Constrained layer damping

Constrained-Layer Treatments. Constrained-layer damping treatments consist of a thin layer (/ m) of viscoelastic material sandwiched between a base material and an outer constraining layer of sheet metal or other stmctural material. Some of these treatments are available with self-adhesives on both sides of the viscoelastic material and act as a bonding agent between the base and constraining layers others have the constraining layer already bonded to the inner layer so they need only be appHed to the base material. 

Table I. Comparison of Extensional and Constrained Layer Damping...

The development of constrained-layer damping materials through the use of dynamic mechanical testing and mathematical modeling has been described. It has been shown how different types and loadings of fillers will affect the measured viscoelastic properties of chlorobutyl rubbers. It has then been shown how these changes will affect the damping performance of these materials in constrained layer structures. 

Figure 7. Constrained-layer damping of extensional and flexural vibrations of bars and plates.

Constrained-Layer Damping Materials for Control of Noise and Vibration, Soundcoat Company. Inc.. Publication 118010MTP. 

Wetton XSl has described the mechanical characteristics for vibration damping materials in terms of the frequency and temperature dependence of the viscoelastic properties of polymeric materials. Use of polymeric materials in free-layer and constrained layer damping configurations has been discussed in the literature by Ungar (10-12). Kerwin (13.14). and others (15.16). 

Figure 9. Measured Loss Factor of Segmented Constrained Layer Damping for Various Segment Lengths on a 36-in.-Long Bar (The curve for 3 segments may actually be for 2.) (Adapted from ref. 22)...

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. 

Noise and vibration measurements are made with microphones and accelerometers. Sometimes, sophisticated instruments like laser vibrometers are used for NVH work. Common noise fixes include cutting slots and/or chamfers on the brake pads and linings, the application of constrained layer damping noise insulators to the back of the brake pad shoe plates, and detuning the resonant frequency of mechanical brake corner components. 

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.

Figure 13.13. Proposed use of gradient IPN s as constrained layer damping materials. Left, A is the substrate to be damped, B is a gradient IPN with the plastic component increasing in concentration toward the outside, as shown on the right.

The advantages of the latex IPN constrained layer damping system are twofold ... 

Figure 8.6. Extensional and constrained layer damping of formula G as a function of temperature. ...

L. H. Sperling, T.-W. Chiu, R. G. Gramlich, and D. A. Thomas, Synthesis and Behavior of Prototype Silent Paint, J. Paint Technol. 46,47 (1974). Constrained layer damping. Latex IPNs. Methacrylic/acrylic compositions. 

Constrained layer damping, where a stiff material is placed on the top of the damping polymer to increase the shearing action. Sometimes a simple sandwich arrangement is used, where two thin layers of sheet metal (the bread) have a thin layer of polymer between them (the jelly). 

Liu, Q. Chattopadhyay, A. Gu, H. and Zhou, X. Use of segmented constrained layer damping treatment for improved helicopter aeromechanical stability. Smart Mater. Struct., 9 (2000), pp. 523-532... 

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