GB2348163A

GB2348163A - A fibre-reinforced composite

Info

Publication number: GB2348163A
Application number: GB9906750A
Authority: GB
Inventors: Garry Michael Wells; John Michael Bayldon
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1999-03-24
Filing date: 1999-03-24
Publication date: 2000-09-27
Also published as: WO2000056524A1; AU2122000A; GB2363616B; GB0120501D0; GB2363616A; GB9906750D0

Abstract

A method of manufacturing a fibre reinforced composite comprises the steps of providing a fibre reinforcement layer and a first matrix adjacent to a first surface of the fibre reinforcement layer, enclosing it in an envelope and injecting a second matrix material into the envelope, the second matrix material being a thermoset resin matrix which infuses into the second surface of the reinforcement layer. The first matrix material may be a thermoplastic or a thermoset. Depending on the matrix materials used, the fibre and matrix may be heated and cooled during the production of the composite. The first matrix may comprise a filler. A distribution means may be positioned between the fibre reinforcement and the envelope. The envelope may be subject to a vacuum and/or an external pressure during or after injection. The fibre reinforcement layer may comprise a plurality of dry plies. A fibre reinforced composite manufactured in accordance with the method described is also claimed.

Description

Method of Manufacture of Composite Materials This invention relates to a method of manufacture of composite materials and composite materials manufactured by this method.

Conventionally, there are a number of ways to manufacture composite materials. The method used will depend on the quality of product required and the number of parts to be manufactured. The cheapest way to manufacture composites is to use hand lay-up. The are a number of problems associated with this technique including reproducibility and exposure of the laminator to emissions from the resin system used. A more reproducible method of manufacturing composites is to inject the resin into a dry fibre preform which is enclosed in a mould. This can be done either by creating a vacuum around the fibre preform to draw the resin through the layers of fibre as in a liquid resin infusion technique or, by injecting the resin into the fibres under pressure as used in resin transfer moulding (RTM). Both of these techniques allow for the production of near net shape parts and control the emissions of volatile organic compounds (VOC's). The cost of processing for both the liquid resin infusion technique and RTM processes is more than for hand lay-up, with RTM being the more expensive as the pressure used is higher.

Another technique that can be used is resin film infusion where a film or a slab of uncured resin in placed in communication with a preform. The application of heat and pressure melts the resin, which then infuses into the preform and subsequently cures.

For some applications, it would be desirable to have a composite with properties that varied throughout its thickness. For example, one of the surfaces may need to be fire or chemical resistant whilst the whole composite would have to meet certain structural requirements. The use of chemical or fire resistant resins and additives tends to be expensive and can result in a reduction of other desirable properties. If these expensive materials are only present in the composite where they are required, the cost of producing such composites is reduced.

Currently, the only way of manufacturing such composites is in number of steps which reduces any cost benefit as it increases the time of manufacture.

It is an object of the present invention to provide a method of manufacture of composite parts which can have variable properties through the thickness of the composite. The method utilises the advantages of closed mould techniques, namely the production of near net shape parts with controlled emissions of VOC's, without the disadvantages of conventional routes used to manufacture composites with variable properties through its thickness.

According to a first aspect of this invention, a method of manufacture of fibre reinforced composite materials comprises the steps of providing a fibre reinforcement layer, providing a first matrix adjacent to a first surface of the fibre reinforcement layer, enclosing the fibre reinforcement layer and first matrix in an envelope and injecting a second matrix material into the envelope, the second matrix material being a thermoset resin matrix, whereby the second matrix infuses into the second surface of the fibre reinforcement layer.

The second matrix material, is preferably a liquid of low viscosity to enable injection and infusion throughout the dry portion of the fibre reinforcement layer prior to the curing of the material. Suitable thermoset materials include polyesters, epoxies, phenolics, vinyl-esters, acrylics, bismaleimides. Whichever suitable material is chosen would depend on the properties required in the final composite.

Preferably, the first matrix material is a thermoplastic and the method includes the additional step of heating the first matrix material prior to injection of the second matrix material. The temperature and duration of the heating would be determined by the thermoplastic material used and the degree of infusion of the thermoplastic through the fibre reinforcement layer from the first surface that is required.

Preferably, the fibre reinforcement layer is cooled prior to the injection of the second matrix material. This allows for better control of the degree of infusion by the first matrix.

Preferably the first matrix material is a thermoset resin which is preferably in a solid or highly viscous form at ambient to enable correct placing of the matrix material with respect to the fibre reinforcement layer and enclosure of them under the envelope.

Preferably, the first matrix material is a high temperature cure thermoset resin. In order to cure the resin, the fibre reinforcement layer and first matrix material are preferably heated.

The temperature chosen will depend on the resin system used and the required degree of cure.

Preferably, the fibre reinforcement layer and first matrix material are cooled after the required degree of cure of the first matrix material has been achieved. This would allow the first and second resin matrices to chemically react and so produce a strong bond between the different layers.

Preferably, the fibre reinforcement layer is heated to a suitable temperature either prior to or during injection of the subsequent matrix material. The temperature being maintained until the resin has reached the desired degree of cure. This step would occur after the cooling step.

In order to produce a composite material with a variation in properties though its thickness, the second matrix material is preferably different to the first matrix material. When selecting the different matrix materials and processing conditions, a person skilled in the art will appreciate that care would be required in order to produce a high quality composite. One problem that could be encountered is the presence of residual stresses in the composite as a result of a difference in shrinkage percentages and rates of the matrix materials.

The properties required in the composite may be inherent in the matrix material itself or, may be imparted or augmented by the use of a suitable filler material.

In order to ensure full infusion of the subsequent matrix material into the dry portion of the fibre reinforcement layer, a distribution means may be positioned between the fibre reinforcement layer and envelope. This is particularly useful if the shape of the composite is complex. A distribution means between the envelope and the fibre reinforcement layer enables fast distribution of the matrix material to all parts of the dry reinforcement layer.

Another advantage of utilising a distribution means is that the infusion time of the subsequent matrix material is reduced, thus allowing it to be cured more quickly so reducing the time to manufacture each part.

Preferably, the envelope is subject to a vacuum prior to injection of the second matrix material. This would allow any gases produced to be removed from the envelope for example if the curing of a thermoset resin results in a condensation reaction. The use of a vacuum would also allow for faster distribution of the matrix material through the fibre reinforcement. If the second matrix material is subject to a vacuum during injection, the envelope is preferably flexible. An alternative to subjecting the envelope to a vacuum would be to inject the second matrix material under pressure. If the second matrix material is subject to a pressure during injection, the envelope is preferably rigid.

In a preferred embodiment, the envelope is subject to additional pressure during the injection of the subsequent matrix material. This pressure may be maintained until the subsequent matrix material has cured. This enables more accurate control of the thickness and the volume fraction of fibre of the composite being manufactured. This is especially useful when a large number of components are being manufactured and reproducibility is important. The additional pressure may also assist in the infusion of the subsequent matrix material into the dry portion of the fibre reinforcement layer.

Preferably, the fibre reinforcement layer comprises a plurality of dry plies. These plies may be stitched. The type of reinforcement, its orientation and the volume fraction desired in the final composite will be a function of the property requirements of the composite when in use.

For some applications it may be desirable to have a mixture of types of fibres. Suitable fibre types include glass, aramids, polyester, polyethylene and carbon.

In a second aspect of this invention, a fibre reinforced composite comprising a fibre reinforcement layer having a first matrix located from a first surface of the fibre reinforcement layer to a depth only partially through the fibre reinforcement layer and a thermoset resin matrix located from a second surface of the fibre reinforcement layer only partially through the fibre reinforcement layer. The first matrix material may be a thermoplastic or a thermoset. The two resin matrices may fully wet the fibre reinforcement layer. However further matrix materials may also be present in the final composite. These may be incorporated in an infusion or an injection process. If the further matrix materials are to be infused, they may be positioned where desired within the fibre reinforcement layer, prior to the infusion step. Alternatively, they may be infused in a separate process. If the further matrix materials are to be injected, they may be injected either prior to the injection of the second matrix material or after it, depending on the properties required in the final composite material. This enables the final composite to not only have a difference in properties between the first surface and the second surface but, also a difference at the first surface and a desirable point between the first surface and the second surface. An example of this, is when the first layer of matrix material at the first surface is cosmetic, the second layer comprises a fire retardant, and the subsequent layer imparts structural support.

When the first and second matrices are both thermoset resins, the matrices may be the same.

The variation of properties through the thickness of the composite would be achieved by a difference in the curing cycle of the resin used in each stage. For example, if the resin were high temperature cure and the first matrix material were heated in order to facilitate curing, by cooling prior to the injection of the second matrix then, heating the fibre and resin on injection, the first matrix would be post cured, resulting in a difference in properties between the first and second matrices.

Claims

Claims 1 A method of manufacturing a fibre reinforced composite comprising the steps of : (i) providing a fibre reinforcement layer; (ii) providing a first matrix adjacent to a first surface of the fibre reinforcement layer; (iii) enclosing the fibre reinforcement layer and first matrix in an envelope; and (iv) injecting a second matrix material into the envelope, the second matrix material being a thermoset resin matrix, whereby the second matrix infuses into the second surface of the fibre reinforcement layer.
2 A method as claimed in claim 1 wherein the first matrix material is a thermoplastic and the method includes the additional step of heating the first matrix after step (iii) whereby the first matrix melts and infuses into the first surface of the fibre reinforcement layer and only partially through the fibre reinforcement layer.
3 A method as claimed in claim 2 wherein the method further comprises the step of cooling the fibre reinforcement layer prior to step (iv).
4 A method as claimed in claim 1 wherein the first matrix material is a thermoset resin.
5 A method as claimed in claim 4 wherein the first matrix material is a high temperature cure thermoset resin.
6 A method as claimed in claim 5 wherein the method further comprises the step of heating the fibre reinforcement layer after step (iii).
7 A method as claimed in claim 6 wherein the method further comprises the step of cooling the fibre reinforcement layer prior to step (iv).
8 A method as claimed in any preceding claim wherein the method further comprises the step of heating the fibre reinforcement layer prior to or during step (iv).
9 A method as claimed in any preceding claim wherein the matrices are different.
10 A method as claimed in any preceding claim wherein the first matrix comprises a filler.
I I A method as claimed in any preceding claim wherein a distribution means is positioned between the fibre reinforcement and the envelope.
12 A method as claimed in any preceding claim wherein the envelope is subject to a vacuum.
13 A method as claimed in any preceding claim wherein the envelope is subjected to an external pressure during or after step (iv).
14 A method as claimed in any preceding claim wherein the fibre reinforcement layer comprises a plurality of dry plies.
15 A method according to any preceding claim wherein the fibre reinforcement layer comprises at least one of glass, aramid, polyester, polyethylene or carbon.
16 A fibre reinforced composite manufactured in accordance with a method as claimed in any preceding claim.
17 A fibre reinforced composite comprising a fibre reinforcement layer having a first matrix located from a first surface of the fibre reinforcement layer to a depth only partially through the fibre reinforcement layer; and a thermoset resin matrix located from a second surface of the fibre reinforcement layer only partially through the fibre reinforcement layer.
18 A composite as claimed in claim 17 wherein the first matrix material is a thermoplastic or a thermoset.
19 A composite as claimed in claim 17 wherein the first and second matrices are the same.
20 A composite as claimed in claims 17 to 19 wherein the fibre reinforcement layer is fully wetted.