Structure having joined unitary structures

A method and apparatus are presented. The apparatus comprises a first unitary structure, a second unitary structure, and a number of joints between the first unitary structure and the second unitary structure. The first unitary structure has a plurality of T-shaped cross-sections. The second unitary structure has a plurality of T-shaped cross-sections.

BACKGROUND INFORMATION

The present disclosure relates generally to structures, and in particular, to forming structures with I-shaped cross-sections. More particularly, the present disclosure relates to forming composite structures by joining unitary structures.

Aircraft are being designed and manufactured with greater and greater percentages of composite materials. Composite materials are used in aircraft to decrease the weight of the aircraft. This decreased weight improves performance features, such as payload capacities and fuel efficiencies. Further, composite materials provide longer service life for various components in an aircraft.

Composite materials are tough, light-weight materials created by combining two or more functional components. For example, a composite material may include reinforcing fibers bound in a polymer resin matrix. The fibers may be unidirectional or may take the form of a woven cloth or fabric. The fibers and resins are arranged and cured to form a composite material.

Further, using composite materials to create aerospace composite structures potentially allows for portions of an aircraft to be manufactured in larger pieces or sections. For example, a fuselage in an aircraft may be created in cylindrical sections and then assembled to form the fuselage of the aircraft. Other examples include, without limitation, wing sections joined to form a wing or stabilizer sections joined to form a stabilizer.

Aircraft include stiffeners, such as I-beams. In some implementations, the stiffeners are arranged into a grid. When formed of composite materials, each stiffener would traditionally be cured prior to being fastened to other stiffeners in the grid. Curing each stiffener individually may use at least one of an undesirable amount of time or an undesirable amount of resources. Further, fastening stiffeners increases the weight of the resulting aircraft. Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues.

SUMMARY

In one illustrative embodiment, an apparatus is presented. The apparatus comprises a first unitary structure, a second unitary structure, and a number of joints between the first unitary structure and the second unitary structure. The first unitary structure has a plurality of T-shaped cross-sections. The second unitary structure has a plurality of T-shaped cross-sections.

Another embodiment of the present disclosure provides a method. A first unitary structure having a plurality of T-shaped cross-sections is formed. A composite skin bonded to a second unitary structure having a plurality of T-shaped cross-sections is formed. A number of joints between the first unitary structure and the second unitary structure is formed.

Yet another embodiment of the present disclosure provides a method. A first plurality of T-shaped stiffeners are co-cured to form a first grid. A second plurality of T-shaped stiffeners are co-cured to form a second grid. A number of joints is formed between the first grid and the second grid.

DETAILED DESCRIPTION

The illustrative embodiments recognize and take into account one or more different considerations. For example, the illustrative embodiments recognize and take into account that unitized composite grids having I-beam cross-sections have a reduced weight over I-beam cross-sections joined using fasteners. The illustrative embodiments recognize and take into account that unitized composite grids having I-beam cross-sections have fewer manufacturing steps than forming, curing, and fastening separate I-beam cross-sections.

The illustrative embodiments further recognize and take into account that forming unitized composite grids having I-beam cross-sections may trap tooling. Accordingly, specialized tooling for applying pressure during curing to unitized composite grids may be developed. For example, inflatable tooling, shrinking tooling, or tooling having a plurality of parts may be used as specialized tooling for applying pressure to unitized composite grids during curing. However, this specialized tooling may be more complicated than desired. Further, using the specialized tooling may take more time that desired. Yet further, the specialized tooling may have a limited number of cure cycles.

The illustrative embodiments recognize and take into account that it may be desirable to form unitized composite structures without trapping tooling. More specifically, the illustrative embodiments recognize and take into account that weight, manufacturing time, quantity of manufacturing steps, and complication of tooling may each be weighed in changing the design of a unified composite structure. Further, the illustrative embodiments recognize and take into account that weight, manufacturing time, cost, and performance characteristics may be weighed in deciding what material is used to form unified structures. Structures may be formed using at least one of a number of metals, a number of polymers, or a number of composite materials.

Referring now to the figures and, in particular, with reference toFIG. 1, an illustration of an aircraft is depicted in which an illustrative embodiment may be implemented. In this illustrative example, aircraft100has wing102and wing104attached to body106. Aircraft100includes engine108attached to wing102and engine110attached to wing104.

Aircraft100is an example of an aircraft having structures that may be formed by joining a first unitary structure and a second unitary structure in accordance with an illustrative embodiment. For example, composite skin in body106may be stiffened using a composite grid formed of a first unitary structure and a second unitary structure.

This illustration of aircraft100is provided for purposes of illustrating one environment in which the different illustrative embodiments may be implemented. The illustration of aircraft100inFIG. 1is not meant to imply architectural limitations as to the manner in which different illustrative embodiments may be implemented. For example, aircraft100is shown as a commercial passenger aircraft. The different illustrative embodiments may be applied to other types of aircraft, such as a private passenger aircraft, a rotorcraft, or other suitable types of aircraft.

Although the illustrative examples for an illustrative embodiment are described with respect to an aircraft, an illustrative embodiment may be applied to other types of platforms. The platform may be, for example, a mobile platform, a stationary platform, a land-based structure, an aquatic-based structure, or a space-based structure. More specifically, the platform may be a surface ship, a tank, a personnel carrier, a train, a spacecraft, a space station, a satellite, a submarine, an automobile, a manufacturing facility, a building, or other suitable platforms.

Turning now toFIG. 2, an illustration of a block diagram of a manufacturing environment is depicted in accordance with an illustrative embodiment. In this illustrative example, manufacturing environment200is an environment in which structures of aircraft100are formed.

As depicted, structure202takes the form of any desirable part. Structure202may be a composite structure of aircraft100ofFIG. 1.

In some illustrative examples, structure202takes the form of stiffener204. More specifically, in one example, stiffener204is grid206. Grid206may be a stiffener for body106of aircraft100ofFIG. 1.

Structure202comprises first unitary structure208having first plurality of T-shaped cross-sections210, second unitary structure212having second plurality of T-shaped cross-sections214, and number of joints216between first unitary structure208and second unitary structure212.

As used herein, “a number of,” when used with reference to items means one or more items. As a result, number of joints216includes one or more joints. In some illustrative examples, number of joints216is a number of Pi-joints.

Number of joints216includes number of openings218in second unitary structure212, number of protrusions220in first unitary structure208, and adhesive222. Although number of openings218is associated with second unitary structure212in this depiction, in other examples, number of openings218is instead associated with first unitary structure208. In these other examples, number of protrusions220is instead associated with second unitary structure212.

In some illustrative examples, number of protrusions220is formed by machining composite material224of first unitary structure208. When number of protrusions220is formed by machining, number of protrusions220includes number of machined surfaces226.

In some illustrative examples, number of openings218is formed by machining composite material228of second unitary structure212. When number of openings218is formed by machining, number of openings218includes number of machined surfaces230.

When first unitary structure208is formed of composite material224and second unitary structure212is formed of composite material228, structure202may be referred to as a composite structure. In some examples, one of first unitary structure208or second unitary structure212is formed of a material other than a composite material. In these examples, the non-composite material is selected to prevent undesirable interactions with the composite material of the other of first unitary structure208or second unitary structure212.

Number of openings218also includes weep holes231. Weep holes231are machined in the side of plies of composite material228. Adhesive222flows through weep holes231during the joining of first unitary structure208and second unitary structure212. Structure202is inspected for adhesive wetout from weep holes231. Adhesive wetout indicates adhesive pull. Adhesive pull is when the adhesive is in contact with desired bonding surfaces. Desirable adhesive pull indicates an adequate bond.

When adhesive wetout is undesirably low, number of joints216may have an undesirable quality. For example, when adhesive wetout is undesirably low, number of joints216may lack the mechanical strength to form first unitary structure208.

When structure202is grid206, first unitary structure208is first grid232and second unitary structure212is second grid234. First grid232and second grid234are joined to form grid206.

Composite skin236is bonded directly to one of first unitary structure208or second unitary structure212. More specifically, in some examples, composite skin236is co-cured with one of first unitary structure208or second unitary structure212. As depicted, composite skin236is directly bonded to second unitary structure212. In some illustrative examples, first unitary structure208, second unitary structure212, and composite skin236form a component of an aircraft, such as aircraft100ofFIG. 1.

In some examples, using resin infusion equipment244, rather than prepreg composite materials, creates first unitary structure208and second unitary structure212with desirable characteristics. In these examples, resin infusion equipment244infuses resin into dry preforms instead of using prepreg composite materials. For example, using resin infusion equipment244provides desirable tolerances for first unitary structure208and second unitary structure212. Desirable tolerances include tolerances for first unitary structure208and second unitary structure212such that first unitary structure208and second unitary structure212may be joined. More specifically, the dimensions of resin infusion equipment244are well-controlled, and as a result, create well-controlled tolerances for first unitary structure208and second unitary structure212.

Composite material224is formed by resin infusing dry fiber material using resin infusion equipment244. More specifically, resin infusion equipment244resin infuses a first dry structure to form an infused first structure. After forming composite material224, composite material224is cured using first tool240and autoclave248. More specifically, the infused first structure is cured to form first unitary structure208. After curing, first tool240is removed from first unitary structure208. First plurality of T-shaped cross-sections210allows for removal of first tool240.

First tool240is a rigid tool used to apply equal pressure to composite material224during curing. First plurality of T-shaped cross-sections210are co-cured to form first grid232. First tool240is formed of any desirable material. In one illustrative example, first tool240is formed of a metal.

Composite material228is formed by resin infusing dry fiber material using resin infusion equipment244. More specifically, resin infusion equipment244resin infuses a second dry structure to form an infused second structure. After forming composite material228, composite material228is cured using second tool242and autoclave248. More specifically, the infused second structure is cured to form second unitary structure212. After curing, second tool242is removed from second unitary structure212. Second plurality of T-shaped cross-sections214allows for removal of second tool242.

Second tool242is a rigid tool used to apply equal pressure to composite material228during curing. Second plurality of T-shaped cross-sections214are co-cured to form second grid234. Second tool242is formed of any desirable material. In one illustrative example, second tool242is formed of a metal.

As depicted, composite skin236is directly bonded to second unitary structure212. In some examples, a composite skin layup is co-cured with the infused second structure to form composite skin236bonded to second unitary structure212.

After forming first unitary structure208and second unitary structure212, first unitary structure208and second unitary structure212are prepared for joining. Preparing first unitary structure208and second unitary structure212for joining includes forming at least one of number of protrusions220or number of openings218.

In some examples, number of protrusions220are present in the first dry structure. In these examples, number of protrusions220are formed prior to curing. In other examples, at least a portion of number of protrusions220are formed using machining equipment246. Number of protrusions220are machined such that first unitary structure208and second unitary structure212are within tolerances for joining.

Number of openings218are formed using machining equipment246. Number of openings218may have any desirable shape or size such that a desirable amount of adhesive222is present.

Further, number of openings218optionally includes number of centering elements250. Number of centering elements250centers number of protrusions220within number of openings218. By centering number of protrusions220within number of openings218, bond line thickness is controlled. Controlling bond line thickness affects structural capability of structure202.

Number of centering elements250takes the form of any desirable components. When number of centering elements250is present, the walls of number of openings218are not planar. In some examples, number of centering elements250includes at least one of bumps, dimples, channels, protrusions, or other physical structures. In some examples, number of centering elements250is integral to number of openings218. For example, number of centering elements250is formed from the material of second unitary structure212. In other examples, number of centering elements250is formed from a different material added to second unitary structure212.

For example, although not depicted in manufacturing environment200ofFIG. 2, manufacturing equipment238may further include non-destructive inspection equipment. Non-destructive inspection equipment may be used to further inspect any desirable portion of structure202, such as number of joints216, first unitary structure208, or second unitary structure212.

As another example, although first unitary structure208is described as being formed of composite material224and second unitary structure212is described as being formed of composite material228, at least one of first unitary structure208or second unitary structure212may be formed of a material other than a composite material. In some examples, at least one of first unitary structure208or second unitary structure212is formed of a polymeric material, a metal, or some other desirable non-composite material. In these examples, manufacturing equipment238includes additional equipment such as additive manufacturing equipment, injection equipment, molding equipment, or any other desirable type of equipment.

As yet a further example, at least one of composite material224or composite material228is formed of a prepreg material. In this example, manufacturing equipment238includes desirable equipment to place the prepreg material such as at least one of pick and place equipment, a composite tape laying head, or other desirable equipment.

Turning now toFIG. 3, an illustration of a fuselage having a number of unitized structures is depicted in accordance with an illustrative embodiment. Stiffener300of fuselage302is a physical implementation of structure202ofFIG. 2. Further, view304of fuselage302may be an interior view of body106ofFIG. 1.

Fuselage302includes composite skin306and stiffener300. As depicted, stiffener300takes the form of grid308. Grid308may be a physical implementation of grid206ofFIG. 2.

Turning now toFIG. 4, an illustration of a structure formed by joining two unitized structures is depicted in accordance with an illustrative embodiment. Structure400is a physical implementation of structure202ofFIG. 2. In some examples, structure400is a portion of stiffener300ofFIG. 3.

Structure400includes first unitary structure402, second unitary structure404, and number of joints406. Second unitary structure404is directly bonded to composite skin408.

If structure400was cured as one piece, a tool would be trapped within cavity410. However, by forming and curing first unitary structure402and second unitary structure404separately, tooling is not trapped within cavity410.

Turning now toFIG. 5, an illustration of a tool, a second unitary structure, and composite skin is depicted in accordance with an illustrative embodiment. Manufacturing environment500may be a physical implementation of manufacturing environment200ofFIG. 2. Manufacturing environment500includes second unitary structure502, composite skin504, and tool506. As depicted, tool506is removed from second unitary structure502after second unitary structure502is cured. In this example, second unitary structure502and composite skin504are co-cured. By co-curing second unitary structure502and composite skin504, composite skin504is directly bonded to second unitary structure502.

After removing tool506, portions of second unitary structure502are machined. For example, after removing tool506, a number of openings is machined into T-shaped cross-section508, T-shaped cross-section510, T-shaped cross-section512, and T-shaped cross-section514. The number of openings receives a number of protrusions from a first unitary structure.

Turning now toFIG. 6, an illustration of a forming tool and a first unitary structure is depicted in accordance with an illustrative embodiment. Manufacturing environment600may be a physical implementation of manufacturing environment200ofFIG. 2. In some examples, manufacturing environment600is the same as manufacturing environment500ofFIG. 5. Manufacturing environment600includes first unitary structure602and tool604. As depicted, tool604is removed from first unitary structure602after first unitary structure602is cured.

In some examples, after removing tool604, portions of first unitary structure602are machined. For example, after removing tool604, a number of protrusions is machined into T-shaped cross-section606, T-shaped cross-section608, T-shaped cross-section610, and T-shaped cross-section612. In other examples, first unitary structure602is not machined. In these examples, the number of protrusions is part of the shape of first unitary structure602prior to curing. After forming, the number of protrusions is inserted into the number of openings of second unitary structure502.

Turning now toFIG. 7, an illustration of a first unitary structure positioned relative to a second unitary structure is depicted in accordance with an illustrative embodiment. In view700, first unitary structure602has been rotated 180 degrees from the view ofFIG. 6. First unitary structure602is positioned over second unitary structure502ofFIG. 5. To form a structure, such as structure202ofFIG. 2, adhesive is applied to number of openings702in secondary unitary structure502. After applying adhesive to the number of openings702, number of protrusions704of first unitary structure602is inserted into number of openings702. Inserting number of protrusions704into number of openings702forms number of joints406of structure400ofFIG. 4.

Turning now toFIG. 8, an illustration of a cross-sectional view of a joint between a first unitary structure and a second unitary structure is depicted in accordance with an illustrative embodiment. View800is a cross-sectional view of a portion of a structure, such as structure400ofFIG. 4.

Structure802of view800includes first unitary structure804, second unitary structure806, and joint808. First unitary structure804has protrusion810. Second unitary structure806has opening812. At least one of protrusion810or opening812is machined. By machining at least one of protrusion810or opening812, first unitary structure804and second unitary structure806are within tolerance for joining.

As depicted, weephole814is machined into second unitary structure806. Weephole814allows for adhesive wetout from opening812. Adhesive wetout is visible from weephole814. Observing adhesive wetout from weephole814allows for inspection of joint808without use of inspection equipment.

Joint808is positioned in a web portion of structure802. The location of joint808within the web portion may be positioned at any desirable height of structure802. Joint808can be placed at or near the neutral axis of the web portion to minimize shear loads from bending moments of the I-shaped cross-section of structure802.

As depicted, weephole814is machined into second unitary structure806in only one side. However, in other examples, weephole814may be machined through both sides of opening812of second unitary structure806. Further, in other examples, weephole814may be desirably machined into the opposite side of second unitary structure806instead.

Turning now toFIG. 9, an illustration of a cross-sectional view of a joint between a first unitary structure and a second unitary structure is depicted in accordance with an illustrative embodiment. View900is a cross-sectional view of a portion of a structure, such as structure400ofFIG. 4.

Structure902of view900includes first unitary structure904, second unitary structure906, and joint908. First unitary structure904has protrusion910. Second unitary structure906has opening912. In some examples, at least one of protrusion910or opening912is machined. By machining at least one of protrusion910or opening912, first unitary structure904and second unitary structure906are within tolerance for joining.

As depicted, weephole914is machined into second unitary structure906. Weephole914allows for adhesive wetout from opening912. Adhesive wetout is visible from weephole914. Observing adhesive wetout from weephole914allows for inspection of joint908without use of inspection equipment.

Joint908is positioned in a web portion of structure902. The location of joint908within the web portion may be positioned at any desirable height of structure902. Joint908can be placed at or near the neutral axis of the web portion to minimize shear loads from bending moments of the I-shaped cross-section of structure902.

As depicted, weephole914is machined into second unitary structure906in only one side. However, in other examples, weephole914may be machined through both sides of opening912of second unitary structure906. Further, in other examples, weephole914may be desirably machined into the opposite side of second unitary structure906instead.

In this depicted example, opening912includes number of centering elements916. Number of centering elements916center protrusion910within opening912. As depicted, number of centering elements916are a number of bumps. In other examples, number of centering elements916may take the form of dimples, channels, protrusions, or other nonplanar elements.

Turning now toFIG. 10, an illustration of a flowchart of a process for forming a structure is depicted in accordance with an illustrative embodiment. Process1000may be implemented in manufacturing environment200ofFIG. 2to form structure202ofFIG. 2. Structure400ofFIG. 4may be formed using process1000. Process1000may be implemented to form structures of aircraft100ofFIG. 1.

Process1000forms a first unitary structure having a plurality of T-shaped cross-sections (operation1002). In some examples, forming the first unitary structure comprises resin infusing a first dry structure to form an infused first structure; and curing the infused first structure to form the first unitary structure.

Process1000forms a composite skin bonded to a second unitary structure having a plurality of T-shaped cross-sections (operation1004). In some examples, forming the composite skin bonded to the second unitary structure comprises resin infusing a second dry structure to form an infused second structure; and curing the infused second structure to form the second unitary structure. In some examples, forming the composite skin bonded to the second unitary structure further comprises co-curing a composite skin layup and the infused second structure to form the composite skin bonded to the second unitary structure.

Process1000forms a number of joints between the first unitary structure and the second unitary structure (operation1006). In some examples, forming the number of joints between the first unitary structure and the second unitary structure comprises applying an adhesive to a number of openings in the second unitary structure, and inserting a number of protrusions of the first unitary structure into the number of openings.

Turning now toFIG. 11, an illustration of a flowchart of a process for forming a composite structure is depicted in accordance with an illustrative embodiment. Process1100may be implemented in manufacturing environment200ofFIG. 2to form structure202ofFIG. 2. Structure400ofFIG. 4may be formed using process1100. Process1100may be implemented to form composite structures of aircraft100ofFIG. 1.

Process1100co-cures a first plurality of T-shaped stiffeners to form a first grid (operation1102). Process1100also co-cures a second plurality of T-shaped stiffeners to form a second grid (operation1104).

Process1100then forms a number of joints between the first grid and the second grid (operation1106). Afterwards, the process terminates. In some examples, forming the number of joints comprises applying adhesive to a number of openings of the second grid; and inserting a number of protrusions of the first grid into the number of openings of the second grid.

In one example, process1000further comprises machining the second unitary structure to form the number of openings. In one example, process1000further comprises machining weep holes into the number of openings.

In some examples, process1100further comprises machining weep holes into the second grid, and determining an amount of adhesive wetout from the weep holes. In some examples, process1100further comprises machining the number of openings into the second grid. In some examples, process1100further comprises machining the first grid to form the number of protrusions. In some examples, process1100further comprises co-curing a composite skin to at least one of the first grid or the second grid.

The illustrative embodiments of the disclosure may be described in the context of aircraft manufacturing and service method1200as shown inFIG. 12and aircraft1300as shown inFIG. 13. Turning first toFIG. 12, an illustration of an aircraft manufacturing and service method is depicted in accordance with an illustrative embodiment. During pre-production, aircraft manufacturing and service method1200may include specification and design1202of aircraft1300inFIG. 13and material procurement1204.

During production, component and subassembly manufacturing1206and system integration1208of aircraft1300takes place. Thereafter, aircraft1300may go through certification and delivery1210in order to be placed in service1212. While in service1212by a customer, aircraft1300is scheduled for routine maintenance and service1214, which may include modification, reconfiguration, refurbishment, and other maintenance or service.

With reference now toFIG. 13, an illustration of an aircraft is depicted in which an illustrative embodiment may be implemented. In this example, aircraft1300is produced by aircraft manufacturing and service method1200inFIG. 12and may include airframe1302with plurality of systems1304and interior1306. Examples of systems1304include one or more of propulsion system1308, electrical system1310, hydraulic system1312, and environmental system1314. Any number of other systems may be included. Although an aerospace example is shown, different illustrative embodiments may be applied to other industries, such as the automotive industry.

Apparatuses and methods embodied herein may be employed during at least one of the stages of aircraft manufacturing and service method1200inFIG. 12. One or more illustrative embodiments may be used during component and subassembly manufacturing1206. For example, manufacturing environment200inFIG. 2may be used during component and subassembly manufacturing1206. Specifically, structure202inFIG. 2may be assembled during component and subassembly manufacturing1206. For example, process1000ofFIG. 10or process1100ofFIG. 11may be used during component and subassembly manufacturing1206to form a portion of aircraft1300. Further, structure202may also be used to perform replacements and upgrades during maintenance and service1214.

The illustrative embodiments provide a method and apparatus for forming a structure. The structure comprises a first unitary structure having a plurality of T-shaped cross-sections; a second unitary structure having a plurality of T-shaped cross-sections; and a number of joints between the first unitary structure and the second unitary structure. More specifically, the plurality of T-shaped cross-sections of the first unitary structure and the plurality of T-shaped cross-sections of the second unitary structure are joined to form an I-shaped cross-section for the structure.

The number of joints is positioned in any desirable location within a web of the structure. In some examples, the number of joints is positioned at or near the neutral axis of the web to minimize shear loads from the bending moments of the beams.

By forming the first unitary structure and second unitary structure separately, forming tools may be removed from the first unitary structure and second unitary structure after curing. The first unitary structure and the second unitary structure both have open ends to allow for removal of tools in respective cavities during curing.

The illustrative embodiments recognize and take into account that tolerances of square or grid shaped structures affects the joining of the structures. Small differences in one or more portions of square or grid shaped structures may prevent the square or grid shaped structures from being joined.

Resin infusion of dry preforms provides better tolerances than laying up pre-impregnated composite materials. As a result, first unitary structure and second unitary structure are formed by resin infusion. By forming first unitary structure and second unitary structure by resin infusion, the tolerances may be acceptable to join first unitary structure and second unitary structure.

Further, the number of joints is formed by a number of machined surfaces. At least one of a number of openings or a number of protrusions of the number of joints is formed by machining. The machined surfaces are within tolerance for joining. By machining surfaces, some inconsistencies in size or shape of first unitary structure or second unitary structure may be removed or compensated for through machining.