The subject of vibration control has received considerable attention due to vibration problems occurring wherever there are rotating or moving part in a machine. Apart from the machinery itself, the surrounding structure also faces the vibration hazard because of these vibrating machinery. So, there is a need to reduce unwanted vibrations. Many researchers have done research and given their views to reduce the unwanted vibration. Some of them have investigated the model for optimum control of vibrations.
The vibration control has been carried out by several means including reduction of excitations, avoiding of resonance by proper choice of stiffness and mass parameters, use of vibration absorbers and dampers. The dampers are of viscous damping type, coulomb damping, materials or hysteretic damping types using conventional materials. For vibration control over a wide range as in aerospace, automotive and other applications, the above methods have limitations and the use of viscoelstic damping involving use of polymeric or elastomeric materials is finding considerable importance. Sandwich structure with embedded viscoelastic materials are widely used in aerospace, aeronautical, automobile industries due to their performance in attenuating structural vibrations. The vibratory energy is dissipated through the shear strain induced in the soft viscoelastic layer by relative displacements of the stiffer surface layer. Surface damping treatments are usually classified according to whether the damping material is subjected to extensional or shear deformation. The former is referred to as unconstrained or free layer damping treatment and the latter as constrained layer damping treatment which is more efficient than unconstrained treatment for a given added weight. The growing use of such treatments has motivated the conduct of many studies in order to predict the dynamic behavior of visco-elastically damped structure.
Polymeric materials, essentially visco-elastic materials which are easily available with high damping can be used to control vibratory response. Such materials cannot be used alone because of strength and rigidity reasons, and hence a composite structure of metal and polymers can achieve both strength and high damping. There are two types of such a damping treatment, namely, unconstrained and constrained.
It is seen in different studies that the use of composite material (sandwiched metallic plates and polymers) gives better reduction in the vibration response of a structure as compare to the any other mode of vibration control.
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