Patent Application
20130224035
Composite materials offer potential design improvements in gas turbine engines. For example, in recent years composite materials have been replacing metals in gas turbine engines, for example in fan blades, because of their high strength and low weight. Most metal gas turbine engine fan blades are titanium alloy. The ductility of titanium fan blades enables the fan to incur a bird strike and remain operable or be safely shut down, as well as other requirements. The same requirements apply to composite fan blades.
A composite airfoil has a root, which connects to the fan mechanism, and a tip opposite the root. A composite airfoil for a turbine engine fan blade is typically designed with a divergent root portion known as a dovetail root. The thickness of the airfoil changes over a short length at the dovetail root. The dovetail root enables the airfoil to withstand typical operational loads from rotation and bending and loads from foreign object strikes.
The composite airfoil can have a hybrid construction with a three-dimensional woven core at the center and two-dimensional filament reinforced plies or laminations on either side, can be completely woven with no plies or laminations or can be made completely of two-dimensional plies. To form the composite airfoil with a woven core and laminations, individual two-dimensional laminations typically are cut and stacked in a mold with the woven core. The woven core extends from the root to the tip of the airfoil and the plies are stacked on either side of the woven core to form the desired exterior surface profile. The mold is injected with a resin or matrix material using a resin transfer molding process and cured. Completely woven blade preforms can be placed in a mold and injected with a resin or matrix material without the laminations added.
Fan blades properties can be changed throughout different regions of the blade by various methods, such as changing the weave pattern throughout the blade and changing the laminate architecture (i.e. stacking sequence and/or orientation of plies). This can help a blade to withstand impact damage, for example at locations where it is susceptible to foreign object damage.
A composite airfoil includes a woven preform with warp yarns of a first material, the preform with a tip, root, leading edge, trailing edge and an intermediate region positioned between the root and the tip; and a first matrix made of a first resin maintaining the relative positions of the preform yarns. The composite blade further includes at least one of: fill yarns of a second material in the woven preform; and a second matrix made of a second resin maintaining the relative positions of the preform yarns in a portion of the airfoil.
A method of forming a composite airfoil includes weaving warp yarns and fill yarns to form a woven preform; inserting the preform into a mold; injecting a first portion of the mold with a first resin to form a first matrix for maintaining the relative positions of the yarns; injecting a second portion of the mold with a second resin to form a second matrix for maintaining the relative positions of the yarns; and curing the resins.
The portion of inlet air which is taken in through fan 12 and not directed through compressor section 14 is typically referred to as bypass air. Bypass air is directed through bypass duct 26 by guide vanes 28. Then the bypass air flows through opening 30 to cool combustor section 16, high-pressure compressor 22 and turbine section 18. Fan 12 includes a plurality of composite blades 32.
Dovetail root 44 has a divergent shape such that root 44 is thicker than intermediate region 42 and tip 40. Composite blade 32 is connected to the fan mechanism of turbofan 12 by root 44. The additional thickness of root 44 enables composite blade 32 to withstand forces from standard operation and from foreign object impacts.
Preform 48 is a woven core formed from two-dimensional weaves, as shown in
The yarns of preform 48 are formed from bundles of fibers. Example fibers for the yarns of preform 48 include but are not limited to graphite fibers, glass fibers, silicon carbide fibers and boron fibers and combinations thereof. Warp fibers 52 are made of a high-strength material, for example, a material with about 900 ksi tensile strength. Fill fibers 50 are made of a high stiffness material, for example, a material with about 80 Msi tensile modulus.
Example resins to form matrix include but are not limited to epoxy resins and epoxy resins containing additives such as rubber particulates or other toughening agents. First matrix 54 is high-toughness and is used in tip 40 and intermediate region 42 of blade 32 and is designed to give tip 40 region of blade 32 greater impact resistance, as this is the region most susceptible to bird strike. Second matrix 52 is used in root 44 of blade, and is a high-strength matrix designed to give root 44 greater static strength properties, including in-plane strength and interlaminar strength. As root 44 of blade is thick in comparison to airfoil 33, and the relative impact velocity in root 44 is comparatively lower, local bird strike impact damage in that region is not general a design driver. Therefore, matrix 52 is designed to be high strength to improve resistance to bending from impacts in other regions of blade 32.
As blades can be susceptible in differing amounts to damage in different regions, it is sometimes desirable to vary blade characteristics and properties according to the region of the blade. For example, in past hollow metallic blades, the hollow cavities were oriented spanwise in the root to optimize longitudinal stiffness and chordwise at the tip to improve bird impact resistance.
Blade 32 is able to better resist bird strike and other abnormal loading by varying materials throughout blade 32. Near tip 40, where bird-strike is more likely, high-toughness impact resistant matrix 54 is used. In root 44, where resistance to bending is desired, high-strength matrix 56 is used. In weave, high-strength warp fibers 52 are used to improve blade 32 strength properties in the spanwise direction, and high-stiffness fill fibers 52 are used to improve resistance to deformation in the chordwise direction. By varying materials in blade 32 (fill fibers 50, warp fibers 52, matrix 54, 56), blade 32 structural properties can be locally tailored to improve blade 32 weight and performance.
The embodiment shown in
Preform 48 is a three-dimensional woven core formed from a plurality of yarns as described further below. In the example shown, preform 48 extends the spanwise length of composite blade 32 from root 44 to tip 40 the chordwise width of composite blade 32 from leading edge 34 to trailing edge 36. In some embodiments, preform 48 would not extend the entire spanwise length or chorwise width of the blade, and/or can have laminate sections positioned on either side of preform 48.
Yarns 62, 64 and 66 extend in the longitudinal (or spanwise) direction of preform 48. Fill yarns 60 are placed at a 90 degree angle to the direction of warp weaver yarns 62 and 64, and stuffer yarns 66 and are aligned in the chordwise direction of preform 48. Warp weaver yarns 62 and 64 are woven with fill yarns 60 to interlock the yarns. Warp weaver yarns 64 interlock fill yarns 60.
Stuffer yarns 66 extend between fill yarns 60. Stuffer yarns 66 do not interlock with fill yarns 60. One skilled in the art will recognize that yarns 62, 64 and 66 extend through separate warp yarn planes. A single warp yarn plane contains only one of yarns 62, 64 and 66.
The material used for yarns 60, 62, 64 and 66 can be varied to locally tailor blade 32 properties. This can help to increase strength and/or stiffness in particular regions of the blade, making it better able to resist damage from a foreign object strike. Additionally, as discussed in relation to
Varying the matrix and fiber materials affects the physical properties of blade 32, allowing local tailoring to improve blade 32 weight and performance. For example, varying matrix material to provide a high-toughness matrix near tip 40 and a high strength matrix near root 44 can give blade 32 extra resistance to bird strike damage while providing added strength in root 44 to resist bending in the event of a bird strike. This improves the ability of composite blade 32 to withstand stresses from operation and foreign object strikes. The use of higher-toughness or strength matrix, or higher strength or stiffness fibers can replace the extra material that was used in some prior art blades to resist bird impact, keeping the weight of blade 32 to a minimum. Additionally materials could be chosen and placed in regions to offer acoustic dampening properties desired (e.g., use a matrix at the tip that can absorb noise due to high speeds at the tip generating a lot of noise), conform blade 32 to temperature constraints, resist corrosion in areas of blade 32 most susceptible (e.g., tip 40 or leading edge 34), resist delamination and locally tailor regions of blade 32 according to any other material properties desired.
Varying materials also provides blade 32 with a great deal of flexibility to locally tailor physical properties without complicating the manufacturing process. Preform 48 has a uniform weave pattern despite varying materials used in different regions of blade 32. The uniform weave pattern maintains an integrated structure and improves the ease of manufacturing preform 48.
The specific examples of the varying of materials in blade 32 discussed in relation to
A composite airfoil includes a woven preform with warp yarns of a first material, the preform with a tip, root, leading edge, trailing edge and an intermediate region positioned between the root and the tip; and a first matrix made of a first resin maintaining the relative positions of the preform yarns. The composite airfoil further includes at least one of: fill yarns of a second material in the woven preform; and a second matrix made of a second resin maintaining the relative positions of the preform yarns in a portion of the airfoil.
Alternative and/or additional embodiments include the woven preform being a three-dimensional weave and further including stuffer yarns; having a leading edge sheath on the leading edge of the preform; having stuffer yarns of a third material; having a third matrix made of a third resin maintaining the relative positions of the preform yarns in a portion of the airfoil; and/or the airfoil being a blade.
A composite airfoil includes a preform of yarns woven, the preform having a leading edge, trailing edge, tip region, a root region and an intermediate region positioned between the tip region and the root region, with the yarns comprising warp yarns forming a longitudinal axis of the preform; and fill yarns positioned at about a 90 degree angle to the warp yarns, wherein the warp yarns are a different material than then fill yarns. The airfoil further comprises a first matrix to maintain the relative positions of the preform yarns.
Additional and/or alternative embodiments include the leading edge having a sheath, stuffer yarns in the preform woven with the warp yarns and the fill yarns; the stuffer yarns being a different material than the warp yarns or the fill yarns; a second matrix used in portions of the preform to maintain relative positions of the preform yarns in those portions of the preform, wherein the second matrix has different material properties than the first matrix; the second matrix being used in the tip region of the preform and the first matrix is used in the intermediate and root regions of the preform; a third matrix used in portions of the preform to maintain relative positions of the preform yarns in those portions of the preform, wherein the third matrix has different material properties than the first matrix and the second matrix; the second matrix is used in the tip region of the preform and the first matrix is used in the root region of the preform.
A method of forming a composite airfoil includes weaving warp yarns and fill yarns to form a woven preform; inserting the preform into a mold; injecting a first portion of the mold with a first resin to form a first matrix for maintaining the relative positions of the yarns; injecting a second portion of the mold with a second resin to form a second matrix for maintaining the relative positions of the yarns; and curing the resins.
Additional and/or alternative embodiments include the warp yarns being of a different material than the fill yarns; weaving and stuffer yarns to form a three-dimensional woven preform; having one of the warp yarns, the fill yarns and the stuffer yarns is of a different material than the other yarns; having the warp yarns be a first material, the fill yarns be a second material and the stuffer yarns be a third material; the first matrix and the second matrix having different material properties; and/or injecting a third portion of the mold with a third resin to form a third matrix for maintaining the relative positions of the yarns.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
