Method of connecting a composite skin to a truss

Abstract

This invention relates to a method for connecting a composite material skin to a truss; a prefabricated component for connection to the truss is fabricated, the prefabricated component including a connecting part and a locating part, the connecting part including a first connecting segment and a second connecting segment; a fiber-reinforced fabric is cut according to the cross-sectional area of ​​the connecting part and laid on the truss to form a first composite material skin; a second connecting segment passes through the first composite material skin and is fixed to the truss; a fiber-reinforced fabric is cut according to the shape of the locating part and laid on the first composite material skin to form a second composite material skin; a third composite material skin and a fourth composite material skin are laid on the second composite material skin and cured to complete the connection between the composite material skin and the truss; by integrally molding the composite material skin with the prefabricated component, the technical problems of fastening the composite material skin to the truss with screws or rivets, requiring hole machining, resulting in deformation in local areas of the skin, failure of related connections under overload, and skin detachment are solved.

Description

Technical Field

[0001] This invention relates to the field of composite materials, and in particular to a method for connecting a composite material skin to a truss. Background Technology

[0002] Since their advent, composite materials have been favored by various industries for their superior performance and have been widely used in defense, aerospace, information technology, energy engineering, shipbuilding and marine engineering, and other fields. Compared with traditional materials, composite materials have advantages such as light weight, high specific strength, high specific stiffness, good corrosion resistance and fatigue resistance, and designability of layup layers. Composite shipbuilding is one of the most important applications of composite materials in the field of shipbuilding and marine engineering.

[0003] Compared with steel materials, its advantages are: light weight, high specific strength, good impact resistance; good fatigue resistance; non-magnetic, which can achieve good stealth function and effectively avoid various attack equipment; good corrosion resistance, which can extend service life, resist marine organism adhesion, and reduce maintenance; it can be made according to the required performance; the surface can be processed multiple times; in addition, it also has a series of advantages such as excellent acoustic / dielectric properties, high temperature resistance, and shock absorption.

[0004] Composite materials have been applied to fairing components, such as bulbous bows of ships, fairings of underwater vehicles, and fairings and cones of aircraft. In these applications, a combination of truss structures and composite skins is a common approach. Beyond simply reducing the overall structural weight, composite materials are designed to perform various functions, such as heat resistance, ablation resistance, and wave transmission—functions impossible with metallic materials. Therefore, the application of composite materials in this component field is inevitable. However, because the connection performance between the composite material and the truss is relatively weak compared to the strength of the composite material itself and the truss, separation often occurs under heavy loads. Strengthening the connection performance between the composite material and the truss has become a key focus of research.

[0005] The current technical solutions mostly involve molding the composite material skin, fitting and fixing the skin to the truss, performing post-processing and drilling on the skin surface, and mechanically connecting it to the truss. This technical solution calculates the size and density of screws or rivets based on the connection load and has been applied to the wing or cabin skin parts of some small aircraft.

[0006] Existing technical solutions and single mechanical connections, using screws or rivets to fasten composite skins to metal trusses, often require machining numerous holes in a single component. Secondly, during the fitting process between the skin and truss, perfect conformal conformal is often impossible, resulting in localized deformation of the composite material. Although fastened to the truss, significant stress exists, posing a potential hazard during subsequent use. Thirdly, the connection between the composite skin and truss, relying solely on screws, means that the connection strength depends on the shear properties of the composite material at the screw base. Under overload, the actual failure mode is that the composite skin first fails at the screw base, leading to related local connection failures and ultimately skin detachment. Therefore, without changing the connection method, the connection performance between the composite skin and truss cannot be effectively improved.

[0007] Therefore, in order to address the above problems, the present invention urgently needs to provide a method for connecting composite material skin to truss. Summary of the Invention

[0008] The purpose of this invention is to provide a method for connecting composite material skin to a truss. By integrally molding the composite material skin with the prefabricated component, the technical problems of fastening the composite material skin to the truss with screws or rivets, requiring the machining of many holes, causing deformation in local areas of the composite material skin, failure of related local connections under overload, and resulting in the composite material skin falling off are solved.

[0009] The present invention provides a method for connecting a composite material skin to a truss, comprising the following steps:

[0010] S1: Fabricate a prefabricated component for connection with the truss. The prefabricated component includes a connecting part and a steric hindrance part. The connecting part includes a first connecting section and a second connecting section. The second connecting section is provided with threads. The dimensions of the first connecting section and the steric hindrance part are determined according to the compressive strength, total thickness and cross-sectional area of ​​the composite material skin laid on the truss. The thickness of the steric hindrance part, the height of the first connecting section and the total thickness of the composite material skin satisfy the formula 1 / 2h≤h2≤2 / 3h, where h is the total thickness of the composite material skin, h1 is the thickness of the steric hindrance part and h2 is the height of the first connecting section.

[0011] S2: Cut the fiber-reinforced fabric according to the cross-sectional area of ​​the connection part, so that the first perforation through which the connection part can pass is formed on the fiber-reinforced fabric. Lay the cut fiber-reinforced fabric layer by layer on the truss to form the first composite material skin. The thickness of the first composite material skin is equal to the height of the first connection section.

[0012] S3: Pass one end of the connecting part through the first perforation of the first composite material skin, and extend the second connecting section of the connecting part into the truss and screw it into the truss for fastening.

[0013] S4: Cut the fiber-reinforced fabric according to the shape of the steric hindrance, so that a second perforation through which the steric hindrance can pass is formed on the fiber-reinforced fabric. Lay the cut fiber-reinforced fabric layer by layer on the first composite material skin to form a second composite material skin. The thickness of the second composite material skin is the same as the thickness of the steric hindrance.

[0014] S5: Reinforcing fiber and reinforcing fabric are laid layer by layer on the second composite material skin to form the third and fourth composite material skins. The first, second, third, and fourth composite material skins are heated and cured. The first, second, third, and fourth composite material skins are integrally formed with the precast component, completing the connection between the composite material skins and the truss.

[0015] The method for connecting composite material skin to trusses provided by this invention optimizes the connection from a mechanical connection to a hybrid connection structure formed by prefabricated components by adding prefabricated structures between the composite material skin and the truss. This fully utilizes the designability of prefabricated components, improving problems such as weak connection performance between the composite material skin and the truss, easy local detachment of the composite material skin, and breakage of connecting screws, thus enhancing the connection performance between the composite material skin and the truss. Through a modular design concept, parameters such as the thickness of the composite material skin, the size, quantity, spacing, and spatial arrangement of the prefabricated components within the composite material skin can be adjusted according to the actual situation of the truss to obtain the optimal connection performance between the composite material skin and the truss. Structurally, it improves the connection performance between the composite material skin and the truss, and the molding and preparation method has good feasibility and reliability, significantly reducing the molding difficulty and making the structure more suitable for practical applications, thus having broad application prospects.

[0016] Preferably, the load-bearing capacity design of the precast component satisfies the following formula:

[0017] F a = F1+F2+F3;

[0018] Where F1 = σ1S1;

[0019] F2 = σ2(S1 - S2);

[0020] F3 = σ3S2;

[0021] Among them, F a For the load-bearing capacity of the preform, F1 is the load on the upper surface of the steric hindrance, F2 is the load on the lower surface of the steric hindrance, F3 is the load at the bottom of the second connecting section, σ1 is the interlayer bonding strength between the upper surface of the steric hindrance and the third composite material skin, σ2 is the interlayer bonding strength between the first composite material skin, the second composite material skin and the third composite material skin, and σ3 is the tensile / compressive strength of the preform material.

[0022] S1 is the area of ​​the upper surface of the potential resistance part, and S2 is the cross-sectional area of ​​the connection part.

[0023] σ1, σ2 and σ3 are obtained from test data or by consulting relevant materials. σ3 is the tensile or compressive strength of the preform material, which depends on the direction of the load.

[0024] When F2 > F3 and the difference is large, the failure mode of the connection structure is the breakage and detachment of the connection part, resulting in structural failure.

[0025] When F2 < F3 and the difference is large, the failure mode of the connection structure is compression damage of the first composite material skin or damage to the steric hindrance of the preform, resulting in structural failure.

[0026] Therefore, during the design process, attention should be paid to ensuring that F2 and F3 are equal or similar, so as to maximize their synergistic load-bearing capacity and form the optimal solution.

[0027] Preferably, the failure load design of the precast component satisfies the following formula:

[0028] F b =σ3h1=σ2h2;

[0029] Among them, F b This refers to the destructive load on the precast component.

[0030] The design of prefabricated components changes the stress mode of composite skin under load, changing the failure mode from interlaminar shear to compression and bending. This improves the connection performance between the composite skin and the truss. To effectively control the overall structural weight and improve production efficiency, under the premise of a fixed total thickness h of the composite skin and cross-sectional area S2 of the connection, a reasonable prefabricated component structural design is carried out to form the optimal solution, and experimental verification is conducted to maximize the performance of the overall connection structure.

[0031] Preferably, in step S1, the preform is pretreated by at least one of acid-alkali treatment, sandblasting, surface anodizing, or spraying a surface treatment agent. The preform treatment method is tested and verified, and the preferred method is one that matches the selected composite material system.

[0032] Preferably, after laying the third composite material skin in step S5, the first composite material skin, the second composite material skin, the third composite material skin and the preform are needle-punched Z-direction reinforced. 2.5D needle-punched stitch reinforcement can be used, which helps to improve the overall mechanical properties and shear resistance of the area. Then, the fourth composite material skin is laid. The selection of the fourth composite material skin can be selected according to the actual working conditions.

[0033] Preferably, the shape of the resistive part is one of dot matrix, cross, or straight, and the shape and size of the resistive part can be adjusted according to the structure of the truss.

[0034] Preferably, the fiber-reinforced fabric is at least one of unidirectional fabric, checkered fabric, or tetraaxial fabric.

[0035] Preferably, the fiber-reinforced fabric is made of at least one of carbon fiber, glass fiber, quartz fiber or aramid fiber. This invention can also be applied to prepreg molding processes.

[0036] Preferably, the truss is a metal structure or a metal truss with a core material in the middle, and the core material is a rigid and lightweight material; more preferably, the core material is at least one of glass microsphere floating material, balsa wood, polyvinyl chloride foam, NOMEX paper honeycomb, rigid polyurethane foam, polymethacrylamide or rubber.

[0037] The present invention also provides a composite material obtained based on the method for connecting the composite material skin and the truss described in any one of the above-mentioned methods.

[0038] The composite material for connecting the composite material skin and the truss in this invention differs from the typical mechanical connection structure of composite material skin and truss. It is composed of composite material skin, prefabricated parts, and truss. The prefabricated parts are limited by a positional resistance part and fastened to the truss by a connecting screw part. At the same time, during the molding process, the connection performance of the composite material skin and truss connection structure is comprehensively improved by improving the interface performance between the prefabricated parts and the composite material skin.

[0039] The connection structure and method for connecting composite material skin and truss provided by this invention have the following advantages compared with the prior art:

[0040] 1. The method for connecting composite material skin and truss provided by this invention optimizes the connection between the composite material skin and truss from a mechanical connection to a hybrid connection structure formed by prefabricated components by adding prefabricated components between the composite material skin and truss. This fully utilizes the designability of prefabricated components, improving problems such as weak connection performance between the composite material skin and truss, easy local detachment of the composite material skin, and breakage of connecting screws, thereby improving the connection performance between the composite material skin and truss. Through the modular design concept, parameters such as the thickness of the composite material skin, the size, quantity, spacing, and spatial arrangement of the prefabricated components inside the composite material skin can be adjusted according to the actual situation of the truss to obtain the best connection performance between the composite material skin and truss.

[0041] 2. The method for connecting composite material skin and truss provided by the present invention improves the connection performance between composite material skin and truss in terms of structure. The molding and preparation method has good feasibility and reliability, and the molding difficulty is significantly reduced, making the structure more in line with practical applications and having broad application prospects. Attached Figure Description

[0042] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram (sectional view) of the connection structure between the composite material and the truss described in this invention.

[0044] Figure 2 This is a schematic diagram of the connection structure between the prefabricated component and the truss described in this invention (without the first composite material skin).

[0045] Figure 3 This is a schematic diagram (sectional view) of the dot matrix prefabricated structure described in this invention.

[0046] Figure 4 This is a dimensional diagram (sectional view) of the dot matrix prefabricated component described in the embodiments of the present invention.

[0047] Figure 5 This is a dimensional diagram (sectional view) of the composite material skin and truss in the embodiments of the present invention.

[0048] Explanation of reference numerals in the attached figures:

[0049] 1. Truss; 2. Precast component; 21. Connecting part; 211. First connecting section; 212. Second connecting section; 22. Holsteric part; 3. First composite material skin; 4. Second composite material skin; 5. Third composite material skin; 6. Fourth composite material skin. Detailed Implementation

[0050] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] This embodiment provides a method for connecting a composite material skin to a truss, including the following steps:

[0052] S1: As Figure 2 , Figure 3 , Figure 4 , Figure 5As shown, a prefabricated component 2 for connection with truss 1 is fabricated. The prefabricated component 2 includes a connecting part 21 and a steric hindrance part 22. The connecting part 21 includes a first connecting section 211 and a second connecting section 212. The second connecting section 212 is threaded. The dimensions of the first connecting section 211 and the steric hindrance part 22 are determined based on the compressive strength, total thickness, and cross-sectional area of ​​the composite material skin laid on truss 1. The dimensions of the prefabricated component 2 are designed to satisfy the following formula:

[0053] F a = F1+F2+F3;

[0054] F1=σ1S1;

[0055] F2 = σ2(S1 - S2);

[0056] F3 = σ3S2;

[0057] F b =σ3h1=σ2h2;

[0058] 1 / 2h ≤ h2 ≤ 2 / 3h;

[0059] Among them, F a For the load-bearing capacity of precast component 2, F1 is the load on the upper surface of the steric hindrance part 22, F2 is the load on the lower surface of the steric hindrance part 22, and F3 is the load at the bottom of the second connecting section 212. b The destructive load of precast component 2;

[0060] σ1 is the interlayer bonding strength between the upper surface of the steric hindrance part 22 and the third composite material skin 5, σ2 is the interlayer bonding strength between the first composite material skin 3, the second composite material skin 4 and the third composite material skin 5, and σ3 is the tensile / compressive strength of the preform 2 material.

[0061] S1 is the area of ​​the upper surface of the potential resistance part 22, and S2 is the cross-sectional area of ​​the connecting part 21;

[0062] h is the total thickness of the composite material skin, h1 is the thickness of the steric part 22, and h2 is the height of the first connecting section 211.

[0063] Precast component 2 is made of steel and adopts a dot-matrix structure. The total thickness h of the composite material skin is 10mm, and the diameter d2 of the connecting part 21 is 6mm, meaning the cross-sectional area S2 of the connecting part 21 is 28.26mm². 2 The bonding strength σ1 between the upper surface of the steric hindrance part 22 and the third composite material skin 5 is 15 MPa. The interlayer bonding strength σ2 between the pre-laid first composite material skin 3, second composite material skin 4 and third composite material skin 5 is 80 MPa. The tensile strength σ3 of the preform 2 is 300 MPa.

[0064] Based on the above formula and known parameters, we know that h1 / h2=σ2 / σ3=80 / 300=0.27.

[0065] When the height h2 of the first connecting section 211 is 1 / 2h, h2 = 5mm, then h1 = 0.27 × h2 = 1.35mm; the height h2 can be appropriately increased, so the height h2 of the first connecting section 211 is 2 / 3h, then h2 = 6.67mm, h1 = 1.8mm, and the thickness of the composite material skin is more reasonable at this time.

[0066] When F2 and F3 are equal or close, the synergistic load-bearing capacity of truss 1 and precast component 2 is maximized, forming the optimal solution, i.e., σ2(S1-S2) = σ3S2. Therefore, the area S1 of the upper surface of the steric hindrance part 22 is 134.24 mm². 2 .

[0067] In summary, the area S1 of the upper surface of the steric portion 22 of the preform 2 is 134.24 mm². 2 The cross-sectional area S2 of the connecting part 21 is 28.26 mm². 2 The thickness h1 of the potential resistor 22 is 1.8 mm, and the height h2 of the first connecting section 211 is 6.67 mm.

[0068] After the precast component is manufactured, the surface of precast component 2 is subjected to sandblasting surface treatment.

[0069] S2: The fiber-reinforced fabric is cut according to the cross-sectional area of ​​the connecting part 21, so that a first perforation through which the connecting part 21 can pass is formed on the fiber-reinforced fabric. The cut fiber-reinforced fabric is laid layer by layer on the truss 1 to form the first composite material skin 3. The thickness of the first composite material skin 3 is equal to the height of the first connecting section 211. The thickness of the first composite material skin 3 is 6.67mm. The truss 1 is cleaned before laying. The areal density of the fiber-reinforced fabric is selected to be 800±50g / m². 2 A single layer of tetraaxial E-glass fiber fabric with a thickness of 0.5 mm;

[0070] S3: Pass one end of the connecting part 21 through the first perforation of the first composite material skin 3, and extend the second connecting section 212 of the connecting part 21 into the truss 1 and screw it into the truss 1 for fastening.

[0071] S4: Cut the fiber-reinforced fabric according to the shape of the steric hindrance 22 so that a second perforation through which the steric hindrance 22 can pass is formed on the fiber-reinforced fabric. Lay the cut fiber-reinforced fabric layer by layer on the first composite material skin 3 to form the second composite material skin 4. The thickness of the second composite material skin 4 is the same as the thickness of the steric hindrance 22. The thickness of the second composite material skin 4 is 1.8mm.

[0072] S5: As Figure 1As shown, reinforcing fiber fabric is laid layer by layer on the second composite material skin 4 to form the third composite material skin 5 and the fourth composite material skin 6. After heating and curing, the first composite material skin 3, the second composite material skin 4, the third composite material skin 5 and the fourth composite material skin 6 are integrally formed with the preform 2, completing the connection between the composite material skin and the truss 1. After the third composite material skin 5 is laid, the first composite material skin 3, the second composite material skin 4, the third composite material skin 5 and the preform 2 are needle-punched in the Z direction at the position of the preform 2. Then the fourth composite material skin 6 is laid. After the composite material skin is laid, a release cloth is laid on the upper surface of the fourth composite material skin 6, and auxiliary materials such as the guide net, resin pipeline, vacuum pipeline, and vacuum bag film are laid in sequence. After the layering is completed, the mold is closed to check the air tightness. After ensuring that the air tightness meets the requirements, the vacuum introduction process is used to form the composite material skin. The resin is a vinyl resin system: the amount is about 5kg. After curing at room temperature for 24 hours, the product is obtained after demolding.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for connecting a composite skin and a truss, characterized in that, comprising the following steps: S1: preparing a prefabricated part (2) for connecting with the truss (1), the prefabricated part (2) comprising a connecting part (21) and a steric hindrance part (22), the connecting part (21) comprising a first connecting section (211) and a second connecting section (212), the second connecting section (212) being provided with a thread, the size of the first connecting section (211) and the steric hindrance part (22) being determined according to the compressive strength, the total thickness of the composite skin laid on the truss (1) and the cross-sectional area of the connecting part (21), wherein the thickness of the steric hindrance part (22), the height of the first connecting section (211) and the total thickness of the composite skin satisfy the formula 1 / 2h≤h2≤2 / 3h, h being the total thickness of the composite skin, h1 being the thickness of the steric hindrance part (22), and h2 being the height of the first connecting section (211); S2: cutting the fiber reinforced fabric according to the cross-sectional area of the connecting part (21) so that a first perforation through which the connecting part (21) can pass is formed on the fiber reinforced fabric, and laying the cut fiber reinforced fabric layer by layer on the truss (1) to form a first composite skin (3), the thickness of the first composite skin (3) being equal to the height of the first connecting section (211); S3: passing one end of the connecting part (21) through the first perforation of the first composite skin (3), and screwing the second connecting section (212) of the connecting part (21) into the truss (1) to fasten it with the truss (1); S4: cutting the fiber reinforced fabric according to the shape of the steric hindrance part (22) so that a second perforation through which the steric hindrance part (22) can pass is formed on the fiber reinforced fabric, and laying the cut fiber reinforced fabric layer by layer on the first composite skin (3) to form a second composite skin (4), the thickness of the second composite skin (4) being the same as the thickness of the steric hindrance part (22); S5: laying the fiber reinforced fabric layer by layer on the second composite skin (4) to form a third composite skin (5) and a fourth composite skin (6), and heating and curing, the first composite skin (3), the second composite skin (4), the third composite skin (5) and the fourth composite skin (6) being integrally formed with the prefabricated part (2), thereby completing the connection of the composite skin and the truss (1); The carrying capacity of the prefabricated part (2) is designed to satisfy the following formula: Wherein, F1=σ1S1; F2=σ2(S1-S2); F3=σ3S2; S1 is the surface area of the steric hindrance part (22), and S2 is the cross-sectional area of the connecting part (21). F a = F1+F2+F3; 2.The method for connecting a composite skin and a truss according to claim 1, characterized in that, the breaking load of the prefabricated part (2) is designed to satisfy the following formula: The prefabricated part (2) is pretreated in step S1, and the pretreatment method is at least one of acid-base treatment, sand blasting, surface anodizing treatment or spraying a surface treatment agent. ​ Wherein, F a F1 is the upper surface load of the resistance part (22), F2 is the lower surface load of the resistance part (22), F3 is the bottom end load of the second connecting section (212), σ1 is the interlayer bonding strength of the upper surface of the resistance part (22) and the third composite skin (5), σ2 is the interlayer bonding strength of the first composite skin (3), the second composite skin (4) and the third composite skin (5), and σ3 is the tensile / compressive strength of the preform (2). ​ ​ ​ F b = σ3h1= σ2h2; where F b is the breaking load of the preform (2).

3. The method of joining a composite skin to a truss of claim 2, wherein, ​ 4. The method of joining a composite skin to a truss of claim 3, wherein, After laying the third composite skin (5) in step S5, the first composite skin (3), the second composite skin (4), the third composite skin (5) and the preform (2) are needled in the Z direction to reinforce, and the fourth composite skin (6) is laid.

5. The method of joining a composite skin to a truss of claim 4, wherein, The shape of the steric hindrance part (22) is one of dot matrix, cross or straight line.

6. The method of joining a composite skin to a truss of claim 5, wherein, The fiber reinforced fabric is at least one of unidirectional fabric, square fabric or four axial fabric.

7. The method of joining a composite skin to a truss of claim 6, wherein, The material of the fiber reinforced fabric is at least one of carbon fiber, glass fiber, quartz fiber or aramid fiber.

8. The method of joining a composite skin to a truss of claim 7, wherein, The truss (1) is a metal structure or a metal truss filled with a core material.

9. A composite material obtained based on the connection method of the composite skin and the truss according to any one of claims 1-8.

Images