APPLICATION OF VISCOUS AND IWAN MODAL DAMPING MODELS TO EXPERIMENTAL MEASUREMENTS FROM BOLTED STRUCTURES

Measurements are presented from a two-beam structure with several bolted interfaces in order to characterize the nonlinear damping introduced by the joints. The measurements (at force levels below macro-slip) reveal that each underlying mode of the structure is well approximated by a single degree-of-freedom system with a nonlinear mechanical joint. At low enough force levels the measurements show dissipation that scales as the second power of the applied force, agreeing with theory for a linear viscously damped system. This is attabuted to linear viscous behavior of the material and/or damping provided by the support structure, which simulates free-free boundary conditions. At larger force levels the damping is observed to behave nonlinearly, suggesting that damping from the mechanical joints is dominant. A model is presented that captures these effects, consisting of a spring and viscous damping element in parallel with a 4-Parameter Iwan model. The parameters of this model are identified for each mode of the structure and comparisons suggest that the model captures the linear and nonlinear damping accurately over a range of forcing levels.