression in conventional computer numerical control (CNC) machine tools during manufacture or overhaul. The compressive residual stress field design method employing the FDD approach developed at Lambda Technologies is described in application to mitigate fretting damage. The depth and magnitude of compression and the fatigue and damage tolerance achieved are presented. It was found that microcracks as deep as 0.030in.(0.75mm) large enough to be readily detected by current nondestructive inspection (NDI) technology can be fully arrested by LPB. The depth of compression achieved could allow NDI screening followed by LPB processing of critical components to reliably restore fatigue performance and extend component life.

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Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

A close-up view of the dovetail EOB region prone to microcracking (dark arrows) due to fretting

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Figure 2

A close-up view of the dovetail disk post slots

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Figure 3

(a) Optical photo of typical network of parallel microcracks found in the dovetail EOB. (b) Optical micrograph of the cross section showing the depth of the microcrack (arrows). As seen here, the fine microcrack is less than 0.003in.(0.08mm) deep from the surface.

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Figure 4

FDD for Ti–6Al–4V to demonstrate the method of determination of minimum and maximum residual compression to restore or enhance fatigue performance

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Figure 5

(a) LPB processing of the surface of a Ti–6Al–4V compressor blade dovetail contact region using a specially designed LPB tool; (b) LPB processing of a Ti–6Al–4V compressor disk dovetail post contact region using a specially designed LPB tool

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Figure 7

Comparison of LSP, LPB, SP, and gravity peening depth of compression

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Figure 8

(a) S-N data showing the fretting fatigue results for Ti–6Al–4V test specimens in the base line (untreated) condition; (b) FDD with the SWT line for the effective kf≈2.6

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Figure 9

(a) Residual stress profile as a function of depth in LPB treated specimen; (b) S-N data showing the fretting fatigue results for Ti–6Al–4V test specimens in the LPB treated conditions

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Figure 10

(a) LPB treated compressor blade dovetail contact region; (b) residual stress distribution on the dovetail section of the LPB treated blade

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Figure 11

FEA simulation of the residual stresses from Fig. 1 identifies the location (red arrow) and magnitude of the compensatory tensile residual stresses in the blade

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Figure 12

S-N data for the compressor blades

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Figure 13

Photo of the LPB treated disk post; this post was removed from the compressor disk after LPB treatment

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Figure 14

Residual stress distribution on the compressor disk post dovetail contact region after LPB treatment; these results are comparable to Fig. 1 for the blade dovetail contact surface

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