Patent Grant
9545757
1. Field of the Invention
The invention relates generally to the field of composite design and more specifically to the field of structural detail fabrication.
2. Description of the Related Art
Laminates contain fibers having a given direction of the fibers within a resin. Unidirectional laminates are usually suitable for carrying loads in only one direction. They are usually weak in the transverse direction to ply orientation. The properties of unidirectional composites are quite different from isotropic materials. Unidirectional materials are highly anisotropic and have exceptional properties, for example, strength, in the fiber direction and mediocre properties perpendicular to the fiber direction. On the other hand, isotropic laminates may be equally strong in all directions.
There are limited applications where composites are used (or bear a load) purely in a unidirectional configuration. In most applications, there will be some loading away from the direction of the fibers. In this situation, if a unidirectional laminate is used, it is only the resin, which is not itself reinforced, that resists this off-axis load. Hence, composite structures are conventionally made by combining unidirectional fibers in different directions relative to one another to enhance load bearing capacity. Such laminates are known as multi-directional laminates.
Stacking laminates with plies in different orientations is useful when there is a need to optimize multi-directional load-carrying capacity. One common way of creating these multi-directional laminates is to layer the laminates with each laminate layer having a ply bias or fiber orientation angle different from the next. A common sequence of layering uses ply bias angles of +45°, −45°, 0° and 90° relative to the reference plane defined by the component to be built. For example, the reference plane may be defined relative to the long axis of a long, straight component such as a stringer, or relative to the central axis of a radial component such as a frame for a fuselage. This sequential stacking of additional ply bias angles creates an isotropic laminate that is more suitable for carrying loads in more than one direction. However, in order to form a circular axis, such as the central axis of a fuselage frame, some material must be sectioned and/or positioned at an orientation that is not ideal, potentially leading to lower strengths, increased labor, manufacturing time and waste.
Orientation requirements for conventional isotropic composite lay ups require layer by layer application of laminates to a bond tool, for example using laminates having the +45, −45, 0 and 90 degree ply angles described above. Thus, conventional methods of manufacturing larger composite parts with curved portions may require the use of multiple ply sections for each ply layer in order to maintain the ply orientation tolerance necessary to create an isotropic composite structure.
In one aspect, the invention provides a method for fabricating a fiber reinforced composite structure which allows formation of a curved structure using a straight multi-ply charge. In an embodiment, the curved structure has a curved longitudinal or circumferential axis. The curved structure may be formed using a bond tool having a curved longitudinal or circumferential axis.
Forming a circular axis while maintaining orientation of 0 degree and 90 degree layers relative to the axis typically requires sectioning the material forming these layers. Attempting to stretch or compress layers whose fibers are oriented at 0° or 90° relative to the circular axis amounts to stretching or compressing in the direction of the fibers, which leads to distortion of the material layers (e.g., bunching). Thus, in order to maintain both a flat composite layer and the desired 0°/90° fiber orientation, the 0 degree and 90 degree layers are typically cut into many smaller pieces and individually placed about the circular axis. In addition to increasing labor, manufacturing time and waste, such sectioning compromises strength of a layer. For large, curved objects such as a fuselage frame, excessive sectioning of the 0 degree and 90 degree layers may reduce strength to the point that a laminate formed with +45°, −45°, 0° and 90° ply angles is not significantly stronger than a laminate formed of alternating +45° and −45° ply angles.
In one embodiment, a method for fabricating a fiber reinforced composite structure includes layering prepreg fiber reinforced composite plies into a tool layup. The plies may be layered in one at a time or in groups. In an embodiment, the bias angles of the plies in the charge are selected to facilitate formation of curved structures with little to no wrinkling or bunching of the plies. In an embodiment, the ply layup is not isotropic or quasi-isotropic. In an embodiment, bias angles of plies in the charge are other than 0 degrees and other 90 degrees with respect to the longitudinal axis of the charge. In another embodiment, there are no full plies in the charges with bias angles of 0 degrees or 90 degrees. For example, the bias angle in a unidirectional or a woven full ply layer may be from 30 to 60 degrees or from −30 to −60 degrees with respect to the longitudinal axis of the charge. Consecutive plies of the charge may be layered such that the fibers of one ply are at approximately 90 degrees relative to the fibers of a proximate ply. Each ply is cut on the bias at either plus 45 degrees or minus 45 degrees. The bias angles of the layered plies alternate one relative to the next. The layered plies are cured after layering.
In one embodiment, a fiber reinforced composite structure includes multiple plies of prepreg fiber reinforced material. Consecutive plies are layered such that (a) the fibers of one ply are at 90 degrees relative to the fibers of a proximate ply, and (b) the fibers of each ply are oriented at positive or negative 45 degrees with respect to a reference plane of the fiber reinforced composite structure.
Illustrative embodiments of the present invention are described in detail below with reference to the attached drawing figures, which are incorporated by reference herein and wherein:
The present disclosure provides systems and methods for composite layup configuration to support detail fabrication. Composite layups may be formed using a non-standard ply bias layer orientation along with special trimmed features that allows for flat ply stacking of the composite laminate layers, reduces the number of required ply sections per ply layer orientation, and reduces waste of composite laminate materials. Hereafter, composite laminate layers may also be referred to as “plies, “composite layers” or simply “layers.”
Each composite layer of the laminate comprises fibers and a matrix. The fibers may be continuous fibers rather than chopped fibers. Suitable fibers for use with the invention include, but not limited to carbon, graphite, fiberglass, KEVLAR® (aramid), Innegra™ (high modulus polypropylene for Innegra S), ceramic, and boron fibers. The matrix material may be a synthetic resin. The laminate may comprise partial plies which do not span the composite structure as well as full plies.
The positioning of the fibers in a given ply may be described by a characteristic fiber orientation. In a given ply, the bias angle of the fibers within the ply layer may characterize the fiber orientation. For a ply comprising fibers which are substantially unidirectionally oriented, the bias angle describes fiber orientation in the ply with respect to a reference, such as the longitudinal axis of the ply stack. The bias angle of the fibers may be in woven materials or in unidirectional materials. Embodiments of the present disclosure are equally useful for unidirectional ply layers and woven ply layers. For a ply with woven fibers, there may be more than one bias angle present in the layer. For example, the warp fibers may have one bias angle and the weft fibers another.
In an embodiment, the characteristic fiber orientation of each full-width ply of a straight charge is from 30 to 60 degrees or from −30 to −60 degrees with respect to the longitudinal axis of the straight charge and the sign of the characteristic fiber orientation of each full width ply of the straight charge alternates with respect to the sign of the characteristic fiber orientation of each neighboring ply (i.e. the plies of the stack alternate between + and − orientations). In an embodiment, the characteristic fiber orientation of each full width ply of the straight charge forms an angle of 80 to 100 degrees with respect to the characteristic fiber orientation of each neighboring ply. The bias angle of the fibers within a ply layer may also be limited to 40 to 50 degrees or −40 to −50 degrees, or limited to +45° or −45° relative to the longitudinal axis of the charge.
A curved composite layup may be formed by placing a multi-layer straight charge into a tool layup comprising a bond tool, the bond tool comprising a curved longitudinal or circumferential axis. The straight charge is reshaped to conform to at least a portion of the bond tool, thereby forming a composite layup with a curved longitudinal or circumferential axis. Placing layers with bias angles from 30 to 60 degrees or from −30 to −60 degrees can allow the layers to be shaped to a curved structure with significantly less to no bunching than would be obtained for layers with bias angles near 90 degrees to the longitudinal axis of the ply stack. In an embodiment, manipulating the layers does not push or pull directly on the fibers, but rather changes the relationship of the fibers to one another. In an embodiment, each full width ply of the composite layup comprises a characteristic fiber orientation that is from 30 to 60 degrees or from −30 to −60 degrees with respect to the bond tool axis and the sign of the characteristic fiber orientation of each full width ply in alternates with respect to the sign of characteristic fiber orientation of each neighboring ply. In an embodiment, the characteristic fiber orientation of each full width ply of the layup forms an angle of 80 to 100 degrees with respect to the characteristic fiber orientation of each neighboring ply. In other embodiments, the bias angle of the fibers within a ply layer may be limited to 40 to 50 degrees or −40 to −50 degrees, or limited to +45° or −45° relative to the reference plane defined by the structure to be created. For example, bias angles may be limited to +45° or −45° relative to the long axis of a stringer.
Limiting layer orientation to +45 degrees or −45 degrees provides a more efficient method of manufacturing composites, especially those that have complex shapes, such as a curved runner of a fuselage skeleton. Layering alternating ply layers having a fiber bias of +45 degrees and −45 degrees creates a composite structure, the strength of which is not reduced from that of a typical isotropic laminate because this orientation eliminates ply splices and related off-axis ply orientation. Additionally, waste is reduced by layering alternating ply layers having a fiber bias angle of +45 degrees and −45 degrees when making a curved composite structure. Layers having a bias angle of +45 degrees and −45 degrees through an arc, such as a curved runner, are still within the tolerances that allow for the additional strength imparted to the composite structure through a pseudo-isotropic laminate.
In an embodiment, the mold 302 comprises a first surface 310 on which the laminate stack may be placed. The first surface may be substantially horizontal and/or may form an upper surface of the mold. The first surface of the mold may also be substantially flat or planar. As used herein, a surface is substantially horizontal when at least 50% of the surface is within +/−10 degrees of horizontal. The first surface of the mold may also be curved so that the radius of curvature lies in the plane of the first surface of the mold, as shown in
The mold 302 may also comprise a second surface which makes a specified angle with respect to the first surface. In an embodiment, the first surface is an upper surface and the second surface is a side surface that makes an angle of approximately 90 degrees with respect to the upper surface. For example, the angle between the upper surface and the side surface may be from 90 to 100 degrees. When the ply stack conforms to these first and second surfaces, the edge of the ply stack will be bent relative to the center portion to form a composite layup with a “leg” that is generally transverse to the center portion. In an embodiment, the charge further comprises a plurality of partial plies of unidirectionally oriented fibers, the characteristic fiber orientation of each of the partial plies being generally aligned with the longitudinal axis of the charge. For example, the characteristic fiber orientation of each of the partial plies may be from +5 degrees to −5 degrees with respect to the longitudinal axis of the charge. The partial plies may be located near a longitudinal edge of the ply stack, with the edge of the each partial ply generally aligning with the longitudinal edge of the ply stack. In an embodiment, if cutouts are formed at one longitudinal edge of the ply stack the partial plies are located are located at the other longitudinal edge of the ply stack. The width of the partial plies may be selected so that the partial plies do not extend across the first surface of the mold. In an embodiment, the width of each partial ply is from 20% to 30% or about 25% of the width of the full plies. After formation of the composite structure, these partial plies are located at the outer edges or “caps” of the composite structure. The fiber orientation in the “leg” of the composite structure may be generally aligned with the longitudinal or circumferential axis of the bond tool.
Structural features 304 impart additional features to the composite structure formed in mold 302. Structural features 304 are depicted in a configuration that allows for stringers to be fixed to an arcuate runner formed by mold 302. Structural features 304 may be configured to impart any structural feature to the composite structures formed with mold 302 and made with bond tool 300. Cutouts 210 of layers 202-208 may be shaped and sized to fit with structural features 304 of mold 302.
As shown, composite structure 400 is an arcuate runner having stringer cut outs 404 (not all labeled). As its laminate layers are not sectioned, or less sectioned, than layers at 0 degrees or 90 degrees relative to the circular axis of structure 400, composite structure 400 may be as strong as an arcuate runner formed with multi-sectioned 0 degree or 90 degree composite layers.
In step 506, the strips of composite material are stacked together in alternating bias layers, and the stack is trimmed to form plies (composite layers) of a composite laminate structure. In one example of step 506, the +45 degree angle strips are described above are alternated with the −45 degree angle strips of composite material, and the stack is trimmed such that the +45 degree strips form plies 202 and 206 and the −45 degree strips form plies 204 and 208 (
The stacked plies are placed with the bond tool (i.e., with the mold), in step 508. Due to prior stacking and trimming to fit features of the bond tool/mold, fibers of the composite layers may be oriented at +45 degrees and/or −45 degrees relative to the reference plane of the mold. In one example of step 508, where the mold is for an arcuate runner, placing the ply stack with the bond tool includes manipulating the stack to lie flat while conforming to the curved shape of the mold, which may be facilitated by reshaping the ply stack such that cutouts 210 conform to the plurality of structural features 304. Cutouts 210 may have a first spacing therebetween that is less than a second spacing between structural features 304 due to the location of structural features 304 along the radially outward edge of curved mold 302.
Step 510 is a decision. If the desired layering is achieved, for example to form a particular composite component, the layers may be additionally trimmed, if necessary, in optional step 512, and the layup is cured, in step 514. In one example of method 500, up to six layers are stacked and trimmed together and placed in the bond tool mold (steps 504-508). If additional layers are desired (decision 510), steps 504-508 MAY repeat until the desired layering is achieved. In another example of method 500, strips of material are layered and trimmed in groups of three to four layers until the desired layering is achieved. It will be appreciated that the layup formed by method 500 may be cured according to methods known in the art (for example, under heat and/or pressure), or according to methods and/or using systems laid out in the copending U.S. Patent Applications incorporated by reference above. It will also be appreciated that optional trimming step 512 may be unnecessary, as adequate trimming of the stacked layers may be achieved at step 506.
Changes may be made in the above system and method without departing from the scope hereof. It should thus be noted that the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present system and method, which, as a matter of language, might be said to fall there between.
This application is a continuation-in-part of U.S. patent application Ser. No. 13/763,543, filed Feb. 8, 2013, which claims priority of U.S. Provisional Patent Application No. 61/596,604, filed Feb. 8, 2012, both of which are incorporated herein by reference.
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| Number | Date | Country | |
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| Number | Date | Country | |
|---|---|---|---|
| Parent | 13763543 | Feb 2013 | US |
| Child | 14152532 | US |
