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Design and fabrication of integrally damped composite fan blades

The design, analysis, and fabrication methods of embedding small viscoelastic damping patches into scaled composite fan blades is presented, where the goal is to improve the blade fatigue characteristics by increasing the damping in the chord-wise modes. This discussion concentrates on improving the damping levels in a research composite shell/titanium spar fan blade, developed by NASA-Lewis and Pratt and Whitney. First, the geometry and material definition of the existing composite fan blade are presented. Second, methods for sizing and locating the damping patch are presented based upon the modal strain energy method. The layered damping patch is composed of outer layers of a TEDLAR (or KAPTON) barrier film, which encompasses a viscoelastic damping material and loose- weave scrim cloth (creep protection). Two different patch sizes and locations are discussed to provide maximum damping as well as optimal damping. Finally, procedures are outlined for fabricating the integrally damped composite fan blades. Fabricated blades will be tested at the NASA-Lewis vacuum facility.