Predicting Damping of a Cantilever Beam With a Bolted Joint Using Quasi-Static Modal Analysis

Abstract

Bolted joints are common in assembled structures and are a large contributor to the damping in these assemblies. The joints can cause the structure to behave nonlinearly, and introduce uncertainty because the effective stiffness and damping at the joint are typically unknown. Consequently, improved modeling methods are desired that will address the nonlinearity of the jointed structured while also providing reasonable predictions of the effective stiffness and damping of the joint as a function of loading. A method proposed by Festjens, Chevallier and Dion addresses this by using a sort of nonlinear modal analysis based on the response of the structure to quasi-static loading. This was further developed by Allen and Lacayo and thoroughly demonstrated for structures with discrete Iwan joints. This work explores the efficacy of quasi-static modal analysis for 2D and 3D finite element models in which the geometry, contact pressure and friction in the joint are modeled in detail. The mesh density, contact laws, and other solver settings are explored to understand what is needed to obtain convergence for this type of problem. For the 2D case study, the effect of bolt preload and coefficient of friction are explored and shown to produce reasonable trends. Three dimensional models prove far more challenging and significant effort was required to obtain convergence and then to obtain results that are physically realistic; these efforts are reported as well as the lessons learned.