Radius filler and method of manufacturing same

A method of manufacturing a radius filler may include providing a plurality of fibers, braiding the plurality of fibers into a braided preform, shaping the braided preform into a braided radius filler, and cutting the braided radius filler to a desired length.

FIELD

The present disclosure relates generally to composite structures and, more particularly, to composite radius fillers for composite structures, and methods for manufacturing the same.

BACKGROUND

Composite structures are used in a wide variety of applications due to their high strength-to-weight ratio, corrosion resistance, and other favorable properties. In aircraft construction, composites are used in increasing quantities to form the fuselage, wings, horizontal and vertical stabilizer, and other components. For example, the horizontal stabilizer of an aircraft may be formed of composite skin panels co-bonded or co-cured to internal composite structures such as composite stiffeners or spars. The composite spars may extend from the root to the tip of the horizontal stabilizer and may generally taper in thickness along a spanwise direction to improve the stiffness characteristics of the horizontal stabilizer and reduce weight.

Composite stiffeners or spars may be provided in a variety of cross-sectional shapes. For example, a composite spar or stiffener may be formed in an I-beam shape by bonding or curing together the vertical webs of two C-shaped composite channels in back-to-back arrangement. Each one of the C-shaped channels may have horizontal flanges extending outwardly from upper and lower ends of a web. Each horizontal flange may transition into the web at a radiused web-flange transition. When the C-shaped channels are joined back-to-back to form the I-beam shaped stiffener, the radiused web-flange transitions result in a lengthwise notch along the upper and lower ends of the I-beam stiffener. The lengthwise notches may be referred to as radius filler regions or noodle regions. To improve the strength, stiffness, and durability of a composite structure, radius filler regions may be filled with radius fillers or noodles formed of composite material.

Unfortunately, existing radius fillers suffer from several drawbacks that detract from their utility. For example, existing radius fillers may exhibit cracking due to residual stress that may occur during the manufacturing process such as during cool-down from curing. The residual stress may occur as a result of a thermal mismatch between the radius filler and the adjacent composite laminates surrounding the radius filler. In addition, certain radius fillers may result in sub-optimal pull-off strength at the bond between the stiffener and the skin panel under structural loading.

As can be seen, there exists a need in the art for a radius filler that minimizes cracking during the composite manufacturing process and which provides favorable pull-off strength and which can be manufactured in a timely and cost-effective manner

SUMMARY

The above-noted needs associated with joining composite components are specifically addressed by the present disclosure which provides a method of manufacturing a radius filler or noodle. The method may include providing a plurality of fibers, and braiding the plurality of fibers into a braided preform. The method may further include shaping the braided preform into a braided radius filler, and cutting the braided radius filler to a desired length. As described in greater detail below, in some examples, the fibers may be reinforcing fibers (e.g., carbon fibers, glass fibers, Kevlar® fibers, etc.) to which resin or matrix material may be applied. The matrix material may be a thermosetting matrix material (e.g., epoxy) or a thermoplastic matrix material (e.g., polyetherketoneketone, polyetheretherketone, etc.). In some examples, the fibers may include reinforcing fibers braided with thermoplastic fibers that may melt when heated to infuse with the reinforcing fibers, as described below. In other examples, the fibers may comprise only thermoplastic fibers that may be braided together and which may melt and fuse together during the process of heating, shaping, and solidifying the radius filler.

Also disclosed is a method of fabricating a composite structure. The method may include mounting a braided radius filler in a radius filler region between opposing stiffener laminates. The method may additionally include assembling a base laminate with the stiffener laminates to encapsulate the braided radius filler within the radius filler region and form a laminate assembly. The method may further include curing the laminate assembly by applying heat to form a composite structure.

In a further embodiment, disclosed is a method of manufacturing a radius filler. The method may include providing a radius filler core, and fabricating a sleeve. The method may additionally include covering the radius filler core with the sleeve to form a sleeved radius filler.

Also disclosed is a method of fabricating a composite structure. The method may include mounting a sleeved radius filler in the radius filler region between opposing stiffener laminates, and assembling a base laminate with the stiffener laminates to encapsulate the sleeved radius filler within the radius filler region to form a laminate assembly. The method may also include curing the laminate assembly by applying heat to form a composite structure.

Additionally disclosed is a radius filler for installing in a radius filler region of a laminate assembly. The radius filler may include a plurality of fibers encapsulated in resin and braided into a braided radius filler. The braided radius filler may have a generally triangular shape with concave radius filler side surfaces and a generally planar radius filler base surface.

Further disclosed is a radius filler. The radius filler may include a radius filler core. The radius filler may additionally include a sleeve covering the radius filler core. The sleeved radius filler may have opposing radius filler side surfaces and a radius filler base surface. The radius filler side surfaces may be concave. The radius filler base surface may be generally planar.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for purposes of illustrating various embodiments of the disclosure, shown inFIG. 1is a perspective view of an aircraft100having a fuselage102extending from a forward end of the aircraft100to an aft end of the aircraft100. The aft end may include an empennage110having one or more tail surfaces for directional control of the aircraft100such as a vertical stabilizer112and a pair of horizontal stabilizers114. The aircraft100may further include a pair of wings108extending outwardly from the fuselage102and one or more propulsion units104. The fuselage102, the wings108, the vertical stabilizer112, the horizontal stabilizers114, and/or other aircraft components may be formed as composite structures106.

Referring toFIG. 2shown is a partial cutaway view of a portion of a horizontal stabilizer114of the aircraft100ofFIG. 1. The horizontal stabilizer114may extend along an outboard direction from a stabilizer root to a stabilizer tip. As indicated above, the horizontal stabilizer114may be formed of composite skin panels150that may be co-cured or co-bonded to one or more composite stiffeners152or spars. InFIG. 2, the composite stiffener152is shown as an I-beam160although the composite stiffener152may be provided in a variety of other cross-sectional shapes.

Referring toFIG. 3, shown is a partially exploded view of the composite stiffener152ofFIG. 2. The composite stiffener152may be comprised of a pair of C-channels164in back-to-back relationship to form an I-beam160. Each C-channel164includes a web166having flanges168at the upper and lower ends of the C-channel164. Each flange168transitions from the web166at a radiused web-flange transition and results in a lengthwise radius filler region158extending along the upper portion and the lower portion of the I-beam160. Each radius filler region158on the upper and lower portion may be filled with a noodle or radius filler in one of many embodiments disclosed herein.

InFIG. 4, shown is a schematic diagram of a portion of a composite structure106and illustrating a pulloff load178acting on an interface between the stiffener laminates162and a base laminate172. The pulloff load178is an out-of-plane load that may be transmitted through the web166of the C-channels164creating a reaction force180on opposite sides of the braided radius filler230. The pulloff load178and the reaction forces180may be oriented normal to the plane of the base laminate172and may tend to separate or de-bond the flanges168from the base laminate172and/or delaminate the composite plies that make up the stiffener flanges168and the base laminate172. The pulloff load178may be of greatest magnitude at the location of the tangent points156of the flanges168with the corresponding stiffener outer radius154.

InFIG. 5, shown is an embodiment of a braided radius filler230in its final shape. The braided radius filler230may be formed of continuous fibers308that are braided in multiple directions instead of a single axial direction typical of conventional radius fillers. The multiple fiber directions of the braided radius filler230may advantageously prevent or reduce or minimize the propagation of a crack into the composite laminates that surround the radius filler region158. As indicated above, cracking in a radius filler may occur during manufacturing of the radius filler as a result of mismatches in tooling or due to residual strain resulting from processing (e.g., curing) operations. In this regard, residual strain may occur in a radius filler due to a mismatch in the coefficient of thermal expansion of the radius filler relative to coefficient of thermal expansion of the composite laminates surrounding the radius filler. Advantageously, the braided radius filler230as disclosed herein may provide improved resistance to crack initiation and/or improved resistance to crack growth. By reducing crack initiation or crack growth, the composite stiffener152may exhibit improved pulloff load capability relative to conventional composite stiffeners.

InFIG. 5, the braided radius filler230may be formed of a plurality of composite reinforcing fibers308. The fibers308may be dry fibers324that may be braided via a braiding machine304and then later wetted in a resin bath330. Alternatively, the fibers308may be provided as prepreg fibers that may be pre-impregnated or pre-coated with resin such as thermoplastic resin or thermosetting resin. Types of thermoplastic resin may include polypropylene, polyethylene terephthalate, polyetherketoneketone (i.e., PEKK), polyetheretherketone (i.e., PEEK), polyphenylene sulfide, polyetherimide (i.e., PEI), polyamide, and other types of thermoplastic resin. Types of thermosetting resin may include epoxy or other thermosetting resin compositions. As indicated above, the fibers308may be generally continuous along the length of the braided radius filler230. In one embodiment, the fibers308may be formed as continuous composite tape310such as unidirectional slit tape. The fibers308may comprise carbon fibers, aramid fibers, Kevlar® fibers, glass fibers, or any other type of reinforcing fiber material or combination of materials.

The braided radius filler230may be formed into a generally triangular shape with opposing concave radius filler side surfaces232and may have a generally planar radius filler base surface234. The radius filler side surfaces232may be sized and shaped complementary to the opposing stiffener outer radii154of the composite stiffener152. In this regard, any one the radius filler embodiments disclosed herein may be applied to stiffener shapes other than the I-beam160configuration. For example, any one of the radius filler embodiments disclosed herein may be installed in the radius filler region158of a hat-section stiffener, an L-shaped stiffener, a Z-shaped stiffener, and any one of a variety of other stiffener configurations. Furthermore, the radius filler embodiments disclosed herein may be used in fabricating composite structures for any application, without limitation, and are not limited for use in composite aircraft structures such as the horizontal stabilizer114illustrated inFIG. 2.

Referring toFIG. 6, shown is a flowchart illustrating one or more operations that may be included in a method500of manufacturing a braided radius filler230. Any one of the steps, in whole or in part, of the method500may be performed using a manufacturing system300illustrated inFIG. 7. Step502of the method500may include providing a plurality of fibers308at a braiding station302of the manufacturing system300. The fibers308may be provided on braiding spools306mounted on a creel of a braiding machine304. The fibers308may be provided in any one of a variety of different forms. For example, in an embodiment, the fibers308may be provided as prepreg unidirectional slit tape which may be pre-impregnated with thermoplastic resin as indicated above. However, in other embodiments, the fibers308may be provided as dry fibers324that may be wetted in a resin bath330prior to braiding into a braided preform200or after braiding into a braided preform200. As described in greater detail below, for dry fibers324, the method may include heating the resin coating the dry fibers324, and at least partially curing the resin after shaping, compacting, and/or consolidating the braided preform200into the braided radius filler230prior to installing the braided radius filler230in a radius filler region158of a composite stiffener152.

FIG. 7illustrates an embodiment of the manufacturing system300for fabricating a braided radius filler230. The manufacturing system300may include any number of braiding machines304. Each braiding machine304may include a plurality of braiding spools306containing dry fibers324. The manufacturing system300may include a pulling mechanism382for continuously drawing the fibers308from the braiding spools306and assembling the braided fibers308via a braiding guide312to form a braided preform200in a biaxial braiding configuration. The pulling mechanism382may continuously pull the braided preform200through the different stages of the manufacturing system300. Although not shown, the braiding machine304may be configured to provide fibers308assembled as uni-axial fibers. The uni-axial fibers may be braided with cross-braided fibers to form a tri-axial braiding configuration of the braided preform200.

In some embodiments, the dry fibers324may be passed through a set of feed rollers328and into a resin bath330located downstream of the braiding station302for coating the dry fibers324with resin. In other embodiments, the fibers308may be braided over an inner core242(seeFIG. 19) as described below. In further embodiments, the resin bath330may be omitted and the fibers308may be provided as prepreg fibers308such as composite tape310pre-impregnated with resin. For example, the composite tape may be provided as prepreg unidirectional tape such as slit tape. The composite tape may be provided in any width such as one-eighth inch, one-quarter inch, or in any other width. The fibers in the composite tape may be formed of any material including graphite or carbon, glass, ceramic, aramid, and any other type of reinforcing fiber material as mentioned above. In any one of the examples disclosed herein, the fibers308may include a blend of reinforcing fibers and thermoplastic fibers. The reinforcing fibers may include high-strength fibers such as the above-mentioned carbon fibers, graphite fibers, aramid fibers, Kevlar® fibers, glass fibers, and other reinforcing and/or high-strength fiber material.

In some embodiments, the reinforcing fibers may be combined or blended with thermoplastic fibers such as by braiding the reinforcing fibers with the thermoplastic fibers as described herein. In some examples, the reinforcing fibers may be combined with the thermoplastic fibers to form a core around which reinforcing fibers and/or thermoplastic fibers may be braided. The thermoplastic fibers may be subjected to heating during the process of forming the radius filler. The heating of the thermoplastic fibers may at least partially melt the thermoplastic fibers and reduce the viscosity thereof allowing the melted thermoplastic material to infuse into the reinforcing fibers during the process of forming the radius filler. In a further embodiment, the fibers308may be substantially all thermoplastic fibers that may be braided together as disclosed herein. Heat may be applied to the substantially all thermoplastic fibers allowing for melting and fusing together of the thermoplastic fibers during the process of shaping and curing (e.g., solidifying) the braided radius filler230.

Step504of the method500ofFIG. 6may include braiding the plurality of fibers308into a braided preform200using one or more braiding machines304. Although the manufacturing system300inFIG. 7includes a single braiding machine304, any number of braiding machines304may be provided. In some embodiments, the braiding machine304may braid the fibers308into a braided cylinder202as shown inFIGS. 8-9. In other embodiments, the braiding machine304may be configured to braid the fibers308into a braided preform200having a triangular cross-sectional shape (not shown) with generally straight sides. In still other embodiments, the fibers308may be braided over an inner core242as shown inFIG. 16-19and described in greater detail below. The inner core242may have a cross-sectional size that is smaller that the braided radius filler230. The inner core242may be formed of the same material or a different material than the fibers308of the braided radius filler230. In some embodiments, the material of the inner core242may have a specific functionality. For example, the inner core242may be formed of material providing a relatively high electrical conductivity. In other embodiments, the inner core242may be formed of material providing acoustic damping capability, impact resistance, or the inner core242may be formed of material that may function as a conduit for communication signals or data signals.

Step506of the method500ofFIG. 6may include shaping and/or compacting the braided preform200into a braided radius filler230by passing the braided preform200through a compaction station338. In the compaction station338, the braided preform200may be shaped into a generally triangular cross-sectional shape having concave radius filler side surfaces232and a generally planar radius filler base surface234as shown inFIG. 12. In this regard, the compaction station338may include one or more forming dies for shaping the braided preform200. For example,FIG. 7illustrates the compaction station338including a series of roller sets for progressively shaping the braided cylinder202into a triangular shape with concave radius filler side surfaces232.

FIG. 10illustrates the initial shaping of the braided cylinder202into a rounded triangular cross-sectional shape by passing the braided cylinder202through a first roller die set340. The first roller die set340may include a first upper die342and a first lower die344, each of which may be rotatable about a respective rotational axis. The first upper die342may have a first die cavity346having a first cross-sectional shape348with a triangular configuration. In some embodiments, the first roller die set340may be heated to allow for heating and softening of the resin coating the fibers308of the braided preform200to facilitate the shaping of the braided preform200. In other embodiments, the manufacturing system300may include one or more ovens380or other heating mechanisms for further heating and softening the resin to facilitate the shaping of the braided preform200. Although the oven380is shown positioned between the first roller die set340and the second roller die set350, the oven380or other heating mechanism may be located at any position along the manufacturing system300. In some embodiments described below, resistive wiring may be braided into the braided preform200to allow for internally heating and softening the resin and the braided preform200, as described below.

InFIG. 7, the braided preform200may be passed through a second roller die set350having a second upper die352and a second lower die354.FIG. 11illustrates a cross-section of the second upper die352having a second die cavity356with a second cross-sectional shape358to shape the braided preform200closer toward the final shape of the braided radius filler230. The second roller die set350may optionally be heated to facilitate softening of the resin and shaping of the braided preform200.FIG. 12illustrates the third roller die set360which may also be heated and which may include a third upper die362and a third lower die364. The third upper die362may include a third cross-sectional shape368to form the concave radius filler side surfaces232and the generally planar radius filler base surface234of the braided radius filler230. Although the manufacturing system300ofFIG. 7illustrates a series of roller dies for shaping the braided preform200in a continuously moving process, the manufacturing system300may include one or more forming dies of any size, shape, and configuration, without limitation. For example, the manufacturing system300may include one or more upper and lower clamping dies (not shown), or one or more stationary dies (not shown) having internal die cavities for progressively shaping the fibers308into the final shape of the braided radius filler230. In some embodiments, one or more of the forming dies may include provisions for forming adhesive tips244on the radius filler corners236to fill in the extreme corners of the cross-sectional shape of the radius filler region158of a composite stiffener152. For example,FIG. 17illustrates adhesive tips244that may be formed on a braided radius filler230by injecting adhesive into the corners of the die cavity.

Step508of the method500ofFIG. 6may include cutting the braided radius filler230to a desired length. In an embodiment, a cutting station (not shown) may be included downstream of the pulling mechanism382. As indicated above, the pulling mechanism382may be configured to draw the fibers308from the braiding station302and through the compaction station338on a continuous basis. However, it is contemplated that for a manufacturing system300having vertically movable clamping dies (not shown) for compacting and/or shaping the braided radius filler230, the pulling mechanism382may be configured to operate on a pulse feed basis (e.g. start-and-stop basis) for pulling the fibers308through the various stages of the manufacturing system300. The cutting station may be configured to cut the braided radius filler230to a length substantially equivalent to the length of the radius filler region158into which the radius filler may be assembled. In some cases, the braided radius filler230may be cut into relatively long lengths such as up to 50 feet or more in length for a single braided radius filler230.

Referring toFIG. 13, shown is a further embodiment of a manufacturing system300having a core fabricating station320for fabricating an inner core242(FIG. 16) over which the braided radius filler230may be braided. The inner core242may be formed of fibers308drawn from one or more core spools322using a pulling mechanism382. The fibers308of the inner core242may be assembled at a core guide326. In some embodiments, the inner core242may be formed into a generally cylindrical shape although other shapes are contemplated for the inner core242. In some examples, the fibers308of the inner core242may be formed of the same material or a different material than the fibers308that are braided over the inner core242. In the embodiment shown, the fibers308may be provided as dry fibers324which may be passed through a set of feed rollers328and into a resin bath330for coating the dry fibers324with resin. However, the resin bath330may be omitted and the fibers308for the inner core242may be provided as prepreg fibers308such as prepreg composite tape310. Fibers308may be braided over the inner core242to form a braided preform200such as a braided cylinder202(e.g.,FIG. 8). However, the inner core242may be provided in a non-cylindrical shape such as a generally triangular cross-sectional shape or other shape resulting in a correspondingly shaped braided preform (not shown).

InFIG. 13, the prepreg composite tape310of the braided preform200may be heated such as by using one or more heated roller dies or an optional oven380to soften the resin and allow for intermingling of the resin in the strands of composite tape that make up the braided preform200. The braided radius filler230may be allowed to cool and solidify after exiting the last roller die set of the compaction station338. For thermosetting prepreg tape, heat may provided for curing the resin after the braided preform200has been formed into the desired shape by the forming dies. In an optional embodiment, the fibers308of the braiding machine304may be provided as dry fibers324that may be passed through a resin bath330for wetting the fibers similar to the wetting of the fibers at the core fabricating station320.

FIG. 14is an exploded side view of a final forming station460for consolidating and/or curing the braided radius filler230after the braided preform200is cut to a desired length upon exiting the compacting station338shown inFIG. 13. The final forming station460may include a forming die set462having an upper forming die464and a lower forming die466. The forming die set462may be formed in a length that is complementary to the length of the braided preform200. The upper forming die464may be vertically movable to allow for installing the braided radius filler230in the lower forming die466. The method of manufacturing the radius filler may include mounting the braided radius filler230in the final forming die set462as shown inFIG. 16. The braided radius filler230may optionally include an inner core242. However, the braided radius filler230may be formed without any inner core242.

InFIG. 16, the lower forming die466may include a cavity having a contour that approximates the contour (e.g., seeFIG. 22) of the radius filler region158of the laminate assembly176into which the final radius filler may be installed (FIG. 22) as described below. As shown inFIGS. 15 and 17, the upper forming die464may be mated to the lower forming die466with the braided radius filler230captured there-between. In some embodiments, the braided radius filler230may be provided in a size that results in an intentional overfill of the braided radius filler230within the forming die cavity such that after consolidation, the braided radius filler230has a final volume that substantially matches the volume of the radius filler region158. The method of manufacturing the radius filler may include applying heat and/or pressure386(FIG. 15) to the braided radius filler230in the final forming die set462, and contouring the opposing radius filler side surfaces232into a final shape that is complementary to a contour (e.g.,FIG. 22) of the radius filler region158of the laminate assembly176into which the radius filler may be installed.

InFIGS. 16-17, the forming die set462may optionally include one or more adhesive fill ports468for injecting adhesive into the cavity containing the braided radius filler230to form adhesive tips244at the radius filler corners236. The adhesive tips244may advantageously fill the void that may otherwise occur due to the inability of the braided fibers308to fit within the relatively narrow thickness at the extreme ends or tips of the radius filler corners236. In this regard, the method of manufacturing the braided radius filler230may include mounting the braided radius filler230in the final forming die set462as shown inFIG. 16, and injecting adhesive into the final forming die set462as shown inFIG. 17to form an adhesive tip244on each radius filler corner236as shown inFIG. 18. The adhesive tips244may be allowed to cool and solidify with the resin in the composite plies after which the braided radius filler230may be removed from the final forming die set462.

Referring toFIGS. 19-20, shown is an embodiment of the braided preform200having localized changes204in the cross-sectional area or size of the braided preform200. The localized changes204in the cross-sectional area or size of the braided preform200may facilitate the forming of localized changes238in the cross-sectional area or size of the braided radius filler230as shown inFIG. 21. In this regard, the localized changes238may be formed in the braided radius filler230to accommodate a non-uniform contour in the radius filler region158of the composite structure106. For example, one or both of the stiffener laminates162may include ply additions184or ply drops182along the length of the stiffener laminates162. Ply additions184may be included in the stiffener laminates162to provide localized increase in the strength of the stiffener such as to accommodate increased loads at that location or to accommodate mounting brackets or other hardware mounted to the stiffener at that location.

Referring briefly toFIG. 13, localized changes238in the cross-sectional area of the braided radius filler230may be formed by adjusting the tension force or pulling force384on the braided preform200as the fibers308are drawn from the braiding spools306and braided into the braiding guide312. In this regard, the method of manufacturing the braided radius filler230may include varying the pulling force384on the braided preform200for different time intervals when braiding the braided preform200. In response to varying the pulling force384, the bias angle of the fibers308may be varied. For example, by increasing the pulling force384on the fibers308drawn through the braiding guide312, the bias angle of the fibers308relative to the longitudinal axis206may increase from a relatively large first bias angle208of the braided preform200to a smaller second bias angle210as shown inFIG. 20. A larger bias angle may result in a larger cross-sectional size of the braided radius filler230. A smaller bias angle may result in a smaller cross-sectional size of the braided radius filler230. The bias angle of the fibers308relative to the longitudinal axis206may be varied in any range (e.g., from 10 degrees to 80 degrees). The process of varying the bias angle of the fibers308may result in varying the cross-sectional size of the braided preform200as shown inFIGS. 19-20. In this regard, increasing the pulling force384on the braided preform200may decrease the cross-sectional area of the braided preform200. Conversely, decreasing the pulling force384on the braided preform200may increase the cross-sectional area of the braided preform200.

The length of the localized change204in cross-sectional size and the location along the length of the braided preform200may be controlled by controlling the pulling mechanism382to adjust the pulling force384on the braided preform200as the braided preform200is pulled through the braiding guide312. The localized changes204in the cross-sectional size of the braided preform200may be formed complementary to the localized changes in the contour along the length of the radius filler region158(e.g., seeFIG. 22). In this regard, the cavity in the lower forming die466(e.g., seeFIG. 16) may be contoured along the length in a manner substantially duplicating the contour along the length of the radius filler region158of the laminate assembly176(FIG. 22). In some embodiments, the bias angle may be varied in order to achieve a desired stiffness or load-carrying capability of the braided radius filler230.

InFIG. 23, shown is an exploded illustration of an adhesive-wrapped braided radius filler230prior to assembly of the braided radius filler230with the stiffener laminates162and the base laminate172. In some examples, an adhesive layer240may be applied to the radius filler side surfaces232and the radius filler base surface234prior to installing the adhesive-wrapped braided radius filler230in the radius filler region158. In other examples, the adhesive layer240may be applied to the surfaces of the opposing stiffener outer radii154prior to installing the braided radius filler230in the radius filler region158, as described in greater detail below and illustrated inFIG. 39. The radius filler base surface234may be over-wrapped with the adhesive layer240as shown inFIG. 40prior to installing the base laminate172over the braided radius filler230. Advantageously, the adhesive-wrapped braided radius filler230may improve the toughness, durability, and crack-resistance at the boundary of the braided radius filler230with the stiffener laminates162and the base laminate172. As described in greater detail below, the stiffener laminates162may also be provided with a relatively large radius to improve the stress distribution at the boundary between the radius filler side surfaces232and the stiffener outer radii154and thereby improve the pull-off strength of the stiffener laminates162relative to the base laminate172. The adhesive-wrapped braided radius filler230may be manufactured using any one of the manufacturing systems300and methods described herein.

FIG. 24illustrates an embodiment of a manufacturing system300using a mandrel forming station420located downstream of a braiding station302to consolidate and/or cure the braided radius filler230. The manufacturing system300may include a braiding station302having one or more braiding machines304similar to that which are described above. The pulling mechanism382may pull the braided preform200through the braiding guides312. The mandrel forming station420may include a mandrel forming system422to form the braided preform200into the desired final shape of the braided radius filler230. The manufacturing system300may be operated in a pulse flow manner wherein successive lengths of braided preform200may be shaped, consolidated, and/or cured using the mandrel forming system422in combination with a press system400.

Referring toFIG. 25, the mandrel forming system422may include a mandrel die424and a mandrel forming base426which may be mated to one another. The mandrel die424may include a mandrel die cavity428that may be sized and configured to receive the braided preform200and provide additional space between the mandrel die cavity428and the surfaces of the braided preform200. In the embodiment shown, the braided preform200may be braided into a triangular cross-sectional shape that may approximate the final shape of the braided radius filler230although the braided preform200may be braided into other cross-sectional shapes. Although not shown, the braided preform200may optionally include an inner core242as described above. In a further embodiment, the braided preform200may include one or more internal heater wires246such as electrical resistance wires. The heater wires246may be spooled onto one or more of the braiding spools306of one or more braiding machines304causing the heater wires246to be internally braided into the braided preform200.

AlthoughFIG. 25illustrates three (3) heater wires246internally braided into the braided preform200, any number of heater wires246may be included. The heater wires246may be arranged in any manner within the braided preform200, and are not limited to the triangularly-shaped arrangement of the heater wires246shown in the figures. For example, the heater wires246may be braided such that some heater wires246are positioned adjacent to one or more surface of the braided preform200, or the heater wires246may be positioned internally and on or near one or more surfaces of the braided preform200. In an embodiment, the heater wires246may be resistively heated by passing electrical current through the heater wires246. The heater wires246may be used to heat388and soften the resin coating the prepreg fibers308of the braided preform200to allow for consolidation, curing, and/or solidification of the braided radius filler230. The heater wires246may soften the resin prior to and/or during the consolidation of the braided radius filler230contained within the mandrel forming system422. The heater wires246may also assist in heating the expandable ceramic matrix432(e.g., seeFIG. 26) causing expansion thereof when the mandrel forming system422is clamped within the press system400, as described in greater detail below.

FIG. 26illustrates the injection of expandable soluble ceramic matrix432into one or more fill ports430in the mandrel die424of the mandrel forming system422. The ceramic matrix432may be provided as a slurry or in a semi-liquid composition. The injected ceramic matrix432may fill the volume of space between the braided radius filler side surfaces232and the walls of the mandrel die cavity428. The ceramic matrix432may be continuously introduced into one of the ports430until excess ceramic matrix432starts flowing out of an another port.FIG. 27illustrates the ceramic matrix432in a hardened state after which the ports430may be closed off with plugs434.

FIG. 28illustrates the mandrel forming system422clamped over the braided radius filler230and moved into the press system400. The mandrel die424and the mandrel forming base426may be clamped within the press system400between the movable upper press402and the press base404as shown inFIG. 29. The press system400may include an actuator406such as a mechanical or hydraulic actuator for vertically moving the movable upper press402relative to the press base404between an open position (FIGS. 24 and 30) and a closed position (FIG. 28-29). The clamping of the mandrel forming system422within the press system400(FIG. 29) may prevent relative movement of the mandrel die424during expansion of the ceramic matrix432as a result of heating thereof. Heat may be applied to the mandrel forming system422in a conventional manner such as by placing the press system400in an autoclave or an oven380. Alternatively, the mandrel forming system422may be integrally heated to facilitate heating of the expandable ceramic matrix432and cause expansion thereof and consolidation of the braided preform200while the mandrel forming system422is clamped between the movable upper press402and the press base404. For example, in an embodiment not shown, the movable upper press402and the press base404may respectively include an upper susceptor face sheet (not shown) and/or a lower susceptor face sheet (not shown) that may be respectively positionable in contact with the mandrel die424and the mandrel forming base426. The upper and/or lower susceptor face sheets may be inductively heated in response to alternating current that may be passed through one or more induction coils (not shown) extending through the movable upper press402and/or the press base404similar to the arrangement disclosed in U.S. application Ser. No. 13/305,297 entitled SYSTEM AND METHOD OF ADJUSTING THE EQUILIBRIUM TEMPERATURE OF AN INDUCTIVELY-HEATED SUSCEPTOR filed on Nov. 28, 2011, the entire contents of which is incorporated by reference herein.

As disclosed in Ser. No. 13/305,297, the upper and/or lower susceptor face sheet may be formed of an electrically conductive ferromagnetic alloy having a Curie temperature that is dependent on the composition of the ferromagnetic alloy. In this regard, the ferromagnetic alloy from which the upper and/or lower susceptor face sheets are formed may be selected based on the desired temperature to which the expandable ceramic matrix432may be heated. For example, the ferromagnetic alloy composition may be selected having a Curie temperature that results in an equilibrium temperature of the upper and/or lower susceptor face sheet that approximately corresponds to a temperature at which the ceramic matrix432expands in a manner causing consolidation of the braided radius filler230within the mandrel forming system422. In a further embodiment, the ferromagnetic alloy composition of the upper and lower susceptor face sheets may be selected based on a processing temperature of the resin (e.g., the glass transition temperature or melt temperature of a thermoplastic resin; the curing temperature of a thermosetting resin, etc.) contained in the braided radius filler230captured within the mandrel die cavity428. Advantageously, by using an inductive-susceptor system with upper and/or lower susceptor face sheets, the time associated with heating the mandrel forming system422and the ceramic matrix432and/or resin contained in the prepreg fibers308may be significantly reduced relative to the significant time required to heat the mandrel forming system422using conventional heating techniques such as an autoclave or an oven due to the large thermal mass associated with autoclaves and ovens.

FIGS. 29-31illustrate a method of manufacturing a braided preform200by mounting the braided preform200in the mandrel forming system422, and injecting ceramic matrix432into the mandrel die cavity428containing the braided preform200. The method may include heating the resin of the fibers308to a temperature causing softening of the resin. In addition, the method may include heating388(FIG. 29) the ceramic matrix432in a manner causing expansion thereof while the mandrel forming system422is clamped within the press system400. The method may further include consolidating the braided radius filler230in response to expansion of the ceramic matrix432, and allowing the resin to cool and solidify after which the braided radius filler230may be inspected in an inspection station450located downstream of the press system400. The inspection may be configured to inspect the consolidated or compacted radius filler for defects such as voids, porosity, or other defects. In some embodiments, the inspection station may include nondestructive inspection equipment such as through-transmission ultrasonic inspection equipment.

InFIG. 31, the mandrel forming system422may be re-used after consolidating the braided radius filler230by separating the mandrel die424from the mandrel forming base426, removing the braided radius filler230, and applying a solvent to the hardened matrix436in order to remove the hardened matrix436. For example water may be sprayed onto the hardened matrix436to solubilize the hardened matrix436and allow for removal of the hardened matrix436from the mandrel die cavity428so that the mandrel forming system422may be used on another length of the braided radius filler230.

In an embodiment (e.g. seeFIG. 32), the mandrel forming station420may be located offline and/or physically separate from the braiding station302and inspection station450. In this regard, the mandrel forming station420may be positioned at a location separate from the braiding station302and may utilize a dummy radius filler438to form the ceramic matrix432into a soluble mandrel which may then be positioned over a length of the braided radius filler230and clamped within the press system400.FIG. 33illustrates a cross-section of the mandrel forming system422which may be mounted on a movable table or other support. The dummy radius filler438may have a shape or contour that may match the shape or contour of the radius filler region158into which the radius filler may be installed as shown inFIG. 22and described above.

FIG. 34illustrates the injection of ceramic matrix432into the ports430to fill the space between the side surfaces of the dummy radius filler438and the surfaces of the mandrel die cavity428.FIG. 35illustrates the ceramic matrix432hardening such as at room temperature. After the ceramic matrix432hardens, the ports430may be closed off with plugs434similar to that described above and the dummy radius filler438may be removed from the mandrel forming system422. The mandrel forming system422may then be mounted in the press system400.FIG. 36illustrates the mandrel die424separated from the mandrel forming base426to allow for clamping the mandrel forming system422over a length of the braided radius filler230as shown inFIG. 29. The process of heating388the hardened ceramic matrix432to cause expansion thereof and consolidation of the braided radius filler230(FIG. 29) may be performed as described above. Following consolidation of the braided radius filler230, the mandrel die424may be separated from the mandrel forming base426and the hardened matrix436may be solublized using a solvent (e.g., water) and removed from the mandrel die424as shown inFIG. 31to allow for re-use of the mandrel forming system422on another length of the braided preform200.

FIG. 37is a flowchart illustrating one or more operations that may be included in a method600of installing a braided radius filler230in a radius filler region158of a composite structure106. The method600is schematically illustrated inFIGS. 38-42. The method600may include applying an adhesive layer240such as an adhesive sheet onto the surfaces of the opposing stiffener outer radii154. The stiffener outer radii154are part of a pair of back-to-back stiffener laminates162. The stiffener laminates162may be provided as back-to-back C-channels164, L-sections, or other shapes that result in a radius filler region158. As shown inFIG. 39, the adhesive layer240may extend from the tangent point156of a horizontal portion of the flange168and may be applied inside the radius filler region158to the common tangent point156between the webs166. The adhesive layer240may then be applied over the opposing stiffener outer radius154with an excess portion of the adhesive layer240extending beyond the tangent point156. Step602of the method600may include mounting the braided radius filler230onto the adhesive layer240as shown inFIG. 40such that radius filler side surfaces232are in contact with the adhesive layer240.FIG. 40additionally illustrates the over-wrapping of the radius filler base surface234with the adhesive layer240.

Step604of the method600ofFIG. 37may include assembling the base laminate172with the stiffener laminates162to encapsulate the braided radius filler230within the radius filler region158and form a laminate assembly176as shown inFIG. 41. The base laminate172may be mounted on the flanges168of the stiffener laminates162such that the base laminate faying surface174is in contact with the flange faying surfaces170. Ideally, the adhesive layer240and the braided radius filler230are sized and shaped to completely fill the radius filler region158defined by the stiffener outer radii154and the lower surface of the base laminate172. Step606of the method600may include curing the laminate assembly176(FIG. 42) by applying heat and/or pressure to form a composite structure106. For example, the laminate assembly176may be vacuum-bagged and positioned within an autoclave to co-cure and/or co-bond the stiffener laminates162with the base laminate172.

Referring toFIG. 43, shown is a flowchart having one or more operations that may be included in a method700of manufacturing a sleeved radius filler260. Step702of the method may include providing a radius filler core266as shown inFIG. 44. In some embodiments, the radius filler core266may be provided with a size, shape, and/or configuration that substantially matches the radius filler region158of the composite laminate with which the sleeved radius filler260may be assembled (e.g.,FIGS. 3 and 22). In some examples, the radius filler core266may be a non-braided core and may be formed of fibers308such as thermoplastic or thermosetting prepreg unidirectional tape which may be stacked or layered. The fibers308of the radius filler core266may be similar to the fibers308of the sleeve.

In some examples, the radius filler core266may be comprised of chopped fibers or short fibers embedded within a thermoplastic resin matrix or thermosetting resin matrix. Advantageously, chopped fibers or short fibers may be oriented in a variety of directions which may minimize the coefficient of thermal expansion of the radius filler in a transverse direction (e.g., normal to the long axis) and thereby reduce thermal shrinkage in the transverse direction during cool-down from curing or solidifying of the radius filler. In this regard, a radius filler core266formed of chopped fibers or short fibers may have reduced shrinkage relative to the amount of shrinkage that may occur in a conventional radius filler having axial fibers extending along the length of the conventional radius filler. Advantageously, reduced shrinkage in the transverse direction may result in reduced interlaminar stresses at the interface between the radius filler side surfaces232and the stiffener laminates162and may thereby reduce the propensity for cracking. In some embodiments, a triangular cross-sectional shape radius filler core266may be formed of short fibers or chopped fibers by extruding, casting, or rolling the radius filler core266into the desired shape. In other embodiments, the radius filler core266may be formed of foam, metallic or non-metallic tubing or rod, or other material. Metallic material of a radius filler core266may include titanium, aluminum, steel, or other alloys. Non-metallic materials of a radius filler core266may include ceramic material and polymeric material.

In some embodiments, the radius filler core266may be formed of material having a specific functionality in addition to the radius filler core266assisting in transferring loads between the base laminate172and the stiffener laminates162. For example, the radius filler core266may be formed of conductive material for conducting electricity such as for dissipating static charge buildup within a composite structure106. In other embodiments, the radius filler core266may be formed of material that functions as a conduit for communication or data transmission. In still other embodiments, the radius filler core266may be selected of material that provides acoustic damping to a composite structure106as indicated above.

Step704of the method700ofFIG. 43may include fabricating a sleeve for the sleeved radius filler260. In some embodiments, the sleeve may be fabricated as a hollow braided tube264having a cylindrical shape as shown inFIG. 45. In other embodiments, the sleeve may be braided in a hollow triangular shape (not shown) that may approximate the shape of the radius filler core266. As indicated above, the fibers308of a braided sleeve262may be formed of the same material as the fibers308of the radius filler core266.

Step706of the method700ofFIG. 43may include covering the radius filler core266with a sleeve to form a sleeved radius filler260as shown inFIG. 46. For example, some embodiments may include braiding fibers308over the radius filler core266to form a braided sleeve262covering the radius filler core266. The assembled radius filler and sleeve may then be consolidated and/or cured to form the sleeved radius filler260. Other embodiments may include braiding fibers308over a dummy radius filler438. For example, the dummy radius filler438may be formed of any suitable material including, but not limited to, a foam core, an inflatable core, a soluble core, or an otherwise removable core. After the sleeve is formed, the method may include removing the dummy radius filler438from the braided sleeve262, and then pulling the braided sleeve262over the radius filler core266. The sleeved radius filler260may then be installed in a radius filler region158to form a laminate assembly176similar to that which is illustrated inFIG. 47.

In some embodiments, the method may include fabricating the sleeve as a legged sleeve270as shown inFIG. 48. The legged sleeve270may have at least one leg274extending outwardly from a main sleeve portion272. The leg274of the legged sleeve270may extend along a length of the main sleeve portion272. The legged sleeve270may be configured such that one or more legs274intersects the main sleeve portion272at one or more of the radius filler corners236of the radius filler. In some embodiments, the legged sleeve270may be formed in a generally triangular cross-sectional shape similar to the shape of the radius filler core266.

FIG. 48illustrates a sleeve with three legs274extending outwardly from each one of three radius filler corners236. The legged sleeve270may be configured such that at least one of the legs274has a leg width276that is at least as wide as the radius filler base surface234and/or a radius filler side surface232. However, the legs274may be provided in any width276, without limitation. Furthermore, the legged sleeve270may be provided in an asymmetric configuration wherein one of the legs274may be less wide than one or both of the remaining legs274. In some embodiments, the method of fabricating the sleeve may include braiding fibers308into a legged sleeve270wherein the legs274and the main sleeve portion272are braided as a unitary structure288(not shown). In this regard, the legged sleeve270may be fabricated such that the juncture284of each leg274with the main sleeve portion272is seamless.

In other embodiments, the method may include assembling the sleeve from woven material280to form a woven sleeve278. For example,FIGS. 48-50illustrate a legged sleeve270formed of woven material280. The method of fabricating the legged sleeve270may include using through-thickness stitching282to connect at least one leg274to the main sleeve portion272along a length of the sleeve. The through-thickness stitching282may be installed along the radius filler corner236of the main sleeve portion272as shown inFIG. 48. In this regard,FIG. 48illustrates an assembled legged sleeve270covering a radius filler core266and showing the through-thickness stitching282connecting each leg274to the main sleeve portion272at each one of the radius filler corners236. Advantageously, the through-thickness stitching282at the radius filler corners236may reduce or prevent delamination at the radius filler corners236of an assembled composite structure106.

FIG. 51illustrates a legged sleeve270braided around a dummy radius filler438having a cylindrical cross-sectional shape. The braided sleeve262includes a main sleeve portion272and three legs274extending outwardly from the main sleeve portion272and integrally formed with the main sleeve portion272. In this regard, the braided sleeve262is formed as unitary structure288. The legs274are joined to the main sleeve portion272at a location such that when the sleeve is pulled over the radius filler core266, the juncture284of each leg274with the main sleeve portion272is located at one of the corners of the radius filler core266as shown inFIG. 53.

FIG. 52illustrates a legged sleeve270braided over a dummy radius filler438having a triangular cross-sectional shape. The dummy radius filler438is sized and configured such that the juncture284of the legs274with the main sleeve portion272coincides with the location of the radius filler corners236as shown inFIG. 53.FIG. 53illustrates a sleeved radius filler having a legged sleeve installed over a radius filler core266. The legged sleeve270may be formed as a braided sleeve262.

FIG. 54is an exploded view of a sleeved radius filler260assembled with a pair of stiffener laminates162and a base laminate172. Each leg274of the sleeved radius filler260may be joined to the main sleeve portion272at a nodal joint286located at a corner of the radius filler. In an embodiment, each nodal joint286may comprise through-thickness stitching282or other joining mechanism for joining the leg274to the main sleeve portion272.

FIG. 55illustrates the assembly of the stiffener laminates162with the base laminate172capturing the sleeved radius filler260therebetween. The through-thickness stitching282in the sleeved radius filler260is coincident with the tangent points156of the flanges168on each stiffener laminate162. Ideally, the through-thickness stitching282has minimal thickness in order to allow the flange faying surfaces170to be placed in abutting contact with the faying surface174of the base laminate172for bonding the laminates together during co-curing or co-consolidation of the laminates.

FIG. 56illustrates a further embodiment of a composite structure106wherein the vertical leg274of a lower radius filler is common to the vertical leg274of an upper radius filler. The interconnection of the lower and upper radius filler may improve the pulloff load178capability of the composite stiffener152. In addition,FIG. 56illustrates the horizontal legs274of the lower radius filler being longer than the horizontal legs274of the upper radius filler. The increased length of the horizontal legs274of the lower radius filler may provide improved pulloff load178capability of the lower flanges168with the lower base laminate172. It should be noted that the legged radius filler may not necessarily be provided with symmetrical legs274. For example, a leg274on one side of a radius filler may be longer than a leg274on an opposite side of the radius filler.

Advantageously, the radius filler having a legged sleeve270may reduce the propensity for delamination or disbonding at the interface between the radius filler and the laminate plies. In this regard, the radius filler with legged sleeve270may act as a truss interconnecting the laminates and may thereby reduce stress in the radius filler region158at the radius filler corners236. In addition, the radius filler with legged sleeve270may spread out or distribute the load being transferred between the webs166and the flanges168of the stiffener laminates162. In this regard, the legged sleeve270may prevent localized concentrations of stress in the radius filler region158. In addition, the legged sleeve270may accommodate thermal expansion mismatch between the radius filler region158and the adjacent laminates such as during shrinkage after cool-down from curing or consolidating of the composite laminates that make up the composite structure106.

Additional modifications and improvements of the present disclosure may be apparent to those of ordinary skill in the art. Thus, the particular combination of parts described and illustrated herein is intended to represent only certain embodiments of the present disclosure and is not intended to serve as limitations of alternative embodiments or devices within the spirit and scope of the disclosure.