Nonlinear joint model updating in assembled structures

Dynamic response of mechanical structures is significantly affected by joints. Joints introduce remarkable frictional damping and localized flexibility to the structure; hence, to obtain a more accurate representation of a system's dynamics, it is crucial to take these effects into account. This paper investigates the application of finite-element model updating on characterization of a nonlinear joint interface. A thin layer of virtual elements is used at a joint location to represent the nonlinear behavior of the coupling in the tangential direction. The material properties of the elements are described by a nonlinear constitutive stress-strain equation that defines the nonlinear state of the joint interface. In this study, Richard-Abbot elastic-plastic material was considered, which is capable of characterizing energy dissipation and softening phenomena in a joint at a nonlinear state. Uncertain material parameters are adjusted to minimize the residual between the numerical and experimental nonlinear frequency responses. Minimization was carried out based on iterative sensitivity-based optimization. The procedure was implemented on an assembled structure consisting of two steel threaded pipes coupled to each other by a nut interface. It was demonstrated that the proposed technique significantly reduced the uncertainties in the joint modeling and led to a more reliable description of the assembled structure.