Vibration of metal plates covered with vibration damping layers

Abstract

It is well known that thin metal plates used for covering machines and vehicles vibrate as a result of the original vibrations and airborne sounds, and through their own resonances and radiation properties become new noise sources. These disturbing effects can be fought by stiffening the plates or using layers of high internal viscosity on the plates. For practical purposes our research group has carried out a series of measurements in order to examine the effectiveness of vibration damping layers. Generally, we investigated plates of 2×1 m2 which, at the same time, we coated with viscoelastic damping layers of different compounds. The method of investigation was in one case excitation by an electromagnetic transducer driven with constantly varied frequency or with white noise of third-octave bands, and in the other case an impulsive excitation carried out by hitting the plate. The latter method seemed to be more suitable for determining the damping factor as a function of frequency. The frequency dependence was investigated using third-octave band filters. The results showed that the resinous layers made with filler, and smeared evenly over the plate, reduced the bending vibration of the plates by a factor which was a function of frequency. When the damping material was added as a band on the sides of the plates we obtained good results only if the plate was mounted in a frame and the frame was excited. At the same time we investigated the added effect of multi-layered sheets and found the changes to be dependent upon the experimental procedure, and not always significant. Our results were given to the industrial organizations dealing with noise abatement and use will be made of these results in the production of trains and buses.