Constraining layer

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. 

Fig. 1. Oscilloscope traces of vibration decay. Characteristics of an undamped reed(a), and a damped reed(b). Steel reed damped with an IPN constrained layer system. (Reprinted with permission from ref. 5. Copyright 1975 Wiley.)...

Broadly speaking, extensional damping utilizes E while constrained layer... 

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

The damping of the composite structure will be affected by the thicknesses of the various layers, stiffnesses of the base and top plates, and the viscoelastic properties of the constrained layer (12). In the present instance (13), it was desired to develop a a broad-band material to damp a model composite structure consisting of a 2.54 cm. base plate (H ), 0.079 cm. polymer layer (H ), and 0.159 cm. cover (Ho)fi oase and cover were composed oi brass with a modulus of 10 Pa. In this instance, the only variable was the viscoelastic behavior of the polymer layer. A temperature range from 0 to 20 degrees Centigrade and a frequency range from 100 Hz to 10 kHz were desired. 

Fig. 2. Schematic of three member constrained-layer structure and mechanism of loss.

Fig. 12. Composite loss factor for three-layer constrained layer assembly as a function of frequency at 5 degrees Centigrade as predicted by the RKU model for the formulations listed in Figs. 10 and 11.

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. 

Capps, R.N. Beumel, L.L. "Influence of Fillers on Constrained-Layer Vibration-Damping Capabilities of Chlorobutyl Elastomers", J. Acoust. Soc. Am. 83, S82(A), 1988. 

Schulze, K.D. "Investigation of Damping Characteristics of Constrained Layer Plates and Small Homogenous Specimens," Thesis, September 1985, Naval Postgraduate School, Monterey, CA 9343-5100. 

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

Cold-Rolled Steel Constraining Layer 3M ISD 112 Viscoelastic Shear Layer... 

Figure 8. Design of a barbell test assembly used to evaluate the extensional damping performance of constrained-layer treatments.

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). 

In contrast to the free layer, the operation of the constrained viscoelastic layer (Fig.9b) involves shear deformation of the layer [47]. Significant dampling can be achieved in the frequency range where there is a balance between the shear stiffness of the viscoelastic layer (2) and the extensional stiffness of the constraining layer (3). In this region the composite loss factor varies approximately as follows. 

The Constrained Viscoelastic Laver. The second of our two general damping treatments is the constrained viscoelastic layer shown in Figure 3(b). The complete constrained-layer configuration is a three-layer laminate comprising base layer to be damped, viscoelastic layer, and constraining... 

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