Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Noninterengaged fiber-containing paper-free web or sheet...
Reexamination Certificate
2000-05-02
2003-02-25
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C428S212000, C428S414000, C428S415000, C428S411100, C248S560000, C248S608000, C248S636000, C248S638000
Reexamination Certificate
active
06524692
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a structural laminate useful for noise and vibration damping when used as a strut, tube, beam, or a stiffened or unstiffened panel or shell structural member having specified stiffness properties.
2. Related Background Art
The use of viscoelastic materials to attenuate noise and vibration in passive damping devices is well known, as disclosed for example in U.S. Pat. No. 3,079,277. Sandwiching elastomeric layers between non-elastomeric layers to produce a vibration-damping laminate is also known, as disclosed in U.S. Pat. No. 4,278,726. The use of opposing fiber orientations to obtain damping in combination with a spring is disclosed in U.S. Pat. No. 3,892,398.
In all of these devices, noise and vibrational energy is damped through development of internal shear stresses in the viscoelastic material. The damping efficiency increases with the amount of internal shear developed. With the exception of U.S. Pat. No. 3,892,398, in which a spring provides energy absorption, damping is produced through tension-tension coupling between the elastomeric and the non-elastomeric layers, resulting in shear development in the viscoelastic material. However, in this type of coupling, shear is developed only at or near the free edges of the viscoelastic material. As a result, after the length of the device reaches the shear length, damping performance is not improved by further increases in length alone.
The tension-shear coupling characteristics of certain fiber-reinforced materials provide another means of creating structural damping. U.S. Pat. No. 5,203,435 to Dolgin describes a composite damping strut having a viscoelastic material sandwiched between two layers of fiber-reinforced composite material, with the fiber-reinforced layers having opposing orientations. The disclosure of Dolgin claims that the tension-shear coupling for layers of linear fibers at an angle to the load direction can produce tension-twist coupling in a tube, thereby producing shear throughout the viscoelastic layer. In fact, this configuration can produce shear only at and near the edges of the viscoelastic layer. Use of a very low-stiffness viscoelastic material can extend the length of the region in which damping occurs, but at the penalty of a reduction of stiffness of the device. The limitations of this edge effect in composite laminates are well known; see, e.g., R. M. Jones, Mechanics of Composite Materials, Hemisphere Publishing (1975). Moreover, when the strut is clamped at the ends, as would be typical in most applications, the non-elastomeric layers will not displace relative to each other. In this case, shear at the edges is eliminated, drastically reducing the desired vibration-damping characteristics. Dolgin also describes the use of “V-shaped” plies having opposite orientations in the reinforced layers, and claims that this configuration produces shear throughout the viscoelastic layer. In this case, shear will be produced only at and near the edges of the viscoelastic layer and in the vicinity of the vertex of the “V” shape. Finally, Dolgin discloses without explanation or supporting data, in
FIG. 8
, sine-wave-shaped plies in which the sine waves in the two reinforced layers appear to be 180° out of phase.
SUMMARY OF THE INVENTION
The present invention is directed to an energy absorbing structural laminate comprising: (a) a first layer of composite material comprising x
1
plies; wherein x
1
is from 1 to 50; and wherein at least 0.5x
1
plies contain fibers arranged in a shape of a continuous curve; wherein said continuous curve is the same or different in different plies; (b) a second layer of composite material comprising x
2
plies; wherein x
2
is from 1 to 50; and wherein at least 0.5x
2
plies contain fibers arranged in a shape of a continuous curve; wherein said continuous curve is the same or different in different plies; and (c) a viscoelastic layer disposed between the first and second layers such that shear strains are substantially distributed throughout the viscoelastic layer when a load is applied to the structural laminate;
provided that no more than 0.75x
1
plies of said first layer and no more than 0.75x
1
plies of said second layer contain fibers arranged in a shape of sine curves in which: (i) angular axes in said 0.75x
1
plies and said 0.75x
2
plies are substantially parallel to a principal maximum load direction, and wavelengths and amplitudes are substantially equal; (ii) sine curves within said 0.75x
1
plies are substantially in phase, and sine curves within said 0.75x
2
plies are substantially in phase; and (iii) a phase difference between said 0.75x
1
plies and said 0.75x
2
plies is within about 30
1
° of 180°.
REFERENCES:
patent: 4278726 (1981-07-01), Wieme
patent: 5087491 (1992-02-01), Barrett
patent: 5203435 (1993-04-01), Dolgin
patent: 5250132 (1993-10-01), Lapp et al.
patent: 5573344 (1996-11-01), Crane et al.
Buchanan Ingersoll P.C.
Dixon Merrick
Koons, Jr. Robert A.
McWilliams Matthew P.
Structured Composites, LP
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