In situ determination of dynamic stiffness for resilient elements

Abstract

An in situ method for the measurement of a resilient elements dynamic transfer stiffness is outlined and validated. Unlike current methods, the proposed in situ approach allows for the characterisation of a resilient element whilst incorporated into an assembly, and therefore under representative mounting conditions. Potential advantages of the proposed method include the simultaneous attainment of both translational and rotational transfer stiffness components over a broad frequency range without the need for any cumbersome test rigs. These rotational components are obtained via the application of a finite difference approximation. A further advantage is provided via an extension to the method allowing for the use of remote measurement positions. Such an extension allows for the possible characterisation of hard-to-reach elements, as well as the over-determination of the problem. The proposed method can thus be broken into two sub-methods: direct and remote. Preliminary results are shown for the direct method on a simple mass-isolator-mass laboratory test rig along with a more realistic beam-isolator-plate system. Validation of this method is provided for by a transmissibility prediction, in which an obtained dynamic stiffness value is used to predict the transmissibility of a separate system. Further results are presented for the remote case using a beam-isolator-plate system. In all cases the results are obtained over a substantial frequency range and are of a sufficient quality to be used as part of structure borne sound and vibration predictions.