Patent Description:
Vehicles include many different structural components that are under force during use. For example, skin panels of an aircraft form a surface that is acted upon by aerodynamic forces during flight. As such, the aircraft includes structures configured to reinforce the skin panels and impart aerodynamic forces acting upon the skin panels to load-bearing support structures. For example, structures referred to as "stringers" are used to stiffen skin panels and transmit aerodynamic forces acting upon the skin panels to load-bearing structures such as spars and/or ribs. These stiffeners can take various forms. As examples, some stiffeners have a blade-shaped cross section with a flange and a web, while others have a hollow interior and a cross-sectional shape akin to a top hat.

In some vehicles, one or more structural components are made from composite materials, such as a carbon fiber/epoxy system. In such vehicles, skin and stiffeners are formed as a unitary structure by bonding, co-curing or infusing the skin and stiffeners together. However, forming such unitary composite parts can pose various challenges. For example, a fiber layer used in a composite part can have limits on formability, such as a minimum radius of curvature to which it can be bent without damaging the fiber, introducing defects into the composite part, creating a void (e.g., a deltoid) at the radius, or distorting surrounding material. Radius fillers can be employed at intersections between surfaces where the fiber layer is bent, thereby preventing distortion in the surrounding material as it transitions from one surface to another.

<NPL>, XP055855785, in accordance with its abstract, states that three-dimensional (3D) profiled woven fabrics with varying cross-sections along the component parts are needed in a number of industrial applications. One of the main advantages of the ribbon loom weaving technique is the ability to produce diverse structures with open or closed edges. The realization of 3D profiled woven fabrics that satisfy the requirements is directly connected to the ability to process high-performance fibers in the weft direction. The processing of high-performance yarns in the weft direction with low fiber damage will open new application areas for shuttle weaving machines. By employing modified mechanical loom elements, the variety of producible structures can be increased.

<CIT>, in accordance with its abstract, states that one or more layers of fiber material are braided or wound around a two part tool core. One part of the core is then removed and the wound fiber structure remaining on the other half is compressed to create a preform. The preform is placed in a resin transfer molding tool, impregnated with resin and cured. The core half remaining in the molded fiber reinforced plastic (FRP) component is then removed.

To address the above issues, according to one aspect of the present disclosure, a composite part comprising a three-dimensional (3D) textile preform is defined in appended claim <NUM>.

The composite part comprises a composite skin comprising one or more material layers. A composite load-bearing structure is coupled to the composite skin. The composite load-bearing structure comprises the 3D textile preform. The 3D textile preform comprises a flange portion adjacent to the one or more material layers of the composite skin. A stiffener portion extends upwardly from the flange portion. The stiffener portion comprises a first wall portion that extends from the flange portion and a second wall portion that extends from the flange portion at a location spaced from the first wall portion. A connecting portion connects the first wall portion and the second wall portion at a location spaced from the flange portion. The stiffener portion further comprises a web portion extending from the connecting portion.

The composite part further comprises a cured polymer matrix at least partially surrounding the one or more material layers of the composite skin and the 3D textile preform.

According to another aspect of the present disclosure defined in appended claim <NUM>, a vehicle comprises the composite part.

According to another aspect of the present disclosure defined in appended claim <NUM>, a method of forming a composite part for a vehicle comprises forming the 3D textile preform which comprises said flange portion and said stiffener portion.

The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or can be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings.

As introduced above, various components of a vehicle can be made from composite materials. <FIG> shows one example of a vehicle in the form of an aircraft <NUM> comprising composite parts. In other examples, the vehicle can take the form of a ground-based vehicle (e.g., a car or truck), a drone, a surface watercraft, a submarine, a spacecraft, or any other suitable vehicle. Although, an aircraft and stringers are used as an example, it is contemplated that the approach here could apply to other vehicles and structures.

The aircraft <NUM> includes a wing <NUM>. The wing <NUM> comprises a framework of load-bearing components, including a plurality of frame components <NUM> and stiffeners in the form of stringers <NUM>. The stringers <NUM> stiffen a lower skin <NUM> of the aircraft and transfer loads from the skin <NUM> to the frame components <NUM> to distribute loads throughout the aircraft <NUM>.

In some examples, the skin <NUM>, the stringers <NUM>, and/or any other suitable components of the aircraft <NUM> are formed from composite materials. For example, and as introduced above, the skin <NUM> and one or more stiffeners (e.g., stringers <NUM>) are formed as a unitary composite structure by constructing a preform that includes the skin and the one or more stiffeners, infusing the preform with liquid resin, and curing the parts together. In other examples, a composite skin and composite stiffener can be formed and cured separately, and then joined after both parts are cured.

Forming such a potentially complex composite part can pose various challenges. For example, as mentioned above, some fiber layers for use in composites have limits regarding how tight of an angle can be formed by the fiber layer, requiring a radiused bend to be used where the fiber layer changes direction. Introducing a radius between two or more components of a stiffener can result in an open or enclosed void, also referred to a deltoid, in the resulting composite part. The deltoid can be strengthened by packing the void with a filler material, such as a "noodle" (an elongated filler shaped to fit the void).

In contrast with such approaches, a technical effect of embodiments herein includes reduced costs and manufacturing steps compared to traditional forming techniques by avoiding the use of a noodle or other filler that can comprise a different material than the rest of the composite part. As such a filler can add weight, and require modifications to cure cycles, processing temperatures and/or pressures, other technical effects of embodiments herein include reduced weight and manufacturing times. Yet other technical effects include avoiding the matching of coefficients of thermal expansion, stiffnesses, and/or other properties compared to the use of fillers.

Accordingly, examples are disclosed that relate to the use of 3D textile preforms in composite parts for vehicles. Briefly, a 3D textile preform according to the present disclosure comprises a flange portion and a stiffener portion extending upwardly from the flange portion. The stiffener portion comprises a first wall portion that extends from the flange portion and a second wall portion that extends from the flange portion at a location spaced from the first wall portion. A connecting portion connects the first wall portion and the second wall portion at a location spaced from the flange portion. In some examples, the stiffener portion further comprises a web portion extending from the connecting portion, with a bulb portion located at a distal end of the web.

The use of 3D textile preforms allows for the convenient fabrication of complex composite parts in a time and cost-saving manner compared to the use of individual fiber layers. For example, a 3D textile preform having a complex shape can be formed as a unitary structure using a single pass on a weaving or braiding apparatus. Further, the 3D textile preform can be formed in curved shapes without wrinkling. In addition, the 3D textile preform can be formed without introducing voids (e.g., a deltoid) in the structure, obviating the use of a noodle or other filler materials.

As mentioned above, a 3D textile preform can be woven, e.g., using orthogonal 3D weaving techniques, or braided. In a 3D woven structure, a set of warp fibers, weft fibers, and binder fibers are interlaced in three dimensions. The warp fibers and weft fibers form each of a plurality of two-dimensional layers (e.g., in the XY plane), while the binder fibers interlace the structure in a through-thickness (e.g., Z-axis) direction. In such a braided structure, three or more sets of yarn are inter-plaited.

In contrast to other techniques, such as a stitching process in which two-dimensional textile layers are joined together by a sewing process utilizing a needle weaving or braiding can allow all parts of a complex 3D textile preform to be made integral to a single structure without stitching layers together with a needle. Nevertheless, stitching also can be used to form a 3D textile preform in some examples by stitching together multiple two-dimensional (2D) fiber layers.

As one example of a 3D preform, a preform for a stringer is formed by 3D textile manufacturing processes. In contrast with the use of 2D fiber layers to form such structures, fabricating a 3D textile preform does not introduce voids (e.g., a deltoid) in the structure, thereby allowing the omission of a noodle or other filler. When incorporated in a composite part, the absence of voids can increase resistance to delamination and interlaminar fracturing, and increase tolerance to tensile strain. In addition, the 3D textile preform renders the composite part more resistant to ballistic and impact damage than a similarly shaped laminar composite.

<FIG> shows a perspective view of an example of a composite part <NUM> according to the present disclosure. The composite part <NUM> in the illustrated example is a stringer, but as mentioned above, the composite part <NUM> can be any other suitable part of a vehicle. The composite part <NUM> comprises a composite skin <NUM> and a composite load-bearing structure <NUM>. The composite skin <NUM> comprises one or more fiber layers contained within a hardened resin matrix and can be formed from any suitable materials. Examples of suitable fiber materials include carbon fiber, fiberglass, polyimide fibers, aramid fibers, basalt, and polypropylene fibers.

In some examples, the composite skin <NUM> comprises two or more different fiber materials. Examples of suitable resin materials include epoxies, bis-maleimides (BMI), benzoxazines, phenolics, polyimides, phthalonitrile, other thermoplastic or thermosetting resins or adhesives, and combinations thereof.

The composite load-bearing structure <NUM> comprises a 3D textile preform (schematically depicted at <NUM>) contained within a hardened resin matrix, instead of individual layers of fiber material. The 3D textile preform <NUM> is described in more detail below with reference to <FIG>. The depicted example composite load-bearing structure comprises a flange <NUM> and a stiffener <NUM> extending upwardly from the flange <NUM>. The flange <NUM> is secured to the composite skin <NUM>. In some examples, the flange <NUM> is secured to the composite skin by co-infusion of the 3D preform <NUM> of the composite load-bearing structure <NUM> and a preform for the skin <NUM>. In other examples the flange <NUM> is secured to the skin after forming the composite load-bearing structure <NUM> and the skin <NUM> separately.

The composite load-bearing structure further comprises a first wall <NUM>, a second wall <NUM>, and a connector <NUM> extending between the first wall <NUM> and the second wall <NUM>. The first wall <NUM>, the second wall <NUM>, and the connector <NUM> define a channel <NUM> above the flange <NUM>. The channel extends through the composite structure along a long dimension of the structure (e.g., the y-axis direction, which corresponds to a length of a stringer). In some examples, other structures (e.g., vehicle components or systems, for example wires) can be routed inside the channel (e.g., to and through), which can help free space outside of the composite part and potentially reduce weight and other stresses applied to the composite part.

The composite load-bearing structure further comprises a web <NUM> extending from the connector <NUM>. The web <NUM> comprises a bulb <NUM> at a distal end, which can help strengthen the stiffener by increasing a mass of the web.

<FIG> shows an end view of the 3D textile preform <NUM> of <FIG>. The 3D textile preform <NUM> is infused with a resin matrix and joined with a composite skin (either by co-infusion or joined after resin infusion) to form a composite load-bearing structure.

The 3D textile preform <NUM> comprises a flange portion <NUM> and a stiffener portion <NUM>. The flange portion <NUM>, when infused with a resin matrix that is cured or otherwise hardened, forms a flange within a composite load-bearing structure. Likewise, the stiffener portion <NUM> forms a stiffener within the composite load-bearing structure.

The stiffener portion <NUM> comprises a first wall portion <NUM> and a second wall portion <NUM> that extend from the flange portion <NUM>. As introduced above, by using 3D textile fabrication techniques such as 3D weaving or 3D braiding, the flange portion <NUM> and the stiffener portion <NUM> are integrally formed. The illustrated example is devoid of deltoids where the first wall portion <NUM> and the second wall portion <NUM> meet the flange portion <NUM>.

As shown in cutout <NUM>, the 3D textile preform <NUM> comprises a plurality of warp fibers <NUM>, a plurality of weft fibers <NUM>, and a plurality of binder fibers <NUM>. In some examples, each of the warp fibers <NUM>, the weft fibers <NUM>, and the binder fibers <NUM> comprises a carbon fiber yarn. In other examples, the fibers comprise any other suitable material, examples of which include yarns formed from glass fibers, polyimide fibers, aramid fibers, basalt, and polypropylene fibers. In yet other examples, the warp fibers <NUM>, the weft fibers <NUM>, or the binder fibers <NUM> comprise two or more different materials. The term "fiber" as used herein represents any fibrous material used in a 3D textile. In other examples, the 3D textile preform <NUM> can be braided or sewn, rather than woven.

In the example of <FIG>, the warp fibers <NUM> and the weft fibers <NUM> are orthogonal to each other but can have any other suitable relative orientation in other examples. The binder fibers <NUM> interlace with the warp fibers <NUM> and the weft fibers <NUM> in a through-thickness direction. By weaving the 3D textile preform in this way, all components of the 3D textile preform are integral to a common textile structure. With this configuration, stresses on the stiffener portion <NUM> can be distributed along the flange portion <NUM>, thereby increasing resilience in a composite formed from the 3D textile preform <NUM> over laminar composites.

In some examples, mode I interlaminar fracture toughness and crack propagation values (G1C) were increased up to <NUM> times over two-dimensional reinforced epoxy laminates as measured using ASTM standard test method D5528-<NUM>. The interlaced binder fibers <NUM> also help to increase strength between layers of the warp fibers <NUM> and the weft fibers <NUM>, which can increase impact resistance relative to laminar composites (e.g., as determined by compression after impact (CAI); ASTM standard test method D7137).

In some examples, the warp fibers <NUM>, weft fibers <NUM>, and binder fibers <NUM> can form a mesh structure that can be bent or stretched to an extent after the 3D textile preform is fabricated without damaging the preform or introducing wrinkles. Further, as mentioned above, a 3D textile preform can be formed in shapes that can pose difficulties for conventional 2D fiber sheets.

For example, <FIG> shows a 3D textile preform <NUM> formed to have curvature along its length. Depending upon the amount of curvature and the 3D textile process used to form a preform, such curvature also can be imparted to a straight preform in some examples. In contrast, forming such a structure with conventional 2D fiber sheets can cause the sheets to wrinkle.

With reference again to <FIG>, the 3D textile preform <NUM> comprises radii where the first wall portion <NUM> meets the flange portion <NUM> and where the second wall portion <NUM> meets the flange portion <NUM>. More specifically, the 3D textile preform <NUM> comprises a first internal radius <NUM> between the first wall portion <NUM> and the flange portion <NUM>, located on an internal side of the stiffener portion that faces the second wall portion <NUM>. The 3D textile preform <NUM> further comprises a first external radius <NUM> between the first wall portion <NUM> and the flange portion <NUM>. The first external radius <NUM> is located on an external side of the stiffener portion that faces away from the second wall portion <NUM>. The first internal radius <NUM> and the first external radius <NUM> help to distribute force where the first wall portion <NUM> meets the flange portion <NUM>.

Likewise, the 3D textile preform <NUM> comprises a second internal radius <NUM> between the second wall portion <NUM> and the flange portion <NUM>. The second internal radius <NUM> is located on an internal side of the stiffener portion that faces the first wall portion <NUM>. A second external radius <NUM> is located between the second wall portion <NUM> and the flange portion <NUM> on an external side of the stiffener portion that faces away from the first wall portion <NUM>. The second internal radius <NUM> and the second external radius <NUM> help to distribute force where the second wall portion <NUM> meets the flange portion <NUM>. With both the external and internal radii where wall portions meet the flange portion, no deltoids exist where the flange portions and web portion meet.

The second wall portion <NUM> is spaced from the first wall portion <NUM> at distal ends of the wall portions. As such, a connecting portion <NUM> connects the first wall portion <NUM> and the second wall portion <NUM> at the distal ends of the wall portions. In this manner, the first wall portion <NUM>, the second wall portion <NUM>, and the connecting portion <NUM> define a channel <NUM> above the flange portion <NUM>.

The channel <NUM> extends through the 3D textile preform <NUM> along a long dimension of the preform (e.g., the y-axis direction, which corresponds to a length of a stringer). In the illustrated example, the channel <NUM> is enclosed by the flange portion <NUM>, the first wall portion <NUM>, the second wall portion <NUM>, and the connecting portion <NUM> along the length of the 3D textile preform but is open at both ends of the 3D textile preform. In other examples, the channel can be enclosed at the ends of the 3D textile preform and/or include one or more openings along the length of the preform.

In some examples, one or more vehicle systems can be installed within the channel <NUM>. For example, one or more electrical cables, fuel and/or other fluid lines, pneumatic tubing, and/or mechanical parts (e.g., manual control cables) of an aircraft can be routed through the channel. In this manner the composite part formed from the preform <NUM> can help to protect any components that are routed through the channel. Further, components can be routed through the channel that would otherwise be attached to an exterior portion of the composite part (e.g., via clips or brackets), reducing weight and other stresses applied to the composite part and freeing space outside of the composite part. In some examples, the channel can be hermetically sealed and/or vaporproof, allowing fluids and/or gasses (e.g., jet fuel or nitrogen gas) to be directly transferred through the channel.

In the 3D textile preform <NUM> of <FIG>, the first wall portion <NUM>, the second wall portion <NUM>, and the connecting portion <NUM> together comprise a top-hat cross-section. In other examples, the 3D textile preform can have any other suitable cross-sectional shape.

For example, <FIG> shows another example of a 3D textile preform <NUM> comprising an elliptical channel. Like the 3D textile preform <NUM> of <FIG>, the 3D textile preform <NUM> comprises a flange portion <NUM> and a stiffener portion <NUM> extending upwardly from the flange portion <NUM>. The stiffener portion <NUM> comprises a first wall portion <NUM> and a second wall portion <NUM> that extend from the flange portion <NUM>. The first wall portion <NUM> and the second wall portion <NUM> are joined at a connecting portion <NUM> of the 3D textile preform <NUM>. As shown in <FIG>, the first wall portion <NUM>, the second wall portion <NUM>, and the connecting portion <NUM> form an elliptical channel <NUM> above the flange portion <NUM>.

Returning to the example of <FIG>, the 3D textile preform <NUM> further comprises a web portion <NUM> extending from the connecting portion <NUM>. The web portion <NUM> extends from the top of the connecting portion <NUM> in the positive Z-axis direction. <FIG> shows a height <NUM> of the web portion <NUM> above the connecting portion <NUM> of the 3D textile preform. In some examples, the height <NUM> is in a range of <NUM> to <NUM> inches. In other examples, the height <NUM> is in a range of <NUM> to <NUM> inches. In yet other examples, the height <NUM> is in a range of <NUM> to <NUM> inches. It will also be appreciated that the height <NUM> can have any other suitable value.

In some examples, the web portion <NUM> comprises a consistent thickness <NUM> (e.g., <NUM> inches) along at least a portion of its height. The height <NUM> and the thickness <NUM> of the web portion <NUM> both contribute to a stiffness (e.g., as defined by the product EI of Young's modulus (E) and the second moment of area (I)) of the composite part formed from the preform <NUM>. In some examples, the thickness <NUM> is in a range of <NUM> to <NUM> inches. In other examples, the thickness <NUM> is in a range of <NUM> to <NUM> inches. In yet other examples, the thickness <NUM> is in a range of <NUM> to <NUM> inches. In other examples, the thickness <NUM> can have any other suitable value.

Further, in yet other examples, the web portion comprises a thickness that varies along its height. <FIG> shows another example of a 3D textile preform <NUM> comprising a tapered web portion <NUM>. Like the web portion <NUM> of <FIG>, the tapered web portion <NUM> extends from a connecting portion <NUM> of the 3D textile preform <NUM>. However, the tapered web portion <NUM> comprises a thickness <NUM> that decreases as a function of distance from the connecting portion <NUM>.

With reference again to <FIG>, the 3D textile preform <NUM> further comprises a bulb portion <NUM> located at a distal end of the web portion <NUM>, opposite to the connecting portion <NUM>. The bulb portion <NUM> increases a mass of the stiffener portion <NUM> of the 3D textile preform, and thereby increases stiffness of the resulting composite part. In some examples, by increasing a mass of the bulb portion <NUM>, the stiffness of the composite part is increased without increasing the height <NUM> of the web portion <NUM>. In this manner, the composite part formed from the preform <NUM> can be able to fit within confined spaces, such as inside of a small aircraft.

In some examples, the bulb portion <NUM> further increases damage tolerance of the composite part formed from the preform <NUM>. For example, impact forces can be dissipated by the bulb portion <NUM>, which can help to prevent delamination and other damage that could potentially occur in a laminar composite structure. In addition, an impact can leave a visible mark on a surface of the bulb portion <NUM>, thereby making it easy to identify and assess the effects of any damage sustained.

In the example of <FIG>, the bulb portion <NUM> comprises an elliptical shape. The elliptical bulb portion can dissipate impact forces received from any angle around the bulb. In some examples, the bulb portion <NUM> comprises a radius of <NUM> to <NUM> ( <NUM> to <NUM> inches). In other examples, the radius is in a range of <NUM> to <NUM> (<NUM> to <NUM> inches). In yet other examples, the radius is in a range of <NUM> to <NUM> (<NUM> to <NUM> inches).

In other examples, the bulb portion <NUM> comprises any other suitable radius. Further, in other examples a bulb portion can have any other suitable shape.

The web thickness <NUM>, the web height <NUM>, the bulb radius, and/or any other suitable dimension of the 3D textile preform <NUM> can be tailored to meet one or more mechanical, thermal, or design specifications for a vehicle. For example, the dimensions of the 3D textile preform <NUM> can be determined based on a size of an aircraft, the aircraft's wing length, fuselage curvature, etc. In some examples, these dimensions are determined using a computational algorithm.

<FIG> illustrates a flow diagram depicting an example method <NUM> of forming a 3D textile preform for a composite part. It will be appreciated that the following description of method <NUM> is provided by way of example and is not meant to be limiting.

At <NUM>, the method <NUM> includes forming a 3D textile preform. As described above, the 3D textile preform comprises a flange portion and a stiffener portion extending upwardly from the flange portion. The stiffener portion comprises a first wall portion that extends from the flange portion. A second wall portion extends from the flange portion at a location spaced from the first wall portion. A connecting portion connects the first wall portion and the second wall portion at a location spaced from the flange portion. As indicated at <NUM>, forming the 3D textile preform can comprise weaving or braiding the 3D textile preform. As described above, in other examples, forming the 3D textile preform can include sewing the 3D textile preform or forming the 3D textile preform using any other suitable technique.

At <NUM>, the method <NUM> optionally includes forming a web portion extending from the connecting portion. In some such examples, as indicated at <NUM>, the method <NUM> includes forming a bulb portion located at a distal end of the web portion.

The method <NUM> includes, at <NUM>, at least partially surrounding the 3D textile with a liquid resin. At <NUM>, the method <NUM> includes curing or otherwise hardening the liquid resin to form a polymer matrix, thereby forming a composite part from the 3D textile preform. As described above and as indicated at <NUM>, the composite part can comprise at least a portion of a stringer or any other suitable part.

The use of 3D textile preforms according of the present disclosure can allow for the convenient fabrication of complex composite parts in a time and cost-saving manner compared to the use of individual fiber layers, which can require more complex and time-consuming lay-up. In addition, by weaving or braiding the 3D textile preform, a composite part can be formed without introducing voids, thereby increasing resistance to delamination and interlaminar fracturing relative to a similarly shaped laminar composite without having to use a void filler, such as a noodle.

Claim 1:
A composite part (<NUM>) for a vehicle, the composite part (<NUM>) comprising:
- a composite skin (<NUM>) comprising one or more material layers,
- a composite load-bearing structure (<NUM>) which is coupled to the composite skin (<NUM>) and which comprises a three-dimensional (3D) textile preform (<NUM>), and
- a cured polymer matrix at least partially surrounding the one or more material layers of the composite skin (<NUM>) and the three-dimensional textile preform (<NUM>),
wherein the three-dimensional textile preform (<NUM>) comprises:
a flange portion (<NUM>) adjacent to the one or more material layers; and
a stiffener portion (<NUM>) extending upwardly from the flange portion (<NUM>), the stiffener portion (<NUM>) comprising:
a first wall portion (<NUM>) that extends from the flange portion (<NUM>),
a second wall portion (<NUM>) that extends from the flange portion (<NUM>) at a location spaced from the first wall portion (<NUM>), and
a connecting portion (<NUM>) that connects the first wall portion (<NUM>) and the second wall portion (<NUM>) at a location spaced from the flange portion (<NUM>),
wherein the stiffener portion (<NUM>) further comprises a web portion (<NUM>) extending from the connecting portion (<NUM>).