Pre-embedded hollow insert for composite material connecting structure and preparation process of pre-embedded hollow insert
By using pre-embedded hollow inserts, the compressive load of the fastener on the CFRP hole wall is transformed into an interlaminar shear load, which solves the problem of early failure of CFRP bolted connections and realizes efficient preparation and performance improvement of composite material connection structures.
Patent Information
- Application Number
- CN202511538113.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-27
- Publication Date
- 2025-12-12
AI Technical Summary
In existing technologies, carbon fiber reinforced composite materials (CFRP) are prone to early failures such as delamination, peeling, or local crushing due to hole edge compressive loads during bolted connections, affecting the load-bearing capacity and durability of the connection structure. Traditional reinforcement methods have problems such as complex processes, increased weight, or limited reinforcement effects.
Design a pre-embedded hollow insert, including an insert inner ring and a pre-embedded structure. The insert inner ring contacts the fastener to bear the compressive load and converts it into an interlaminar shear load. The hollow structure is used to transfer the shear load. The insert material is titanium alloy or stainless steel. The insert is bonded to CFRP through an integrated molding process.
It effectively improves the stress state at the hole edge, avoids early failure, enhances the load-bearing capacity and durability of composite material connection structures, simplifies the manufacturing process, and is suitable for mass production applications.
Smart Images
Figure CN121105439A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of composite material connection, and relates to a pre-embedded hollow insert for a composite material connection structure and a preparation process thereof, in particular to a pre-embedded insert for a fiber-reinforced composite material connection structure and a preparation process thereof, and is especially suitable for structural reinforcement of a carbon fiber-reinforced polymer (CFRP) bolt connection hole. BACKGROUND
[0002] Fiber-reinforced polymer (FRP), especially carbon fiber-reinforced polymer (CFRP), is widely used in aerospace, automotive and shipbuilding fields due to its high specific strength, large specific stiffness and excellent corrosion resistance. In practical applications, the connection between CFRP components and metal or composite materials is mostly achieved by mechanical fastening, among which bolt connection is the most common and reliable connection form.
[0003] However, due to the weak mechanical properties of composite materials in the thickness direction, the interlaminar strength is significantly lower than the fiber direction strength. When the fastener applies a compressive load at the hole wall, CFRP is prone to delamination, peeling or local crushing failure at the hole edge. Such early failure not only reduces the load capacity of the joint, but also limits the application of composite materials in high-reliability connection structures.
[0004] In the prior art, researchers have tried to improve the stress state at the hole edge by adding a local reinforcement layer at the hole edge, using an adhesive metal sleeve, or increasing the support area of the fastener. However, these methods have defects such as complex process, increased additional weight, limited stress transfer efficiency, and still cannot fundamentally solve the problem of hole wall compression failure.
[0005] Therefore, there is an urgent need for a new structural design and preparation method to reasonably convert the compressive load generated by the fastener on the CFRP hole wall into interlaminar shear load, thereby effectively improving the stress state at the hole edge, avoiding early failure, and improving the overall reliability and durability of the composite material connection structure. SUMMARY
[0006] The existing carbon fiber reinforced composite material (CFRP) is connected by mechanical fastening such as bolts, and the hole edge area often appears delamination, peeling or local crushing under the action of large compression load, which seriously affects the bearing capacity and durability of the connected structure. Although the traditional local reinforcement, sleeve or expanding contact area method can alleviate the stress concentration of the hole wall to a certain extent, it has problems such as complex process, weight increase or limited reinforcement effect. In view of the above problems existing in the prior art, the present application provides a pre-embedded hollow insert for composite material connection structure and a preparation process thereof, so that the compression load of the fastener on the hole wall can be reasonably converted into the shear load between the CFRP layers, thereby improving the stress state of the hole edge, avoiding premature failure, and improving the overall performance of the composite material connection structure.
[0007] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is:
[0008] A pre-embedded hollow insert for composite material connection structure, the pre-embedded hollow insert is a disc structure, including an insert inner ring 11 in the middle and a pre-embedded structure 12 arranged circumferentially outside the insert inner ring 11.
[0009] The insert inner ring 11 is a hollow and open-top and bottom cylindrical structure, and the axial height is greater than the maximum size of the pre-embedded structure 12. The inner diameter of the insert inner ring 11 matches the diameter of the rod part of the fastener, directly contacts the fastener and bears the compression load applied by the fastener. Since the fastener is fixed through the insert inner ring 11, the compression load is converted into the shear load between the CFRP layers, which can avoid premature failure of the hole edge.
[0010] The pre-embedded structure 12 is annular and has a hollow structure, and the outer diameter is greater than the hole diameter of the fastener (bolt). It is located between the carbon fiber reinforced composite material CFRP layers and used to contact the carbon fiber reinforced composite material CFRP and transfer the shear load.
[0011] Further, the hollow structure can be a radial hole, a grid hole or a honeycomb hole;
[0012] Further, the hollow structure can be filled with short fiber composite material;
[0013] Further, the material of the insert inner ring 11 can be titanium alloy, stainless steel or other high-strength metal;
[0014] Further, the inner diameter of the insert inner ring 11 matches the diameter of the rod part of the fastener to ensure reasonable force transmission and prevent plastic deformation under the action of bolt pretightening force.
[0015] A preparation process of a pre-embedded hollow insert for composite material connection structure, comprising the following steps:
[0016] First, prepare a perforated composite material laminate;
[0017] In the CFRP prepreg laying process, a half-formed structure with bolt hole positions is formed, and the thickness of the half-formed structure is half of the finished product;
[0018] Second step, insert placement: place the embedded hollow insert in the hole position of the half-formed structure obtained in the first step. Specifically:
[0019] The embedded hollow insert includes an insert inner ring 11 and an embedded structure 12, and during placement, the CFRP half-formed structure, the embedded hollow insert, and the CFRP half-formed structure are stacked in turn. The hollow structure of the embedded structure 12 can ensure that the upper and lower CFRP prepregs can be bonded to each other through the hollow area during the forming process.
[0020] Third step, stacking and molding: cover another half-hole CFRP prepreg on the embedded hollow insert and the half-formed structure above, and combine with the lower layer to form an overall layup structure;
[0021] Fourth step, forming and curing: complete curing through a heat press tank or compression molding process, embed the insert in the laminate hole, and realize the bonding of the embedded part and the upper and lower CFRP;
[0022] Fifth step, load regulation and response: after fastener assembly, the embedded hollow insert realizes the conversion of hole wall compression load to CFRP interlaminar shear load.
[0023] Compared with the prior art, the present application has the following beneficial effects:
[0024] (1) The present application converts the compression load generated by the fastener on the CFRP hole wall into interlaminar shear load through the design of the insert structure, effectively improves the stress state of the hole edge, and avoids early crushing or delamination failure;
[0025] (2) The embedded structure designed in the present application adopts a hollow ring structure, so that the upper and lower prepregs can be bonded through during the forming process, significantly enhancing the bonding strength and shear resistance of the embedded hollow insert and the composite material;
[0026] (3) The embedded hollow insert designed in the present application is integrally formed with CFRP, without the need for additional secondary processing procedures, and the preparation process is simple, suitable for batch application;
[0027] (4) The present application improves the bearing capacity and durability of the composite material connection structure, and expands the application prospect of CFRP in high-reliability structure connection.
[0028] In summary, the present application forms a synergistic optimization insert regulation mechanism in terms of structure design, manufacturing process and service response, and has significant engineering practical value and popularization prospect. BRIEF DESCRIPTION OF DRAWINGS
[0029] Figure 1 is a schematic view of a pre-embedded hollow insert; Figure 1 (a) in is a front isometric view of a pre-embedded hollow insert; Figure 1 (b) in is a top view; Figure 1 (c) in is a front view.
[0030] Figure 2 is a schematic view of an open-hole CFRP provided with a pre-embedded hollow insert.
[0031] Figure 3 is a schematic view of two open-hole CFRPs provided with pre-embedded hollow inserts assembled by bolt connection.
[0032] Figure 4 is a schematic view of a pre-embedded hollow insert under stress.
[0033] In the figure: 1 pre-embedded hollow insert; 11 insert inner ring; 12 pre-embedded structure; 2 fiber-reinforced composite material laminate; 3 bolt. DETAILED DESCRIPTION
[0034] The application will be further described below in combination with specific implementation cases.
[0035] Example 1
[0036] The insert comprises two parts: an insert inner ring and a pre-embedded part:
[0037] The insert inner ring is the part in direct contact with the fastener, the inner diameter of which matches the diameter of the shank of the fastener, and is used to bear and transmit the compression load applied by the fastener;
[0038] The pre-embedded part is a ring-shaped hollow structure, the outer diameter of which is greater than the diameter of the bolt hole, and is located between the composite material layers. The hollow structure can adopt radial holes, grid holes or honeycomb holes to ensure that the upper and lower composite material prepregs can pass through the hollow area to realize bonding and fusion during the molding process, thereby enhancing the bonding strength of the insert and the matrix.
[0039] Preferably, the insert material is titanium alloy, stainless steel or other high-strength metal to ensure that no plastic deformation occurs under the action of the bolt pretightening force.
[0040] The preparation process of the application comprises the following steps:
[0041] Step S1: preparation of one half of the open-hole composite material laminate
[0042] The CFRP prepreg with a layer thickness of 0.125 mm is laid according to the designed layer direction, and an open-hole area at the position of the bolt hole is formed during the laying process, to obtain a semi-formed structure with predetermined hole positions.
[0043] Step S2: insert placement
[0044] The pre-embedded insert is accurately placed at the hole site of the semi-formed structure, with the inner ring of the insert aligned with the bolt hole, and the pre-embedded portion completely placed into the composite interlayer. The positioning tolerance is ≤0.3 mm.
[0045] Step S3: stacking and mold closing
[0046] The other half of the CFRP prepreg with the corresponding hole site is covered on the insert and the semi-formed structure, and is combined with the lower layer to form an overall layup structure. At this time, the pre-embedded portion of the insert is in the interlayer position, and the upper and lower prepregs can be bonded to each other through the hollow area.
[0047] Step S4: forming and curing
[0048] The overall structure is placed in a hot press or compression molding equipment, and pressure and temperature are applied to complete curing (forming temperature: 235°C, pressure: 0.5-3.0 MPa, pressure holding time: 60 min). After curing, the insert is firmly embedded in the composite hole, the pre-embedded portion is fused with the upper and lower layers of composite material, and integrated connection is achieved.
[0049] Step S5: load regulation and response
[0050] During the fastener assembly process, the fastener bears the compression load through the inner ring of the insert, and the compression load is converted into interlayer shear load through the pre-embedded portion, thereby effectively avoiding delamination or crushing failure of the hole edge due to excessive compression stress.
[0051] The composite connection structure prepared by the process is tested and shown to have significantly improved mechanical properties of the joint. The maximum bearing capacity measured by experiment is 37.69 kN (finite element prediction 37.56 kN), and the first damage load is 27.62 kN (finite element prediction 30.85 kN). More importantly, the local load of the most dangerous hole is reduced from 7.67 kN to 2.85 kN by the insert, with a decrease of 62.8%; the variance of the bolt load distribution is reduced from 4.23 to 0.10, a decrease of about 97.6%. These results show that the insert not only improves the bearing capacity and damage threshold of the joint, but also achieves stress release and load redistribution in the hole edge area, thereby significantly improving the early failure mode and enhancing the reliability and durability of the connection.
[0052] The above-described embodiments only express the implementation of the present application, but cannot be construed as limiting the scope of the present patent. It should be noted that, for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of protection of the present application.
Claims
1. A pre-embedded hollow insert for a composite material connection structure, characterized in that, The pre-embedded hollow insert is a disc structure, including an inner ring (11) in the middle and a pre-embedded structure (12) arranged circumferentially on the outer edge of the inner ring (11); The insert inner ring (11) is a hollow cylindrical structure with openings at the top and bottom, and its axial height is greater than the maximum size of the pre-embedded structure (12); the inner diameter of the insert inner ring (11) matches the diameter of the fastener rod; the fastener is fixed by the insert inner ring (11), so that the compressive load is converted into the shear load between the CFRP layers, avoiding premature failure of the hole edge. The pre-embedded structure (12) is annular and has a hollow structure. Its outer diameter is larger than that of the fastener hole. It is located between the carbon fiber reinforced composite (CFRP) layers and is used to contact the CFRP and transfer shear load.
2. The embedded hollow insert for a composite material connection structure according to claim 1, characterized in that, The hollow structure is a radial hole, a grid hole, or a honeycomb hole.
3. The embedded hollow insert for a composite material connection structure according to claim 1, characterized in that, The hollow structure can be filled with short fiber composite material.
4. The embedded hollow insert for a composite material connection structure according to claim 1, characterized in that, The material of the inner ring (11) of the insert is titanium alloy, stainless steel or other high-strength metal.
5. A manufacturing process for a pre-embedded hollow insert for a composite material connection structure according to any one of claims 1-4, characterized in that, Includes the following steps: The first step is to prepare an open-cell composite laminate; During the CFRP prepreg laying process, a semi-formed structure with bolt hole locations is formed, and the thickness of the semi-formed structure is half that of the finished product. The second step is to place the insert; Place the pre-embedded hollow insert at the hole position of the semi-formed structure obtained in the first step; The third step is stacking and molding; The other half of the open-cell CFRP prepreg is covered on top of the embedded hollow insert and the semi-formed structure, and then stacked with the lower layer to form an integral layup structure. The fourth step is molding and curing. After curing, the insert is embedded in the cavity of the laminate and the embedded part is bonded to the upper and lower CFRP layers. Step 5: Load regulation and response; After the fasteners are assembled, the hole wall compressive load is converted into CFRP interlayer shear load by pre-embedded hollow inserts.
6. The manufacturing process of the pre-embedded hollow insert for the composite material connection structure according to claim 5, characterized in that, The second step is as follows: during the placement process, the CFRP semi-molded structure, the pre-embedded hollow insert, and the CFRP semi-molded structure are stacked in sequence; among them, the hollow structure of the pre-embedded structure (12) can ensure that the upper and lower layers of CFRP prepreg can be bonded to each other through the hollow area during the molding process.
7. The manufacturing process of the pre-embedded hollow insert for the composite material connection structure according to claim 5, characterized in that, In the fourth step, curing is completed by autoclaving or compression molding.