Using a Dovetail Fixture to Study Fretting Fatigue and Fretting Palliatives

[+] Author and Article Information
B. P. Conner

 Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge MA 02139bpconner@alum.mit.edu

T. Nicholas

 University of Dayton Research Institute, Structural Integrity Division, 300 College Park Drive, Dayton, OH 45469

J. Eng. Mater. Technol 128(2), 133-141 (Jul 15, 2003) (9 pages) doi:10.1115/1.2172272 History: Received April 14, 2003; Revised July 15, 2003

Fretting fatigue damage can reduce the service life of engineering components in contact. The attachment between blades and disks in the fan and compressor stages of gas turbine engines is often a dovetail geometry. As a result, normal and tangential cyclic contact loads are present. Results of fretting fatigue tests using a new dovetail fixture are detailed here. Dovetail specimens and three types of contact pads were all machined out of Ti6A14V. Two types of palliatives are also examined: aluminum bronze coatings and low-plasticity burnishing. While the palliatives were effective in increasing the fatigue life, the three pad geometries produced essentially the same fatigue life.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

A schematic of a blade-disk dovetail attachment in an aeroengine

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Figure 2

A photograph of the dovetail fixture with specimen and contact pads

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Figure 6

The strain versus load response measured at the strain gauge compared to the calculated response from the model

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Figure 7

The evolution of shear tractions from 5% of maximum load to 100% of maximum load for a dovetail specimen contacted by a cylindrical pad. f=0.8.

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Figure 8

The maximum load required for failure at R=0.1 for a fatigue life of 106 cycles to failure for a short pad geometry

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Figure 9

The number of fatigue cycles for a maximum load of 18.3kN at R=0.1 using the short pad geometry

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Figure 10

Fretting fatigue scar of a short flat pad is shown. Cracks develop near the maximum extent of contact.

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Figure 11

(a) A 3-D surface profile showing material removal to a depth of 29μm in a small section of the slip zone from a coated specimen. (b) An uncoated specimen showing significantly less material removed in the slip region. (c) and (d) show 2-D surface profiles taken in (a) and (b), respectively.

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Figure 12

Calculated elastic stresses at the surface for both the coated and uncoated specimens at loads of 18.3kN and 22.6kN. These can be considered “pseudostresses” as an elastic-plastic analysis was not conducted.

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Figure 13

X-ray diffraction measurements of the burnishing induced residual stresses under the fretting fatigue scar and 3mm away from the fretting region. Error bars cannot be seen since the largest error was ±8MPa.

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Figure 3

A photograph of a LPB treated specimen in the dovetail fixture. Notice the polished appearance of the specimen regions near the contact pad.

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Figure 4

The global mesh for the dovetail finite element model. Notice that the mesh in both the specimen and the fixture becomes refined closer to the interface.

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Figure 5

The hystersis loop over two cycles of loading for several values of the coefficient of the friction. Data from the second cycle plotted over data from the first cycle.

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Figure 14

A plot showing the stress intensity factors as a function of crack length for a crack at the edge of contact and normal to the surface. Three different test conditions are considered corresponding to an untreated specimen at baseline loads, a specimen treated with LPB at baseline loads, and specimen treated with LPB with a 50% increase in maximum load resulting in failure at 106 cycles.



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