Application of quasi-static modal analysis to a finite element model and experimental correlation

Bolted joints not only provide critical connections in assembled structures but are also a significant source of damping. The damping induced by joints is often nonlinear, which is currently not captured by typical modeling practices. A method that was recently proposed by Festjens, Chevallier, and Dion addresses this by using a quasi-static loading to infer the effective stiffness and damping of each mode of a structure. Allen and Lacayo further developed this method, demonstrated its efficacy for structures where the joints were represented with discrete Iwan elements, and dubbed the method quasi-static modal analysis. This work expands on those studies by applying quasi-static modal analysis to 2-D and 3-D FE models in which the geometry, contact pressure, and friction in the joint are modeled in detail. Coulomb friction is assumed between the nominally flat contacting surfaces. In order to obtain confidence in the predictions, the mesh density, contact laws, and other solver settings are explored to understand what is needed to obtain accurate results for this type of problem. The studies are culminated with a first ever comparison between measurements and quasi-static predictions of the amplitude dependent natural frequency and damping ratio of a mode of a real structure. The results to date are promising but highlight areas in which further research is needed.