Experimental Characterization of a New Benchmark Structure for Prediction of Damping Nonlinearity

Spacecraft, airplanes, automobiles, machines and civil structures are all constructed from multiple parts joined by bolts, rivets or other fasteners and these joints lead to large uncertainties in the structural stiffness, damping and can even introduce nonlinearity. Even with the best available simulation tools, it is still difficult to predict the effective stiffness and damping of bolted interfaces, and so these parameters are often assumed and updated after tests have been performed. Damping estimates are critical to limit the resonant vibration response of a structure and thus prevent failure. Even so, it remains poorly understood and available methods for modeling damping are inaccurate and computationally expensive. A new benchmark structure has been created that is designed so as to be predictable with current simulation tools. This paper presents a thorough experimental characterization of this new benchmark structure using the Hilbert transform method applied to modally filtered time data. The nonlinear frequency and damping of each mode is characterized for various levels of bolt preload and excitation amplitude. The interfaces of the bolted structure are also characterized in detail by measuring the contact pressure distribution using pressure sensitive film. The resulting data presents a set of well characterized tests that can be used to validate numerical methods that seek to predict the nonlinear behavior of bolted interfaces.