Composite embedded joint structure

Abstract

The utility model provides a kind of composite material embedded connection structure, including outer sleeve, it is embedded in the corresponding mounting hole place of composite material matrix, inner thread sleeve, coaxial sleeve is set in outer sleeve, its inner wall is equipped with thread structure, for with external threaded connecting piece connection, elastic buffer section, connect outer sleeve with inner thread sleeve, for absorbing axial elastic deformation. Solve the problem that composite material is connected and is easily cracked due to thermal expansion mismatch, low thickness direction strength and easy delamination.

Description

Technical Field

[0001] This utility model relates to the field of composite material processing technology, and in particular to a composite material embedded connection structure. Background Technology

[0002] In fields such as new energy vehicles, intelligent robots, and aerospace, fiber-reinforced composite materials are widely used in the manufacture of structural components, such as battery housings, sensor brackets, or robotic arm shells, due to their advantages such as high specific strength, low density, and corrosion resistance. However, the coefficient of thermal expansion of these materials is usually much lower than that of metal fasteners. Under temperature variations, significant thermal stress is generated between the screw and the matrix, which can easily lead to cracking or delamination around the mounting holes. At the same time, composite materials have low strength in the thickness direction, and traditional through bolt connections are prone to interlaminar delamination during pre-tightening.

[0003] In existing technologies, pre-embedded metal inserts are often used to achieve threaded connections. However, the inserts and the substrate often rely on adhesive bonding or simple interference fits, resulting in limited interfacial bonding strength. Under vibration or thermal cycling conditions, they are prone to axial dislodgement or rotational loosening. Some solutions introduce wire thread inserts or press-fit nuts, but these require penetration into the substrate or the use of specialized equipment, making them unsuitable for blind hole or closed cavity structures, and difficult to reliably install in non-metallic substrates.

[0004] Therefore, there is an urgent need for an embedded connection structure that can adapt to the properties of composite materials with low thermal expansion coefficients, which can effectively buffer differences in thermal deformation and provide reliable resistance to pull-out and delamination. Utility Model Content The main objective of this invention is to provide a composite material embedded connection structure that solves the problems of easy cracking due to thermal expansion mismatch, low strength in the thickness direction, and easy delamination when connecting composite materials.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is: a composite material embedded connection structure, including an outer sleeve, which is embedded in the composite material matrix at the corresponding mounting hole; An internal threaded sleeve is coaxially fitted inside an outer sleeve, and its inner wall has a threaded structure for connecting with external threaded fasteners. The elastic buffer section connects the outer sleeve and the inner threaded sleeve, and is used to absorb axial elastic deformation.

[0006] In the preferred embodiment, the elastic buffer section is a corrugated tubular structure, and its axial interface has a continuous periodic undulating waveform profile. The upper end of the elastic buffer section is integrally connected to the top inner edge of the outer sleeve, and the lower end is integrally connected to the bottom outer edge of the internal thread sleeve.

[0007] In the preferred embodiment, a first convex ring is provided on the inner edge of the top end of the outer sleeve; The first convex ring extends radially inward, and its inner diameter is larger than the minor diameter of the internal thread of the internal threaded sleeve, but smaller than the outer diameter of the internal threaded sleeve.

[0008] In a preferred embodiment, the inner wall of the outer sleeve is provided with a second convex ring extending radially inward at a predetermined distance above the bottom end; The bottom end of the internal threaded sleeve is provided with a third convex ring extending radially outward; The second and third convex rings are axially opposite each other to limit the axial buffer stroke of the elastic buffer section.

[0009] In the preferred embodiment, the outer wall of the outer sleeve is provided with at least one annular groove to accommodate the infiltrated composite matrix, which, after curing, forms a mechanical anchoring structure.

[0010] In the preferred embodiment, multiple radially extending anchor claws are evenly provided on the outer circumferential side of the bottom end of the outer sleeve; The anchor claws extend upwards in a cantilever shape from the bottom edge of the outer sleeve, and are used to embed between adjacent layers of the composite matrix during installation.

[0011] In the preferred embodiment, the total axial height of the outer sleeve is set to span at least two adjacent layups in the composite matrix.

[0012] In a preferred embodiment, a reinforcing ring is coaxially fitted around the outer periphery of the outer sleeve between two adjacent plies at the height of the uppermost surface of the composite matrix, in order to reduce stress concentration at the ply mounting holes of the composite matrix.

[0013] In the preferred embodiment, the top end face of the outer sleeve is flush with the surface of the composite matrix after installation.

[0014] This invention provides a composite material embedded connection structure that absorbs the thermal deformation difference between the composite matrix and the metal fastener through an elastic buffer section. When the ambient temperature changes, the axial elastic deformation of the bellows can offset the displacement caused by the difference in their thermal expansion coefficients, preventing thermal stress from acting directly on the composite material mounting hole wall and significantly reducing the risk of peri-hole cracking. Under vibration conditions, the bellows can also dissipate dynamic load energy, reduce stress amplitude, and extend the structural life. Its wall thickness and waveform parameters are optimized to ensure that it maintains elasticity under rated preload, avoiding plastic failure.

[0015] The structure's multiple anchoring design enhances its pull-out and torsional resistance. The annular grooves on the outer wall of the outer sleeve are filled with resin during composite curing, forming mechanical barbs that strengthen resistance to axial pull-out forces. The radial anchors at the bottom employ a cantilever design, allowing them to flexibly bend and embed between adjacent layers. This interlayer interlocking disperses axial tensile forces, reducing the risk of delamination, while the circumferentially distributed anchors generate torsional resistance torque, suppressing circumferential loosening of threaded connections. The outer sleeve spans the height of at least two layers, further transferring loads to deeper fibers and preventing stress concentration.

[0016] To address the weak interlaminar strength of composite materials, anti-delamination reinforcement measures were implemented at key locations. The outer sleeve covers multiple plies, distributing the anchoring force. A reinforcing ring, made of a high-modulus material, was added to the uppermost ply area. By increasing the local stiffness around the hole, it effectively suppressed surface delamination caused by bolt preload, while also preventing the introduction of additional thermal mismatch issues.

[0017] This design also considers assembly applicability and technological advantages. The top of the outer sleeve is flush with the substrate surface, avoiding interference with sealing or assembly of adjacent components, adapting to compact space requirements, and reducing dead zones for liquid accumulation and the risk of external impact. The pre-embedding process during the composite material layup stage allows the insert and substrate to form an integrated bond during curing, avoiding damage to the fibers during subsequent machining and ensuring the integrity of the substrate structure. The metallurgical bonding of the bellows with the outer sleeve and internal threaded sleeve eliminates the risk of adhesive aging and ensures interface stability under thermal cycling conditions. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a partial structural diagram of the composite material matrix after curing. Figure 2 This is a cross-sectional structural diagram of the embedded part after the composite matrix of this utility model has been cured; Figure 3 This is a cross-sectional view of the insert of this utility model; Figure 4 This is a disassembled structural diagram of each layer of the composite matrix and the inserts of this utility model; Figure 5 This is a disassembled structural diagram of the embedded component of this utility model.

[0019] In the figure: composite material matrix 1; mounting hole 101; outer sleeve 2; first convex ring 201; second convex ring 202; annular groove 203; anchor claw 204; internal threaded sleeve 3; third convex ring 301; elastic buffer section 4; reinforcing ring 5. Detailed Implementation

[0020] Example 1 like Figure 1-5 As shown, a composite material embedded connection structure includes an outer sleeve 2, which is embedded in the composite material matrix 1 at the corresponding mounting hole 101. The internal threaded sleeve 3 is coaxially sleeved inside the outer sleeve 2, and its inner wall is provided with a threaded structure for connection with external threaded connectors. The elastic buffer section 4 connects the outer sleeve 2 and the inner threaded sleeve 3, and is used to absorb axial elastic deformation.

[0021] This application addresses the problem of thermal stress damage caused by the difference in thermal expansion coefficients between fiber-reinforced composite materials such as carbon fiber, epoxy resin, glass fiber, and nylon and metal fasteners by embedding the connecting structure during the composite material manufacturing stage, while also enhancing its anti-delamination ability in the thickness direction.

[0022] Intervention is required during the composite material layup manufacturing stage. First, prepreg or dry fiber is laid layer by layer according to the designed thickness. When stacked to the predetermined position, the insert is integrally placed at the corresponding mounting point. Then, mounting holes 101, matching the outer diameter of the outer sleeve 2, are machined at the corresponding locations of the subsequent prepreg or dry fiber layers. The layup continues until the required thickness of the composite material is achieved, and then the layup is cured in an autoclave. This process allows the structural component and the matrix to form an integrated bond during curing, avoiding fiber cutting problems caused by later machining.

[0023] In the preferred embodiment, the elastic buffer section 4 is a corrugated tubular structure, and its axial interface has a continuous periodic undulating waveform profile. The upper end of the elastic buffer section 4 is integrally connected to the top inner edge of the outer sleeve 2, and the lower end is integrally connected to the bottom outer edge of the internal thread sleeve 3.

[0024] The corrugated pipe structure of the elastic buffer section 4 is the core solution to the thermal stress problem. Its waveform profile achieves axial elastic deformation capability through a periodic undulating structure. When the ambient temperature changes, the coefficient of thermal expansion of metal fasteners such as screws is significantly higher than that of the composite matrix 1. The axial expansion and contraction of the corrugated pipe can absorb the displacement difference caused by the temperature difference between the two, avoid stress being directly transmitted to the wall of the composite mounting hole, and suppress the risk of cracking.

[0025] Under vibration conditions, the elastic deformation of the bellows can dissipate some of the dynamic load energy and reduce the amplitude of alternating stress. The bellows wall thickness and waveform amplitude are designed according to actual working conditions and optimized by finite element analysis to ensure linear elastic deformation under rated preload and avoid plastic failure.

[0026] The upper and lower ends of the corrugated pipe are respectively welded to the inner edge of the top of the outer sleeve 2 and the outer edge of the bottom of the inner threaded sleeve 3 to achieve metallurgical bonding, eliminating the risk of adhesive aging and maintaining the stability of interface strength under thermal cycling conditions; the metallurgical bonding with the components at both ends provides a uniform stress transmission path and avoids local stress concentration.

[0027] In the preferred embodiment, a first protruding ring 201 is provided on the inner edge of the top end of the outer sleeve 2; The first convex ring 201 extends radially inward, and its inner diameter is larger than the minor diameter of the internal thread of the internal thread sleeve 3 and smaller than the outer diameter of the internal thread sleeve 3.

[0028] In a preferred embodiment, the inner wall of the outer sleeve 2 is provided with a second convex ring 202 extending radially inward at a predetermined distance above the bottom end; The bottom end of the internal threaded sleeve 3 is provided with a third convex ring 301 that extends radially outward; The second convex ring 202 and the third convex ring 301 are axially opposite each other and are used to limit the axial buffer stroke of the elastic buffer section 4.

[0029] The first convex ring 201, the second convex ring 202, and the third convex ring 301 together limit the stroke of the internal threaded sleeve 3 relative to the outer sleeve 2. The first convex ring 201 prevents the internal threaded sleeve 3 from dislodging from the outer sleeve 2 without affecting the screwing in of metal fasteners such as screws. When the thermal deformation exceeds the elastic limit of the bellows, the convex rings form a rigid stop, preventing the bellows from being crushed or overstretched and ensuring structural integrity.

[0030] In the preferred embodiment, the outer wall of the outer sleeve 2 is provided with at least one annular groove 203 to accommodate the infiltrated composite matrix 1 to form a mechanical anchoring structure after curing.

[0031] In the preferred embodiment, a plurality of radially extending anchor claws 204 are uniformly provided on the outer circumferential side of the bottom end of the outer sleeve 2; Anchor claw 204 extends upward in a cantilever shape from the bottom edge of outer sleeve 2, and is used to embed between adjacent plies of composite matrix 1 during installation.

[0032] The annular groove 203 is filled by the flow of the substrate during the curing of the composite material, forming a barbed mechanical lock. After curing, the composite material in the groove forms local protrusions, which resist axial pull-out force. The groove edge adopts a rounded transition to avoid stress concentration that could lead to microcracks in the matrix.

[0033] The radial anchor 204 adopts a cantilever design, allowing it to be flexibly bent and embedded between adjacent layers during pre-embedding. The circumferential distribution of the anchor 204 generates shear resistance moment between layers, resisting the circumferential torsional load of the threaded connection; at the same time, its interlayer interlocking structure disperses the axial tensile force to multiple fiber layers, significantly reducing the risk of interlayer delamination.

[0034] In a preferred embodiment, the total axial height of the outer sleeve 2 is set to span at least two adjacent layups in the composite matrix 1.

[0035] The height setting of the outer sleeve 2 ensures that its anchoring force is transferred to the deep fibers, avoiding stress concentration in a single layer.

[0036] In a preferred embodiment, between two adjacent plies at the height of the uppermost surface of the composite matrix 1, a reinforcing ring 5 is coaxially sleeved on the outer periphery of the outer sleeve 2 to reduce stress concentration at the ply mounting holes 101 of the composite matrix 1.

[0037] The reinforcing ring 5 is made of a high-modulus composite material compatible with the matrix, such as carbon fiber, epoxy resin, or titanium alloy, to avoid introducing additional thermal mismatch. It is fitted onto the top layer of the ply and reduces the radial stress peak generated by the bolt preload by increasing the local stiffness of the hole edge, thus inhibiting the initiation of surface delamination.

[0038] In the preferred embodiment, the top end face of the outer sleeve 2 is flush with the surface of the composite matrix 1 after installation.

[0039] The top of the outer sleeve 2 is flush with the surface of the base to ensure assembly compatibility, avoid protrusions interfering with the assembly of the sealing ring or adjacent components, and adapt to various space-sensitive installation occasions; eliminate dead corners for liquid accumulation at steps, improve environmental resistance, and reduce the risk of direct impact from external impacts on protruding structures.

[0040] The above embodiments are merely preferred technical solutions of this utility model and should not be considered as limitations on this utility model. The protection scope of this utility model should be the technical solution described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the protection scope of this utility model.

Claims

1. A composite material embedded connection structure, characterized in that: Includes an outer sleeve (2), which is embedded in the composite matrix (1) at the corresponding mounting hole (101); The inner threaded sleeve (3) is coaxially sleeved inside the outer sleeve (2), and its inner wall is provided with a threaded structure for connecting with the external threaded connector; The elastic buffer section (4) connects the outer sleeve (2) and the inner threaded sleeve (3) to absorb axial elastic deformation.

2. The composite material embedded connection structure according to claim 1, characterized in that: The elastic buffer section (4) is a corrugated tube structure, and its axial interface has a continuous periodic undulating waveform profile. The upper end of the elastic buffer section (4) is integrally connected to the top inner edge of the outer sleeve (2), and the lower end is integrally connected to the bottom outer edge of the inner thread sleeve (3).

3. The composite material embedded connection structure according to claim 2, characterized in that: The top inner edge of the outer sleeve (2) is provided with a first protruding ring (201); The first convex ring (201) extends radially inward, and its inner diameter is greater than the minor diameter of the internal thread of the internal thread sleeve (3) and less than the outer diameter of the internal thread sleeve (3).

4. The composite material embedded connection structure according to claim 3, characterized in that: The inner wall of the outer sleeve (2) is provided with a second convex ring (202) extending radially inward at a predetermined distance above the bottom end; The bottom end of the internal threaded sleeve (3) is provided with a third convex ring (301) extending radially outward. The second convex ring (202) and the third convex ring (301) are axially opposite each other to limit the axial buffer stroke of the elastic buffer section (4).

5. The composite material embedded connection structure according to claim 1, characterized in that: The outer wall of the outer sleeve (2) is provided with at least one annular groove (203) to accommodate the infiltrated composite matrix (1) to form a mechanical anchoring structure after curing.

6. The composite material embedded connection structure according to claim 1, characterized in that: Multiple radially extending anchor claws (204) are evenly provided on the outer circumference of the bottom end of the outer sleeve (2). Anchor claws (204) extend upward in a cantilever shape from the bottom edge of the outer sleeve (2) for embedding between adjacent layers of the composite matrix (1) during installation.

7. The composite material embedded connection structure according to claim 1, characterized in that: The total axial height of the outer sleeve (2) is set to span at least two adjacent layups in the composite matrix (1).

8. The composite material embedded connection structure according to claim 1, characterized in that: in Between two adjacent plies at the height of the uppermost surface of the composite matrix (1), a reinforcing ring (5) is also coaxially fitted on the outer periphery of the outer sleeve (2) to reduce stress concentration at the ply mounting hole (101) of the composite matrix (1).

9. The composite material embedded connection structure according to claim 1, characterized in that: After installation, the top end face of the outer sleeve (2) is flush with the surface of the composite matrix (1).

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