WO2020011617A1

WO2020011617A1 - Fan blade containment

Info

Publication number: WO2020011617A1
Application number: PCT/EP2019/067852
Authority: WO
Inventors: Kevin MEE; David Groves
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2018-07-13
Filing date: 2019-07-03
Publication date: 2020-01-16
Anticipated expiration: 2021-01-13
Also published as: GB201811547D0

Abstract

A structural support casing (22) for supporting a fan track liner (26) on an inboard surface of the structural support casing in a gas turbine engine comprises at least one region (30) in which two or more sub-laminates (31, 32, 33) of fibre-reinforced composite material are spaced apart from one another by layers of cellular material (34,35).

Description

FAN BLADE CONTAINMENT

Field The present disclosure concerns structural support casings for fan blade containment in gas turbine engines.

Background Gas turbine engines include a fan having fan blades in front of the engine. The fan may be contained in a hardwall fan containment case. During operation, any one of the fan blades may break off from the fan and impact the hardwall fan containment case. This is generally referred to as a fan blade-off (FBO) event. After a turbine engine fan loses a blade, the loads on the fan containment case rise well above those experienced in normal flight conditions because of the fan imbalance. During engine shut down, which is typically about a few seconds, cracks can propagate rapidly in the hardwall fan containment case from the damage caused by the impact of the FBO, which may lead to containment failure. Hardwall fan containment cases are typically made of titanium and are designed to stop a broken blade. More recently, hardwall fan containment cases made of fibre-reinforced composite materials have been proposed. Such composite fan containment cases are strong and typically lighter than cases made of titanium, but can be susceptible to brittle fracture on impact of a broken fan blade.

Summary of invention

According to a first aspect, there is provided a structural support casing for supporting a fan track liner on an inboard surface of the structural support casing of a gas turbine engine, the structural support 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 cellular material.

The structural support casing may be a fan containment casing (e.g. a fan containment case). The structural support casing may be a hardwall fan containment casing (e.g. a hardwall fan containment case). The structural support casing may be a (e.g. hardwall) barrel of a fan containment arrangement.

The cellular material may have a honeycomb structure. The honeycomb structure may comprise a plurality of cells formed between cell walls. The cells may be substantially hollow. The honeycomb structure may be described as a network of connected cell walls at least partially enclosing a plurality of cells, for example, substantially hollow cells. The cell walls may be thin relative to the cell dimensions. For example, the cell walls may have a thickness no greater than 10 %, for example, no greater than 5 %, or no greater than 1%, of a characteristic cell dimension, for example, a cell width. The cell walls may also be thin relative to a thickness of the cellular material. The cell walls may also be thin relative to the distance between adjacent pairs of sub-laminates of fibre-reinforced composite material. The cells may be arranged regularly on a lattice. The cells may be columnar. The cells may be columnar and arranged substantially parallel to one another, i.e. such that the longitudinal axis of each columnar cell is substantially parallel to the longitudinal axis of each other columnar cell.

The two or more sub-laminates of fibre-reinforced composite material may be spaced apart from one another by one or more layers of cellular material. Each sub-laminate (i.e. each sub-laminate of the two or more sub-laminates of fibre-reinforced composite material) may be spaced apart from each adjacent sub-laminate by one layer (e.g. a single layer) of cellular material, that is to say, one layer (e.g. a single layer) of cellular material may be provided between (and may therefore space apart) each adjacent pair of sub-laminates of fibre-reinforced composite material. In embodiments in which the cellular material has a honeycomb structure, the cell walls of the honeycomb structure (and consequently the longitudinal axes of each cell) in each layer may extend substantially perpendicular to the (tangential) plane in which the said layer extends, i.e. substantially perpendicular to an interface between the cellular material and any adjacent sub-laminate.

The honeycomb structure may be a hexagonal honeycomb structure. The columnar cells may be hexagonal in cross-section. The honeycomb structure may be an expanded honeycomb structure (i.e. an “over-expanded” honeycomb structure), a reinforced hexagonal honeycomb structure (i.e. a primarily hexagonal honeycomb structure reinforced by additional cell walls), or a rectangular honeycomb structure. The honeycomb structure may comprise a periodic repeating pattern of cell walls. The repeating pattern may be regular. The repeating pattern may be hierarchical. The repeating pattern may form cells having two or more, or three or more, or four or more, different cell shapes.

The cellular material may comprise one or more polymers. The cellular material may be formed from one or more polymers. The cellular material may be formed from an aramid polymer. The cellular material may be formed from a meta-aramid polymer. The cellular material may be formed from poly (m-phenylene isophthalamide) (otherwise known as Nomex^®). The cellular material may be formed from a para-aramid polymer. The cellular material may be formed from poly paraphenylene terephthalamide (otherwise known as Kevlar^®).

The honeycomb structure may be formed from one or more polymers. The honeycomb structure may be formed from an aramid polymer. The honeycomb structure may be formed from a meta-aramid polymer. The honeycomb structure may be formed from poly (m-phenylene isophthalamide) (otherwise known as Nomex^®). The honeycomb structure may be formed from a para-aramid polymer such as poly paraphenylene terephthalamide (otherwise known as Kevlar^®). The honeycomb structure may be formed from a network of aramid polymer (for example, a meta-aramid polymer such as poly (m-phenylene isophthalamide) or a para-aramid polymer such as poly paraphenylene terephthalamide) cell walls coated in a resin, for example, a phenol or polyimide resin. The honeycomb structure may comprise cell walls formed from poly (m- phenylene isophthalamide) paper (i.e. Nomex^® paper) or poly paraphenylene terephthalamide paper (i.e. Kevlar^® paper) coated in a resin, for example, a phenol or polyimide resin.

The cellular material may comprise one or more fibre-reinforced polymer materials. The cellular material may be formed from one or more fibre-reinforced polymer materials. The cellular material may be formed from carbon fibre reinforced polymer (CFRP) material or glass fibre reinforced polymer (i.e. fibreglass) material.

The honeycomb structure may be formed from one or more fibre-reinforced polymer materials, such as carbon fibre reinforced polymer (CFRP) material or glass fibre reinforced polymer (i.e. fibreglass) material. The honeycomb structure may comprise walls formed from one or more fibre-reinforced polymer materials, such as carbon fibre reinforced polymer (CFRP) material or glass fibre reinforced polymer (i.e. fibreglass) material.

The cellular material may comprise metal, for example, aluminium, titanium or one or more alloys thereof. The cellular material may be formed from metal, for example, aluminium, titanium or one or more alloys thereof.

The honeycomb structure may be formed from metal, for example, aluminium, titanium or one or more alloys thereof. The honeycomb structure may comprise walls formed from metal, for example, aluminium, titanium or one or more alloys thereof.

The cellular material may have a foam structure. The cellular material may be a foam. The cellular material may have a closed-cell foam structure. The cellular material may be a closed-cell foam. The cellular material may have an open-cell foam structure. The cellular material may be an open-cell foam.

The foam structure (e.g. the foam, for example the closed-cell or open-cell foam) may be formed from one or more polymers. The foam structure (e.g. the foam, for example the closed-cell or open-cell foam) may be formed from one or more thermosetting polymers. Alternatively, the foam structure (e.g. the foam, for example the closed-cell or open-cell foam) may be formed from one or more thermoplastic polymers.

The foam structure (e.g. the foam, for example the closed-cell or open-cell foam) may be formed from one or more of the following: epoxy resin, polyethylene (PE), cross-linked polyethylene (e.g. AZOTE^® closed-cell cross-linked polyethylene), polyethylene terephthalate (PET), polyisocyanurate, polyvinyl chloride (PVC), polyurethane, melamine, polymethacrylimide (PMI), polyetherimide (PEI), polystyrene, polyethersulfone (PES).

The foam structure (e.g. the foam, for example the closed-cell or open-cell foam) may be formed from metal, for example, aluminium or alloys thereof.

It will be appreciated that the mechanical properties of cellular materials may be anisotropic, that is to say, the mechanical properties of cellular materials may differ when measured along different axes. Mechanical property anisotropy in a cellular material may arise due to an asymmetric arrangement of cell walls. For example, in a honeycomb structure having aligned columnar cells, out of plane mechanical properties (measured substantially parallel to the cell longitudinal axes and therefore substantially parallel to the cell walls) may be significantly different from in plane mechanical properties (measured substantially perpendicular to the cell longitudinal axes and therefore substantially perpendicular to the cell walls). In contrast, foams may have randomly arranged cells and consequently substantially isotropic mechanical properties.

The cellular material may have an out of plane compressive strength of at least about 0.1 MPa, for example, at least about 0.5 MPa. The cellular material may have an out of plane compressive strength of no greater than about 100 MPa, for example, no greater than about 80 MPa, or no greater than about 70 MPa, or no greater than about 60 MPa, or no greater than about 50 MPa. The cellular material may have an out of plane compressive strength of from about 0.1 MPa to about 100 MPa, for example, from about 0.1 MPa to about 80 MPa, or from about 0.5 MPa to about 60 MPa, or from about 0.5 MPa to about 50 MPa. It may be that the compressive strength of the fibre-reinforced composite material is no less than about 500 MPa, for example, no less than about 750 MPa, or no less than about 1000 MPa, or no less than about 1250 MPa, or no less than about 1500 MPa.

It will be understood that the term“compressive strength” of a material refers to the ultimate compressive strength of that material, i.e. the maximum stress experienced by a sample of material when that sample is loaded in compression until failure.

The cellular material may have an in-plane (i.e. plate) shear strength of at least about 0.05 MPa, for example, at least about 0.1 MPa. The cellular material may have an in- plane (i.e. plate) shear strength of no greater than about 30 MPa, for example, no greater than about 20 MPa, or no greater than about 10 MPa. The cellular material may have an in-plane (i.e. plate) shear strength of from about 0.05 MPa to about 30 MPa, for example, from about 0.1 MPa to about 20 MPa, orfrom about 0.1 MPa to about 10 MPa.

It will be understood that the term“shear strength” of a material refers to the ultimate shear strength (USS) of that material, i.e. the maximum stress experienced by a sample of material when that sample is loaded in shear until failure. In embodiments in which the cellular material has a honeycomb structure, the in-plane (i.e. plate) shear strength may be measured in the L (ribbon) or W directions of the honeycomb structure.

When a load is applied to a cellular material such as a honeycomb structure or a foam structure, it typically undergoes three stages of deformation. First, the cellular material may yield elastically. Second, with increasing strain (for example, above about 5 % strain, dependent on the material), the cell walls in the cellular structure may proceed to buckle and collapse (i.e. undergoing plastic deformation) at a relatively constant stress until, for example, about 50 % strain. The stress at which the deformation of the cellular material transitions from elastic to plastic strain is commonly referred to as the“crush strength” of the material. Third, with ever increasing strain, the cellular material may enter a densification regime in which cell walls contact one another and stress increases rapidly with strain.

The cellular material may have an out of plane crush strength of at least about 0.5 MPa, for example, at least about 1 MPa. The cellular material may have an out of plane crush strength of no greater than about 20 MPa, for example, no greater than about 10 MPa. The cellular material may have an out of plane crush strength of from about 0.5 MPa to about 20 MPa, for example, from about 1 MPa to about 10 MPa.

It may be that the out of plane tensile modulus of the cellular material is no greater than about 2000 MPa, for example, no greater than about 1500 MPa, or no greater than about 1000 MPa. It may be that the out of plane tensile modulus of the cellular material is no less than about 1 MPa, for example, no less than about 5 MPa, or no less than about 10 MPa. It may be that the tensile modulus of the fibre-reinforced composite material is no less than about 70 GPa, for example, no less than about 80 GPa, or no less than about 90 GPa, or no less than about 100 GPa, or no less than about 1 10 GPa, or no less than about 120 GPa.

It will be understood that the term“tensile modulus” refers to the elastic modulus, i.e. Young’s modulus, when measured in tension. The tensile modulus for a material is determined as the ratio of stress to strain along the axis of a sample of the material to which a tensile force is applied, measured at relatively low strains such that Hooke’s law applies (i.e. in the linear region of a stress-strain plot). It may be that the out of plane compressive modulus of the cellular material is no greater than about 2000 MPa, for example, no greater than about 1500 MPa, or no greater than about 1000 MPa. It may be that the out of plane compressive modulus of the cellular material is no less than about 1 MPa, for example, no less than about 5 MPa, or no less than about 10 MPa.

It will be understood that the term“compressive modulus” refers to the elastic modulus, i.e. Young’s modulus, when measured in compression. The compressive modulus for a material is determined as the ratio of stress to strain along the axis of a sample of the material to which a compressive force is applied, measured at relatively low strains such that Hooke’s law applies (i.e. in the linear region of a stress-strain plot).

It may be that the in plane shear modulus of the cellular material is no greater than about 400 MPa, for example, no greater than about 300 MPa, or no greater than about 200 MPa. It may be that the in plane shear modulus of the cellular material is no less than about 1 GPa, for example, no less than about 5 GPa.

It will be understood that the term“shear modulus” refers to the elastic modulus, i.e. Young’s modulus, when measured in shear. The tensile modulus for a material is determined as the ratio of shear stress to shear strain in a sample of the material to which a shearing force is applied, measured at relatively low shear strains such that Hooke’s law applies (i.e. in the linear region of a shear stress-strain plot).

The cellular material may have a density of no greater than about 200 kg/m³, for example, no greater than about 180 kg/m³, or no greater than about 160 kg/m³, or no greater than about 150 kg/m³. The cellular material may have a density of no less than about 10 kg/m³, for example, no less than about 25 kg/m³, or no less than about 50 kg/m³. The cellular material may have a density of from about 10 kg/m³ to about 200 kg/m³, for example, from about 25 kg/m³ to about 180 kg/m³, or from about 50 kg/m³ to about 160 kg/m³, or from about 50 kg/m³ to about 150 kg/m³.

A relative density, R , of the cellular material may be defined as

wherein p^* is the density of the cellular material and p is the density of the solid material from which the cellular material (i.e. the cellular material walls) is formed. The cellular material may have a relative density, R, of no greater than about 0.5, for example, no greater than about 0.4, or no greater than about 0.3, or no greater than about 0.2.

It will be appreciated that the mechanical properties (including tensile and shear moduli, elongation to failure, tensile strength, yield strength, fracture toughness, and hardness) of fibre-reinforced composite materials may be anisotropic, that is to say, the mechanical properties of fibre-reinforced composite materials may differ when measured along different axes. Mechanical property anisotropy in a fibre-reinforced composite material may arise due to an asymmetric arrangement of reinforcing fibres within the composite material.

A laminate or sub-laminate of fibre-reinforced composite material may comprise a plurality of reinforcing fibre plies arranged (i.e. embedded) in a laminated structure within a matrix material. Mechanical property anisotropy in fibre-reinforced composite material laminates or sub-laminates may arise due to (a) the asymmetry caused by the arrangement of reinforcing fibre plies to form a laminate or sub-laminate structure and/or (b) the asymmetry caused by orientation of reinforcing fibres within individual plies. In particular, within each individual ply, reinforcing fibres may be substantially aligned along a single direction (i.e.“unidirectional” plies) or they may be randomly orientated with respect to one another in the plane of the ply. In addition, within each laminate or sub- laminate, different plies may contain reinforcing fibres aligned along different directions. For example, a laminate or sub-laminate may comprise one or more plies in which reinforcing fibres are aligned along a first direction (referred to as a 0° orientation) and one or more plies in which reinforcing fibres are aligned along a second direction substantially perpendicular to the first direction (referred to as a 90° orientation). Additionally or alternatively, laminates or sub-laminates may comprise plies arranged at, for example, 30°, 45°, and/or 60° orientations. By combining multiple plies having different orientations to form a single laminate or sub-laminate, the in-plane mechanical properties of that laminate or sub-laminate may be rendered effectively isotropic (while out-of-plane mechanical properties perpendicular to the plies, i.e. along the ply stacking direction, may remain different from the in-plane properties). Unless otherwise stated, throughout this specification and the appended claims, references to tensile and shear moduli, tensile strength, elongation to failure and yield strength of fibre-reinforced composite materials, or of laminates or sub-laminates comprising fibre-reinforced composite materials, are references to said mechanical properties measured in-plane, i.e. in or parallel to the planes in which individual reinforcing fibre plies lie. In contrast, unless otherwise stated, references to fracture toughness and hardness of fibre-reinforced composite materials, or of laminates or sub- laminates comprising fibre-reinforced composite materials, are references to said mechanical properties measured out-of-plane, i.e. perpendicular to the plane of individual plies.

Some fibre-reinforced composite material laminates or sub-laminates have anisotropic in-plane mechanical properties (e.g. unidirectional laminates or sub-laminates in which most or all of the reinforcing fibre plies are aligned along a single reinforcing fibre axis). Accordingly, unless otherwise stated, references to tensile and shear moduli, tensile strength and yield strength of fibre-reinforced composite materials, or of laminates or sub-laminates comprising fibre-reinforced composite materials, are references to the minimum values of said in-plane mechanical properties for the said fibre-reinforced composite materials, or of laminates or sub-laminates comprising fibre-reinforced composite materials, for example, when measured across a range of in-plane orientations (e.g. at 0°, 45° and 90° to a reinforcing fibre axis). Similarly, unless otherwise stated, references to the elongation to failure of fibre-reinforced composite materials, or of laminates or sub-laminates comprising fibre-reinforced composite materials, are references to the maximum value of said in-plane elongation to failure for said fibre-reinforced composite materials, or of laminates or sub-laminates comprising fibre-reinforced composite materials, for example, when measured across a range of in- plane orientations (e.g. at 0°, 45° and 90° to the reinforcing fibre axis).

It will be appreciated that the observed mechanical properties of cellular materials may depend on the thickness of the cellular material. Throughout this specification and the appended claims, unless stated otherwise, mechanical properties (such as tensile or compressive strength, crush strength or elastic moduli) are measured in accordance with AMS-STD-401 at 0.500 inch material thickness. It may be that the thickness (i.e. along the radial direction) of the cellular material, provided between each (i.e. adjacent) pair of sub-laminates of fibre-reinforced composite material, is no greater than the thickness (i.e. along the said radial direction) of any one of the two or more sub-laminates of fibre-reinforced composite material. For example, it may be that the maximum thickness (i.e. along the radial direction) of the one or more layers of cellular material is no greater than the thickness (i.e. along the said radial direction) of any one of the two or more sub-laminates of fibre-reinforced composite material. It may be that the thickness (i.e. along the radial direction) of (e.g. the one or more layers of) the cellular material is no greater than about 50 % of the thickness (i.e. along the radial direction) of any one of the two or more sub-laminates of fibre-reinforced composite material.

It may be that the thickness of the cellular material provided between each adjacent pair of the two or more sub-laminates of fibre-reinforced composite material is no greater than about 2.0 mm, for example, no greater than about 1.5 mm, or no greater than about 1.0 mm. It may be that the maximum thickness of each of the one or more layers of cellular material is no greater than about 2.0 mm, for example, no greater than about 1.5 mm, or no greater than about 1.0 mm.

It may be that each sub-laminate of fibre-reinforced composite material comprises reinforcing fibre plies having a thickness of no greater than about 1.0 mm, for example, no greater than about 0.8 mm, or no greater than about 0.6 mm, or no greater than about 0.4 mm, or no greater than about 0.3 mm.

It may be that each sub-laminate of fibre-reinforced composite material comprises at least two, for example, at least three, or at least four, or at least five, reinforcing fibre plies. It may be that each sub-laminate of fibre-reinforced composite material has a thickness of no less than about 0.6 mm, for example, no less than about 0.8 mm, or no less than about 1 .0 mm, or no less than about 1.2 mm, or no less than about 1.4 mm, or no less than about 1 .6 mm, or no less than about 1 .8 mm, or no less than about 2.0 mm. It may be that each sub-laminate of fibre-reinforced composite material has a thickness of no greater than about 10.0 mm, for example, no greater than about 8.0 mm, or no greater than about 6.0 mm, or no greater than about 4.0 mm. Each layer of cellular material may be thinner than each sub-laminate of fibre-reinforced composite material. Each layer of cellular material may have a thickness of no greater than 80 %, for example, no greater than 70 %, or no greater than 60 %, or no greater than 50 %, or no greater than 40 %, or no greater than 30 %, or no greater than 20 %, of the thickness of any of the sub-laminates of fibre-reinforced composite material.

It may be that the cellular material has an average cell diameter (i.e. cell size) of no greater than about 20 mm, for example, no greater than about 15 mm, or no greater than about 10 mm. It may be that the cellular material has an average cell diameter of no less than about 0.5 mm, for example, no less than about 1 mm. It may be that the cellular material has an average cell diameter of from about 0.1 mm to about 20 mm, for example from about 1 mm to about 15 mm, or from about 1 mm to about 10 mm.

For a cellular material having a honeycomb structure having columnar cell walls, a maximum in-plane cell diameter may be defined as the maximum straight line distance between opposing cell walls measured in cross-section through the cell perpendicular to the cell walls. For a cellular material having a honeycomb structure having columnar cell walls, a minimum in-plane cell diameter may be defined as the minimum straight line distance between opposing cell walls measured in cross-section through the cell perpendicular to the cell walls.

It may be that the cellular material has a maximum in-plane cell diameter of no greater than about 20 mm, for example, no greater than about 15 mm, or no greater than about 10 mm. It may be that the cellular material has a maximum in-plane cell diameter of no less than about 0.1 mm, for example, no less than about 1 mm, or no less than about 3 mm. It may be that the cellular material has a maximum in-plane cell diameter of from about 0.1 mm to about 20 mm, for example from about 1 mm to about 15 mm, or from about 1 mm to about 10 mm, or from about 3 mm to about 10 mm.

It may be that the cellular material has a minimum in-plane cell diameter of no greater than about 20 mm, for example, no greater than about 15 mm, or no greater than about 10 mm. It may be that the cellular material has a minimum in-plane cell diameter of no less than about 0.1 mm, for example, no less than about 1 mm, or no less than about 3 mm. It may be that the cellular material has a minimum in-plane cell diameter of from about 0.1 mm to about 20 mm, for example from about 1 mm to about 15 mm, or from about 1 mm to about 10 mm, or from about 5 mm to about 10 mm.

Alternatively, for a foam structure, an approximated spherical diameter for each cell may be defined as the diameter of a sphere having the same volume as the said cell. The average cell diameter of the foam structure may then be defined as the approximated spherical diameter averaged over all cells in the cellular material. Accordingly, it may be that the cellular material has an average spherical diameter of no greater than about 20 mm, for example, no greater than about 15 mm, or no greater than about 10 mm. It may be that the cellular material has an average spherical diameter of no less than about 0.1 mm, for example, no less than about 1 mm, or no less than about 3 mm. It may be that the cellular material has an average spherical diameter of from about 0.1 mm to about 20 mm, for example from about 1 mm to about 15 mm, or from about 1 mm to about 10 mm, or from about 3 mm to about 10 mm.

The cellular material may comprise substantially hollow cells. It may be that the majority (for example, all) of the cells in the cellular material are substantially hollow.

It may be that some, for example, the majority (e.g., all), of the cells in the cellular material are filled with gas. For example, it may be that some, for example, the majority (e.g., all), of the cells in the cellular material are filled with air. It may be that at least some, for example, the majority, or substantially all, of the cells of the cellular material are gas- filled cells, for example, air-filled cells.

It may be that the fibre-reinforced composite material is manufactured by curing a matrix material in which reinforcing fibre plies are embedded. It may be that the cellular polymeric is not susceptible to degradation (i.e. does not degrade) during the curing process.

It may be that some, for example, the majority (e.g., all), of the cells in the cellular material are filled with solid material. For example it may be that some, for example, the majority (e.g., all), of the cells in the cellular material are filled with polymer. It may be that some, for example, the majority (e.g., all), of the cells in the cellular material are filled with matrix material (i.e. matrix material from the two or more sub-laminates of fibre-reinforced composite material). It may be that polymer, e.g. matrix material, infiltrates some, for example, the majority (e.g., all), of the cells of the cellular material on curing a preform to form the structural support casing.

It may be that curing the matrix material requires heating the matrix material to a curing temperature. It may be that the cellular material is not susceptible to degradation (i.e. does not degrade) at the curing temperature of the matrix material. It may be that the cellular material is not susceptible to thermal degradation (i.e. does not degrade) at or below a temperature of 300 °C, for example, at or below a temperature of 250 °C, or at or below a temperature of 200 °C, or at or below a temperature of 180 °C.

It may be that the cellular material is stable (e.g. chemically and/or physically stable) at the curing temperature of the matrix material. It may be that the cellular material is stable (e.g. chemically and/or physically stable) at or below a temperature of 300 °C, for example, at or below a temperature of 250 °C, or at or below a temperature of 200 °C, or at or below a temperature of 180 °C.

It may be that the cellular material has a melting temperature higher than the curing temperature of the matrix material. It may be that the cellular material has a melting temperature higher than 180 °C, for example, higher than 200 °C, or higher than 250 °C, or higher than 300 °C.

It may be that the cellular material has a glass transition temperature higher than the curing temperature of the matrix material. It may be that the cellular material has a glass transition temperature higher than 180 °C, for example, higher than 200 °C, or higher than 250 °C, or higher than 300 °C.

It may be that the cellular material has a degradation temperature higher than the curing temperature of the matrix material. It may be that the cellular material has a degradation temperature higher than 180 °C, for example, higher than 200 °C, or higher than 250 °C, or higher than 300 °C.

The fibre-reinforced composite material may be fibre-reinforced polymer, i.e. the matrix material of the fibre-reinforced composite material may be a polymer. The matrix material of the fibre-reinforced composite material may be a thermosetting polymer (i.e. a thermoset). The fibre-reinforced composite material may comprise carbon reinforcing fibres. The fibre-reinforced composite material may be carbon fibre reinforced polymer (CFRP). The fibre-reinforced composite material may comprise resin-bonded unidirectional carbon fibre plies.

The fibre-reinforced composite material may comprise aramid (i.e. aromatic polyamide) reinforcing fibres. The fibre-reinforced composite material may comprise para-aramid reinforcing fibres. For example, the fibre-reinforced composite material may comprise reinforcing fibres formed from poly-paraphenylene terephthalamide (Kevlar^®) or p- phenylene terephthalamide (Twaron^®).

The fibre-reinforced composite material may comprise reinforcing fibres formed from a thermoset liquid-crystalline polyoxazole. For example, the fibre-reinforced composite material may comprise reinforcing fibres formed from poly(p-phenylene-2,6- benzobisoxazole) (PBO or Zylon^®).

The matrix material may comprise (e.g. consist of) one or more of the following: epoxy (i.e. cured epoxy resin), polyester, vinyl ester, polyamide (e.g. aliphatic or semi-aromatic polyamides, for example, nylon).

It may be that only two sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material. Alternatively, it may be that more than two sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material. It may be that at least three, for example, at least four, or at least five, sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material.

It may be that the two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by one or more layers of cellular material.

It may be that each of the two or more sub-laminates of fibre-reinforced composite material is spaced apart from each adjacent sub-laminate of fibre-reinforced composite material by a (for example, only one) layer of cellular material. It may be that the cellular material is not fibre-reinforced, i.e. the cellular material may be unreinforced.

It may be that the two or more sub-laminates of fibre-reinforced composite material and one or more layers of cellular material are arranged (e.g. stacked) alternately (i.e. in a laminar fashion) along a radial direction substantially perpendicular to a longitudinal axis of the structural support casing (i.e. to form a laminate).

It may be that the two or more sub-laminates and the cellular material are bonded to one another. The two or more sub-laminates and the cellular material may be bonded to one another by an adhesive. Alternatively, the two or more sub-laminates and the cellular material may be bonded to one another without use of an adhesive. The two or more sub-laminates and the cellular material may be bonded to one another by polymeric material, for example matrix material, which is continuous or semi-continuous between the two or more sub-laminates and the cellular material. For example, it may be that matrix material extends from the two or more sub-laminates into portions of the cellular material. That is to say, it may be that at least some of the cells of the cellular material contain the same matrix material as present in the fibre-reinforced composite sub- laminates. Accordingly, a bond may be formed between the two or more sub-laminates and the cellular material on curing a preform during manufacture of the structural support casing. For example, it may be that, on curing the preform during manufacture of the structural support casing, matrix material from the two or more sub-laminates of fibre- reinforced composite material flows into at least some of the cells of the cellular material.

It may be that the two or more sub-laminates and the cellular material are not bonded to one another. It may be that cellular material is held between the two or more sub- laminates by pressure from a surrounding laminate structure.

One or more interfaces between the cellular material and the two or more sub-laminates may be brittle. For example, it may be that each interface between cellular material and the two or more sub-laminates is brittle. The said interfaces may be configured to fail in the event that the structural support casing is impacted by a broken fan blade.

The structural support casing may form part of a fan containment arrangement for a gas turbine engine. The fan containment arrangement may comprise the structural support casing and one or more impact liners mounted to an inboard surface of the structural support casing. The structural support casing may be configured to provide the fan containment arrangement with strength and rigidity. The structural support casing may function as an external barrier to fan blade material escaping from the engine during an FBO event. It is therefore desirable that the structural support casing remains intact (i.e. does not fail to permit penetration of fan blade material through the structural support casing) on impact of a fan blade. In contrast, the one or more impact liners may be configured to dissipate energy on impact of a fan blade during an FBO event before the fan blade impacts the structural support casing. The one or more impact liners may function as initial, internal barriers to fan blade material escaping from the engine during an FBO event. Accordingly, the one or more impact liners may be formed from materials or structures which are designed to fail on impact of a blade in a way which maximises impact energy absorption.

The structural support casing may enclose one or more fan liners. The structural support casing may be a structural support casing for enclosing one or more fan liners, for example, a structural support casing configured to enclose one or more fan liners. The structural support casing may support one or more fan liners. The structural support casing may be a structural support casing for supporting one or more fan liners, for example, a structural support casing configured to support one or more fan liners. The one or more fan liners may comprise (e.g. be) one or more impact liners. The one or more fan liners may comprise (e.g. be) one or more acoustic liners. The one or more fan liners may be provided inboard of the structural support casing (e.g. mounted to an inboard surface of the structural support casing, which faces the fan blades when in use in a gas turbine engine).

The at least one region, in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material, may extend around at least about 10 %, for example, at least about 25 %, or at least about 50 %, of the circumference of the structural support casing. The at least one region, in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material, may extend around the majority of, for example, the entire, circumference of the structural support casing. The at least one region, in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material, may extend longitudinally along at least about 5 %, for example, at least about 10 %, or at least about 20 %, or at least about 30 %, or at least about 40 %, or at least about 50 %, of the length of the structural support casing. The at least one region, in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material, may extend longitudinally along the majority of the length, for example, the entire length, of the structural support casing. The at least one region, in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material, may form at least about 1 %, for example, at least about 5 %, or at least about 10 %, or at least about 15 %, or at least about 20 %, or at least about 25 %, or at least about 30 %, or at least about 35 %, or at least about 40 %, or at least about 45 %, or at least about 50 %, of the radial thickness of the structural support casing (i.e. the radial thickness of the structural support casing proximate the said at least one region). The at least one region, in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material, may form the majority, for example, the entirety of the radial thickness of the structural support casing (i.e. the radial thickness of the structural support casing proximate the said at least one region).

The at least one region, in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material, may itself be surrounded by fibre-reinforced composite material. The at least one region, in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material, may be embedded in a larger region of fibre-reinforced composite material. For example, the majority of the structural support casing may be formed from fibre-reinforced composite material. The majority (e.g. entirety) of the structural support casing may be formed from fibre-reinforced composite material other than in the at least one region in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material. The fibre- reinforced composite material present in the at least one region, in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material, may be continuous with (i.e. extend continuously into) the fibre- reinforced composite material surrounding the said at least one region. The two or more sub-laminates of fibre-reinforced composite material may be continuous with (e.g. extend continuously into) the fibre-reinforced composite material surrounding the at least one region. The two or more sub-laminates of fibre-reinforced composite material may be continuous with (e.g. extend continuously into) a greater fibre-reinforced composite material laminate structure surrounding the at least one region.

The structural support casing may comprise one single region in which two or more sub- laminates of fibre-reinforced composite material are spaced apart from one another by cellular material.

The structural support casing may comprise two or more, for example, three or more, or four or more, or five or more, regions in which two or more sub-laminates of fibre- reinforced composite material are spaced apart from one another by cellular material. At least two (for example, each) of the two or more, for example, three or more, or four or more, or five or more, regions may be spaced apart from one another. At least two (for example, each) of the said regions may be spaced apart from one another around the circumference of the structural support casing. At least two (for example, each) of the said regions may be spaced apart from one another along the length of the structural support casing. At least two (for example, each) of the said regions may be spaced apart from one another along a radial direction, i.e. along the radial thickness of the structural support casing (e.g. proximate the two or more regions). The at least two (for example, each) of the said regions which are spaced apart from one another may be spaced apart from one another by fibre-reinforced composite material. The at least two (for example, each) of the said regions which are spaced apart from one another may be spaced apart from one another by joining regions of fibre-reinforced composite material. The fibre- reinforced composite material present in the at least two (for example, each) of the said regions which are spaced apart from one another may be continuous with the fibre- reinforced composite material in the joining regions. The two or more, for example, three or more, or four or more, or five or more, regions, in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material, may partially overlap one another. For example, the said regions may be spaced apart from one another along a radial direction but at least partially overlap around the circumference and/or along the length of the structural support casing.

The structural support casing may include, along an axial extent thereof, a forward portion, a middle portion and an aft portion. The axial extent of the structural support casing may corresponding to the axial location of a fan when the structural support casing is installed in a gas turbine engine. The forward portion and the aft portion may be thinner than the middle portion. Each of the forward portion and the aft portion may be reduced in thickness with distance away from the middle portion. The at least one region, in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material, may be located in the middle portion. The at least one region, in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material, may be selectively located in a portion of the structural support casing configured to surround the fan. The at least one region, in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material, may selectively be located in a projected path of a fan blade during an FBO event. The at least one region, in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material, may be at least one impact region, i.e. at least one impact region most likely to be impacted by a fan blade during an FBO event.

At least a portion of the structural support casing may be formed by the at least one region in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material. The structural support casing may be a fibre-reinforced composite structural support casing formed predominantly from sub-laminates of fibre-reinforced composite material except in the at least one region in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material.

The forward portion of the structural support casing may be forward of the at least one region in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material. The aft portion of the structural support casing may be aft of the at least one region in which two or more sub-laminates of fibre-reinforced composite material are spaced apart from one another by cellular material. The forward and/or aft portions may be free of cellular material, for example, the forward and/or aft portions may comprise stacked plies of fibre-reinforced composite material throughout the component thickness of the said forward and/or aft regions.

The front portion of the structural support casing may comprise a front flange (e.g. a front flange to which an intake may be mounted). The aft portion of the structural support casing may comprise an aft flange. The structural support casing may support the intake. The structural support casing may support a nacelle. The structural support casing may, in use, be supported on a wing of an aircraft by a pylon.

It may be that one, for example, two, of the two or more sub-laminates of fibre-reinforced composite material forms a surface of the structural support casing, for example, an outboard surface or an inboard surface.

According to a second aspect, there is provided a gas turbine engine comprising the structural support casing according to the first aspect. The structural support casing may enclose (e.g. support) a fan liner, for example, a fan impact liner and/or an acoustic liner. The structural support casing may enclose a fan. The structural support casing may be a unitary annular body and the fan liner may comprise a plurality of angularly arranged fan liner panels structurally supported (i.e. mounted on) the structural support casing.

According to a third aspect, there is provided a method of laying up a preform for a structural support casing (i.e. a structural support casing for supporting a fan track liner on an inboard surface of the structural support 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 cellular material onto the first fibre-reinforced composite sub- laminate; and applying a second fibre-reinforced composite sub-laminate onto the cellular material.

The preform may be a preform for an entire structural support casing. The preform may be a preform for a portion of a structural support casing. The structural support casing may be a fan containment casing (e.g. a fan containment case), for example, a hardwall fan containment casing (e.g. a hardwall fan containment case). The preform may be an uncured preform. The first and second fibre-reinforced composite sub-laminates may both be uncured fibre-reinforced composite sub-laminates. The tool may be a mandrel.

Applying the first fibre-reinforced composite sub-laminate to the tool may comprise (e.g. consist of) applying one or more reinforcing fibre plies to the tool. Applying the first fibre- reinforced composite sub-laminate to the tool may comprise (e.g. consist of) stacking the one or more plies on top of one another on the tool. The one or more reinforcing fibre plies may be applied individually to the tool. Alternatively, multiple reinforcing fibre plies may be applied to the tool together (i.e. at the same time). The one or more reinforcing fibre plies may be impregnated with uncured matrix material and/or one or more precursors to matrix material, i.e. said reinforcing fibre plies may be“pre-preg” reinforcing fibre plies. The one or more reinforcing fibre plies may be provided in the form of reinforcing fibre tape. The reinforcing fibre tape may be impregnated with uncured matrix material and/or one or more precursors to matrix material, i.e. said reinforcing fibre tape may be a“pre-preg” reinforcing fibre tape. Alternatively, matrix material may be injected into the preform after the reinforcing fibre plies have been applied.

Applying cellular material onto the first fibre-reinforced composite sub-laminate may comprise applying cellular material sheet onto the first fibre-reinforced composite sub- laminate. Applying cellular material onto the first fibre-reinforced composite sub- laminate may comprise wrapping cellular material sheet around the first fibre-reinforced composite sub-laminate.

Applying the second fibre-reinforced composite sub-laminate onto the cellular material may comprise (e.g. consist of) applying one or more reinforcing fibre plies onto the cellular material. Applying the second fibre-reinforced composite sub-laminate onto the cellular material may comprise (e.g. consist of) stacking the one or more reinforcing fibre plies on top of one another on the cellular material. The one or more reinforcing fibre plies may be applied individually onto the cellular material. Alternatively, multiple reinforcing fibre plies may be applied onto the cellular material together (i.e. at the same time). The one or more reinforcing fibre plies may be impregnated with uncured matrix material and/or one or more precursors to matrix material, i.e. said reinforcing fibre plies may be“pre-preg” reinforcing fibre plies. The one or more reinforcing fibre plies may be provided in the form of reinforcing fibre tape. The reinforcing fibre tape may be impregnated with uncured matrix material and/or one or more precursors to matrix material, i.e. said reinforcing fibre tape may be a “pre-preg” reinforcing fibre tape. Alternatively, matrix material may be injected into the preform after the reinforcing fibre plies have been applied.

The steps of applying cellular material and applying fibre-reinforced composite sub- laminate may be repeated to build up a preform comprising three or more, for example, four or more, or five or more, sub-laminates of fibre-reinforced composite material spaced apart from one another by cellular material. For example, the method may comprise applying the first fibre-reinforced composite sub-laminate to the tool; applying the cellular material onto the first fibre-reinforced composite sub-laminate; applying the second fibre-reinforced composite sub-laminate onto the cellular material; applying cellular material onto the second fibre-reinforced composite sub-laminate; and applying a third fibre-reinforced composite sub-laminate onto the cellular material provided on the second fibre-reinforced composite sub-laminate.

The cellular material may be formed from one or more polymers, for example, an aramid polymer, such as poly (m-phenylene isophthalamide) (otherwise known as Nomex^®) or poly paraphenylene terephthalamide (otherwise known as Kevlar^®). The cellular material may be formed from one or more fibre-reinforced polymer materials, for example, carbon fibre reinforced polymer (CFRP) or glass fibre reinforced polymer (i.e. fibreglass). The cellular material may be formed from metal, for example, titanium, aluminium, or alloys thereof.

The fibre-reinforced composite material may be fibre-reinforced polymer, i.e. the (i.e. cured) matrix material of the fibre-reinforced composite material may be a polymer. The matrix material of the fibre-reinforced composite material may be a thermosetting polymer (i.e. a thermoset). The uncured matrix material may comprise one or more of the following: epoxy resin, polyester resin, polyimide resin, silicone resin, benzoxazine resin, bis-maleimide resin, cyanate ester resin, vinyl ester resin, phenolic resin, polyurethane resin. The uncured matrix material may comprise one or more catalysts or initiators. The cured matrix material may comprise one or more of the following: epoxy (i.e. cured epoxy resin), polyester, polyimide, polysiloxane, vinyl ester, polyamide, polyurethane, polybenzoxazine, bis-maleimide, cyanate ester.

The fibre-reinforced composite material may comprise carbon reinforcing fibres. The fibre-reinforced composite material may be carbon fibre reinforced polymer (CFRP). The fibre-reinforced composite material may comprise aramid (i.e. aromatic polyamide) reinforcing fibres. The fibre-reinforced composite material may comprise para-aramid reinforcing fibres. For example, the fibre-reinforced composite material may comprise reinforcing fibres formed from poly-paraphenylene terephthalamide (Kevlar^®) or p- phenylene terephthalamide (Twaron^®). The fibre-reinforced composite material may comprise reinforcing fibres formed from a thermoset liquid-crystalline polyoxazole. For example, the fibre-reinforced composite material may comprise reinforcing fibres formed from poly(p-phenylene-2,6-benzobisoxazole) (Zylon^®). According to a fourth aspect, there is provided a method of manufacturing a structural support casing for fan blade containment in a gas turbine engine, the method comprising: laying up a preform for the structural support casing by the method according to the third aspect; and curing the preform.

Curing the preform may comprise heating the preform. Curing the preform may comprise heating the preform to a temperature no greater than 300 °C, for example, no greater than 250 °C, or no greater than 200 °C, or no greater than 180 °C. Curing the preform may comprise heating the preform to a temperature no less than 100 °C, for example, a temperature no less than 150 °C.

Additionally or alternatively, curing the preform may comprise applying pressure to the preform.

The method may further comprise forming or shaping the preform prior to curing and/or forming or shaping the structural support casing after curing.

According to a fifth aspect, there is provided a carbon fibre reinforced polymer (CFRP) composite structural support casing for supporting a fan track liner on an inboard surface of the structural support casing of a gas turbine engine, the CFRP composite structural support casing comprising at least one region in which two or more CFRP sub-laminates are spaced apart from one another by one or more layers of cellular material comprising an aramid (e.g., poly (m-phenylene isophthalamide) or poly paraphenylene terephthalamide), metal or fibre-reinforced polymer honeycomb structure, each of the one or more layers of cellular material being no greater than about 2.0 mm, for example, no greater than about 1.5 mm, or no greater than about 1 .0 mm, thick.

The skilled person will appreciate that, except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore, except where mutually exclusive, any feature described herein may be applied to any aspect and/or combined with any other feature described herein. Figures Embodiments will now be described by way of example only, with reference to the Figures, in which: Figure 1 is a sectional side view of a gas turbine engine;

Figure 2 is a sectional side view of a fan containment case;

Figure 3 is a schematic sectional view through a portion of a fan containment case;

Figure 4 is a diagrammatic representation of shear force distribution through a portion of a fan containment case; and Figure 5 is a flow diagram of a method of manufacturing a fan containment case.

Detailed description

With reference to Figure 1 , a gas turbine engine is generally indicated at 10, having a principal and rotational axis 1 1 . 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.

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.

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.

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.

The structure of the fan containment case 22 is illustrated in more detail in Figure 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 (i.e. forward flange) 24 and an aft portion (i.e. aft flange) 25. The fan containment case 22 is formed predominantly from fibre-reinforced composite material and is located around the fan 13.

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.

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 Figure 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 34 and 35 of cellular material which in this example is honeycomb formed from poly (m-phenylene isophthalamide) (otherwise known as Nomex^®) paper coated in resin. The layers of honeycomb 34 and 35 are bonded to the CFRP sub-laminates, by matrix material which extends from the CFRP sub-laminates into some of the honeycomb cells, in a laminate structure.

The layers of honeycomb may be substantially thinner than the CFRP sub-laminates. For example, it is possible to form layers of poly (m-phenylene isophthalamide) honeycomb about 1.0 mm thick, while each CFRP sub-laminate may be about 3.0 mm thick. Sheets of poly (m-phenylene isophthalamide) honeycomb down to thicknesses of 1.0 mm are commercially available, for example, 1.0 mm thick Nomex^® honeycomb sheet from DUPONT™. However, the poly (m-phenylene isophthalamide) honeycomb could be replaced by any suitable cellular material, including honeycomb materials such as another aramid honeycomb material, for example, Kevlar^® honeycomb, or metal or fibre-reinforced polymer honeycomb materials, which are manufacturable at thicknesses of about 1.0 mm. The cellular material should also have a cell size of between about 1 mm to about 10 mm. The cell size should not be too large otherwise surrounding material tends to collapse into the honeycomb cells and leads to excessive consolidation.

In certain embodiments, the layers of cellular material could be layers of closed-cell polymer foam (such as a polyetherimide (PEI) or polymethacrylimide (PMI) foam) able to withstand temperatures between -74°C and 120°C without disbonding. However, closed-cell polymer foams may have lower crush strengths and lower tensile moduli than aramid honeycombs such as Nomex^® honeycomb. It may also be more difficult to form closed-cell polymer foams around curved components.

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 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 honeycomb, although the structure of the impact portion 30 may also be repeated in other regions, for example, throughout, the fan containment case. 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, cellular materials like honeycomb are typically able to absorb the energy of an impact by mechanical deformation through three regimes: an initial elastic deformation regime; a subsequent cell collapse regime, in which cell walls buckle and collapse due to plastic deformation; and finally a densification regime in which adjacent cell walls are pressed into one another and the relative density of the cellular material increases significantly. Accordingly, on impact of a fan blade during an FBO event, the layers of cellular material in the impact portion of the fan containment case are able to undergo substantially more deformation compared to the dense and relatively brittle sub-laminates of CFRP. As the cellular material fails, so does the coupling between adjacent sub-laminates of CFRP. The layers of cellular material essentially behave independently of the CFRP sub- laminates, and adjacent CFRP sub-laminates behave independently of one another; consequently, shear stress transfer between adjacent sub-laminates is minimal.

This effect is illustrated in Figure 4 which shows that an impact occurring at 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 collapsing cellular 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 cellular material 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.

By including the layers of cellular material, the CFRP sub-laminates are able to bend more before failure than could be achieved using a laminate of CFRP material alone, such as a monolithic slab of CFRP material. Effectively, the ductility of the overall laminate structure is increased by inclusion of the layers of cellular material. The impact region of the fan containment case is therefore able to absorb significantly more energy on impact of a fan blade. When a blade impacts the fan containment case, deformation of the cellular material dissipates impact energy around the laminate, by causing relative strain between adjacent sub-laminates, rather than radially through the laminate structure.

In addition, because the cellular material fails completely on impact and adjacent sub- laminates are therefore essentially decoupled from one another, crack propagation through the thickness of the laminate structure is hindered (i.e. the initiation energy required to start a crack between the CFRP sub-laminates is increased). The likelihood of brittle failure of the entire laminate on impact is therefore reduced.

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 may involve repeatedly applying layers of carbon-fibre plies to a shaped tool such as a mandrel. 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.

The impact region of the preform may be constructed by, in the impact region, providing a sheet of the chosen cellular material between carbon fibre plies (i.e. instead of further carbon fibre plies). When provided in a thickness of about 1.0 mm or less, cellular materials such as aramid honeycomb become sufficiently formable to be wrapped around the mandrel and therefore integrated into the laminate preform. Similarly, even generally rigid and brittle closed-cell foam materials become sufficiently flexible for wrapping around the mandrel at low thicknesses. For example, in the impact region, a sheet of cellular material may be inserted between every four carbon-fibre plies.

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.

After laying-up and/or shaping orforming is completed, the preform is cured, for example, by heating to the curing temperature of the matrix material and/or applying pressure to the preform. A simplified method of manufacturing the fan containment case is illustrated in a flow diagram in Figure 5. 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, cellular material is applied onto the first sub-laminate. In block 103, a second carbon fibre ply impregnated with matrix material is applied to the cellular 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. 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.

Claims

1. A hardwall fan containment casing for supporting a fan track liner on an inboard surface of the structural support casing of a gas turbine engine, the structural support 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 cellular material.

2. A hardwall fan containment casing according to claim 1 , wherein the cellular material has a honeycomb structure.

3. A hardwall fan containment casing according to claim 2, wherein the honeycomb structure is one of the following: a hexagonal honeycomb structure, an expanded honeycomb structure, a reinforced hexagonal honeycomb structure, a rectangular honeycomb structure.

4. A hardwall fan containment casing according to claim 2 or claim 3, wherein the honeycomb structure is formed from an aramid polymer, for example, a meta- aramid polymer such as poly (m-phenylene isophthalamide).

5. A hardwall fan containment casing according to claim 1 , wherein the cellular material has a foam structure, for example, a closed-cell foam structure.

6. A hardwall fan containment casing according to any preceding claim, wherein the cellular material has an out of plane compressive strength of from about 0.5 MPa to about 50 MPa.

7. A hardwall fan containment casing according to any preceding claim, wherein the cellular material has an out of plane crush strength of from about 1 MPa to about 10 MPa.

8. A hardwall fan containment casing according to any preceding claim, wherein the cellular material has an in plane shear modulus of from about 5 MPa to about 200 MPa.

9. A hardwall fan containment casing according to any preceding claim, wherein the cellular material has a density of from about 20 kg/m³ to about 150 kg/m³.

10. A hardwall fan containment casing according to any preceding claim, wherein the thickness of cellular material between each pair of sub-laminates of fibre-reinforced material is no greater than about 1.5 mm, for example, no greater than about 1.0 mm.

11. A hardwall fan containment casing according to any preceding claim, wherein the cellular material has an average cell diameter of from about 1 mm to about 10 mm.

12. A hardwall fan containment casing according to any preceding claim, wherein the fibre-reinforced composite material is a fibre-reinforced polymer, for example, carbon fibre reinforced polymer.

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

14. A gas turbine engine comprising the hardwall fan containment casing according to any one preceding claim.

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

16. A method of manufacturing a hardwall fan containment casing for fan blade containment in a gas turbine engine, the method comprising laying up a preform for the hardwall fan containment casing by the method according to claim 13 and curing the preform.