Woven preform, composite, and method of making thereof

Abstract

A three dimensional woven preform, a fiber reinforced composite incorporating the preform, and methods of making thereof are disclosed. The woven preform includes one or more layers of a warp steered fabric. A portion of the warp steered fabric is compressed into a mold to form an upstanding leg. The preform includes the upstanding leg and a joggle in a body portion. The body portion and upstanding leg are integrally woven so there is continuous fiber across the preform. A portion of the warp steered fabric includes stretch broken carbon fibers in the warp direction, and another portion includes conventional carbon fibers. The warp steered fabric can be woven on a loom equipped with a differential take-up mechanism. The warp steered fabric can be a single or multilayer fabric. The preform or the composite can be a portion of an aircraft window frame.

Claims

1. A method of forming a three dimensional woven preform, the method comprising the steps of: weaving a warp steered fabric having weft fibers and warp fibers that is curved in an X-Y plane; and laying one or more layers of said warp steered fabric to form a predetermined shape, wherein a first portion of the warp steered fabric including warp fibers which are elongatable fibers or discontinuous tows: a second portion of the warp steered fabric including warp fibers which are not stretch broken carbon fibers, and a third portion of the warp steered fabric including fibers which are elongatable fibers or discontinuous tows; forming the steered fabric to cause the elongatable fibers or discontinuous tows in the first portion to elongate in a circumferential direction of the X-Y plane to form a joggle of a body portion of the perform, and causing the third portion of the steered fabric to curve and form an upstanding leg in Z direction, the body portion of the preform comprising the first portion and the second portion of the warp steered fabric.

2. The method of claim 1, wherein the forming step includes compressing the steered fabric into a mold to form the three dimensional woven preform.

3. The method of claim 1, wherein said body portion and upstanding leg are integrally woven so there is continuous fiber across the preform.

4. The method of claim 3, wherein said preform is a portion of a window frame.

5. The method of claim 4, wherein said preform is a portion of an aircraft window frame.

6. The method of claim 1, wherein said warp steered fabric is woven on a loom equipped with a differential take-up mechanism.

7. The method of claim 1, wherein said warp steered fabric is a multilayer fabric.

8. The method of claim 7, wherein a warp fiber pattern in said warp steered fabric is a pattern selected from the group consisting of ply-to-ply, orthogonal, and angle interlock.

9. The method of claim 1, wherein said warp steered fabric is formed by interweaving a plurality of warp and weft yarns or fibers, said warp and weft yarns or fibers being selected from the group consisting of carbon, nylon, rayon, fiberglass, cotton, ceramic, aramid, polyester, and metal yarns, and metal fibers.

10. A method of forming a fiber reinforced composite, the method comprising the steps of: forming a three dimensional woven preform according to claim 1; and impregnating said preform in a matrix material.

11. The method of claim 10, wherein said matrix material is a resin, and said composite is formed from a process selected from the group consisting of resin transfer molding and chemical vapor infiltration.

12. The method of claim 10, wherein said matrix material is selected from the group consisting of epoxy, bismaleimide, polyester, vinyl-ester, ceramic, and carbon.

13. The method of claim 1, further comprising the step of interspersing between the plurality of warp steered fabrics one or more layers of fabric with fibers oriented in off-axis directions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are included to provide a further understanding of the invention, are incorporated in and constitute a part of this specification. The drawings presented herein illustrate different embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:

(2) FIG. 1 is a schematic of an aircraft window frame;

(3) FIG. 2 is a cross-sectional view of the aircraft window frame shown in FIG. 1 along line 2-2;

(4) FIG. 3 is a schematic of an oval fabric produced using steered weaving, according to one aspect of the present invention;

(5) FIGS. 4-5 show steps involved in forming a three dimensional woven preform, according to one aspect of the invention; and

(6) FIG. 6 shows a step involved in forming a three dimensional woven preform, according to one aspect of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) The instant invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these illustrated embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

(8) In the following description, like reference characters designate like or corresponding parts throughout the figures. Additionally, in the following description, it is understood that such terms as upper, lower, top, bottom, first, second, and the like are words of convenience and are not to be construed as limiting terms.

(9) Turning now to the figures, the invention according to one embodiment is a method of fabricating a three dimensional woven preform for use in high-strength applications, such as for example, aircraft window frames, composite turbine fan cases, jet engine containment rings, aircraft fuselage frames or in flanged rings for attaching nacelles to aircraft engines. Although the preferred embodiments described herein relate to an aircraft window frame, the present invention is not limited as such. For example, the woven preforms or methods described herein may be used in the manufacture of any of the structures listed above, or the like.

(10) The method according to one exemplary embodiment uses a unique textile manufacturing technique, or what is known as warp steering. The term warp steering refers to a differential take-up system for the warp yarns, which steers them into a required shape, and allows straight weaving, polar weaving or a combination thereof to produce a preform that can practically take any shape in the X-Y plane of the fabric or preform. An example of such a warp steered oval fabric 30 produced using steered weaving, according to one aspect of the present invention, is shown in FIG. 3 where oval fabric 30 may be flat in one plane, and has a curved shape in the X-Y plane. In such an arrangement, each warp yarn 32 can have a different path length, similar to lines around a running track, while each weft yarn 34 is always perpendicular or orthogonal to the edges of the fabric. This is to say that at points where a weft yarn 34 may be interwoven with one or more warp yarns 32, the weft yarn 34 is always orthogonal to the one or more warp yarns 32 irrespective of the curvilinear path the warp yarns 32 take.

(11) This technique may be used, according to one exemplary embodiment, to fabricate a composite window frame, such as that described with respect to FIG. 1, which includes features such as an upstanding leg 20 and a joggle 15, but does not require the darting required by conventional materials. The method according to this embodiment uses stretch broken carbon fibers (SBCF) as circumferential fibers in selected regions so that the upstanding leg and joggle can be integrally formed into the preform. The woven preform as a result will have continuous fiber in the circumferential and radial directions of the frame.

(12) Steered weaving according to this method can be carried out on a loom that uses a programmable differential take-up mechanism to produce the desired oval shape of the window frame. In the steered fabric 30, the warp fiber may be continuous in the circumferential direction and the weft fiber is always oriented in the radial direction, relative to the local radius of curvature.

(13) Multiple continuous layers of fabric can be laid on top of one another to build up the desired thickness. Additional layers of fabric with fibers oriented in off-axis directions (again, relative to the local radius of curvature) can also be interspersed between the layers of steered fabric if additional strength and/or stiffness is required. Alternatively, the steered fabric may be woven as a multilayer fabric where two or more layers of the multilayer fabric are integrally held by one or more warp and/or weft yarns in a desired pattern. The fabric can be woven using any convenient pattern for the warp fiber, i.e., ply-to-ply, through thickness angle interlock, orthogonal, etc. The fabric itself can be woven using any conventional weave pattern, such as plain, twill, satin etc. While carbon fiber is preferred, the invention may be applicable to practically any other fiber type including but not limited to those that can be stretch broken, e.g. stretch broken carbon fiber, glass, ceramic, and those that cannot be stretch broken or need not be stretch broken. For example, the fiber used in the present invention can be Discotex, a discontinuous tow produced by Pepin Associates Inc., which when woven into a textile structure allows the textile structure to stretch in its reinforcement direction, permitting the formation of complex shapes from simple preform starting shapes.

(14) Discotex is produced by cutting reinforcing yarns or tows into discrete lengths and aligning the cut yarns or tows to form a discontinuous tow. This tow is composed of long, discontinuous and overlapped reinforcing tow segments combined with aligned continuous fiber and an overwrap. The aligned continuous fiber and overwrap fiber are required to handle the DiscoTex tow during textile operations but they can also be used as the matrix precursor material. In cases where the continuous fiber is not needed in later processing steps it can be removed to yield an all discontinuous textile material. DiscoTex fabric stretching permits the rapid fabrication of complex contours while preserving fiber orientation and fiber volume fraction. Labor intensive cutting and darting of the fabric can be eliminated, and the technology is applicable to any type of reinforcing yarn including glass, carbon, and ceramic.

(15) It should be noted that the initial preform or fabric 30 is flat. The final shape of the three dimensional preform, however, may be developed using a forming process to generate the upstanding leg, joggle, and general curved shape along the major axis. This forming depends on the use of SBCF in the warp direction of the steered fabric, which will allow the fabric to elongate as needed in the circumferential direction so that the preform is flat with no wrinkles. Conventional fiber may be used in the weft direction, and the width of the fabric may be set to the total arc length of the cross section. SBCF may be used in the weft direction if needed in some local geometry that requires the weft to stretch. When using SBCF, the actual forming process may be engineered to ensure that the total elongation required does not exceed the yield elongation limit of the fiber.

(16) The method, according to one embodiment, can be carried out as illustrated in FIGS. 4-5. In this embodiment, woven preform 30 may be formed using SBCF as warp fiber in one portion 36 of the fabric, for example, and conventional carbon fiber warp in another portion 38 of the fabric. Portion 36 may be, for example, the inner circumferential region of the oval preform, while portion 38 may be, for example, the outer circumferential region. In this case the outside edge 40 of the preform 30 may be clamped to the top of a forming tool 45, for example, and the preform 30 may be compressed into a female mold or forming tool surface 42. The SBCF in portion 36 elongate as the fibers are formed from the smaller radii of the initial preform into the larger radii of the final part. The compression of preform 30 into the female mold or forming tool surface 42 may be accomplished with radial compression, or using one of several known techniques. One such method may be using an inflatable tool that is pressurized to get uniform radial force on the preform 30. Another method may use multiple section tooling to move and fix the preform 30 into place under radial loading for subsequent molding.

(17) It should be noted that the SBCF at the inner edge of the preform can have the highest percent elongation, and the maximum elongation depends on the height of the upstanding leg, the depth of the joggle, the total width of the preform, and the minimum local radius of curvature.

(18) The method according to another embodiment is illustrated in FIG. 6. In this embodiment, woven preform 30 may be formed, for example, using SBCF in the warp direction in edge portions 36, 36 (inner and outer circumferential regions of the oval preform or fabric 30), and conventional carbon fiber warp in the center portion 38 of the fabric. The portion of the preform 30 that will become the upstanding leg 20 is actually woven so that it may be folded back over the main body of the preform. This feature is necessary to ensure that the upstanding leg 20 does not go into circumferential compression during forming.

(19) Preform 30 may be clamped into the tool over the area 22 that contains the conventional warp fiber. The joggle 15 may be then formed by pressing the left side of the preform 36 into the mold 42, and the upstanding leg 20 may be formed by uniformly pushing the right side 36 of the preform 30 up and out into the mold 42. The compression of preform 30 into the female mold or forming tool surface 42 may be, as described earlier, accomplished with radial compression, or using one of the several known techniques. One such method may be using an inflatable tool that may be pressurized to get uniform radial force on the preform 30. Another method may use multiple section tooling to move and fix the preform 30 into place under radial loading for subsequent molding.

(20) It should be noted that the SBCF warp at the inner edge of the preform will usually have the highest percent elongation, and it is this feature that will usually determine if either forming approach is feasible. The maximum elongation also depends on the height of the upstanding leg, the depth of the joggle, the total width of the preform, and the minimum local radius of curvature.

(21) After the fabric is molded to take the desired three dimensional shape, preform 30 can be processed into a composite using a conventional resin infusion method, such as resin transfer molding. For example, the preform according to one embodiment can be processed into an aircraft window frame 10 as shown in FIG. 1. The structure 10 comprises the woven preforms described in the previous embodiments. The preforms may be produced without cutting and darting of the individual plies. Eliminating these cuts and darts improves the strength as well as performance of the resulting structure.

(22) The preforms of the present invention can be woven using any convenient pattern for the warp fiber, i.e., ply-to-ply, through thickness angle interlock, orthogonal, etc. While carbon fiber is preferred, the invention may be applicable to practically any other fiber type that can be stretch broken e.g., carbon, nylon, rayon, fiberglass, cotton, ceramic, aramid, polyester, and metal yarns or fibers.

(23) The warp steered fabric of the invention may be made from materials, such as for example, carbon, nylon, rayon, polyester, fiberglass, cotton, glass, ceramic, aramid, and polyethylene, or any other material commonly known in the art. The final structure may be impregnated with a matrix material, such as for example, epoxy, bismaleimide, polyester, vinyl-ester, ceramic, and carbon, using resin impregnation methods such as resin transfer molding or chemical vapor infiltration, thereby forming a three dimensional composite structure.

(24) Potential applications for the woven preform of the invention include any structural application that utilizes a contoured frame with a stiffened leg, although an aircraft window frame is described as an example herein.

(25) Although preferred embodiments of the present invention and modifications thereof have been described in detail herein, it is to be understood that this invention is not limited to this precise embodiment and modifications, and that other modifications and variations may be effected by one skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.