Substructuring of a Nonlinear Beam Using a Modal Iwan Framework, Part I: Nonlinear Modal Model Identification

This work uses a method whereby weak nonlinearity in a substructure, as typically arises due to microslip in bolted interfaces, can be captured and modeled on a mode-by-mode basis. The method relies on the fact that the modes of a weakly nonlinear structure tend to remain uncoupled so long as their natural frequencies are distinct and higher harmonics generated by the nonlinearity do not produce significant response in other modes. A single degree-of-freedom (DOF) system with an Iwan joint, which is known as a modal Iwan model, effectively captures the way in which the stiffness and damping depend on amplitude for each mode. This work presents the experiments used to generate these modal Iwan models. In a companion paper this model is assembled to another component using dynamic substructuring techniques to estimate the amplitude dependent frequency and damping of the full assembly.