Co-Cured Extension-Twist Coupled Damped Composite Strut

Abstract

A co-cured damped composite strut that uses the extension-shear coupling mechanism of off-angle composite material to enhance the damping performance of a viscoelastic damping material is presented. The damping material was placed between two graphite shells. Composite material replaced the damping material at each strut end. The inner shell contains plies oriented at a positive ply angle in the first half of the strut length and plies oriented at a negative ply angle in the second half. Due to the extension-shear coupling, the shell center section rotates when the strut undergoes extension deformation. The induced torque of each shell cancel each other so that there is a negligible net twist at each strut end. The outer shell plies are oriented in the opposite manner so that the outer shell center rotates in the opposite direction. The relative rotation at the strut center between the two shells places the damping material into shear, providing damping. Finite element analysis was used to determine optimal damping material shear modulus and ply orientation to maximize strut imaginary stiffness. Modal tests were performed on undamped and damped struts. Damping increased by factors of 6.2, 12.8, and 29.3 for first bending, extension, and torsion modes, respectively, over the undamped strut. Corresponding strut bending, extension, and torsion stiffness decreased by 50, 14, and 50%, respectively.