Tethered corners and flanges and articles comprising the same

Tethered flange corners including at least one ply of barrier fibers and at least one fiber tow wrapped about the barrier fibers. Also included are flanges having a tethered corner containing at least one ply of barrier fibers, at least one fiber tow wrapped about the barrier fibers, at least one ply of filler fibers applied over the fiber tow, and at least one ply of flange fibers applied over the filler fibers. Additionally included are articles incorporating a composite structure having a flange with a tethered corner containing at least one ply of barrier fibers and at least one fiber tow wrapped about the barrier fibers.

TECHNICAL FIELD

Embodiments described herein generally relate to tethered corners and flanges and articles comprising the same. More particularly, embodiments herein generally describe tethered corners that can help eliminate the occurrence of bridging of composite materials during flange layup and cure.

BACKGROUND OF THE INVENTION

In recent years composite materials have become increasingly popular for use in a variety of aerospace applications because of their durability and relative lightweight. Although composite materials can provide superior strength and weight properties, designing flanges on structures fabricated from composite materials still remains a challenge.

Current flange lay-up processes can generally involve repeatedly applying plies, or layers, of fabric to a composite structure until a flange having the desired dimensions is obtained. One issue that can arise during this process is that when a second ply of fabric is applied, it can cover the first ply of fabric, thereby making it nearly impossible to monitor the first ply to ensure its placement is unchanged. As a result, bridging of the fabric may occur.

Bridging is when the initial, or first, fabric ply pulls away from the flange corner and spans across the corner rather than remaining tightly adhered thereto. Bridging may result in resin richness, which is an undesired agglomeration of excess resin beneath the first ply of fabric that can locally weaken the laminate.

Bridging may be caused by any of several factors. For example, bridging may result from inadequately placing the initial fabric plies into the corner of the flange such that as subsequent plies are applied during lay-up the initial plies may be jostled causing bridging. Also, inadequately removing bulk from the fabric plies during layup can result in an excess length of composite material, which can lead to bridging during the curing process. Additionally, bridging may result from differences in thermal expansion of the tooling versus the fabric during the curing process.

Regardless of the cause, there is currently no way for operators to easily monitor the initial fabric ply once it has been covered to help ensure that bridging is prevented and that the first ply of fabric remains adhered in the flange corner. The best current practice is to terminate the fabric plies at the corner to allow fabric slippage. However, this practice is generally only beneficial in addressing the issue of differences in thermal expansion during cure and does nothing to prevent bridging that occurs as a result of jostling or inadequate bulk removal.

Accordingly, it would be desirable to produce a composite flange that is less susceptible to bridging and the previously described fabrication concerns.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments herein generally relate to tethered flange corners comprising at least one ply of barrier fibers and at least one fiber tow wrapped about the barrier fibers.

Embodiments herein also generally relate to flanges having a tethered corner comprising at least one ply of barrier fibers, at least one fiber tow wrapped about the barrier fibers, at least one ply of filler fibers applied over the fiber tow, and at least one ply of flange fibers applied over the filler fibers.

Embodiments herein also generally relate to articles comprising a composite structure including a flange having a tethered corner comprising at least one ply of barrier fibers and at least one fiber tow wrapped about the barrier fibers.

These and other features, aspects and advantages will become evident to those skilled in the art from the following disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments described herein generally relate to tethered corners, as well as flange and articles comprising the same that can help eliminate the occurrence of bridging during flange layup and cure. While embodiments herein may generally focus on composite flanges on fan casings of gas turbine engines, it will be understood by those skilled in the art that the description should not be limited to such. Indeed, as the following description explains, the tethered flange corners described herein may be utilized on any flange fabricated from composite materials.

Turning to the figures,FIG. 1illustrates one embodiment of an acceptable composite structure10. As used herein, “composite structure” refers to any component fabricated from a composite material or combination of composite materials. Composite structure10may comprise a generally cylindrical member, such as fan casing12. Fan casing12may have a circumference, as shown inFIG. 2, and as previously mentioned may be fabricated from any acceptable material. In one embodiment, however, fan casing12may be fabricated from a material selected from the group consisting of glass fibers, graphite fibers, carbon fibers, ceramic fibers, aromatic polyamide fibers such as poly(p-phenylenetherephtalamide) fibers (i.e. KEVLAR®), and combinations thereof. In one embodiment, fan casing12may be fabricated from carbon fibers.

As shown inFIG. 1, fan casing12may generally comprise a cylindrical body14having a forward end16and an aft end18. As used herein, “fan casing” is used to refer to both pre- and post-cure composite fan casings. Those skilled in the art will understand which stage is being referenced from the present description. Fan casing12may also comprise any number of end flanges20, as shown generally inFIGS. 1 and 2, and/or mounting flanges22, as shown generally inFIG. 1. As used herein, “mounting flange” refers to any flange interposed circumferentially about body14of fan casing12, or other composite structure. By “interposed” it is meant that mounting flange22may be located circumferentially about body14of fan casing12, as opposed to about either of forward end16or aft end18. In contrast, end flange20may be located about either or both of forward end16or aft end18.

Fan casing12may be fabricated using any acceptable fabrication method or tooling known to those skilled in the art. See, for example, U.S. Patent Application Nos. 2006/0201135 to Xie et al., and 2006/0134251 to Blanton et al. In one embodiment, as shown inFIG. 3, a composite structure forming tool24may be used, which has a circumference, a generally cylindrically shaped core26, as well as a first endplate28and a second endplate30that may be removeably coupled to core26of tool24.

InFIG. 4an illustrative embodiment of an end flange preform32is shown on fan casing12. It will be understood by those skilled in the art that the following flange and lay-up descriptions may be equally applicable to mounting flanges. End flange preform32may include a tethered flange corner33which can help anchor flange preform32in place during layup and cure. Tethered flange corner33may comprise at least one ply of barrier fibers34and at least one fiber tow36wrapped circumferentially thereabout, as described herein below.

More specifically, tethered corner flange may generally include at least one ply of barrier fibers34applied adjacent to first endplate28of tool24and fan casing12, for example. Barrier fibers34may be comprised of multidirectional textile performs such as weaves or braids. As used herein, “multidirectional” refers to textile preforms comprising fiber tows oriented in more than one direction. Fiber tows of barrier fibers34may be comprised of any suitable reinforcing fiber known to those skilled in the art, including, but not limited to, glass fibers, graphite fibers, carbon fibers, ceramic fibers, aromatic polyamide fibers, and combinations thereof. In one embodiment, barrier fibers34may be comprised of glass fibers. Additionally, each fiber tow of barrier fibers34may comprise from about 3000 to about 24,000 fiber filaments.

Barrier fibers34may be applied in flange corner37adjacent to first endplate28of tool24and fan casing12by wrapping barrier fibers34circumferentially about tool24and fan casing12until the desired thickness is obtained. If so desired, barrier fibers34may be tackified initially and upon completion of application to fan casing12to hold barrier fibers34in place. Any acceptable resin known to those skilled in the art may be used to tackify barrier fibers34, such as epoxy, for example.

Next, at least one individual fiber tow36may be wrapped circumferentially about fan casing12over barrier fibers34in flange corner37. In this way, fiber tow36can complete tethered flange corner33and help secure barrier fibers34in the desired location. While fiber tow36may be wrapped about the circumference of fan casing12any number of times, in one embodiment, fiber tow36may be wrapped from about 3 to about 6 times about the circumference of fan casing12. Alternately, more than one fiber tow36may be wrapped about fan casing12one or more times to achieve the same result. Fiber tow36may be fabricated from any acceptable material known to those skilled in the art including, but not limited to glass fibers, graphite fibers, carbon fibers, ceramic fibers, aromatic polyamide fibers, and combinations thereof. However, in one embodiment, fiber tow36may be fabricated from carbon fibers. Additionally, each fiber tow36utilized may comprise from about 3000 to about 24,000 fiber filaments, and in one embodiment, about 12,000 fiber filaments. Once fiber tow36is securely wrapped about barrier fibers34of tethered flange corner33it may be tackified using any acceptable resin known to those skilled in the art, for example, epoxy, to hold it in place during the fabrication of the remainder of end flange preform32.

At least one ply of filler fibers38may then be applied over fiber tow36to help fill in any space that may be present between tethered flange corner33and the flange fibers that will be subsequently applied. Similar to barrier fibers34, a ply of filler fibers38may be a multidirectional textile preform comprised of any suitable reinforcing fiber known to those skilled in the art, including, but not limited to, glass fibers, graphite fibers, carbon fibers, ceramic fibers, aromatic polyamide fibers, and combinations thereof. Also similar to barrier fibers34, filler fibers may be wrapped about the circumference of fan casing12, adjacent to first endplate28and over barrier fibers34and fiber tow36until the desired thickness is obtained. If necessary, filler fibers38may be tackified using any acceptable resin known to those skilled in the art to help hold filler fibers38in place throughout the rest of the fabrication process.

Flange fibers40may then be applied over filler fibers38using any known flange fabrication method known in the art to complete fabrication of end flange preform32. Once again, flange fibers may comprise any suitable material such as glass fibers, graphite fibers, carbon fibers, ceramic fibers, aromatic polyamide fibers, and combinations thereof that can be wound about tool24over filler fibers38.

To consolidate end flange preform32, a debulking step may be performed. In particular, reinforcing fibers, such as barrier fibers34, filler fibers38and flange fibers40may inherently have a substantial amount of bulk. In order to help prevent wrinkles and/or voids during the final cure of the material, and to utilize near net shape tooling during the final cure, the fibers of the material can be consolidated, or compressed, into a dimension that is closer to the desired final cured thickness. This consolidation occurs during debulk.

Debulk can be carried out using any common method known to those skilled in the art, such as, for example, by applying pressure to the composite fibers with either a vacuum bag, shrink tape, or other mechanical means. Resin applied to the fibers before debulk can help tack, or lock, the fibers in place once the pressure is applied. If the tackified fibers cannot be consolidated as desired at room temperature, then heat may be applied to lower the viscosity of the resin. The resin may then better infiltrate the composite fibers and allowing the consolidation to be carried out to the desired degree.

Having finished laying up and debulking end flange preform32, final cure tooling can be placed about fan casing12, including any end flange performs and mounting flange performs, to serve as a mold during the curing process. As will be understood by those skilled in the art, the final cure tooling and process may vary according to such factors as resin used, part geometry, and equipment capability.

As previously described, the foregoing is equally applicable to mounting flanges as well as end flanges. When fabricating a mounting flange preform41, which is located about the body of fan casing12, a guide42may be used in place of first or second endplate to provide a surface against which to apply barrier fibers34and fiber tow36, as shown generally inFIG. 5. In one embodiment, guide42may be comprised of discrete arcuate members, each spanning about 180 degrees so as to fit correspondingly about fan casing12. The arcs of guide42may be releaseably connected together for easy placement and adjustment about fan casing12. It will be understood, however, that guide42may be comprised of any number of pieces and have any shape that corresponds to the shape of the composite structure. As previously discussed, guide42can serve as a support for the application of both barrier fibers34and fiber tow36, as well as the remaining fiber layers of the flange preform41. Guide42may be circumferential and have an L-shaped cross-section as shown, and may be constructed from any rigid, lightweight material such as, for example, aluminum or composite. Once one side of mounting flange preform41is constructed, as shown inFIG. 5, guide42may be removed. The other side of mounting flange preform41may then be constructed in the same manner as the first side.

Embodiments of the tethered corner described herein can provide several benefits. For example, applying the fiber tow about the barrier fibers allows the fiber tow to serve as a tether to hold the barrier fibers in the corner of the flange during subsequent lay-up steps. More specifically, as additional plies of filler fibers and/or flange fibers are placed and jostled, the barrier fibers stay tethered in the corner because of the wrapped fiber tow. This can help reduce or even eliminate the bridging issue often faced in current flange fabrication processes.

Additionally, during curing, the composite structure forming tool endplate and core have a tendency to expand and pull away from one another due to the heat and pressure of the curing process. This in turn can cause the barrier fibers to be pulled out of the corner and result in bridging. The tethered corner created by the fiber tow can help address this issue in two ways. First, the tethered corner can reduce the occurrence of bridging in the first instance by helping to hold the barrier fibers taught. Second, during the curing process, the previously described expansion of the composite structure forming tool can tighten the fiber tow of the tethered corner, thereby effectively pulling it and the barrier fibers against one another in the desired orientation and reinforcing the adhesion therebetween.