FAN CONTAINMENT CASING

Abstract

A structural support casing for fan blade containment in a gas turbine engine includes at least one region in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by ductile polymeric material.

Claims

1. A hardwall fan containment casing for fan blade containment in a gas turbine engine, the hardwall fan containment casing comprising at least one region in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by ductile polymeric material.

2. The hardwall fan containment casing according to claim 1, wherein a tensile modulus of the ductile polymeric material is no greater than about 50% of a tensile modulus of the fibre-reinforced composite material.

3. The hardwall fan containment casing according to claim 1, wherein a tensile modulus of the ductile polymeric material is no greater than about 10 GPa.

4. The hardwall fan containment casing according to claim 1, wherein an elongation to failure of the ductile polymeric material is at least five times, for example, at least ten times, the an elongation to failure of the fibre-reinforced composite material.

5. The hardwall fan containment casing according to any claim 1, wherein an elongation to failure of the ductile polymeric material is at least about 50%.

6. The hardwall fan containment casing according to claim 5, wherein an elongation to failure of the fibre-reinforced composite material (31, 32, 33) is no greater than about 10%.

7. The hardwall fan containment casing according to claim 1, wherein the fibre-reinforced composite material has a tensile strength of at least about 1000 MPa and the ductile polymeric material has a tensile strength of no greater than about 200 MPa.

8. The hardwall fan containment casing according to any preceding claim 1, wherein the ductile polymeric material is not susceptible to thermal degradation at or below a temperature of 200° C.

9. The hardwall fan containment casing according to claim 1, wherein the ductile polymeric material comprises polyurethane and/or phenolic resin and the fibre-reinforced composite material is a fibre-reinforced polymer.

10. The hardwall fan containment casing according to claim 1, wherein the two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by one or more solid layers of unreinforced, ductile polymeric material.

11. The hardwall fan containment casing according to claim 1, wherein a thickness of the ductile polymeric material provided between each of one or more adjacent pairs of sub-laminates of fibre-reinforced composite material, is no greater than a thickness of any one of the two or more sub-laminates of fibre-reinforced composite material of the pair.

12. The hardwall fan containment casing according to claim 1, wherein the at least one region, in which the two or more sub-laminates of fibre-reinforced composite material are spaced apart from another by the ductile polymeric material, extends around a majority of a circumference of the structural support casing.

13. (canceled)

14. A method of laying up a preform for a hardwall fan containment casing for fan blade containment in a gas turbine engine, the method comprising: applying a first fibre-reinforced composite sub-laminate to a tool; applying ductile polymeric material onto the first fibre-reinforced composite sub-laminate; and applying a second fibre-reinforced composite sub-laminate onto the ductile polymeric material.

15. The method according to claim 14, further comprising curing the preform to provide the hardwall fan containment casing for fan blade containment in a gas turbine engine.

16. The method according to claim 14, wherein the ductile polymeric material which spaces apart the two or more sub-laminates is a thermoplastic polymer.

17. The hardwall fan containment casing according to claim 1, wherein the ductile polymeric material which spaces apart the two or more sub-laminates is a thermoplastic polymer.

18. The hardwall fan containment casing according to claim 11, wherein the thickness of ductile polymeric material, provided between each adjacent pair of sub-laminates of fibre-reinforced composite material, is no greater than about 50% of the thickness of any one of the two or more sub-laminates of fibre-reinforced composite material of the pair.

19. A hardwall fan containment casing for fan blade containment in a gas turbine engine, the hardwall fan containment casing comprising at least one region in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by ductile polymeric material; wherein a tensile modulus of the ductile polymeric material is no greater than about 50% of a tensile modulus of the fibre-reinforced composite material; and wherein an elongation to failure of the ductile polymeric material is at least five times an elongation to failure of the fibre-reinforced composite material.

20. The hardwall fan containment casing according to claim 19, wherein the tensile modulus of the ductile polymeric material is no greater than about 25% of the tensile modulus of the fibre-reinforced composite material.

21. The hardwall fan containment casing according to claim 19, wherein the elongation to failure of the ductile polymeric material is at least ten times the elongation to failure of the fibre-reinforced composite material.

Description

FIGURES

[0090] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0091] a. FIG. 1 is a sectional side view of a gas turbine engine;

[0092] b. FIG. 2 is a sectional side view of a fan containment case;

[0093] c. FIG. 3 is a schematic sectional view through a portion of a fan containment case;

[0094] d. FIG. 4 is a diagrammatic representation of shear force distribution through a portion of a fan containment case;

[0095] e. FIG. 5 is a plot of energy absorbed on impact of a fan blade for three example materials;

[0096] f. FIG. 6 is a force-displacement plot for carbon-fibre and ductile polymer composite materials; and

[0097] g. FIG. 7 is a flow diagram of a method of manufacturing a fan containment case.

DETAILED DESCRIPTION

[0098] With reference to FIG. 1, a gas turbine engine is generally indicated at 10, having a principal and rotational axis 11. The engine 10 comprises, in axial flow series, an air intake 12, a propulsive fan 13, an intermediate pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, an intermediate pressure turbine 18, a low-pressure turbine 19 and an exhaust nozzle 20. A nacelle 21 generally surrounds the engine 10 and defines both the intake 12 and the exhaust nozzle 20. A fan containment case 22 extends around the fan 13 inboard the nacelle 21.

[0099] The gas turbine engine 10 works in the conventional manner so that air entering the intake 12 is accelerated by the fan 13 to produce two air flows: a first air flow into the intermediate pressure compressor 14 and a second air flow which passes through a bypass duct 23 to provide propulsive thrust. The intermediate pressure compressor 14 compresses the air flow directed into it before delivering that air to the high pressure compressor 15 where further compression takes place.

[0100] The compressed air exhausted from the high-pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 17, 18, 19 before being exhausted through the nozzle 20 to provide additional propulsive thrust. The high 17, intermediate 18 and low 19 pressure turbines drive respectively the high pressure compressor 15, intermediate pressure compressor 14 and fan 13, each by suitable interconnecting shaft.

[0101] Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. By way of example such engines may have an alternative number of interconnecting shafts (e.g. two) and/or an alternative number of compressors and/or turbines. Further the engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan.

[0102] The structure of the fan containment case 22 is illustrated in more detail in FIG. 2 which shows a sectional view of one portion of the fan containment case. The fan containment case 22 comprises a middle portion (a barrel) 23 which extends between a forward portion 24 and an aft portion 25. The fan containment case 22 is formed predominantly from fibre-reinforced composite material and is located around the fan 13.

[0103] A fan impact liner 26 is adhered to an inboard surface of the middle portion 23 of the fan containment case 22. The fan impact liner 26 is constructed from layers of fibre-reinforced composite material and honeycomb material and is designed to absorb a substantial amount of energy on impact of a blade during a fan blade-off (FBO) event. An abradable layer 27 constructed from honeycomb material is adhered to the fan impact liner 26. Forward and aft acoustic liners 28 and 29 are adhered to the fan containment case 22 proximate the forward 24 and aft 25 portions respectively. The fan containment case 22 acts as a rigid structural support for the fan impact liner 26, abradable layer 27, and acoustic liners 28 and 29.

[0104] The internal structure of an impact portion 30 of the middle portion 23 of the fan containment case 22 is shown in more detail in FIG. 3. This portion 30 of the fan containment case 22 is formed from alternating sub-laminate layers of carbon-fibre reinforced polymer (CFRP) material 31, 32 and 33 spaced apart from one another by layers of a ductile polymeric material 34 and 35, for example, polyurethane or phenolic resin. The layers of ductile polymeric material 34 and 35 are bonded directly to the CFRP sub-laminates to provide a laminate structure. The layers of ductile polymeric material are typically substantially thinner than the CFRP sub-laminates. For example, the layers of ductile polymeric material may be about 0.5 mm thick while each CFRP sub-laminate may be about 3.0 mm thick. The CFRP material comprises unidirectional carbon fibre plies bonded to one another in a resin matrix, although it will be appreciated that the CFRP material could be replaced by any fibre-reinforced composite material the skilled person considers suitable for use. The ductile polymeric layers are solid polymer films.

[0105] The impact portion 30 extends angularly completely around the engine (i.e. completely around the circumference of the fan containment case 22) in the region of the fan containment case 22 which is proximate the fan. The remainder of the fan containment case 22 may be formed from CFRP material without layers of ductile polymeric material, although the structure of the impact portion 30 may also be repeated in other regions, for example, throughout the fan containment case.

[0106] The structure of the impact portion 30 is designed to absorb a significant amount of energy from an impacting fan blade during an FBO event. In particular, ductile polymeric materials, like polyurethane or phenolic resins, are significantly more ductile and flexible than fibre-reinforced materials like CFRP. For example, ductile polymeric materials like polyurethane or phenolic resins typically have significantly higher elongations to failure and significantly lower elastic moduli (in particular, tensile elastic moduli) than fibre-reinforced materials like CFRP. Accordingly, on impact of a fan blade during an FBO event, the layers of ductile polymeric material in the impact portion of the fan containment case are able to undergo substantially more elastic and plastic deformation compared to the sub-laminates of CFRP. This means that, on impact, the ductile polymeric layers effectively behave independently of the CFRP sub-laminates and shear stress transfer between adjacent ductile polymeric layers and CFRP sub-laminates is minimal.

[0107] This effect is illustrated in FIG. 4 which shows that an impact occurring on an inboard surface at point I leads to shear stress distributions shown schematically at D1, D2 and D3 for sub-laminates 31, 32 and 33 and minimal stress supported by the ductile polymeric layers 34 and 35. The resultant compressive stress experienced by the CRFP sub-laminate 33 on the inboard side of the impact portion (indicated by arrows 37 at point I) and the tensile stress experienced by the CFRP sub-laminate 31 on the outboard side of the impact portion (indicated by arrows 38 at point O) is much reduced compared to the compressive and tensile stresses which would be experienced were the ductile polymeric layers not present. This reduces the likelihood that the ultimate tensile or compressive strengths of the carbon fibres in the CFRP sub-laminates will be reached and, consequently, reduces the likelihood of brittle failure of the CFRP sub-laminates.

[0108] By including the layers of ductile polymeric material, the CFRP sub-laminates are able to bend more before failure than could be achieved using a monolithic slab of CFRP material. Effectively, the ductility of the CFRP laminate structure is increased by inclusion of the layers of ductile polymeric material. The impact region of the fan containment case is therefore able to absorb significantly more energy on impact of a fan blade. In addition, crack propagation through the thickness of the laminate structure is hindered by the presence of the ductile polymeric material layers which deform first elastically and then plastically on impact rather than undergoing brittle failure.

[0109] FIG. 5 compares the amount of energy which can be absorbed by a test portion of a fan containment case comprising an impact region containing ductile polymeric layers with the baseline amount of energy absorbed by a reference test portion of a pure CFRP fan containment case under the same impact conditions. In FIG. 5, the amounts of energy absorbed by phenolic and polyurethane layers are expressed as percentages relative to a normalised baseline of 100%. Use of both phenolic resins and polyurethane layers leads to an increase in the amount of energy absorbed. The ductile polymeric layers increase the amount of energy required to initiate a crack through the laminate structure or to initiate fibre failure (referred to as the “initiation energy”), both of which mechanisms can result in a reduction in load carrying capacity. Of these two examples, use of polyurethane in particular, which has a higher elongation to failure, leads to a substantial increase in the total amount of energy absorbed on impact.

[0110] FIG. 6 shows force-displacement plots measured for CFRP sub-laminates spaced apart by a polyurethane ductile polymeric material (dark grey) and for a CFRP laminate structure lacking ductile polymeric material (light grey). The ductility of the laminate is increased significantly by addition of the ductile polymeric layers, as indicated by the increased maximum displacement before yield. The energy absorbed by the structures can be determined by the area under the force-displacement plots.

[0111] The fan containment case 22 may be manufactured using standard composite manufacturing techniques well-known in the field. For example, fan containment case 22 may be manufactured by first laying up a preform for the fan containment case and subsequently curing the preform. Laying up the preform typically involves repeatedly applying carbon-fibre plies to a shaped tool such as a mandrel in a layer-wise manner. Carbon-fibre plies may be applied in the form of carbon-fibre tapes, particularly carbon-fibre tapes pre-impregnated with uncured matrix material such as an uncured resin. Alternatively, uncured matrix material may be injected into the preform after laying up has been completed.

[0112] The impact region of the preform may be constructed by, in the impact region, applying a sheet of the chosen ductile polymeric material instead of individual carbon-fibre plies. The ductile polymeric material may also be provided in the form of a polymer tape so that the same automated lay-up tools may be used to lay up both carbon-fibre and polymer materials. For example, in the impact region, every fifth carbon-fibre ply may be replaced by a sheet of the ductile polymeric material.

[0113] The preform may be shaped or formed prior to curing using any composite shaping or forming techniques known in the art, for example, to form the shaped forward and aft portions of the fan containment case.

[0114] After laying-up and/or shaping or forming is completed, the preform is cured, typically by heating to the curing temperature of the matrix material and/or applying pressure to the preform.

[0115] A simplified method of manufacturing the fan containment case is illustrated in a flow diagram in FIG. 7. In block 101, a first carbon fibre ply impregnated with matrix material is applied to a tool to form a first sub-laminate. In block 102, ductile polymeric material is applied onto the first sub-laminate. In block 103, a second carbon fibre ply impregnated with matrix material is applied to the ductile polymeric material to form a second sub-laminate, thereby forming a preform for the fan containment case. In block 104, the preform structure is cured, for example, by application of heat and pressure.

[0116] It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.