Challenging an experimental nonlinear modal analysis method with a new strongly friction-damped structure

TL;DR

This paper demonstrates that a recent experimental nonlinear modal analysis method effectively characterizes strongly nonlinear, friction-damped structures, validated through a specially designed test rig with significant damping and frequency shifts.

Contribution

The study introduces a new test rig and validates the extended periodic motion-based modal analysis method for highly nonlinear systems with frictional damping.

Findings

Method accurately tracks modal properties despite large nonlinearities.

Single-point excitation suffices for modal property identification.

Computed responses align well with experimental data.

Abstract

In this work, we show that a recently proposed method for experimental nonlinear modal analysis based on the extended periodic motion concept is well suited to extract modal properties for strongly nonlinear systems (i.e. in the presence of large frequency shifts, high and nonlinear damping, changes of the mode shape, and higher harmonics). To this end, we design a new test rig that exhibits a large extent of friction-induced damping (modal damping ratio up to 15 %) and frequency shift by 36 %. The specimen, called RubBeR, is a cantilevered beam under the influence of dry friction, ranging from full stick to mainly sliding. With the specimen's design, the measurements are well repeatable for a system subjected to dry frictional force. Then, we apply the method to the specimen and show that single-point excitation is sufficient to track the modal properties even though the deflection shape changes with amplitude. Computed frequency responses using a single nonlinear-modal oscillator with the identified modal properties agree well with measured reference curves of different excitation levels, indicating the modal properties' significance and accuracy.