Hybrid three-dimensional woven/laminated struts for composite structural applications

[0001] The present invention relates to the geometric configuration of three-dimensional woven preforms for reinforced composite structures having quasi-isotropic or multidirectional reinforcement at one or two ends of the structure and approximately unidirectional reinforcement in all other areas.

Background of the Invention [0002] The use of reinforced composite materials for the production of structural elements is now widespread, especially in applications where their desired characteristics of lightness, strength, hardness, thermal resistance, self-supporting and adaptability to forming and shaping are sought. Such components are used, for example, in the aeronautics, space, satellite and battery industries, as well as for recreational applications such as boats and racing cars, and countless other applications. The three-dimensional fabric generally consists of fibers oriented in three directions, each fiber extending along a direction perpendicular to other fibers, i.e. along the directions of the X, Y and Z axes.

[0003] Typically, elements formed from such fabrics consist of reinforcing materials embedded in matrix materials. The reinforcing component may be made of materials such as glass, carbon, ceramics, aramid (e.g., "KEVLAR^®"), Polyethylene, and / or other materials that exhibit the desired physical, thermal, chemical and / or other properties, among which the main is high strength against stress damage. By using such reinforcing materials, which eventually become part of the finished component, the desired characteristics of the reinforcing materials, such as high strength, are imparted to the finished composite component. The constituent reinforcing materials may typically be woven, knitted or otherwise oriented in the desired configurations and shapes for reinforcing preforms. Special attention is usually paid to ensuring optimal use of the properties for which these reinforcing materials have been selected. Generally, such reinforcing preforms are combined with the matrix material to form the desired finished ingredients or provide a working stock for the final production of finished ingredients.

[0004] Once the desired reinforcing preform has been constructed, the matrix material can be introduced and combined with the preform so that the reinforcing preform is encapsulated in the matrix material and the matrix material fills the interstitial areas between the components of the reinforcing preform. The matrix material can be any of a variety of materials, such as epoxy, polyester, vinyl ester, ceramics, carbon and / or other materials that also exhibit the desired physical, thermal, chemical and / or other properties. The materials selected for use as the matrix may or may not be the same as the reinforcing preform materials and may or may not have comparable physical, chemical, thermal or other properties. Typically, however, they will not be made of the same materials or have comparable physical, chemical, thermal or other properties as reinforcing preforms, since the usual goal to achieve when using composites is primarily to obtain a combination of finished product features that is not achievable. by using one component material.

[0005] Once combined, the reinforcing preform and matrix material can then be cured and stabilized in the same operation by thermosetting or other known methods, and then subjected to other operations to produce the desired element. It is important to note that after such curing, such solidified masses of matrix material usually stick very strongly to the reinforcing material (e.g., reinforcing preforms). As a result, the stress on the finished element, especially through its matrix material acting as a binder between the fibers, can be effectively transferred to and borne by the reinforcing material of the reinforcing preform.

[0006] Typically, simple two-dimensional fabric or unidirectional fibers are produced by the material supplier and sent to the customer who cuts patterns and arranges the end part band-by-band. ply-by-ply]. The simplest woven materials are flat, essentially two-dimensional structures with fibers in only two directions. They are created by interlacing two sets of yarns perpendicular to each other. For two-dimensional weaving, 0 ° yarn is called warp yarns or yarns, and 90 ° yarn is called yarns or weft yarns. For the resin transfer molding method (RTM), a series of fabrics can be combined to form a dry prelaminate, which is placed in the mold and the resin is injected. These fabrics can be preformed using the "cutting and sewing" technique or thermoformed and "basted" using a binding resin.

[0007] Two-dimensional woven structures, however, have limitations. The preforming stage requires considerable manual work on the pre-laminate. Two-dimensional woven structures are not as strong or tensile along axes other than 0 ° and 90 °, especially at angles distal to the fiber axis. One way to circumvent this possible limitation is to add twill fibers to the weave, woven fibers so that they diagonally cut the fabric at an intermediate angle, preferably ± 45 ° relative to the weft fiber axis.

[0008] Simple woven preforms are also single-layer. This limits the possible strength of the material. One possible solution is to increase the fiber size. Another is the use of multiple layers or bands. layers or plies]. An additional benefit of using multiple layers is that certain layers can be oriented such that the warp and weft axes of the various layers have different directions, thereby operating as previously discussed oblique fibers. If these layers are a stack of individual layers laminated together with resin, however, there is a problem of delamination. If the layers are sewn together, then many woven fibers may be damaged during the sewing process and overall tensile strength may suffer. In addition, for both lamination and stitching of multiple strands, manual pre-lamination is usually required to level the layers. Alternatively, the layers can be interlaced as part of the weaving process. Creating multiple interwoven fabric layers, especially with integrated twill fibers, is a difficult task.

[0009] One example in which composite materials are used to manufacture structural elements is the manufacture of braces and brackets. struts and braces]. Braces and brackets typically include a central column having projections. lugs] at each end of the structure. These projections can have a male or female configuration (forks) and are used to attach a brace or tetany to a structure that is reinforced or bonded. As discussed earlier, in order to achieve increased strength of the composite structure, multiple layers or bands are used for the projection and column of braces and brackets. Although the use of multiple layers is preferred because the individual layers can be oriented to create a reinforcement in the 0 ° and 90 ° directions, as well as they can be oriented obliquely to create a reinforcement in additional directions such as ± 45 ° if they are laminated together , delamination of layers with resin can create problems. Alternatively, if the layers are sewn together, as discussed earlier, many woven fibers may be damaged during the sewing process, which reduces the overall tensile strength of the final structure.

[0010] There are many examples of laminated projections, some use hybrid materials (i.e. alternating carbon and titanium layers), however the laminated projections have not been combined with a three-dimensional woven column. The utility of laminated composite lugs for heavily loaded structures has been demonstrated in several government-funded programs. However, to the knowledge of the Applicant, none of these programs included the use of three-dimensional woven preforms.

[0011] Thus, three-dimensional preforms for use in struts and brackets having laminated ends or parts of projections and a monolithic three-dimensional woven central column are desirable. The benefits of using a three-dimensional structure in the central part of the preform are that this reduces the work required to cut and lay all the strands needed for a thick composite and provides greater damage tolerance than conventional laminated composites. The advantage of independent layers at the ends is that the laminate can be adjusted to have specific properties.

[0012] US Patent Publication No. 4,737,998 describes three-dimensional non-crimped integral woven reinforcements for structural elements formed as an integral woven set of warp and weft fibers, e.g. graphite fibers, in multiple layers, with light binding yarn, e.g., fiberglass, passing from one side of the layer system to the other. Woven reinforcement forms of various shapes, such as I-sections, can be made using a specific percentage of fiber 0 degrees (warp) and 90 degrees (weft), e.g., graphite, to form multiple layers comprising fabric and flanges with I-section reinforcement, and having the desired the number of layers and the thickness of the fabric and flanges, and the passing of binding yarn, e.g. fiberglass back and forth from one side of the fabric to the other, and in the same way from one side of the flanges to the other, and extending lengthwise towards the warp of the material. The woven set is then impregnated with resin, e.g. epoxy, in stage "B", placed in a suitable mold, and heated and cured in a conventional manner.

[0013] US Patent Publication No. 4,622,254 describes a fiber material for reinforcing plastics produced by laminating at least one first fiber substrate in which the reinforcing fibers extend in two directions, including longitudinal and transverse, intersecting under a substantially right angle with at least one other fiber substrate in which the reinforcing fibers extend in two directions, including directions having angles of +/- (25-65) degrees to the longitudinal direction. As well as a fiber material for reinforcing plastics produced by laminating at least one first fiber substrate in which the reinforcing fibers extend in at least one of two directions, including longitudinal and transverse, intersecting at a substantially right angle with at least one other fiber substrate wherein the reinforcing fibers extend in a direction having an angle of (25-65) degrees with respect to the longitudinal direction and at least one third of a fiber substrate in which the reinforcing fibers extend in a direction having an angle of (25-65) degrees with the longitudinal direction. The above laminate compacts are integrated with each other by stitching yarn passing repeatedly in the lamination direction.

[0014] US Patent Publication No. US 2002/056484 describes a solid structural material utilizing a three-dimensional five-axis W fabric. When weaving a three-dimensional five-axis fabric W using a three-dimensional weaving machine, divisible woven sections S1 are formed in parts of the produced three-dimensional five-axis fabric by alternatively moving the upper and lower insertion elements 2,3 for entering the vertical yarn Z from above and below, respectively, in such a way, that each of the introductory elements and the rapier introducing the thread are driven with different synchronizations. [0015] Accordingly, there is a need for a woven preform having an integrally woven three-dimensional central portion with laminated ends of the projection comprising independent woven layers.

SUMMARY OF THE INVENTION [0016] Thus, the main object of the invention is to provide a three-dimensional woven preform having an interlaced columnar portion and a pile of separately woven fabrics at the ends of the projection for use in the composite structure.

[0017] A further object of the invention is to provide a woven preform for a thick composite structure that has quasiisotropic or multidirectional reinforcement at one or two ends and almost unidirectional reinforcement in all areas.

[0018] Still another object of the invention is to provide a composite structure that can be used to carry large concentrated loads.

[0019] These and other objects and advantages are provided by the present invention. In this regard, the present invention is directed to a woven preform that is used to reinforce a composite structure according to claim 1 and a method for producing such a preform according to claim 9.

[0020] The various features of novelty that characterize the invention are listed in detail in the claims attached to and forming part of this disclosure. For a better understanding of the invention, its operating advantages and the specific purposes pursued by its use, reference should be made to the accompanying description, in which preferred embodiments of the invention are illustrated in the accompanying drawings, in which the respective components have been identified by the same reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS [0021] The following detailed description, given by way of example and without the intention of limiting the present invention to it alone, may be best appreciated in connection with the accompanying drawings, in which the same reference numerals designate similar elements and parts in which :

Fig. 1 is a plan view of a composite structure having a column portion with the ends of the projection having the male configuration;

Fig. 2 is a plan view of a composite structure having a column portion with the ends of the protrusion having a female or vista configuration;

Fig. 3 is a plan view of a preform constructed in accordance with one embodiment of the present invention;

Fig. 4A is a plan view of a preform having projecting ends with a symmetrical configuration constructed in accordance with one embodiment of the present invention;

FIG. 4B is a plan view of a preform having the ends of a projection with a symmetrical configuration constructed in accordance with one embodiment of the present invention;

FIG. 4C is a plan view of a preform having projecting ends with an asymmetric configuration constructed in accordance with one embodiment of the present invention;

FIG. 4D is a plan view of a preform having the ends of the protrusion with an asymmetric configuration constructed in accordance with one embodiment of the present invention; and

Fig. 5 is a plan view of a preform constructed according to one embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [0022] The present invention is described more fully below with reference to the accompanying drawings, in which preferred embodiments of the invention are set forth. However, this invention may be implemented in a variety of forms and should not be construed as limited to the illustrated embodiments illustrated herein. Rather, these illustrated embodiments are provided so that the disclosure is accurate and complete and that it fully reflects the scope of the invention to those skilled in the art.

[0023] In the following description, like reference symbols mean similar or corresponding parts in the figures. In addition, in the following description, it is to be understood that terms such as "top," "bottom," "top" and "bottom" and the like are words used for convenience and should not be construed as limiting terms.

[0024] The present invention is a concept for a preform for a composite structure or beam that has quasi-isotropic or omnidirectional reinforcement at one or two ends and almost unidirectional reinforcement in all other areas. This configuration is desirable for structures that are to carry large concentrated loads, such as braces and brackets. Quasi-isotropic or multidirectionally reinforced ends provide good load-bearing properties and more balanced tensile, compressive and shear strengths, making them a good choice for the ends of a structure protrusion. These ends of the performance can have both male and female (forked) configurations. The unidirectional part provides high axial rigidity, which is useful for preventing buckling or destruction of the column, and is a good choice for the main strut or brace column. In FIG. 1 illustrates a brace or brace 2 having the ends of a projection 4 and a three-dimensional main column portion 6. The ends of the projection 4 in FIG. 1 have the male configuration. FIG. 2 shows a brace or brace 8 with a three-dimensional main column portion 10 and ends of the projection 12 having a female or forked configuration.

[0025] The advantages of using a three-dimensional structure in the central part of the preform are that it reduces the work required to cut and compile all the bands required for a thick composite and provides better damage tolerance than conventional laminated composites. The advantage of independent layers at the ends of the structure is that the laminate can be adjusted to have specific properties. As disclosed, the ends of the projection are considered quasi-isotropic or multidirectionally reinforced, but they can practically have any laminated configuration.

[0026] The present preform is composed of a three-dimensional woven part consisting of a number of layers and a similar number of independent oblique layers. In the central or columnar part of the three-dimensional woven fragment, all layers are interwoven or integrally woven together to form a monolithic block of woven material. The architecture of the fiber used in this part may be any conventional pattern for a thick preform, including, but not limited to, "band-to-band" architecture, by thickness, angular weave, or orthogonal architecture. At the ends of the structure, the individual layers intertwine independently to form a pile of fabric with reinforcement in 0 ° and 90 ° directions, where 0 ° is the direction along the length of the structure. The oblique layers or strands, which are constructed separately, provide reinforcement in additional directions relative to 0 ° / 90 ° directions such as ± 45 °, and are interwoven between 0 ° / 90 ° layers of fabric to form a more conventional laminate. The oblique layers or strands may be woven using warp and weft fibers or yarns, or may be non-woven, knitted, or be a matrix of MD or CD fibers or yarns. In the following figures, the warp direction is 0 ° or along the length of the structure and is indicated by an arrow of 100.

[0027] All preform layers, including the central or columnar part, are woven from warp or fiber yarns or yarns or threads using a jacquard loom and a captured shuttle, however any conventional weaving technique can be used for weaving layers. Fibers or yarns can be either synthetic or natural materials such as, without limitation, carbon, nylon, rayon, polyester, fiberglass, cotton, glass, ceramics, aramid ("KEVLAR^®") And polyethylene. The finished woven preform is then processed into a woven / laminated composite structure by incorporating a matrix material such as, without limitation, epoxy, polyester, vinyl ester, ceramics, carbon and / or other materials that also exhibit the desired physical, thermal, chemical and / or others, using conventional techniques such as, without limitation, compression molding or chemical gas infiltration.

[0028] In accordance with one embodiment of the present invention, FIG. 3 shows a segment of structure 14 having a thick central portion 16 integral with the two thinner male ends of the projection 18, which are located on each side of the central portion 16. As can be seen in FIG. 3, the thick central portion 16 is a monolithic, three-dimensional woven column comprising a plurality of woven layers 20 that are interwoven [ interwoven] or woven together. To obtain the thinner male ends of the projection 18, layers of warp fibers from the thick central column 16 are woven from the preform weave to form a conical passage 22 from the column 16 to the thinner ends of the projection 18.

[0029] When the desired number of warp fibers are woven from the preform weave to narrow the bottom of the column to the desired projection thickness, additional layers of warp fibers are woven from the preform weave onto the thinner ends of the projection 18 to provide a gap or space for the oblique fabric strands. The remaining warp fibers at the thinner ends of the projection 18, which are woven integrally with multiple layers 20 in the column or central portion 16 and are continuous along the length of the structure, form individual strands 24 that are woven independently of each other. This pile of strands or fabrics provides reinforcement at the thinner ends of projection 18 in 0 ° and 90 ° directions. Since the 24 ° / 90 ° strands are not interleaved together, the oblique strands 26 that provide reinforcement in additional directions, such as the ± 45 ° direction, can be interlaced in the gaps between the 24 ° / 90 ° layers, creating a pile of fabrics, which upon application of the matrix material forms a laminated structure providing quasi-isotropic or omnidirectional reinforcement at the thinner ends of the projection 18. In addition, as illustrated in FIG. 3, the structure has a continuous surface fiber 28, which is formed from the outermost warp fibers of the thick column 16.

[0030] If desired, unlike the previously disclosed structure for this embodiment, which has a central portion 16 with two thinner ends of projection 18 on each side of central portion 16, a structure having only one thinner end of projection 18 may be constructed in accordance with the disclosed example of implementation. In this case, the structure will include one end similar to the monolithic three-dimensional woven central portion 16 and one thinner end of projection 18 as disclosed above. A structure constructed in this way will be more similar to FIG. 3.

[0031] Another embodiment of the present invention is illustrated in FIGURES 4A-4D, which show a segment with structure 30 comprising two ends of projection 32 that are thicker than the monolithic three-dimensional woven central columnar part 34 of structure 30. As with the previous embodiment, the central part Column 34 is composed of a plurality of woven layers 35 that are interwoven or woven together. However, in this configuration, there is no need to weave warp fibers 36 from column portion 34 to produce thicker ends of projection 32. Instead, all warp fibers 36 used to build column portion 34 are used to build thicker ends of projection 32. However, warp fibers 36 of column portion 24 are not interleaved together at the thicker ends of projection 32. This allows the oblique strands 38 to be interlaced between the warp fibers 40 at the thicker ends of the projection 32, which are strands providing reinforcement in the 0 ° / 90 ° direction. Thus, the thicker ends of the protrusion 32 have a fabric stack consisting of strands or 0 ° / 90 ° oriented fabrics and separately constructed strands oriented in directions other than 0 ° / 90 °, for example strands or fabrics oriented ± 45 °, which when applied matrix material, resulting in a laminated projection having quasi-isotropic or multidirectional reinforcement. In addition, as can be seen in FIGURES 4A-4D, structures constructed in accordance with this embodiment will have a stepped transition 42 from the thicker laminated end 32 to the monolithic column portion 34, thereby improving load transfer from one portion to another.

[0032] As can be seen in FIGURES 4A-4D, the length and arrangement of the oblique bands 38 is different in the various figures. FIGURES 4A and 4B illustrate the end of the projection 32 having a symmetrical configuration. That is, the length and arrangement of the oblique bands 38 at the end of the projection 32 are symmetrical about the center line or the longitudinal axis AA. FIG. 4A illustrates a symmetrical configuration in which the length of successive oblique bands 38 increases in the upper half 39 and lower half 41 of the end of the projection 32 as it moves from center line AA towards the upper surface 43 and the lower surface 45 of the end of the projection 32. FIG. 4B illustrates a symmetrical configuration in which the length of successive oblique bands 38 decreases in both halves, 39 and 41, of the end of the projection 32 when moving from center line AA towards the upper surface 43 and the lower surface 45 of the end of the projection 32.

[0033] FIGURES 4C and 4D illustrate the end of the projection 32 having an asymmetrical configuration. That is, the length of the subsequent oblique bands 38 at the end of the projection 32 only increases or decreases as it moves from the lower surface 45 to the upper surface 43 of the end of the projection 32. FIG. 4C depicts an asymmetrical configuration in which the length of successive oblique bands 38 at the end of the projection 32 increases as it moves from the lower surface 45 to the upper surface 43 of the end of the projection 32. As shown in FIG. 4D, it is also possible to build the asymmetrical end of the projection 32, in which the length of the subsequent oblique strands 38 decreases as it moves from the lower surface 45 to the upper surface 43 of the end of the projection 32. [0034] If desired, unlike the previously disclosed structures for the embodiment that has the central portion 34 with the two thicker ends of the projection 32 on each side of the central portion 34, a structure having only one thicker end of the projection 32 according to disclosed embodiment. In this case, the structure will include one end similar to the monolithic three-dimensional woven central portion 34 and one thicker end of projection 32 as disclosed above. The structure constructed in this way will look more closely like the structures illustrated in FIGURES 4A-4D.

[0035] In another embodiment of the present invention, FIG. 5 illustrates a segment of structure 44 having a monolithic three-dimensional woven central column portion 46 with two female projections or forks 48. As can be seen in FIG. 5, the female ends of the projection 48 are directed at an angle relative to the central column portion 46, such that the female ends of the projection 48 are not in line or not collinear with the central column portion 46. As in previous embodiments, the central column portion 46 is composed of a plurality of woven layers 50 that are interwoven or woven together. To obtain the female ends of the protrusion or forks 48, the monolithic column portion 46 is woven so that it splits 52 to form both halves of the fork. Layers 54 0 ° / 90 ° in the first or angled portion 56 of each half of the forks are still stitched together.

[0036] To obtain a gap between the reinforcement layers 58 0/90 ° for the oblique strands of fabric 60 in the parallel or end portions 62 of the bifurcation, the warp fibers are woven from the weave from the angular portions 56 of the preform. The remaining warp fibers at the ends of projection 48, which are integrally woven with multiple woven layers 50 in the central column portion 46 and angular portions 54, form individual layers that are woven independently of each other and provide reinforcement at the fork 48 in 0 ° and 90 ° directions . Since the 58 ° / 90 ° layers are not interleaved together, the reinforcement in directions other than the 0 ° / 90 ° direction, e.g. the ± 45 ° direction is provided by the oblique 60 strands interlaced between the 0 ° / 90 ° layers 58, forming fabric stacks on forks providing quasi-isotropic or omnidirectional reinforcement when matrix material is added to the preform.

[0037] If desired, unlike the previously disclosed structure for this embodiment, which has a central portion 46 with two female ends of the projection or forks 48 on each side of the central portion 46, a structure having only one female end of the projection 48 according to disclosed embodiment. In such a case, the structure will include one end similar to the monolithic three-dimensional woven central portion 46 and one female end of the projection or fork 48 as disclosed above. A structure constructed in this manner will be closer to the structure illustrated in FIG. 5.

[0038] In all disclosed embodiments, after inserting the oblique bands at the ends of the projection, the woven preform can be braided with a layer of glass material to improve the abrasion resistance of the preform.

[0039] As is apparent to those skilled in the art, the structures disclosed above may have many forms in addition to those disclosed herein. For example, structures may have a thick monolithic three-dimensional woven column with a female or forked configuration of the projection. The structure may also have a thick monolithic three-dimensional woven column, with a male protrusion at one end and a female protrusion at the other end. In addition, the structure may have a thin monolithic three-dimensional woven column with female protrusions at each end or a male protrusion at one end and a female protrusion at the other end. Finally, all configurations can have: both protrusions in line or in line with the main column portion; both projections at an angle to the main column portion; or one protrusion may be aligned with the main part and one protrusion may be at an angle to the main part. Although, as disclosed above, the ends of the projection are considered quasi-isotropic or multidirectionally reinforced, the ends of the projection may have virtually any laminate configuration. Thus, the present structures, for example braces or brackets, can be designed to have different configurations to obtain different types of reinforcement or stiffening depending on the specific needs or the desired use of the structure.

[0040] Although a preferred embodiment of the present invention and its modifications are described in detail herein, it should be understood that the invention is not limited to this exact embodiment and modification, and that one skilled in the art may make other modifications and variations without departing from the scope of the invention as defined in the appended claims.