Evaluation of the Damping Characteristics of a Hard Coating on Titanium

Engine failures due to fatigue have cost the Air Force an estimated $400 million dollars per year over the past two decades (Garrison, 2001). 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. The material and aspect ratio were chosen to approximate the low aspect ratio blades found in military gas turbine fans. The plates were tested with a cantilevered boundary condition, using electrodynamics shaker excitation. The effective test area of each specimen was 4-1/2 in. x 4-1/2 in. The nominal plate thickness was 1/8 in. Mag spinel was applied to both sides of the plate, at a thickness of .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 chordwise 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. The test results are presented in this document.Air Force Inst of Tech Wright-Patterson AFB OH School of Engineering and Management is the author of 'Evaluation of the Damping Characteristics of a Hard Coating on Titanium', published 2004 under ISBN 9781423516781 and ISBN 1423516788.