Stringer assemblies and methods of forming thereof

Described herein are stringer assemblies, such as blade stringers, and methods of forming thereof. A stringer assembly comprises a first fabric composite stiffener, a second fabric composite stiffener, and an intermediate tape composite stiffener, disposed between and connected to each of the first and second stiffeners. Using three separate components allows forming sharp bends, eliminating voids and gap fillers, and adding new features, such as edge reinforcements. Each of the first and second fabric composite stiffeners comprises a web portion, a flange portion, and a curved portion, positioned between the web and flange portions. The web portions surround and are attached to the intermediate tape composite stiffener and, in some examples, include tapered-out edges for additional rigidity. The flange portions are attached to the composite base. The curved portions conform to the flared-out edges of the intermediate tape composite stiffener, which extends and connects to the composite base.

BACKGROUND

Modern aircraft designs use various components, such as stringers, to resist bending, torsional, shear, and direct loads. Stringers are typically formed from lightweight composites, such as tapes with fibers embedded into resin matrixes. Blade stringers represent a specific class of stringers, which is common in aircraft and other applications. However, manufacturing of all-tape blade stringers has been challenging. One particular challenge involves forming tape plies into blade stringers, particularly around sharp bends. Conventional methods for forming blade stringers involve complex build-up procedures using numerous parts including, for instance, gap fillers, There is a need for stringer assemblies and associated method for forming the stringer assemblies that involve less complex build-up procedures using fewer parts.

SUMMARY

Described herein are stringer assemblies, such as blade stringers, and methods of forming thereof. A stringer assembly comprises a first fabric composite stiffener, a second fabric composite stiffener, and an intermediate tape composite stiffener, disposed between and connected to each of the first and second stiffeners. In some examples, a first fabric composite stiffener is formed entirely from a composite fabric and may be referred to as a first all-fabric composite stiffener. Similarly, in some examples, a second fabric composite stiffener is formed entirely from a composite fabric and may be referred to as a second all-fabric composite stiffener. Finally, in some examples, an intermediate tape composite stiffener is formed entirely from a composite tape and may be referred to as an intermediate all-tape composite stiffener.

Composite tapes have much smaller widths than composite fabrics, e.g., a composite tape is typically at least about two times narrower, three times narrower, or even four times narrower than a composite fabric. In some examples, the width of the tape is up to about 400 millimeters or, more specifically, up to about 300 millimeters, which is typically limited by the tape application techniques. On the other hand, the width of composite fabrics is often as much as 760 millimeters or 152.0 millimeters, A composite part formed from a composite tape typically requires less surface treatment than that formed from a composite fabric. However, a composite fabric requires less material handling and tends to be easier to form on contours and corners, making it more suitable for the first and second composite stiffeners, described above. In general, composite fabrics have better drapability, allowing the fabrics to follow contours surfaces. The fabric integrity is maintained by the interlocking of the fibers. This produces undulation in the final form at the fiber scale, which improves drapability and damage resistance. On the other hand, composite tapes (e.g., unidirectional tapes) are straight and uncrimped. This results in the highest possible fiber properties in the intermediate tape composite stiffener. Crimp is another distinguishing factor such that different crimp levels influence fiber volume fraction, thickness of fabric, and/or mechanical performance of fabrics. High crimp leads to reduced tensile and compressive properties, increased shear modulus in the resulting composite, and fewer regions for localized delamination between individual yarns. As a result, composite tapes have higher axial stiffness composite fabrics, but tend to be less suitable for outer layers. Furthermore, a composite fabric tends to be more resistance to surface breakouts and delamination. Finally, composite tapes and composite fabrics differ in fiber arrangements. For example, fibers of composite fabrics are arrangement in a variety of forms, such as a plain weave, a harness satin, braided, and the like.

Using three separate components allows forming sharp bends, eliminating voids and gap fillers, and adding new features, such as edge reinforcements. Each of the first and second fabric composite stiffeners comprises a web portion, a flange portion, and a curved portion, positioned between the web and flange portions. The web portions surround and are attached to the intermediate tape composite stiffener and, in some examples, include tapered-out edges for additional rigidity. The flange portions are attached to the composite base. The curved portions conform to the flared-out edges of the intermediate tape composite stiffener, which extends and connects to the composite base.

In some examples, a stringer assembly comprises a first fabric composite stiffener and second fabric composite stiffener, each comprising a web portion, a flange portion, and a curved portion, disposed between the web portion and the flange portion. The web portion comprises a tapered-out edge. The stringer assembly further comprises an intermediate tape composite stiffener, disposed between the first fabric composite stiffener and the second fabric composite stiffener and comprising flared-out edges. Each flared-out edge contacts and conforms to a corresponding one of the curved portions of the first fabric composite stiffener and the second fabric composite stiffener.

In some examples, a method of forming a stringer assembly comprises joining a first end of an intermediate tape composite stiffener to a composite base. The first end comprises flared-out edges. The method further comprises joining a first fabric composite stiffener and a second fabric composite stiffener to the composite base and to the intermediate tape composite stiffener. Each of the first fabric composite stiffener and the second fabric composite stiffener comprises a web portion, a flange portion, and a curved portion, the curved portion disposed between the web portion and the flange portion. The curved portion conforms to a corresponding one of the flared-out edges of the intermediate tape composite stiffener.

In some examples, a method for forming a stringer assembly comprises forming a first fabric composite stiffener and a second fabric composite stiffener. The method further comprises joining a first end of an intermediate tape composite stiffener to a composite base. The first end comprises flared-out edges. The method comprises bending the first fabric composite stiffener and the second fabric composite stiffener to conform to the composite base and to the intermediate tape composite stiffener. Each of the first fabric composite stiffener and the second fabric composite stiffener comprises a web portion, a flange portion, and a curved portion, disposed between the web portion and the flange portion. After bending, the curved portion of each of the first fabric composite stiffener and the second fabric composite stiffener conforms to a corresponding one of the flared-out edges of the intermediate tape composite stiffener.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the presented concepts. In some examples, the presented concepts are practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail so as to not unnecessarily obscure the described concepts. While some concepts will be described in conjunction with the specific examples, it will be understood that these examples are not intended to be limiting.

Introduction

Stringer assemblies, described herein, enable new stringer designs and features, such as sharper bends and reinforcement features. Furthermore, these stringer assemblies not only simplify manufacturing by eliminating complex operations and components, such as gap fillers, which are also known as “noodles”, but these stringer assemblies also eliminate the persistent and consequential wrinkles and noodle cracking. These gap fillers have been a barrier for a broader application of composite structures with complex shapes due to manufacturing complexities and high costs. Overall, in comparison to conventional stringers and methods of fabricating thereof, these novel stringer assemblies provide less complex build-up procedures using fewer parts. Furthermore, these novel stringer assemblies allow implementation of various automation aspects during fabrication. These novel stringer assemblies also provide enhanced bending stiffness without a need for large structure heights. This feature is particularly helpful for small aircrafts, e.g., aircrafts with a small wing depth, which is defined as a distance between the centroid of the upper and lower wing panels. The minimal size of composite structures and, in particular, of composite stringers has been a limiting factor for new applications.

A novel stringer assembly comprises a first fabric composite stiffener, a second fabric composite stiffener, and an intermediate tape composite stiffener, disposed between the first fabric composite stiffener and the second fabric composite stiffener. More specifically, the intermediate tape composite stiffener directly interfaces and is bonded to portions of the first fabric composite stiffener and the second fabric composite stiffener, which are referred to as web portions. For example, the first fabric composite stiffener, the second fabric composite stiffener, and the intermediate tape composite stiffener are be first arranged into a sub-assembly (e.g., over a composite base). In this arrangement, the first fabric composite stiffener and the second fabric composite stiffener conform to the intermediate tape composite stiffener and to the composite base. This arrangement is then cured.

Having three separate components in a stringer assembly allows achieving sharp bends. Specifically, the thickness of each of the first and second fabric composite stiffeners is selected specifically based on the desired bend radius. In some examples, the intermediate tape composite stiffener is thicker than each of the first and second fabric composite stiffeners. However, unlike the first and second fabric composite stiffeners, the intermediate tape composite stiffener is not bent. Specifically, each of the first and second fabric composite stiffeners comprises a web portion, a flange portion, and a curved portion. The curved portion is positioned between the web and flange portions. The web portions surround and are attached to the intermediate tape composite stiffener, thereby increasing the overall thickness of the stringer assembly. The flange portions are attached to the composite base and extend away from the intermediate tape composite stiffener. Specifically, the flange portions provide a greater contact area between a sub-assembly of the first and second fabric composite stiffeners, the second fabric composite stiffener, and the intermediate tape composite stiffener and the composite base to which this sub-assembly is connected. The curved portions of the first and second fabric composite stiffeners conform to the flared-out edges of the intermediate tape composite stiffener, thereby preventing any gaps within the sub-assembly and the overall assembly, e.g., between the sub-assembly and the composite base.

Examples of Stringer Assemblies

Referring toFIG.1A, in some examples, stringer assembly100comprises first fabric composite stiffener110, second fabric composite stiffener120, and intermediate tape composite stiffener130. Intermediate tape composite stiffener130is positioned between first fabric composite stiffener110and second fabric composite stiffener120. More specifically, intermediate tape composite stiffener130is attached/bonded to each of first fabric composite stiffener110and second fabric composite stiffener120. A combination of first fabric composite stiffener110, second fabric composite stiffener120, and intermediate tape composite stiffener130may be also referred to a sub-assembly.

As show inFIG.1A, each of first fabric composite stiffener110, second fabric composite stiffener120, and intermediate tape composite stiffener130extends along the Z-axis, which may be referred to as a principal axis of stringer assembly100. WhileFIG.1Aillustrates each of the sub-assemblies (e.g., first fabric composite stiffener110, second fabric composite stiffener120, and intermediate tape composite stiffener130) is straight along the Z-axis, other examples are also within the scope. In some examples, the sub-assembly has one or more bends about the X-axis and/or one or more bends about the Y-axis. These bends are formed, e.g., prior to curing the sub-assembly.

Referring toFIG.1A, in some examples, stringer assembly100comprises composite base140. Each of first fabric composite stiffener110, second fabric composite stiffener120, and intermediate tape composite stiffener130is connected to composite base140. More specifically, each of first fabric composite stiffener110, second fabric composite stiffener120, and intermediate tape composite stiffener130independently interfaces and is directly connected to composite base140. For example, stringer assembly100comprises adhesive150, which is disposed between and adheres to composite base140and each of first fabric composite stiffener110, second fabric composite stiffener120, and intermediate tape composite stiffener130. In some examples, composite base140is an interleaved skin, Specifically, interleaving is defined as interspersing a limited number of zero degree fibers to a base skin. The interleaving skin under provides various structural and manufacturing benefits, such as (a) increasing the skin panel axial stiffness while keeping the centroid of the skin-stringer close to the skin minimizing eccentricity induced residual loads, (b) limiting crack propagating in a chord-wise direction within the skin.

Referring toFIG.1B, in some examples, each of first fabric composite stiffener110and second fabric composite stiffener120comprises web portion112, flange portion114, and curved portion116. Curved portion116is disposed between web portion112and flange portion114and monolithic with web portion112and flange portion114. Within examples, web portion112, flange portion114, and curved portion116of both first fabric composite stiffener110and second fabric composite stiffener120are formed together from the same layup as further described below with reference toFIGS.4A-4E.

In some examples, web portion112comprises tapered-out edge113. Tapered-out edge113provides additional reinforcement to an end of stringer assembly100, which extends away from composite base140. For example, tapered-out edge113protects an end of stringer assembly100from various types of impacts (e.g., tools falling on stringer assembly100), Furthermore, tapered-out edge113helps to provide additional stiffness to a sub-assembly of first fabric composite stiffener110, intermediate tape composite stiffener130, and second fabric composite stiffener120.

In some examples, tapered-out edge113is characterized by thickness differences of web portion112at tapered-out edge113and away from tapered-out edge113.FIG.1Cillustrates the thickness (T1WP′) of web portion112at the widest point of tapered-out edge113, e.g., at the end of web portion112furthest away from composite base140.FIG.1Calso illustrates the thickness (T1WP) of web portion112away from tapered-out edge113, e.g., at neck portion160. In some examples, the ratio of these thicknesses (T1WP′/T1WP) is between 1.1 and 2.0. In some examples, the ratio of these thicknesses (T1WP′/T1WP) is, more specifically, between 1.2 and 1.6. As such, the tapered-out edge113of web portion112is between 10% and 100% thicker or, more specifically, 20% to 60% thicker than the remaining part of web portion112. In some examples, the length of tapered-out edge113(in the Y direction) relative to the over length of web portion112is between 0.2 and 1. In some examples, the length of tapered-out edge113(in the Y direction) relative to the over length of web portion112is between 0.4 and 0.8.

Referring toFIG.1B, in some examples, flange portion114of each of first fabric composite stiffener110and second fabric composite stiffener120comprises tapered-in edge115. More specifically, tapered-in edge115is positioned at the end of each flange portion114, i.e., the end that extends away from intermediate tape composite stiffener130. Flange portion114is attached to composite base140and provides additional reinforcement to composite base140, Tapered-in edge115provides a gradual transition in support to composite base140. Specifically, this support ranges from a full support (provided by a part of flange portion114away from tapered-in edge115, i.e., the part of flange portion114having a full thickness) to no support. As such, composite base140does not experience a rapid drop in mechanical support (e.g., from the full support to no support) at the end of each flange portion114.

In some examples, tapered-in edge115is characterized by thickness differences of flange portion114at tapered-in edge115and away from tapered-in edge115.FIG.1Cillustrates the thickness (T1FP′) of flange portion114at the narrowing point of tapered-in edge115, e.g., at the end of flange portion114furthest away from intermediate tape composite stiffener130.FIG.1C, also illustrates the thickness (T1FP) of flange portion114, away from tapered-in edge115. In some examples, the ratio of these thicknesses (T1FP′/T1FP) is between 0.1 and 0.8, In some examples, the ratio of these thicknesses (T1FP′/T1FP) is between 0.2 and 0.5, In some examples, the length of tapered-in edge115(in the X direction) relative to the over length of flange portion114is between 0.2 and 1. In some examples, the length of tapered-in edge115(in the X direction) relative to the over length of flange portion114is between 0.4 and 0.8.

In some examples, web portion112and flange portion114of each of first fabric composite stiffener110and second fabric composite stiffener120are substantially perpendicular. Flange portion114conforms to the surface of composite base140. Web portion112extends away from this surface of composite base140and provides rigidity to composite base140. The perpendicular orientation provides the greatest degree of extension from composite base140for a given height of web portion112. Furthermore, the perpendicular orientation helps to resist certain bend angles, e.g., about the X-axis. For purposes of this disclosure, the term “substantially perpendicular” is defined as an angle of between 80° and 100°. In some examples, the substantially perpendicular orientation is between 85° and 95°.

Referring toFIG.1C, in some examples, the interior radius (R1CPor R2CP) of curved portion116is between 3-10 millimeters or, more specifically, between 4-7 millimeters. While layups tend to be difficult to bend, the separation of stringer assembly100into three independent components (i.e., first fabric composite stiffener110, intermediate tape composite stiffener130, and second fabric composite stiffener120) provides additional flexibility. First fabric composite stiffener110and second fabric composite stiffener120are bent prior to bonding to intermediate tape composite stiffener130. In other words, first fabric composite stiffener110and second fabric composite stiffener120are bent individually, allowing for sharper bends, in comparison to, e.g., bending the entire sub-assembly in a joint state. It should be noted that, in some examples, intermediate tape composite stiffener130is used as a form for shaping first fabric composite stiffener110and second fabric composite stiffener120. In other words, first fabric composite stiffener110and second fabric composite stiffener120are bent against intermediate tape composite stiffener130and the intermediate tape composite stiffener130acts as a forming tool during this bending operation.

Referring toFIG.1B, intermediate tape composite stiffener130is disposed between first fabric composite stiffener110and second fabric composite stiffener120. More specifically, intermediate tape composite stiffener130contacts and conforms to web portion112and curved portion116of each of first fabric composite stiffener110and second fabric composite stiffener120. Furthermore, intermediate tape composite stiffener130comprises flared-out edges131. For instance, as seen inFIG.1B, intermediate tape composite stiffener130includes two flared-out edges. Flared-out edges131are configured to fill any gap between intermediate tape composite stiffener130and each of first fabric composite stiffener110and second fabric composite stiffener120, and in particular, between intermediate tape composite stiffener130and curved portion116of each of first fabric composite stiffener110and second fabric composite stiffener120. Curved portion116has a certain exterior radius, which is filled by flared-out edges131. Each of flared-out edges131contacts and conforms to a corresponding one of curved portions116of first fabric composite stiffener110and second fabric composite stiffener120. That is, one of flared-out edges131of intermediate tape composite stiffener130contacts and conforms to curved portion116of first fabric composite stiffener110, while the other one of flared-out edges131of intermediate tape composite stiffener130contacts and conforms to curved portion116of second fabric composite stiffener120.

Referring toFIG.1B, in some examples, intermediate tape composite stiffener130comprises outer layer tapes135, identified with dashed lines. Outer layer tapes135directly face each of first fabric composite stiffener110and second fabric composite stiffener120. Furthermore, in some examples, outer layer tapes135have a 0°-match to contacting fabric117of web portion112of each of first fabric composite stiffener110and second fabric composite stiffener120. Contacting fabric117is also identified with dashed lines inFIG.1B. This 0°-match enhances bonding and allows uniform load transition between intermediate tape composite stiffener130and each of first fabric composite stiffener110and second fabric composite stiffener120.

In some examples, intermediate tape composite stiffener130comprises a unidirectional tape reinforcement material. Furthermore, in some examples, the composition of intermediate tape composite stiffener130is substantially uniform throughout an entire volume of intermediate tape composite stiffener130, including flared-out edges131, For purposes of this disclosure, the term “substantially uniform” is defined as different parts of the components are made from the same set of material system. It should be noted that a component may include multiple materials (e.g., fibers and resins) such that the distribution of these materials is substantially the same within different areas of the component.

Intermediate tape composite stiffener130is bonded to each of first fabric composite stiffener110and second fabric composite stiffener120. For example, intermediate tape composite stiffener130is adhered (e.g., using adhesive) or otherwise bonded to each of first fabric composite stiffener110and second fabric composite stiffener120during fabrication of stringer assembly100as further described below with reference toFIGS.2and3, For example, a sub-assembly of first fabric composite stiffener110, intermediate tape composite stiffener130, and second fabric composite stiffener120is cured together, which may be also referred to as a co-curing. More specifically, intermediate tape composite stiffener130is bonded to web portion112and curved portion116of each of first fabric composite stiffener110and second fabric composite stiffener120. At the same time, flange portion114is bonded to composite base140. Similarly, intermediate tape composite stiffener130is also bonded to composite base140.

Referring toFIG.1C, in some examples, intermediate tape composite stiffener130and web portion112of each of first fabric composite stiffener110and second fabric composite stiffener120form neck portion160. Neck portion160is positioned away from tapered-out edge113or, more specifically, between tapered-out edge113and curved portion116of each of first fabric composite stiffener110and second fabric composite stiffener120. The thickness of neck portion160(Tneck) is a combination of multiple thicknesses, i.e., the thickness (Tis) of intermediate tape composite stiffener130, the thickness (T1wp) of web portion112of first fabric composite stiffener110, and the thickness (T2wp) of web portion112of second fabric composite stiffener120. It should be noted that in some examples, the thickness (T1wp) of web portion112of first fabric composite stiffener110is the same as the thickness (T2wp) of web portion112of second fabric composite stiffener120(e.g., T1wp=T2wp). In some examples, the thickness ratio (Tis/Tneck) of intermediate tape composite stiffener130(Tis) relative to neck portion160(Tneck) is at least 0.3 or even at least 0.5. In other words, intermediate tape composite stiffener130represents at least 30% of the total thickness or even at least 50%. In some examples, the thickness ratio (T1w/Tneck) of web portion112relative to neck portion160is less than 0.5. In some examples, the thickness ratio of web portion112, at the widest point of tapered-out edge113, relative to web portion112, at neck portion160, is between 1.2 and 1.6.

In some examples, stringer assembly100is a part of an aircraft, such as a winged aircraft. For example, stringer assembly100is used as a stiffening member for supporting a skin, in particular, a load carrying skin, such as a skin on aircraft wings. More specifically, stringer assembly100presents the skin from bending when compression and/or shear loads are applied to the skin. Furthermore, stringer assembly100is used to transfer loads (e.g., acting on the skin) to an aircraft frame. Aircraft applications of stringer assembly100include, but are not limited to, wings, stabilizers, fuselage, and the like.

Within examples, stringer assembly100, disclosed herein, provides enhanced bending stiffness without having large structure heights. Stringer assembly100is able to provide desired wing bending stiffness for aircrafts with small wing depth (e.g., short wing depth). Furthermore, in some examples, stringer assembly100have shortened web height compared to conventional blade stringer assemblies, and the tapered-out edges of the web portion can help compensate for the shortened web height.

Examples of Methods of Forming Stringer Assemblies

FIG.2is a process flowchart corresponding to method300for forming stringer assembly100. Various examples of stringer assembly100are described above with reference toFIGS.1A-1C. Furthermore, various applications of stringer assembly100are described below with reference toFIGS.7and8, Various types of production equipment may be used for operations of method300, such as composite layup equipment, composite curing equipment, and the like.

In some examples, method300comprises forming (block310) first fabric composite stiffener110and second fabric composite stiffener120. It should be noted that first fabric composite stiffener110and second fabric composite stiffener120are formed independently from intermediate tape composite stiffener130. The process of forming intermediate tape composite stiffener130is described below. Therefore, in some examples, the material of intermediate tape composite stiffener130is different from the first fabric composite stiffener110and second fabric composite stiffener120.

Referring toFIG.2, in some examples, the process (block310) of forming first fabric composite stiffener110and second fabric composite stiffener120starts with forming (block312) composite layup180. In some examples, composite layup180is formed by laying up one or more layers of composite sheets of a temporary support.FIG.4Ais a schematic representation of composite layup180. Composite layup180comprises first layup end181and second layup end182, opposite of first layup end181. The thickness of composite layup180is determined by the thickness of each of web portion112, flange portion114, and curved portion116. In some examples, web portion112, flange portion114, and curved portion116of both first fabric composite stiffener110and second fabric composite stiffener120have the same thickness, with exception of tapered-out edge113and tapered-in edge115. The length/width of composite layup180is determined by a combined length of web portion112, flange portion114, and curved portion116of both first fabric composite stiffener110and second fabric composite stiffener120, with reference to the cross-section of stringer assembly100shown inFIG.1C.

Referring toFIG.2, in some examples, the process (block310) of forming first fabric composite stiffener110and second fabric composite stiffener120continues with building up (block314) layup tapered-out edge183at each of first layup end181and second layup end182.FIG.4Bis a schematic representation of composite layup180with layup tapered-out edge183formed on each of first layup end181and second layup end182. It should be noted that layup tapered-out edge183correspond to tapered-out edges113, various examples and features of which are described above.

Referring toFIG.2, in some examples, the process (block310) of forming first fabric composite stiffener110and second fabric composite stiffener120continues with forming (block316) tapered layup opening185between first layup end181and second layup end182.FIG.4Cis a schematic representation of composite layup180after tapered layup opening185is formed. For example, a portion of composite layup180is removed by selective cutting. In some examples, tapered layup opening185is formed in intermediate portion186of composite layup180, e.g., in the middle between first layup end181and second layup end182. The size of tapered layup opening185depends on the size of tapered-in edge115, which is described above.

Referring toFIG.2, in some examples, the process (block310) of forming first fabric composite stiffener110and second fabric composite stiffener120continues with cutting (block318) composite layup180between first layup end181and second layup end182.FIG.4Dis a schematic representation after cutting composite layup180, which forms first fabric composite stiffener110and second fabric composite stiffener120. In some examples, composite layup180is cut in intermediate portion186of composite layup180, e.g., in the middle between first layup end181and second layup end182. In more specific examples, composite layup180is cut within tapered layup opening185. Furthermore, in some examples, first fabric composite stiffener110and second fabric composite stiffener120are substantially planar.

In some examples, method300further comprises bending (block319and/or block334) each of first fabric composite stiffener110and second fabric composite stiffener120. Block319refers to the operation when first fabric composite stiffener110and second fabric composite stiffener120are bent in in a standalone operation as, for example, is schematically shown inFIG.4E. Block334refers to the operation when first fabric composite stiffener110and second fabric composite stiffener120are bent while being conformed to intermediate tape composite stiffener130. More specifically, each of first fabric composite stiffener110and second fabric composite stiffener120is bent against intermediate tape composite stiffener130until curved portion116conforms to flared-out edges131of intermediate tape composite stiffener130, which is further described below. In some examples, operations corresponding to both block319and block334are performed. For example, first fabric composite stiffener110and second fabric composite stiffener120are first pre-bent (block319) and later further bent (block334) to conform to intermediate tape composite stiffener130.

In some examples, method300further comprises forming (block320) intermediate tape composite stiffener130. More specifically, this operation involves forming (block322) intermediate composite layup190(e.g., shown inFIG.5A) and building up (block324) intermediate layup tapered-out edges193at first intermediate layup end191(e.g., shown inFIG.5B). In some examples, intermediate composite layup190is formed by laying up one or more layers of composites sheets. Referring toFIG.5A, intermediate composite layup190comprises first intermediate layup end191and second intermediate layup end192, opposite of first intermediate layup end191. Referring toFIG.5B, intermediate layup tapered-out edges193are formed at first intermediate layup end191. First intermediate layup end191corresponds to first end133, when intermediate composite layup190is formed in intermediate tape composite stiffener130.

The thickness of intermediate composite layup190is determined by the thickness of intermediate tape composite stiffener130, away from flared-out edges131. The length of intermediate composite layup190is determined by the height of intermediate tape composite stiffener130.

In some examples, method300further comprises applying (block326) adhesive150to composite base140. Adhesive150joins first end133of intermediate tape composite stiffener130and each of first fabric composite stiffener110and second fabric composite stiffener120to composite base140. In some examples, adhesive150gap-fills spacing (e.g., fills remaining gaps) between flared-out edges131and curved portion116of each of first fabric composite stiffener110and second fabric composite stiffener120. However, unlike conventional stringer assembly processes, no special gap fillers (e.g., “noodles”) are used herein.

Method300comprises joining (block328) first end133of intermediate tape composite stiffener130to composite base140as, e.g., is shown inFIG.6A. In some examples, first end133comprises flared-out edges131. Flared-out edges131provide additional contact surfaces between intermediate tape composite stiffener130and composite base140as well as conformance to first fabric composite stiffener110and second fabric composite stiffener120as further described below. At this stage, intermediate tape composite stiffener130is not permanently attached to composite base140; this attachment is performed at later stages.

Method300comprises joining (block330) first fabric composite stiffener110and second fabric composite stiffener120to composite base140and also to intermediate tape composite stiffener130as, e.g., is shown inFIG.6B. In some examples, each of first fabric composite stiffener110and second fabric composite stiffener120comprises web portion112, flange portion114, and curved portion116, disposed between web portion112and flange portion114. After this joining operation, each curved portion116of first fabric composite stiffener110and second fabric composite stiffener120conforms to a corresponding one of the flared-out edges131of intermediate tape composite stiffener130. That is, curved portion116of first fabric composite stiffener110conforms to one of flared-out edges131of intermediate tape composite stiffener130and curved portion116of second fabric composite stiffener120conforms to the other one of flared-out edges131of intermediate tape composite stiffener130.

In some examples, first fabric composite stiffener110and second fabric composite stiffener120are bent (block334) while being conformed to intermediate tape composite stiffener130. More specifically, each of first fabric composite stiffener110and second fabric composite stiffener120is bent against intermediate tape composite stiffener130until curved portion116of each of first fabric composite stiffener110and second fabric composite stiffener120conforms to a corresponding one flared-out edges131of intermediate tape composite stiffener130, which is further described below. In other words, intermediate tape composite stiffener130is used as a forming tool during this operation.

In some examples, method300further comprises co-curing (block338) intermediate tape composite stiffener130, first fabric composite stiffener110, and second fabric composite stiffener120. During this operation, intermediate tape composite stiffener130, first fabric composite stiffener110, and second fabric composite stiffener120are bonded together. Furthermore, during this operation, intermediate tape composite stiffener130, first fabric composite stiffener110, and second fabric composite stiffener120are each bonded to composite base140.

FIG.3is a schematic illustration of method350for forming stringer assembly100, in accordance with some examples. Method350comprises forming (block360) first fabric composite stiffener110and second fabric composite stiffener120. In some examples, this operation is similar to the operation corresponding to block310, described above with reference toFIG.2andFIGS.4A-4E.

Method350comprises joining (block370) first end133of intermediate tape composite stiffener130to composite base140, with first end133comprising flared-out edges131. In some examples, this operation is similar to the operation corresponding to block328, described above with reference toFIG.2andFIG.6A. Specifically, first end133comprises flared-out edges131, which provide additional contact surfaces between intermediate tape composite stiffener130and composite base140as well as conforming to first fabric composite stiffener110and second fabric composite stiffener120as further described below.

Method350comprises bending (block374) first fabric composite stiffener110and second fabric composite stiffener120to conform to composite base140and to intermediate tape composite stiffener130. As described above, each of first fabric composite stiffener110and second fabric composite stiffener120comprises web portion112, flange portion114, and curved portion116, disposed between web portion112and flange portion114. In some examples, prior to bending, each of first fabric composite stiffener110and second fabric composite stiffener120are substantially planar.

During this bending operation, each curved portion116is formed and conforms to a corresponding one of the flared-out edges131of intermediate tape composite stiffener130. More specifically, after bending, curved portion116of each of first fabric composite stiffener110and second fabric composite stiffener120conforms to one of the flared-out edges131of intermediate tape composite stiffener130. It should be noted that intermediate tape composite stiffener130and composite base140act as a forming tool during this bending operation.

Furthermore, the ends of web portion112and intermediate tape composite stiffener130are aligned during this bending operation. In some examples, web portion112comprises tapered-out edge113. Second end134of intermediate tape composite stiffener130, opposite of first end133, is positioned between tapered-out edge113of first fabric composite stiffener110and tapered-out edge113of second fabric composite stiffener120.

Overall, in some examples, after bending, web portion112of each of first fabric composite stiffener110and second fabric composite stiffener120conforms to intermediate tape composite stiffener130. Flange portion114of each of first fabric composite stiffener110and second fabric composite stiffener120conforms to composite base140.

In some examples, method350further comprises joining (block380) first fabric composite stiffener110and second fabric composite stiffener120to each of composite base140and intermediate tape composite stiffener130. In some examples, this operation is similar to the operation corresponding to block330, described above with reference toFIG.2andFIG.6A, In more specific examples, joining (block380) first fabric composite stiffener110and second fabric composite stiffener120to each of composite base140and intermediate tape composite stiffener130comprises co-curing (block382) intermediate tape composite stiffener130, first fabric composite stiffener110, and second fabric composite stiffener120.

Aircraft Examples

In some examples, methods and systems described above are used on aircraft and, more generally, by the aerospace industry. Specifically, these methods and systems can be used during fabrication of aircraft as well as during aircraft service and maintenance.

Accordingly, the apparatus and methods described above are applicable for aircraft manufacturing and service method900as shown inFIG.7and for aircraft902as shown inFIG.8. During pre-production, method900includes specification and design904of aircraft902and material procurement906. During production, component and subassembly manufacturing908and system integration910of aircraft902takes place. Thereafter, aircraft902goes through certification and delivery912in order to be placed in service914. While in service by a customer, aircraft902is scheduled for routine maintenance and service916, which also includes modification, reconfiguration, refurbishment, and so on.

In some examples, each of the processes of method900is performed or carried out by a system integrator, a third party, and/or an operator, e.g., a customer. For the purposes of this description, a system integrator includes without limitation any number of aircraft manufacturers and major-system subcontractors; a third party includes without limitation any number of venders, subcontractors, and suppliers; and an operator can be an airline, leasing company, military entity, service organization, and so on.

As shown inFIG.8, aircraft902produced by method900includes airframe918with plurality of systems920, and interior922. The airframe918includes wings of the aircraft902. Examples of systems920include one or more of propulsion system924, electrical system926, hydraulic system928, and environmental system930. Any number of other systems can be included. Although an aerospace example is shown, the principles of the examples described herein is applied to other industries, such as the automotive industry.

Apparatus and methods presented herein can be employed during any one or more of the stages of method900. For example, components or subassemblies corresponding to manufacturing908are fabricated or manufactured in a manner similar to components or subassemblies produced while aircraft902is in service. Also, one or more apparatus examples, method examples, or a combination thereof is utilized during manufacturing908and system integration910, for example, by substantially expediting assembly of or reducing the cost of an aircraft902. Similarly, one or more of apparatus examples, method examples, or a combination thereof is utilized while aircraft902is in service, for example and without limitation, to maintenance and service916.

Further Examples

Further, description includes examples according to following clauses:

Clause 1. A stringer assembly comprising:

a first fabric composite stiffener and second fabric composite stiffener, each comprising a web portion, a flange portion, and a curved portion, disposed between the web portion and the flange portion, wherein the web portion comprises a tapered-out edge; and

an intermediate tape composite stiffener, disposed between the first fabric composite stiffener and the second fabric composite stiffener and comprising flared-out edges, each of the flared-out edges contacting and conforming to a corresponding one the curved portions of the first fabric composite stiffener and the second fabric composite stiffener.

Clause 2. The stringer assembly of clause 1, further comprising a composite base and an adhesive, disposed between and adhering to the composite base and each of the first fabric composite stiffener, the second fabric composite stiffener, and the intermediate tape composite stiffener.

Clause 3. The stringer assembly of clause 2, wherein the composite base is an interleaved skin.

Clause 4. The stringer assembly of any one of clauses 1-3, wherein the intermediate tape composite stiffener is bonded to each of the first fabric composite stiffener and the second fabric composite stiffener.

Clause 5. The stringer assembly of clause 4, wherein the intermediate tape composite stiffener is bonded to the web portion and the curved portion of each of the first fabric composite stiffener and the second fabric composite stiffener.

Clause 6. The stringer assembly of any one of clauses 1-5, wherein an interior radius (R) of the curved portion is between 3-10 millimeters.

Clause 7. The stringer assembly of any one of clauses 1-6, wherein the intermediate tape composite stiffener comprises outer layer tapes, having a 0°-match to a contacting fabric of the web portion of each of the first fabric composite stiffener and the second fabric composite stiffener.

Clause 8. The stringer assembly of any one of clauses 1-7, wherein the intermediate tape composite stiffener comprises a unidirectional tape reinforcement material.

Clause 9. The stringer assembly of any one of clauses 1-8, wherein a composition of the intermediate tape composite stiffener is substantially uniform throughout an entire volume of the intermediate tape composite stiffener.

Clause 10. The stringer assembly of any one of clauses 1-9, wherein:

the intermediate tape composite stiffener and the web portion of each of the first fabric composite stiffener and the second fabric composite stiffener form a neck portion, away from the tapered-out edge; and

a thickness ratio of the intermediate tape composite stiffener relative to the neck portion is at least 0.3.

Clause 11. The stringer assembly of clause 10, wherein a thickness ratio of the web portion, at the neck portion, relative to the neck portion is less than 0.5.

Clause 12. The stringer assembly of clause 10, wherein a thickness ratio of the web portion, at a widest point of the tapered-out edge, relative to the web portion, at the neck portion, is between about 1.2 and 1.6.

Clause 13. The stringer assembly of any one of clauses 1-12, wherein the flange portion comprises a tapered-in edge.

Clause 14. The stringer assembly of any one of clauses 1-13, wherein the web portion and the flange portion of each of the first fabric composite stiffener and the second fabric composite stiffener are substantially perpendicular.

Clause 15. A method of forming a stringer assembly, the method comprising:

joining a first end of an intermediate tape composite stiffener to a composite base, the first end comprising flared-out edges; and

joining a first fabric composite stiffener and a second fabric composite stiffener to the composite base and to the intermediate tape composite stiffener,

wherein each of the first fabric composite stiffener and the second fabric composite stiffener comprises a web portion, a flange portion, and a curved portion, the curved portion disposed between the web portion and the flange portion and conforming to a corresponding one of the flared-out edges of the intermediate tape composite stiffener.

Clause 16. The method of clause 15, wherein:

the web portion comprises a tapered-out edge; and

a second end of the intermediate tape composite stiffener, opposite of the first end, is positioned between the tapered-out edge of the first fabric composite stiffener and the tapered-out edge of the second fabric composite stiffener.

Clause 17. The method of any one of clauses 15-16, wherein the flange portion of each of the first fabric composite stiffener and the second fabric composite stiffener conforms to the composite base.

Clause 18. The method of any one of clauses 15-17, wherein the flange portion each of the first fabric composite stiffener and the second fabric composite stiffener comprises a tapered-in edge extending away from the intermediate tape composite stiffener.

Clause 19. The method of any one of clauses 15-18, further comprising forming the first fabric composite stiffener and the second fabric composite stiffener.

Clause 20. The method of clause 19, wherein forming the first fabric composite stiffener and the second fabric composite stiffener comprises:

forming a composite layup, comprising a first layup end and a second layup end, opposite of the first layup end;

building up a layup tapered-out edge at each of the first layup end and the second layup end;

forming a tapered layup opening between the first layup end and the second layup end; and

cutting the composite layup between the first layup end and the second layup end, thereby forming the first fabric composite stiffener and the second fabric composite stiffener.

Clause 21. The method of clause 20, wherein the tapered layup opening is formed in an intermediate portion between the first layup end and the second layup end.

Clause 22. The method of clause 20-21, wherein the composite layup is cut in an intermediate p between the first layup end and the second layup end.

Clause 23. The method of clause 20-22, further comprising bending each of the first fabric composite stiffener and the second fabric composite stiffener.

Clause 24. The method of clause 23, wherein each of the first fabric composite stiffener and the second fabric composite stiffener is bent against the intermediate tape composite stiffener until the curved portion conforms to the flared-out edges of the intermediate tape composite stiffener.

Clause 25. The method of any one of clauses 15-24, further comprising forming the intermediate tape composite stiffener, wherein forming the intermediate tape composite stiffener comprises:

forming an intermediate composite layup, comprising a first intermediate layup end and a second intermediate layup end, opposite of the first intermediate layup end; and

building up intermediate layup tapered-out edges at the first intermediate layup end.

Clause 26. The method of any one of clauses 15-25, further comprising applying an adhesive to the composite base, wherein the adhesive joins the first end of the intermediate tape composite stiffener and each of the first fabric composite stiffener and the second fabric composite stiffener to the composite base.

Clause 27. The method of clause 26, wherein the adhesive gap-fills spacing between the flared-out edges and the curved portion of each of the first fabric composite stiffener and the second fabric composite stiffener.

Clause 28. The method of any one of clauses 15-27, further comprising co-curing the intermediate tape composite stiffener, the first fabric composite stiffener, and the second fabric composite stiffener.

Clause 29. A method for forming a stringer assembly, the method comprising:

forming a first fabric composite stiffener and a second fabric composite stiffener;

joining a first end of an intermediate tape composite stiffener to a composite base, the first end comprising flared-out edges; and

bending the first fabric composite stiffener and the second fabric composite stiffener to conform to the composite base and to the intermediate tape composite stiffener,wherein each of the first fabric composite stiffener and the second fabric composite stiffener comprises a web portion, a flange portion, and a curved portion, disposed between the web portion and the flange portion; andwherein, after bending, the curved portion of each of the first fabric composite stiffener and the second fabric composite stiffener conforms to the flared-out edges of the intermediate tape composite stiffener.

Clause 30. The method of clause 29, wherein, after bending, the web portion of each of the first fabric composite stiffener and the second fabric composite stiffener conforms to the intermediate tape composite stiffener.

Clause 31. The method of any one of clauses 29-30, wherein, after bending, flange portion of each of the first fabric composite stiffener and the second fabric composite stiffener conforms to the composite base.

Clause 32. The method of any one of clauses 29-31, wherein, prior to bending, each of the first fabric composite stiffener and the second fabric composite stiffener are substantially planar.

Clause 33. The method of any one of clauses 29-32, further comprising joining the first fabric composite stiffener and the second fabric composite stiffener to each of the composite base and the intermediate tape composite stiffener.

Clause 34. The method of clause 33, wherein joining the first fabric composite stiffener and the second fabric composite stiffener to each of the composite base and the intermediate tape composite stiffener comprises co-curing the intermediate tape composite stiffener, the first fabric composite stiffener, and the second fabric composite stiffener.

Clause 35. The method of any one of clauses 29-34, wherein:

the web portion comprises a tapered-out edge; and

a second end of the intermediate tape composite stiffener, opposite of the first end, is positioned between the tapered-out edge of the first fabric composite stiffener and the tapered-out edge of the second fabric composite stiffener.

CONCLUSION

Although the foregoing concepts have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the processes, systems, and apparatus. Accordingly, the present examples are to be considered as illustrative and not restrictive.