A sacrificial layer and method of laying for an aircraft

Abstract

The present application relates to a kind of for aircraft sacrificial layer and laying method, the sacrificial layer is laid on the body to be laid of the aircraft, the body to be laid is the wing spar, skin and wing rib in the wing, tail wing and central wing section of aircraft;The sacrificial layer includes unidirectional tape and / or fabric, the unidirectional tape and / or fabric is multilayer, and each layer unidirectional tape and / or fabric laying coordinate system is consistent with the laying coordinate system of body to be laid, and the unidirectional tape and / or fabric is laid according to the designed laying angle in laying coordinate system when laying.The sacrificial layer of the present application is laid at a specific angle, so that the composite material structure body is little and controllable;In addition, the material of sacrificial layer is selected according to the material of body to be laid, to ensure that all surfaces or profiles are not deformed during laying processing, and the actual position is consistent with the theoretical position, and the deviation is within the allowable range.

Description

Technical Field

[0001] This invention relates to the field of composite material processing and manufacturing, and particularly to a sacrificial layer for aircraft and a method for its application. Background Technology

[0002] Currently, in the design of civil aircraft wings and tail structures, corresponding tolerance and accuracy requirements are usually specified for the dimensions of parts. However, in the manufacturing process of composite material parts, process factors such as raw material thickness tolerance, curing deformation, poor surface quality of the bonding surface, and tooling tolerance can cause deviations in the profile of the cured composite material structure, which may lead to interference or gaps at the assembly interface. Although methods such as leaving gaps and adding shims are used, these only solve the assembly problem to a certain extent, but do not fundamentally solve the aforementioned defects that occur during assembly. Summary of the Invention

[0003] The present invention aims to provide a sacrificial layer for aircraft and a method for its application, in order to solve the aforementioned problems existing in the prior art.

[0004] The above-mentioned technical objectives of the present invention will be achieved through the technical solutions described below.

[0005] A sacrificial layer for an aircraft, the sacrificial layer being laid on the body of the aircraft to be laid, the body being laid being the spars, skin and ribs of the wings, tail and central wing section of the aircraft.

[0006] The sacrificial layer includes unidirectional tape and / or fabric, which are multiple layers, and the coordinate system of each layer of unidirectional tape and / or fabric is consistent with the coordinate system of the body to be covered. The unidirectional tape and / or fabric are laid in the coordinate system according to the laying angle.

[0007] Furthermore, the laying angle of each layer of the unidirectional tape is 0°, 45°, -45° or 90°.

[0008] Furthermore, the fiber angles within each layer of the fabric include 45 degrees and 90 degrees. The laying angle of the fabric with a 45-degree angle is [0° / 45°] or [90° / -45°]; the laying angle of the fabric with a 90-degree angle is [0° / 90°] or [45° / -45°].

[0009] Furthermore, the material of the substrate to be laid is carbon fiber, and correspondingly, the material of the multi-layer unidirectional tape or fabric of the sacrificial layer is also carbon fiber; or the multi-layer unidirectional tape is carbon fiber, and the multi-layer fabric is glass fiber.

[0010] Furthermore, when the material of the substrate to be laid is glass fiber, the material of the multilayer unidirectional tape and / or fabric of the sacrificial layer is also glass fiber.

[0011] Furthermore, when the sacrificial layer only includes the unidirectional strip, the laying angle of the multi-layer unidirectional strip is repeated in the order of 45°, -45°; or in the order of 0°, 45°, -45°, 90°, and the laying method is to lay the strips in the laying coordinate system according to the laying angle order described above.

[0012] Furthermore, when the sacrificial layer only includes the fabric, the fabric has at least two layers, and the different included angles of the fabric are repeated in the order of laying angle [0° / 45°], [90° / -45°] or [0° / 90°], [45° / -45°], and the fabric is laid in the laying coordinate system.

[0013] This invention provides a method for applying a sacrificial layer from an aircraft, wherein the sacrificial layer is applied to the body to be applied using an application process, and the thickness of the sacrificial layer is 0%-30% of the body to be applied.

[0014] Furthermore, the laying process can be either co-curing or co-bonding, in which an adhesive film material is used to bond the sacrificial layer and the substrate to be laid.

[0015] Furthermore, the paving area includes the area where the wing spars connect to the skin, the area where the wing spars web connects to the main landing gear, the area where the wing spars, skin, and suspension connect, the area where the wing / tail ribs connect to the skin, and the area where the wing / tail spars web connects to the ribs.

[0016] Beneficial technical effects of the present invention

[0017] The embodiments provided by this invention provide a sacrificial layer for an aircraft, wherein the sacrificial layer is laid on the aircraft body to be covered; the sacrificial layer includes unidirectional tape and / or fabric, the unidirectional tape and / or fabric being multi-layered, and each layer of unidirectional tape and / or fabric being designed and laid according to a laying angle; the sacrificial layer is laid on the body to be covered using a laying process, and the thickness of the sacrificial layer is 0%-30% of the body to be covered. Compared with existing technologies, the sacrificial layer and laying method of this invention lay the sacrificial layer at a specific angle, thereby minimizing and controlling the deformation of the composite material structure; in addition, the material of the sacrificial layer is selected according to the material of the body to be covered, ensuring that all surfaces or profiles do not deform during the laying process, and that the actual position matches the theoretical position with deviations within allowable ranges; the thickness of the sacrificial layer is set according to the thickness of the body to be covered, determining the range of sacrificial layer thickness to ensure that after laying, the sacrificial layer has sufficient thickness for machining, and ensuring that the outline of the body to be covered remains unchanged. Attached Figure Description

[0018] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0019] Figure 1 This is a schematic diagram of the coordinate system for the sacrificial layer in an embodiment of the present invention;

[0020] Figure 2 This is a schematic diagram of the sacrificial layer being applied to the connection area between the wing spars and the skin in an embodiment of the present invention.

[0021] Figure 3 A schematic diagram of the sacrificial layer being applied to the wing spars in an embodiment of the present invention;

[0022] Figure 4 A schematic diagram of the sacrificial layer being laid on the web of a beam in an embodiment of the present invention.

[0023] The reference numerals in the attached figures are explained as follows:

[0024] 1. Outer surface of the upper edge strip of the beam; 2. Inner surface of the lower edge strip of the beam; 3. Outer surface of the lower edge strip of the beam; 4. Outer surface of the upper wall plate; 5. Inner surface of the upper wall plate; 6. Inner surface of the upper edge strip of the beam; 7. Inner surface of the web of the beam; 8. Inner surface of the lower edge strip of the beam; 9. Inner surface of the lower wall plate; 10. Outer surface of the lower wall plate; 11. Outer surface of the web of the beam; 12. Sacrificial layer of the outer surface of the web of the beam; 13. Upper edge strip of the beam; 14. Lower edge strip of the beam; 15. Sacrificial layer of the upper edge strip of the beam; 16. Sacrificial layer of the lower edge strip of the beam; 17. Web of the beam; 18. Connector on the web of the beam; 19. Sacrificial layer of the web of the beam; 20. Boundary of the connector on the web of the beam; 21. Boundary of the sacrificial layer of the web of the beam. Detailed Implementation

[0025] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments, but the implementation of the present invention is not limited thereto.

[0026] Sacrificial layer: Most components on an aircraft are not directly connected to each other. A sacrificial layer needs to be designed and applied to at least one of the components to prevent bending and deformation caused by direct connection. In this invention, the component requiring the application of the sacrificial layer is referred to as the body to be covered.

[0027] Unidirectional belt: In composite materials, a unidirectional belt refers to a single-layer composite material in which all fibers are oriented in one direction.

[0028] Fabric: Composite fabric refers to a single-layer composite material in which the fibers are arranged at a certain angle, usually 90 degrees or 45 degrees between fibers.

[0029] Laying coordinate system: In the process of manufacturing composite parts, a laying coordinate system is defined. The laying coordinate system is in a plane and includes four angles: 0 degrees, 45 degrees, 90 degrees and -45 degrees. Among them, -45 degrees is equivalent to 135 degrees.

[0030] Laying Angle: In the manufacturing process of composite materials, unidirectional tapes or fabrics are laid layer by layer to achieve the required thickness. During each layer laying process, it is necessary to lay the layers at the specified angle according to the design requirements.

[0031] like Figure 1 As shown, in this embodiment, the sacrificial layer of the aircraft is laid on the body of the aircraft to be covered; the sacrificial layer includes unidirectional tape and / or fabric, the unidirectional tape and / or fabric is multi-layered, and each layer of unidirectional tape and / or fabric is laid in the same laying coordinate system as the body to be covered. Figure 1 As shown, the laying angles include 0°, 45°, -45°, and 90°. In this embodiment, the sacrificial layer is a composite material, including unidirectional tape and / or fabric. The unidirectional tape fibers face one direction, and the fabric fibers face two directions with an included angle between them. The included angle between the fibers in the fabric is 45 degrees or 90 degrees.

[0032] In the design of the sacrificial layer, various combinations of layup angles can be formed depending on the number of material layers used. The combination of layup angles determines whether the manufactured sacrificial layer can be effectively applied to the aircraft body to be laid. Only a specific layup angle design can effectively ensure that the deformation of the composite material structure of the sacrificial layer is minimized and controllable. This embodiment lists several layup angle design methods, but the present invention is not limited to these design methods:

[0033] When the sacrificial layer consists only of pure unidirectional bands, the sacrificial layer shall be manufactured in the following order.

[0034] If the number of unidirectional tape layers is two, the sacrificial layer is designed to be laid at an angle of 45° / -45°. In the laying coordinate system, the first layer of unidirectional tape is laid with the fiber direction of 45° in the laying coordinate system, and the second layer of unidirectional tape is laid with the fiber direction of -45° in the laying coordinate system, thus forming the sacrificial layer.

[0035] If the number of unidirectional tape layers is four or a multiple of four, the sacrificial layer is designed with a layup angle of 0° / 90° / 45° / -45° / 0° / 90° / 45° / -45°, that is, it is designed in units of four layers. In the layup coordinate system, the unidirectional tape fibers are laid sequentially in the layup coordinate system in the order of layup angle 0° / 90° / 45° / -45° / 0° / 90° / 45° / -45°, which finally forms the sacrificial layer.

[0036] If the sacrificial layer has four or more unidirectional bands in an odd number, then design it in the following order:

[0037] For example, when the unidirectional strip has five layers, the sacrificial layer is designed to be laid at an angle of 0° / 90° / 45° / -45° / 0°.

[0038] For example, when the design requires the laying angle sequence to be 45° / -45° / 0° / 45° / 90°, when using unidirectional tape for manufacturing, taking a sacrificial layer containing 5 layers of unidirectional tape as an example, the first layer of unidirectional tape is laid with the fiber direction in the 45° direction of the laying coordinate system, the second layer of unidirectional tape is laid with the fiber direction in the -45° direction of the laying coordinate system, the third layer of unidirectional tape is laid with the fiber direction in the 0° direction of the laying coordinate system, the fourth layer of unidirectional tape is laid with the fiber direction in the 45° direction of the laying coordinate system, and the fifth layer of unidirectional tape is laid with the fiber direction in the 90° direction of the laying coordinate system.

[0039] For example, when the unidirectional strip has seven layers, the sacrificial layer is designed to be laid at an angle of 0° / 90° / 45° / -45° / 0° / 90° / 45°.

[0040] For example, when the unidirectional strip has nine layers, the sacrificial layer is designed to be laid at angles of 0° / 90° / 45° / -45° / 0° / 90° / 45° / -45° / 0°. If multiple layers are designed, they are laid sequentially according to the laying angle sequence of 0° / 90° / 45° / -45°…

[0041] Preferably, this embodiment also provides the following design method, in which the unidirectional layer is symmetrically arranged from left to right, and the number of all tiling angles is balanced, that is, the number is approximately the same.

[0042] For example, when there are eight layers of unidirectional tape, the laying angle of each layer of unidirectional tape in the plane where the body to be laid is 45° / -45° / 0° / 90° / 90° / 0° / -45° / 45°.

[0043] When the sacrificial layer consists only of pure fabric, the sacrificial layer shall be manufactured in the following order.

[0044] When the fiber angle in the fabric is 45 degrees, and the number of fabric layers in the sacrificial layer is required to be two or a multiple of two, then the sacrificial layer is designed to be laid at an angle of 0° / 45° / 90° / -45°, and the fabric is laid repeatedly in units of two layers.

[0045] For example, if the design requires the laying angle sequence to be 45° / -45° / 0° / 90° / 0° / 90°, and a fabric with a fiber angle of 90 degrees is used, the sacrificial layer contains 3 layers of fabric. The fiber direction of the first layer of fabric is laid according to the 45° / -45° direction in the laying coordinate system; the fiber direction of the second layer of fabric is laid according to the 0° / 90° direction in the laying coordinate system; and the fiber direction of the third layer of fabric is laid according to the 0° / 90° direction in the laying coordinate system.

[0046] For example, if the design requires the layup angle sequence to be 0° / 45° / 90° / -45° / 45° / 90°, and a fabric with a fiber angle of 45 degrees is used, the sacrificial layer consists of three layers of fabric. The first layer's fiber direction follows the 0° / 45° direction in the layup coordinate system; the second layer's fiber direction follows the 90° / -45° direction; and the third layer's fiber direction follows the 45° / 90° direction.

[0047] For example, when the sacrificial layer is designed to be a six-layer fabric, the sacrificial layer design lay-up angle is 0° / 45° / 90° / -45° / 0° / 45° / 90° / -45° / 0° / 45° / 90° / -45°;

[0048] For example, when the sacrificial layer is an odd number of fabric layers with two or more layers, the sacrificial layer is designed to be laid in the following order of angle: 0° / 45° / 90° / -45° / 0° / 45° / 90° / -45° / 0° / 45°…

[0049] For example, when the sacrificial layer is designed as a five-layer fabric, the sacrificial layer design angle is 0° / 45° / 90° / -45° / 0° / 45° / 90° / -45° / 0° / 45°;

[0050] Preferably, when the fiber angle within the fabric is 90 degrees, the following laying method is used:

[0051] For example, if the number of fabric layers in the sacrificial layer is required to be two or a multiple of two, then the design laying angle of the sacrificial layer is 0° / 90° / 45° / -45°…, that is, the fabric is repeatedly laid in units of two layers;

[0052] For example, if the sacrificial layer is designed to be six layers of fabric, then the sacrificial layer design lay-up angle is 0° / 90° / -45° / 45° / 0° / 90° / -45° / 45° / 0° / 90° / -45° / 45°;

[0053] For example, when the sacrificial layer is an odd number of fabric layers with two or more layers, the sacrificial layer is designed to be laid at angles of 0° / 90° / -45° / 45° / 0° / 90° / -45° / 45° / 0° / 90°…, that is, it is laid repeatedly in the above-mentioned laying angle sequence;

[0054] For example, if the sacrificial layer is designed as a five-layer fabric, then the design angle of the sacrificial layer is 0° / 90° / -45° / 45° / 0° / 90° / -45° / 45° / 0° / 90°.

[0055] If the sacrificial layer includes both unidirectional tape and fabric, i.e., unidirectional tape and fabric are used together for laying, with one layer of unidirectional tape counted as 1 and one layer of fabric counted as 2, then when the total number of counts is even, the overall structure of the sacrificial layer must be symmetrical and balanced. When the total number of counts is odd, the sacrificial layer must be balanced except for the middle layer.

[0056] For example, when the sacrificial layer comprises four layers of unidirectional tape and two layers of fabric, the sacrificial layer is designed with the following layup angles: 45° / -45° / 90° / 0° / 0° / 90° / 45° / -45°. When laying the sacrificial layer in other ways, it is necessary to ensure that the angles of all unidirectional tapes and fabrics are symmetrical and balanced. This invention does not exhaustively list all design angles, but all design angles that combine the above features are within the scope of protection of this invention.

[0057] In a preferred embodiment, due to various reasons such as layup design and curvature variations, the substrate to be laid may experience warping or other deformations during manufacturing. Therefore, this invention employs co-curing or co-bonding processes to cure the prepared sacrificial layer together with the substrate to be laid. These processes ensure that the sacrificial layer and the substrate to be laid become a single unit, preventing easy breakage or separation. When using co-bonding and co-curing processes, an adhesive film material is used to bond the sacrificial layer and the substrate to be laid, ensuring good performance of the resulting substrate. In this invention, a colored adhesive film is preferably used to facilitate differentiation between the sacrificial layer and the substrate to be laid, improving identifiability during machining.

[0058] Before applying the sacrificial layer to the substrate, i.e., before using co-curing or co-bonding processes, the thickness of the sacrificial layer needs to be determined in advance. If the sacrificial layer thickness is too small, it will require machining down to the substrate to find the theoretical outline. However, for safety reasons, machining of the substrate after co-curing or co-bonding is not permitted.

[0059] If the sacrificial layer is too thick, for example, half the thickness of the substrate to be covered, then when the sacrificial layer and the substrate are co-cured or co-bonded, the sacrificial layer structure will have a significant impact on the structure of the substrate, causing irreversible deformation. This will result in deformation of the surfaces of the substrate without the sacrificial layer. While the surfaces with the sacrificial layer can have their shape accuracy ensured through machining of the sacrificial layer, the deformed surfaces will not meet the project's acceptance requirements. Therefore, repeated experimentation and practical verification are necessary to determine the appropriate thickness of the sacrificial layer.

[0060] In this invention, the thickness of the sacrificial layer is designed to be 0%-30% of the thickness of the substrate to be laid, depending on the thickness of the substrate itself. This range takes into account various factors such as the material and structure of the sacrificial layer. Preferably, it is between 5% and 25%, calculated by rounding down based on the thickness of the unidirectional tape and / or fabric in the selected sacrificial layer. This method of thickness determination ensures that the sacrificial layer has sufficient thickness for machining after laying, thereby ensuring the outline of the substrate to be laid, while preventing damage to the substrate during machining.

[0061] The subject to be covered in this invention is composite material spars, skins, ribs, and other parts of aircraft components such as wings, tails, and center wings; the selected covering areas are the areas where the wing / tail spars connect to the skin, the areas where the wing spars web connects to the main landing gear, the areas where the wing spars, skins, and suspensions connect, the areas where the wing / tail ribs connect to the skin, and the areas where the wing / tail spars web connects to the ribs.

[0062] Selection of sacrificial layer material

[0063] The sacrificial layer material can be selected from carbon fiber reinforced unidirectional tape, fabric, and / or glass fiber reinforced unidirectional tape, fabric. In this invention, the material of the sacrificial layer is related to the material of the substrate to be laid. If the substrate is made of carbon fiber, then carbon fiber reinforced unidirectional tape or fabric is the best choice for the sacrificial layer material, followed by carbon fiber unidirectional tape and glass fiber fabric. Preferably, 50% of the thickness is achieved using the carbon fiber unidirectional tape and 50% using the glass fiber fabric, but glass fiber fabric is not used alone. If the substrate is made of glass fiber, then the sacrificial structure material is glass fiber unidirectional tape and / or fabric, but not carbon fiber. The material combination scheme of this invention has been verified as an optimal design through practice, which can avoid reducing the influence of the sacrificial layer material on the substrate material and achieve the invention's objective of optimal design.

[0064] Example 1

[0065] like Figure 2As shown, the present invention is illustrated using the connection area between the wing beam and the skin as an example. The connection area includes the outer surface 1 of the upper edge strip of the beam; the inner surface 2 of the lower edge strip of the beam; the outer surface 3 of the lower edge strip of the beam; the outer surface 4 of the upper wall panel; the inner surface 5 of the upper wall panel; the inner surface 6 of the upper edge strip of the beam; the inner surface 7 of the web of the beam; the inner surface 8 of the lower edge strip of the beam; the inner surface 9 of the lower wall panel; and the outer surface 10 of the lower wall panel.

[0066] The sacrificial layer design region is determined on the cross-section of the upper edge strip of the wing sparence, and also along the length of the wing sparence, as follows: Figure 3 As shown, at this time, the inner surface 6 of the upper edge strip, the inner surface 7 of the web, and the inner surface 8 of the lower edge strip form a C-shaped opening, which is called the spanwise direction of the outer surface 11 of the web from right to left. The upper edge strip is above. In the spanwise direction of the wing beam in the figure, the sacrificial layer is designed at the joint or nailing point of the outer surface 1 of the upper edge strip and the inner surface 5 of the upper wall plate. If it is assumed that the inner surface 5 of the upper wall plate is only in contact with the outer surface 1 of the upper edge strip from the left within a range of 1m, then the sacrificial layer on the outer surface 1 of the upper edge strip only needs to be designed within a range of 1m from the left, that is, the length of the sacrificial layer 15 of the upper edge strip is within a range of 1m from the left.

[0067] After determining the spanwise sacrificial layer range, a beam web outer surface sacrificial layer 12 is set on the beam web outer surface 11, a beam upper edge strip sacrificial layer 15 is set on the beam upper edge strip 13, and a beam lower edge strip sacrificial layer 16 is set on the beam lower edge strip 14. At this time, the beam web outer surface sacrificial layer 12, the beam upper edge strip 13, and the beam lower edge strip 14 are designed separately.

[0068] When a sacrificial web layer 19 is provided in the beam web 17, see [reference needed]. Figure 4 As shown, the area of ​​the sacrificial layer of the beam web should be larger than that of the connector 18 on the beam web. The connector 18 on the beam web can be a main joint, a metal stiffener, or other parts. The distance between the boundary 21 of the sacrificial layer of the beam web and the boundary 20 of the connector on the beam web is 5mm. This design can achieve the following technical effects for the assembly of the connector 18 on the beam web and the beam web:

[0069] (1) The most accurate and effective way to achieve the shape of the wing beam is 5mm, which can meet the positioning deviation of the connecting part 18 on the web plate 17 of the beam, and avoid interference or gap when assembling the parts with the web plate.

[0070] (2) Refined design: 5mm can reduce the size of the sacrificial layer in the beam web, reduce the weight of the sacrificial layer 19, and ultimately reduce the weight of the beam structure.

[0071] (3) Functional requirements: 5mm can meet the functional requirements of aircraft such as lightning protection, corrosion protection, and abnormal potential protection.

[0072] After the tiling is completed, digital measurement methods such as coordinate measuring machines, laser trackers, and scanners can be used to determine the deviation between the tiled surface and the theoretical surface. Then, using five-axis or three-axis machine tools, a sacrificial layer is machined onto the surface of the tiling body, referencing the theoretical surface. Within the thickness range of the sacrificial layer, the outer surface of the tiling body is ensured to match the theoretical outer surface. Finally, the tiling body and the machined sacrificial layer together form a complete tiling body that meets the theoretical requirements, achieving perfect assembly.

[0073] The foregoing description illustrates and describes several preferred embodiments of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A sacrificial layer for an aircraft, characterized in that, The sacrificial layer is laid on the body of the aircraft to be covered, which is the spars, skin and ribs in the wings, tail and central wing section of the aircraft. The material of the substrate to be laid is carbon fiber, and correspondingly, the material of the fabric of the sacrificial layer is also carbon fiber; When the material of the substrate to be laid is glass fiber, the material of the fabric of the sacrificial layer is also glass fiber; The sacrificial layer includes both unidirectional tape and fabric, that is, unidirectional tape and fabric are used together for laying. One layer of unidirectional tape is counted as 1 and one layer of fabric is counted as 2. When the total number of counts is even, the overall structure of the sacrificial layer must be symmetrical and balanced. When the total number of counts is odd, the sacrificial layer except for the middle layer must be symmetrical and balanced. The laying angle of each layer of the unidirectional tape is 0°, 45°, -45° or 90°; For fabrics with an internal fiber angle of 90 degrees, the lay-up angle is [0° / 90°], [45° / -45°]. The thickness of the sacrificial layer is 5%-25% of the substrate to be covered.

2. A method for applying the sacrificial layer for aircraft as described in claim 1, characterized in that, The sacrificial layer is applied to the substrate to be covered using a tiling process.

3. The method according to claim 2, characterized in that, The installation process can be either co-curing or co-bonding. In both processes, an adhesive film material is used to bond the sacrificial layer and the substrate to be installed.

4. The method according to claim 2, characterized in that, The areas to be covered include the wing spars and skin connection areas, the wing spars web and main landing gear connection areas, the wing spars, skin and pylon connection areas, the wing / tail ribs and skin connection areas, and the wing / tail spars webs and ribs connection areas.

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