The practical problems of assessing damping treatments

Abstract

This paper first discusses the practical situations in which damping treatments can be beneficial in attenuating noise and vibration. Consideration is given to systems under shock, periodic and random excitation. Special reference is made to jet and propeller excited vibrations of aeroplane structures (to the associated stress levels and transmitted noise) and also to vibrations excited by boundary layer pressure fluctuations. The manner in which some of these response quantities depend on the basic structural parameters (stiffness, damping and mass) is next discussed, with a view to finding the most desirable characteristics of an artificially-damped structure. This leads to the development of certain criteria for assessing the effectiveness of damping treatments; the limitations, in this respect, of the simple flexural loss factor become apparent. The problem of selecting the best damping treatment for a given situation is then dealt with. The difficulties of estimating the damping and stiffness of a treated reinforced plate structure are considered and the measurement of the damping of such systems is also discussed, with descriptions of some recent work. Finally, the needs for further work are outlined.