Thermal protection structure block jointing method

Abstract

The application provides a thermal protection structure block joint method. The thermal protection structure is composed of a panel, a thermal insulation material and a strain isolation pad. The thermal insulation material needs to be divided into blocks and jointed. The thermal protection structure block joint method is determined by a thermal insulation material failure criterion, and comprises the following steps: (1) determining the thermal insulation material failure criterion; (2) determining the change rule of the thermal insulation material failure area with the block size and the gap between the blocks; (3) determining the thermal protection structure block method; and (4) determining the thermal protection structure joint method. The thermal protection structure block joint method is suitable for a reusable large-area thermal protection structure, can solve the deformation matching and structure failure problems of the reusable thermal protection structure in engineering application, and is also suitable for the block and joint design of other thermal protection structures.

Description

Technical Field

[0001] This invention relates to a method for segmented overlapping of a thermal protection structure, belonging to the research field of thermal protection structures. Background Technology

[0002] During high-speed flight, aerodynamic heating of the surfaces of spacecraft and their recovery launch capsules can cause structural failure at high temperatures, necessitating thermal protection designs for the structural surfaces. Developing a reusable thermal protection structure is crucial not only for ensuring the survival of spacecraft and their recovery launch capsules at high temperatures but also for effectively reducing the cost of thermal protection for these vehicles. Therefore, the development of such a reusable thermal protection structure is urgently needed.

[0003] Thermal protection structures deform under load and during aerodynamic heating. Because the temperature and thermal stress along the thickness of the structure exhibit a gradient distribution, and the stiffness of each layer differs, delamination can easily occur, leading to excessive shear force and ultimately failure. Therefore, thermal protection structures are often segmented to reduce shear stress and prevent failure. However, these segments may experience crushing damage during deformation, necessitating gaps between them. A well-designed overlapping method for segmented thermal protection structures can resolve deformation matching and structural failure issues in engineering applications.

[0004] Currently, the existing methods for segmenting and overlapping thermal protection structures mainly rely on engineering experience. These methods divide the thermal protection structure into several fixed-size blocks, and then use experimental methods to sequentially test whether the thermal protection structure fails, thereby determining the appropriate segmentation and overlapping method. However, the research on the basis and mechanism of segmentation is not in-depth enough, and it contains a certain degree of subjectivity. There is still no systematic research on the segmentation mechanism and methods of thermal protection structures. Summary of the Invention

[0005] To address the aforementioned shortcomings, this invention proposes a method for segmenting and overlapping thermal protection structures. It identifies the main failure modes of thermal insulation materials under load, determines the failure criteria for these materials, further clarifies the variation of the failure area of ​​the thermal insulation material with the segment size and inter-segment gap, and finally determines the segmenting and overlapping method for the thermal protection structure.

[0006] The technical solution of this invention is: a method for segmented overlapping of a thermal protection structure. The method steps are as follows:

[0007] Step 1: Determine the failure criteria of the thermal insulation material of the thermal protection structure based on the failure mode of the thermal protection structure;

[0008] Step 2: Based on the failure criteria of thermal insulation materials in thermal protection structures, determine the variation law of the failure area of ​​thermal insulation materials with the size of the blocks and the gap between the blocks;

[0009] Step 3: Determine the segmentation method of the thermal protection structure based on the failure criteria of thermal insulation materials and the variation law of the failure area of ​​thermal insulation materials with the segment size;

[0010] Step 4: Determine the overlapping method of the thermal protection structure based on the failure criteria of thermal insulation materials and the variation law of the failure area of ​​thermal insulation materials with the gap between blocks.

[0011] In step 1, the main failure mode of the thermal protection structure is shear failure at the contact surface between the insulation material and the panel. A three-dimensional modified maximum shear stress criterion is used as the failure criterion for the insulation material. Where τ... 12 τ 13 For shear stress, S 12 These are the longitudinal and transverse shear strengths, respectively.

[0012] ,in (1)

[0013] In step 2, based on the failure criteria of thermal insulation materials in thermal protection structures, the specific implementation process for determining the variation of the failure area of ​​the thermal insulation material with the block size and the gap between blocks is as follows:

[0014] Step 2-1: Based on the shear failure mode of the thermal protection structure, the three-dimensional modified maximum shear stress criterion is selected as the failure criterion of the thermal insulation material.

[0015] Step 2-2: In Abaqus or other finite element analysis software, establish numerical models of thermal protection structures with different block sizes and gaps between blocks under strain insulation pad connection and bolt connection methods. Then, perform heat transfer analysis and thermo-mechanical coupling analysis on the thermal protection structure according to the load and boundary conditions of the thermal protection structure.

[0016] Steps 2-3: Based on the failure criteria of the thermal insulation material and the thermo-mechanical coupling analysis results obtained by the finite element method, determine the variation law of the failure area of ​​the thermal insulation material with the size of the thermal insulation material blocks and the gap between the blocks under the two connection methods, select the appropriate connection method, and determine the maximum block size and minimum gap between the blocks when the thermal insulation material of the thermal protection structure has not failed.

[0017] The thermal protection structure segmentation method in step 3 includes: the thermal protection structure segments are arranged symmetrically and uniformly, the segments are square in shape, and each segment has the same size. The size of the segment is determined based on the failure criteria of the thermal insulation material and the variation law of the failure area of ​​the thermal insulation material with the size of the segment.

[0018] The thermal protection structure overlapping method in step 4 includes: the thermal protection structure overlapping adopts a stepped overlapping method, the gap between the blocks is filled with aerogel thermal insulation material to prevent the heat flow between the blocks, and the size of the gap between the blocks is determined according to the failure criteria of the thermal insulation material and the change law of the failure area of ​​the thermal insulation material with the gap between the blocks.

[0019] Furthermore, in step 2-2, the connection between the thermal insulation material and the body structure can be achieved by two methods: one is by bonding with strain gauges, and the other is by removing the strain gauges and connecting with bolts, with the bolts distributed at the four corners of the thermal insulation material blocks.

[0020] Furthermore, the thermal protection structure consists of a panel, thermal insulation material, and strain gauge pads. The thickness of the panel is 0.1-20mm (e.g., 0.1, 1, 5, 10, 15, or 20mm), the thickness of the thermal insulation material is 1-100mm (e.g., 1, 2, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, or 100mm), and the thickness of the strain gauge pads is 0.1-20mm (e.g., 0.1, 1, 5, 10, 15, or 20mm).

[0021] Furthermore, this method is applicable to reusable thermal protection structures, such as metal thermal protection structures, cover-type thermal protection structures, rigid ceramic tile-type thermal protection structures, and flexible thermal insulation felt-type thermal protection structures.

[0022] The advantages and beneficial effects of this invention are as follows:

[0023] (1) The segmented overlapping method proposed in this invention can effectively simulate the failure of the thermal protection structure under load, so as to strengthen some areas of the thermal protection structure.

[0024] (2) The method for determining the segmented overlapping of the thermal protection structure based on the failure criteria of thermal insulation materials proposed in this invention provides a theoretical basis for the segmented overlapping design of the thermal protection structure and avoids the problems of deformation incoordination and structural failure of the thermal protection structure during use.

[0025] (3) The method of segmented overlapping of thermal protection structure proposed in this invention is not only applicable to sandwich thermal protection structure, but also applicable to segmented overlapping of other thermal protection structures.

[0026] (4) The thermal protection structure block overlapping method proposed in this invention adopts symmetrical and uniform block arrangement, stepped overlapping, and adhesive connection of each layer of structure. The structure is simple, reliable, and does not have too many bolt connections. Each thermal protection structure block can be directly replaced, and it is easy to use and maintain. Attached Figure Description

[0027] Figure 1 This is a flowchart of the method for segmenting and overlapping the thermal protection structure in an embodiment of the present invention.

[0028] Figure 2 This is a diagram showing the composition of the thermal protection structure in step 1 of an embodiment of the present invention.

[0029] Figure 3 This is a block diagram of the thermal protection structure in step 3-1 of the embodiment of the present invention.

[0030] Figure 4 This is a diagram showing the overlap of the thermal protection structure in step 3-1 of an embodiment of the present invention.

[0031] Figure 5A Figure 5B This is a diagram showing the carbon foam damage area in the thermal protection structure under different connection methods in steps 3-3 of the embodiments of the present invention.

[0032] Figure 6 This is an analysis result diagram of the thermal protection structure designed using a block method and an overlapping method in step 6 of the embodiment of the present invention. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely typical embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0034] Figure 1 This is a flowchart illustrating the method for segmenting and overlapping the thermal protection structure in an embodiment of the present invention. Figure 1 As shown, a method for segmenting and overlapping a thermal protection structure includes the following steps: determining the failure mode of the thermal protection structure; determining the failure criterion of the thermal protection structure based on the failure mode; establishing finite element models of the thermal protection structure with different segmentation and overlapping schemes under different connection methods and performing simulation analysis; determining the variation law of the failure area of ​​the thermal protection structure with the segment size and the gap between segments; determining the maximum segment size and the minimum segment gap; then determining the segmentation method of the thermal protection structure; determining the overlapping method of the thermal protection structure; determining the design of the thermal protection structure based on the segmentation and overlapping method of the thermal protection structure, and performing performance analysis on the thermal protection structure to verify the feasibility of the segmentation and overlapping method of the thermal protection structure.

[0035] This invention provides a method for segmenting and overlapping a thermal protection structure, including determining the composition of the thermal protection structure, determining the failure criteria of the insulation material, determining the variation law of the failure area of ​​the insulation material with the segment size and the gap between segments, determining the segmentation and overlapping method of the thermal protection structure, and verifying the segmentation and overlapping method of the thermal protection structure.

[0036] 1. Determine the structural form, material system, and connection method of the thermal protection structure. The specific process is as follows:

[0037] The thermal protection structure, from the outside in, consists of a panel, thermal insulation material, and a strain gauge, such as... Figure 2 As shown, the thermal protection structure is laid on the outer surface of the body structure. The panel is made of ceramic matrix composite material with a thickness of 2mm, serving as heat protection. The thermal insulation material is coal-based carbon foam with low thermal conductivity, 30mm thick, serving as insulation, with a shear strength of 2.1MPa. The strain isolation pad is made of needle-punched aramid 1313 fiber with a thickness of 2mm, coordinating the deformation between the body structure and the carbon foam. The layers of the thermal protection structure are bonded together with high-temperature resistant adhesive, with an adhesive layer thickness of 0.2mm and a shear strength of 20MPa. Because the overall structural stress level is relatively low and the adhesive layer is thin, it does not affect the results; therefore, the adhesive layer is not modeled in this embodiment. Table 1 shows the material physical properties of each layer of the carbon foam thermal protection structure in step 1 of the embodiment of the present invention. Table 2 shows the mechanical properties of each layer of the carbon foam thermal protection structure in step 1 of the embodiment of the present invention.

[0038] The material performance parameters of each layer of the thermal protection structure are shown in Tables 1 and 2.

[0039] Table 1 Physical property parameters of materials for each layer of the thermal insulation structure

[0040]

[0041] Table 2 Mechanical property parameters of thermal insulation structural materials

[0042]

[0043] 2. Determine the failure criteria for thermal insulation materials in thermal protection structures. The specific process is as follows:

[0044] Based on the characteristic that the main failure mode of thermal protection structures is shear failure at the contact surface between carbon foam and the panel, a three-dimensional modified maximum shear stress criterion is adopted as the failure criterion for the thermal insulation material of the thermal protection structure, as shown in Equation 1. Where the longitudinal and transverse shear strengths of the carbon foam are S... 12 The shear stress is 2.1 MPa. Where τ12 and τ13 are the shear stresses of the carbon foam.

[0045] ,in (1)

[0046] 3. Determine the variation of the failure area of ​​the thermal insulation material with the size of the blocks and the gap between the blocks. The specific process is as follows:

[0047] 3-1. The overall dimensions of the thermal protection structure model are determined to be 700mm × 1100mm. The carbon foam thermal protection structure is divided into blocks according to the size of the blocks and the spacing between them. Combined with... Figure 3Under the strain gauge connection method, the block schemes 1-6 correspond to (a)-(f) in the figure: the gap between the thermal protection structure schemes 1-3 is 2mm, scheme 1 is evenly divided into 2×3 blocks, scheme 2 is evenly divided into 3×4 blocks, and scheme 3 is evenly divided into 4×5 blocks; the gap between the thermal protection structure schemes 4-6 is 3mm, scheme 4 is evenly divided into 2×3 blocks, scheme 5 is evenly divided into 3×4 blocks, and scheme 6 is evenly divided into 4×5 blocks. Under the bolt connection method, the block schemes 7-12 correspond to (a)-(f) in the figure: the gap between the thermal protection structure schemes 7-9 is 2mm, scheme 7 is evenly divided into 2×3 blocks, scheme 8 is evenly divided into 3×4 blocks, and scheme 9 is evenly divided into 4×5 blocks; the gap between the thermal protection structure schemes 10-12 is 3mm, scheme 10 is evenly divided into 2×3 blocks, scheme 11 is evenly divided into 3×4 blocks, and scheme 12 is evenly divided into 4×5 blocks. Figure 4 The carbon foam blocks are connected by steps, and the gaps between the blocks are filled with aerogel.

[0048] 3-2. Preprocessing of the finite element model analysis involves assigning relevant material properties to the model and meshing it. For heat transfer analysis, DC3D8 3D 8-node thermal transfer elements are used; for thermo-mechanical coupling analysis, C3D8R 3D stress 8-node reduced elements are used. Contact relationships are set to be bonded at all contact surfaces. The convection exchange coefficient on the inner surface of the fuselage structure is 25 W / h, and the initial ambient temperature is 25℃. The fuselage structure is subjected to a spanwise compressive load of 71.3 MPa and a chordal shear load of 10.55 MPa, with Z-direction displacement restricted on both sides. The entire thermal protection structure and the end faces of the fuselage structure are hinged. The surface temperature of the thermal protection structure is 600℃.

[0049] 3-3. Perform heat transfer analysis on the finite element model sequentially. After completing the heat transfer analysis, import the obtained temperature field as a predefined field into the thermo-mechanical coupling analysis to obtain the carbon foam failure region map under different block sizes and inter-block gaps, such as... Figure 5A , Figure 5B As shown, compared with the thermal protection structure scheme under the bolt connection method, the thermal protection structure under the corresponding strain isolation pad connection method has a smaller failure area; compared with the 2mm inter-block gap, the thermal protection structure with the same block has a smaller failure area; under the same connection method and inter-block gap, the failure area of ​​the thermal protection structure decreases with the increase of the number of blocks; the thermal protection structure with the smallest failure area in scheme 6 is almost undamaged.

[0050] 3-4. Based on the carbon foam failure criteria and finite element analysis results, the variation of the carbon foam failure area with the block size and inter-block gap was determined. It can be seen that, under both connection methods between carbon foam and the body structure, the smaller the carbon foam block size, the smaller the carbon foam failure area; conversely, the larger the inter-block gap, the smaller the carbon foam failure area.

[0051] 3-5 Based on the carbon foam failure criteria in step 3-4 and the variation law of the carbon foam failure area with the block size and the gap between blocks, determine the maximum allowable block size and the minimum gap between blocks for the thermal protection structure. The block scheme is Scheme 6, 4×5 blocks, with a maximum block size of approximately 200mm and a gap between blocks of 3mm.

[0052] 4. Determine the method for dividing the thermal protection structure into blocks. The thermal protection structure is divided into blocks in a symmetrical and uniform manner. The blocks are square in shape and have the same size. The maximum block size determined in steps 3-5 is selected, which is approximately 200mm.

[0053] 5. Determine the overlapping method of the thermal protection structure. The thermal protection structure adopts a stepped overlapping method. The gap between the blocks is filled with aerogel insulation material to prevent the heat flow between the blocks. The minimum gap between the blocks is selected from the minimum gap determined in steps 3-5, which is 3mm.

[0054] 6. Verify the segmented overlapping method of the thermal protection structure. Based on the carbon foam failure criterion, a strain gauge connection method is adopted. The segmented thermal protection method in step 4 and the overlapping method in step 5 are selected. The boundary conditions of the thermal protection structure end faces are changed to flexible connections. The thermal protection structure is modeled and finite element analysis is performed. The analysis results are as follows: Figure 6 As shown, the highest temperature of the body structure is 142℃, the maximum deformation of the thermal protection structure is 4.24mm, the maximum stress of the ceramic matrix composite material is 15MPa, the maximum stress of the carbon foam is 2.7MPa, the maximum strain of the body structure is 6300με, the carbon foam did not fail, the thermal protection structure did not fail, and the segmented overlapping method of the thermal protection structure is feasible.

[0055] The parts of this invention not described in detail are well-known to those skilled in the art. The embodiments described above are merely preferred embodiments of the invention, and do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Various modifications and improvements to the technical solutions of this invention made by those skilled in the art without departing from the spirit of the invention should fall within the protection scope defined by the claims of this invention.

Claims

1. A method for overlapping sections of a thermal protection structure, characterized in that: Includes the following steps: Step 1: Determine the failure criteria of the thermal insulation material of the thermal protection structure based on the failure mode of the thermal protection structure; Step 2: Based on the failure criteria of thermal insulation materials in thermal protection structures, determine the variation law of the failure area of ​​the thermal insulation material with the size of the blocks and the gap between the blocks; the specific implementation process of step 2 is as follows: Step 2-1: Establish numerical models of thermal protection structures with different connection methods, different block sizes, and different gaps between blocks for thermal insulation materials and body structures. Use the finite element method to perform heat transfer analysis and thermo-mechanical coupling analysis on the thermal protection structure in sequence. Step 2-2: Based on the failure criteria of the thermal insulation material and the thermo-mechanical coupling analysis results obtained by the finite element method, determine the variation law of the failure area of ​​the thermal insulation material with the size of the thermal insulation material blocks and the gap between the blocks under different connection methods between the thermal insulation material and the body structure; Step 3: Determine the segmentation method of the thermal protection structure based on the failure criteria of thermal insulation materials and the variation law of the failure area of ​​thermal insulation materials with the segment size; Step 4: Determine the overlapping method of the thermal protection structure based on the failure criteria of thermal insulation materials and the variation law of the failure area of ​​thermal insulation materials with the gap between blocks.

2. The method for segmented overlapping of a thermal protection structure according to claim 1, characterized in that: In step 1, the failure mode of the thermal protection structure is shear failure of the thermal insulation material, and the failure criterion of the thermal insulation material is the three-dimensional modified maximum shear stress criterion. The three-dimensional modified maximum shear stress criterion is as follows: ,in (1) In the formula, τ 12 τ 13 For shear stress, S 12 It represents the longitudinal and transverse shear strength.

3. The method for segmented overlapping of a thermal protection structure according to claim 1, characterized in that: In step 3, the method for dividing the thermal protection structure into blocks is determined. The thermal protection structure blocks are arranged in a symmetrical and uniform manner. The thermal insulation material blocks of the thermal protection structure are square blocks of the same size, and the block size is determined by the failure criteria of the thermal insulation material.

4. The method for segmented overlapping of a thermal protection structure according to claim 1, characterized in that: In step 4, the overlapping method of the thermal protection structure is determined. The overlapping of the thermal protection structure adopts a stepped overlapping method, and the gap between the blocks is filled with aerogel insulation material for insulation. The size of the gap between the blocks is determined by the failure criterion of the insulation material.

5. The method for segmented overlapping of a thermal protection structure according to claim 1, characterized in that: In step 2-1, the connection method between the thermal insulation material and the body structure includes one method of bonding by means of strain gauge pads or another method of removing the strain gauge pads and connecting by bolts, wherein the bolts are distributed at the four corners of the thermal insulation material blocks.

6. The method for segmented overlapping of a thermal protection structure according to any one of claims 1-5, characterized in that: The thermal protection structure consists of a panel, thermal insulation material, and strain gauge pad. The thickness of the panel is 0.1-20mm, the thickness of the thermal insulation material is 1-100mm, and the thickness of the strain gauge pad is 0.1-20mm.

7. The method for segmented overlapping of a thermal protection structure according to claim 1, characterized in that: This method is applicable to reusable thermal protection structures, which are metal thermal protection structures, cover-type thermal protection structures, rigid ceramic tile-type thermal protection structures, or flexible thermal insulation felt thermal protection structures.

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