GB2556057A

GB2556057A - The repair of structures and components formed of composite material

Info

Publication number: GB2556057A
Application number: GB1619382.3A
Authority: GB
Inventors: Wilson Steven; Meyer Jonathan; Astwood Simon; Lynas Christopher; Hobday John; Bestley Christine; Burchell Pete; Lane Ian
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2016-11-16
Filing date: 2016-11-16
Publication date: 2018-05-23

Abstract

An apparatus and method for repairing a composite structure comprises a flexible mould tool 16 with a flexible heating member 20 with a heating-fluid pathway. Vacuum can be applied to the pathway to circulate heating fluid in the pathway. The tool may be used to apply heat to a composite repair patch 18 applied to the wing fuel tank of an aircraft. A vacuum bag 26 may be applied over the heating member to compress the patch. The vacuum bag may comprise an insulating layer 36 and an outer membrane with a perforated section 34. The apparatus may comprise a remote source of heated fluid (44, figure 3) such as water or silicon oil and fluid passage thermocouples 48, 50, 52 used to control fluid heating and circulation rate. The apparatus may comprise a remote vacuum source (38).

Description

(71) Applicant(s):

Airbus Operations Limited

Pegasus House, Aerospace Avenue, Filton, BRISTOL, BS34 7PA, United Kingdom (72) Inventor(s):

Steven Wilson Jonathan Meyer Simon Astwood Christopher Lynas John Hobday Christine Bestley Pete Burchell Ian Lane (74) Agent and/or Address for Service:

Airbus Operations Ltd

UK IP Department, Aerospace Avenue, Filton, BRISTOL, BS34 7PA, United Kingdom (51) INT CL:

B29C 73/34 (2006.01) (56) Documents Cited:

US 8113242 A US 6149844 A

US 2975476 A US 2579898 A (58) Field of Search:

INT CL B29C

Other: WPI, EPODOC, Patent Fulltext (54) Title of the Invention: The repair of structures and components formed of composite material Abstract Title: A flexible mould heating element heated by fluid circulated by vacuum (57) An apparatus and method for repairing a composite structure comprises a flexible mould tool 16 with a flexible heating member 20 with a heating-fluid pathway. Vacuum can be applied to the pathway to circulate heating fluid in the pathway. The tool may be used to apply heat to a composite repair patch 18 applied to the wing fuel tank of an aircraft. A vacuum bag 26 may be applied over the heating member to compress the patch. The vacuum bag may comprise an insulating layer 36 and an outer membrane with a perforated section 34. The apparatus may comprise a remote source of heated fluid (44, figure 3) such as water or silicon oil and fluid passage thermocouples 48, 50, 52 used to control fluid heating and circulation rate. The apparatus may comprise a remote vacuum source (38).

1/5

Figure 1

2/5

Figure 2

3/5

Figure 3

4/5

Figure 4

5/5

Figure 5

THE REPAIR OF STRUCTURES AND COMPONENTS FORMED OF COMPOSITE

MATERIAL

FIELD OF THE INVENTION [0001] The present invention relates to the repair of structures and components formed of composite materials.

BACKGROUND OF THE INVENTION [0002] Synthetic composite materials commonly comprise one or more layers of fibre material infused with a resin and cured to form a desired structure. Such synthetic composite materials include carbon fibre reinforced plastic (CFRP) and glass fibre reinforced plastic.

[0003] In instances in which structures or components formed of composite materials become damaged or compromised, it is often impractical to replace the component or structure as a whole, hence there is a need for practical and cost effective high quality methods of repairing such structures or components. Further, such repairs may need to be performed in situ where the structure or component is large or a part of a larger structure, such as an aircraft.

[0004] The repair of composite material structures and components typically requires the placement of a repair patch, comprising the constituent elements of a composite material, over a repair area followed by curing in situ such that the repair patch becomes an integral part of the pre-existing structure or component.

[0005] As per standard composite material manufacturing techniques, the repair process requires the application of pressure and heat to cure the composite repair patch to form a unitary composite with the pre-existing structure.

[0006] Pressure is exerted upon the composite material to remove trapped air and ensure consolidation of the constituent elements and heat is applied to induce a phase change the thermoplastic or thermoset matrix material.

[0007] It is known to use electrical heat blankets as a source of heat in in-situ composite repairs. However, these are reliant upon an electrical supply which may be impractical for repairs in small spaces or with restricted access. Heat blankets also present a potential ignition source in volatile environments and tend to be rigid, making them unsuitable for use in repairs on curved or complex shaped components. Although bespoke heat blankets are available, manufacturing cost and significant lead time can be impractical for one-off repairs.

SUMMARY OF INVENTION [0008] According to a first aspect of the invention, there is provided a an apparatus for repairing a composite structure for use with a composite repair patch, the apparatus comprising a flexible mould tool, the flexible mould tool comprising a flexible heating member defining a fluid suction pathway for a heating fluid comprising a fluid vacuum port for applying a vacuum within the fluid suction pathway, such that, in use, when the vacuum is applied, a heating fluid is circulated within the flexible heating member such that the flexible mould tool applies heat to the composite repair patch.

[0009] According to a second aspect of the invention, there is provided a method of repairing a composite structure using a composite repair patch, the method comprising laying a flexible mould tool comprising a flexible heating member over a composite repair patch located on a repair area of a composite structure, applying a vacuum to the flexible heating member to circulate a heating fluid within the flexible heating member, heating the flexible heating member by heating the heating fluid within the flexible heating member to a curing temperature sufficient to cure the composite repair patch, and maintaining the flexible heating member at the curing temperature for a period sufficient to cure the composite repair patch.

[0010] It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects. For example, the method of the present invention may incorporate any of the features described with reference to the apparatus of the present invention and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS [0011] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which:

[0012] Figure 1 shows an aircraft including fuel tanks;

[0013] Figure 2 schematically shows the apparatus for use within the aircraft according to a first embodiment and external supporting equipment for use according to a first embodiment;

[0014] Figure 4 schematically shows the apparatus for use in the method according to a second embodiment; and [0015] Figure 5 schematically shows the steps of the method according to the first embodiment.

DETAILED DESCRIPTION OF THE INVENTION [0016] Figure 1 shows an aircraft 2 with two wings 4, 6 and an exemplary fuel tank 8, 10 in each wing. Fuel tank 10 has a repair area 12. Located externally to the aircraft is supporting equipment 14 for attaching to apparatus required to carry out the repair method of the exemplary embodiments within the aircraft wing 6. Either or both of the fuel tanks indicated may be repaired using the apparatus and method as described in Figures 2 to 5.

[0017] Referring to Figure 2, a wet lay-up composite repair patch 18 is provided on a repair area 12 of a composite structure forming a fuel tank 10. In the exemplary embodiments, the composite structure or component to be repaired is shown as having a flat profile but it will be appreciated that the structure or component may incorporate an aerodynamic or complex profile appropriate to its specific application.

The composite repair patch 105 may comprise a pre-preg material or a dry fibre lay up with a resin film overlay.

[0018] A flexible mould tool 16 comprising a flexible heating member 20 is used to cure the composite repair patch 18. A flexible heating member 20 comprising a fluid suction pathway for containing a heating fluid is laid over the composite repair patch 18. The flexible heating member 20 is sufficiently flexible to conform to the shape or profile of the surface of repair area 16 and is sized to cover the surface area of the composite repair patch 18 to ensure that the composite repair patch can be cured in its entirety. [0019] The flexible heating member 20 has a fluid vacuum port comprised of a fluid inlet 22 and a fluid outlet 24 for connection to a vacuum source 38 and a heating fluid source 40 providing heating fluid 44, as shown in Figure 3.

[0020] In a preferred embodiment, the fluid suction path of the flexible heating member 20 is formed of tubing arranged in a coil forming a mat. The material of the flexible heating member 20 is selected to withstand temperatures up to and including the curing temperature, which is typically up to 200°c. In the preferred embodiment, the flexible heating member 20 is comprised of a plastics material.

[0021] In a preferred embodiment, thermocouples 48, 50 are provided at the fluid inlet 22 and the fluid outlet 24 for monitoring the fluid temperature circulating within the fluid suction pathway of the flexible heating member 20. An optional, further thermocouple 52 is provided on the flexible heating member 20 to provide temperature information at a further location to enable monitoring of heat loss and transfer. Said thermocouples may be connected to one or more recording and/or processing devices as required, in wired or wireless communication.

[0022] A vacuum bag 26 is laid over the flexible heating member 20 to hold the flexible heating member 20 in place and to provide pressure to the composite repair patch 18 during curing. The vacuum bag 26 is comprised of an outer membrane 28, and is of known construction, typically containing a breather, a bleeder and a parting film (not shown). An insulating layer 36 is provided within vacuum bag 26 to retain the heat generated by the heating fluid in the flexible heating member 20 and encourage heat transfer between the flexible heating member 20 and the composite repair patch 18 in use.

[0023] The outer membrane 28 is selected to withstand the temperatures required for curing the composite repair patch 18, which are typically up to 200°c. Advantageously, the outer membrane 28 of vacuum bag 26 has a perforated surface 34 that allows for the ingress of excess resin during the consolidation of the composite repair patchl8. The vacuum bag 26 has a vacuum port comprised of a vacuum inlet 30 and a vacuum outlet 32 for connecting the vacuum bag 26 to a vacuum source 46, as shown in Figure 3 Advantageously, application of the vacuum to the vacuum bag 26 causes pressure to be applied to the composite repair patch 18. Said pressure encourages the resin of the composite repair patch 18 to migrate through the thickness of the patch for even distribution, with any excess resin migrating through the perforated surface 34.

[0024] Referring to Figure 3, supporting equipment 14 is comprised of a heating fluid source 40, a vacuum supply for supplying a vacuum to the flexible heating member 20, and a vacuum source 46 for supplying a vacuum to the vacuum bag 26. The supporting equipment 14 is located outside the aircraft and remotely from the flexible mould tool 16 that is inserted into the aircraft wing through one or more access panels for use in repairs to the internal structure and components of the aircraft wing. This is particularly advantageous for performing repairs in small or difficult to access areas as well as in safety critical areas such as fuel tanks in which contamination must be kept to a minimum.

[0025] The supporting equipment is connected to the flexible mould tool 16 by known means to allow vacuum and fluid communication between the supporting equipment 14 and the flexible mould tool 16 and to allow wired or wireless electronic communication between the thermocouples 48, 50, 52 and processing and/or recording devices as required. The supporting equipment 14 further comprises a processor and recording medium for receiving, storing and processing data provided by the thermocouples 48, 50, 52.

[0026] The heating fluid source 40 is connected to the fluid inlet 22 and the fluid outlet 24 of the flexible heating member 20 in a closed circuit. The heating fluid source 40 comprises a fluid heater 42 for heating the heating fluid to a curing temperature remotely from the repair area. Heating fluid 44 provided by the heating fluid source 40 is circulated within the flexible heating member 20 by means of a vacuum provided by vacuum source 38. The vacuum source 38 is also connected to the fluid inlet 22 and the fluid outlet 24 of the flexible heating member 20 in a closed circuit.

[0027] Advantageously, the flexible mould tool 16 does not require electrical connectivity and therefore presents no ignition risk around flammable substances. The location of the supporting equipment 14 outside of the aircraft minimizes the amount of equipment that must be accommodated within the aircraft and restricts electrical equipment and therefore sparking hazards to areas away from the aircraft 2 and fuel tanks 8, 10.

[0028] Should the flexible heating member 20 or the connections between the heating fluid source 40 and the flexible heating member 20 become damaged, the breach of the closed circuit will result in air or other atmospheric gas being ingested into the fluid suction pathway. Advantageously, the pressure in the closed circuit is low and substantially equivalent to atmospheric pressure. As such, should the circuit be breached the heating fluid 44 will simply leak away presenting an advantage over systems in which heating fluid is pumped through a system.

[0029] The vacuum source 46 is connected to vacuum inlet 30 and vacuum outlet 32 of the vacuum bag 26 in a closed circuit. When activated, the vacuum source 46 provides a vacuum to the vacuum bag 26 to remove air or atmospheric gas from the internal cavity of the vacuum bag 26. The evacuated vacuum bag 26 provides a pressure force on the flexible heating member 20 and thus the composite repair patch 18 by a suction force provided through the perforated surface 34 of outer membrane 28. This retention action prevents and removes gaps forming between the flexible heating member 20 and the composite repair patch 18 that may result in inefficient heat transfer or uneven pressure that can negatively impact upon consolidation of the composite repair patch 18. Said gaps may result from a complex surface profile of the repair structure or gravity, particularly where the repair area is not substantially horizontal.

[0030] As per the first embodiment, the supporting equipment as shown in Figure 3 is also applicable to the second embodiment. Referring to Figure 4, in a second embodiment the flexible mould tool 16 is comprised of a flexible heating member 20 and a vacuum bag 26 arrangement in which the flexible heating member 20 is integral to the vacuum bag 26. In order to accommodate the flexible heating member 20, the vacuum bag 26 further comprises a flexible heating member inlet 54 and a flexible heating member outlet 56. The flexible heating member inlet 54 and flexible heating member outlet 56 forms an air tight seal around the flexible heating member 20 to seal the vacuum bag 26 around the flexible heating member 20.

[0031] In the second embodiment, the perforated surface 34 of the outer membrane 28 of the vacuum bag 26 is located between the flexible heating member 20 and the composite repair patch 18. Advantageously, excess resin from the wet lay up composite repair patch 18 may easily migrate through the perforated surface 34 for capture within the vacuum bag 26.

[0032] The composite repair patch 18 of the second embodiment is shown as recessed into the surface of the composite structure of the repair area 12 of fuel tank 10. Repair of existing structures often requires the removal of damaged layers at or near the surface of the structure or component to be repaired. Consequently, in such circumstances the composite repair patch 18 will be recessed into the surface of the repair area 12. The flexible mould tool 16 of the first and the second embodiments is applicable to repairs in which the composite repair patch 18 is laid upon the surface of the repair area 12 and to repairs in which the composite repair patch 18 is recessed into the surface of the structure or component under repair.

[0033] Advantageously, the flexible mould tool 16 may be reused. The flexible mould tool 16 is particularly advantageous in applications in which the profile of the structure to be repaired is complex and different in every repair. The need for bespoke tooling for each repair is therefore mitigated.

[0034] In the method of repairing a composite structure, as represented in Figure 5, apparatus according to the first embodiment is arranged over a repair area 12 of a composite structure.

[0035] In a first step 58, a flexible mould tool 16 is laid over a composite repair patch 18 located on a repair area 12 of a composite structure. The flexible mould tool 16 comprises a flexible heating member 20 as described with reference to Figures 2 and 3.

[0036] In a second step 60, the flexible heating member 20 is connected to a vacuum source 38 that applies a vacuum for supplying a heating fluid to the flexible heating member 20 and circulates said fluid through the flexible heating member 20 in a fluid suction pathway.

[0037] In a third step 62, the flexible heating member 20 is heated by heating the heating fluid 44 to a temperature sufficient for curing the composite repair patch 18. A fluid heating device 42 heats the heating fluid 44 at a remote location prior to the heating fluid 44 entering the fluid suction pathway. The heating fluid 44 is heated to and held at a temperature sufficient to cure the composite repair patch 18.

The required curing temperature, and thus the heating fluid 44 temperature, will depend upon the matrix materials selected for and provided with the composite repair patch 18. The material selection will depend on the required mechanical properties of the resulting unitary structure. It is envisaged that the matrix material could be a thermoplastic material or a thermosetting material. In a preferred embodiment, the heating fluid 44 is water that is heated to 100°C.

[0038] In a fourth step 62, the flexible heating member 20 is maintained at a curing temperature for a period of time sufficient for the composite repair patch 18 to cure, forming a unitary structure with the repair area 12.

[0039] A vacuum bag 26 is connected to a remote vacuum source 46 for applying a light vacuum to the vacuum bag 26 to retain the vacuum bag in position over the composite repair patch 18. Immediately prior to or during the curing step, the level of vacuum applied to the vacuum bag 26 may be increased to apply a stronger vacuum, the latter aiding consolidation of the composite repair patch 18 such that the composite repair patch 18 forms a unitary structure with the repair area 12.

[0040] The heating fluid 44 temperature may be monitored to ensure that a consistent temperature distribution is applied across the composite repair patch 18 for uniform consolidation. In a preferred embodiment, thermocouples 48, 50, 52 are located at or near a fluid inlet 22 and a fluid outlet 24 of the flexible heating member 20. Readings taken by thermocouples 48, 50, 52 may be compared to establish that heat transfer is taking place.

[0041] Advantageously, measurements taken by the thermocouples 48, 50, 52 can be used to optimize the heating temperature and the heating fluid 44 circulation rate to ensure a stable temperature distribution and a complete curing cycle. Any difference between the temperature measured at the fluid inlet 22 of the flexible heating member 20 and the temperature measured at the fluid outlet 24 of the flexible heating member 20 that is outside of a pre-determined range may be minimized by adjusting the vacuum output of the vacuum source 38 and/or the temperature to which the fluid heater 42 heats the heating fluid 44 to ensure that the readings at both the fluid inlet 22 and the fluid outlet 24 are within the pre-determined range of one another. If desired, the vacuum level may be reduced such that the heating fluid 44 is at rest within the flexible heating member 20 for a period sufficient for a desired heat transfer to take place. Alternatively, the vacuum level may be reduced or increased to respectively decrease or increase the flow rate of the heating fluid 44 to achieve an optimal heat transfer from the heating fluid 44 to the composite repair patch 18 via the flexible heating member 20.

[0042] In a preferred embodiment, the heating step is performed prior to the step of applying the vacuum from vacuum source 155 such that the heating fluid circulated in the flexible heating memberl 10 is heated prior to circulation.

[0043] In a preferred embodiment, the vacuum source 155 may be connected to the fluid inlet 115 and the fluid outlet 120 in an open circuit.

[0044] In a preferred embodiment, the vacuum source 170 may be connected to vacuum inlet 135 and a vacuum outlet 140 in an open circuit.

[0045] In a preferred embodiment, a single vacuum supply may be utilized to both evacuate the vacuum bag 125 and circulate the heating fluid in a fluid suction pathway in the flexible heating member 110. [0046] The heating fluid in a preferred embodiment is water. Water has the advantage that it is readily available and may be heated to a level sufficient to cure matrix materials requiring temperatures up to 100°c. Should the flexible heating member 110 or the connections between the heating fluid source 160 and the flexible heating member 110 become damaged and the heating fluid contaminate the repair area, the cleaning operations required to address the area of contamination is significantly less involved and les safety critical than for other substances.

[0047] In a further preferred embodiment, the heating fluid may be oil based. Advantageously, the heating fluid is silicon based oil. Unlike mineral oils that begin to degrade at 200°c, silicon oil can withstand the highest composite material curing temperatures, is non-flammable and has desirable heat transfer properties.

[0048] In a preferred embodiment, the heating fluid is heated to a temperature of 180°C. In a further preferred embodiment, the heating fluid is heated to a temperature of 200°C.

[0049] In a preferred embodiment, the heating fluid source 160 may be connected to the fluid inlet 115 and the fluid outlet 120 in an open circuit. In a preferred embodiment, the fluid suction path of the flexible heating member is a lattice of interconnected tubing forming a mat.

[0050] In a preferred embodiment, the flexible heating member is comprised of a material suitable to withstand the temperature to which the heating oil is heated during the curing process. Suitable materials include polymers, metals, alloys or other materials suitably flexible and heat resistant.

[0051] In a preferred embodiment, a pair of thermocouples is provided at the fluid inlet 22 and fluid outlet 24 of the flexible heating member 20. Optionally, further thermocouples may be provided at selected points across the flexible heating member as desired.

[0052] In a preferred embodiment, the processor and recording medium for receiving, storing and processing data provided by the thermocouples is remote from both the aircraft and the supporting equipment.

[0053] The exemplary embodiments relate to repairs performed within a fuel tank in an aircraft wing. It should be noted that embodiments of the present application may be directed towards repairs in fuel tanks of other vehicles or to other aircraft structures within or relating to an aircraft airframe. Said embodiments may also be directed towards applications for technologies outside the aerospace industry (e.g., automotive, etc.). Furthermore, the exemplary repair method can be directed to any suitable structure. [0054] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

1. An apparatus for repairing a composite structure for use with a composite repair patch, the apparatus comprising a flexible mould tool, the flexible mould tool comprising:

a flexible heating member defining a fluid suction pathway for a heating fluid comprising a fluid vacuum port for applying a vacuum within the fluid suction pathway, such that, in use, when the vacuum is applied, a heating fluid is circulated within the flexible heating member such that the flexible mould tool applies heat to the composite repair patch.

2. An apparatus according to claim 1, wherein the flexible mould tool comprises a vacuum bag, the vacuum bag comprising an outer membrane defining an internal cavity and a vacuum bag port for applying a first vacuum within the internal cavity.

3. An apparatus according to claim 2, wherein the vacuum bag further comprises a layer of insulating material disposed between the outer membrane and the flexible heating member.

4. An apparatus according to claim 2 or claim 3, wherein the outer membrane comprises a perforated section arranged adjacent the composite structure.

5. An apparatus according to any preceding claim, wherein, the flexible mould tool can substantially conform to the surface of the structure to be repaired.

6. An apparatus for repairing a composite structure according to any preceding claim, wherein, when the heating fluid is circulated within the flexible heating member, the heat applied by the flexible heating member to the composite repair patch is sufficient to cure the composite patch.

7. An apparatus for repairing a composite structure according to any one of claims 2 to 6, wherein the vacuum bag port comprises a vacuum inlet and a vacuum outlet for connection to a vacuum source.

8. An apparatus for repairing a composite structure according to any one of claims 2 to 7, wherein, when a vacuum is applied to the vacuum bag port, the vacuum bag applies a retaining force to retain a composite repair patch in contact with a composite structure.

9. An apparatus for repairing a composite structure according to any preceding claim, wherein the fluid vacuum port comprises a fluid inlet and a fluid outlet for connection to a remote vacuum source.

10. An apparatus for repairing a composite structure according to claim 9, wherein the fluid inlet and the fluid outlet are connected to a remote heating fluid source.

11. An apparatus for repairing a composite structure according to claim 10, wherein the remote heating fluid source comprises a fluid heater.

12. An apparatus for repairing a composite structure according to claim 10 or claim 11, wherein the remote heating fluid source is a source of water.

13. An apparatus for repairing a composite structure according to any one of claims 10, 11 or 12, wherein the remote heating fluid source is a source of oil.

14. An apparatus for repairing a composite structure according to any one of claims 10 to 13, wherein the heating fluid is silicon oil.

15. An apparatus for repairing a composite structure according to any preceding claim, wherein the fluid suction pathway comprises one or more thermocouples.

16. An apparatus for repairing a composite structure according to claim 15, wherein the one or more thermocouples is located at the fluid inlet and/or at the fluid outlet.

17. An apparatus for repairing a composite structure according to claim 15 or claim 16, wherein the one or more thermocouples is located at the fluid suction pathway.

18. An apparatus for repairing a composite structure according to any one of claims 2 to 17, wherein the internal cavity of the vacuum bag comprises the flexible heating member.

19. An apparatus for repairing a composite structure according to claim 18, wherein the vacuum bag further comprises a flexible heating member inlet and a flexible heating member outlet, forming an air tight seal around the flexible heating member.

20. An apparatus for repairing a composite structure according to any one of claims 1 to 17, wherein the flexible heating member is arranged adjacent the composite structure and the vacuum bag is arranged to overlie the flexible heating member.

21. A method of repairing a composite structure using a composite repair patch, the method comprising:

laying a flexible mould tool comprising a flexible heating member over a composite repair patch located on a repair area of a composite structure, applying a vacuum to the flexible heating member to circulate a heating fluid within the flexible heating member, heating the flexible heating member by heating the heating fluid within the flexible heating member to a curing temperature sufficient to cure the composite repair patch, and maintaining the flexible heating member at the curing temperature for a period sufficient to cure the composite repair patch.

22. A method of repairing a composite structure according to claim 21, wherein the flexible mould tool comprises a vacuum bag and a flexible heating member.

23. A method of repairing a composite structure according to claim 22, further comprising the step of applying a vacuum to the vacuum bag to retain the flexible mould tool in pressure contact with the composite repair patch, prior to applying the vacuum to the flexible heating member.

24. A method of repairing a composite structure according to any one of claims 21 to 23, wherein the heating step is performed prior to the step of applying the vacuum to the flexible heating member.

25. A method of repairing a composite structure according to any one of claims 21 to 24, wherein the heating fluid is heated at a location upstream of and remote from the flexible heating member.

26. A method of repairing a composite structure according to any one of claims 21 to 25, further comprising the step of monitoring the temperature of the heating fluid within the flexible heating member.

27. A method of repairing a composite structure according to claim 26, wherein the temperature is monitored by a first thermocouple located at a fluid inlet of the flexible heating member and a second thermocouple located at a fluid outlet of the flexible heating member.

28. A method of repairing a composite structure according to any one of claims 21 to 27, further comprising the step of monitoring the circulation of the heating fluid within the flexible heating member.

29. A method of repairing a composite structure according to any one of claims 21 to 28, further comprising the step of adjusting the temperature of the heating fluid to modify the temperature of the heating fluid within the flexible heating member.

30. A method of repairing a composite structure according to any one of claims 21 to 29, further comprising the step of adjusting the circulation of the heating fluid to modify the temperature of the heating fluid within the flexible heating member.

31. A method of repairing a composite structure according to any one of claims 21 to 30, further comprising the step of varying the second vacuum pressure to adjust the circulation rate of the heating fluid within the flexible heating member.

32. A method of repairing a composite structure according to any one of claims 21 to 31, wherein the vacuum source providing the vacuum to the vacuum bag is remote from the flexible mould tool.

33. A method of repairing a composite structure according to any one of claims 21 to 32, wherein the vacuum source providing the vacuum to the flexible heating member is remote from the flexible mould tool.

34. A method of repairing a composite structure according to any one of claims 21 to 33, wherein the heating fluid source is remote from the flexible mould tool.

35. A method of repairing a composite structure according to claim 34, wherein the heating fluid source comprises a storage tank.

36. A method of repairing a composite structure according to any one of claims 21 to 35, wherein the flexible heating member comprises piping.

37. A method of repairing a composite structure according to claim 36, wherein the piping is arranged to form a mat of concentric rings.

38. A method of repairing a composite structure according to claim 36, wherein the piping is arranged to form a mesh.

39. A method of repairing a composite structure according to any one of claims 21 to 38, wherein the heating fluid comprises water.

40. A method of repairing a composite structure according to any one of claims 21 to 38, wherein the heating fluid comprises an oil.

41. A method of repairing a composite structure according to claim 40, wherein the oil is siliconbased.

42. A method of repairing a composite structure according to claim 40 or claim 41, wherein heating fluid is heated up to 200°c in the curing step.

43. An apparatus for repairing a composite structure substantially as described with reference to

Figures 1 to 4.

44. A method of repairing a composite structure substantially as described with reference to figure 5.

Intellectual

Property

Office

Application No: GB1619382.3 Examiner: Tim James