Damping Layers

1 Application of Dampers and Isolators Discrete Design OF Dampers and Isolators for Equipment 

FIGURE 14.13 Free and constrained viscoelastic-layer damping treatments, (a) Unconstrained and (b) constrained. (Adapted from Corsaro, R. D. and L. H. Sperling, eds., Sound and Vibration Damping with Polymers, ACS Symposium Series 424, R T. Weissman and R. P. Chartoff, Washington, DC, p. 115, 1990.) 

K = constant, often the contact area is used as this value. 

An interesting example, albeit low-technology example, is the common stainless-steel kitchen sink. Historically, stainless-steel kitchen sinks were sprayed with a damping material that covered the entire bottom of the sink. Recently, sinks have been produced that have pads of damping material adhered to the bottom of the pans. The pads are placed in locations of high vibration, where they will be most effective. 

FIGURE 14.14 Effect of free damping layer thickness on loss factor. (Adapted from Oberst, H., Acustica, 2, p. 186, 1952.) 

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The modern ski is a good example of the use of composites to make a product with unique properties (Figure 8.3). The top and sides are composed of ABS polymer that has a low Tg allowing it to remain flexible even at low temperatures. It is employed for cosmetic and containment purposes. PU forms the core and a damping layer that acts as filler and to... 

Only thin layers of powder may be dried since in thick layers the surface may acquire a dry skin, leaving a damp layer underneath. This may upset the uniformity of burning. 

The Free Viscoelastic Layer. As we see in Figure 3, the free viscoelastic layer is bonded to the plate to be damped. As the plate vibrates in bending, the viscoelastic layer is deformed principally in extension and compression in planes parallel to the plate surface. Such damping layers have long been known, and at first were applied more-or-less empirically. In the early 1950s Oberst 3.,D and Lienard (, ) published analyses describing quantitative analytical models of free layer behavior. 

Sound and vibration damping research with IPNs began in the early 1970 s and resulted in the formation of a constrained layer damping system with the inner damping layer a latex IPN paint (3 ). The constrained layer system results in a shearing effect within the IPN layer along with flexural and extensional motions as the composite panel vibrates. The added shear mechanism, not present in extensional applications, increases the amount of energy that is dissipated in each vibrational cycle. 

Apart from this, combined and multilayered films containing a damping layer foamed by Cl vapors are known [3,24]. 

A plastic damping layer can be applied to one or both sides of the metal (unconstrained damping), or the damping layer can be sandwiched between the panel and a thin metal skin (constrained damping Fig. 7.14). Often the metal skin, typically 0.5 mm thick and the polymer layer 0.2 mm thick are supplied with a self-adhesive layer. 

Figure 7.14 Sections of (a) Floor pan of a car, showing the external and internal damping layers, (b) Constrained layer damping of a flat metal panel.

A common configuration involves sandwiching the polymer between two sheets of metal to make a true composite material. While such composites exhibit optimum damping characteristics, they necessarily have limited form-ability. Alternatively, damping tapes (Wollek, 1965) have found important applications. In these systems, the adhesive serves also as the damping layer, and aluminum foil as the backing multiple layers may be applied with good effect. 

Uncoupling the mass from the ground motion up) by introdueing a base isolation by an elastic and damping layer between surrounding ground and the base of the edifice (Chopra 2000, pp. 741-766). 

They demonstrate the variation of the acoustic impedance of the nanocomposite polymeric materials over 30 and 40% to be possible for the longitudinal and shear acoustic waves, respectively, within the same technological procedure. At that, the longitudinal and shear bulk acoustic wave velocities may be purposefully altered over 40 and 29%, respectively. These results may be useful in the development of the matching and damping layers with the low acoustic impedance for various acoustic devices. 

Fig. 1.11. Bonded overarm with stiffening and damping layers, (a) Original bonded overarm, without any stiffening or damping layer, (b) Overarm with one layer of sound-deadening steel, (c) Two layers of sound-deadening steel, (d) Three layers of sound-deadening steel and a PVC layer.

When designing metallic structures, the incorporation of damping is often through the use of damping layers or discrete dampers (such as automobile shock... 

Figure 14.14 demonstrates the effect of damping layer thickness, modulus, and loss factor on the composite loss factor. 

The kitchen sink example of free damping layers is a one-dimensional vibration (normal to pan) application. For this example the amplitude of vibration will depend spatially on the two directions perpendicular to the normal vibration. Often damping layers are applied to long slender beams or rods where the transverse vibration can also be described as one dimensional (normal to the long axis). In this case, the amplitude of vibration typically is dependent only on the distance along the long axis. 

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