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Shock and Vibration
Volume 14 (2007), Issue 1, Pages 37-51
http://dx.doi.org/10.1155/2007/260183

The Evaluation of the Damping Characteristics of a Hard Coating on Titanium

Christopher Blackwell,1 Anthony Palazotto,1 Tommy J. George,2 and Charles J. Cross2

1Department of Aeronautics and Astronautics: Air Force Institute of Technology, 2950 Hobson Way, Building 640, WPAFB, OH 45433-7765, USA
2Air Force Research Laboratory: Propulsion Directorate, 1950 Fifth Street, WPAFB, OH 45433, USA

Received 17 November 2005; Revised 7 February 2006

Copyright © 2007 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Engine failures due to fatigue have cost the Air Force an estimated $400 million dollars per year over the past two decades. Damping treatments capable of reducing the internal stresses of fan and turbine blades to levels where fatigue is less likely to occur have the potential for reducing cost while enhancing reliability. This research evaluates the damping characteristics of magnesium aluminate spinel, MgO+Al2O3, (mag spinel) on titanium plates from an experimental point of view. The material and aspect ratio were chosen to approximate the low aspect ratio blades found in military gas turbine fans. In the past, work has generally been performed on cantilever supported beams, and thus the two-dimensional features of damping were lost. In this study plates were tested with a cantilevered boundary condition, using electrodynamic shaker excitation. The effective test area of each specimen was 4.5 in × 4.5 in. The nominal plate thickness was 0.125 in. Mag spinel was applied to both sides of the plate, at a thickness of 0.01 in, and damping tests were run at room temperature. The effect of the coating was evaluated at the 2nd bending mode (mode 3) and the chord wise bending mode (mode 4). A scanning laser vibrometer revealed the frequency and shape of each mode for the plates. Sine sweeps were used to characterize the damping of the coated and uncoated specimens for the modes tested. The coating increased damping nonlinearly for both modes tested in which the general outcome was similar to that found in beams.