JPH0449713B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a front sheet for a noise panel and a method for manufacturing the same.

In order to attenuate the energy of the noise over a wide range of noise frequencies, so-called "linear" acoustic panels have already been proposed (see GB 2056367A) with the following layer structure:

(a) a non-porous backing layer; (b) an apertured layer having a number of through apertures of predetermined and directed dimensions and spacing such that the apertures define the aperture area characteristics; c) a multivesicular layer fixed between the nonporous layer and the open layer;
In this, a first end of all the vesicles is covered by a non-porous layer and an opposite second end is closed by an open layer, with a number of openings communicating with each of the vesicles, thereby creating a Helmholtz resonance cavity. (d) a porous layer, the pores of which are adhered to the surface of the aperture layer opposite to the surface to which the porous layer is adhered, constituting the outer surface of the panel onto which airborne noise is incident; The dimensions are substantially smaller than the apertures in the aperture layer.

In such panels, the honeycomb and porous layers together provide the necessary wide-range noise attenuation, and the aperture layer is a structural member that constitutes a support for the other layers, and which allows the panel to be placed adjacent to the aircraft. Fixed to the structure. The performance of the panel is impaired when the percentage of the surface area of the open layer that is open between the porous layer and the cells of the multivesicular layer changes substantially from a predetermined value.

On the one hand, layer separation of the panel during and before use should occur as little as possible, and on the other hand, separation of the layers of the panel during and before use should be avoided as much as possible, and on the other hand, separation of the layers should be avoided so that the characteristic open area of the aperture layer would be lost and the efficiency of sound attenuation would be impaired. It is not easy to join four layers of such a panel to each other in such a way that the joining step is accomplished without blocking the many openings and/or holes. The purpose of the invention is to eliminate these difficulties.

Another objective is to provide panels that are lighter than traditional equivalents.

Another object is to provide a panel structure and a method for assembling the same that facilitates the construction of panels with complex shapes.

According to one aspect of the invention, there is provided a front sheet comprising an open layer and a porous layer, the open layer being formed from a synthetic material of fiber/resin matrix.

According to a second aspect of the invention, the invention comprises a fiber-resin matrix composite material having a number of through openings of predetermined and directed dimensions and spacing, such openings defining the opening area characteristics. comprising the steps of preparing an aperture layer, providing a porous layer having pores with dimensions substantially smaller than the apertures in the aperture layer, and adhering the aperture layer and the porous layer face-to-face to form a front sheet; Provided is a method for manufacturing a front sheet for an acoustic panel characterized by the following.

This use of a synthetic material in place of the traditional material, which is aluminum, provides many advantages.

First, the apertures can be formed when the resin matrix of the synthetic material is in a partially cured state. This is probably significantly cheaper than forming the same number of apertures in a metal sheet.

Second, the resin matrix of the synthetic material itself becomes an adhesive medium, which allows the porous layer to adhere to the open layer.

Thirdly, the fibrous component of the synthetic material can be arranged in the pattern, for example by weaving, which itself forms the required number of apertures, thus eliminating the need for a separate aperture formation step at all.

Fourth, special problems with electrolytic corrosion are eliminated. One panel has an open layer of aluminum and a porous layer of stainless steel woven into a screen or felt. If these two layers were to come into electrical contact, electrolytic corrosion could occur in wet conditions. Conventional construction methods may include extra steps to minimize the risk that some portions of the netting or felt will come into contact with the underlying open layer in the finished assembly. The carbon fiber/epoxy resin composite material has essentially the same electrode potential as the upper stainless steel porous layer, so there is no possibility of galvanic corrosion and the assembly to prevent contact between the porous layer and the open layer. No special steps are necessary.

fixing the layers together with the resin by holding one of the adjacent layers in contact with the synthetic material layer when the resin is not fully cured and curing the resin together with both layers held in contact; It is advantageous to employ a method for manufacturing the noise damping device according to the invention, which is characterized by a step whereby a layer of synthetic material is fixed to one of the adjacent layers. Desired resins are so-called "controlled flow" resins, ie resins of sufficiently high viscosity that they remain jelly-like rather than completely fluid during the early stages of curing. It is advantageous to provide a "skin layer" as described below for the absorption of excess resin.

In previously proposed panels, an aperture layer is used to secure the panel to an adjacent support structure. In one embodiment of the invention, a non-porous backing layer is used in such applications. It has been found that the ratio of open aperture area to protruding surface area of the aperture layer is approximately
30% is desirable for fixation in the open layer.

Such a high percentage of open surface area and the desire to keep the panel as light as possible makes it inappropriate to use an open layer to attach the panel to the support structure.

An embodiment of the present invention will be described in detail below with reference to the drawings.

As shown in FIG. 1, the panel 10 includes a non-porous metal backing layer 11 of aluminum alloy to which a porous honeycomb layer 12 is secured by an epoxy resin adhesive E1. Each cell has at least one drainage hole 18. At the other end of the beehive,
An aperture layer 13 as described in detail below is fixed by epoxy resin E2. A fine wire stainless steel mesh 14 is glued to the outer surface of the layer 13. Opening layer 13
and mesh 14 are collectively referred to herein as the front sheet of panel 10.

Panel 10 forms part of the inward facing surface of the nose cowl duct of a turbofan aeroengine, and the panel is one of several arcuate panels located immediately upstream of the engine fan. It is therefore extremely important that the panel does not deteriorate during use, and in particular that there are no parts that become detached from its support structure. This structure has support flanges or support stringers, only one of which is shown at 15. The panel 10 is secured to the stringer by bonding means known to those skilled in the art, but it should be noted that it is the backing layer 11 of the panel that is secured to the panel mounting flange 16 of the stringer 15, and not the aperture layer. Not 13. The gap 17 between the outer surface of the panel 10 and the surrounding structure may remain open, but it can also be sealed or closed, for example using mastic.

Referring to FIG. 2, the aperture layer 13 has three sets 20, 2
It is formed from a woven material of 1,22 threads, each thread consisting of many carbon fibers F. three sets 2
0, 21, and 22 are arranged so as to be at a temperature of 60° C., so that many hexagonal openings H are formed. As can be seen from the superimposed outline C of one of the honey vacuoles of the multivesicular layer 12, there are a number of openings H for one of the open ends of the vacuole C.

The uncured resin R surrounds the fibers F within the threads of the woven material without blocking the openings H. During the manufacture of the panel 10, the resin R is cured in an autoclave with the aperture layer 13 supported and arranged in the shape required for the finished panel, which may be curved in three dimensions.

Applying a layer of woven nylon cloth (as a so-called "skin") to each side of the aperture layer 13 during the curing stage not only completely eliminates any "flash" of adhesive from within the aperture, but also A pattern is applied to the surface of the sheet to which a subsequently applied adhesive adheres. Preferably, however, the outer layer 14 is held pressed against the aperture layer 13 during the curing step, so that the resin serves to adhere both layers of the front sheet of the panel 10 to each other.

One particular way of effectively carrying out such a method is described below with reference to FIG.

A forming tool 30, herein referred to as a tool, having a forming surface 31 in the shape of a portion of panel 10 is typically cleaned using methyl ethyl ketone and then cleaned with Frekote, available from Frekote Inc., USA.
Two coats 32 of mold release agent, such as 33, are received at a time interval such that air drying can be achieved between the coats. The mold release agent is then cured for 30 minutes at 121°C.

A 720/150 stainless steel screen 33 of sufficient width to cover the working area of the tool 30 (720/150 indicates the number of wires per inch or approximately 25 mm of fabric length in the warp and weft, respectively). Rust-free steel mesh (available for example from G. Bopp & Co. Ltd., London N2, UK under the name "Robusta Weave") is subjected to active steam degreasing. This is then hung loosely over the tool 30, taking great care to avoid wrinkles, and secured in position by tape (not shown) applied around its circumference.
If the tool 30 is curved in three dimensions, the mesh may be torn to cause it to assume the position specified in the design and manufacturing specifications. A thin film of a suitable adhesive around the perimeter of the mesh and/or around the tear areas of the mesh to improve the adhesion between the mesh and the fiber-resin composite material subsequently placed on top of this mesh. It may be desirable to add .

The openings P between the warp and weft strands of the net 33 constitute the pores of this porous layer.

Next, a sufficiently wide open-weave carbon fiber cloth 34, as shown in FIG. 2, impregnated with a co-curing resin system is carefully placed on the screen 33. This fabric supports a layer 34P of nylon fabric as a "skin" on the surface of this carbon fiber fabric 34 opposite the steel mesh 33.

Curing of the resin system is accomplished in an autoclave 29 under reduced pressure. Depressurization is accomplished by overlaying tool 30 and layered structures 33, 34 with a nylon vacuum containment membrane 35 in a manner as illustrated in FIG. 3 and described below.

Disposed around the circumference of the fabric 34 is a band 36 of gas permeable breathing material approximately 2-5 cm wide.
Thin release film suitable for use at high temperatures37
is placed on the exposed surface of the uncured fabric 34, covering the band 36 by about 1-1.5 cm. Disposed over release film 36 and band 36 is a breathing sheet 38 of the same material forming band 36. The vacuum membrane 35 surrounds the uncured workpiece and the breathing member placed over it. Tool 3
A sealing strip 35S of high temperature mastic sealant is provided around the circumference of membrane 35 where it meets zero.

Next, a test for leakage in the vacuum membrane 35 and the sealed part of the tool 30 is carried out, during which the pressure inside the bag formed by the membrane is reduced by the vacuum pump 40 to 50 cmHg on the gauge 41. . The vacuum line 42 is then shut off at the pot 43 and the pressure build-up inside the bag is monitored. 12 pressure rise for 5 minutes
It is passed if it is not higher than cmHg.

Autoclave curing is then initiated while the air within the bag is still under vacuum. Inside the autoclave, the atmospheric pressure outside the bag is brought to 3.1±0.35 bar. The bag is vented to outside air when the pressure inside the bag has increased to 1.4 ^+0.69 _-0 , after which this is maintained at 0 ^+0.35 _-0 bar during the remaining curing process.

Regarding temperature, this is controlled by a temperature controller 44 which receives temperature data from a thermocouple 45 located near the workpiece. As a result, the rate of temperature rise of the workpiece is suppressed within the range of 1 to 2.5°C/min until the curing temperature reaches 177 ± 5°C, and this curing temperature is maintained for 120 ⁺⁶⁰ _-0 minutes. . After that, the material to be treated is heated at a rate of 1.5℃/min.
It can be cooled to below 60°C, the autoclave pressure is released, and the workpiece is taken out.

As an alternative to tearing the mesh 33, complex shapes with three-dimensional curvature can be formed by weaving the mesh along a shaper of the desired shape, or by weaving many individual pieces of mesh around their circumference. They can be formed by welding them together.

Other methods are also possible. Apertures can also be formed after weaving, but before curing, by moving the yarn and restraining it in a new position to obtain the desired aperture. The porous layer can be attached to the aperture layer after it has been cured to the desired shape.

Referring to FIG. 1, the unopened (but normally woven) synthetic material for layer 13 can be cured into the desired shape, and only then the apertures may be added to layer 1.
3, the outer layer 14 is then applied. However, certain advantages of the invention may not be obtained by using this method.

Sheets of synthetic material can be perforated while flat, uncured or partially cured;
It can then be brought into contact with the porous layer so as to be bonded thereto and cured into the desired shape.

The cured face sheet is then adhered to one side of the multicellular layer 12, both using an epoxy adhesive and made of aluminum or fiber-resin composite, as shown in FIG. A backing layer 11 is adhered to the other side. Adhesion of the front sheet is aided by the weave of the "skin" remaining on its cured resin surface. Multivesicular layer 12
is Nomex available from Ciba-Geigy (described below),
One type of nylon paper material is sufficient. The cells are dimensioned such that the largest circle inscribed in each cell has a diameter of 9 mm.

The epoxy adhesive is Ciba from Cambridge, UK.
Geigy Plastics and Additives Co. Limited, and triaxially woven carbon fiber materials are available from Barber-Colman Co., Lockford, Illinois, USA. UK slurry light water
Hexcel (UK) Limited impregnates fabric with its F593 'controlled flow' resin and supplies the impregnated fabric between sheets of Polythene.
The porous woven layer was manufactured by the British company G.Bopp as mentioned above.
Available from. As an alternative to Bopp materials, Brunswick, DeHand, Florida, USA
A sintered stainless steel fiber product sold by the Corporation as "Brunsmet" can be used. Alternative woven carbon fiber mesh products are available in Birban, France.
Available from Brochier Industrjes.

If a non-metallic porous layer is employed, for example a woven polyester mesh, this has the advantage of being lighter than an equivalent metal mesh. The adhesive and resin need not be epoxies, but may be, for example, phenolic resins or polyimide resins. Instead of carbon fibers, other fibers can also be used if they have good mechanical properties. Glass fiber and Kevlar are believed to produce inferior results than carbon fiber for this application.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view transverse to the panel plane showing the edge area of a noise-damping acoustic panel; FIG. 2 shows one of the hexagonal cells of the lower multicellular layer with the porous layer removed for clarity; An enlarged plan view of a portion of the aperture layer of the panel of FIG. 1 shown in outline, FIG. FIG. 3 is a sectional view showing the vacuum bag together. In the drawing, 10 is a sound absorbing panel, 20, 2
1 and 22 are three sets of threads, 13 and 34 are open layers, 14
and 33 are porous layers, F is fibers, H is openings, and P is pores.

Claims (1)

Claims: 1. A sheet with a number of through apertures of predetermined and directed dimensions and spacing, such that the apertures define the aperture area characteristics, and an aperture in the aperture layer. A front sheet for a sound-absorbing panel comprising a porous layer having pores with dimensions substantially smaller than that of the aperture layer and a porous layer adhered to the surface of the aperture layer, characterized in that the aperture layer is formed from a synthetic material of fiber/resin matrix. front seat. 2. A front sheet according to claim 1, wherein the synthetic material is an open weave material, in which the openings are formed by the stitches between the threads of the weave. 3. A front sheet according to claim 2, wherein the woven material is comprised of three sets of threads arranged at 60° C. with respect to each other to provide a hexagonal opening. 4. The front sheet according to any one of claims 1, 2, and 3, wherein the porous layer and the open layer have substantially the same electrode potential. 5. The front sheet according to claim 4, wherein the fibers of the synthetic material are made of carbon and the porous layer is made of stainless steel. 6. Prepare an aperture layer of a synthetic material of fiber/resin matrix with a number of through apertures of predetermined and specified dimensions and spacing such that the aperture area characteristics are determined by such apertures, and from the apertures of the aperture layer Manufacturing a front sheet for an acoustic panel comprising the steps of: preparing a porous layer having pores of substantially small size; and adhering the aperture layer and the porous layer facing each other to form the front sheet. how to. 7. A patent claim in which the steps of adhering the aperture layer and the porous layer to each other and the step of curing the resin of the synthetic material are carried out simultaneously by using the resin to also act as an adhesive between the aperture layer and the porous layer. The method described in item 6 of the scope of 8. The method of claim 6, further comprising shaping the aperture layer on a tool and curing the layer to the desired shape on the tool before the step of adhering the aperture layer and the porous layer to each other. 9. Claim 6 or 8, wherein the opening area is determined before the curing of the resin of the synthetic material is completed.
The method described in section. 10. The method according to claim 7 or 9, wherein the step of determining the open area is a weaving step. 11. The method according to any one of claims 7, 9 and 10, wherein a skin layer is adhered to at least one surface of the aperture layer during the step of curing the resin of the synthetic material. 12. The method of claim 11, wherein the at least one surface is the surface of the apertured layer of the cured face sheet that does not face the porous layer.