Method for extracting and reconstructing micro-morphology of c / c composite material after surface ablation

Abstract

The application discloses a kind of C / C composite material surface ablation after micro morphology extraction and reconstruction method, it is related to C / C composite material ablation behavior analysis field, comprising: the micro representative volume unit of C / C composite material is constructed;C / C composite material micro thermal chemical ablation model is established, and it is solved;Based on the solution result, the micro surface ablation morphology evolution of C / C composite material is carried out;The morphology after the micro surface ablation of C / C composite material is extracted;The morphology after the micro surface ablation of C / C composite material is reconstructed.The application solves the problem that existing airflow ablation research does not consider the influence of ablation morphology evolution.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of C / C composite ablation behavior analysis, and particularly relates to a method for extracting and reconstructing the micro-morphology of C / C composite after surface ablation. BACKGROUND

[0002] High-speed flying devices face extreme thermal environment of high temperature, long time and oxygen during reentry, and the surface temperature can reach several thousand degrees Celsius. Thermal protection technology plays a crucial role. Ablation thermal protection technology, as a kind of semi-active thermal protection method, removes heat from the surface of the flying device by losing its own mass, achieving the effect of thermal protection. C / C composite material has the characteristics of low density, good thermodynamic performance and excellent ablation and erosion resistance, and is an ideal material for thermal protection system of reentry high-speed flying devices and rocket engine nozzles. In the hypersonic environment, C / C composite material suffers severe thermo-chemical ablation (phenomenon of material degradation due to thermo-chemical reaction between C / C composite material and boundary layer gas components) and airflow erosion (phenomenon of material surface being stripped due to the shear action of airflow and the attenuation of high-temperature mechanical properties of the material), resulting in material mass loss and surface recession, and further affecting the working performance of the flying device. In the past, the research on the ablation behavior of C / C composite material was mainly on the macro scale by solving the boundary layer multi-component thermo-chemical equilibrium equation, the element mass conservation equation and the heat conduction equation to analyze the heat and mass transfer behavior in C / C composite material. However, the macroscopic thermo-chemical ablation model ignores the differences in ablation rates of material components and the influence of microstructure characteristics, which not only leads to large prediction deviation, but also cannot simulate the surface roughness phenomenon produced in the thermo-chemical ablation process of C / C composite material. In addition, airflow erosion is mainly related to the roughness characteristics of the material surface and aerodynamic force, so the macroscopic thermo-chemical ablation model is difficult to accurately characterize the airflow erosion process. In view of the problems existing in the macroscopic thermo-chemical ablation analysis method, in recent years, many scholars have studied the thermo-chemical ablation behavior analysis of C / C composite material on the micro scale, such as the direct numerical simulation method based on molecular random motion, the method based on solving the coupled partial differential equation set of reaction, diffusion and interface movement, etc. By analyzing the micro thermo-chemical ablation behavior of C / C composite material, the surface roughness and surface ablation morphology after ablation can be obtained, so as to analyze the airflow erosion. However, during the ablation process, the surface morphology of the material changes continuously with the ablation time, and the ablation morphology is greatly affected by the microstructure characteristics of the material. The current airflow erosion research almost does not consider the influence of ablation morphology evolution. Therefore, it is urgent to develop a method for extracting the micro-morphology of C / C composite after surface ablation for the thermo-chemical ablation-erosion coupling behavior analysis of C / C composite. SUMMARY

[0003] The C / C composite surface ablation micro-morphology extraction and reconstruction method provided by the application solves the problem that the influence of ablation morphology evolution is not considered in the existing airflow ablation research.

[0004] In order to achieve the above-mentioned application purposes, the technical scheme adopted by the application is as follows: a C / C composite surface ablation micro-morphology extraction and reconstruction method, comprising the following steps:

[0005] S1: constructing a micro-representative volume unit of the C / C composite material;

[0006] S2: establishing a micro-thermal chemical ablation model of the C / C composite material and solving it;

[0007] S3: based on the solving result, performing micro-surface ablation morphology evolution of the C / C composite material;

[0008] S4: extracting the micro-surface ablation morphology of the C / C composite material;

[0009] S5: reconstructing the micro-surface ablation morphology of the C / C composite material.

[0010] Further, the micro-thermal chemical ablation model of the C / C composite material established in S2 is as follows:

[0011]

[0012]

[0013]

[0014]

[0015]

[0016]

[0017] wherein, is an interface function, is time, is an ablation rate, is a vector operator, , and are three coordinate axes, is a molar volume, is an oxidation molar rate, is a normal vector, is reactivity, and the subscript indicates different carbon phases, including fiber phase and matrix phase, is oxygen concentration, is the diffusion rate;

[0018] In a unit control volume, the interface recession and the diffusion equation of gas concentration caused by gas / solid phase reaction are written as:

[0019]

[0020]

[0021] wherein, is the time increment, ε s is the solid volume fraction, V is the control volume, V f is the gas volume in the control volume, V s is the solid volume in the control volume, is the gas / solid interface area, is the molar volume in the solid unit, is the ablation reaction rate;

[0022] The diffusion equation set is solved by the finite volume method for analyzing the micro surface ablation behavior of C / C composite materials.

[0023] Further, the micro surface ablation morphology evolution of the C / C composite material in the S3 is specifically: the matrix / fiber reactivity ratio is set to 2, the reaction / diffusion ratio is set to 0.5, and the diffusion rate is set to 2*10 -4 m 2 / s, and the micro surface ablation morphology of the C / C composite material is obtained.

[0024] Further, the S4 includes the following steps:

[0025] S41: uniformly numbering the solid phase units of the C / C composite material which has not ablated at the initial time in the order of X, Y and Z directions;

[0026] S42: uniformly numbering all the nodes contained in the numbered solid phase units in the order of X, Y and Z directions;

[0027] S43: dividing the morphology after ablation at a certain time into gas phase units and solid phase units, if , the unit is a gas phase unit, if , the unit is a mixed unit, if , the unit is a solid phase unit, and the node coordinate value of the solid phase unit is stored;

[0028] S44: dividing the value of X, Y and Z direction corresponding to the stored node coordinate value of the solid phase unit by the corresponding grid length to determine the node number;

[0029] S45: repeating step S44 until all nodes of the ablated morphology are traversed;

[0030] S46: according to the solid phase unit and the corresponding node number in steps S41 and S42, cyclically screening the unit number of the ablated morphology.

[0031] Further, the remaining unit of the micro surface of the C / C composite material after ablation in S5 is reconstructed, including the following steps:

[0032] S51: writing node number and coordinate value;

[0033] S52: writing unit number and giving the node number corresponding to the unit;

[0034] S53: writing the unit number of the yarn and the matrix;

[0035] S54: writing the unit direction value of the yarn and the matrix;

[0036] S55: generating a grid file in the software to realize the reconstruction of the morphology of the micro surface of the C / C composite material after ablation.

[0037] The beneficial effects of the present application are:

[0038] (1) the present application establishes an analysis model for characterizing the thermal-chemical ablation morphology of the micro surface of the C / C composite material, which can consider the ablation performance difference of components and the microstructure characteristics, and can characterize the roughness change of the ablated surface of the material.

[0039] (2) the present application proposes a node extraction method for the surface ablation morphology of the C / C composite material, which can screen the corresponding grid unit according to the node value calculated in real time by the above ablation model.

[0040] (3) the present application proposes a reconstruction method for the surface ablation morphology of the C / C composite material, which can reconstruct the geometric and finite element grid model for airflow ablation analysis according to the calculation result of the ablation model, and provides a basis for the thermal-chemical ablation-erosion coupling analysis of the C / C composite material.

[0041] (4) In previous research and engineering applications, the coupling relationship between thermochemical ablation and airflow ablation of C / C composite materials has usually been separated. This has led to the inability to properly explain the surface ablation phenomenon of C / C composite materials and has also caused great trouble for practical applications. This invention can effectively fill the gap in the coupled analysis method of thermochemical ablation-ablation of C / C composite materials and provide a basis for airflow ablation analysis that considers the thermochemical ablation morphology. Attached Figure Description

[0042] Figure 1 This is a flowchart of a method for extracting and reconstructing the microstructure of a C / C composite material surface after ablation.

[0043] Figure 2 This is a diagram of the braided structure and mesh model of C / C composite material.

[0044] Figure 3 This is a diagram showing the evolution of the ablation morphology on the surface of the C / C composite material.

[0045] Figure 4 This is a voxel grid cell diagram.

[0046] Figure 5 This is a comparison image of the mesh cells before and after ablation.

[0047] Figure 6 Create an example diagram for node and cell numbering.

[0048] Figure 7 The images show a comparison between the ablation morphology and the reconstructed morphology. Detailed Implementation

[0049] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0050] like Figure 1 As shown, a method for extracting and reconstructing the microstructure of a C / C composite material surface after ablation includes the following steps:

[0051] S1: Constructing the mesoscopic representative volume element of the C / C composite material;

[0052] S2: Establish a microscopic thermochemical ablation model for C / C composite materials and solve it;

[0053] S3: Based on the solution results, the evolution of the microscopic surface ablation morphology of C / C composite material is carried out;

[0054] S4: Extract the morphology of the microscopic surface of the C / C composite material after ablation;

[0055] S5: Reconstruct the morphology of the microscopic surface of the C / C composite material after ablation.

[0056] The S1 specifically includes: constructing a mesoscopic representative volume element of C / C woven composite material in TexGen software; as Figure 2 The representative volume element is composed of yarns and matrix, and has 4 layers of yarns in the Z direction, the yarns include weft yarns along the Y direction and warp yarns or filling yarns along the X direction, and the warp yarns pass through the weft yarns of different layers, which greatly improves the interlaminar shear resistance of the woven composite material. The sizes of the X, Y and Z directions are 4 mm, 3.2 mm and 0.99 mm respectively, the fiber volume fraction is 51.91%, and the cross section of the yarn is elliptical (0.7 mm x 1 mm). After the mesoscopic representative volume element of the C / C composite material is established, the corresponding voxel grid is derived for numerical calculation, and the voxel grid is a regular hexahedral grid, and all the grids have the same size. The grid numbers of the X, Y and Z directions are 100, 80 and 40 respectively.

[0057] The mesoscopic thermo-chemical ablation model of C / C composite material can consider the difference in ablation performance of component materials and the competition mechanism of reaction / diffusion. The S2 establishes a mesoscopic thermo-chemical ablation model of C / C composite material as follows:

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064] wherein, is an interface function, is time, is ablation rate, is a vector operator, , and are three coordinate axes, is molar volume, is oxidation molar rate, is normal vector, is reactivity, and subscript represents different carbon phases, including fiber phase and matrix phase, is oxygen concentration, is diffusion rate;

[0065] The meso-thermal chemical ablation of C / C composite material involves the interface recession caused by gas / solid phase reaction and the diffusion problem of gas concentration. In order to solve the complex multi-phase and interface movement problem, the solid volume fraction is introduced by referring to the simulation method of gas-liquid two-phase flow. In a unit control volume, the interface recession caused by gas / solid phase reaction and the diffusion equation of gas concentration are written as:

[0066]

[0067]

[0068] wherein, is a time increment, ε s is a solid volume fraction, V is a control volume, V f is a gas volume in the control volume, V s is a solid volume in the control volume, is a gas-solid interface area, is a molar volume in the solid unit, is an ablation reaction rate;

[0069] The diffusion equation group is solved by the finite volume method, which is used for analyzing the meso-surface ablation behavior of C / C composite material.

[0070] The meso-surface ablation morphology evolution of C / C composite material is carried out in the S3, and specifically, the matrix / fiber reactivity ratio is set to 2, the reaction / diffusion ratio is set to 0.5, and the diffusion rate is set to 2*10 -4 m 2 / s, and the meso-surface ablation morphology of C / C composite material is obtained.

[0071] As Figure 3 shown. It can be seen from the figure that due to the ablation rate difference between the fiber and the matrix, the ablation surface becomes rough. With the increase of ablation time, the surface roughness becomes larger and larger. In addition, it can also be seen that the surface ablation morphology is also related to the meso-structural characteristics of C / C composite material. The yarns in the figure are divided into warp yarns and weft yarns, and the ablation morphologies of the two are different.

[0072] Since the above meso-thermal chemical morphology grid is a surface grid, it cannot be used for mechanical damage and failure behavior analysis of gas flow ablation, therefore, the morphology after the surface ablation of C / C composite material needs to be extracted to construct a voxel grid unit. The specific extraction steps are as follows:

[0073] The S4 includes the following steps:

[0074] S41: Solid units of C / C composite materials that have not undergone ablation at the initial moment are uniformly numbered in the order of X, Y and Z directions;

[0075] Taking 2×2×2 solid units as an example, such as Figure 4 As shown in Figure (a), the dashed lines at the top represent gas phase units, which are not numbered, while the solid lines represent solid phase units. According to the numbering rules, the numbers of the eight units are marked in the figure.

[0076] S42: All nodes contained in the numbered solid element are uniformly numbered in the order of X, Y and Z directions;

[0077] Taking 2×2×2 solid units as an example, such as Figure 4 As shown in Figure (b), the top dashed line represents the gas phase unit, which is not numbered. The solid line represents the solid phase unit. According to the node numbering rules, the numbers of its 27 unit nodes are marked in the figure.

[0078] S43: Divide the morphology after ablation at a certain time into gas phase units and solid phase units, if If so, then this unit is a gas phase unit and is not considered. If so, then the unit is a mixed unit and should be discarded. If the element is solid, then the element is a solid element and the node coordinates of the solid element are stored.

[0079] like Figure 5 Taking the unit types before and after ablation as an example, Figure 5 In the middle (a), the unit type before ablation is shown. Figure 5 In (b), the unit type after ablation is shown. After the solid phase unit is completely ablated, it becomes a gas phase unit, while the unit during the ablation process is a gas-solid mixed unit.

[0080] S44: Divide the X, Y, and Z direction values ​​corresponding to the node coordinates of the stored solid element by the corresponding mesh side length to determine the node number;

[0081] S45: Repeat step S44 until all nodes of the ablation morphology have been traversed;

[0082] S46: Based on the solid phase units and corresponding node numbers in steps S41 and S42, cyclically filter the unit numbers of the morphology after ablation.

[0083] Based on the above, the remaining elements of the C / C composite material's post-ablation morphology have been determined. Now, these elements need to be reconstructed to build a geometric and finite element mesh model for airflow erosion analysis. The specific reconstruction steps are as follows:

[0084] The morphology reconstruction of the remaining units after microscopic surface ablation of the C / C composite material in S5 includes the following steps:

[0085] S51: Write the node number and coordinate values;

[0086] by Figure 4 Taking node 1 in (b) as an example, its coordinates are (0, 0, 0). Assuming the side lengths of the grid in the X, Y, and Z directions are all 1mm, then the coordinates of node 2 are (1, 0, 0), the coordinates of node 4 are (0, 1, 0), and the coordinates of node 10 are (0, 0, 1). Figure 6 As shown in (a) Figure 5 The grid nodes 1, 2, and 3 and their corresponding coordinate values;

[0087] S52: Write the unit number and give the corresponding node number of the unit;

[0088] like Figure 6 As shown in (b) Figure 5 The grid cells 1, 2, and 3 and their corresponding node numbers;

[0089] S53: Write the unit numbering for yarn and matrix;

[0090] according to Figure 2 The mesh file exported by the Texgen software can be used to write the element numbers for the yarn and matrix;

[0091] S54: Write the unit orientation values ​​for yarn and matrix;

[0092] Similarly, according to Figure 2 Use the element orientation file exported from the Texgen software to write the element orientation values ​​for the yarn and matrix;

[0093] S55: Generate mesh files in the software to reconstruct the morphology of C / C composite material after microscopic surface ablation.

[0094] like Figure 7 The figures show a comparison between the ablation morphology and the morphology extracted and reconstructed based on the ablation node values. (a) shows the surface morphology after ablation at time t / τ, and (b) shows the extracted and reconstructed surface morphology. It can be seen that the two figures match well, with only minor differences in the boundary regions between meshes. This is because the node extraction and morphology reconstruction methods neglect the mixed phase elements, but this deviation is negligible for the overall mechanical failure analysis of airflow ablation. (c) shows the yarn morphology after ablation, and (d) shows the matrix morphology after ablation. It can be seen that after ablation, the structure of the yarn and matrix will no longer be complete, significantly affecting the mechanical properties of the structure.

[0095] Those skilled in the art will appreciate that the embodiments described herein are presented for purposes of illustration and that the inventive principles are not limited to these particular embodiments. Other variations and modifications can be made to the embodiments without departing from the spirit and scope of the inventive principles.

Claims

1. A method for extracting and reconstructing the micro-morphology of a C / C composite material after surface ablation, characterized in that, The method comprises the following steps: S1: constructing a mesoscopic representative volume element of C / C composite material; S2: establishing a mesoscopic thermo-chemical ablation model of C / C composite material and solving it; S3: based on the solving result, performing mesoscopic surface ablation morphology evolution of C / C composite material; S4: extracting the morphology of C / C composite material after mesoscopic surface ablation; The S4 comprises the following steps: S41: numbering the solid-phase elements of C / C composite material which do not ablate at the initial time in the order of X, Y and Z directions; S42: numbering all nodes contained in the numbered solid-phase elements in the order of X, Y and Z directions; S43: dividing the ablated morphology at a certain time into gas-phase elements and solid-phase elements, and storing the node coordinate values of the solid-phase elements; The S43 comprises the following steps: If , the unit is a gas phase unit, if , the unit is a mixed unit, if , the unit is a solid phase unit, and the node coordinate value of the solid phase unit is stored, wherein is the solid volume fraction; S44: dividing the node coordinate values of the stored solid-phase elements into the values of X, Y and Z directions, and determining the node number by dividing the corresponding grid length; S45: repeating step S44 until all nodes of the ablated morphology are traversed; S46: according to the solid-phase elements and corresponding node numbers in steps S41 and S42, cyclically screening the element numbers of the ablated morphology; S5: reconstructing the morphology of C / C composite material after mesoscopic surface ablation; The S5 comprises the following steps: S51: writing node numbers and coordinate values; S52: writing element numbers and giving the node numbers corresponding to the elements; S53: writing element numbers of yarns and matrixes; S54: writing element direction values of yarns and matrixes; S55: generating a grid file in software to realize the morphology reconstruction of C / C composite material after mesoscopic surface ablation.

2. The method of claim 1, wherein the method is characterized by: The S2 comprises the following steps: wherein, is an interface function, is time, is ablation rate, is a vector operator, , and are three coordinate axes, is molar volume, is oxidation molar rate, is a normal vector, is reactivity, subscript denotes different carbon phases, including fiber phase and matrix phase, is oxygen concentration, is diffusion rate.

3. The method of claim 2, wherein the method further comprises: In a unit control volume, the interface recession and gas concentration diffusion equations caused by gas / solid phase reaction are written as: wherein, is the time increment, is the solid volume fraction, V is the control volume, V f is the gas volume in the control volume, V s is the solid volume in the control volume, is the gas-solid interface area, is the molar volume in the solid element, is the ablation reaction rate.

4. The method of claim 3, wherein the method further comprises: The diffusion equations are solved by finite volume method, which is used to analyze the mesoscopic surface ablation behavior of C / C composite material.

5. The method of claim 1, wherein the method is characterized by: The micro surface ablation morphology evolution of the C / C composite in the S3 is as follows: the matrix / fiber reactivity ratio is set to 2, the reaction / diffusion ratio is set to 0.5, and the diffusion rate is set to 2*10 -4 m 2 / s, and the micro surface ablation morphology of the C / C composite is obtained.

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