Nonlinear Response Behaviour of Passive Isolators Subjected To Low Values of Base Sine Excitation

Abstract

Passive isolators are widely employed in reducing the vibrations experienced by an equipment. Isolator with linear response is preferred as the isolation is independent of amplitude of excitation. However, an example of such a linear isolator exhibited nonlinear behavior during testing, where the resonance frequency was getting significantly reduced as the amplitude of excitation is increased. This behavior is investigated in this work. It is shown that the isolators exhibit linear response when subjected to rated deformations, but can develop nonlinear type response behavior when the deformations are low and excited through the base. A cubic spring-mass model with the applicable nonlinear parameters is able to represent this behavior. The measured responses and the theoretically estimated responses agree with these characteristics, but needs improvement in the prediction, especially at intermediate levels of excitations. The nonlinearity seen in the force-deformation relation of such isolator appears to be small and the frequency of the free oscillation does not vary much from the linear natural frequency. However, it is shown in this work that a predominant nonlinear response behaviour is developed in the isolators when they are subjected to low levels of base excitation. This nonlinear behaviour needs to be considered when employing such passive isolators in applications where base excitations are present and the deformations are very low relative to the rated specifications.