Stress dispersion bolt assembly for composite material connection and connection method
By converting radial compressive stress into axial stress through stress-dispersing bolt assemblies, the problem of hole wall damage in composite material connections is solved, achieving efficient and reliable connection protection and monitoring functions.
Patent Information
- Application Number
- CN202511524519.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-24
- Publication Date
- 2026-01-20
AI Technical Summary
Composite material structures have low interlaminar strength and poor shear and extrusion resistance. Traditional bolted connections can easily cause damage to the hole walls, such as delamination, splitting, and crushing. Furthermore, existing improved solutions suffer from problems such as complex installation, high cost, and thermal stress differences.
The stress-dispersing bolt assembly, consisting of a non-metallic stress-dispersing sleeve and a bolt body, converts radial compressive stress into axial stress through a tapered design. It can also be equipped with intelligent monitoring and thermal activation functions, and utilizes the plastic deformation and expansion effect of the sleeve to achieve uniform stress distribution.
It effectively protects the pore walls of composite materials, ensures uniform stress distribution, is easy to install, provides real-time monitoring and highly reliable connections, improves pull-out resistance and sealing performance, and reduces the risk of pore wall damage.
Smart Images
Figure CN121363573A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of mechanical connection, in particular to a bolt assembly for composite material structure connection and a connection method thereof, and is especially suitable for the connection of brittle and low interlaminar strength materials such as carbon fiber reinforced composites. BACKGROUND
[0002] Composite materials are widely used in aerospace, rail transportation and other fields due to their excellent properties such as high specific strength and high specific stiffness. However, the interlaminar strength of composite materials is low, and the shear and extrusion resistance is poor. The traditional bolt connection method has significant problems: when the pre-tightening force is applied, a large radial extrusion stress is generated between the bolt rod and the hole wall, which easily leads to delamination, splitting, crushing and other damages around the hole wall, and seriously weakens the fatigue life and load-carrying capacity of the connected structure.
[0003] In order to alleviate the above problems, various improvement schemes have been proposed in the prior art, but all have obvious defects: Metal bushing scheme: a metal bushing is inserted into the composite material hole to disperse stress, but the matching gap between the bushing and the hole wall and the bushing and the bolt rod is difficult to accurately control, and micro-motion wear is easily generated under vibration load, and the difference in thermal expansion coefficient between metal and composite material will introduce additional thermal stress; High-lock bolt scheme: although it can provide accurate pre-tightening force, the working principle of relying on radial expansion of the rod body to achieve locking will produce more severe extrusion effect on the composite material hole wall, and special installation tools are required, which is high in cost and difficult to maintain; Flexible washer scheme: a flexible washer is arranged between the bolt head and the surface of the composite material, which can only alleviate the surface contact stress and cannot solve the stress concentration problem inside the hole wall.
[0004] Therefore, there is an urgent need for a connection scheme that can effectively protect the composite material hole wall, has uniform stress, is easy to install and has high reliability. SUMMARY
[0005] In order to overcome the above-mentioned defects of the prior art, the present application aims to provide a stress dispersion bolt assembly and method for composite material connection, which converts concentrated radial extrusion stress into dispersed axial stress through a unique sleeve design, and optionally integrates intelligent monitoring, bionic anchoring or thermal activation functions, thereby fundamentally solving the problem of easy damage to the composite material bolt connection hole wall.
[0006] To achieve the above-mentioned purposes, the present application adopts the following technical solutions: A stress dispersion bolt assembly for composite material connection, comprising a bolt body and a stress dispersion sleeve; the bolt body comprises a head and a shank; the stress dispersion sleeve is made of non-metallic material, sleeved on the outer side of the working section of the shank, the inner wall is a tapered surface, the outer wall is a cylindrical surface, the wall thickness gradually decreases from the end close to the head to the other end, the section of the shank matched with the stress dispersion sleeve is an outer tapered surface matched with the inner wall; the initial outer diameter of the stress dispersion sleeve before installation is smaller than the hole diameter of the composite material connection hole.
[0007] Further, the material of the stress dispersion sleeve is engineering plastic, nylon, polyether ether ketone or fiber reinforced composite material.
[0008] Further, one or more through grooves extending along the axial direction are arranged on the side wall of the stress dispersion sleeve, the length of the through groove is smaller than the total length of the sleeve, which is used to reduce the radial stiffness of the sleeve and make it easier to expand. Preferably, the through grooves are at least three and are uniformly distributed in the circumferential direction of the sleeve side wall.
[0009] Further, a lubricating coating is arranged on the outer surface of the stress dispersion sleeve or the stress dispersion sleeve is made of self-lubricating material to reduce the installation resistance.
[0010] Further, the end face of the stress dispersion sleeve close to the head is a pressure bearing surface for contacting the lower surface of the head. A positioning convex ring can be arranged on the pressure bearing surface, and a positioning ring groove matched with the positioning convex ring is arranged on the head to fix the circumferential relative position of the sleeve and the bolt and prevent relative rotation during installation.
[0011] Further, as a high-value implementation, at least one sensing unit (such as a resistance strain gauge or a fiber optic grating sensor) is embedded in the stress dispersion sleeve to monitor the strain state of the stress dispersion sleeve; the bolt assembly can further comprise a data processing and transmission module integrated in the head or independently packaged, which is connected with the sensing unit for collecting, processing and wirelessly transmitting sensing data to external equipment to realize online real-time monitoring and early warning of the connection state; the module can be completely embedded in the head or realized by a packaging body fixed on the outer surface of the head.
[0012] Further, as another high-value implementation, a plurality of anchor rings in the shape of barbs are arranged on the outer wall of the stress dispersion sleeve in the circumferential direction, the cross section of the anchor ring is asymmetrically sawtooth-shaped, and the inclined surface faces the head direction; the material of the stress dispersion sleeve is an engineering plastic with excellent toughness, so that the anchor ring can produce permanent plastic deformation and form mechanical interlocking after being embedded in the hole wall during radial expansion of the sleeve, thereby providing extremely high pull-out resistance and anti-vibration loosening capability.
[0013] Further, as another high-value implementation, the stress dispersion sleeve is made of a thermoplastic polymer or a shape memory polymer with a thermal expansion coefficient significantly higher than that of the bolt metal material; the head is provided with a blind hole coaxial with the shank, and a heating element is arranged in the blind hole; during installation, the shank and the sleeve are locally heated to activate the thermal expansion effect of the sleeve, causing it to actively and uniformly expand to fill the gap between the hole walls, achieving high-precision pre-tightening force control and excellent sealing performance.
[0014] The application also provides a connecting method for a composite material structure using any of the above-mentioned bolt assemblies, comprising the following steps: sleeving the stress dispersion sleeve on the shank working section of the bolt; inserting the assembly into the composite material connecting hole; installing the nut and tightening; during the tightening process, the shank of the bolt is subjected to tension to generate axial tension, which is converted by the inner tapered surface of the stress dispersion sleeve into a force that causes the stress dispersion sleeve to expand radially, and the stress dispersion sleeve plastically deforms and fully adheres to the hole wall to disperse and transmit the pre-tightening force; when a heat-activated sleeve is used, the thermal expansion effect of the sleeve needs to be activated by the heating element before or at the same time as tightening.
[0015] The application has the following advantages: 1. Excellent hole wall protection: the non-metallic sleeve acts as a buffer, and its tapered design converts concentrated radial extrusion stress into dispersed axial stress and adheres to the hole wall through uniform plastic deformation, greatly reducing the stress concentration at the edge of the composite material hole and effectively preventing delamination and crushing.
[0016] 2. Multiple functions and performance improvement: through different sleeve designs, additional functions such as real-time health monitoring, extremely high anti-pullout and anti-looseness performance, high-precision pre-tightening force control, and excellent sealing performance can be obtained, meeting the high-end needs of different application scenarios.
[0017] 3. Easy installation and strong compatibility: based on the structure of an ordinary bolt, no special installation tools are required, and conventional torque methods can be used, which is low in cost and widely applicable.
[0018] 4. High reliability: the plastic deformation of the sleeve can compensate for the hole diameter tolerance, providing stable and consistent contact pressure and connection performance. BRIEF DESCRIPTION OF DRAWINGS
[0019] Figure 1 It is a sectional view of the overall structure of the bolt assembly embodiment one; Figure 2 It is a sectional view of the overall structure of the bolt assembly embodiment one; Figure 3 It is a sectional view of the overall structure of the bolt assembly embodiment one; Figure 4 It is a stress dispersion sleeve structure diagram of the bolt assembly embodiment two (bionic anchoring structure); Figure 5Figure 2 is a schematic view of the cross-sectional structure of the bolt assembly embodiment 2; Figure 6 Figure 3 is a structural diagram of the bolt assembly embodiment 3.
[0020] Figure 1: 1-bolt body; 11-head; 12-shaft; 13-positioning ring groove; 2-stress dispersion sleeve; 21-inner wall; 22-outer wall; 23-through groove; 24-pressure bearing surface; 25-positioning convex ring; 3-sensing unit; 4-data processing and transmission module; 5-anchoring ring; 6-blind hole; 7-heating element; 8-nut; 9-connected part. DETAILED DESCRIPTION
[0021] The structure and principles of the present application will be fully described in combination with specific embodiments, so that those skilled in the art can fully understand and implement them. EMBODIMENTS
[0022] As shown in Figure 1 , Figure 2 , Figure 3 A stress dispersion bolt assembly for composite material connection includes a bolt body 1 and a stress dispersion sleeve 2. The bolt body 1 is a standard hexagonal head bolt, including a head 11 and a shaft 12. The stress dispersion sleeve 2 is made of PEEK material and is sleeved on the working section of the shaft 12. The inner wall 21 of the stress dispersion sleeve 2 is a tapered surface, the outer wall 22 is a cylindrical surface, and the wall thickness gradually thins from one end (the head 11) to the other end, and the outer surface has a lubricating coating; the section of the shaft 12 matched with the stress dispersion sleeve 2 is an outer tapered surface matched with the inner wall 21. One end of the stress dispersion sleeve 2 (close to the head 11) is a pressure bearing surface 24, and the positioning convex ring 25 thereon cooperates with the positioning ring groove 13 below the bolt head 11 to prevent rotation. An optical fiber grating sensor is embedded in the stress dispersion sleeve 2 as a sensing unit 3, and a data processing and transmission module 4 is packaged in the head 11 and connected with the sensing unit 3.
[0023] During installation, the stress dispersion sleeve 2 is sleeved on the bolt, inserted into the hole of the composite material, and then the nut is tightened. The rod part 12 is in tension, and the stress dispersion sleeve 2 is extruded by the inner tapered surface 21 to deform radially and tightly fit the hole wall, thereby protecting the hole wall and transmitting the load. At the same time, the sensing unit 3 monitors the strain of the stress dispersion sleeve 2 in real time, and the data is transmitted wirelessly after being processed by the data processing and transmission module 4, thereby realizing online monitoring of the connection state. In addition, due to the limitation of the structure design of the stress dispersion sleeve 2, the inner diameter of the upper end of the rod part 12 is small, and during installation, the following methods can be used, including but not limited to: ①. By using the thermal expansion characteristics of engineering plastics, the stress dispersion sleeve 2 is heated to near its glass transition temperature before installation, so that it softens and the inner diameter slightly expands. The operator can use special clamps or gloves to quickly sleeve it into the specified position of the bolt rod part 12 while it is hot, until the positioning convex ring 25 is embedded in the positioning ring groove 13. After cooling, the sleeve shrinks and tightly fits the bolt rod part. ②. A simple tapered mandrel is used as a pre-assembly tool. During installation, the tapered mandrel is first inserted from the end of the stress dispersion sleeve 2 with a larger hole diameter, and is gently knocked or pressed to slightly expand the sleeve by the taper of the mandrel. Keep the mandrel in place, sleeve the sleeve and mandrel onto the bolt rod part 12, and make the positioning convex ring 25 of the sleeve and the positioning ring groove 13 of the bolt head preliminarily aligned. Then pull out the mandrel, and the stress dispersion sleeve 2 temporarily expands due to its elasticity and rebounds, thereby wrapping the bolt rod part 12 and completing the preliminary assembly of the bolt and the sleeve. The final installation needs to insert the assembly into the connection hole and tighten the nut, so that the sleeve plastically deforms in the hole.
[0024] The working principle of the present application is key to the transmission path and mode of force. In traditional bolt connection, the axial tension of the rod body is directly converted into concentrated radial extrusion stress on the hole wall, which is easy to cause delamination of the composite material. In the present embodiment, the stress dispersion sleeve 2 acts as a “mechanical transformer” and “energy dissipation element”, and its action process is as follows: first, the axial displacement of the bolt rod part 12 is converted into the force driving the sleeve to expand radially through the inner wall 21 (inner tapered surface); then, the stress dispersion sleeve 2 significantly plastically deforms, and the radial compressive stress generated is dispersed and uniform due to the softness of the material and the design of the through groove 23, which greatly reduces the stress peak of the hole wall; finally, the energy generated by the pre-tightening force is mainly used to overcome the axial tensile deformation caused by the radial expansion of the stress dispersion sleeve 2 itself (i.e. converted into the axial tensile stress inside the sleeve), rather than all acting on the hole wall. This design cleverly converts the concentrated radial extrusion, which is the most destructive to the composite material, into the axial tension that the sleeve itself bears, which is relatively safe, thereby fundamentally improving the stress state of the hole wall and achieving excellent protection effect. Embodiment
[0025] As Figure 4 , Figure 5As shown, this embodiment differs from Embodiment 1 in that the stress-dispersing sleeve 2 is made of tough nylon, and its outer wall 22 is machined with four sets of circumferentially evenly distributed, barbed anchoring rings 5 with an asymmetrical serrated cross-section. Specifically, the angle between the bearing surface of the serrations (i.e., the main stress-bearing surface, facing the head 11) and the sleeve axis is small, at 30°, to provide efficient pull-out resistance; while the angle between the guide surface of the serrations (facing the nut 8) and the sleeve axis is large, at 80°, to facilitate smooth insertion of the sleeve into the composite material hole wall during expansion installation.
[0026] During installation, the stress-dispersing sleeve 2 expands, and the anchoring ring 5 undergoes permanent plastic deformation under pressure and embeds into the composite material hole wall, forming a strong mechanical interlock, which greatly improves the pull-out resistance and vibration resistance of the connection. Example
[0027] like Figure 6 As shown, this embodiment differs from Embodiment 1 in that the stress-dispersing sleeve 2 is made of thermoplastic with a high coefficient of thermal expansion; a blind hole 6, coaxial with and extending to the rod 12, is machined at the center of the head 11, and a heating element 7 (miniature heating rod) is installed inside the hole. During installation, the bolt assembly is inserted first, and then the heating element 7 is inserted into the blind hole 6 and heated for approximately 45 seconds. The stress-dispersing sleeve 2 softens upon heating and actively expands radially, filling all gaps. The nut is then tightened, and heating is maintained until tightening is complete. After cooling, the stress-dispersing sleeve 2 contracts, generating a large and uniform residual preload, forming an excellent seal.
[0028] Furthermore, the present invention also discloses a method for connecting the above-mentioned bolt assembly, comprising the following steps: S1: Prepare the bolt assembly and fit the stress-dispersing sleeve onto the bolt shank; S2: Insert the assembly into the hole of the composite material plate to be connected; S3: If it is a thermally activated type, insert the heating element and turn on the power to heat it; S4: Install the nut on the threaded end and tighten it to the specified value using a torque wrench; S5: The sleeve undergoes plastic deformation under extrusion and / or heat, completely fitting against the hole wall to complete the connection; S6: If it is a thermally activated type, remove the heating element; if it is an intelligent type, it can start receiving monitoring data.
[0029] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A stress dispersion bolt assembly for composite material joints, characterized by, It comprises: a bolt body (1) comprising a head (11) and a shank (12); a stress dispersion sleeve (2) made of non-metallic material, which is sleeved on the outer side of the working section of the shank (12); the inner wall (21) of the stress dispersion sleeve (2) is a conical surface, the outer wall (22) is a cylindrical surface, and the wall thickness gradually decreases from one end close to the head (11) to the other end; the section of the shank (12) matched with the stress dispersion sleeve (2) is an outer conical surface matched with the inner wall (21); the initial outer diameter of the stress dispersion sleeve (2) before installation is smaller than the hole diameter of the composite material connecting hole.
2. A stress dispersing bolt assembly for composite joints according to claim 1, characterized in that: The material of the stress dispersion sleeve (2) is engineering plastic, nylon, polyether ether ketone or fiber reinforced composite material.
3. A stress dispersing bolt assembly for composite joints according to claim 1 or 2, characterised in that: One or more through grooves (23) extending in the axial direction are arranged on the side wall of the stress dispersion sleeve (2), and the length of the through groove (23) is smaller than the total length of the sleeve.
4. A stress dispersing bolt assembly for composite joints according to claim 3, wherein: The through groove (23) is at least three, and is uniformly distributed in the circumferential direction on the side wall of the stress dispersion sleeve (2).
5. A stress dispersing bolt assembly for composite joints according to claim 1, wherein: The outer surface of the stress dispersion sleeve (2) is provided with a lubricating coating or is made of self-lubricating material.
6. A stress dispersing bolt assembly for composite joints according to claim 1, wherein: The end face of the stress dispersion sleeve (2) close to the head (11) is a pressure bearing surface (24), which is used to contact the lower surface of the head (11), and the pressure bearing surface (24) is provided with a positioning convex ring (25), and the head (11) is provided with a positioning ring groove (13) matched with the positioning convex ring (25).
7. A stress dispersing bolt assembly for composite joints according to claim 1, wherein: At least one sensing unit (3) is embedded in the stress dispersion sleeve (2), the sensing unit (3) is a resistance strain gauge or a fiber grating sensor, which is used to monitor the strain state of the stress dispersion sleeve (2); the bolt assembly further comprises a data processing and transmission module (4) integrated in the head (11) or a separate encapsulated data processing and transmission module (4), which is electrically connected with the sensing unit (3), and is used to collect, process and wirelessly transmit sensing data to an external receiving device.
8. A stress dispersing bolt assembly for composite joints according to claim 1, wherein: A plurality of anchor rings (5) in the shape of barbs are arranged on the outer wall (22) of the stress dispersion sleeve (2) and surround the sleeve in the circumferential direction, and the cross section of the anchor ring (5) is asymmetrically sawtooth-shaped; the material of the stress dispersion sleeve (2) is engineering plastic, so that the anchor ring (5) can produce permanent plastic deformation and form mechanical interlocking after being embedded in the composite material hole wall by radial expansion of the stress dispersion sleeve (2).
9. A stress dispersing bolt assembly for composite joints according to claim 1, wherein: The stress dispersion sleeve (2) is made of a thermoplastic polymer or a shape memory polymer with a thermal expansion coefficient significantly higher than that of the bolt metal material; the head (11) is provided with a blind hole (6) coaxial with the shank (12) and extending to the shank (12), and a heating element (7) is arranged in the blind hole (6).
10. A method of joining composite structural members using the bolt assembly of claim 9, wherein, The method comprises the following steps: sleeving the stress dispersion sleeve (2) on the working section of the shank (12) of the bolt (1); inserting the assembled bolt (1) and stress dispersion sleeve (2) into the hole of the composite material plate to be connected; installing a nut on the threaded end of the bolt (1) and tightening it; During the tightening process, the shaft (12) of the bolt (1) generates an axial tension force, which is converted by the inner conical surface (21) of the stress dispersion sleeve (2) into a force that causes the stress dispersion sleeve (2) to expand radially; The stress dispersion sleeve (2) plastically deforms, the outer wall (22) completely adheres to the hole wall of the composite material, and the pre-tightening force is transmitted to the composite material structure in a dispersed form, completing the connection; Before or at the same time as tightening the nut, the thermal expansion effect of the stress dispersion sleeve (2) is activated by the heating element (7).