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This paper documents the design, fabrication, and testing of a co-cured damped composite strut that uses the extension-shear coupling mechanism of off-angle composite materials to enhance the damping performance of a viscoelastic material. The viscoelastic material was placed between two graphite shells. The inner shell contains plies oriented at a positive ply angle in the first half of the tube and plies oriented at a negative ply angle in the second half of the strut. Due to the extension-shear coupling, the tube center section rotates when the tube undergoes axial deformation. The outer tube plies are oriented in the opposite manner so that the tube center rotates in the opposite direction as the inner tube for a given axial deformation. The relative rotation between the two shells places the viscoelastic material into shear providing damping, where the ply is determined that maximizes the damping performance. The same extension-shear coupling mechanism also allows the tube to damp torsion motion. The two shells were hard mounted to each other at their ends, by replacing the viscoelastic material with composite material, so that both tubes carry static loads. A finite element model was developed to predict axial and torsion properties. Stiffness properties were `measured' analytically via static condensation of the complex stiffness matrix. Trade studies were performed to determine optimal ply orientation and to determine the strut's effectiveness as a torsion damper for structural components such as a damped composite drive shaft. The approach is validated by performing a modal survey on a fabricated damped strut and on a baseline undamped strut (i.e. viscoelastic material is replaced with 4 plies of unidirectional graphite/epoxy with fibers oriented in the hoop direction). Natural frequency damping levels are presented for both strut's first bending and first axial modes.
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