Composite material built-in metal insert connecting structure and connecting structure preparation method

Abstract

The application discloses a connecting structure of a composite material built-in metal insert and a preparation method thereof, and belongs to the technical field of composite materials. A groove is arranged on the metal insert, a connecting reinforcing material is arranged in the groove by winding fibers, the reinforcing material is connected with a main body of the composite material, and the remaining part of the groove is filled with filling fibers. Under the premise of realizing the connecting function of the metal insert, the groove structure reduces the weight of the metal insert, increases the contact area of the composite material and the metal insert, increases the torsional resistance, and provides double-side limiting in the axial direction of the metal insert, so that a three-dimensional connecting structure based on continuous fibers is established between the metal insert and the main body of the composite material, and the technical problems of the metal insert lacking double-side axial limiting and the small contact area leading to insufficient torsional resistance in the prior art are solved.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, and relates to a connection structure for a composite material with an embedded metal insert, as well as a method for preparing the connection structure for a composite material with an embedded metal insert. Background Technology

[0002] Due to stress concentration, joints are often weak points in structures, making them one of the most challenging tasks in structural design. Composite materials are anisotropic, and joint areas contain various discontinuities in structural shape, often resulting in material discontinuities and thus localized high stress concentrations. Furthermore, stress concentration in anisotropic materials is more complex, depending not only on geometry but also on the layup method. In addition, metals are ductile materials with the ability to redistribute loads, while commonly used thermosetting resin-based composites, lacking a yield point, are brittle and essentially lack load redistribution capabilities. Therefore, metal inserts are often incorporated into composite structures, with connection mechanisms integrated into these inserts to mitigate the inherent weaknesses of composite joints.

[0003] Chinese patent CN116872518A discloses a molding method for a hemispherical composite material liner. The product includes a metal insert for reinforcement, which is placed on a semi-finished pre-pressed part. Prepreg layers are then laid and molded sequentially. The metal insert mentioned in this patent serves a reinforcing function and does not involve a connection structure. Chinese patent CN112013004A discloses a connection structure for a composite material joint. By embedding the outer bottom and outer sides of a semi-circular annular metal insert with threaded holes into the composite material joint body, the problem of thread damage caused by repeated disassembly and assembly is solved. Chinese patent CN112571825 relates to a composite material joint and its preparation method. An asymmetric platform is completely embedded in the composite material matrix, exposing only the small-end mounting mechanism. A prepreg layer structure perpendicular to the axis of the metal insert restricts the position of the metal insert, and the connection between the composite material body and the metal insert is achieved through a metal / resin interface. Chinese patent CN116766623A discloses a three-dimensional reinforced composite material joint, in which a metal insert penetrates the composite material layer and is exposed at both ends on the surface of the composite material body. The metal insert is installed by secondary curing. The installation hole is machined on the composite material joint body, and then adhesive is applied and bonded after the installation hole is opened.

[0004] Current technical solutions involve embedding conical metal inserts into the composite material body for integral molding. This not only increases the volume of the metal insert, reducing the weight reduction effect of the composite product, but also lacks bilateral axial restraint, resulting in insufficient torsional resistance due to the small contact area. Furthermore, the metal / resin interface connecting the metal insert and the composite material body still relies on pure resin for bonding. Under structural load, stress remains concentrated at this interface, leading to poor connection reliability. The resin / adhesive / metal interface produced by machining, drilling, and secondary bonding is more complex and fragile than the metal / resin interface formed by pre-embedded metal inserts, resulting in even lower connection strength. Composite material propulsion systems, due to limitations in design, manufacturing processes, cost, and maintenance, often have areas on the hub or duct requiring connections. These structures are thin-walled, and when the composite material body cannot meet the operating conditions, pre-embedded metal inserts are needed to strengthen the connections. In underwater environments, if the connection fails and cracks form, seawater may seep in, corroding both the metal insert and the composite material body at the connection points. Summary of the Invention

[0005] The primary objective of this invention is to provide a connection structure for a composite material with an embedded metal insert, which solves the technical problem in the prior art where the metal insert lacks bilateral axial restraint and has a small contact area, resulting in insufficient torsional resistance.

[0006] The second objective of this invention is to provide a method for preparing a connection structure with an embedded metal insert in a composite material.

[0007] The first technical solution adopted in this invention is a connection structure with a metal insert built into the composite material body, including a metal insert and a composite material body. The outer wall of the metal insert is surrounded by an arc-shaped groove. Several layers of reinforcing material extending out of the groove are laid in the curved surface of the groove. The several layers of reinforcing material are connected to the metal insert by winding fibers one by one. The several layers of reinforcing material are laid at intervals along the interlayer normal of the composite material body. The part of the reinforcing material extending out of the groove is fixed to the composite material body. The cavity formed by the reinforcing material in the groove is filled with filling fibers.

[0008] The first technical solution of the present invention is further characterized in that,

[0009] Blind holes are provided along the axis of the metal insert.

[0010] The reinforcing material is a unidirectional prepreg or plain weave fabric.

[0011] The dimension of the reinforcing material extending out of the groove shall not exceed 1 / 8 of the circumference or width of the groove of the metal insert 1.

[0012] The thickness of the entanglement between the wound fiber and the metal insert is less than the thickness of the single-layer reinforcement material.

[0013] Let A be the fiber content per unit area of ​​the composite material body. The fiber content per unit area of ​​the multilayer reinforcement material and the composite material body is less than A / 2.

[0014] The second technical solution adopted in this invention is a method for preparing a connection structure for a composite material body with an embedded metal insert, which is used to prepare the above-mentioned connection structure for a composite material body with an embedded metal insert, specifically including the following steps:

[0015] S1, Select a cylindrical or frustum-shaped metal block as a metal insert, and machine an arc-shaped groove on the side wall of the metal insert;

[0016] S2, cut the reinforcing material to the size of the groove so that the reinforcing material extends out of the metal insert. The size of the part of the reinforcing material extending out of the groove shall not exceed 1 / 8 of the circumference or width of the groove of the metal insert. Then lay the cut reinforcing material around the arc-shaped groove.

[0017] S3 uses wound fibers to embed the center of the reinforcing material into the groove of the metal insert;

[0018] S4, repeat S2 and S3 until the increased number of reinforcing material layers causes the fiber content per unit area to approach 1 / 2 of the specified fiber content range of the current composite material body;

[0019] S5, fill the empty part of the groove with filling fiber;

[0020] S6, the reinforcing material extending from the metal insert is embedded into the preform of the composite material body. After the molding and curing are completed, a connection structure is formed between the metal insert and the composite material body.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] While achieving the function of connecting metal inserts, this invention reduces the weight of metal inserts through a groove structure, increases the contact area between the composite material and the metal insert, increases torsional resistance, and provides double-sided axial restraint for the metal insert. This allows the establishment of a three-dimensional connection structure based on continuous fibers between the metal insert and the composite material body, solving the technical problem in the prior art where the metal insert lacks double-sided axial restraint and the small contact area leads to insufficient torsional resistance.

[0023] This invention can be applied to the field of composite material propulsion, specifically to areas on the rotor hub and duct of a composite material propulsion that require connection to other components. It improves stress concentration in the connection areas and enhances the reliability of the connection structure. Attached Figure Description

[0024] Figure 1This is a schematic diagram of the connection structure of the composite material embedded metal insert of the present invention;

[0025] Figure 2 This is a schematic diagram of the arrangement of reinforcing materials in the connection structure of the composite material embedded metal insert of the present invention;

[0026] Figure 3 This is a schematic diagram of the connection structure between the wound fiber and the reinforcing material in the connection structure of the composite material embedded metal insert of the present invention.

[0027] In the figure, 1. Metal insert, 2. Reinforcing material, 3. Wound fiber, 4. Filler fiber, 5. Composite material body. Detailed Implementation

[0028] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0029] like Figures 1-3 As shown, the connection structure of the composite material body with built-in metal insert disclosed in this invention includes a metal insert 1 and a composite material body 5. The outer wall of the metal insert 1 is surrounded by an arc-shaped groove. Several layers of reinforcing material 2 extending out of the groove are laid in the curved surface of the groove. The several layers of reinforcing material 2 are connected to the metal insert 1 by winding fibers 3 one by one. The several layers of reinforcing material 2 are laid at intervals along the interlayer normal of the composite material body 5. The part of the reinforcing material 2 extending out of the groove is fixed to the composite material body 5. The cavity formed by the reinforcing material 2 in the groove is filled with filling fibers 4.

[0030] In this invention, the metal insert 1 is a cylindrical or frustum-shaped metal block. Before use, a groove is machined around its side to make the cross-section of the metal insert 1 resemble an I-beam or a "C"-shaped half-section. Several layers of reinforcing material 2 are laid and wound together layer by layer to form a three-dimensional fiber extension structure. Then, the remaining grooves on the sidewalls of the metal insert 1 are filled by filling fiber winding to prevent cavities from forming after curing. The reinforcing material 2 extending from the metal insert 1 is laid at intervals along the interlayer normal of the composite material body 5 on the preform of the composite material body 5. Then, the preform is cured by resin transfer molding / compression molding, so that a three-dimensional connection structure based on continuous fibers is established between the metal insert 1 and the composite material body 5. The reinforcing material 2 extending from the metal insert 1 is laid into the preform. In order to avoid excessive local fiber content, the reinforcing material 2 should be laid at least 1 layer apart. The reinforcing material 2 extending from the metal insert 1 is embedded in the preform of the composite material body 5. After the molding and curing are completed, a three-dimensional connection structure based on the wound fiber 3 is established between the metal insert 1 and the composite material body 5.

[0031] Furthermore, blind holes are provided along the axis of the metal insert 1. This reduces the weight of the metal insert 1 while still fulfilling its function.

[0032] Furthermore, the reinforcing material 2 is made of unidirectional prepreg or plain weave fabric.

[0033] The reinforcing material is selected based on the process route. For prepreg compression molding, unidirectional prepreg is used, while for resin transfer molding, plain weave fabric is selected as the reinforcing material.

[0034] Furthermore, the dimension of the part of the reinforcing material 2 extending out of the groove does not exceed 1 / 8 of the circumference or width of the groove of the metal insert 1, which reduces the interface generated in the composite material body 5 due to the insertion of the reinforcing material 2, and ensures the integrity of the composite material structure of the current layer.

[0035] Furthermore, the thickness of the entanglement between the wound fiber 3 and the metal insert 1 is less than the thickness of the single-layer reinforcing material 2.

[0036] The connection between the reinforcing material 2 and the metal insert 1 is achieved by winding the reinforcing fiber 3 around the axis of the metal insert 1, so that the middle part of the reinforcing material 2 is inserted into the groove of the metal insert 1 and connected to the axis of the metal insert 1 to form a two-dimensional reinforcing structure. The winding thickness of the winding fiber 3 does not exceed the thickness of one layer of the reinforcing material 2 to avoid the formation of cavities between the layers of the reinforcing material 2.

[0037] Furthermore, let A be the fiber content per unit area of ​​the composite material body 5. The fiber content per unit area of ​​the multilayer reinforcing material 2 and the composite material body 5 is less than A / 2.

[0038] The three-dimensional fiber extension structure is based on the thickness of the metal insert 1 and the distance between the upper and lower ends. The two-dimensional reinforcement structure is repeated, and several layers of reinforcement material 2 are laid and wound and connected layer by layer. The specific number of layers is determined according to the fiber content of the preform. The fiber content per unit area caused by the increase in the number of layers should not exceed 1 / 2 of the fiber content range specified in the current preform. Then, the remaining grooves on the side wall of the metal insert 1 are filled by wrapping the filling fiber 4 until the grooves on the metal insert 1 are completely filled.

[0039] Example 1

[0040] A hexahedral metal insert with a radius of 20 mm and a thickness of 10 mm, the same as the preform thickness, needs to be embedded in a width of approximately 400 mm for the flat shell cover. The prepreg used for the layup is T700-12K unidirectional prepreg with a areal density of 300 g / cm3 and a carbon fiber content tolerance of ±3%. T700-12K carbon fiber is selected as the continuous fiber for winding, and T700-12K unidirectional prepreg with an areal density of 150 g / cm3 is selected as the reinforcing material with a thickness of approximately 0.15 mm.

[0041] A groove with a maximum width of 6mm was punched on the side of the insert. Plain carbon cloth was cut into strips 40mm wide and laid into the groove. It was then fixed with continuous fiber winding to a thickness of about 0.15mm. Based on the preform evaluation, a total of 3 layers of extended reinforcement structure were made. The remaining groove was filled by continuous fiber winding.

[0042] The prepared metal insert with a three-dimensional extension structure is installed into the corresponding position of the preform, and the extended reinforcing structure is laid inside with two layers at intervals. It is then cured and formed by molding, and positioning holes are drilled at the specified positions by machining.

[0043] Example 2

[0044] An RTM-molded propeller stator hub needs to have a cylindrical metal insert embedded at a circumference of approximately 180 mm. The insert has a radius of 6 mm and a thickness of 8 mm, the same as the preform thickness. The preform has a carbon fiber content of 60%, with an allowable carbon fiber content tolerance of ±3%. T700-12K carbon fiber is selected as the continuous fiber for winding, and T300-3K plain weave carbon cloth with an areal density of 200 g / cm3 is selected as the reinforcing material with a thickness of approximately 0.11 mm.

[0045] A groove with a maximum width of 4mm was punched on the side of the insert. Plain carbon cloth was cut into strips 20mm wide and laid into the groove. It was then fixed with continuous fiber winding to a thickness of about 0.1mm. Based on the preform evaluation, a total of 3 layers of extended reinforcement structure were made. The remaining groove was filled by continuous fiber winding.

[0046] The prepared metal insert with a three-dimensional extension structure is installed into the large end of the preform prepared by laying T300-3K plain weave carbon cloth layer by layer, and the extended reinforcing structure is laid inside and cured by RTM process. Positioning holes are drilled at the specified positions by machining.

[0047] Example 3

[0048] A cylindrical metal insert with a radius of 5 mm and a thickness of 6 mm, the same as the preform thickness, needs to be embedded in the propeller duct with a width of approximately 300 mm. The prepreg used for the layup is T300-3K unidirectional prepreg with a surface density of 200 g / cm3 and an allowable carbon fiber content tolerance of ±3%. T700-12K carbon fiber is selected as the continuous fiber for winding, and T700-12K unidirectional prepreg with a surface density of 150 g / cm3 is selected as the reinforcing material with a thickness of approximately 0.15 mm.

[0049] A groove with a maximum width of 3mm was punched on the side of the insert. Plain carbon cloth was cut into strips 30mm wide and laid into the groove. It was then fixed with continuous fiber winding to a thickness of about 0.15mm. Based on the preform evaluation, a total of 2 layers of extended reinforcement structure were made. The remaining groove was filled by continuous fiber winding.

[0050] The prepared metal insert with a three-dimensional extension structure is installed into the corresponding position of the preform, and the extended reinforcing structure is laid inside with one layer at intervals. It is then cured and formed by molding, and positioning holes are drilled at the specified positions by machining.

[0051] This invention also discloses a method for preparing a connection structure for a composite material body with an embedded metal insert, which is used to prepare the above-mentioned connection structure for a composite material body with an embedded metal insert, specifically including the following steps:

[0052] S1, Select a cylindrical or frustum-shaped metal block as the metal insert 1, and machine an arc-shaped groove on the side wall of the metal insert 1.

[0053] S2, cut the reinforcing material 2 to the size of the groove so that the reinforcing material 2 extends out of the metal insert 1. The size of the part of the reinforcing material 2 that extends out of the groove does not exceed 1 / 8 of the circumference or width of the groove of the metal insert 1. Then lay the cut reinforcing material 2 around the arc-shaped groove.

[0054] For the laying of reinforcing material 2, the selected reinforcing material 2 is laid around the concave curved surface of the side wall of the pre-processed metal insert 1. The reinforcing material 2 extending from both ends of the groove is bent to form a two-dimensional planar structure at both the upper and lower ends. If there are wrinkles, a cut is made or the wrinkles are cut off directly. Alternatively, the reinforcing material 2 required for laying around the groove can be cut into 3-8 pieces before laying, and then laid around the groove piece by piece.

[0055] S3, the reinforcing material 2 is inserted into the groove of the metal insert 1 by wrapping the fiber 3;

[0056] S4, repeat S2 and S3 until the number of reinforcing material 2 layers increases to the point that the fiber content per unit area is infinitely close to 1 / 2 of the fiber content range specified in the current composite material body 5;

[0057] S5, use filling fiber 4 to fill the empty part of the groove;

[0058] S6, the reinforcing material 2 extending from the metal insert 1 is embedded into the preform of the composite material body 5. After the molding and curing are completed, a connection structure is formed between the metal insert 1 and the composite material body 5.

Claims

1. A connection structure with a built-in metal insert in a composite material body, characterized in that, The device includes a metal insert (1) and a composite material body (5). The metal insert (1) has an arc-shaped groove around its outer circumferential wall. Several layers of reinforcing material (2) extending out of the groove are laid in the curved surface of the groove. The several layers of reinforcing material (2) are connected to the metal insert (1) by winding fibers (3) layer by layer. The several layers of reinforcing material (2) are laid at intervals along the interlayer normal of the composite material body (5). The part of the reinforcing material (2) extending out of the groove is fixed to the composite material body (5). The cavity formed by the reinforcing material (2) in the groove is filled with filling fibers (4).

2. The connection structure of the composite material body with built-in metal insert according to claim 1, characterized in that, A blind hole is provided along the axis of the metal insert (1).

3. The connection structure of the composite material body with built-in metal insert according to claim 1, characterized in that, The reinforcing material (2) is a unidirectional prepreg or plain weave fabric.

4. The connection structure of the composite material body with built-in metal insert according to claim 1, characterized in that, The size of the portion of the reinforcing material (2) extending out of the groove does not exceed 1 / 8 of the circumference or width of the groove of the metal insert (1).

5. The connection structure of the composite material body with built-in metal insert according to claim 1, characterized in that, The thickness of the entanglement between the wound fiber (3) and the metal insert (1) is less than the thickness of the single-layer reinforcing material (2).

6. The connection structure of the composite material body with built-in metal insert according to claim 1, characterized in that, Let A be the fiber content per unit area of ​​the composite material body (5). The fiber content per unit area of ​​the multilayer reinforcing material (2) and the composite material body (5) is less than A / 2.

7. A method for preparing a connection structure with an embedded metal insert in a composite material body, characterized in that, The method for preparing a connection structure for a composite material body with an embedded metal insert as described in any one of claims 1-6 specifically includes the following steps: S1, a cylindrical or frustum-shaped metal block is selected as a metal insert (1), and an arc-shaped groove is machined on the side wall of the metal insert (1). S2, cut the reinforcing material (2) according to the groove size, so that the reinforcing material (2) extends out of the metal insert (1), and lay the cut reinforcing material (2) around the arc-shaped groove; S3, using wound fibers (3) to embed the middle part of the reinforcing material (2) into the groove of the metal insert (1); S4, repeat S2 and S3 until the number of reinforcing material (2) layers increases to the point that the fiber content per unit area is infinitely close to 1 / 2 of the fiber content range specified in the current composite material matrix (5); S5, fill the empty part of the groove with filling fiber (4); S6, the reinforcing material (2) extending from the metal insert (1) is embedded into the preform of the composite body (5). After the molding and curing are completed, a connection structure is formed between the metal insert (1) and the composite body (5).

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