Multifunctional gradient heat-proof structure suitable for planetary exploration reentry capsule

Abstract

The invention relates to a multifunctional gradient heat protection structure suitable for a planetary exploration reentry capsule, which comprises a large-area heat protection layer, an end cap, a bearing structure, a silicone rubber layer, a connecting screw and a gasket, and is characterized in that the large-area heat protection layer comprises a surface anti-ablation layer and an internal heat insulation layer; the internal heat insulation layer and the bearing structure are glued through a silicone rubber layer, and a surface anti-ablation layer is laid on the outer surface of the internal heat insulation layer; the end cap is embedded into the large-area heat-proof layer and glued with the anti-ablation layer and the heat insulation layer, and the part, embedded into the end cap, of the large-area heat-proof layer is fixedly connected with the internal force bearing structure through a connecting screw and a gasket; an inclined angle of 10-20 degrees is formed between the surface anti-ablation layer and the local airflow direction; the end cap is a 2.5 D woven viscose-based carbon fiber / phenolic aldehyde end cap. The problems that a single heat-proof material cannot meet the requirements for heat protection, heat insulation, light weight and miniaturization at the same time, and interface layers of different materials crack and peel off at the ultrahigh temperature are solved, and the connection reliability of the heat-proof structure is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of heat protection, and relates to a multifunctional gradient heat protection structure suitable for a planet exploration return capsule. BACKGROUND

[0002] In a planet exploration mission, a return capsule (an entry capsule) will experience extremely severe space environment and return aerodynamic force heat environment. The return capsule will bear low temperature (lower than -120 DEG C), high temperature (higher than 120 DEG C) and high-low temperature cyclic alternation, high vacuum (lower than 10-12 Pa) in space flight. The return capsule will carry extraterrestrial samples, and when re-entering at a super second cosmic speed (12 km / s), the return capsule will bear extremely severe aerodynamic heat environment and aerodynamic force environment at the large bottom position. The heat protection structure faces the environment of super high heat flow density (≥12 MW / m 2 ), super high enthalpy (≥75 MJ / kg), super high shear force (≥850 Pa), etc.; at the same time, the return capsule is small in size and extremely strict in lightweight requirement.

[0003] The conventional heat protection structure of a spacecraft adopts a cemented structure of a single homogeneous heat protection layer and a force bearing structure, as shown in Figure 1 .

[0004] The conventional heat protection structure form cannot meet the multi-lateral constraint conditions of the planet exploration mission, and there are mainly the following problems:

[0005] (1) A single heat protection material cannot meet the multiple requirements of heat protection, heat insulation, and lightweight and small size: an ablative material, such as high-density carbon phenolic material and carbon-carbon material, has excellent ablative and erosion resistance, but has high density and high thermal conductivity, and the weight of the designed heat protection structure cannot meet the requirements. A heat insulation material, such as low-density lightweight silicon-based material or quartz material, has excellent heat insulation performance, but has poor ablative and shear resistance, and has large ablation and design thickness, which cannot meet the deep space lightweight and small size requirements.

[0006] (2) Interface problem is prominent: a single heat protection material and a force bearing structure are usually combined through glueing or mechanical connection, and in the process of space high-low temperature alternation and return, under super high temperature, due to the mismatch of thermal expansion coefficients, great thermal stress and thermal deformation are easily generated, thereby leading to failure modes such as interlayer cracking and peeling.

[0007] (3) In the ablation process, the heat protection structure is seriously mechanically ablated under the action of large shear force: the heat protection structure with traditional flat or vertical layers has small layer angle at the stagnation point position, and is easily mechanically ablated under the action of aerodynamic shear force in the ablation process, which causes large ablation recession, uncontrollable aerodynamic shape, increases the uncertainty of aerodynamic heat, and threatens flight safety.

[0008] (4) Connection reliability is insufficient: for the stagnation point part (such as the end cap), the simple connection mode is prone to looseness or failure under the severe thermal-mechanical combined environment.

[0009] Therefore, there is an urgent need for a multifunctional gradient heat protection structure suitable for a planetary exploration return capsule, which can realize the multifunctional, lightweight and integrated design of heat insulation, heat protection, load bearing, buffering and the like of the return capsule, and meet the requirements of light and small size and high reliability. SUMMARY

[0010] The technical problems solved by the present application are: (1) under the extremely harsh aerodynamic force and aerodynamic heat environment of super-second cosmic speed reentry (entry), a single heat protection material cannot simultaneously meet the multiple requirements of heat protection, heat insulation and light and small size. (2) During space low temperature, high temperature, high-low temperature alternation and return process under super-high temperature, the interface layer between different materials cracks and peels off. (3) During ablation process, the mechanical ablation of the heat protection structure under large shear force is serious. (4) Connection reliability problem of the heat protection structure.

[0011] The technical problem solving scheme of the present application is: a multifunctional gradient heat protection structure suitable for a planetary exploration return capsule, comprising a large-area heat protection layer, an end cap, a load-bearing structure, a silicone rubber layer, a connecting screw and a gasket, the large-area heat protection layer comprising a surface ablation-resistant layer and an internal heat insulation layer.

[0012] The internal heat insulation layer is cemented with the silicone rubber layer between the internal heat insulation layer and the load-bearing structure, and the surface ablation-resistant layer is laid on the outer surface of the internal heat insulation layer.

[0013] The end cap is embedded in the large-area heat protection layer and cemented with the ablation-resistant layer and the heat insulation layer, and the part of the large-area heat protection layer embedded in the end cap is fastened and connected with the internal load-bearing structure through the connecting screw and the gasket.

[0014] The surface ablation-resistant layer is inclined at an angle of 10°-20° to the local airflow direction.

[0015] Further, the end cap adopts a 2.5D woven viscose-based carbon fiber / phenolic end cap.

[0016] Further, a low-surface-energy coating is coated on the surface of the viscose-based carbon fiber, including one of polysiloxane or epoxy resin diluent.

[0017] Further, the pressure jointing angle of the end cap is 10°-20°.

[0018] Further, the surface ablation-resistant layer adopts high-density carbon fiber / phenolic resin-based composite material or carbon-carbon composite material, and the density is 1.30-1.40 g / cm 3 .

[0019] Furthermore, the internal insulation layer uses lightweight carbon fiber / phenolic material or modified quartz phenolic composite material with a density of 0.65–0.75 g / cm³. 3 .

[0020] Furthermore, the end cap is bonded to the ablation-resistant layer and the heat insulation layer using a room-temperature curing, high-temperature resistant adhesive, with the adhesive layer thickness controlled between 0.1mm and 0.3mm.

[0021] Furthermore, the thickness of the silicone rubber layer is 1.0-1.5 mm.

[0022] Furthermore, the internal insulation layer prefabricated body is pre-cured at 80℃-120℃ for 2h-4h; the surface ablation-resistant layer prefabricated body is laid on the outer surface of the internal insulation layer, at an angle of 10° to 20° with the local airflow direction, and pre-cured at 80℃ to 120℃ for 2h to 4h to form a pre-cured large-area heat-resistant layer.

[0023] Furthermore, the pre-cured large-area heat-resistant layer is cured for 4 to 6 hours at 140°C to 180°C and 0.1 MPa to 0.2 MPa pressure.

[0024] The advantages of this invention compared to the prior art are:

[0025] (1) This invention designs a functionally graded heat-resistant structure, which achieves good ablation resistance on the surface of the heat-resistant structure, good thermal insulation inside, and withstands a total heating load of not less than 320 MJ / m. 2 The surface ablation-resistant layer is 13±0.5mm thick; the inner insulation layer is 5±0.5mm thick, which can ensure that the temperature of the load-bearing structure does not exceed 200℃; the total thickness is not more than 19mm, realizing the miniaturization of the return capsule structure.

[0026] (2) The present invention develops an integrated co-curing molding process, which solves the problem of the interface between conventional heat-resistant structures and avoids the peeling problem caused by thermal mismatch; by designing a 1mm to 1.5mm silicone rubber layer between the heat-resistant structure and the load-bearing structure, the problem of thermal matching between the heat-resistant structure and the load-bearing structure is solved.

[0027] (3) The present invention designs the heat protection structure to achieve the best comprehensive effect of heat protection, heat insulation and erosion resistance when the layup angle of carbon fiber cloth or prepreg forms a certain acute angle (10°~20°) with the airflow direction; at the same time, it solves the problem of severe mechanical erosion of the heat protection structure under large shear force.

[0028] (4) The present invention designed a 2.5D adhesive carbon phenolic end cap, which enhances the interlayer toughness, shear resistance and anti-cracking ability of the heat-resistant structure at the stagnation point; and designed four M6 high-strength screws for mechanical reinforcement. The "adhesive-mechanical" hybrid connection method improves the connection safety and reliability in high and low temperature environments in space and in ultra-high temperature environments upon return. Attached Figure Description

[0029] Figure 1 It is a conventional heat-resistant structural form;

[0030] Figure 2 This is a schematic cross-sectional view of the functional gradient heat protection structure of the present invention;

[0031] Figure 3 This is a partially enlarged schematic diagram showing the relationship between the slant angle design and the airflow direction of the present invention;

[0032] Figure 4 This is a schematic diagram of the end cap structure and its screw connection diagram of the present invention. Detailed Implementation

[0033] like Figure 2 As shown, the multifunctional gradient heat protection structure of the present invention consists of a large-area heat protection layer, an end cap 201, a load-bearing structure 301, a silicone rubber layer 401, and four connecting screws and washers 501. The large-area heat protection layer includes a surface anti-ablation layer 101 and an internal heat insulation layer 102.

[0034] The internal heat insulation layer 102 is bonded to the load-bearing structure 301 by a silicone rubber layer 401, and the outer surface of the internal heat insulation layer 102 is covered with a surface anti-ablation layer 101.

[0035] The end cap 201 is embedded in the large-area heat-insulating layer and bonded to the ablation-resistant layer 101 and the heat insulation layer 102. The part of the large-area heat-insulating layer embedded in the end cap 201 is fastened to the internal load-bearing structure 301 by four connecting screws and washers 501, forming a double protection.

[0036] like Figure 3 As shown, the surface anti-ablation layer 101 is tilted at a set angle α with the local airflow direction 601. This angle is optimized to be 10° to 20° according to the specific aerodynamic environment.

[0037] like Figure 4 As shown, the end cap 201 has a crimped angle of 10° to 20° to prevent sparking.

[0038] End cap 201 uses 2.5D woven viscose-based carbon fiber / phenolic end cap, with a low surface energy coating, such as polysiloxane, epoxy resin diluent, etc., applied to the surface of viscose-based carbon fiber; surface modification is performed to reduce the friction and intermolecular forces between carbon fibers during weaving.

[0039] The end cap 201 is bonded to the ablation-resistant layer 101 and the heat insulation layer 102 using a room temperature curing high temperature resistant adhesive (such as SG-200 adhesive), and the adhesive layer thickness is controlled between 0.1mm and 0.3mm.

[0040] The thickness of the 401 silicone rubber layer is controlled between 1.0 and 1.5 mm.

[0041] The surface ablation-resistant layer 101 is made of high-density carbon fiber / phenolic resin matrix composite material or carbon-carbon composite material, with a density of 1.30~1.40g / cm³. 3 The internal insulation layer 102 is made of lightweight carbon fiber / phenolic material or modified quartz phenolic composite material, with a density of 0.65~0.75g / cm³. 3 .

[0042] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0043] Example 1

[0044] The multifunctional gradient heat protection structure of this embodiment consists of a large-area heat protection layer, an end cap 201, a load-bearing structure 301, a silicone rubber layer 401, and four connecting screws and washers 501. The large-area heat protection layer includes a surface anti-ablation layer 101 and an internal heat insulation layer 102.

[0045] Surface ablation-resistant layer: A high-density carbon fiber / phenolic resin matrix composite or carbon-carbon composite material was designed, with a density of 1.30–1.40 g / cm³. 3 It can withstand a maximum heat flux density greater than or equal to 18 MW / m³. 2 Its main function is to resist extreme high-temperature ablation and violent erosion by airflow, maintaining its shape integrity.

[0046] Internal insulation layer: Designed with a porous, lightweight carbon fiber / phenolic material or modified quartz phenolic composite material with gradually decreasing density, density: 0.65~0.75g / cm³ 3 It has a thermal conductivity of ≤0.2W / mK. Its main function is to provide efficient thermal insulation and prevent heat from being transferred to the internal structure. Through the design of woven fabric and prefabrication, the thermal expansion coefficient of the insulation layer is made close to that of the load-bearing structure. In addition, the low-density heat-insulating material has good adaptability, which solves the problem of thermal matching between the two.

[0047] Different functional heat-resistant material layers are integrally molded through co-curing. After laying variable-density prepreg or preforms in a mold, they are subjected to one or two high-temperature and high-pressure curing cycles to form a continuous heat-resistant structure with a seamless microstructure, compatible interfaces, and no weak points. This process completely eliminates the traditional interlayer interface and avoids delamination problems caused by thermal mismatch.

[0048] This invention breaks through the traditional orthogonal or vertical layup method and proposes a design method of "inclined three-dimensional layup with airflow".

[0049] The layup angle of carbon fiber cloth or prepreg is designed as follows: a large layup angle is beneficial for erosion and mechanical erosion resistance, but it leads to a shorter heat transfer path along the fiber, resulting in increased thermal conductivity and higher back wall temperature. A small layup angle, with a longer heat transfer path along the fiber in the thickness direction, is beneficial for thermal insulation, but it is prone to mechanical erosion under strong airflow. Based on the analysis of local airflow direction during reentry or flight obtained from computational fluid dynamics (CFD) simulations, the thermal protection structure achieves the best overall effect of thermal protection, thermal insulation, and erosion resistance when the layup angle of carbon fiber cloth or prepreg forms a certain acute angle (10°~20°) with the airflow direction.

[0050] This design optimizes the heat transfer path during the ablation process, avoids mechanical erosion during ablation, makes the ablation process more uniform and stable, guides the formation of a smooth and expected ablation morphology, thereby maintaining excellent aerodynamic characteristics and significantly improving safety and predictability in the face of complex aerodynamic and thermal environments.

[0051] To address the problem of ablation and mechanical erosion at the most critical thermal location (the end section) and improve the erosion resistance of the heat-resistant structure, this invention designs a high-performance 2.5D woven viscose-based carbon fiber / phenolic resin end cap (density: 1.30~1.40g / cm³). 3 Thermal conductivity ≤ 0.8 W / mK.

[0052] Material and process innovation: Traditional pitch-based carbon fiber was abandoned in favor of viscose-based carbon fiber as the reinforcement. Composite materials made from viscose-based carbon fiber have lower thermal conductivity; the ablation carbides exhibit higher purity and superior ablation resistance, especially forming a robust carbonized layer under high enthalpy conditions, ensuring ultimate ablation protection. To address the adhesion problem during the weaving process of viscose-based carbon fiber, a surface modification process was employed, coating the carbon fiber surface with a low surface energy coating (such as polysiloxane, epoxy resin diluent, etc.) to reduce inter-fiber friction and intermolecular forces.

[0053] The bottom stagnation area of ​​the return capsule uses a 2.5D braided cap to overcome the erosion caused by airflow from different directions. The 2.5D braided cap structure lies between two-dimensional and three-dimensional, and is connected by interlayer yarns, giving the material excellent interlayer toughness, shear resistance, and anti-fracture ability. This overcomes the shortcomings of traditional 2D materials, such as easy delamination under airflow, and the high density and high thermal conductivity of 3D braids.

[0054] To ensure the reliability of the connection between critical components and the main heat-resistant structure, the end cap is glued to the large-area heat-resistant structure, and four M6 high-strength screws are added for mechanical reinforcement. This hybrid "glue-mechanical" connection method provides redundancy and greatly improves the connection safety factor in high and low temperature environments in space and in ultra-high temperature environments upon return.

[0055] The steps for fabricating the multifunctional gradient thermal protection structure are as follows:

[0056] 1. Lay the internal insulation layer 102 preform on the molding fixture and pre-cur it at 80℃-120℃ for 2h-4h; then machine the outer surface of the internal insulation layer according to the designed thickness L1.

[0057] 2. A surface anti-ablation layer 101 is laid on the outer surface of the inner heat insulation layer 102. The surface anti-ablation layer preform is inclined at a set angle (10°~20°) with the local airflow direction 601. It is pre-cured at 80℃~120℃ for 2h~4h to form a pre-cured large-area heat protection layer.

[0058] 3. The large-area heat-insulating layer pre-cured body is co-cured for 4h to 6h at 140℃~180℃ and 0.1MPa~0.2MPa pressure environment, so that the surface anti-ablation layer 101 and the internal heat insulation layer 102 phenolic resin are fully co-cured, and the interfacial bonding force is enhanced.

[0059] 4. The large-area heat-insulating layer (surface ablation-resistant layer 101 and internal heat insulation layer 102) is machined with inner and outer surfaces and interfaces with the end cap to ensure that the angle between the end cap 201 and the direct pressing surface of the large-area heat-insulating layer is between 10° and 20°.

[0060] 5. Install end caps: End caps 201 are bonded to the ablation-resistant layer 101 and the heat insulation layer 102 with SG-200 adhesive. The thickness of the adhesive layer is controlled between 0.1mm and 0.3mm to form a heat-resistant structural assembly.

[0061] 6. The heat-resistant structure assembly and the load-bearing structure 301 are bonded together with a 1.0-1.5mm silicone rubber layer. At the same time, four evenly distributed M6 screws 501 are installed to fasten the internal load-bearing structure 301. The heads of the M6 ​​screws are coated with silicone rubber.

[0062] 7. While ensuring the thickness L2 of the surface ablation-resistant layer 101, machine the aerodynamic shape.

[0063] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

[0064] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A multifunctional gradient heat protection structure suitable for planetary probe return capsules, characterized in that, It includes a large-area heat-insulating layer, an end cap (201), a load-bearing structure (301), a silicone rubber layer (401), connecting screws and washers (501), wherein the large-area heat-insulating layer includes a surface ablation-resistant layer (101) and an internal heat insulation layer (102); The internal heat insulation layer (102) is bonded to the load-bearing structure (301) through a silicone rubber layer (401), and the outer surface of the internal heat insulation layer (102) is covered with a surface anti-ablation layer (101). The end cap (201) is embedded in the large-area heat-insulating layer and bonded to the ablation-resistant layer (101) and the heat insulation layer (102). The part of the large-area heat-insulating layer embedded in the end cap (201) is fastened to the internal load-bearing structure (301) by connecting screws and washers (501). The surface anti-ablation layer (101) is inclined at an angle of 10° to 20° with the local airflow direction.

2. The multifunctional gradient heat protection structure suitable for planetary exploration return capsules according to claim 1, characterized in that, The end cap (201) is made of 2.5D woven viscose-based carbon fiber / phenolic end cap.

3. A multifunctional gradient heat protection structure suitable for planetary probe return capsules according to claim 2, characterized in that, A low surface energy coating is applied to the surface of viscose-based carbon fibers, including a polysiloxane or epoxy resin diluent.

4. A multifunctional gradient heat protection structure suitable for planetary exploration return capsules according to claim 1, characterized in that, The end cap (201) has a crimped oblique cone angle of 10° to 20°.

5. A multifunctional gradient heat protection structure suitable for planetary exploration return capsules according to claim 1, characterized in that, The surface ablation-resistant layer (101) is made of high-density carbon fiber / phenolic resin matrix composite material or carbon-carbon composite material, with a density of 1.30~1.40g / cm³. 3 .

6. A multifunctional gradient heat protection structure suitable for planetary exploration return capsules according to claim 1, characterized in that, The internal insulation layer (102) is made of lightweight carbon fiber / phenolic material or modified quartz phenolic composite material with a density of 0.65-0.75 g / cm³. 3 .

7. A multifunctional gradient heat protection structure suitable for planetary exploration return capsules according to claim 1, characterized in that, The end cap (201) is bonded to the ablation-resistant layer (101) and the heat insulation layer (102) using a room temperature curing high temperature resistant adhesive, and the thickness of the adhesive layer is controlled between 0.1mm and 0.3mm.

8. A multifunctional gradient heat protection structure suitable for planetary exploration return capsules according to claim 1, characterized in that, The thickness of the silicone rubber layer (401) is 1.0-1.5 mm.

9. A multifunctional gradient heat protection structure suitable for planetary exploration return capsules according to claim 1, characterized in that, The internal heat insulation layer (102) preform is pre-cured at 80℃-120℃ for 2h-4h; the surface anti-ablation layer (101) preform is laid on the outer surface of the internal heat insulation layer (102) at an angle of 10° to 20° with the local airflow direction, and is pre-cured at 80℃ to 120℃ for 2h to 4h to form a pre-cured large-area heat-resistant layer.

10. A multifunctional gradient heat protection structure suitable for planetary probe return capsules according to claim 9, characterized in that, The pre-cured large-area heat-resistant layer is cured for 4 to 6 hours at 140℃ to 180℃ and 0.1MPa to 0.2MPa pressure.

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