AU8006791A

AU8006791A - Manufacture of a composite material

Info

Publication number: AU8006791A
Application number: AU80067/91A
Authority: AU
Inventors: Mark Anthony Braniff; Robert Samuel Wilson
Original assignee: Short Brothers PLC
Current assignee: Short Brothers PLC
Priority date: 1990-07-03
Filing date: 1991-06-26
Publication date: 1992-02-04
Also published as: IL98585A0; WO1992000845A1; GB2245862A; EP0648159A1; GB9014770D0; GB9113766D0; BR9106615A; JPH05508362A; FI925805A; GB2245862B; CA2085253A1; FI925805A0

Description

MANUFACTURE OF A COMPOSITE MATERIAL

The present invention relates to apparatus for and a method of manufacturing a composite material such as, for example, a composite material particularly suitable for forming the outer surface material of an aircraft.

The term ^■■material" includes any suitable component or structure, such as for example a laminate joint, depending on the application of the invention.

A previously proposed composite material has been manufactured by embedding high strength fibres having a high modulus of elasticity within a homogeneous matrix. In one example of such a material, the fibres are made of carbon, aramid or boron, and the matrix can be formed of material such as an epoxy, bismalemide or polyimide resin.

The fibres are supplied in a uni-directional, woven or fibrous mat format which is pre-impregnated with slightly cured resin to form an intermediate fabric material. This intermediate fabric material is flexible and tacky, and the positions of the fibre filaments therein are not fixed. Layers of these intermediate fabric materials are assembled one upon the other in a mould, and then compressed and heated. The heating action accelerates the curing of the resin, and the combination of the heating and compression joins together the intermediate fabric materials to form the composite material.

In our co-pending patent application publication No. GB2238977A there is disclosed a method of manufacturing a composite material comprising placing together face to face a plurality of layers of intermediate fabric material, each layer comprising high strength fibres have a high modulus of elasticity in a tacky homogeneous resin matrix, fastening together said layers at spaced locations thereon, and then compressing and heating the layer assembly to cure the resin.

The present invention is particularly concerned with apparatus for and a method of fastening together the layers of intermediate fabric material at spaced locations thereon.

According to one aspect of the invention there is provided apparatus for fastening together a plurality of layers of intermediate fabric material located in a stack, . said apparatus comprising first means to make a passage through the stack, second means to draw a loop of prepared material through the passage to extend from both faces of the stack, third means to cut the loop at a pre¬ selected distance from one face of the stack to form two independent pieces of prepared material, and means to fold back the end portions of each piece onto the opposite faces of the stack to extend away from the other piece.

According to another aspect of the invention, there is provided a method of fastening together a plurality of layers of intermediate fabric material located in a stack, said method comprising making a passage through the stack, drawing a loop of prepared material through the passage to extend from both faces of the stack, cutting the loop at a preselected- distance from one face of the stack to form two independent pieces of prepared material, and folding back the end portions of each piece onto the opposite faces of the stack to extend away from the other piece. The stack of fastened layers of intermediate fabric material may then be compressed and heated to cure the resin.

In one embodiment of the invention a moveable flat, narrow blade having a longitudinal slot adjacent its forward cutting edge may constitute both the first and second means of the invention. In operation, the blade is advanced to make a passage through the stack. A loop of prepared material is then threaded through the longitudinal slot in the blade so that the blade is located at the mid-point of the loop, and the blade is withdrawn through the stack so that the loop is located in the passage with the mid portion and end portions of the loop extending from opposite faces of the stack. The third means may comprise a static blade to cut the loop when the mid-point of the loop has been positioned at a pre-selected distance from one face of the stack so as to form two independent pieces of prepared material. The length of the material forming the loop, and the position of the static blade are arranged so that the two pieces each project an equal distance from opposite faces of the stack.

An embodiment of the invention will now be described by way of example with reference to the accompanying illustrative drawings in which:-

Figures l to 7 are diagrammatic illustrations of seven stages in the fastening together of layers of intermediate fabric material previously referred to herein;

Figures 0a and Ob are a top plan view and side view respectively of a tow of prepared material for fastening - A - together the layers of intermediate fabric material; and Figures 9 and 10 are illustrations of a modified fastening technique.

Referring to Figures 1 to 7, a stack 2 of intermediate fabric material is supplied on a release film (not shown) which is removed before commencement of the fastening operation. The stack has been compacted or debulked under vacuum at room temperature. This compaction or debulking gives to the stack a degree of structural rigidity which aids assembly of the proposed composite material. The stack consists of a plurality of layers of the material placed together face to face. Each layer of intermediate fabric material is formed by embedding high strength fibres having a high modulus of elasticity in a homogeneous matrix which may be an epoxy, bis alemide or a polyimide resin. The fibres may be uni-directional, woven or in the form of a fibrous mat, and the fibres may be made of materials such as carbon, aramid or boron. Each intermediate fabric material layer is supplied with the resin matrix slightly cured to ensure that the fabric layer is tacky and flexible, and at this stage the fibres are not in a fixed position in the matrix. The stack 2 is rectangular in shape, and is located in a horizontal position beneath a moveable knife blade 4 having a forward cutting edge 6. The blade has its minor dimension in the plane of the drawings, and its major dimension in the plane perpendicular to that of the drawings. The blade 4 is also flat, by which is meant that it lies completely in a plane perpendicular to the plane of the drawings. An elongate longitudinal slot 8 is located in the blade 4 adjacent to the blade cutting edge 6.

A second flat, narrow blade 10, similar in form to the first blade 4, is located in sliding contact with the first blade 4. This blade 10 is static, and its forward cutting edge 12 is located a pre-selected distance "h" above the upper surface 13 of the stack 2.

In operation, the blade 4 is advanced from its rest position illustrated in Figure 1 to cut through the stack 2 thereby forming a slit-shaped passage 14 through the stack 2. The blade 4 is advanced until the slot 0 is clear of the lower face 16 of the stack 2. A pre-cut, pre-selected length of a tow IB of a prepared material is threaded through the slot 0 so as to extend equal distances from each side of the blade 4. Referring to Figures 8a and 8b, it will be seen that the tow 18 is of substantially rectangular cross-section. This tow 18 is made from a^' plurality of layers of woven and/or undirectional material which may be in a pre-impregnated (prepreg) or a dry (without resin) condition. Each layer may be made of thermo-setting and/or thermo-plastic material, including a reinforcement made of Kevlar, carbon or boron. The term prepreg refers to a reinforcement impregnated with a B-staged resin system. The term B-staged refers to a resin which has undergone limited curing in order to increase its viscosity and tc.ck so as to improve the handling quality of prepreg fabrics. This is the condition in which thermoset prepregs, whether woven or undirectional, are supplied by the processors and is in no way unique to this particular invention. The layers of tow material (stack) are in a debulked condition which refers to a stack of material consolidated under vacuum at room temperature only.

The blade 4 is then withdrawn as shown in Figures 4 and 5, and when the lower edge of the slot 8 is withdrawn to a distance "h" above the upper face 13 of the stack 2, the cutting edge 12 of the static blade 10 cuts the loop of tow 18 to form two independent pieces of tow 20 and 22 as illustrated in Figure 5. The position of the static blade 10, and the length of the tow pieces 20 and 22 are arranged so that the pieces 20 and 22 are of equal length to one another, and each extend equal distances from the upper and lower faces 13 and 16 of the stack 2.

Referring to Figure 6, the tow pieces 20 and 22 are each folded back onto the upper and lower faces 13 and 16 of the stack 2 so that the end portions of each piece 20 and 22 extend away from one another.

The above-mentioned operation is repeated so as to locate a plurality of fastening tows 18 in the stack 2 at required spaced locations from one another, and the stack 2, and the located tow fasteners are then cured.

Referring to Figure 9, if desired, additional layers of intermediate fabric material may be placed over the folded back tow pieces 20 and 22. These additional layers may be dimensioned to cover only the tow pieces 20 and 22, or the entire upper and lower faces 13 and 16 of the stack 2.

Referring to Figure 10, the stack and the tow fasteners are then cured to encapsulate the tow fasteners.

One suitable apparatus and process for curing the stack 2 and tow fasteners is described in our co-pending patent application publication No. GB2238977A.

In a modified version of this embodiment, the single stack 2 can be replaced by two stacks of intermediate fabric material which are placed in over lapping relationship as disclosed in our co-pending patent application publication No. GB2238977A.

The described and illustrated embodiment of this invention possesses the following advantageous features:-

(a) Improved impact resistance, tensile, peel and shear strength together with an increased resilience to crack propagation.

(b) The structural elements of the tows can be positioned so as to align more accurately with the load applied to the fastened material then is the case with previously known mechanical fasteners.

(c) It can overcome the following principal problems associated with known mechanical joints:-

(1) An increase in the thickness of the stack is less than the increase caused by known mechanical fasteners. This is because the cutting blade makes a clean cut through the material of the stack, and any increase in stack thickness is at least partially removed during the subsequent curing process.

(2) Typical problems associated with drilling, jigging, counter sinking and riveting used with the technique of mechanical fastenings are avoided.

(3) The joints are self sealing, and in consequence are ideal for use in a hostile environment. One example of such use is for containing fuel in the wing of an aircraft which is used in all weather conditions.

(4) The fasteners are lighter than mechanical fasteners. (5) The completed joints are aerodynamically smooth on the outer surfaces of the stack, and consequently it is not necessary to carry out any filling, feathering, smoothing or counter-sinking operations.

(d) The joints can be used to provide local reinforcement for the stack, for example at the end of the stack to:-

(1) Act as anti-peel fasteners to prevent the intermediate fabric layers from peeling away.

(2) Secure accurately in position the intermediate fabric layers of the stack prior to and during the curing operation.

(e) The fastening operation is more labour efficient than the operation with mechanical fasteners because it can be completed in a single automated operation.

(f) There is a higher safety factor because the fasteners are non-metallic. For example, if the fasteners are used in fuel cell environment the risk of arcing is avoided.

(g) The fasteners can be located in regions where extra fastening is required, and where fasteners would not normally be used, such as for example with blades and stiffeners webs.

(h) The tow fasteners may be employed to increase the structural strength of advanced composite materials, i.e. to prevent delamination of the plies. (i) Galvanic corrosion problems associated with metallic fasteners do not arise with the fasteners_of this invention.

(j) High strength or high modulus materials may be selected for the tows in order to accommodate the loading requirements of the fastened material.

Claims

CLAIMS;

1. Apparatus for fastening together a plurality of layers of intermediate fabric material located in a stack (2) , said apparatus comprising first means to make a passage (14) through the stack (2) , second means to draw a loop (18) of prepared material through the passage to extend from both faces of the stack (2) , third means to cut the loop at a pre-selected distance from one face (13) of the stack, to form two independent pieces of prepared material (20,22), and means to fold back the end portions of each piece onto the opposite faces (13,16) of the stack (2) to extend away from the other piece.

2. Apparatus as claimed in claim 1, characterised in that said first means is a first knife blade (4) .

3. Apparatus as claimed in claim 2, characterised in that said second means is said first knife blade (4) .

4. Apparatus as claimed in claim 3, characterised in that said first knife blade (4) has an aperture (8) therethrough to receive said loop (18) .

5. Apparatus as claimed in any preceding claim characterised in that said third means is a second knife blade (10) having its cutting edge (12) located at said preselected distance from said one face (13) of the stack (2).

6. Apparatus as claimed in claim 5 characterised in that said blades (4,10) are in sliding contact with one another.

7. A method of fastening together a plurality of layers of intermediate fabric material located in the stack (2) , said method comprising making a passage (14) through the stack, drawing a loop (18) of prepared material through the passage to extend from both faces (13,16) of the stack (2) , cutting the loop at a pre-selected distance from one face (13) of the stack to form two independent pieces of prepared material (20,22), and folding back the end portions of each piece onto the opposite faces of the stack to extend away from the other piece.

8. A method as claimed in claim 7 characterised in that the length of the loop (18) and the said pre-selected distance are arranged so that the two independent pieces (20,22) each project an equal distance from opposite faces of the stack (2) .

9. A method as claimed in claim 7 or claim 8, further including placing at least one additional layer of intermediate fabric material over the folded back end portions on each face of the stack (2) .

10. A method as claimed in claim 7 or claim 9, further including repeating said operations at required spaced locations from one another.

11. A method as claimed in any one of claims 7 to 10 further including curing the fastened layers.