Three-dimensional reinforced composite joint, preparation method and application

Abstract

The application discloses a three-dimensional reinforced composite material joint structure, which mainly comprises a carbon fiber composite material layer, a reinforcing body and a metal insert. The composite material layer is formed by laminating and pressing carbon fiber prepreg layers, and is used for ensuring the overall strength of the joint and maintaining the shape structure; the reinforcing body is composed of metal reinforcing microrods and a supporting net, and is used for reinforcing the composite material layers and improving the bearing capacity of the joint structure; and the metal insert is formed by metal machining, and is provided with a threaded hole at one end and is used for being connected with an external mechanism. The application optimizes the structure form of the composite material joint, implants the metal reinforcing microrods in the direction perpendicular to the carbon fiber laminating direction, hinders the crack propagation through the interlayer reinforcing effect of the microrods on the composite material, avoids the overall structure from being broken due to the brittle fracture of the interlayer resin layer under load, and thus improves the structural stability and the ultimate load of the composite material joint.

Description

Technical Field

[0001] This invention relates to the field of aerospace engine housings, and in particular to a composite material joint structure, its preparation method, and its application. Background Technology

[0002] With the expanding application of carbon fiber composite materials in the aerospace field, more and more metal components are being replaced by composite materials, thereby further reducing the negative mass of solid rocket motor casings and improving the payload and carrying capacity of rocket engines. Among them, the joint flange, a key load-bearing component of solid rocket motor casings, is also beginning to utilize carbon fiber composite materials.

[0003] Most of the currently disclosed composite material joint structures are formed by laying and curing carbon fiber prepreg. The biggest weakness of this layered composite material structure lies in the internal interlayer. Due to the high brittleness of the interlayer resin layer and the lack of fiber reinforcement and toughening effect, the composite material joint matrix is ​​subjected to the impact of fuel gas flow during launch. Cracks are prone to propagate along the interlayer, leading to structural delamination fracture and premature failure. This seriously affects the load of the composite joint component and the overall structural stability of the rocket engine. Summary of the Invention

[0004] Therefore, the technical problem to be solved by this invention is to provide a three-dimensional reinforced composite material joint structure that can enhance and toughen the interlaminar resin within brittle composite materials. A method for preparing this three-dimensional reinforced composite material joint structure is also provided. Applications of this three-dimensional reinforced composite material joint structure are also provided.

[0005] The technical solution of the present invention is,

[0006] A three-dimensional reinforced composite material joint includes a composite material layer, a plurality of reinforcements embedded in the composite material layer, and a plurality of metal inserts within the composite material layer;

[0007] The composite material layer is circular and is formed by layup, molding and curing of carbon fiber prepreg. The composite material layer is divided into an outermost surface layer and a flat layer below the surface layer. The surface layer is made of carbon fiber woven fabric prepreg and the flat layer is made of carbon fiber unidirectional tape prepreg.

[0008] The reinforcement is composed of metal-reinforced microrods and a support mesh; the metal-reinforced microrods are connected to the support mesh, and the support mesh is located between the surface layer and the ply layer of the composite material layer.

[0009] The metal insert penetrates the composite material layer, and the metal insert has a threaded hole with an effective thread depth of more than 30% of the height of the metal insert.

[0010] The lay layer and the surface layer are essentially made of the same material, both being carbon fiber resin prepreg. The only difference is that the surface layer uses woven fabric, while the lay layer uses unidirectional tape. The surface layer is designed to protect the lay layer from damage during machining.

[0011] During the production of composite material layers, the reinforcement is embedded in the structure and becomes part of the composite material layer structure. Later, when mounting holes for metal inserts are machined into the composite material layer, the reinforcement at the corresponding position is machined away.

[0012] The metal insert penetrates the composite material layer, with both ends exposed on the surface of the composite material layer.

[0013] According to a three-dimensional reinforced composite material joint of the present invention, preferably, the carbon fiber of the surface layer is T300 grade or higher carbon fiber; the carbon fiber of the lay-up layer is T700 grade or higher carbon fiber; and the metal reinforcing microrods on the reinforcement are vertically implanted into the composite material layer.

[0014] The outermost layer of this composite material layer structure is the surface layer, which uses T300 grade or higher carbon fiber woven fabric prepreg for layup. This is used to beautify the product appearance and protect the inner flat layer, preventing delamination and structural breakage of the inner upper unidirectional carbon fiber during later machining. The reinforcement, which consists of metal reinforcing microrods and support mesh, is used for interlayer reinforcement of carbon fiber composite materials, improving the interlayer strength and toughness of composite materials, and enhancing the load-bearing capacity of the overall joint structure.

[0015] According to a three-dimensional reinforced composite material joint of the present invention, preferably, the length of the metal reinforcing microrods corresponding to each part of the reinforcement is consistent with the thickness of the composite material layer at that location. Alternatively, the length of the metal reinforcing microrods corresponding to each part of the reinforcement may be slightly less than the thickness of the composite material layer at that location.

[0016] According to a three-dimensional reinforced composite material joint of the present invention, preferably, the metal reinforcing microrods are arranged in 5 to 15 concentric circles with the central axis as the center, and are divided into 100 to 360 equal parts in the circumferential direction.

[0017] According to a three-dimensional reinforced composite material joint of the present invention, preferably, one end of the metal reinforcing microrod is connected to a support mesh. The support mesh is located between the surface layer and the ply layer of the composite material, serving to support and fix the metal reinforcing microrod.

[0018] According to a three-dimensional reinforced composite material joint of the present invention, preferably, the metal insert is tapered; and the small end has a threaded hole.

[0019] Furthermore, the threaded hole depth is approximately 80-90% of the insert height. Furthermore, the effective thread depth is approximately 30-40% of the insert height. A threaded hole depth of approximately 80-90% of the insert height better reduces the weight of the metal insert; an effective thread depth of approximately 30-40% of the insert height better ensures the strength of the threaded connection.

[0020] This invention also provides a method for preparing the above-mentioned three-dimensional reinforced composite material joint structure, the method comprising:

[0021] (1) Mold cleaning and assembly: First, use high-pressure gas and organic solvent to clean each part of the mold, remove dust, oil and other impurities from the mold surface, then apply release agent to each contact surface of the mold, and finally assemble the female mold according to the mold drawing for use;

[0022] (2) Cutting and sorting of prepreg sheets: The shape, size and fiber arrangement angle of the sheets required for each layer of the composite material structure are determined by design. Then, the prepreg sheets are cut by an automatic feeder and numbered according to the layup sequence.

[0023] (3) Prepreg laying and preforming: The assembled female mold is laid with prepreg. The specific laying scheme is as follows:

[0024] First, lay the bottom surface layer, which is a single layer of carbon fiber woven fabric prepreg.

[0025] Next, the internal flat layers are laid. This area uses unidirectional carbon fiber prepreg. The number of prepreg layers is determined according to the product thickness and design documents. The layers are laid one by one using a variable cross-section incremental layup method. The laying angles are [(0° / 45° / 90° / -45° / 0°)s]n°, and pre-forming steps are interspersed during the laying process; this is the laying angle that ensures optimal strength.

[0026] (4) Reinforcement installation: The reinforcement is implanted into the composite material layer, ensuring that the metal reinforcement microrods are vertically inserted between the flat layers. Finally, the woven fabric prepreg on the top surface is laid on the surface of the support net. After the mold is closed, it is placed on the hot press platform for final cold pressing preforming.

[0027] (5) Curing: A temperature measuring device is arranged inside the mold and connected to a temperature measuring instrument to control the mold temperature. The curing process is completed according to the temperature / pressure-time curing curve in the process instruction document, and then the pressure is released and the mold is demolded.

[0028] (6) Machining: Machining holes for metal inserts are made on the composite material joint body. The number and size of the holes are matched with the metal inserts. The specific values ​​are determined according to the structural and strength design scheme.

[0029] (7) Installation of metal inserts: After cleaning the surface of the column, apply adhesive and install it into the mounting hole on the joint. Apply pressure and heat, and obtain the finished composite material joint after the adhesive has cured.

[0030] In step (5), the temperature measuring device can be a thermocouple for temperature detection and display, and the curing process can be heated by the heating plate of the hot press.

[0031] According to a method for preparing a three-dimensional reinforced composite material joint structure based on the present invention, preferably, the height of the metal insert should be slightly shorter than the machining mounting hole size of the composite material layer.

[0032] According to the present invention, a method for preparing a three-dimensional reinforced composite material joint structure is preferred, wherein the release agent application in step (1) is as follows: the release agent is sprayed on the surface of each block of the mold, and the spraying is repeated 2-4 times, with an interval of 20-30 minutes between each application. Finally, the assembly step is carried out after the release agent has completely dried and formed a film.

[0033] According to a method for preparing a three-dimensional reinforced composite material joint structure of the present invention, preferably, the preforming step in step (3) includes, but is not limited to, vacuuming or cold pressing preforming using a multi-segment male mold; and step (7) involves sandblasting the surface of the metal insert column before applying the adhesive. Sandblasting can enhance the bonding strength.

[0034] This invention also provides the application of the above-mentioned three-dimensional reinforced composite material joint structure in the aerospace field, especially in solid rocket engine casings.

[0035] This invention provides a three-dimensional reinforced composite material joint structure. This structure, by implanting metal reinforcing microrods perpendicular to the carbon fiber planar layers, strengthens and toughens the interlaminar resin within the brittle composite material, inhibiting crack propagation in the interlaminar layers and thus improving the overall load-bearing capacity of the composite joint structure. Furthermore, this invention also improves the related manufacturing process, ensuring the manufacturability of the product.

[0036] The beneficial effects of this invention are:

[0037] This invention addresses the problems of high interlayer brittleness and susceptibility to delamination fracture in the internal structure of composite material joints for solid rocket motor casings. By improving existing technologies and structural defects, it provides a three-dimensional reinforced composite material joint structure. Through the implantation of metal microrod reinforcements and the improvement of layup methods, the structure and process of the composite material joint are optimized. The metal microrods provide interlayer reinforcement and toughening effects in the direction perpendicular to the carbon fiber plane layer, thereby inhibiting crack propagation between layers and significantly improving the ultimate load and impact resistance of the composite material joint. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of a three-dimensional reinforced composite material joint structure according to the present invention.

[0039] Figure 2 yes Figure 1 Enlarged diagram of point A in the middle.

[0040] Figure 3 This is a cross-sectional view of a three-dimensional reinforced composite material joint structure according to the present invention.

[0041] Figure 4 yes Figure 3 Enlarged diagram of point A in the middle.

[0042] Figure 5 This is a schematic diagram of a three-dimensional reinforced composite material joint structure metal insert according to the present invention.

[0043] Figure 6 This is a schematic diagram of the reinforcement of a three-dimensional reinforced composite material joint structure according to the present invention.

[0044] In the diagram, ① is the carbon fiber composite layer, ② is the metal insert, and ③ is the metal reinforcement. Metal-reinforced microrods Support network. Detailed Implementation

[0045] like Figure 1 , Figure 2 As shown, a three-dimensional reinforced composite material joint structure has a basic shape of a flange with an annular boss. The main structure consists of carbon fiber composite material layers ①, with externally connected metal inserts ② and metal reinforcements ③ interspersed between the composite material layers.

[0046] like Figure 3 , Figure 4 As shown, the carbon fiber composite layer is formed by layup and curing of carbon fiber prepreg, with a maximum thickness of 55 mm. It includes carbon fiber woven fabric prepreg and carbon fiber unidirectional tape prepreg, wherein the areal density of the carbon fiber woven fabric prepreg is 320 g / m³. 2 The carbon fiber is 3K T300 grade, woven perpendicularly, and the resin is MT3 type epoxy resin with a curing temperature of 132.5 ± 2.5℃. The areal density of the unidirectional tape prepreg is 300 g / m². 2 It contains 12K T700 grade carbon fiber and HT2 type epoxy resin, with a curing temperature of 182.5 ± 2.5℃.

[0047] like Figure 5As shown, the metal insert is machined from high-strength alloy steel 30CrMnSi and is mounted on the composite material layer through a connecting hole for connection to external mechanisms. The metal insert is tapered, with a large end diameter of 30mm and a small end diameter of 18mm. A threaded hole, M10 in size, is located at the small end of the insert, with a hole depth of 42mm and an effective thread depth of 35mm. The side of the insert serves as a load-bearing surface to prevent axial torsion.

[0048] like Figure 6 As shown, the reinforcing metal microrod and support network The structure consists of vertically interspersed between the composite material layers. The support mesh has the same dimensions as the bottom surface of the composite material. The metal reinforcing microrods are arranged in six concentric circles with the central axis as the center, with a radial spacing of 15 mm and a circumferential division of 120 equal parts. The length of the metal reinforcing microrods at each location is consistent with the thickness of the composite material layer at that location.

[0049] The following is a fabrication process for a three-dimensional reinforced composite material joint structure:

[0050] (1) Mold cleaning and assembly: Clean the mold with a high-pressure air gun and acetone respectively. After the acetone has completely evaporated, apply Kentian PMR non-silicone release agent three times, with an interval of 30 minutes between each application.

[0051] (2) Prepreg cutting and sorting: Use an automatic feeder to cut and number the required shape, size and fiber arrangement angle of each layer of prepreg;

[0052] (3) Prepreg laying and preforming: Lay the assembled female mold, first lay one layer of woven fabric prepreg on the bottom surface, and then lay other unidirectional strip prepregs layer by layer by layer through variable cross-section incremental lay-up method, with the lay-up angles being [(0° / 45° / 90° / -45° / 0°)]. s ] n° Vacuum bagging and vacuum pre-forming are performed every 3 layers of material, each lasting 15 minutes.

[0053] (4) Reinforcement installation: The reinforcement is implanted into the composite material layer, and finally the woven fabric prepreg of the top layer is laid on the top surface. After the mold is closed, it is placed on the hot press platform for cold pressing preforming for 60 minutes at a pressure of 1.73 MPa.

[0054] (5) Curing: Complete the curing process according to the temperature / pressure-time curing curve in the process instruction document, and then release the pressure and demold;

[0055] (6) Machining: Trim the edges of the composite material layer, and then machine the corresponding size of the mounting holes on the composite material layer according to the metal inserts;

[0056] (7) Metal insert bonding: After the surface of the metal insert column is sandblasted and cleaned, adhesive is applied and it is installed into the mounting hole on the joint. After the adhesive cures, the production of composite material joint is completed.

[0057] This invention utilizes microrods to reinforce the interlayer structure within the composite material, thereby hindering crack propagation and preventing premature failure of the overall structure under load due to brittle fracture of the interlayer resin layer. This improves the structural stability and ultimate load capacity of the composite material joint.

[0058] The above description is merely an example embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the concept of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A three-dimensional reinforced composite material joint, characterized in that: It includes a composite material layer, several reinforcements embedded in the composite material layer, and several metal inserts within the composite material layer; The composite material layer is circular and is formed by layup, molding and curing of carbon fiber prepreg. The composite material layer is divided into an outermost surface layer and a flat layer under the surface layer. The surface layer is made of carbon fiber woven fabric prepreg. The lay-up layer uses carbon fiber unidirectional tape prepreg; The reinforcement is composed of metal-reinforced microrods and a support mesh; Metal-reinforced microrods are connected to a support mesh, which is located between the surface layer and the paving layer of the composite material layer; the metal-reinforced microrods on the reinforcement are vertically implanted into the composite material layer; the length of the metal-reinforced microrods at each part of the reinforcement is consistent with the thickness of the composite material layer at that location. The metal insert penetrates the composite material layer. The metal insert is conical and has a threaded hole with an effective thread depth of more than 30% of the height of the metal insert.

2. The three-dimensional reinforced composite material joint according to claim 1, characterized in that: The carbon fiber in the surface layer is of grade T300 or higher; the carbon fiber in the lay-up layer is of grade T700 or higher.

3. The three-dimensional reinforced composite material joint according to claim 1, characterized in that: The metal-reinforced microrods are arranged in 5 to 15 concentric circles with the central axis as the center, and are divided into 100 to 360 equal parts in the circumferential direction.

4. A three-dimensional reinforced composite material joint according to claim 1, characterized in that: One end of the metal-reinforced microrod is connected to the support mesh.

5. A three-dimensional reinforced composite material joint according to claim 1, characterized in that: The small end of the metal insert has a threaded hole.

6. A three-dimensional reinforced composite material joint according to claim 1, characterized in that: The threaded hole depth is 80-90% of the insert height; the effective thread depth is 30-40% of the insert height.

7. The method for preparing a three-dimensional reinforced composite material joint according to claim 1, characterized in that: The method includes: (1) Mold cleaning and assembly: First, use high-pressure gas and organic solvent to clean each part of the mold, remove dust, oil and other impurities from the mold surface, then apply release agent to each contact surface of the mold, and finally assemble the female mold according to the mold drawing for use; (2) Cutting and sorting of prepreg sheets: The shape, size and fiber arrangement angle of each layer of the composite material structure are determined by design. Then, the prepreg sheets are cut by an automatic feeder and numbered according to the layup sequence. (3) Prepreg laying and preforming: The assembled female mold is laid with prepreg, and the specific laying scheme is as follows: First, lay the bottom surface layer, which is a single layer of carbon fiber woven fabric prepreg. Then, the internal flat layer is laid. This area uses carbon fiber unidirectional tape prepreg. The number of prepreg layers is determined according to the product thickness and design documents. The layers are laid one by one through a variable cross-section incremental layup method. (4) Reinforcement installation: The reinforcement is implanted into the composite material layer to ensure that the metal reinforcement microrods are vertically inserted between the layers. Finally, the woven fabric prepreg on the top surface is laid on the support mesh surface. After the mold is closed, it is placed on the hot press platform for final cold pressing preforming. (5) Curing: A temperature measuring device is arranged inside the mold and connected to a thermometer to control the mold temperature. The curing process is completed according to the temperature / pressure-time curing curve in the process instruction document, and then the pressure is released and the mold is demolded. (6) Machining: Machining holes for metal inserts are made on the composite material joint body. The number and size of the holes are matched with the metal inserts. The specific values ​​are determined according to the structural and strength design scheme. (7) Installation of metal inserts: After cleaning the surface of the column, apply adhesive and install it into the mounting hole on the joint. Apply pressure and heat, and obtain the finished composite material joint after the adhesive has cured.

8. The method for preparing a three-dimensional reinforced composite material joint according to claim 7, characterized in that: The height of the metal insert should be slightly shorter than the machining mounting hole size of the composite layer.

9. The method for preparing a three-dimensional reinforced composite material joint according to claim 7, characterized in that: The application of release agent in step (1) is as follows: release agent needs to be sprayed on the surface of each block of the mold, and sprayed repeatedly 2-4 times, with an interval of 20-30 minutes each time. Finally, after the release agent has completely dried and formed a film, the assembly step is carried out.

10. The method for preparing a three-dimensional reinforced composite material joint according to claim 7, characterized in that: Step (3) Pre-forming process includes, but is not limited to, vacuuming or cold pressing pre-forming through multiple male molds; Step (7) Sandblasting the surface of the metal insert column before applying adhesive.

11. The application of the three-dimensional reinforced composite material joint of claim 1 in solid rocket motor casings.

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