Composite material flange screw hole protection structure

Abstract

The invention discloses a composite material flange screw hole protection structure. The composite material flange screw hole protection structure comprises a first screw hole protection structure or a second screw hole protection structure; the first screw hole protection structure is of a T-shaped structure, the upper portion of the T-shaped structure is of a trapezoidal structure, the lower portion of the T-shaped structure extends into a second mounting hole formed in the bottom face of the flange, and a first mounting hole is formed in the center of the first screw hole protection structure. The trapezoidal structure is connected with the bottom surface of the flange; the bolt penetrates through the first mounting hole; the second screw hole protection structure comprises a T-shaped structure, the upper portion of the T-shaped structure is of a trapezoidal structure, the lower portion of the T-shaped structure extends into a fifth mounting hole formed in the bottom face of the flange, and a sixth mounting hole is formed in the center of the trapezoidal structure. The plate-shaped structure is connected to one side of the trapezoidal structure; the trapezoidal structure and the plate-shaped structure are respectively connected with the bottom surface and the side surface of the flange; and a bolt penetrates through the sixth mounting hole. The bearing capacity and reliability of the composite material structure can be greatly improved, the weakness of the composite material is made up, and the comprehensive mechanical property of the carrier rocket composite material structure can be greatly improved.

Description

Technical Field

[0001] This invention relates to a composite material flange bolt hole protection structure, which can be used in the design of composite material flange structures for launch vehicles and belongs to the field of aerospace structural design technology. Background Technology

[0002] Composite materials possess excellent mechanical properties, with significantly higher specific strength and specific stiffness than metallic materials. They have been widely used in aerospace structures, making outstanding contributions to the lightweighting of aerospace structures. However, the joint strength of composite materials is their weakness. Composite structures often fail at the joints, with the main failure modes being extrusion and shear failure of bolt holes. In addition, composite materials are brittle materials, and compared with ductile metals, their failure exhibits greater dispersion. Summary of the Invention

[0003] The purpose of this invention is to overcome the aforementioned defects and provide a composite material flange bolt hole protection structure, solving the technical problem of damage at the connection points in existing composite material structures. This invention can significantly improve the load-bearing capacity and reliability of composite material structures, compensate for weak points in composite materials, and greatly enhance the overall mechanical properties of composite material structures for launch vehicles.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0005] A composite material flange bolt hole protection structure, comprising: a first structure or a second structure;

[0006] The first structure includes a first bolt hole protection structure; the first bolt hole protection structure is a T-shaped structure, the upper part of the T-shaped structure is a trapezoidal structure with a larger bottom and a smaller top, the lower part of the T-shaped structure extends into the second mounting hole provided on the bottom surface of the composite material flange, and the center of the first bolt hole protection structure has a first mounting hole that penetrates the upper and lower parts of the T-shaped structure; the trapezoidal structure is fixedly connected to the bottom surface of the composite material flange, and the bolt passes through the first mounting hole to realize the connection between the composite material flange and the connection boundary;

[0007] The second structure includes a second bolt hole protection structure; the second bolt hole protection structure includes a T-shaped structure, the upper part of which is a trapezoidal structure with a larger bottom and a smaller top, the lower part of which extends into the fifth mounting hole on the bottom surface of the composite material flange, and the center of the T-shaped structure has a sixth mounting hole that penetrates the upper and lower parts; the second bolt hole protection structure also includes a plate-like structure connected to one side of the trapezoidal structure; the trapezoidal structure is fixedly connected to the bottom surface of the composite material flange, and the plate-like structure is connected to the side surface of the composite material flange; after the bolt passes through the sixth mounting hole, the composite material flange is connected to the connection boundary.

[0008] Furthermore, composite material flange bolt hole protection structures are used when the following conditions are met:

[0009] 0.12Dw d < T < 0.24D w d;

[0010] Among them, D w d is the gasket diameter in a traditional composite flange connection structure, d is the thickness of the composite flange, and T is the axial tensile load borne by the composite flange.

[0011] When 0.12D w d < T < 0.18D w d, using the first structure, when 0.18D w d≤T<0.24D w d, adopts the second structure.

[0012] Furthermore, in the first structure, the trapezoidal structure of the first screw hole protection structure is connected to the bottom surface of the composite material flange by fixing bolts;

[0013] In the second structure, the trapezoidal structure is connected to the bottom surface of the composite material flange by fixing bolts, and the side surface of the plate-shaped composite material flange is connected by fixing rivets.

[0014] Furthermore, the materials used for the first and second screw hole protection structures are aluminum alloy, titanium alloy, or steel.

[0015] The fixing rivets are titanium alloy blind rivets.

[0016] Furthermore, the diameters of the first and sixth mounting holes, D1, are D + 0.2 to 0.5 mm.

[0017] The diameters of the second and fifth mounting holes, D2 = D1 + 2mm;

[0018] D is the bolt diameter.

[0019] Furthermore, the diameter D3 of the fixing bolt mounting holes provided on the first and second screw hole protection structures is 3 to 5 mm;

[0020] The diameter of the fixing rivet mounting hole on the second screw hole protection structure is D4 = 4~7mm, and the hole edge distance is 8~10mm.

[0021] Furthermore, in the first and second screw hole protection structures, the width W1 of the trapezoidal structure is 4 × D;

[0022] In the first and second screw hole protection structures, the thickness d1 of the upper part of the trapezoidal structure is 3-8 mm, and the thickness d2 of the lower part is d-0.2 mm, where d is the thickness of the composite material flange; the tangent angle α of the trapezoidal structure is 15-25 degrees; and the length L1 of the trapezoidal structure is 4D+2d1.

[0023] Furthermore, the thickness d1 of the upper part of the trapezoidal structure in the first and second screw hole protection structures is determined as follows:

[0024] If the bolt is used with a washer, then If the bolts are installed directly without using washers, then Where, σ s T is the yield strength of the gasket material, T is the axial tensile load borne by the composite flange, and D is the bolt diameter.

[0025] Furthermore, the bottom and side connections of the composite material flange are provided with a first fillet, and the first bolt hole protection structure is provided with a second fillet at the corresponding position that connects with the first fillet;

[0026] The second screw hole protection structure has a third fillet at the connection between the trapezoidal structure and the plate structure. The radius of the third fillet is the maximum value under the premise of satisfying the bolt installation space.

[0027] Furthermore, the height of the plate-like structure in the second screw hole protection structure is W2 = d1 + r2 + 2D4 + B2;

[0028] Wherein, d1 is the thickness of the upper part of the trapezoidal structure, r2 is the radius of the third fillet at the connection between the trapezoidal structure and the plate structure of the second screw hole protection structure, D4 ​​is the diameter of the fixing rivet mounting hole, and B2 is the edge distance of the fixing rivet mounting hole.

[0029] Compared with the prior art, the present invention has at least one of the following advantages:

[0030] (1) The invention provides a composite material flange bolt hole protection structure, which increases the structural load-bearing capacity by more than 30% with very little weight increase (generally, the weight increase at each connecting bolt position does not exceed 50g);

[0031] (2) This invention provides whether to use a screw hole protection structure and the selection criteria for the screw hole protection structure, which can meet the needs of various application scenarios.

[0032] (3) This invention provides two specific parameter design methods for screw hole protection structures. The screw hole protection structure with these parameters has the best comprehensive performance in terms of strength and reliability. Attached Figure Description

[0033] Figure 1 This is a structural diagram of a traditional composite material flange connection according to the present invention;

[0034] Figure 2 A schematic diagram showing the dimensions of traditional flanges and gaskets;

[0035] Figure 3 Diagram showing typical failure modes of bolt holes in composite material flanges;

[0036] Figure 4 This is a structural diagram of a composite material flange connection for the first type of protection structure;

[0037] Figure 5 This is a cross-sectional view of the composite material flange connection structure of the first type of protection structure;

[0038] Figure 6 This is a partial view of the composite material flange and the first type of protective structure;

[0039] Figure 7 This is a cross-sectional view of the composite material flange and the first type of protective structure;

[0040] Figure 8 This is a schematic diagram of the dimensions of the first type of protective structure; the upper left is the front view, the upper right is the perspective view, and the lower left is the top view.

[0041] Figure 9 This is a structural diagram of a composite material flange connection for the second type of protection structure;

[0042] Figure 10 This is a schematic diagram of the dimensions of the second type of protective structure, where the left image is a front view and the right image is a side view;

[0043] Figure 11 The results are from a failure test under axial tensile load.

[0044] Figure 12 The results are simulation results of the finite element model under the traditional connection method;

[0045] Figure 13 The results show the comparison between the load-displacement curve and the experimental results;

[0046] Figure 14 The results are from the finite element model simulation when a screw hole protection structure is used. Detailed Implementation

[0047] The features and advantages of the present invention will become clearer and more apparent from the following detailed description.

[0048] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0049] A composite material flange bolt hole protection structure was designed, which significantly improves the load-bearing capacity and reliability of composite material structures, compensates for the weak points of composite materials, and can greatly improve the comprehensive mechanical properties of launch vehicle composite material structures.

[0050] This invention proposes a composite material flange bolt hole protection structure, which uses ductile metal to protect the bolt holes, significantly improving the load-bearing capacity.

[0051] A composite material flange bolt hole protection structure is proposed to strengthen the weak points of the composite material flange structure of the launch vehicle, thereby improving the overall load-bearing capacity and reliability of the structure.

[0052] Traditional composite material flange connection structures, such as Figure 1 As shown, it consists of a composite material flange 1, a connecting boundary 2, bolts 3, gaskets 4, and nuts 5. Dimensions are as follows. Figure 2 D w d is the gasket diameter, and d is the flange thickness.

[0053] Flange connection structures primarily bear axial tensile loads T. Under axial tensile load T, composite flange bolt holes are prone to shear failure at relatively low loads. Typical failure modes of composite flange bolt holes are as follows: Figure 3 As shown.

[0054] For composite flange connection structures, first, determine whether the composite bolt holes require a protective structure. If the tensile force T meets 0.12D... w d < T < 0.24D w d. In this case, a protective structure is necessary. Based on experimental data, as shown in Table 1, when the screw tension T > 0.12D... w When d, ordinary gaskets cannot meet the strength requirements, so a protective structure should be considered; however, the protective structure has an upper limit on its load-bearing capacity, and it is necessary to ensure that the screw tensile force T < 0.24D. w d.

[0055] Table 1. Destructive test data of traditional circular gaskets

[0056]

[0057] Then, choose the form of the protective structure:

[0058] (1) If the screw tension T satisfies 0.12D w d < T < 0.18D w d, adopts the first type of protection structure.

[0059] The first type of protective structure is as follows Figure 4 As shown, the cross-sectional view is as follows Figure 5 As shown, the connection structure consists of a composite material flange 1, a connection boundary 2, bolts 3, nuts 5, a bolt hole protection structure 12, and fixing screws 6. (See details below.) Figure 6 As shown, the cross-sectional view is as follows Figure 7As shown, the screw hole protection structure 12 is connected to the composite material flange 1 by two fixing screws 6. The fixing screws 6 are 120-degree M3 countersunk screws, and the fixing screws 6 are screwed onto the screw hole protection structure 12.

[0060] The basic dimensions of the composite material flange 1 include flange width W, flange thickness d, and fillet radius r. The diameter of bolt 3 is D.

[0061] The dimensions of the screw hole protection structure 12 are as follows: Figure 8 As shown, the material is aluminum alloy, titanium alloy, or steel. Mounting hole D1 is D+0.2~0.5mm, D2=D1+2mm, D3=3mm. The width is W1, the size of which is related to the bolt diameter D, generally W1=4×D, ensuring that the bolt hole protection structure 12 and the composite material flange 1 are connected at the fillet position. The thickness dimension d1 is 3~8mm, d2=d-0.2mm, d3 is approximately 2mm, the chamfer α=20 degrees, and the fillet r1=r. The method for determining d1 is: (a) If bolt 3 is used with a common round washer 4, then... σ s (a) The yield strength of the gasket material; (b) If a round gasket is not used and bolt 3 is installed directly, then The length is L1, which is generally around 50mm. The method for determining L1 is: L1 = 4D + 2d1.

[0062] (2) If the screw tension T satisfies 0.18D w d < T < 0.24D w d, adopts the second type of protective structure.

[0063] The second type of composite material flange connection structure is as follows: Figure 9 As shown, the connection structure consists of a composite material flange 1, a connection boundary 2, bolts 3, nuts 5, a bolt hole protection structure 13, fixing screws 6, and fixing rivets 14. The bolt hole protection structure 13 is connected to the composite material flange 1 by two fixing screws 6 and three fixing rivets 14. The fixing screws 6 are 120-degree M3 countersunk screws, which are screwed onto the bolt hole protection structure 13. The fixing rivets 14 are titanium alloy blind rivets.

[0064] The dimensions of the screw hole protection structure 13 are as follows: Figure 10 As shown, the material is aluminum alloy, titanium alloy, or steel. The method for determining D1, D2, D3, W1, d1, and L1 is the same as that for the first type of screw hole protection structure. The fillet radius r2 should be as large as possible while satisfying the installation space of bolt 3. The connecting hole diameter D4 of fixing rivet 14 is 4mm, the hole edge distance B1 ≥ 8mm, B2 is approximately 10mm, W2 = d1 + r2 + 2D4 + B2, d3 is taken as 2 / 3d1 ~ d1, and r3 = B2.

[0065] Example:

[0066] Example 1

[0067] The material is epoxy-based T700 carbon fiber reinforced composite material. The flange thickness is d=6mm and r=2mm. The flange adopts a quasi-isotropic layup [(45 / -45 / 0 / 90)3(45 / -45 / 90)]s, with a unidirectional tape thickness of 0.2mm and a total of 30 layers.

[0068] Bolt D = 8mm, using traditional connection method, round washer diameter D w =16mm, destructive test was carried out under axial tensile load, such as Figure 11 As shown, the test specimen consists of 3 connecting bolts, with a failure load of 36.7 kN and a failure load of 12.2 kN at each bolt location.

[0069] For this destructive test, a finite element model was established for simulation analysis. The model is as follows: Figure 12 As shown, the load-displacement curves and experimental comparisons are... Figure 13 As shown, the finite element calculation results for the failure load are close to the maximum load of the test results. The maximum load T of the progressive damage calculation results for test piece 2# is 33.85kN, while the maximum load T of the test is 36.7kN. The finite element calculation error is 7.7%, which shows high accuracy.

[0070] A screw-hole protection structure is adopted, and the material is titanium alloy with thicknesses d1 of 3.5mm, 5.5mm, and 7.5mm respectively. A finite element model is established for analysis, such as... Figure 14 As shown. Calculation results show that: when the thickness of the screw hole protection structure is 3.5mm (weight 30g), the breaking load is 45.44kN, and the percentage increase in load-bearing capacity is 45.44 / 33.85-1 = 34.2%; when the thickness of the screw hole protection structure is 5.5mm (weight 47g), the breaking load is 50.72kN, and the percentage increase in load-bearing capacity is 50.72 / 33.85-1 = 49.8%; when the thickness of the screw hole protection structure is 7.5mm (weight 64g), the breaking load is 56.81kN, and the percentage increase in load-bearing capacity is 56.81 / 33.85-1 = 67.8%.

[0071] Example 2:

[0072] Example of determining the protective structure form and parameters using the method of this invention: If the tensile force T in the operating condition is 16kN, the bolt diameter D = 8mm, and the washer diameter D... w =16mm, flange thickness d=6mm, then 0.12D w d = 11.52 kN, 0.18D w d = 17.28 kN, based on the judgment condition 0.12D wIf d < T < 0.18Dwd, then the first type of screw hole protection structure is adopted. The key dimensions of the protection structure are determined as follows: width W1 = 4 × D = 32 mm. Considering the case where round washers are not used, the material of the protection structure is titanium alloy, with a yield strength σ... s If the pressure is 800 MPa, then the thickness is... d1 can be taken as 6.5mm. According to the interpolation of the finite element calculation results, the bearing capacity of a single bolt is (50.72+56.81) / 2.0 / 3.0=17.9kN, which is greater than the tensile force T=16kN in the working condition. The strength meets the requirements, and the residual strength coefficient is 17.9 / 16.0=1.12.

[0073] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0074] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A composite material flange bolt hole protection structure, characterized in that, include: The first structure or the second structure; The first structure includes a first screw hole protection structure (12); The first screw hole protection structure (12) is a T-shaped structure. The upper part of the T-shaped structure is a trapezoidal structure with a larger bottom and a smaller top. The lower part of the T-shaped structure extends into the second mounting hole provided on the bottom surface of the composite material flange (1). The center of the first screw hole protection structure (12) is provided with a first mounting hole that penetrates the upper and lower parts of the T-shaped structure. The trapezoidal structure is fixedly connected to the bottom surface of the composite material flange (1). After the bolt (3) passes through the first mounting hole, the composite material flange (1) is connected to the connection boundary (2). The second structure includes a second screw hole protection structure (13); the second screw hole protection structure (13) includes a T-shaped structure, the upper part of which is a trapezoidal structure with a larger bottom and a smaller top, the lower part of which extends into the fifth mounting hole provided on the bottom surface of the composite material flange (1), and the center of the T-shaped structure is provided with a sixth mounting hole that penetrates the upper and lower parts; the second screw hole protection structure (13) also includes a plate-shaped structure connected to one side of the trapezoidal structure; the trapezoidal structure is fixedly connected to the bottom surface of the composite material flange (1), and the plate-shaped structure is connected to the side surface of the composite material flange (1); the bolt (3) passes through the sixth mounting hole to realize the connection between the composite material flange (1) and the connection boundary (2).

2. The composite material flange bolt hole protection structure according to claim 1, characterized in that, Composite material flange bolt hole protection structures are used when the following conditions are met: 0.12D w d<T<0.24D w d; Among them, D w d is the diameter of the gasket (4) in the traditional composite flange connection structure, d is the thickness of the composite flange (1), and T is the axial tensile load borne by the composite flange (1). When 0.12D w d < T < 0.18D w d, using the first structure, when 0.18D w d≤T<0.24D w d, adopts the second structure.

3. The composite material flange bolt hole protection structure according to claim 1, characterized in that, In the first structure, the trapezoidal structure of the first screw hole protection structure (12) is connected to the bottom surface of the composite material flange (1) by fixing bolts; In the second structure, the trapezoidal structure is connected to the bottom surface of the composite material flange (1) by fixing bolts, and the side surface of the plate-shaped composite material flange (1) is connected by fixing rivets.

4. The composite material flange bolt hole protection structure according to claim 1, characterized in that, The materials used for the first screw hole protection structure (12) and the second screw hole protection structure (13) are aluminum alloy, titanium alloy or steel; The fixing rivets are titanium alloy blind rivets.

5. The composite material flange bolt hole protection structure according to claim 1, characterized in that, The diameters of the first and sixth mounting holes, D1, are D + 0.2 to 0.5 mm. The diameters of the second and fifth mounting holes, D2 = D1 + 2mm; D is the diameter of bolt (3).

6. The composite material flange bolt hole protection structure according to claim 3, characterized in that, The diameter D3 of the fixing bolt mounting holes provided on the first screw hole protection structure (12) and the second screw hole protection structure (13) is 3 to 5 mm. The diameter of the fixing rivet mounting hole on the second screw hole protection structure (13) is D4 = 4~7mm, and the hole edge distance is 8~10mm.

7. The composite material flange bolt hole protection structure according to claim 5, characterized in that, The width W1 of the trapezoidal structure in the first screw hole protection structure (12) and the second screw hole protection structure (13) is 4×D; In the first screw hole protection structure (12) and the second screw hole protection structure (13), the thickness d1 of the upper part of the trapezoidal structure is 3 to 8 mm, and the thickness d2 of the lower part is d-0.2 mm, where d is the thickness of the composite material flange (1); the tangent angle α of the trapezoidal structure is 15 to 25 degrees; the length L1 of the trapezoidal structure is 4D+2d1.

8. The composite material flange bolt hole protection structure according to claim 1, characterized in that, The thickness d1 of the upper part of the trapezoidal structure in the first screw hole protection structure (12) and the second screw hole protection structure (13) is determined according to the following method: If bolt (3) is used in conjunction with washer (4), then If the gasket (4) is not used and the bolt (3) is installed directly, then Where, σ s T is the yield strength of the gasket material, T is the axial tensile load borne by the composite flange (1), and D is the diameter of the bolt (3).

9. The composite material flange bolt hole protection structure according to claim 1, characterized in that, The bottom and side connections of the composite material flange (1) are provided with a first fillet, and the first screw hole protection structure (12) is provided with a second fillet at the corresponding position that connects with the first fillet; The second screw hole protection structure (13) has a third rounded corner at the connection between the trapezoidal structure and the plate structure. The radius of the third rounded corner is the maximum value under the premise of satisfying the installation space of the bolt (3).

10. The composite material flange bolt hole protection structure according to claim 1, characterized in that, The height of the plate structure in the second screw hole protection structure (13) is W2=d1+r2+2D4+B2; Wherein, d1 is the thickness of the upper part of the trapezoidal structure, r2 is the third fillet radius set at the connection between the trapezoidal structure and the plate structure of the second screw hole protection structure (13), D4 is the diameter of the fixing rivet mounting hole, and B2 is the hole edge distance of the fixing rivet mounting hole.

Images