Add-On Damping Treatment for the F-15 Upper-Outer Wing Skin

TLDR: In this article, the F-15 upper-outer wing skin has experienced high cycle fatigue cracks caused by separated flow on the upper wing surface and in turn induces large vibratory loads on the lower wing and associated substructure.

Abstract: : The purpose of this investigation was to design, fabricate, and verify candidate add-on damping treatments for the F-15 upper-outer wing skin. The F-15 upper-outer wing skin has experienced high cycle fatigue cracks caused by separated flow on the upper wing surface. The separated flow results during high load factor maneuvers, and in turn induces large vibratory loads on the upper wing skin and associated substructure. The capability of the F-15 to sustain these maneuvers allows the excitation to occur for sufficiently long periods of time to result in damage. Damage accumulates due to the resonant vibration of local skin/stiffener modes. The cracks initiate at the fastener holes adjacent to the integrally machined 'T' stiffeners and tend to propagate parallel to the stiffeners. Two damping treatments resulted from the investigation and were recommended for F-15 fleet retrofit. One was an external constrained-layer treatment and the other was an internal 'stand-off' treatment. Laboratory vibration, corrosion, and thermal aging tests were conducted as part of the development of the add-on damping treatments. Estimates of the life extension factors for the external and internal damping treatments were 5 and 34 respectively. Aircraft vibration, Resonant vibration, Vibration damping, Constrained layer damping, Viscoelastic damping, Fatigue.