Method for constructing thermal conductivity calculation model of fiber reinforced composite material, thermal conductivity calculation method and device

Abstract

This invention provides a method for constructing a thermal conductivity calculation model for fiber-reinforced composite materials, a method for calculating thermal conductivity, and an apparatus for such calculations. Belonging to the field of computer-based research on material properties, this invention considers the interfacial thermal resistance between the yarn and the matrix at a macroscopic scale in its method for constructing the thermal conductivity calculation model for fiber-reinforced composite materials. It can assign different material parameters to the interfacial layer of yarns with different orientations to characterize the differences in the actual contact state between yarns distributed in different directions and the matrix. Compared to other methods that do not consider the interfacial thermal resistance between the yarn and the matrix, this method can provide more accurate prediction results, thereby reducing experimental costs and promoting the application of fiber-reinforced composite materials in thermal insulation systems.

Description

Technical Field

[0001] This invention belongs to the technical field of using computers to study material properties, specifically relating to a method for constructing a thermal conductivity calculation model for fiber-reinforced composite materials, a method for calculating thermal conductivity, and an apparatus. Background Technology

[0002] Ceramic matrix composites (CMCs) have been widely used in hot-end components in the aerospace and automotive industries due to their excellent thermal stability, low density, and high stiffness. Given the inherent brittleness of bulk ceramics, reinforcing fibers are typically introduced to improve their fracture resistance and mechanical reliability. Among these, three-dimensional braided porous ceramic matrix composites exhibit significant advantages in anti-delamination properties, anisotropic performance, impact resistance, and structural design flexibility. To reduce experimental costs and promote their application in thermal insulation systems, it is necessary to establish models capable of accurately predicting their thermal properties.

[0003] To address the complexity of the internal structure of composite materials, a multi-scale approach is crucial. This approach enables performance prediction by characterizing the microscopic internal structure and establishing its relationship with macroscopic equivalent properties. For braided composites, this framework typically unfolds across three scales: the microscale corresponds to the porous matrix, the mesoscale corresponds to the braided yarns, and the macroscale corresponds to the overall composite material. Existing research primarily focuses on plain-weave composites or polymer-based composites. However, in three-dimensional braided composites, the presence of yarns in the thickness direction significantly alters thermal conductivity, and the impact of these yarns on equivalent thermal conductivity warrants further investigation.

[0004] Regarding the prediction methods used at various scales, the finite element method is widely used due to its ability to characterize complex structural features. Especially at the macroscopic scale, CT-based modeling can more accurately depict the geometry and path of yarns, thus obtaining more reliable thermal conductivity prediction results through finite element analysis. At the microscopic scale of porous matrices and the mesoscopic scale of woven yarns, their structures are usually considered to be regular structures.

[0005] However, the finite element method (FEM) presents significant challenges because geometric modeling and mesh generation often require individualized processing for each specific situation. Therefore, in micro- and meso-scale analyses, where structures can typically be idealized into regular configurations, theoretical methods are preferred to reduce computational costs. Several theoretical models have been used to predict the equivalent properties of particle-reinforced composites. The equivalent medium theory based on Maxwell's far-field matching method, due to its ability to capture the percolation threshold, is widely used to predict the electrical properties of particle-reinforced composites and exhibits good accuracy in both mechanical and thermal domains. For the thermal conductivity of fiber-reinforced yarns, commonly used models include parallel models, series models, the Pilling model, the Clayton model, and the Russell model. However, when the fiber volume fraction is high, some models may produce inaccurate predictions compared to the FEM results. The reliability of these methods in predicting equivalent thermal conductivity for high-porosity ceramic matrices and fiber-reinforced yarns still requires further verification. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to provide a method for constructing a thermal conductivity calculation model for fiber-reinforced composite materials, a method for calculating thermal conductivity, and an apparatus, with the aim of establishing a model that can accurately predict the thermal properties of fiber-reinforced composite materials, including three-dimensional woven porous ceramic matrix composite materials, reducing experimental costs and promoting the application of fiber-reinforced composite materials in thermal insulation systems.

[0007] This invention provides a method for constructing a calculation model for the thermal conductivity of fiber-reinforced composite materials, including: S100: Calculate the equivalent thermal conductivity of a porous matrix, which includes the matrix and gas in the pores; S200: Calculate the equivalent thermal conductivity of the yarn, which includes unidirectional reinforcing fibers and the porous matrix. The equivalent thermal conductivity of the porous matrix calculated in S100 is used as the material parameter of the porous matrix in the yarn. S300: An interface layer of thickness is added to the surface of the yarn to equivalently measure the interfacial thermal resistance between the yarn and the matrix, thereby obtaining a thermal conductivity calculation model for the fiber-reinforced composite material including the yarn, the matrix, and the interface layer; wherein, the material parameters of the yarn are the equivalent thermal conductivity obtained in S200, the material parameters of the matrix are the equivalent thermal conductivity of the porous matrix obtained in S100, and the thermal conductivity of the interface layer is obtained by conversion from interfacial thermal resistance data.

[0008] In one embodiment, the thermal conductivity calculation model construction method further includes: pre-obtaining the weaving structure of the yarn of the fiber-reinforced composite material, the volume fraction of unidirectional reinforcing fibers inside the yarn, the porosity in the porous matrix, the thermal conductivity of the matrix, reinforcing fibers and pores, and the interfacial thermal resistance between the matrix yarns.

[0009] In one implementation, S100 calculates the equivalent thermal conductivity of the yarn using a theoretical equation derived from the Maxwell far-field matching method; S200 calculates the equivalent thermal conductivity of the yarn using a theoretical equation derived from the Maxwell far-field matching method.

[0010] In one embodiment, the pores of the porous matrix in S100 are modeled as rotating ellipsoidal inclusions randomly distributed in the matrix.

[0011] In one embodiment, in S200, it is assumed that unidirectional reinforcing fibers are randomly distributed in the porous matrix within the cross-section of the yarn; the axial equivalent thermal conductivity and transverse equivalent thermal conductivity of the yarn are derived using the Maxwell far-field matching method.

[0012] In another aspect, the present invention also provides a method for calculating the thermal conductivity of fiber-reinforced composite materials, comprising: obtaining the thermal conductivity of fiber-reinforced composite materials by constructing a thermal conductivity calculation model for fiber-reinforced composite materials using the above method.

[0013] In one implementation, S100 calculates the equivalent thermal conductivity of the yarn using a theoretical equation derived from the Maxwell far-field matching method; S200 calculates the equivalent thermal conductivity of the yarn using a theoretical equation derived from the Maxwell far-field matching method; and S300 calculates the equivalent thermal conductivity of the macroscopic composite material using finite element steady-state heat transfer.

[0014] In one embodiment, the process of converting the thermal conductivity of the interface layer using interface thermal resistance data includes: The thermal conductivity of the interface layer is estimated using the following relationship: ; Where, k int The thermal conductivity of the interface layer; The thickness of the interface layer; To determine the interfacial thermal resistance, experimental methods were used to utilize... The formula can be used to determine the answer, or existing data can be queried. Where q is the interfacial heat flux density, This represents the temperature difference between the two surfaces.

[0015] In one embodiment, the thickness of the interface layer is 0.05 to 0.2 times the shortest axis length of the yarn cross-section.

[0016] Thirdly, the present invention provides a thermal conductivity calculation device for fiber-reinforced composite materials, comprising: a microscale calculation unit for calculating the equivalent thermal conductivity of a porous matrix, wherein the porous matrix includes a matrix and gas in the pores; A microscale calculation unit is used to calculate the equivalent thermal conductivity of the yarn, which includes unidirectional reinforcing fibers and the porous matrix. The equivalent thermal conductivity of the porous matrix calculated by the microscale calculation unit is used as the material parameter of the porous matrix in the yarn. Macro-scale calculation unit: used to calculate the equivalent thermal conductivity of fiber-reinforced composite materials, including: adding an interface layer of thickness to the surface of the yarn to equivalently measure the interfacial thermal resistance between the yarn and the matrix, and obtaining a thermal conductivity calculation model of the fiber-reinforced composite material including the yarn, the matrix, and the interface layer; wherein, the material parameters of the yarn are obtained using the equivalent thermal conductivity obtained by the meso-scale calculation unit, the material parameters of the matrix are obtained using the equivalent thermal conductivity of the porous matrix obtained by the micro-scale calculation unit, and the thermal conductivity of the interface layer is obtained by conversion from interfacial thermal resistance data.

[0017] Beneficial effects: 1. This invention provides a method for constructing a thermal conductivity calculation model for fiber-reinforced composite materials that considers the interfacial thermal resistance between the yarn and the matrix at a macroscopic scale. It can assign different material parameters to the interfacial layer of yarns with different orientations to characterize the differences in the actual contact state between yarns distributed in different directions and the matrix. Compared to other methods that do not consider the interfacial thermal resistance between the yarn and the matrix, this method can provide more accurate prediction results, thereby reducing experimental costs and promoting the application of fiber-reinforced composite materials in thermal insulation systems.

[0018] The method of this application was applied to three-dimensional braided alumina fiber-reinforced porous silica composite materials to verify the reliability of the method. Under the assumption of an ideal interface, the calculated overall equivalent thermal conductivity of the composite material was up to 58% higher than the experimental measurement. However, after incorporating the interfacial thermal resistance into the model using the thermal conductivity calculation model construction method provided in this application, the calculated thermal conductivity results were in better agreement with the experimental values, with a deviation within 20%.

[0019] 2. This invention calculates the equivalent thermal conductivity of composite materials across three scales: porous matrix, braided yarn, and macroscopic composite material. Compared to single-scale calculations, this simplifies modeling and reduces computational requirements. This multi-scale method is applicable not only to three-dimensional braided ceramic matrix composites but also to other braiding methods such as plain weave or corner interlocking materials, as well as polymer matrix composites.

[0020] 3. This invention employs the theoretical framework of Maxwell's far-field matching method at both the microscopic (porous matrix) and mesoscopic (fiber-reinforced yarn) scales to derive analytical formulas for equivalent thermal conductivity, replacing finite element numerical calculations and improving computational efficiency. This method can handle different pore shapes (characterized by aspect ratio) and arbitrary fiber volume fractions. Attached Figure Description

[0021] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0022] Figure 1 This is a schematic diagram of the multi-scale modeling framework for the three-dimensional braided porous ceramic matrix composite material in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the S100 pore shape and its orientation in the matrix in Embodiment 1 of the present invention; Figure 3 This refers to the three-dimensional woven porous ceramic matrix composite material at the macroscopic scale in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram showing the temperature and heat flow distribution of the three-dimensional woven porous ceramic matrix composite material at the macroscopic scale in the X, Y, and Z directions in Embodiment 1 of the present invention. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. The principles and features of the present invention are described below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0024] This invention proposes a method for constructing a calculation model for the thermal conductivity of fiber-reinforced composite materials. A multi-scale modeling framework for thermal conductivity is established, encompassing three length scales: microscale (porous matrix), mesoscale (woven yarn), and macroscale (composite material). At the micro and mesoscale scales, equivalent medium theory based on Maxwell's far-field matching method is used to establish theoretical models applicable to the matrix and yarn, respectively. At the macroscale scale, finite element analysis is conducted based on representative volume elements reconstructed by Micro-CT and incorporating interfacial thermal resistance. The theoretical method significantly reduces computational resources compared to simulation calculations. The macroscale approach, by considering the interfacial thermal resistance between the yarn and matrix, provides more accurate results. Comparison with experimental results verifies the usability of this multi-scale method.

[0025] Example 1 The method for constructing the thermal conductivity calculation model of fiber-reinforced composite materials in this embodiment includes: S000: The weave structure of the yarn in the fiber-reinforced composite material, the volume fraction of unidirectional reinforcing fibers within the yarn, the porosity of the porous matrix, and the thermal conductivity and interfacial thermal resistance of the matrix, reinforcing fibers, and pores are obtained in advance. Specifically, the geometric parameters of the composite material, including the yarn weave structure, the volume fraction of fibers within the yarn, and the porosity of the matrix, can be obtained using Micro-CT. The thermal conductivity of the matrix, fibers, and pores, as well as the interfacial thermal resistance between the matrix and yarns, are assigned based on existing material data or experimental results.

[0026] S100: At the microscale, the equivalent thermal conductivity of the porous matrix is ​​calculated using theoretical equations derived from the Maxwell far-field matching method. The porous matrix includes the matrix and the gas in the pores. S200: At the microscale, the equivalent thermal conductivity of the yarn is calculated using a theoretical equation derived from the Maxwell far-field matching method. The yarn contains unidirectional reinforcing fibers and the porous matrix. The equivalent thermal conductivity of the porous matrix calculated in S100 is used as the material parameter of the porous matrix in the yarn. S300: On a macroscopic scale, an interface layer of thickness is added to the surface of the yarn to equivalently measure the interfacial thermal resistance between the yarn and the matrix, thereby obtaining a fiber-reinforced composite material comprising yarn, matrix, and interface layer; wherein, the material parameters of the yarn are the equivalent thermal conductivity obtained in S200, the material parameters of the matrix are the equivalent thermal conductivity of the porous matrix obtained in S100, and the thermal conductivity of the interface layer is obtained by conversion from interfacial thermal resistance data.

[0027] In one implementation, modeling software such as Solidworks, Texgen, or Digimat is used to establish a geometric model of the macroscopic composite material based on the yarn structure distribution obtained from CT scans.

[0028] This embodiment calculates the equivalent thermal conductivity of composite materials on three scales: porous matrix, braided yarn, and macroscopic composite material. Figure 1 As shown, this multi-scale method simplifies modeling and reduces computational requirements compared to single-scale calculations. This method is applicable not only to 3D braided ceramic matrix composites, but also to other braiding methods such as plain weave or corner interlocking materials, as well as polymer matrix composites.

[0029] This embodiment considers the interfacial thermal resistance between the yarn and the matrix at a macroscopic scale. It can assign different material parameters to the interfacial layer of yarns with different orientations to characterize the differences in the actual contact state between yarns distributed in different directions and the matrix. Compared to other methods that do not consider the interfacial thermal resistance between the yarn and the matrix, this method can provide more accurate prediction results.

[0030] If the fiber and matrix have good contact, that is, if the yarn and matrix have good contact, then only one of the two interfacial thermal resistances needs to be considered. That is, the thermal resistance between the fiber and matrix can be considered only at the microscale, or only at the macroscale, considering the equivalent thermal resistance between the yarn and matrix. Only one scale needs to be introduced for interfacial thermal resistance. In reality, it is difficult for two different materials to have good contact at the interface. This poor contact is more significant at the yarn-matrix interface but negligible at the microscale; therefore, the macroscale yarn-matrix interfacial thermal resistance is considered. Furthermore, using the Maxwell far-field matching method at the microscale, while maintaining the ideal interface assumption, ensures the simplicity of the theoretical derivation.

[0031] The fiber-reinforced composite materials described in this embodiment include not only three-dimensional braided ceramic matrix composite materials, but also unidirectional fiber-reinforced composite materials and laminates composed of unidirectional fiber-reinforced composite materials, but do not include short fiber-reinforced composite materials in which the fibers at the microscale are randomly oriented in the matrix.

[0032] This embodiment provides a specific method for microscale modeling of porous matrices based on the equivalent medium theory: The pores in the porous matrix were modeled as randomly distributed rotating ellipsoidal inclusions within the ceramic matrix. Porosity was determined using Micro-CT scanning. The composite material at the microscale of the porous matrix can be considered to consist of an inclusion phase (phase 1, representing pores) and a matrix (phase 0), whose properties are determined by tensors. and Characterization. The volume fractions of the matrix and inclusion phases are denoted as follows: c 0 and c 1. and satisfy the constraints. To estimate the equivalent property tensor of composite materials. Introduce a property tensor as The reference medium. The first [unclear] embedded in this reference medium i Mutually( i The scattered field of ( =0, 1, e) is denoted as And satisfy the following relationship: (1) in It's Eshelby S The tensor, whose value depends on the shape of the inclusion. Based on the far-field matching condition, i.e., the volume average of the scattered fields of each constituent phase in the composite material is equal to the scattered field of the equivalent medium, we can obtain... Therefore, there is (2) For porous matrices, pores are distributed within the ceramic phase and may interact and connect; therefore, a reference medium is taken as the equivalent medium, i.e. Since Le-Lr is 0, its inverse divergence (infinity) continues even after adding a finite SL term, and the inverse of the whole becomes 0. The corresponding physical meaning is that when the reference medium is taken as the equivalent medium, the equivalent medium itself does not generate a scattering field, that is, the far-field scattering term is zero. In this case, the left side of equation (2) is the zero tensor, which can be simplified to (3) Since it is assumed that the pores are randomly distributed in the matrix, averaging is required across all directions. Euler angles are introduced to describe the orientation of the pores. φ and θ ,like Figure 2 As shown. By averaging across all directions, equation (3) can be rewritten as (4) angle brackets This represents the orientation averaging operation. For a second-order tensor A, A It can be represented as (5) R represents the coordinate transformation matrix, which has the following form: (6) With direction 3 as the axis of symmetry for phase i, its Eshelby tensor S i The three non-zero components are represented as follows: (7) In the above formula, S 11 S 22 S 33 These are the three components of S1 and S0 above. S1 is the Eshelby tensor of phase 1, and S0 is the Eshelby tensor of phase 0. The letter S is bolded to indicate a tensor, and unbolded to indicate a component of the tensor. In heat conduction problems, the Eshelby tensor S of phase i... i It is a second-order tensor. It has three non-zero components located on the diagonal elements, namely S0 and S0. 11 , S 22 , S 33 .

[0033] in, α = λ / l The thickness-to-diameter ratio of the oblate spheroidal inclusion is... λ It refers to the length in three directions, namely the thickness direction. l Let be the lengths in directions 1 and 2. For the matrix, its shape is assumed to be spherical; in this case, the Eshelby tensor of the matrix... S 0 equals 1 / 3I, where I is the unit tensor.

[0034] The thermal conductivity tensors of each constituent phase Substitute tensor L i In the mean, the equivalent thermal conductivity of the porous matrix is... satisfy (8) If the pores are assumed to be spherical, then orientation averaging is not required to obtain the desired result. ,Right now (9) This embodiment provides a specific implementation method for yarn microscale modeling based on the equivalent medium theory: Within the yarn cross-section, it is assumed that unidirectional reinforcing fibers are randomly distributed within a porous matrix. The fiber volume fraction within the yarn is determined based on CT scan results. Similarly, within the unified framework of Maxwell's far-field matching method, the axial and transverse equivalent thermal conductivity of the fiber-reinforced yarn is derived. The fibers and matrix are defined as phase 1 and phase 0, respectively, with the matrix employing the homogenized thermal conductivity of porous ceramic. The matrix medium is taken as the reference medium (…). ), and by applying equation (2), we can obtain (10) To characterize the shape of the fiber, the aspect ratio is... α Let it be +∞, then S e = S 1 = diag(1 / 2, 1 / 2, 0). From this, the axial thermal conductivity of the yarn can be derived. and transverse thermal conductivity satisfy (11) (12) and These represent the volume fractions of the porous matrix and fibers within the yarn, respectively. , and These represent the axial thermal conductivity of the fiber, the transverse thermal conductivity of the fiber, and the equivalent thermal conductivity of the porous matrix, respectively.

[0035] Taking three-dimensional braided porous ceramic matrix composites as an example, this embodiment provides a specific implementation method for macroscopic modeling of composite materials based on representative volume elements: Reference Figure 3 The three-dimensional braided porous ceramic matrix composite material at the macroscopic scale is shown in (a) sample; (b) CT scan image; (c) geometric model under the ideal interface assumption; (d) ideal interface mesh model; and (e) geometric model and mesh model with interface layer.

[0036] At the macroscopic scale, the composite material is considered to consist of a porous matrix and three-dimensional braided yarns. The equivalent thermal conductivity of the matrix and yarns is determined based on calculations at the microscopic and mesoscopic scales, respectively. The structure and dimensions of the representative volumetric element model are established based on CT scan results, such as... Figure 3 As shown in (a)-(c).

[0037] To simulate the interfacial thermal resistance effect, a thin interfacial layer is introduced between the yarn and the matrix. The geometric model is as follows: Figure 3 As shown in (e), the yellow area represents the interface layer. Interface thermal resistance... Depend on Determined through experimental methods or by querying existing data, among which... q For interfacial heat flux density, This represents the temperature difference between the two surfaces. This can be simulated by giving the interface layer a lower thermal conductivity. Due to the thickness of the interface layer... Relative to sufficiently small yarn size, the thermal conductivity of the interface layer k int It can be estimated through the following relationship (13) To ensure the thickness of the interface layer For sufficiently small yarn sizes, the interface layer thickness can be 0.05 to 0.2 times the shortest axis length of the yarn cross-section. Too small a thickness will make mesh generation difficult, while too large a thickness will deviate from the thin-layer assumption.

[0038] The equivalent thermal conductivity can be determined by performing steady-state heat conduction analysis under periodic boundary conditions and homogenizing the results. The temperature at corresponding points on the positive and negative sides of the axis can be expressed as (14) (15) Indicates along The temperature gradient component applied in the direction. ( )express The coordinates of the points corresponding to the positive (negative) side of the axis. T * The temperature correction term has the same value on both opposite faces of the element. Therefore, subtracting the two equations above yields... (16) This condition can be achieved by applying constraint equations at corresponding nodes on opposite surfaces. According to Fourier's law, the equivalent thermal conductivity tensor of the composite material... Depend on Given. Symbol The volume average value of physical quantities within a representative unit is defined as follows: .

[0039] This embodiment employs the theoretical framework of Maxwell's far-field matching method at both the microscopic (porous matrix) and mesoscopic (fiber-reinforced yarn) scales to derive analytical formulas for equivalent thermal conductivity, replacing finite element numerical calculations and improving computational efficiency. This method can handle different pore shapes (characterized by aspect ratio) and arbitrary fiber volume fractions.

[0040] Thermal conductivity was calculated using the aforementioned model for calculating the thermal conductivity of fiber-reinforced composite materials. The results were then compared with experimental results to verify the calculation. This method was applied to a three-dimensional braided alumina fiber-reinforced porous silica composite to verify its reliability. The matrix porosity was 0.3. The fiber volume fraction within the yarn was 0.7. The macroscopic composite model is shown below. Figure 4 As shown in (a) to (c), Figure 4 Heat conduction in a representative volumetric unit at the meso-macro scale, where (a) to (d) represent the X direction; (e) to (h) the Y direction; and (i) to (l) the Z direction. The dimensions are 8.60 × 1.60 × 2.12 mm. The yarn cross-section is assumed to be elliptical. The yarn cross-sectional dimensions distributed along the X, Y, and Z directions are as follows: X-direction major and minor axes are 0.38 mm and 0.7 mm, respectively; Y-direction is 0.15 mm and 0.9 mm, respectively; and Z-direction is 0.4 mm and 2.0 mm, respectively. The volume fractions of the matrix and the yarns in each direction are as follows: 52.5%, 24.4%, 4.8% and 18.3%. The interface layer thickness is 0.015 mm, which is 0.1 times the shortest axis length of the yarn cross-section. Material parameters are shown in Table 1: Table 1 Thermal conductivity of the materials used in the calculation For a three-dimensional braided composite material sample with a porosity of 0.3 and k 0 / k A porous matrix with a 1=38 ohm², assuming spherical pores, is used. Based on this, Maxwell's far-field matching method predicts the equivalent thermal conductivity of the homogenized porous matrix to be 0.57 W / m². -1 K -1 .

[0041] The thermal conductivity of the yarn in the three-dimensional braided porous ceramic matrix composite was calculated using the Maxwell far-field matching method. The equivalent axial and transverse thermal conductivity of the yarn were found to be 4.37 W / m² and 2.13 W / m², respectively. -1K -1 .

[0042] The properties of the previously homogenized porous matrix and yarns were used to predict the equivalent thermal conductivity of a representative volumetric unit at the macroscopic scale in the X, Y, and Z directions. Due to the manufacturing process and the three-dimensional braided composite structure, the contact quality between the Y-direction yarn and the matrix is ​​worse than that of the X and Z-direction yarns. This poor contact translates into higher interfacial thermal resistance. Therefore, the interfacial thermal conductivity at the X and Z-direction yarn interfaces was taken as... k int =0.05 Wm -1 K -1 The Y-axis yarn interface is taken as k int =0.005 Wm -1 K -1 As listed in Table 1.

[0043] To assess the influence of interfacial thermal resistance, finite element analysis was performed on representative volumetric elements with ideal interfaces and representative volumetric elements containing interface layers, and the results were compared with experimental data, as shown in Table 2. The thermal conductivity of the three-dimensional braided composite samples was measured using the laser flash method; detailed experimental methods are provided in Appendix A below. It can be noted that the results based on the ideal interface assumption significantly overestimated the equivalent thermal conductivity of the composite material. After accounting for the interface effect, the relative error between the finite element prediction and the experimental results decreased to within 20%. In summary, interfacial thermal resistance has a significant impact on equivalent performance, and this factor cannot be ignored to accurately predict the equivalent performance of braided composite materials. Macroscopic results validate the reliability of this multi-scale method.

[0044] Table 2. Experimental results of the thermal conductivity of macroscopic composite materials, finite element results under the ideal interface assumption, and results considering interfacial thermal resistance. The temperature and heat flux distribution results for heat conduction in the X, Y, and Z directions are as follows: Figure 4 As shown in the figure, the temperature isosurface and heat flux density distribution along the X-direction clearly demonstrate the hindering effect of the interface on heat transfer. Comparing (a) and (c), it can be seen that after considering the interface thermal resistance, the temperature isosurface near the interface becomes more uneven, as shown by the area indicated by the arrow in the figure. This indicates that an additional temperature drop occurs at the interface, hindering heat transfer. Comparing (b) and (d), it can be seen that after considering the interface, the concentration of heat flux density in the X-direction yarn is more significant, that is, the relative difference in heat flux density inside the X-direction yarn compared to the rest increases, as shown by the circled area in the figure. This is because the X-direction yarn is oriented along the heat transfer direction, providing a more efficient heat transfer path compared to the surrounding matrix. When the interface is present, the heat transfer resistance between this efficient path and the surrounding material increases, forcing the heat flux to concentrate more within the yarn, thus making the concentration of heat flux density more obvious.

[0045] This embodiment also provides a thermal conductivity calculation device for fiber-reinforced composite materials, used to execute the above-described model construction method and calculation method, including... A microscale computing unit is used to calculate the equivalent thermal conductivity of a porous matrix, which includes the matrix and the gas in the pores. A microscale calculation unit is used to calculate the equivalent thermal conductivity of the yarn, which includes unidirectional reinforcing fibers and the porous matrix. The equivalent thermal conductivity of the porous matrix calculated by the microscale calculation unit is used as the material parameter of the porous matrix in the yarn. Macro-scale calculation unit: used to calculate the equivalent thermal conductivity of fiber-reinforced composite materials, including: adding an interface layer of thickness to the surface of the yarn to equivalently measure the interfacial thermal resistance between the yarn and the matrix, and obtaining a thermal conductivity calculation model of the fiber-reinforced composite material including the yarn, the matrix, and the interface layer; wherein, the material parameters of the yarn are obtained using the equivalent thermal conductivity obtained by the meso-scale calculation unit, the material parameters of the matrix are obtained using the equivalent thermal conductivity of the porous matrix obtained by the micro-scale calculation unit, and the thermal conductivity of the interface layer is obtained by conversion from interfacial thermal resistance data.

[0046] The experimental testing methods in this embodiment are as described in Appendix A: The thermal diffusivity of the macroscopic composite material was measured using a laser flare measurement system (NETZSCH-LFA 427). Measurements were performed in a helium atmosphere, with a thin graphite layer coated on the sample surface to prevent direct laser penetration. The thermal conductivity of the three-dimensional braided composite material was also measured. k Then it can be calculated by the following formula: (A.1) In the formula, α Where is the thermal diffusivity, ρ For material density, C p This represents the specific heat capacity of the material.

[0047] The material density was measured using Archimedes' displacement method. The mass of the sample was measured in air. m 1. Then immerse it in anhydrous ethanol and measure its mass. m 2. Sample density ρ Calculated by equation (A.2), where ρ s ρ is the density of the solution.

[0048] (A.2) Specific heat capacity was determined using a differential scanning calorimeter (NETZSCH DSC 214). Measurements were performed under a nitrogen atmosphere at a heating rate of 5 K / min, covering a temperature range of 273–313 K. The heat flow rates of a blank sample, a sapphire standard sample, and the sample to be tested were measured at the same heating rate. The specific heat capacity of the sample to be tested was determined. C p Calculated by the following formula (A.3) In the formula, C p ' , m' and Y' These represent the specific heat capacity, mass, and heat flow rate of the sapphire standard sample, respectively. C p 、m and Y The corresponding parameters of the sample to be tested are used. Three measurements are performed in each of the X, Y, and Z directions. The equivalent thermal conductivity of the macroscopic composite material is calculated using equation (A.1), and the results are summarized in Table A.1. The reported uncertainty corresponds to the standard deviation of the three thermal conductivity calculations.

[0049] Table A.1. Measurement results of thermal diffusivity and thermal conductivity Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for constructing a calculation model for the thermal conductivity of fiber-reinforced composite materials, characterized in that, include: S100: Calculate the equivalent thermal conductivity of a porous matrix, which includes the matrix and gas in the pores; S200: Calculate the equivalent thermal conductivity of the yarn, which includes unidirectional reinforcing fibers and the porous matrix. The equivalent thermal conductivity of the porous matrix calculated in S100 is used as the material parameter of the porous matrix in the yarn. S300: An interface layer of thickness is added to the surface of the yarn to equivalently measure the interfacial thermal resistance between the yarn and the matrix, thereby obtaining a thermal conductivity calculation model for the fiber-reinforced composite material including the yarn, the matrix, and the interface layer; wherein, the material parameters of the yarn are the equivalent thermal conductivity obtained in S200, the material parameters of the matrix are the equivalent thermal conductivity of the porous matrix obtained in S100, and the thermal conductivity of the interface layer is obtained by conversion from interfacial thermal resistance data.

2. The method for constructing a thermal conductivity calculation model according to claim 1, characterized in that, Also includes: The braiding structure of the yarn of the fiber-reinforced composite material, the volume fraction of unidirectional reinforcing fibers inside the yarn, the porosity in the porous matrix, the thermal conductivity of the matrix, reinforcing fibers and pores, and the interfacial thermal resistance between the matrix and yarn are obtained in advance.

3. The method for constructing a thermal conductivity calculation model according to claim 2, characterized in that, S100 uses a theoretical equation derived from the Maxwell far-field matching method to calculate the equivalent thermal conductivity of the yarn; S200 uses a theoretical equation derived from the Maxwell far-field matching method to calculate the equivalent thermal conductivity of the yarn.

4. The method for constructing a thermal conductivity calculation model according to claim 3, characterized in that, In S100, the pores of the porous matrix are modeled as rotating ellipsoidal inclusions randomly distributed in the matrix.

5. The method for constructing a thermal conductivity calculation model according to claim 3, characterized in that, In S200, it is assumed that unidirectional reinforcing fibers are randomly distributed in the porous matrix within the yarn cross-section; the axial equivalent thermal conductivity and transverse equivalent thermal conductivity of the yarn are derived using the Maxwell far-field matching method.

6. A method for calculating the thermal conductivity of fiber-reinforced composite materials, characterized in that, The thermal conductivity of the fiber-reinforced composite material is obtained by using the thermal conductivity calculation model of the fiber-reinforced composite material constructed according to any one of claims 1 to 5.

7. The thermal conductivity calculation method according to claim 6, characterized in that, S100 calculates the equivalent thermal conductivity of the yarn using theoretical equations derived from the Maxwell far-field matching method; S200 calculates the equivalent thermal conductivity of the yarn using theoretical equations derived from the Maxwell far-field matching method; S300 calculates the equivalent thermal conductivity of the macroscopic composite material using finite element steady-state heat transfer.

8. The method for calculating thermal conductivity according to claim 7, characterized in that, The process of converting the thermal conductivity of the interface layer into interface thermal resistance data includes: The thermal conductivity of the interface layer is estimated using the following relationship: ； Where, k int The thermal conductivity of the interface layer; The thickness of the interface layer; To determine the interfacial thermal resistance, experimental methods were used to utilize... The formula can be used to determine the answer, or existing data can be queried. Where q is the interfacial heat flux density, This represents the temperature difference between the two surfaces.

9. The method for calculating thermal conductivity according to claim 8, characterized in that, The thickness of the interface layer is 0.05 to 0.2 times the shortest axis length of the yarn cross-section.

10. A device for calculating the thermal conductivity of fiber-reinforced composite materials, characterized in that, include: A microscale computing unit is used to calculate the equivalent thermal conductivity of a porous matrix, which includes the matrix and the gas in the pores. A microscale calculation unit is used to calculate the equivalent thermal conductivity of the yarn, which includes unidirectional reinforcing fibers and the porous matrix. The equivalent thermal conductivity of the porous matrix calculated by the microscale calculation unit is used as the material parameter of the porous matrix in the yarn. Macro-scale calculation unit: used to calculate the equivalent thermal conductivity of fiber-reinforced composite materials, including: adding an interface layer of thickness to the surface of the yarn to equivalently measure the interfacial thermal resistance between the yarn and the matrix, and obtaining a thermal conductivity calculation model of the fiber-reinforced composite material including the yarn, the matrix, and the interface layer; wherein, the material parameters of the yarn are obtained using the equivalent thermal conductivity obtained by the meso-scale calculation unit, the material parameters of the matrix are obtained using the equivalent thermal conductivity of the porous matrix obtained by the micro-scale calculation unit, and the thermal conductivity of the interface layer is obtained by conversion from interfacial thermal resistance data.

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