Spider Configurations for Models with Discrete Iwan Elements

Abstract

Lacayo et al. (Mechanical Systems and Signal Processing, 118: 133–157, 2019) recently proposed a fast model updating approach for finite element models that include Iwan models to represent mechanical joints. The joints are defined by using RBE3 averaging constraints or RBAR rigid constraints to tie the contact surface nodes to a single node on each side, and these nodes are then connected with discrete Iwan elements to capture tangential frictional forces that contribute to the nonlinear behavior of the mechanical interfaces between bolted joints. Linear spring elements are used in the remaining directions to capture the joint stiffness. The finite element model is reduced using a Hurty/Craig-Bampton approach such that the physical interface nodes are preserved, and the Quasi-Static Modal Analysis approach is used to quickly predict the effective natural frequency and damping ratio as a function of vibration amplitude for each mode of interest. Model updating is then used to iteratively update the model such that it reproduces the correct natural frequency and damping at each amplitude level of interest. In this paper, Lacayo’s updating approach is applied to the S4 Beam (Singh et al., IMAC XXXVI, 2018) giving special attention to the size and type of the multi-point constraints used to connect the structures, and their effect on the linear and nonlinear modal characteristics.