AU596429B2

AU596429B2 - A damping layer

Info

Publication number: AU596429B2
Application number: AU74728/87A
Authority: AU
Inventors: Egidius Arens
Original assignee: Fried Krupp AG
Current assignee: Fried Krupp AG
Priority date: 1986-06-26
Filing date: 1987-06-25
Publication date: 1990-05-03
Anticipated expiration: 2007-06-25
Also published as: EP0250883A3; EP0250883A2; AU7472887A; DE3621318A1

Description

COMMONWEALTH OF AUSTRALIA Patents Act 1952 C O M P L E T E S P E.C T IO N 6429

(ORIGINAL)

Application Number Lodged Complete Specification Lodged Accepted Published Priority 26 June 1986 fhis cjcuCw1ent CO1-tai0S1 kmendmeflts made ull',f Ktin C49 an~d is correct 'r n ting.

Related Art Name of Applicant Address of Applicant Actual Inventor/z Address for Service :FRIED. KRUPP GESELLSCHAFT BESCHRANKTER HAFTUNG

MIT

Altendorfer Strasse 103, D-4300 Essen 1, Federal Republic of Germany Egidius Arens F.B. RICE CO., Patent Attorneys, 28A Montague Street, Balmain N.S.W. 2041 Complete Specification for the invention entitled: A DAMPING LAYER The following statement is a full description of this invention including the best method of performing it known to us:la- A T1anmp"j Leuer The present invention relates to a damping layer of the type having a high internal loss factor, this being used to dampen out flexural resonance.

Flexural resonances caused by the vibration of power systems such as engines or equipment installed within a vehicle occur in the walls of such vehicles. These flexural resonances are then radiated by the wails in the form of noise. Flexural resonance is a particular disadvantage, for example, in submarines, since 1Q,'it picked up as noise or hull noise by the sonar systems used on board such submarines and thus frustrates attempts made to obtain bearings on targets. It is known from the manual by Brueel Kjaer, The Measurement of Mechanical Oscillation and Impact, September, 1970, that flexural resonance within a structural element can be damped if the surface of such elements is ',"coated with a material having a high internal loss factor. Such a damping procedure is used, for example, in the automobile tt industry. The damping becomes even more effective the thicker the coating with, for example, elastico-viscous material used as 2 a damping material, the damping increasing with the square of the I' atio of the thickness of the layer of elastico-viscous material and the wall. In practice, coating thicknesses that are a multiple of the thickness of the wall are used.

1111 ;I 2 It becomes a problem to install a damping layer that provides sufficiently high damping effect if the space available for the coating is limited, as is the case, for example, within vehicles and, in particular, within submarines.

The present invention seeks to create a damping layer of the type described in the introduction hereto, and which, applied to the wall as a thin layer, effectively damps out flexional resonances.

The present invention consists in a damping layer that contains damping material having a high internal loss factor and used to damp resonance oscillations, said damping layer comprising at least one layer of damping material and at least one layer in the form of a fibre mat and which is of high tensile strength, at least in the direction of propagation of the flexural waves.

The present invention also provides a process for the production of a damping layer wherein damping material of o: a first layer is applied thinly to a clean surface portion 20 of a component that radiates the flexural waves; a second layer in the form of a fibre mat is pressed onto said first layer and thereupon, without delay, another layer of damping material is applied, with a further fibre mat 1' layer being pressed onto this, and so on.

-1 25 A layer of an elastic or elastico-viscous material having high internal losses is applied to constructional elements that radiate flexural waves. Rubber, polyurethane, sound absorbing or anti-drumming lagging or compounds can be used to advantage as elastic or q\iso- elastla e.aic- -vis-ous material. The fibre mat arranged as a second layer is of high tensile strength, at least i r: ii a i 7 3 in the direction in which the flexural waves are propagated. The tensile/compression forces when the constructional element flexes are converted into extreme shearing forces and damped out by reason of the high internal loss factor of the damping material. The arrangement of the first layer of damping material next to the component is particularly effective.

A particular advantage of the damping layer according Cpe'erred ec rner±M<2nE o to,the present invention is that it is simple to apply to any structural element since, for example, -tiuvc material used as a damping material, can be brushed on in the same way as a coat of paint and the fibre mat can be bent into any shape, so that it can follow even complicated walls in a very simple manner.

The advantage of using the first damping layer as the means for bonding the structure to the component wall lies in the fact that the need for a special bonding agent, for example, in the form of an adhesive, is avoided.

Installation on structurally complicated walls can be carried out very simply by embedding fibre mat layer in the damping material layer.

Since high tensile strerjth fibre mats can be made extremely thin entails the advantage that the layer of damping material can be made considerably thicker than the layer of fibre mat and that, despite this, it is possible to produce a thin damping layer. The layer that is resistant to bending is then spaced from the structural element that is excited to t t C Cr I St C C(

A

-4flexural oscillation, the space so formed being filled with material that absorbs the shearing stresses and provides a damping effect. However, the thickness of the layer of damping material need no longer amount to a multiple of the thickness of the layer of the structural element, in order to arrive at such damping behaviour, as is the case, for example, with conventional coatings of damping material alone.

According to a further preferred embodiment of the present invention it is particularly advantageous to use fibre mats of carbon fibres, since fibre mat layers with a high level of tensile strength can be made extremely thin using such material and can thus be made flexible. As an example, the thickness of such a layer amounts to S 15 3/10 mm. The tensile strength of the carbon fibres is in the range 2 x 103 to 3.4 x 103 N/mm 2 The construction of a damping layer using a plurality of fibre mats between layers of damping material permits *0@o absorption behaviour relative to flexural waves, such as damping layers of a sandwich-type structure, in which a thin metal sheet is installed on the visco-elastic layer.

Compared to sandwich construction, the damping layer oC.o disclosed has the decided advaqtage that during installation there are no restrictions cqused by the thickness of the metal layer, but rather, the damping layer can be installed in any shape and built up to the same thickness over the whole of the wall.

By using damping material of different elasticity moduli for the various layers and using different materials in i the various fibre mat layers, the frequency-dependent transmission behaviour of the structural elements with the damping layer can i be so influenced that a rectilinear frequency response can be achieved and no more clearly defined natural oscillations or modes can be formed in the constructional element.

Because of the extremely thin structure and the high quality of this damping layer, an application to the inner walls i0 0 of a submarine is particularly advantageous in that only damping 00 0 004 6 layers that are extremely economical with regard to space can be 0O4 00o installed in submarines, in order to ensure the continued functionality of the boat. In particular, the damping layer 0 according to the present invention is of particularly low mass S000o 0 0 and low weight, with the result that the manoeuverability of the 0 00 submarine will not be affected.

00 0.00 The advantage in using the damping layer according to the present invention in a machine base lies in the fact that the propagation of flexural resonances in machinery beds is 2b prevented; such flexural oscillations can occur in a submarine in these structural elements, even though engines and other rotating Smachinery are spring mounted, since its mass cannot be of unrestructed size since submersibility must always be considered.

6 tsco -elasbiC- Regardless of the intended use, an elastic or ee- material can be used as a damping material having a high internal loss factor.

A process for the production of a damping layer according to the present invention, is of Scons'sml en, particular simplicity- gElpessing the fibre visco- elas' c mat onto the previous layer of, for example, -e's v ,ee ,material, the fibre mat can be formed without any problem to the Sshape of the hull wall, so that the structural element can be Scovered without any gaps by the damping layer. The advantage of plastering on an elastico-viscous material as the last layer lies in the fact that this simultaneously provides a protective coating for the structural element.

The present invention will be described in greater detail below with reference to the drawings appended hereto and showing an embodiment for a damping layer used to damp out flexural waves.

In the drawings:- P2O Figure 1: a cross section through a damping layer that is bonded to a structural element; Figure 2: a diagram showing the damping curve as a function of frequency.

7 7- Figure 1 shows a cross section of a section of a wall for example, 10 mm thick, of a structural element on which a damping layer (20) has been applied. This structural element is acted upon by flexural resonances. The damping layer (20) consists of a plurality of layers (21, 22, 23, 24) of an elastic or \j'SCo- e SLc material having a high internal loss factor, this being used as damping material, rubber or sound-absorbing material, and of intermediate layers (25, 26, 27) in the form of high tensile strength fibre mats made of, for example, carbon fibre. The individual layers (21, 25, 22, 26, 23, 27, 24) are bonded together internally and the first layer (21) is bonded to the wall The structures of the individual layers (21, 25, 22, 26, 23, 27, 24) alternate with each other so that in every instance a fibre mat layer is followed by a layer of damping material. The first and preferably also the last layer (21, 24) is in each instance of damping material.

The thickness of the layers (21, 22, 23, 24) of damping material (is equal and in each instance amounts to approximately 1 mm, and the thickness of the layers (25, 26, 27) in the form of fibre mats is, at approximately 0.3 mm, considerably less. The total S'thickness of the damping layer (20) is thus approximately 5 mm, and is approximately half as thick as the wall to which the damping layer (20) is applied.

SI

-17 8 As an example, a sound absorbing mass such as produced by the firm of Stankiewicz and designated 2K 601 is used with fibre mats that are of carbon fibres, such as are commercially available and are used, for example, in aircraft construction.

The carbon fibre mats are of a mesh-like structure having linen bonding, with in each instance a plurality of fibres being combined so as to form the warp and/or the weft.

In the example that is shown in figure 1 the layers (21, 22, 23, 24) consist of sound damping material; all are of the same structure and all have the same characteristics,and the layers 26, 27) are of the same fibre mats. It is also possible to use damping material with different elasticity moduli and fibre lj c.

maTs uo- varius tiieril s i ah layer..L t t *In the production of the damping layer (20) the sound absorbing mass is applied to the wall (10) in a layer that is as thin as possible. The wall (10) must be thoroughly cleaned and free of 0' rust. It is also possible to apply the sound absorbing layer over a coat of paint. Immediately thereafter the carbon fibre mat is pressed onto this layer so that the two layers are bonded firmly together and adhere to the wall Next, more sound absorbing mass is applied. After a hardening period, the multi-layer damping layer produced in this manner displays a damping characteristic as is shown, by way of example, in figure 2.

)J.

9 -9- Figure 2 which shows the frequency-dependent damping behaviour of a multi-layer damping layer that has been applied to a steel plate mm thick. The frequency f/Hz is the ordinate and the damping factor "VdB is the abscissa. The curve (30) shows the envelope of the flexural resonances that are propogated as modes in the uncoated steel plate. Two maxima can be seen plainly at the two frequencies (fl and f 2 The objective of flexural wave damping or hull noise damping is to dampen the maxima so that the damping behaviour remains constant throughout the frequency range. Using a coating on the steel plate with a multi-layer damping layer as shown by way of example in figure 1 it is possible to achieve a damping of more than 20 dB corresponding to the curve (31).

The example shown in the drawings is a section of a structural element shown as a wall. Preferably this wall is part of the internal or outer hull of the submarine or of a base that supports machinery.

S4 1 t i F i

Claims

2. A damping layer as defined in claim 1, wherein the layer of damping material is closer to the components that radiate the flexion waves than the layer of the fibre mat.
3. A damping layer according to claim 2, iherein the damping material forms the first layer and, simultaneously, the bonding agent to the components that radiate the flexural waves, and the fibre mat forms the second layer that is adjacent thereto.
4. A damping layer as defined in claim 3, wherein the fibre mat is imbedded in the damping material. A damping layer as defined in claim i, 2 or 3, wherein the thickness of the fibre mat layer is considerably less than the thickness of the layer of damping material.
6. A damping layer according to claim i, 2 or 3, wherein the fibre mat consists of carbon fibres.
7. A damping layer according to claim 2, wherein the layers that follow the second layer consist of layers of damping material and of fibre mat in alternation.
8. A damping layer as defined in claim 7, wherein the thicknesses of the layers that are of daxping material are equal.
9. A damping layer as defined in claim 8, wherein the damping material in the various layers of damping material is of various elasticity moduli. A damping layer as defined in claim 8 or 9, wherein each layer of fibre mat consists of a different material. ttr C I I
11. A damping layer as defined in claim 1, 2 or 3, when applied to a base used for propulsion machinery in submarines.
12. A damping layer as defined in claim 1, 2 or 3 wherein the damping material is an elastic or visco-elastic material.
13. A process for the production of a damping layer to damp flexural waves as claimed in any one of the preceding claims, comprising the steps: application of at least one layer of a damping material having a high internal loss factor as a first layer to a clean surface portion of a component which radiates the flexural waves, application of at least one layer of a material with high tensile strength, at least in the direction of propogation of the flexural waves, in the form of a fibre mat as a second layer to the first layer, and application of a further layer comprising either at least one layer of the damping material and/or at least one layer of the material in the form of a fibre mat and so on until a predetermined thickness and structure of the damping layer is achieved.
14. A process as defined in claim 13, wherein damping material as applied as the last layer. A damping layer substantially as hereinbefore described with reference to the accompanying figures.
16. A process for the production of a damping layer substantially as hereinbefore described with reference to the accompanying figures. DATED this 21 day of February 1990 FRIED. KRUPP GESELLSCHAFT MIT BESCHRANKTER HAFTUNG Patent Attorneys for the Applicant: F.B. RICE CO. 1 oly 74 728/87 21 27 *m m 4 21 n Fig. 1 dBk f flf 2 Hz Fig. 2