1 Viscoelastic Damping of Structural Joints for Disturbance Isolation and Vibration Attenuation

Damping is an important consideration in state-of-the-art space missions, as it is often used to mitigate launch loads and low-amplitude spacecraft disturbances. Although damping treatments are very effective, their implementation may be limited due to mass, cost and schedule constraints, or due to added complexity to the system design and verification efforts. Damped joints are a simple and cost effective damping option which can be easily incorporated into a spacecraft design. This approach can be used at bus panels, equipment interfaces, isolator ball joints and flexures, and other structural joints. In addition to increased damping, the addition of viscoelastic material to structural joints results in improved joint performance due to removal of nonlinear effects of friction and gaps. A viscoelastic damped ball joint was developed and demonstrated on three applications: 1) tuned-mass damping, resulting in 30-50 % critical damping to fixed-base damper modes; 2) acoustic test panel supports, resulting in up to a factor of 4 reduction of acoustic loads; and 3) reaction wheel isolator struts, resulting in 5-10 % critical damping of isolator modes (and higher at strut modes). An overview of the damped joint design, analysis and testing will be presented in this paper. Nomenclature f = frequency T = temperature G*(f,T) = complex shear modulus as a function of frequency and temperature G (f,T) = shear storage modulus as a function of frequency and temperature (f,T) = loss factor as a function of frequency and temperature I