On Measuring Dynamic Properties of Damping Materials Using Oberst Beam Method

Abstract

The Oberst Beam Method is widely used for the measurement of the mechanical properties of damping materials. This method is a classical method based on a multilayer cantilever beam which consists of a base beam and one or two layers of other materials. The base beam is almost always made of a lightly damped material such as steel and aluminum. If the Oberst Beam Method (OBM) is to be used, it is essential to establish a very accurate measurement methodology. In this respect, the response and the excitation sensors in the Oberst test rig are generally non-contact type. Although the drawbacks of contacting type of transducers are eliminated by this way, there are other critical issues when OBM is used. It is therefore essential to be aware of the parameters that might adversely affect the measured data and also to avoid them as much as possible. Consequently, all the parameters affecting the result need to be optimized in order to obtain the material properties with high accuracy. Although the OBM is referenced in some standards and widely used in scientific studies, detailed information in the literature on how to perform a successful Oberst Beam experiment is very limited. This is the main subject this paper aims to address. In this paper, after setting up the Oberst test rig the effects of various parameters on measured data using an Oberst test rig are examined in an attempt to improve the accuracy of the estimated material properties. Then repeatability measurements are performed and the main parameters affecting the quality of the measured data are identified. After that, extensive tests are performed so as to determine the effect of the amplitude of the excitation force, adverse effects of electromagnetic excitation and the effects of length of the test specimen. Furthermore, it is found that the small differences between individual samples may also affect the results significantly. Finally, some suggestions are given to the potential users of the OBM so as to avoid undesirable effects of certain parameters during such measurements.