A woven composite material thermal conductivity coefficient calculation method based on real material information

Abstract

This invention discloses a method for calculating the thermal conductivity of woven composite materials based on real material information, comprising the following steps: performing Micro-CT scanning on the woven composite material to obtain slice images; processing the slice images to obtain the real material information of the woven composite material; establishing a representative volume element geometric model based on the weaving parameters of the woven composite material; dividing the representative volume element into regions and matching the thermal conductivity calculation model according to the region characteristics; inputting the real material information into the thermal conductivity calculation model, replacing the material partitions in the representative volume element with the real material partitions, calculating the thermal conductivity of each region, and then determining the overall thermal conductivity calculation model and calculating the overall thermal conductivity based on the thermal conductivity and arrangement of each region. Using the above method, the accuracy of predicting the thermal conductivity of woven composite materials is improved, the design and optimization accuracy and efficiency of woven composite materials are enhanced, and the design cycle and design cost are significantly reduced.

Description

Technical Field

[0001] This invention relates to the field of thermal conductivity calculation technology for composite materials, and in particular to a method for calculating the thermal conductivity of woven composite materials based on real material information. Background Technology

[0002] Currently, countries around the world are developing hypersonic vehicles and hypersonic weapons. Higher flight speeds, longer flight times, and harsher aerodynamic and thermal environments place higher demands on the performance of composite materials. When designing composite materials for extreme environments, it is essential to obtain accurate thermophysical parameters and transport parameters to accurately predict the material's service performance and guide its refined design and evaluation.

[0003] Braided composite materials possess advantages such as high strength, minimal ablation retreat, structural stability, and good thermal insulation performance, leading to their widespread application in aerospace materials in recent years. When designing and evaluating the performance of braided composite materials, the thermal conductivity is one of the most crucial input parameters. Currently, methods for predicting the thermal conductivity of braided composite materials broadly fall into two categories: theoretical and numerical methods. Theoretical methods heavily rely on simplifications, such as treating the braided structure as an idealized layered model and calculating using a single parallel method. Numerical methods employ idealized geometric models, resulting in high modeling and computational costs and low efficiency. Furthermore, existing thermal conductivity calculation methods do not adequately consider real material information, lacking the extraction of internal defects and structural characteristics, thus failing to reflect the true material properties. This leads to significant discrepancies between predicted and actual thermal conductivity values, resulting in substantial errors in the service performance prediction of braided composite materials, necessitating increased design margins for thermal protection structures. Therefore, establishing an efficient and accurate thermal conductivity calculation method for braided composite materials that considers real material information is a pressing issue. Summary of the Invention

[0004] The purpose of this invention is to solve the problems existing in the prior art.

[0005] To achieve the above objectives, this invention provides a method for calculating the thermal conductivity of braided composite materials based on real material information, comprising the following steps:

[0006] Step S1: Perform Micro-CT scanning on the woven composite material to obtain slice images in the x, y, and z directions respectively;

[0007] Step S2: Process the sliced ​​image to obtain the actual material information of the woven composite material.

[0008] Step S3: Based on the weaving parameters of the braided composite material, establish a representative volumetric element geometric model;

[0009] Step S4: Divide the representative volume unit into regions and match the thermal conductivity calculation model according to the region characteristics;

[0010] Step S5: Input the real material information into the thermal conductivity calculation model in step S4, replace the material partitions in the representative volume unit with the real material partitions, calculate the thermal conductivity of each region, and then determine the overall thermal conductivity calculation model and calculate the overall thermal conductivity based on the thermal conductivity and arrangement of each region to predict the thermal conductivity.

[0011] Preferably, in step S3, the weaving parameters include the warp cross-sectional dimensions, the weft cross-sectional dimensions, the warp spacing, the weft spacing, and the normal yarn cross-sectional dimensions and spacing.

[0012] Preferably, in step S4,

[0013] The representative volume element is divided into regions according to a direction perpendicular to the global coordinate system, and the regions are divided according to the number of types of materials contained within them. Single-phase zone and A two-phase region, wherein the single-phase region contains one material, and the two-phase region contains two materials.

[0014] Preferably, in step S4,

[0015] When the region is a single-phase region, the thermal conductivity of that region is the same as the thermal conductivity of the material in the single-phase region itself.

[0016] When the region is a two-phase region, the thermal conductivity of that region is calculated as follows:

[0017] When two materials are arranged in series along the direction of heat transfer within the divided regions, a SeriesModel is used.

[0018] The formula for calculating the equivalent thermal conductivity of a region is as follows:

[0019]

[0020] in, This represents the volume fraction of material one. Let be the thermal conductivity of material 1; This represents the volume fraction of material 2. Let be the thermal conductivity of material 2;

[0021] When two materials are arranged in parallel along the direction of heat transfer in the divided regions, a Parallel Model is used.

[0022] The formula for calculating the equivalent thermal conductivity of a region is as follows:

[0023] ;

[0024] When one material is uniformly dispersed in another material within a defined region, and the pores in the dispersed phase are not interconnected, the Maxwell-Eucken Model is used.

[0025] The formula for calculating the equivalent thermal conductivity of a region is as follows:

[0026] ;

[0027] When dividing regions based on fiber orientation and shape, the Lewis and Nielsen Model is used.

[0028] The formula for calculating the equivalent thermal conductivity of a region is as follows:

[0029]

[0030] in, , ; This represents the volume fraction ratio of the matrix to the fiber. Volume fraction of fibers A constant that takes into account fiber orientation and shape.

[0031] Preferably, in step S1, the number of slice images obtained by Micro-CT scanning is greater than a set number, the distance between two slices is not less than 1 / 5 of the minimum dimension of the fiber bundle in each direction, and scanning is performed in three orthogonal directions respectively.

[0032] Preferably, in step S2, the specific process of image processing for the slice is as follows:

[0033] Step S21: Using the Micro-CT image preprocessing module, periodic identification, representative volume unit identification, and feature image extraction are performed on the woven composite material;

[0034] Step S22: Crop, threshold segment, and binarize the feature image;

[0035] Step S23: The region recognition module is used to overlay and segment the processed image into slices in different directions to obtain information on each region of the woven composite material, including internal defects and woven structure features. The region information includes location information, component information and volume fraction information.

[0036] Preferably, the thermal conductivity of the overall composite material is calculated based on the arrangement of each region in the thermal conduction direction.

[0037] When the regions are arranged in series in the direction of thermal conductivity calculation, the formula for calculating the overall thermal conductivity is as follows:

[0038]

[0039] in, Let i be the volume fraction of the i-th region. Let be the thermal conductivity of the i-th region;

[0040] When the regions are arranged in parallel along the direction of thermal conductivity calculation, the formula for calculating the overall thermal conductivity is as follows:

[0041] .

[0042] Therefore, this invention employs a method for calculating the thermal conductivity of woven composite materials based on real material information. It incorporates real material internal structure information and assigns calculation models to different regions, resulting in a high-precision and high-efficiency method for predicting equivalent thermal conductivity. This invention can improve the accuracy and efficiency of woven composite material design and optimization, significantly reduce design cycle and cost, and is particularly relevant for the transformation and application in the thermal protection systems of next-generation hypersonic vehicles.

[0043] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0044] Figure 1 This is a flowchart of a method for calculating the thermal conductivity of woven composite materials based on real material information according to the present invention.

[0045] Figure 2 This is the ideal geometric model of the orthogonal triaxial structure in Example 1;

[0046] Figure 3 The partitioning strategy for the orthogonal three-way structure in Example 1;

[0047] Figure 4 Cropping and preliminary processing of the Micro-CT images in Example 1;

[0048] Figure 5 Representative volumetric unit identification and region segmentation in Example 1;

[0049] Figure 6a A schematic diagram showing two materials arranged in series along the direction of heat transfer in the divided region;

[0050] Figure 6b A schematic diagram showing two materials arranged in parallel along the direction of heat transfer in the divided region;

[0051] Figure 6c A schematic diagram showing one material uniformly dispersed in another material within a defined region.

[0052] Figure 6d This is a schematic diagram showing the regions divided according to fiber direction and shape. Detailed Implementation

[0053] Example

[0054] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0055] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0056] Step S1: Perform Micro-CT scanning on the woven composite material to acquire slice images in the x, y, and z directions. This embodiment uses the z direction as an example. The number of slice images obtained from the Micro-CT scan is greater than a set limit, and the distance between two slices is not less than 1 / 5 of the minimum dimension of the fiber bundle in each direction. Scanning is performed along the three orthogonal directions. The minimum period for this material in the z direction is 2 images.

[0057] Step S2: Perform image processing on the slices to obtain the actual material information of the braided composite material. Obtain the actual material information considering defects and braiding structural characteristics of the braided composite material, including but not limited to different partition locations, material composition, and volume fraction.

[0058] Step S21: Using the Micro-CT image preprocessing module, periodic identification, representative volume unit identification, and feature image extraction are performed on the woven composite material.

[0059] Step S22: Crop, threshold segment, and binarize the feature image.

[0060] Cropping is performed using P1(574,223) and P2(794,418) as endpoints, with a grayscale threshold of 144, followed by binarization. Figure 4 As shown.

[0061] Step S23: The processed image is overlaid and segmented using a region recognition module to obtain information about each region of the woven composite material, including internal defects and woven structure features. This region information includes location information, component information, and volume fraction information. The images obtained from the secondary processing are then overlaid, representative volume element (RVE) is identified, and the region segmentation results are as follows: Figure 5 The identified representative volume units were divided into four regions: two-phase region 1, two-phase region 2, two-phase region 3, and single-phase region 1. The volume fractions of each region are as follows: Region 3 (two-phase region 1): 0.21; Region 4 (two-phase region 2): 0.51; Region 5 (two-phase region 3): 0.20; Region 6 (single-phase region 1): 0.08.

[0062] Step S3: Based on the weaving parameters of the woven composite material, including warp cross-sectional dimensions, weft cross-sectional dimensions, warp spacing, weft spacing, and normal yarn cross-sectional dimensions and spacing, the representative volume unit is divided into regions perpendicular to the global coordinate system. The region division is based on the number of material types contained within. Single-phase zone and A two-phase region, wherein the single-phase region contains one material, and the two-phase region contains two materials.

[0063] Establish a representative volume element geometric model.

[0064] When the region is a single-phase region, the thermal conductivity of that region is the same as the thermal conductivity of the material in the single-phase region itself.

[0065] When the region is a two-phase region, the thermal conductivity of that region is calculated as follows:

[0066] When two materials are arranged in series along the direction of heat transfer in the divided regions, such as Figure 6a As shown, a Series Model is used.

[0067] The formula for calculating the equivalent thermal conductivity of a region is as follows:

[0068]

[0069] in, This represents the volume fraction of material one. Let be the thermal conductivity of material 1; This represents the volume fraction of material 2. Let be the thermal conductivity of material 2;

[0070] When two materials are arranged in parallel along the direction of heat transfer in the divided regions, such as Figure 6b As shown, the Parallel Model is used.

[0071] The formula for calculating the equivalent thermal conductivity of a region is as follows:

[0072] ;

[0073] When one material is uniformly dispersed in another material within a divided region, such as Figure 6c As shown, when the pores in the dispersed phase are not interconnected, the Maxwell-Eucken Model is used.

[0074] The formula for calculating the equivalent thermal conductivity of a region is as follows:

[0075] ;

[0076] When dividing regions according to fiber direction and shape, such as Figure 6d As shown, the Lewis and Nielsen Model is used.

[0077] The formula for calculating the equivalent thermal conductivity of a region is as follows:

[0078]

[0079] in, , ; This represents the volume fraction ratio of the matrix to the fiber. Volume fraction of fibers A constant that takes into account fiber orientation and shape.

[0080] Taking a carbon fiber reinforced resin-based braided composite material as an example, the braided structure of this material is an orthogonal triaxial structure. Taking the calculation of the thermal conductivity in the z-direction as an example, the established ideal model is as follows: Figure 2 As shown.

[0081] Step S4: Divide the representative volume unit into regions and match the thermal conductivity calculation model according to the region characteristics. Assign appropriate thermal conductivity calculation models to different regions and calculate the anisotropic thermal conductivity of each region. For example... Figure 3 The material is partitioned according to the following principle: within a representative volume unit, the partitioning extends from top to bottom along the direction to be calculated (z-axis). In this example, it is divided into four regions: 3, 4, 5, and 6. Region 3 (two-phase region 1) consists of weft yarn (radial) + matrix; region 4 (two-phase region 2) consists of warp yarn (radial) + weft yarn (radial); region 5 (two-phase region 3) consists of warp yarn (radial) + matrix; and region 6 (single-phase region 1) consists of normal yarn (axial). In this example, the porous matrix is ​​considered as air dispersed within a dense matrix, and the calculation model used is Model 3: the Maxwell-Eucken Model.

[0082]

[0083] in These are the equivalent thermal conductivity of the porous matrix, the volume fraction of the dense matrix, the volume fraction of air, the thermal conductivity of the dense matrix, and the thermal conductivity of air, respectively.

[0084] The fiber bundle is considered to consist of 75% carbon fiber and 25% matrix, and the calculation model used is Model 2: Parallel Model.

[0085]

[0086] Where, x i Let y be the volume fraction of the i-th region. i Let m be the thermal conductivity of the i-th region, which is 4 in this embodiment.

[0087] The matrix is ​​considered an isotropic material, while carbon fibers are classified as axially and radially anisotropic materials. The equivalent thermal conductivity of carbon fibers, dense matrix, and porous matrix is ​​shown in Table 1.

[0088] Table 1

[0089]

[0090] Step S5: Input the real material information into the thermal conductivity calculation model in step S4, replace the material partitions in the representative volume unit with the real material partitions, calculate the thermal conductivity of each region, and then determine the overall thermal conductivity calculation model and calculate the overall thermal conductivity based on the thermal conductivity and arrangement of each region to predict the thermal conductivity.

[0091] In this example, the equivalent thermal conductivity calculation model used in each region is the Series Model.

[0092]

[0093] in These represent the equivalent thermal conductivity of the region, the volume fraction of material 1, the volume fraction of material 2, the thermal conductivity of material 1, and the thermal conductivity of material 2, respectively. This model is applicable when materials are arranged in series along the direction of heat transfer.

[0094] The thermal conductivity calculation model used for representative volume elements is the Parallel Model.

[0095]

[0096] Where x i Let y be the volume fraction of the i-th region. iLet be the thermal conductivity of the i-th region. This model is applicable when the materials are arranged in parallel along the heat transfer direction. The calculation results are shown in Table 2 below:

[0097]

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for calculating the thermal conductivity of woven composite materials based on real material information, characterized in that, Includes the following steps: Step S1: Perform Micro-CT scanning on the woven composite material to obtain slice images in the x, y, and z directions respectively; Step S2: Process the sliced ​​images to obtain the real material information of the woven composite material. Use the region recognition module to overlay and segment the processed images of sliced ​​images in different directions to obtain the information of each region of the woven composite material, including internal defects and woven structure features. The region information includes location information, component information and volume fraction information. Step S3: Based on the weaving parameters of the braided composite material, establish a representative volumetric element geometric model; Step S4: Divide the representative volume element into regions. The region division of the representative volume element is carried out in a direction perpendicular to the global coordinate system, and the region division is based on the number of types of materials contained. Single-phase zone and A two-phase region, wherein the single-phase region contains one material, and the two-phase region contains two materials; a thermal conductivity calculation model is matched according to the regional characteristics; when the divided region is a single-phase region, the thermal conductivity of the region is the thermal conductivity of the material of the single-phase region itself; When the region is a two-phase region, the thermal conductivity of that region is calculated as follows: When two materials are arranged in series along the direction of heat transfer within the divided regions, a Series Model is used. The formula for calculating the equivalent thermal conductivity of a region is as follows: in, This is the volume fraction of material one. Let be the thermal conductivity of material 1; This represents the volume fraction of material 2. Let be the thermal conductivity of material 2; When two materials are arranged in parallel along the direction of heat transfer in the divided regions, a Parallel Model is used. The formula for calculating the equivalent thermal conductivity of a region is as follows: ； When one material is uniformly dispersed in another material within a defined region, and the pores in the dispersed phase are not interconnected, the Maxwell-Eucken Model is used. The formula for calculating the equivalent thermal conductivity of a region is as follows: ； When dividing regions based on fiber orientation and shape, the Lewis and Nielsen Model is used. The formula for calculating the equivalent thermal conductivity of a region is as follows: in, , ; This represents the volume fraction ratio of the matrix to the fiber. Volume fraction of fibers A constant to take into account fiber orientation and shape; Step S5: Input the real material information into the thermal conductivity calculation model in step S4, replace the material partitions in the representative volume unit with the real material partitions, calculate the thermal conductivity of each region, and then determine the overall thermal conductivity calculation model and calculate the overall thermal conductivity based on the thermal conductivity and arrangement of each region to predict the thermal conductivity. The thermal conductivity of the overall composite material is calculated based on the arrangement of each region in the thermal conduction direction. When the regions are arranged in series along the direction of thermal conductivity calculation, the formula for calculating the overall thermal conductivity is as follows: in, Let i be the volume fraction of the i-th region. Let be the thermal conductivity of the i-th region; When the regions are arranged in parallel along the direction of thermal conductivity calculation, the formula for calculating the overall thermal conductivity is as follows: 。 2. The method for calculating the thermal conductivity of woven composite materials based on real material information according to claim 1, characterized in that: In step S3, the weaving parameters include the warp cross-sectional dimensions, the weft cross-sectional dimensions, the warp spacing, the weft spacing, and the normal yarn cross-sectional dimensions and spacing.

3. The method for calculating the thermal conductivity of woven composite materials based on real material information according to claim 2, characterized in that: In step S1, the number of slice images obtained by Micro-CT scanning is greater than the set number, the distance between two slices is not less than 1 / 5 of the minimum size of the fiber bundle in each direction, and scanning is performed in three orthogonal directions respectively.

4. The method for calculating the thermal conductivity of woven composite materials based on real material information according to claim 3, characterized in that: In step S2, the specific process of image processing for the slice is as follows: Step S21: Using the Micro-CT image preprocessing module, periodic identification, representative volume unit identification, and feature image extraction are performed on the woven composite material; Step S22: Crop, threshold segment, and binarize the feature image; Step S23: The region recognition module is used to overlay and segment the processed image into slices in different directions to obtain information on each region of the woven composite material, including internal defects and woven structure features. The region information includes location information, component information and volume fraction information.

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