Composite material fillet region structure and composite material structure

Abstract

The application discloses a composite material fillet area structure and a composite material structure, and belongs to the technical field of aircraft body design. The fillet area comprises a plurality of arc-shaped layers from inside to outside. The arc-shaped layers are arranged in sequence. The curvature radii of the arc-shaped layers are the same or the curvature radii of the arc-shaped layers decrease from inside to outside. The equal-curvature design of the fillet area can prevent the curvature radius of the inner surface of the fillet area from being too small to cause large interlaminar tensile stress, and also makes the stress distribution of the fillet area more uniform, thereby reducing the interlaminar stress. The design also increases the bending stiffness and the anti-instability capacity of the fillet area. The equal-curvature design of the fillet area also provides great convenience for local repair of the fillet area, avoids the mismatch of the curvature of the cementing surface between the damaged part and the reinforcing part caused by the different curvature radii of the inner and outer surfaces, and has important practical application significance.

Description

Technical Field

[0001] This invention belongs to the field of aircraft airframe design technology, and particularly relates to a composite material rounded corner structure and a composite material structure. Background Technology

[0002] Composite materials, as a new type of material, are beginning to be widely used in various engineering structures, especially in the aerospace field, such as load-bearing structures like aircraft wings, fuselages, and tail fins. These structures involve connections between composite laminate components in various planar orientations, such as the connections between wing spars, ribs, and skin panels. Typically, these connections are achieved through rounded bends at the ends of the components or by using connectors with rounded corners to achieve bolted or planar adhesive bonding between different planar components. Unlike planar areas, these rounded corner areas generate significant interlaminar tensile stresses when subjected to various loads, especially bending moments, leading to opening deformation. This tensile stress can easily cause delamination within the rounded corner areas, directly affecting the connection strength between composite structural components. Therefore, ensuring the strength requirements of the rounded corner areas of composite materials is a crucial and widely concerned aspect in the design of composite structural components.

[0003] To ensure the fillet regions meet strength requirements, traditional fillet region designs typically employ a sufficient number of plies or increased thickness to keep the interlaminar stress within allowable limits. However, for structures with numerous and varied fillet regions, this approach directly impacts overall structural design efficiency and hinders weight reduction. Therefore, this invention proposes a different method: employing a novel fillet region design to reduce interlaminar stress in the fillet regions, thereby avoiding unnecessary increases in composite material plies or thickness to guarantee strength.

[0004] A fundamental characteristic of traditional rounded corner design is that the rounded corner has different radii of curvature from the inner to the outer surface, with the inner surface having a smaller radius of curvature than the outer surface. This design feature means that under open bending moment, large interlaminar tensile stresses are more likely to occur near the inner surface (approximately one-third of the thickness), leading to delamination.

[0005] To address the aforementioned technical problems, a novel rounded corner structure has been designed and developed, which is of significant practical importance in resolving these issues. Summary of the Invention

[0006] In view of this, the present invention provides a composite material rounded corner region structure and a composite material structure.

[0007] The present invention adopts the following technical solution:

[0008] A composite material rounded corner structure, wherein the rounded corner area includes multiple arc-shaped plies from the inner side to the outer side of the rounded corner, the arc-shaped plies are arranged in sequence, and the radius of curvature of the arc-shaped plies is the same or the radius of curvature of the arc-shaped plies decreases from the inside to the outside.

[0009] Furthermore, when the radii of curvature of the arc-shaped plies are the same, the upper and lower surfaces of each arc-shaped ply are concentric circular arcs.

[0010] Furthermore, a filler material is provided between the arc-shaped plies located in the rounded corner area.

[0011] Furthermore, the arc-shaped ply thickness is the same.

[0012] Furthermore, the filler material includes resin, fiber material, and metal material.

[0013] Furthermore, the curvature centers of all the said arc-shaped plies are located on the geometric center symmetry line of the rounded corner area.

[0014] Furthermore, when the radius of curvature of the arc-shaped ply decreases from the inside to the outside, a filling material is provided between the arc-shaped ply.

[0015] Furthermore, the curvature centers of all the said arc-shaped plies are located on the geometric center symmetry line of the rounded corner area.

[0016] A composite material structure includes a flat region and the aforementioned rounded corner region structure, wherein the arc-shaped ply at the rounded corner region position and the flat ply of the adjacent flat region are smoothly connected.

[0017] Furthermore, the locations of the smooth transition connections are staggered sequentially along the ply thickness direction.

[0018] Beneficial effects:

[0019] The composite material fillet region structure disclosed in this invention features a uniform radius of curvature from the inner to the outer surface. This design prevents the radius of curvature of the inner surface of the fillet region from becoming too small, which could lead to excessive interlaminar tensile stress. It also results in a more uniform stress distribution within the fillet region, thereby reducing interlaminar stress. Simultaneously, this design increases the bending stiffness and instability resistance of the fillet region. Furthermore, this uniform curvature design greatly facilitates localized maintenance of the fillet region, avoiding the mismatch in curvature of the bonding surface between the damaged component and the reinforcing component caused by differences in the radii of curvature between the inner and outer surfaces.

[0020] The design method of making the outer surface curvature radius of the rounded corner area smaller than the inner surface curvature radius further improves the bending stiffness and instability resistance of the rounded corner area, while meeting the design requirement of making the outer surface curvature radius of the rounded corner area as small as possible in specific scenarios.

[0021] The rounded corner structure of the composite material can significantly reduce the interlaminar stress in the rounded corner area, thereby improving the efficiency of structural design. The rounded corner structure of this invention can also improve the bending stiffness of the structure in the rounded corner area, thereby reducing the large deformation of the flange area caused by the typically weak stiffness of the rounded corner area. This invention can effectively improve the large stress gradient caused by traditional design configurations, thus not only helping to reduce the interlaminar stress in the rounded corner area under external loads, but also helping to reduce the influence of residual stress formed during the curing process of the rounded corner area. The equal curvature design features of the inner and outer surfaces of the rounded corner structure of this invention can greatly facilitate local repair or reinforcement of the rounded corner area during structural operation. For example, local repair or reinforcement can be achieved by directly bonding and adhesiveting L-shaped standard parts with the same curvature to the inner or outer surface of the rounded corner area. Due to the addition of an extra adhesive layer in the rounded corner area, this invention can improve the impact resistance of the rounded corner area, and if the added adhesive layer is thermoplastic, it is also beneficial for repairing damage to the rounded corner area during operation. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the equal curvature design configuration of a composite material rounded corner area structure according to the present invention;

[0024] Figure 2 This is a schematic diagram of the design of a composite material rounded corner area with equal curvature and thickness according to the present invention.

[0025] Figure 3 This is a schematic diagram of the design of a rounded corner area structure of composite material with a small external radius of curvature and a large internal radius of curvature according to the present invention;

[0026] Figure 4 This is a schematic diagram of the layup between adjacent ply units and filler material layers in a composite material rounded corner area structure according to the present invention;

[0027] Figure 5 This is a schematic diagram of a composite material rounded corner structure of the present invention, in which the gaps between different ply units of the rounded corner are filled by film stacking.

[0028] Figure 6 This is a comparative schematic diagram of three rounded corner configuration design examples of a composite material rounded corner structure according to the present invention. Detailed Implementation

[0029] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0030] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0031] Example 1

[0032] As shown in the figure Figure 1 This is a schematic diagram of the equal curvature design configuration of a composite material rounded corner area structure according to the present invention. Figure 2 This is a schematic diagram of a composite material fillet region design with equal curvature and thickness according to the present invention. Figure 3 This is a schematic diagram of the design of a rounded corner area structure of composite materials according to the present invention, featuring a small radius of curvature on the outside and a large radius of curvature on the inside. Figure 4 This is a schematic diagram of the layup between adjacent ply units and the filler material layer in a composite material rounded corner area structure according to the present invention. Figure 5 This is a schematic diagram illustrating the composite material rounded corner structure of the present invention, in which film laminations fill the gaps between different layup units in the rounded corner area. Figure 6 This is a comparative schematic diagram of three rounded corner configuration design examples of a composite material rounded corner structure according to the present invention.

[0033] A composite material rounded corner structure, wherein the rounded corner area includes multiple arc-shaped plies from the inner side to the outer side of the rounded corner, the arc-shaped plies are arranged in sequence, and the radius of curvature of the arc-shaped plies is the same or the radius of curvature of the arc-shaped plies decreases from the inside to the outside.

[0034] Furthermore, when the radii of curvature of the arc-shaped plies are the same, the upper and lower surfaces of each arc-shaped ply are concentric circular arcs.

[0035] Furthermore, a filler material is provided between the arc-shaped plies located in the rounded corner area.

[0036] Furthermore, the arc-shaped ply thickness is the same.

[0037] Furthermore, the filler material includes resin, fiber material, and metal material.

[0038] Furthermore, the curvature centers of all the said arc-shaped plies are located on the geometric center symmetry line of the rounded corner area.

[0039] Furthermore, when the radius of curvature of the arc-shaped ply decreases from the inside to the outside, a filling material is provided between the arc-shaped ply.

[0040] Furthermore, the curvature centers of all the said arc-shaped plies are located on the geometric center symmetry line of the rounded corner area.

[0041] A composite material structure includes a flat region and the aforementioned rounded corner region structure, wherein the arc-shaped ply at the rounded corner region position and the flat ply of the adjacent flat region are smoothly connected.

[0042] Furthermore, the locations of the smooth transition connections are staggered sequentially along the ply thickness direction.

[0043] Example 2

[0044] The rounded corner structure of this invention can adopt the following technical solution:

[0045] In the rounded corner region, each arc-shaped ply unit uses the same radius of curvature from the inner surface to the outer surface. For example... Figure 1 As shown, from the inside out, all arc-shaped ply units use the same radius of curvature R.

[0046] The straight sections on both sides of the rounded corner area are arranged in close proximity and stacked from the inside to the outside of each ply unit.

[0047] In the rounded corner section, the upper and lower surfaces of each ply unit are concentric arcs with the same thickness as the straight section.

[0048] In the rounded corner area, infill material is provided between different ply units. When the ply unit thickness is the same, the infill material is arranged at equal intervals.

[0049] The filler material can be made of different materials depending on the performance requirements such as local strength, stiffness, or resistance to instability. It can be a film or resin, a fiber material, or even a metal material.

[0050] In the rounded corner region, all arc-shaped ply units and their adjacent straight ply portions transition smoothly, meaning the tangent slope is continuous at the transition or critical point. All ply units are staggered along the thickness direction, transitioning from an infinite radius of curvature in the straight segments to a finite radius of curvature in the arc segments. This differs from traditional rounded corner designs where all ply units transition from the straight segments to the arc segments at a single point. This staggered transition along the thickness direction can, to some extent, delay or reduce interlaminar stress.

[0051] The curvature centers of all layers in the rounded corner area are located on the geometric center symmetry line of the rounded corner area, and are evenly spaced from the inside to the outside along this symmetry line. Thus, the rounded corner area is a parallelogram of uniform thickness in a certain sense, such as... Figure 2 The CDD'C' shown.

[0052] For a structure or a combination of a single ply unit and its corresponding infill material with a ply with rounded corners of equal curvature, if the thickness of its straight section is t0 and the thickness of its rounded section is t... c If the included angle between the two straight segments in the rounded corner area is β, then...

[0053] t c =t0 / sin(β / 2) (1)

[0054] The thickness of the filling material is t. c -t0.

[0055] For the aforementioned rounded corner region with uniform curvature and thickness, the maximum interlayer tensile stress σ under the action of the open-type distributed bending moment m is... r It can be obtained from the balance relationship, and is expressed as:

[0056]

[0057] In the formula, R, β, and t represent the radius of curvature of the fillet region, the included angle between its two straight sections, and its thickness, respectively. This formula corresponds to the formula for calculating the maximum interlayer tensile stress in traditional fillet region design (where the ply arcs are concentric but have different curvatures).

[0058]

[0059] In the above formula, r in and r out These are the radii of curvature of the inner and outer surfaces of the traditional rounded corner design, respectively. Comparing the two formulas shows that the design of this invention significantly reduces the interlaminar tensile stress in the rounded corner area.

[0060] To further improve the stiffness of the fillet area, the above design concept can be further developed into a trumpet-shaped design configuration with a small external radius of curvature and a large internal radius of curvature, such as... Figure 3 As shown in the figure, the internal radius of curvature can be set as large as possible to minimize the interlayer tensile stress in the fillet region under the action of the opening bending moment, while the external radius of curvature, which has little impact, only needs to be smaller than the internal radius of curvature.

[0061] For a rounded corner structure with a small outer radius of curvature and a large inner radius of curvature, if the thickness of its straight section is t0, the included angle is β, the inner surface radius of curvature is R, and the outer surface radius of curvature is r, then the thickness t at the center line of the rounded corner is... c for

[0062]

[0063] according to Figure 3From the external contour configuration CDD'C' of the rounded corner area and equation (4), it can be seen that for the design of a rounded corner area with a small external radius of curvature and a large internal radius of curvature, the radius of curvature of the ply unit decreases linearly from the inside to the outside. The thickness of the filling material will be greater than the thickness of the filling material with equal curvature. According to equation (4), t0, R, and r can be replaced by the thickness of each ply and the surface curvature radius between adjacent plies. First, t is obtained. c Then subtract t0.

[0064] Example 3

[0065] The rounded corner structure of this invention can be implemented using the following scheme:

[0066] Depending on the specific structural type, layers can be sequentially stacked from the inner surface of the rounded corner area to the outer surface of the rounded corner area, or from the outer surface of the rounded corner area to the inner surface of the rounded corner area, using either a female mold or a male mold paving method.

[0067] Each layup unit can be set as a single layer of preimpregnated composite material or multiple layers of preimpregnated composite material, the specific number of which is determined by specific design requirements.

[0068] Filler material is applied between adjacent ply units within the designated rounded corner area. That is, after the previous ply unit is laid, the designed filler material layer is applied on top of it, and then the next ply unit is applied on top of it, and so on, until the last ply unit. Figure 4 A schematic diagram of the layup between adjacent ply units and the filler layer in a funnel-shaped rounded corner area is provided. The layup method for a parallelogram-shaped rounded corner area with equal curvature is similar and can be found by referring to [the diagram]. Figure 1 As shown.

[0069] The filler material layer has an uneven thickness distribution, being thicker in the middle and approaching zero thickness at the edges. To address this, filler material layers of varying widths, such as adhesive films, can be layered to approximate the desired shape of the filler material layer. Figure 5 As shown. Currently, commercially available resin films can be made to a thickness of 0.05 mm, thus meeting the requirements for designing the rounded corner area of ​​this invention even when using very thin layup units.

[0070] The shape of rounded corner areas, including parallelogram designs with equal curvature and trumpet-shaped designs with non-equidistant curvature, can be controlled and achieved by adjusting the width and thickness distribution of the filling material. Figure 4 As shown.

[0071] When the required filler material layer thickness is large, intercalation and film can be used in combination to simplify the manufacturing process to the greatest extent.

[0072] In addition to using thin films of different widths or other materials such as fiber bundles to approximate the shape requirements of the filling material, non-uniform thickness films can also be produced in one go using an extrusion process, which is suitable for mass production.

[0073] Once all the tiling is complete, traditional curing methods can be used, such as autoclave curing.

[0074] In addition to the most basic tiling process mentioned above, the rounded corner design of this invention can also be achieved by using co-bonding liquid molding technology, depending on the specific characteristics of the problem.

[0075] Example 4

[0076] Validity verification:

[0077] To verify the effectiveness of the rounded corner design in this invention, the NASTRA commercial finite element software was used to perform the following analysis: Figure 6 The three examples of rounded corner configurations shown are compared and analyzed. The first is a traditional rounded corner configuration design, which has a small internal radius of curvature and a large external radius of curvature. The second is the equal curvature rounded corner configuration design proposed in this invention. The third is the trumpet-shaped rounded corner configuration design proposed in this invention, which has a large internal radius of curvature and a small external radius of curvature.

[0078] Calculation results show that, under the same open bending load, the constant curvature rounded corner configuration design of this invention (the second configuration) can significantly reduce the maximum interlaminar tensile stress in the rounded corner region compared with the traditional rounded corner configuration design (the first configuration), with a reduction of 42%, which is basically consistent with the 50% calculation result obtained from formulas (2) and (3). The third trumpet-shaped rounded corner configuration design can also significantly reduce the maximum interlaminar stress of the traditional rounded corner design by up to 28%.

[0079] This invention not only effectively reduces the maximum interlaminar tensile stress in the rounded corner area, but also, compared to the traditional stress distribution pattern in the rounded corner area, it makes the interlaminar stress change significantly and gradually, and avoids the formation of large-scale, continuously distributed interlaminar stress zones. Clearly, this not only helps reduce interlaminar failure caused by external loads but also reduces residual stress and wrinkles during the manufacturing process.

[0080] Furthermore, the calculation results also show that, compared with the traditional rounded corner design, the equal curvature configuration and the flared rounded corner design of the present invention can improve the bending stiffness of the rounded corner by 11.3% and 12.2%, respectively.

[0081] The embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A composite material rounded corner structure, characterized in that, The rounded corner area includes multiple arc-shaped plies from the inner to the outer side of the rounded corner. The arc-shaped plies are stacked sequentially. The arc-shaped plies have the same radius of curvature or the radius of curvature of the arc-shaped plies decreases from the inside to the outside. When the arc-shaped plies have the same radius of curvature, the upper and lower surfaces of each arc-shaped ply are concentric arcs.

2. The composite material rounded corner structure according to claim 1, characterized in that, A filler material is provided between the arc-shaped plies located in the rounded corner area.

3. The composite material rounded corner structure according to claim 2, characterized in that, The arc-shaped plies have the same thickness.

4. The composite material rounded corner structure according to claim 3, characterized in that, The filler material includes resin, fiber material, and metal material.

5. The composite material rounded corner structure according to claim 4, characterized in that, The curvature centers of all the aforementioned arc-shaped plies are located on the geometric center symmetry line of the rounded corner region.

6. A composite material structure, characterized in that, The composite material structure includes a flat region and a rounded corner region structure as described in any one of claims 1-5, wherein the arc-shaped ply at the rounded corner region position and the flat ply of the adjacent flat region are connected by a smooth transition.

7. A composite material structure according to claim 6, characterized in that, The locations of the smooth transition connections are staggered sequentially along the ply thickness direction.

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