Preparation method of replaceable zero-ablation stealth composite empennage

Abstract

The invention relates to a preparation method of a replaceable zero-ablation stealth composite empennage, and solves the problem that the existing empennage preparation technology only carries out repeatable and replicable production and does not fully consider the product viability under a complex electromagnetic environment condition. The empennage structurally comprises an ablative layer, a buffer layer, a stealth layer and a composite heat insulation layer, the ablative layer on the outermost side is formed by RTM of a needling prefabricated part, the buffer layer is made of high-temperature-resistant silicon rubber, the stealth layer in the middle is formed by spraying, and the composite heat insulation layer on the inner layer is formed by laying prepregs. The stealth material is mixed in the empennage through a certain forming process, and the stealth performance of the empennage is achieved by fully utilizing the wave-transparent characteristic of the outer skin of the empennage. Meanwhile, in the empennage design process, an ablation layer, a buffer layer, a stealth layer and a composite heat insulation layer are used, replaceable zero-ablation and repeated use of the empennage are achieved, the survivability of a product is improved, and the use cost of an aerospace product is reduced.

Description

Technical Field

[0001] This invention relates to the manufacture of tail fins for products in the aerospace field, and specifically to a method for preparing a replaceable zero-ablation stealth composite material tail fin. Background Technology

[0002] In the aerospace field, the tail fin serves to provide flight stability and control flight direction. However, with the rapid development of radar detection technology, conventional metal or composite material tail fins are easily detected and locked by radar, exposing aerospace products. To address this issue, various solutions have been proposed both domestically and internationally. Applying a stealth coating to the outer surface of the tail fin is one common method. However, after transportation, assembly, debugging, or multiple flight tests, the coating is susceptible to risks such as peeling, damage, and performance degradation, leading to a weakening of the product's anti-reconnaissance capabilities.

[0003] CN202411564168.5 (A die-casting apparatus for manufacturing tail fins of small aircraft) describes the die-casting process for tail fins of small aircraft, resulting in a metal tail fin with limited performance. CN201810640503.3 (A manufacturing method for a composite material horizontal tail fin for small and medium-sized UAVs) describes a composite molding method using prepreg fabric lay-up, upper and lower skins, and then silicone rubber injection to produce the tail fin. This method features a lightweight design but limited performance and cannot effectively meet the survivability requirements of current complex electromagnetic environments. Existing tail fin manufacturing technologies only enable repetitive and replicable production, failing to fully consider the product's survivability under complex electromagnetic conditions. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a replaceable zero-ablation stealth composite material tail fin that simultaneously meets the stealth function requirements in complex electromagnetic environments in the aerospace field and the low-cost requirement of being replaceable and reusable after multiple flights.

[0005] This invention is achieved through the following technical solutions: A method for preparing a replaceable zero-ablation stealth composite material tail fin includes: I. The tail fin's structural design employs an ablation layer + buffer layer + stealth layer + composite heat insulation layer; II. Tail Fold Forming Method: The outermost ablation layer is formed using RTM (Real-Time Molding) with needle-punched preforms; the buffer layer is primarily made of high-temperature resistant silicone rubber, utilizing its low dielectric constant and dielectric loss, while also exhibiting good transmittance to broadband waves. During flight, it can buffer vibrations from within the product, thus protecting the stealth layer; the middle stealth layer is formed using spray coating; and the inner composite thermal insulation layer is formed using prepreg layup.

[0006] "RTM" stands for Resin Transfer Molding, a method of molding composite materials. It mainly involves placing reinforcing materials, such as fibers, into a mold, closing the mold, pressing it together, injecting resin under certain temperature and pressure, and then curing it into shape.

[0007] Needle-punched preform: This invention produces the outermost ablation layer preform of the tail fin by needle-punching a quartz mesh.

[0008] The stealth coating used in this invention is a lightweight stealth coating with graphene added as an absorbent. The dry film surface density of the coating is ≤1.2kg / m2, the thickness of the stealth coating is 1.3±0.1mm, and the electromagnetic wave reflectivity is ≤-6.5dB in the 9-11GHz frequency band.

[0009] Third, the outer skin of the tail fin, namely the ablation layer, has good wave transmission characteristics. After electromagnetic waves penetrate the ablation layer and the buffer layer, they encounter the stealth layer, which absorbs and scatters the electromagnetic waves, resulting in a reduction of echo and achieving the stealth effect. At the same time, after multiple flights, the ablation layer is removed by processing the buffer layer as the processing standard, and then the ablation layer is re-needled and reshaped for replacement, achieving the function of being replaceable with zero ablation.

[0010] The technical solution of this invention is: (1) Preparation of prepreg.

[0011] (2) Forming of composite insulation layer.

[0012] (3) Stealth layer spraying and performance testing.

[0013] (4) Preparation and shaping of the ablation layer.

[0014] (5) The tail wing is integrally formed and replaced.

[0015] Further, the preparation of the prepreg in step (1) is mainly used to form the composite heat insulation layer of the tail fin, and mainly includes the preparation of prepreg fabric and prepreg yarn. The composite heat insulation layer of the present invention adopts carbon fiber / phenolic prepreg fabric, but is not limited to the above materials; other prepreg materials can also be used. The phenolic resin content of the carbon fiber / phenolic prepreg fabric used in the present invention is 35±5%, and the prepreg fabric is cut according to the parting pattern in the tail fin composite heat insulation layer layup process.

[0016] More preferably, the prepreg used in the preparation of the outer layer of the tail wing composite heat insulation layer of the present invention is a blended woven fabric / low-density phenolic resin prepreg, that is, glass microspheres are added to the phenolic resin, and the amount of glass microspheres added is adjusted according to the density of the composite material. The amount of glass microspheres added in the present invention accounts for 20% of the total volume of the resin. The blended woven fabric is made of carbon fiber and quartz fiber mixed and woven into a two-dimensional plain weave fabric.

[0017] More preferably, the carbon fiber / phenolic prepreg and the blended woven fabric / low-density phenolic resin prepreg are cut according to the parting pattern during the layup process of the tail wing composite insulation layer, that is, after being cut on the fabric cutting machine according to the parting pattern of [(0° / 90°)(45° / -45°)] quasi-isotropic design, the prepregs are numbered, and the angle is distinguished by defining the radial fiber bundle parallel to the prepreg as 0° and the counterclockwise rotation angle as positive.

[0018] More preferably, the prepreg yarn, i.e. the composite insulation layer, is used when the local structural mechanical properties need to be strengthened during the laying process. In this invention, carbon fiber / phenolic unidirectional prepreg yarn is used, and the phenolic resin content is also 35±5%. The carbon fiber is heated to 80°C, impregnated with phenolic resin, and then dried at 80-90°C.

[0019] Further, step (2) is the forming of the composite insulation layer, which is mainly the forming of the tail wing composite insulation layer. Its function is to maintain shape, bear load and provide insulation.

[0020] More preferably, the present invention first uses a carbon fiber / phenolic prepreg to lay up the load-bearing grid structure of the tail fin composite thermal insulation layer, and then pre-cures it. The outer layer of the composite thermal insulation layer uses a blended woven fabric / low-density phenolic resin prepreg to lay up the composite thermal insulation layer, and then the composite thermal insulation layer is co-cured. The carbon fiber / phenolic grid structure is mainly for load-bearing, while the use of blended woven fabric / low-density phenolic resin prepreg to lay up the composite thermal insulation layer is mainly for weight reduction. The composite thermal insulation layer can be recycled after multiple test flights of the tail fin.

[0021] More preferably, the tail fin composite heat insulation layer is first formed by laying carbon fiber / phenolic prepreg into a grid load-bearing structure and then pre-curing it. After assembling the mold and applying a release agent, the mold is placed in an oven and preheated to 50-60°C. The carbon fiber / phenolic prepreg is then laid in a [(0° / 90°)(45° / -45°)] pattern. For the grid forming grooves, cut carbon fiber / phenolic unidirectional prepreg yarns and carbon fiber / phenolic prepreg are mixed and mixed alternately to fill the grooves until the specified layup thickness is reached. After vacuuming, the layer is pre-cured at 100-120°C for 2-2.5 hours.

[0022] More preferably, the composite insulation layer is formed by laying up a blended woven fabric / low-density phenolic resin prepreg, and the composite insulation layer is co-cured. The blended woven fabric / low-density phenolic resin prepreg is also laid up on the pre-cured carbon fiber / phenolic surface of the composite insulation layer according to the [(0° / 90°)(45° / -45°)] parting pattern until the thickness required by the design of the composite insulation layer is achieved.

[0023] More preferably, after the above-mentioned composite thermal insulation layer of the tail fin is completely covered by vacuum, it is placed in an autoclave, the room temperature is raised to 120±5℃ and kept at that temperature for 2 hours; at 100℃, the pressure is increased to 2MPa, and vacuuming is started at 90℃ and maintained at ≤20kpa; the temperature is raised to 150±5℃ in 30 minutes, and the temperature and pressure are maintained at this temperature for 5 hours, and then the temperature is naturally cooled to below 60℃ to obtain the composite thermal insulation layer blank.

[0024] More preferably, the above-mentioned composite insulation layer blank is processed by CNC machine tool to remove the machining allowance, so as to obtain a composite insulation layer with dimensional accuracy that meets the design requirements.

[0025] Further, in step (3), the stealth layer spraying and performance testing involve spraying a lightweight stealth coating with graphene added as an absorbent onto the composite heat insulation layer obtained in step (2). When the stealth coating reaches the specified thickness of 1.3±0.1mm, the electromagnetic wave reflectivity of the coating is tested in the 9-11GHz frequency band, requiring an electromagnetic wave reflectivity ≤-6.5dB.

[0026] More preferably, the stealth coating refers to a coating in which graphite flakes are added and uniformly dispersed to achieve efficient absorption of broadband radar waves.

[0027] More preferably, spraying is a commonly used construction method that can adapt to the difficulties of construction on complex surfaces. The stealth coating used in this invention is suitable for spraying.

[0028] More preferably, the spraying process employs an intermittent application method to prevent paint sagging. The interval between each application is 20-30 minutes, with a total of approximately 86 applications, achieving a thickness of 1.3 ± 0.1 mm. The coating is cured at room temperature for 7 days.

[0029] More preferably, the electromagnetic wave test can be performed in a microwave anechoic chamber using static radar cross section (RCS) measurement and characterization, or dynamically using a portable reflectivity meter.

[0030] Furthermore, in step (4), the ablation layer is prepared and formed. The ablation layer is the outermost layer of the tail fin, which plays a role in resisting ablation and withstanding airflow erosion. In this invention, the outermost ablation layer preform of the tail fin is made by needle-punched quartz mesh, and then formed by RTM molding.

[0031] More preferably, the needle-punched quartz mesh method involves laying down a quartz fiber mesh and satin fabric on the inner surface of the dummy ablation layer, and then needle-punching the amorphous fibers of the quartz fiber mesh in the X direction to the Y direction to improve the interlayer strength of the preform until the specified ablation layer size is achieved. The ablation layer preform can be prepared separately and finally bonded to the stealth layer + composite insulation layer through a buffer layer.

[0032] More preferably, in the RTM molding, the resin used in this invention is low-density phenolic resin. Other vinyl resins, unsaturated polyester resins, bismaleimide resins, and medium-high temperature epoxy resins can also be used as resin materials for composite molding. The curing conditions for the phenolic resin used in this invention are 100-120℃ / 4h. The mold for the ablation layer has a glue injection port on the bottom plate and an overflow port located at the ribs on the upper part of the mold. The mold is formed by bolt pressure and upper and lower mold closing.

[0033] More preferably, the molding method and parameters of the ablation layer are not unique. In this invention, the preform is sealed in a vacuum bag and vacuumed, then sent to an oven at 80°C for 2 hours of pre-pressing. After that, it is placed in a female mold, and a silicone rubber strip is placed in the sealing groove of the male mold. The bolts are tightened to close the mold. A resin injection machine is connected to the injection port, and a vacuum source is connected to the overflow port to maintain a vacuum degree of not less than 0.85MPa. The injection machine temperature is set to 80~90°C, the resin flow rate is 1~5mL / s, and the injection pressure is 0.5~0.6MPa. After the injection is completed, the injection port and the overflow port are closed. The entire mold is placed in an oven at 100-120°C and cured for 4 hours. After natural cooling, it is demolded and assembled.

[0034] Furthermore, the tail wing integral forming and replacement described in step (5) involves bonding the ablation layer and the stealth layer + composite heat insulation layer together through the buffer layer to form an integral tail wing.

[0035] More preferably, the buffer layer is bonded with silicone rubber. The buffer layer serves five purposes: first, to prevent thermal mismatch between the ablation layer and the composite insulation layer in high and low temperature environments, which could lead to increased stress at the interface between the two layers and cause cracking of the tail fin; second, after recovery, the tail fin can be processed and removed by using the buffer layer as a reference layer, enabling rapid replacement; third, the main base material used in the buffer layer is silicone rubber, which has low thermal conductivity and good heat insulation properties, effectively protecting the internal components of the tail fin; fourth, the silicone rubber layer has good light transmission characteristics, allowing the stealth coating to function; and fifth, it achieves the function of protecting the stealth layer by sacrificing the ablation layer.

[0036] More preferably, the buffer layer is made by spraying, which has the characteristics of multi-directionality, all-angle, and strong adaptability to the target shape. The thickness of the buffer layer in this invention is designed to be 0.3-0.4 mm, and the thickness of the buffer layer is measured by wet film gauge during the construction process.

[0037] More preferably, the tail fin is integrally formed, that is, the ablation layer and the stealth layer + composite heat insulation layer are bonded together by the adhesive effect of silicone rubber.

[0038] More preferably, the replacement involves removing the ablation layer after multiple flight tests of the tail fin, based on the buffer layer, and then remanufacturing the buffer layer and the ablation layer. After the tail fin is recovered from its mission, it is placed on a machine tool and processed according to the position and thickness of the buffer layer to remove the carbonized or ablated layer. The buffer layer and the ablation layer are then remanufactured according to the above steps to obtain a replaceable zero-ablation stealth composite material tail fin.

[0039] This invention addresses the high survivability of tail fins in complex electromagnetic environments. By combining the designability of composite materials with the wave transmission properties of fiberglass, stealth materials are embedded within the tail fin through a specific molding process. This fully utilizes the wave transmission characteristics of the outer skin of the tail fin to achieve stealth performance. Furthermore, the tail fin design incorporates an ablation layer, a buffer layer, a stealth layer, and a composite heat insulation layer, enabling the tail fin to be replaceable with zero ablation and reused multiple times, thus improving the product's survivability and reducing the operating costs of aerospace products. Attached Figure Description

[0040] Figure 1 Schematic diagram of the composite thermal insulation layer layup for the tail fin; Figure 2 Schematic diagram of tail fin cross section; The numbers in the diagram indicate: 1. Composite insulation layer; 2. Carbon fiber / phenolic prepreg; 3. Blended woven fabric / low-density phenolic resin prepreg; 4. Stealth layer; 5. Buffer layer; 6. Ablation layer. Detailed Implementation

[0041] The design concept of this invention for a replaceable zero-ablation stealth composite material tail fin is as follows: heat protection is achieved by consuming the ablation layer of the tail fin. After multiple flight tests, the outer ablation layer of the tail fin is replaced, while the inner lightweight composite heat insulation layer and stealth layer are recycled. By reducing the weight of the composite heat insulation layer, the increased thickness of the stealth and ablation layers is achieved, thus realizing the recycling of the tail fin. Ablation layer preforms are fabricated using a needle-punched quartz mesh method and then formed in a non-autoclave manner. The forming process is simple and highly efficient. During the preform fabrication process, the fibers are irregularly interwoven longitudinally, cleverly avoiding the risk of interlayer erosion during flight and fully utilizing the ablation effect of the ablation layer. A buffer layer is designed as an intermediate layer, which can serve as a reference layer for processing and also provide effective heat insulation and wave transmission.

[0042] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description is provided in conjunction with the appendix. Figure 1 , 2 The present invention will be described in detail with reference to specific embodiments.

[0043] (1) Preparation of prepreg.

[0044] The preparation of the prepreg in step (1) is mainly used to form the composite heat insulation layer of the tail fin, mainly including the preparation of prepreg fabric and prepreg yarn. The composite heat insulation layer of the present invention adopts carbon fiber / phenolic prepreg fabric, but is not limited to the above materials, and other prepreg materials can also be used. The phenolic resin content of the carbon fiber / phenolic prepreg fabric used in the present invention is 35±5%. After the prepreg fabric is prepared, it is cut according to the parting pattern in the tail fin composite heat insulation layer layup process. In the present invention, the prepreg fabric used to prepare the inner layer of the tail fin composite heat insulation layer (1) is a blended woven fabric / low-density phenolic resin prepreg fabric (3). The specific method is to add glass microspheres to the phenolic resin and adjust the amount of glass microspheres added according to the density of the composite material. In the present invention, the amount of glass microspheres added accounts for 20% of the total volume of phenolic resin. The blended woven fabric is made of carbon fiber and quartz fiber mixed and woven into a two-dimensional plain weave fabric. The carbon fiber / phenolic prepreg fabric (2) and the blended woven fabric / low-density phenolic resin prepreg fabric (3) prepared above are arranged according to the tail fin composite heat insulation layer (e.g. Figure 1 The prepreg fabric is cut in a pattern during the layup process, i.e., according to the quasi-isotropic design of [(0° / 90°)(45° / -45°)] on the cutting machine. The prepreg fabric is then numbered, and the angle is defined as 0° for the radial fiber bundles parallel to the prepreg fabric, and positive for counterclockwise rotation. The prepreg yarn, i.e., the tail wing composite insulation layer (such as...) Figure 1 When local mechanical properties need to be strengthened during the laying process, this invention uses carbon fiber / phenolic unidirectional prepreg yarn with a phenolic resin content of 35±5%. The carbon fiber is heated to 80°C, impregnated with phenolic resin, and then dried at 80-90°C.

[0045] (2) Forming of composite insulation layer.

[0046] Step (2) Composite insulation layer (e.g.) Figure 1 The molding process mainly describes the composite heat insulation layer of the tail fin (such as...). Figure 1The molding process serves to shape, support, and insulate. In this invention, carbon fiber / phenolic prepreg is first used to lay up the load-bearing grid structure of the tail wing composite heat insulation layer and pre-cur it. Specifically, the tail wing composite heat insulation layer is first laid up using carbon fiber / phenolic prepreg (2) to form the grid load-bearing structure and pre-cured. After the mold is assembled and coated with release agent, it is placed in an oven and the mold temperature is preheated to 50-60℃. The carbon fiber / phenolic prepreg (2) is laid up according to the [(0° / 90°)(45° / -45°)] parting method. For the grid forming groove, the cut carbon fiber / phenolic unidirectional prepreg yarn and carbon fiber / phenolic prepreg (2) are mixed and filled until the specified layup thickness is reached. After vacuuming, it is pre-cured at 100~120℃ for 2~2.5 hours. The outer layer of the composite heat insulation layer (1) is laid up using a blended woven fabric / low-density phenolic resin prepreg (3), and then the composite heat insulation layer (such as Figure 1 Co-curing. The specific operation is as follows: a composite insulation layer is formed by stacking a blended woven fabric / low-density phenolic resin prepreg (3), and the composite insulation layer is co-cured. On the pre-cured carbon fiber / phenolic surface on the outer layer of the composite insulation layer, the blended woven fabric / low-density phenolic resin prepreg (3) is also laid in the [(0° / 90°)(45° / -45°)] pattern until the thickness required by the design of the composite insulation layer (1) is reached.

[0047] More preferably, after the above-mentioned composite heat insulation layer of the tail fin is completely covered with vacuum, it is placed in a thermostatic precipitator, the room temperature is raised to 120±5℃ and kept at that temperature for 2 hours; at 100℃, the pressure is increased to 2MPa, and vacuuming is started at 90℃ and maintained to ≤20kpa; the temperature is raised to 150±5℃ in 30 minutes, and kept at this temperature and pressure for 5 hours, and then naturally cooled to below 60℃ to obtain a composite heat insulation layer blank. The above-mentioned composite heat insulation layer blank is processed by CNC machine tool to remove the machining allowance, and a composite heat insulation layer (1) with dimensional accuracy meeting the design requirements is obtained. The carbon fiber / phenolic grid structure is mainly for load bearing, while the composite heat insulation layer formed by using mixed woven fabric / low-density phenolic resin prepreg (3) is mainly for weight reduction. The composite heat insulation layer is recycled after multiple test flights of the tail fin.

[0048] (3) Stealth layer spraying and performance testing.

[0049] Step (3) involves the spraying and performance testing of the stealth layer (4). A lightweight stealth coating with added graphene as an absorbent is sprayed onto the composite heat insulation layer (1) obtained in step (2). The spraying process is intermittent to prevent coating sagging. The interval between each application is 20-30 minutes, with approximately 86 applications in total, achieving a thickness of 1.3 ± 0.1 mm. The coating is cured at room temperature for 7 days. Static radar cross section (RCS) measurements can be performed in a microwave anechoic chamber within the 9-11 GHz frequency band, or dynamic measurements can be performed using a portable reflectivity meter. The electromagnetic reflectivity of the coating is tested, requiring an electromagnetic reflectivity ≤ -6.5 dB.

[0050] (4) Preparation and shaping of the ablation layer.

[0051] The ablation layer (6) described in step (4) is prepared and formed. The ablation layer (6) is the outermost layer of the tail fin, which plays a role in resisting ablation and withstanding airflow erosion. In this invention, the outermost ablation layer (6) preform of the tail fin is made by needle-punched quartz mesh, and then formed by RTM molding. The needle-punched quartz mesh method is to lay quartz fiber mesh and satin cloth on the inner surface of the dummy of the ablation layer (6), and then use needle punching to amorphously hook the X-direction fibers of the quartz fiber mesh to the Y-direction to improve the interlayer strength of the preform until the specified ablation layer size is reached. The ablation layer (6) preform can be prepared separately and finally bonded to the stealth layer (4) + composite heat insulation layer (1) through a buffer layer (5). The RTM molding process used in this invention employs low-density phenolic resin. Other vinyl resins, unsaturated polyester resins, bismaleimide resins, and medium-high temperature epoxy resins can also be used as resin materials for composite molding. The curing conditions for the phenolic resin used in this invention are 100-120℃ / 4h. The mold for the ablation layer (6) has an injection port on the bottom plate and an overflow port on the rib at the top of the mold. The mold is formed by bolt pressure and upper and lower mold closing.

[0052] The molding method and parameters of the ablation layer (6) are not unique. In this invention, the preform is sealed in a vacuum bag and vacuumed, then sent to an oven and pre-pressed for 2 hours at a temperature of 80°C. After that, it is placed in the female mold, and a silicone rubber strip is placed in the sealing groove of the male mold. The bolts are tightened and the mold is closed. A resin injection machine is connected to the injection port, and a vacuum source is connected to the overflow port to maintain a vacuum degree of not less than 0.85MPa. The temperature of the injection machine is set to 80~90°C, the resin flow rate is 1~5mL / s, and the injection pressure is 0.5~0.6MPa. After the injection is completed, the injection port and the overflow port are closed. The mold is placed in an oven at 100-120°C and cured for 4 hours. After natural cooling, it is demolded and assembled.

[0053] (5) The tail wing is integrally formed and replaced.

[0054] Step (5) describes the overall forming and replacement of the tail fin, which involves bonding the ablation layer (6) and the stealth layer (4) + composite heat insulation layer (1) together through the buffer layer (5) to form an integral tail fin. Figure 2 The buffer layer (5) is made of silicone rubber adhesive. The functions of the buffer layer (5) are: first, to prevent thermal loss between the ablation layer (6) and the composite heat insulation layer (1) in high and low temperature environments, which would increase stress at the interface between the two layers and cause the tail fin to crack; second, after the tail fin is recovered, the buffer layer (5) can be used as a reference layer for the ablation layer (6) to be processed and removed, so as to achieve rapid replacement; third, the main base material used in the buffer layer (5) is silicone rubber, which has low thermal conductivity and good heat insulation properties, and can effectively protect the internal components of the tail fin; fourth, the silicone rubber layer has good wave transmission characteristics, which allows the stealth coating to play a role; and fifth, the stealth layer is protected by sacrificing the ablation layer (6). The buffer layer (5) is made by spraying, which has the characteristics of multi-directionality, all-angle, and strong adaptability to the target shape. The thickness of the buffer layer (5) in this invention is designed to be 0.3-0.4 mm. The thickness of the buffer layer (5) is measured by wet film gauge during the construction process.

[0055] The tail fin is integrally formed, that is, the ablation layer (6) and the stealth layer (4) + composite heat insulation layer (1) are bonded together by the adhesive effect of silicone rubber. The replacement means that after multiple flight tests of the tail fin, the ablation layer (6) is removed based on the buffer layer (5), and the buffer layer (5) and the ablation layer (6) are remade. After the tail fin is recovered after the mission, it is placed on a machine tool and processed according to the position and thickness of the buffer layer (5) to remove the carbonized or ablated ablation layer (6), and the buffer layer (5) and the ablation layer (6) are remade according to the above steps to obtain a replaceable zero-ablation stealth composite material tail fin.

[0056] Compared with the prior art, the present invention has the following advantages: (1) A method for preparing a replaceable zero-ablation stealth composite material tail fin is provided.

[0057] (2) By combining the designability of composite materials with the good process adaptability of spraying, a replaceable zero-ablation stealth tail wing is obtained.

[0058] (3) By replacing the ablation layer of the tail fin, the tail fin can be recycled after multiple flight tests and recovery, with only the ablation layer being replaced.

[0059] (4) The tail wing ablation layer is formed independently and then assembled by bonding with silicone rubber, so that the stealth functional layer can be replaced with zero ablation in terms of process technology.

[0060] (5) By utilizing the wave-transmitting properties of the ablation layer and the buffer layer, the wave-absorbing effect of the stealth layer is fully utilized, and the stealth layer is effectively protected during flight through structural design.

[0061] (6) The buffer layer can not only absorb the stress caused by the different coefficients of thermal expansion between the inner composite heat insulation layer + stealth layer and the outer ablation layer of the tail fin, but also be used as a processing benchmark to remove the outer ablation layer after recycling, without damaging the composite heat insulation layer + stealth layer. A portion of the silicone rubber pad can be left on the stealth layer during processing, and it is almost unaffected by the bonding interface after re-application.

[0062] (7) The composite heat insulation layer of the tail wing is filled with prepreg yarn in the carbon fiber / phenolic grid design, which has structural load-bearing characteristics. The mixed woven fabric / low-density phenolic resin stacking molding has the effect of weight reduction and internal heat insulation.

[0063] (8) By using low-density resin, the weight of the composite insulation layer is effectively reduced to improve the effective ablation thickness of the ablation layer, thereby enabling the tail fin to be recyclable.

Claims

1. A method for preparing a replaceable zero-ablation stealth composite material tail fin, characterized in that: The tail fin structure consists of an ablation layer, a buffer layer, a stealth layer, and a composite heat insulation layer. The outermost ablation layer is formed using RTM molding of needle-punched preforms. The buffer layer is made of high-temperature resistant silicone rubber, which utilizes its low dielectric constant and dielectric loss while maintaining good transmittance to broadband waves. During flight, it can buffer vibrations from within the product, thus protecting the stealth layer. The middle stealth layer is formed by spraying. The inner composite heat insulation layer is formed by prepreg layup. The specific methods include: 1) prepreg preparation; 2) composite heat insulation layer forming; 3) stealth layer spraying and performance testing; 4) ablation layer preparation and forming; and 5) overall tail fin forming and replacement.

2. The method for preparing a replaceable zero-ablation stealth composite material tail fin according to claim 1, characterized in that: The needle-punched preform is fabricated by needle-punching a quartz mesh to create the outermost ablation layer preform of the tail fin. The stealth coating of the stealth layer is a lightweight stealth coating with graphene added as an absorbent. The dry film surface density of the coating is ≤1.2kg / m2, the thickness of the stealth coating is 1.3±0.1mm, and the electromagnetic wave reflectivity is ≤-6.5dB in the 9-11GHz frequency band. The outer skin of the tail fin, i.e., the ablation layer, has good wave transmission characteristics. After electromagnetic waves penetrate the ablation layer and the buffer layer, they encounter the stealth layer, which absorbs and scatters the electromagnetic waves, resulting in reduced echo and achieving the stealth effect. At the same time, after multiple flights, the ablation layer is removed by processing the buffer layer as the processing benchmark, and then the ablation layer is re-needled and formed for replacement, achieving the function of replacement with zero ablation.

3. The method for preparing a replaceable zero-ablation stealth composite material tail fin according to claim 1, characterized in that: In step 1), the preparation of the prepreg is used to form the composite heat insulation layer of the tail fin, including the preparation of prepreg fabric and prepreg yarn. The composite heat insulation layer adopts carbon fiber / phenolic prepreg fabric, and the phenolic resin content used in the carbon fiber / phenolic prepreg fabric is 35±5%. After the prepreg fabric is prepared, it is cut according to the parting pattern in the tail fin composite heat insulation layer layup process. The prepreg fabric used in the inner layer of the tail fin composite heat insulation layer is a blended woven fabric / low-density phenolic resin prepreg fabric. Specifically, glass microspheres are added to the phenolic resin, and the amount of glass microspheres added is adjusted according to the density of the composite material. The amount of glass microspheres added accounts for 20% of the total volume of the phenolic resin. The blended woven fabric uses carbon fiber and... Quartz fibers are blended and woven into a two-dimensional plain weave fabric. The carbon fiber / phenolic prepreg and the blended woven fabric / low-density phenolic resin prepreg prepared above are cut according to the parting pattern in the tail wing composite insulation layer layup process, that is, according to the parting pattern of [(0° / 90°)(45° / -45°)] quasi-isotropic design. After cutting on the fabric cutting machine, the prepregs are numbered. The angle is distinguished by the radial fiber bundle parallel to the prepreg as 0° and the counterclockwise rotation angle as positive. The prepreg yarn uses carbon fiber / phenolic unidirectional prepreg yarn with a phenolic resin content of 35±5%. The carbon fiber is heated to 80°C, impregnated with phenolic resin, and then dried at 80-90°C.

4. The method for preparing a replaceable zero-ablation stealth composite material tail fin according to claim 1, characterized in that: In step 2), the composite heat insulation layer is formed as follows: First, carbon fiber / phenolic prepreg is used to lay up the load-bearing grid structure of the tail wing composite heat insulation layer and pre-cur it. Specifically, the tail wing composite heat insulation layer is first formed by laying up carbon fiber / phenolic prepreg (2) to form the grid load-bearing structure and pre-curing it. After assembling the mold and brushing on the release agent, the mold is placed in an oven and the temperature of the mold is preheated to 50-60°C. The carbon fiber / phenolic prepreg is laid up according to the [(0° / 90°)(45° / -45°)] parting method. For the grid forming groove, the cut carbon fiber / phenolic unidirectional prepreg and carbon fiber / phenolic prepreg are mixed and mixed to fill the groove. Once the specified layer thickness is reached, vacuum is applied and then pre-cured at 100~120℃ for 2~2.5 hours; the outer layer of the composite insulation layer is laid with a blended woven fabric / low-density phenolic resin prepreg, and then the composite insulation layer is co-cured; the specific operation is as follows: the blended woven fabric / low-density phenolic resin prepreg is laid to form a composite insulation layer, and the composite insulation layer is co-cured; the blended woven fabric / low-density phenolic resin prepreg (3) is also laid on the pre-cured carbon fiber / phenolic surface on the outer layer of the composite insulation layer according to the [(0° / 90°)(45° / -45°)] type until the thickness required by the design of the composite insulation layer (1) is reached.

5. The method for preparing a replaceable zero-ablation stealth composite material tail fin according to claim 4, characterized in that: After the composite thermal insulation layer of the tail fin is laid up, it is completely vacuum-sealed and then placed in an autoclave. The room temperature is raised to 120±5℃ and held for 2 hours. At 100℃, the pressure is increased to 2MPa, and a vacuum is drawn at 90℃ and maintained at ≤20kPa. The temperature is raised to 150±5℃ after 30 minutes and held at this temperature and pressure for 5 hours. The temperature is then allowed to cool naturally to below 60℃ to obtain a composite thermal insulation layer blank. The above composite thermal insulation layer blank is then processed using a CNC machine tool to remove the machining allowance, resulting in a composite thermal insulation layer with dimensional accuracy meeting the design requirements. A carbon fiber / phenolic grid structure is used for support, and a composite thermal insulation layer is formed by laying up a mixed woven fabric / low-density phenolic resin prepreg. The composite thermal insulation layer is reused after multiple test flights of the tail fin.

6. The method for preparing a replaceable zero-ablation stealth composite material tail fin according to claim 1, characterized in that: In step 3), the stealth layer spraying and performance testing are as follows: a lightweight stealth coating with graphene added as an absorbent is sprayed onto the composite heat insulation layer obtained in step 2). The spraying process adopts an intermittent construction method to prevent coating sagging. The interval between each spraying is 20-30 minutes, and the thickness reaches 1.3±0.1mm. The coating is cured at room temperature for 7 days. In the 9-11GHz frequency band, static radar cross section (RCS) measurement is performed in a microwave anechoic chamber, or dynamic measurement is performed using a portable reflectivity meter to detect the electromagnetic wave reflectivity of the coating. The electromagnetic wave reflectivity is required to be ≤-6.5dB.

7. The method for preparing a replaceable zero-ablation stealth composite material tail fin according to claim 1, characterized in that: In step 4), the needle-punched quartz mesh method involves laying quartz fiber mesh and satin cloth on the inner surface of the dummy ablation layer, and then needle-punching the amorphous fibers of the quartz fiber mesh in the X direction to the Y direction to improve the interlayer strength of the preform until the specified ablation layer size is reached. The ablation layer preform is prepared separately and finally bonded to the stealth layer + composite heat insulation layer through a buffer layer. The resin used in the RTM molding is low-density phenolic resin, vinyl ester resin, unsaturated polyester resin, bismaleimide resin, and medium-high temperature epoxy resin. The curing conditions for phenolic resin are 100-120℃ / 4h. The mold for the ablation layer has an injection port on the bottom plate and an overflow port on the ribs at the top of the mold. The mold is formed by bolt pressure and upper and lower mold closing.

8. The method for preparing a replaceable zero-ablation stealth composite material tail fin according to claim 7, characterized in that: The ablation layer is formed by encapsulating the preform in a vacuum bag, evacuating it, and then placing it in an oven at 80℃ for 2 hours of pre-pressing. After that, it is placed in a female mold, and a silicone rubber strip is placed in the sealing groove of the male mold. The bolts are tightened to close the mold. A resin injection machine is connected to the injection port, and a vacuum source is connected to the overflow port to maintain a vacuum degree of not less than 0.85MPa. The injection machine temperature is set to 80~90℃, the resin flow rate is 1~5mL / s, and the injection pressure is 0.5~0.6MPa. After injection, the injection port and overflow port are closed. The entire mold is placed in an oven at 100-120℃ and cured for 4 hours. After natural cooling, it is demolded and assembled.

9. The method for preparing a replaceable zero-ablation stealth composite material tail fin according to claim 1, characterized in that: In step 5), the tail fin is integrally formed and replaced: the ablation layer and the stealth layer + composite heat insulation layer are bonded together by a buffer layer to form an integral tail fin; the buffer layer uses silicone rubber as an adhesive. The functions of the buffer layer are: first, to prevent thermal loss between the ablation layer and the composite heat insulation layer in high and low temperature environments, which would increase stress at the interface between the two layers and cause the tail fin to crack; second, after the tail fin is recovered, the buffer layer can be used as a reference layer for the ablation layer to be processed and removed, so as to achieve rapid replacement; third, the main base material used in the buffer layer is silicone rubber, which has low thermal conductivity and good heat insulation properties, and can effectively protect the internal components of the tail fin; fourth, the silicone rubber layer has good light transmission characteristics, which allows the stealth coating to play its role; and fifth, the stealth layer is protected by sacrificing the ablation layer. The buffer layer is made by spraying, and the thickness of the buffer layer is designed to be 0.3-0.4 mm. The thickness of the buffer layer is measured by wet film gauge during the construction process.

10. The method for preparing a replaceable zero-ablation stealth composite material tail fin according to claim 9, characterized in that: The replacement process involves placing the tail fin on a machine tool after it has been recovered from its mission. The machine tool is then used to process the tail fin according to the position and thickness of the buffer layer. The carbonized or ablated layer is removed, and the buffer layer and ablated layer are remade to obtain a replaceable zero-ablation stealth composite material tail fin.

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