Patent Description:
This invention relates to fiber-composite parts.

Various manufacturing methods have been developed to produce fiber-reinforced composite parts. Present methods can be time consuming, limited to the use of certain materials, and/or constrained by part geometries. And such manufacturing methods are not suited for fabricating fiber-reinforced composite parts efficiently at high volume.

<CIT> discloses methods for forming fiber reinforced polymer rod assemblies and fiber reinforced polymer rod assemblies. The method includes heating a portion of a first fiber reinforced polymer rod and of a second fiber reinforced polymer rod. The method further includes intertwining the portions of the first and the second fiber reinforced polymer rod to form a rod connecting section, aligning the first and the second fiber reinforced polymer rod along a linear axis and cooling the portions of the first and the second fiber reinforced polymer rod.

<CIT> refers to a structural component made out of long- fiber reinforced thermoplastic material with integrated continuous fiber (CF)-reinforcement. It includes at least three individually integrated, shaped CF-profiles forming a three-dimensional intersection point. In this, at least one CF-profile lies in an upper plane, at least one CF-profile lies in a lower plane of the intersection point and at least one CF-profile extends continuously in a vertical direction between these CF-profiles of the upper and of the lower main plane. The CF-profiles are connected to one another by shapings of the LFT-mass at the intersection point in a force-transmitting manner.

<CIT> regards a manufacturing method for a molded article of a fiber-reinforced composite material obtaining a molded article of a fiber-reinforced composite material having a three-dimensional shape. The method comprises preparing a sheet-shaped prepreg containing reinforcing fibers and a matrix resin composition; preliminarily shaping the prepreg to produce a plurality of partial preforms having shapes obtained by dividing the shape of the molded article; producing a first and a second partial preform group, which have the shape of the molded article, by combining the plurality of partial preforms so that the ends thereof in the direction perpendicular to the thickness direction do not overlap in the thickness direction; producing a preform by bringing the first and second partial preform groups into close contact with each other in the thickness direction and compression molding the preform using a molding die. <CIT> does not disclose that the preforms are formed from towpreg and that a preform is a sized, or a sized and shaped portion of a towpreg.

The present invention provides fiber-reinforced composite parts ("fiber composites"), and a way to fabricate them that avoids some of the costs and disadvantages of the prior art.

In accordance with the illustrative embodiment, fiber composites are formed from relatively rigid, fiber-bundle-based preforms. Such preforms are formed from towpreg; that is, a preform is a sized, or sized and shaped portion of towpreg. The towpreg, and hence the preforms, contain thousands of fiber that are impregnated with a matrix material, such as polymer resin.

In a most basic embodiment, preforms have a simple linear shape (i.e., a rod). In some alternative embodiments, preforms may have any one of a variety of relatively complex shapes, including, without limitation, non-linear shapes, closed-form shapes, planar shapes, non-planar (3D) shapes, and multi-layer shapes, as appropriate for a particular mold and the part fabricated therefrom.

In accordance with some embodiments, the preforms are organized in a particular arrangement and orientation -a layup- in the mold cavity of a female mold half. The mold is then closed, and a part is fabricated via compression molding techniques (i.e., application of pressure and heat).

In some embodiments, preforms maintain their shape and location in a mold cavity to a substantial extent during the compression-molding process. Consequently, the fibers and matrix from any given preform can be directed to a desired volumetric region of a part being fabricated. In accordance with the present teachings, preforms can be made to differ in any one or more of a variety of characteristics, including, without limitation, the matrix material (e.g., different thermoplastics, different fillers, etc.), fiber type (e.g., carbon fiber vs. glass, etc.), and fiber distribution. Moreover, the fiber-bundle-based preforms disclosed herein can be bent in ways that a ribbon or sheet cannot. In light of these features, the use of fiber-bundle-based preforms as constituents of a layup provides an unprecedented ability to control fiber alignment at arbitrary volumetric locations within a part. As such, the present invention enables characteristics/attributes/properties of arbitrary regions of a part to be controlled to an extent hitherto not possible, such as to address localized stress issues, or impart different degrees of stiffness to different regions of a part, or to selectively provide electrical and/or thermal conductivity or electrical and/or thermal insulation to regions of a part.

The present invention provides a method for fabricating a fiber-composite part, wherein the method comprises:
forming a layup, wherein the layup consists of plural rigid fiber-bundle-based preforms, each consisting of one or more bundles of fibers impregnated with a polymer resin, wherein each of the fiber-bundle-based preforms is formed from towpreg and is a sized, or sized and shaped portion of towpreg, and further wherein within each bundle, the fibers are continuous and co-aligned;:.

The following terms are defined below for use in this disclosure and the appended claims:.

Additional definitions are provided in the specification in context.

Other than in the examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and in the claims are to be understood as being modified in all instances by the term "about. " Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are understood to be approximations that may vary depending upon the desired properties to be obtained in ways that will be understood by those skilled in the art. Generally, this means a variation of at least +/-<NUM>%.

Moreover, it is to be understood that any numerical range recited herein is intended to include all sub-ranges encompassed therein. For example, a range of "<NUM> to <NUM>" is intended to include all sub-ranges between (and including) the recited minimum value of about <NUM> and the recited maximum value of about <NUM>, that is, having a minimum value equal to or greater than about <NUM> and a maximum value of equal to or less than about <NUM>.

<FIG> depicts towpreg <NUM>. The towpreg includes many individual fibers, typically provided in multiples of a thousand (e.g., <NUM>, <NUM>, <NUM>, etc.), which are impregnated with a polymer resin matrix. Towpreg can have any one of a variety of cross-sectional shapes, including, for example, circular, oval, trilobal, polygonal, etc..

Towpreg can be purchased from suppliers thereof, such as Celanese Corporation of Irving, Texas, or others, or formed on-site via well-known processes such as pultrusion, extrusion, or co-extrusion. In the pultrusion process, a plurality of fibers in the form of a fiber "tow"" is pulled through a die and impregnated, under pressure and temperature, with a polymer (typically thermoplastic or thermoset) resin. The process provides, as indicated above, a plurality of fibers embedded within a continuous matrix material.

Referring now to <FIG>, fiber-bundle-based preform <NUM> is formed by removing a segment of towpreg <NUM>. In <FIG>, preform <NUM> is a short, linear segment; this is a most basic embodiment of the preforms to which embodiments of the invention are directed. As described in further detail later in this specification, in other embodiments, preforms may have a more complex shape, including non-linear shapes, closed-form shapes, 3D shapes, and multi-layer shapes, as appropriate for a part being fabricated. Such preforms are, in fact, "building blocks" for fabricating fiber-reinforced parts in accordance with the present teachings.

A preform has a length that is typically substantially greater than its width and substantially greater than its thickness (note that <FIG> is not to scale). The length of a preform is determined based on attributes of the part being fabricated. A major influence on preform length is the size of the part. Generally, it is desirable to use the longest preform possible for any given application since a longer preform can contain longer continuous lengths of fiber. For a given part, longer continuous fibers typically result in stronger parts than shorter-length fibers. So, for a very small part, a preform might have a length of about <NUM> millimeters, while for a large part (e.g., an airplane wing, a vehicle body panel, etc.), a preform might have a length of many meters. Simply put, preform length is application specific.

A preform can have any suitable cross-sectional (i.e., width and height/thickness) dimensions, as appropriate for the part being fabricated. In some embodiments, the width and height (thickness) of a preform are about equal (e.g., circular cross section, square cross section, etc.). The cross-sectional shape of the preform is, in embodiments of the invention, dictated by the cross-sectional shape of the towpreg, discussed above. The shape, height, and width of a preform can be substantially constant along its length, or can vary.

It is desirable for a preform to be easily manipulated, such as for placement by robotics in a mold cavity. Consequently, the materials forming the preform should be in a state that can be readily handled (e.g., solid, rigid, etc.) at the temperature of use (typically about <NUM> to <NUM>). Alternatively, the temperature of the preform can be altered, as necessary, to facilitate handling.

Preform Composition. It is to be understood that the composition/internal structure of a preform is identical to that of the towpreg from which it is sourced.

Regarding the fibers, the individual fibers in towpreg <NUM> can have any diameter, which is typically, but not necessarily, in a range of about <NUM> to about <NUM> microns. Individual fibers can include an exterior coating such as, without limitation, sizing, to facilitate processing, adhesion of binder, minimize self-adhesion of fibers, or impart certain characteristics (e.g., electrical conductivity, etc.).

Each individual fiber can be solid or hollow core. Each individual fiber can be formed of a single material or multiple materials (such as from the materials listed below), or can itself be a composite. For example, an individual fiber can comprise a core (of a first material) that is coated with a second material, such as an electrically conductive material, an electrically insulating material, a thermally conductive material, or a thermally insulating material.

In terms of composition, each individual fiber can be, for example and without limitation, carbon, glass, natural fibers, aramid, boron, metal, ceramic, polymer filaments, and others. Non-limiting examples of metal fibers include steel, titanium, tungsten, aluminum, gold, silver, alloys of any of the foregoing, and shape-memory alloys. "Ceramic" refers to all inorganic and non-metallic materials. Non-limiting examples of ceramic fiber include glass (e.g., S-glass, E-glass, AR-glass, etc.), quartz, metal oxide (e.g., alumina), aluminosilicate, calcium silicate, rock wool, boron nitride, silicon carbide, and combinations of any of the foregoing. Furthermore, carbon nanotubes can be used. Within an individual preform, all fibers typically have the same composition.

With respect to the matrix material, any polymer resin -thermoplastic or thermoset- that bonds to itself under heat and/or pressure can be used. Exemplary thermoplastic resins useful in conjunction with embodiments of the invention include, without limitation, acrylonitrile butadiene styrene (ABS), nylon, polyaryletherketones (PAEK), polybutylene terephthalate (PBT), polycarbonates (PC), and polycarbonate-ABS (PC-ABS), polyetheretherketone (PEEK), polyetherimide (PEI), polyether sulfones (PES), polyethylene (PE), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyphenylsulfone (PPSU), polyphosphoric acid (PPA), polypropylene (PP), polysulfone (PSU), polyurethane (PU), polyvinyl chloride (PVC). An exemplary thermoset is epoxy. In some embodiments, a ceramic can be used as the matrix matrix.

The suitability for use of any particular polymer resin depends, at least in part, on the requirements of the part being fabricated. Such requirements may include desired attributes/characteristics/properties of the part (e.g., aesthetics, density, corrosion resistance, thermal properties, etc.).

In addition to the polymer resin, the matrix material can include other components such as, for example and without limitation, filler, adhesion promoters, rheology control agents, colorants, and combinations of any of the foregoing.

The type and amount of filler can be selected to achieve a certain desired property such as tensile strength, elongation, thermal stability, low-temperature flexibility, chemical resistance, low density, electrical conductivity, thermal conductivity, EMI/RFI shielding, static dissipative, or a combination of any of the foregoing. Non-limiting examples of suitable fillers include inorganic fillers such as silica and calcium carbonate, organic fillers such as thermoplastic beads, electrically conductive fillers such as metal, graphite, and graphene, and low-density fillers such as thermally expanded microcapsules. A filler can have any suitable form such as bead, particles, powders, platelets, sheets, or flakes.

In some embodiments, filler includes non-aligned fiber and/or discontinuous fiber that does not extend fully between the ends of a preform. Such non-aligned fibers can include chopped fibers, milled fibers, or a combination thereof. Non-aligned fibers can include a plurality of non-aligned continuous fibers, including, for example, fiber weaves, twisted fibers, etc..

Preform Internal Structure. Preforms can have a uniform, or a non-uniform internal structure. <FIG> depict preform 102A of a first embodiment of towpreg <NUM> of <FIG>. In the embodiment depicted in <FIG>, preform 102A has a uniform internal structure (because the towpreg from which it is sourced has a uniform internal structure).

<FIG> depicts a longitudinal cross-section of preform 102A. Preform 102A is linear, which is the most basic implementation of a fiber-bundle-based preform. Preform 102A includes a plurality of fibers <NUM>. These fibers are "continuous" since they extend from first end 204A to second end 206A of preform 102A. Furthermore, fibers <NUM> are "co-aligned," since they are all oriented in the same direction. Preform 102A also includes polymer resin matrix <NUM>, which surrounds and wets fibers <NUM>.

<FIG> depicts a transverse cross-section of preform 102A. In this embodiment, the plurality of co-aligned fibers <NUM> are substantially uniformly distributed across the transverse cross section (i.e., radially) of preform 102A.

<FIG> depict preform 102B of a second embodiment of towpreg <NUM> of <FIG>. In the embodiment depicted in <FIG>, preform 102B has a non-uniform internal structure (because the towpreg from which it is sourced has a non-uniform internal structure).

<FIG> depicts a longitudinal cross-section of preform 102B. Like preform 102A, preform 102B includes a plurality of fibers <NUM>, which are continuous since they fully extend between ends 204B and 206B of preform 102B. The fibers in preform 102B are also co-aligned, as in preform 102A.

Referring now to <FIG>, and with continuing reference to <FIG>, it can be seen that fibers <NUM> are not uniformly radially distributed in preform 102B. Notably, fibers <NUM> are arranged in a band that is embedded with matrix <NUM> of preform 102B. In other words, preform 102B has a non-uniform composition in the radial direction. In some other embodiments, preforms can have other non-uniform distributions of fibers.

Preform External Architecture. <FIG> depict several preform architectures in addition to the simple linear architecture of preforms 102A and 102B of <FIG>/B and 3A/B.

<FIG> depicts preform <NUM>, which is an open-form, planar, nonlinear preform in accordance with the present invention. Preform <NUM> is non-linear because it includes one or more bends <NUM>. Preform <NUM> is planar because the bends are within the same plane. Each bend <NUM> can have an angle independently selected from angles in the range of <NUM>° < bend angle <NUM> < <NUM>°.

A nonlinear preform, such as preform <NUM>, can be formed by heating a portion of tow-preg above the softening point of the matrix material therein and then bending the tow-preg, such as via an automatic bending tool. After the appropriate number of bends are made, the tow-preg is sized/cut, thereby creating the preform. Methods of fabricating preforms are disclosed in U. SN <NUM>/<NUM>,<NUM>, and SN <NUM>/<NUM>,<NUM>.

<FIG> depicts preform <NUM>, which is a closed-form, planar, nonlinear preform in accordance with the present invention. A closed-form preform typically comprises a single length of sized tow-preg that is bent such that the two ends thereof are situated proximal to one another, defining an enclosed region. In some embodiments, the two ends are tacked together, such as via adhesive or thermal bonding. (Preform <NUM> is "open form" because the two ends are not proximal to one another and do not define an enclosed region. ) Preform <NUM> is non-linear because it includes four (i.e., one or more) bends <NUM>. Preform <NUM> is planar because the bends are within the same plane.

<FIG> depicts preform <NUM>, which is a combination of preform <NUM> and preform <NUM>. Preform <NUM> is planar and non-linear, and includes both open form and closed form elements. Preform <NUM> can be fabricated by forming preforms <NUM> and <NUM> and then tacking them together.

Preforms characterized as "closed form," such as preforms <NUM>, <NUM>, and <NUM>, are typically, but not necessarily, further or alternatively characterized as being "open-framework" or "open volume" preforms. In some embodiments, such open-framework preforms are used to fabricate "open-framework" parts, as described later in this disclosure in conjunction with <FIG>.

<FIG> depicts preform <NUM>, which is closed form, planar, and non-linear. Although preform <NUM> includes stacked elements <NUM>, it is nevertheless considered to be planar because all bends are in the same plane or in parallel planes. Preform <NUM> includes two instances of element <NUM>, each of which comprises outer square element <NUM> and inner square elements <NUM>.

<FIG> depicts preform <NUM>, which is an open-form, non-planar, non-linear preform. Preform <NUM> is considered to be non-planar because at least one bend is out-of-plane with respect to another bend. In particular, bend <NUM> between segment <NUM> and segment <NUM> is in the y-x plane (i.e., the bend creates two segments that fall in the y-x plane) and bend <NUM> between segment <NUM> and segment <NUM> is in the x-z plane. Such planes are defined herein as being "out-of-plane" with respect to one another. As implied above with respect to preform <NUM>, and as made explicit here, the characterization "out-of-plane" excludes layered or stacked elements that include "bends," wherein such stacked elements are substantially parallel (in parallel planes) to one another.

In preform <NUM>, the bends are in planes that are orthogonal to one another. However, in some other embodiments, the bends, while being out-of-plane with respect to one another, are in planes that are not orthogonal to one another. As disclosed with respect to preform <NUM> of <FIG>, the bend angle for each bend may be individually selected. Thus, bend <NUM> can have any angle greater than <NUM>° and less than <NUM>°.

Although the preforms depicted in <FIG> depict any given bend as being defined by one non-zero vector component (i.e., along the x, y, or z axes and within the x-y, z-x, or y-z planes), in some other embodiments, a bend can be defined by any combination of non-zero x, y, or z vector components.

In some other embodiments, preforms are non-planar, non-linear, and closed form. Furthermore, non-planar, non-linear preforms can comprise non-planar, non-linear elements and planar, non-linear elements. An example of such a preform is a preform that combines, for instance, preform <NUM> of <FIG> and preform <NUM> of <FIG>.

Compression Molding in Accordance with the Present Methods. As previously noted, in accordance with the present teachings, fiber-bundle-based preforms are used to fabricate a part, such as via compression molding. More particularly, in accordance with the present teachings, a part is fabricated by positioning two or more such preforms in a mold cavity, closing and thereby pressurizing the mold cavity, and raising the temperature of the contents of the mold cavity to cause the matrix material to soften to the extent that it flows "i.e., melt flow. " Under such applied pressure and temperature, the two or more preforms are consolidated and, after cooling, a finished part results.

As is well known, compression molding is typically conducted at a pressure of at least about <NUM>,<NUM> bar (about <NUM> psi). The temperature requirements for the process are a function of the matrix material used. For example, for a matrix comprising a thermoplastic resin, the temperature must meet or exceed the resin's glass transition temperature so that resin can flow, but must remain below its degradation temperature. For a matrix comprising a B-stage thermoset or B-stage ceramic, the matrix material must be sufficiently heated to flow, and also meet or exceed the reaction temperature of the co-reactants.

As previously noted, in accordance with the present teachings, two or more fiber-bundle-based preforms are placed in a particular arrangement and/or orientation -a "layup"- in the mold cavity. Arrangement/orientation specifics are based, at least in part, on desired overall part properties (e.g., mechanical properties, aesthetics, etc.) or the properties of a particular region of a part. During placement in the layup, the preforms retain their manufactured shape; this characteristic facilitates directing the fibers from a particular preform to a particular volumetric region of a part.

<FIG> depict female mold half <NUM> having mold cavity <NUM>, as well as two exemplary fiber-bundle-based preform layups <NUM> and <NUM>, respectively, for use in fabricating fiber-composite part <NUM> (<FIG>) via compression molding.

Layup <NUM> depicted in <FIG> includes: (i) six linear preforms <NUM> having a polygonal (square) transverse cross section and arranged in two layers of three preforms each, and (ii) six linear preforms <NUM> having a circular transverse cross section and arranged in two layers of three preforms each. These two groupings of preforms are oriented orthogonally to one another, with one end of each of preforms <NUM> abutting the side of two of the stacked preforms <NUM>.

Layup <NUM> depicted in <FIG> is a more complex arrangement than layup <NUM> and includes: (i) two stacked "L"-shaped (non-linear) preforms <NUM>, (ii) four linear preforms <NUM> organized in two layers of two preforms each, (iii) one linear preform <NUM>, (iv) four linear preforms <NUM> organized in two layers of two preforms each, and (v) two linear preforms <NUM> organized in two layers of two preforms each. Preforms <NUM> and <NUM> are about one-half the length of preform <NUM>. Such different layups might be used as a function of the stresses arising in given volumetric regions of a part as a consequence of the forces to which a part is subjected in use.

In each of the two embodiments depicted, the preforms are arranged in the shape of an "L" to form the layups <NUM> or <NUM>, consistent with the shape of mold cavity <NUM>. In some embodiments, the layups are formed by adding preforms one-by-one to cavity <NUM>, such that layup is formed within the cavity. In some other embodiments, some or all of the preforms are tacked together forming a "preform charge" prior to placement into cavity <NUM>. In embodiments in which all preforms are assembled into a preform charge, the layup (which is then synonymous with the preform charge) is assembled and then placed as a single unit into the mold cavity.

The composition, internal structure, and external architecture of each preform placed in a mold is individually selectable, as appropriate, typically to achieve a desired attribute of a part being fabricated. For example, given a plurality of preforms in a layup, at least one preform can differ from other preforms in the following non-limiting ways:.

To the extent that the matrix material differs from one preform to the next in a layup, such different matrix materials must be compatible with one another. In the present context, "compatible" means that the different matrix materials will bond to one another.

Part Internal Structure. Selective positioning of fiber-bundle-based preforms that can differ from one another as described above in accordance with embodiments of the invention provides an ability to fabricate a part having different material properties in different regions of the part. This is quite advantageous since, among any other considerations, the in-use loads on a part often vary at different regions of a part, arising in different stress vectors therein. Also, designing for a certain stiffness or desired electrical properties in certain regions of a part is facilitated by the foregoing.

A part formed in accordance with the present teachings is considered to comprise two or more "sections. " <FIG> depicts a longitudinal cross section through a segment of arm <NUM> of part <NUM> of <FIG>. This segment has two such sections: section <NUM> and section <NUM>. The various sections of a part adjoin each other to form the part, although such sections are not necessarily discernable as being discrete from one another upon external or internal examination of the part. That is, adjacent sections can be continuous in the sense that there might not be a distinct interface separating one section from an adjacent section. This will occur, for example, when the matrix material in adjacent sections is the same and the fibers in the adjacent sections are the same. Regardless of whether an interface is readily discernable or not, the notion of a "section" is useful for pedagogical purposes, and is used herein to refer to a volume (of a part) having a uniform composition. That is, a transverse cross-section taken anywhere along the length of a given section will exhibit substantially the same fiber and matrix composition/distribution/alignment.

In accordance with the present teachings, each section includes at least one "portion. " Referring again to <FIG>, section <NUM> is composed of portions 1082A, 1082B, and 1082C, and section <NUM> is composed of portions 1086A, 1086B, and 1086C. A "portion" refers to a volume of a part derived from a particular preform. That is, a preform is the source of the fibers and matrix material for a given portion. Thus, for example, if a section is derived from two preforms, that section is considered to contain two portions. Similarly, if a section is derived from three preforms, that section is considered to contain three portions, and so forth. In such embodiments, the composition of each portion of a section is therefore determined by the composition of the preforms from which the section is derived.

As will be appreciated by comparison of <FIG>, there is not necessarily a one-to-one correspondence between preforms and portions. <FIG> depicts a segment of layup <NUM> of <FIG>. The preforms in the segment are the source of some of the fiber and matrix material that form arm <NUM> of part <NUM>. This segment of the layup includes preform <NUM>, two stacked preforms <NUM>, and two stacked preforms <NUM>. Preform <NUM> is disposed on top of the preforms <NUM> and <NUM>. Preforms <NUM> and <NUM> comprise first fiber type <NUM> and preforms <NUM> include second fiber type <NUM>. In this example, all preforms are assumed to comprise the same matrix material <NUM>. In some other embodiments, the matrix material from different preforms -and in different portions- can differ, as long as the matrix materials are compatible with one another. It is notable that the scale (thickness, in particular) of <FIG> is enlarged in comparison to <FIG>.

Co-aligned fibers <NUM> from preform <NUM> appear in both portion 1082A of section <NUM> and in portion 1086A of section <NUM>. Still referring to section <NUM>, co-aligned fibers <NUM> from "upper" preform <NUM> appear in portion 1082B and co-aligned fibers <NUM> from "lower" preform <NUM> appear in portion 1082C.

And in section <NUM>, co-aligned fibers <NUM> from "upper" preform <NUM> appear in portion 1086B and co-aligned fibers <NUM> from "lower" preform <NUM> appear in portion 1086C. The matrix is continuous throughout sections <NUM> and <NUM>.

As is clear from <FIG>, the length of each portion of a section does not necessarily correspond to the length of preform contributing fibers to that section (compare the length of portion 1082A of section <NUM> with the length of preform <NUM>). Furthermore, neither the thickness nor the width of a preform will necessarily correspond to the thickness or the width of a portion. The shape of a portion will, however, be influenced by the shape of the preform. Similar to the situation for "sections," the interface between adjacent "portions" might or might not be discernable.

A section can have the same composition or a different composition as an adjoining section. Regarding the latter situation, from section to section, the compositions can vary in terms of the matrix material composition, the fiber composition, content, and/or fiber distribution, as well as in any other compositional variable(s). Furthermore, adjoining sections can have the same or different fiber alignment.

The composition of section <NUM> differs from that of section <NUM>. In particular, whereas portions 1082B and 1082C of section <NUM> include fibers <NUM>, portions 1086B and 1086C of section <NUM> include fibers <NUM>. This is further evidenced from <FIG>, which depict respective transverse cross sections along axis A-A and axis B-B of <FIG>. A transverse cross section taken anywhere in section <NUM> will appear as depicted in <FIG>. Similarly, a transverse cross section taken anywhere in section <NUM> will appear as depicted in <FIG>. However, a transverse cross section of the interfacial area between sections <NUM> and <NUM> may look somewhat different than the transverse cross sections appearing in either <FIG>.

It is to be understood that in addition to extending in a "vertical" direction and a "longitudinal" direction as depicted in <FIG>, a section can extend in a "transverse" direction as well. In the context of <FIG>, this would, for example, include additional portions adjacent to portions 1082A, 1082B, 1082C, and extending "into the page. " This is depicted with more particularity in <FIG>.

<FIG> depicts an "exploded" view, by section, of part <NUM>. The designation of sections is, to some extent, arbitrary, subject to the definition provided above. But the use of "sections" and "portions" as descriptors provides a useful pedagogical tool in conjunction in describing and defining embodiments of the invention, and serve to highlight the differences between parts made in accordance with the present teachings from those in the prior art.

In the embodiment depicted in <FIG>, five "sections" <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are defined for part <NUM>. Sections <NUM> and <NUM> have been described in conjunction with <FIG> and <FIG>. <FIG> additionally reveals that section <NUM> includes portions 1082D and 1082E and section <NUM> includes portions 1086D and 1086E, which portions were not depicted as being included in their respective sections in <FIG>. With reference to <FIG>, the preforms responsible for at least additional portions 1086D and 1086E are readily visible.

Part <NUM> also includes section <NUM>, which includes portions 1090A through 1090D. Four preforms <NUM>, which are depicted in <FIG>, are the source of material for these portions.

Sections <NUM> and <NUM> derive from stacked L-shaped preforms <NUM> (<FIG>). Although the fibers within preforms <NUM> are assumed to be continuous and colinear, they give rise to two sections rather than one because the fibers sourced from these preforms and present in arm <NUM> and arm <NUM> are oriented orthogonally with respect to one another. Section <NUM> includes portions 1094A and 1094B, and section <NUM> includes portions 1098A and 1098B.

As previously disclosed, the fiber-bundle-based preforms that are the source of material for the various sections/portions of the part can, in accordance with the present teachings:.

Because of capabilities (i), (iii) and (iv), embodiments of the invention provide a largely unencumbered ability to direct fiber and matrix materials from any given preform to an arbitrary volumetric region of a part being fabricated. Because of capability (ii), embodiments of the invention provide an unprecedented ability to tailor attributes/characteristics of a part. These capabilities, in combination, enable a manufacturer to fabricate fiber-composite parts having desired attributes/characteristics at arbitrary volumetric locations of the part. This should be readily apparent from <FIG>.

In light of the foregoing, it will appreciated that the methods described herein can be used to fabricate parts having different material properties in: (i) different sections of the part, (ii) different longitudinal portions of a given section of a part, and/or (iii) in different radial/depth locations of a given section of a part.

For example, with reference to <FIG>, at least some properties of section <NUM> can be expected to differ from such properties of section <NUM>, due to the presence of different types of fibers in the two sections. And at least some properties of portion 1082B -1082E of section <NUM> are expected to differ from such properties of portions 1086B - 1086E of section <NUM> due to the different fibers in those portions. For example, if fibers <NUM> are carbon fiber, and fibers <NUM> are fiberglass, the part can be expected to be weaker in portions 1086B - 1086E than portions 1082A-1082E and 1086A. Furthermore, because of the continuity of the fibers between sections <NUM> and <NUM>, as a consequence of the shape of preforms <NUM>, the region at which the two arms <NUM> and <NUM> of part <NUM> intersect is expected to be stronger near the "outer" corner than the inner corner of the part (since the fibers are not continuous between sections <NUM> and <NUM>).

The difference in properties can be functional, such as, for example, by imparting electrical conductivity to one or more sections of a part, such as through the choice of fiber, filler material, or the like. Or the differences can be mechanical, such as, for example, by imparting high mechanical strength to section(s) of a part by appropriate selection of fiber (e.g., carbon fiber, etc.) and/or by co-aligning all fiber in such sections, and/or by increasing fiber volume fraction.

Recalling the discussion of the preform external architecture and internal structure, and in light of the fact that the fiber-bundle-based preforms are the building blocks of parts in accordance with the present teachings, adjoining sections of a part can be colinear or non-colinear, co-planar or non-coplanar, fibers in the adjoining sections can be co-aligned or non-co-aligned, and uniformly or non-uniformly distributed.

Methods disclose herein, by virtue of the use of fiber-bundle-based preforms, are particularly well suited to fabricating complex parts, including those characterized by open volumes between and/or within solid sections of the part. <FIG> depict non-limiting examples of open-framework parts (i.e., parts having open volumes).

<FIG> depicts frame <NUM>, having open central region <NUM>. <FIG> depicts lattice <NUM> including open volumes <NUM>. <FIG> depicts lattice <NUM> including open volumes <NUM>. <FIG> depicts truss <NUM> having opening volumes <NUM>. And <FIG> depicts honeycomb <NUM> including open volumes <NUM>.

Claim 1:
A method for fabricating a fiber-composite part, wherein the method comprises:
forming a layup, wherein the layup consists of plural rigid fiber-bundle-based preforms (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) each consisting of one or more bundles of fibers impregnated with a polymer resin, wherein each of the fiber-bundle-based preforms is formed from towpreg (<NUM>) and is a sized, or sized and shaped portion of towpreg, and further wherein within each bundle, the fibers are continuous and co-aligned;
consolidating, via compression molding, the layup in a mold cavity (<NUM>); and
cooling the consolidated layup, thereby providing a fiber-composite part (<NUM>).