Nonlinear Dynamic Behaviour of Typical Mechanical Structures

Abstract

The aim of this paper is to emphasize nonlinear dynamic behaviour of some mechanical structures in order to illustrate that such behaviour is not only of academic importance. The assumption of linear behaviour has to be verified to validate consistency of results of a modal analysis test. Popular methods to check linearity are Maxwells reciprocity theorem and the principle of superposition. In this paper, tests on five mechanical structures are represented: checks on linearity indicated the presence of some typical nonlinear dynamic behaviour. These examples are selected to give a survey of common causes of nonlinear dynamic behaviour: backlash and friction in connections, nonlinear type of damping, nonlinear stiffness resulting from the geometrical shape of the structure or the dynamic properties of the material. Following structures have been tested: a longitudinal beam of a car-frame, a roundness measuring-instrument, the IGLOO-module of ESA-spacelab, the grinding wheel-workpiece contact area and the dynamical properties of rubber elements. These structures show a degree of nonlinearity too significant to be neglected if accurate measurements are desired.