Estimation method of thermal conductivity of carbon fiber reinforced ceramic matrix composites under high temperature oxidation

Abstract

The present invention discloses a method for estimating the thermal conductivity of a carbon fiber toughened ceramic matrix composite material under high temperature oxidation. First, the geometric structure characteristic change law of the material when it is oxidized is obtained to establish an RVE model of the material after oxidation; secondly, the oxidation notch depth δ characteristic is introduced into the RVE model to obtain a modified RVE model capable of oxidation characteristics; then, the modified RVE model is divided into five characteristic regions along the fiber axis, and its equivalent axial thermal resistance is established for each characteristic region respectively. The axial thermal resistance of the five regions is connected in series to obtain the overall axial thermal resistance network of the material, and the axial thermal conduction system is obtained by solving; finally, the modified RVE model is divided into the same region to obtain the transverse thermal conductivity. The present invention can predict the thermal conductivity of the material under different oxidation temperatures and oxidation times.

Description

Technical Field

[0001] The invention belongs to the technical field of engineering thermophysics, and particularly relates to a method for estimating thermal conductivity of a carbon fiber-toughened ceramic-based composite material under high-temperature oxidation. Background Art

[0002] Unidirectional carbon fiber reinforced silicon carbide ceramic matrix composites (C / SiC) have broad application prospects in the aerospace field. Compared with super alloys, the beneficial material properties of C / SiC composites include higher strength-to-density ratio, lighter weight, higher temperature performance and better thermal shock resistance. However, under high temperature conditions (temperature above 500 degrees Celsius), the carbon fiber and PyC interface layer in the unidirectional fiber-reinforced C / SiC ceramic matrix composite will undergo redox reactions with oxygen, causing the carbon fiber and PyC to degrade. As a hot end component material, unidirectional fiber-reinforced C / SiC ceramic matrix composites are mainly used in the manufacture of hot end components. For example, the combustion chamber liner of a G gas turbine engine will be continuously loaded for hundreds or even thousands of hours in a high-temperature oxidizing environment. However, the sensitivity of carbon fiber and interphase to oxidation hinders long-term reusable applications in high-temperature oxidizing environments. Therefore, in practical applications, thermal protection design of C / SiC components is required to prevent component damage after high-temperature oxidation.

[0003] To accurately design the thermal properties of C / SiC components, it is necessary to know the heat transfer characteristics of C / SiC materials, that is, the thermal conductivity of the materials. Currently, the research on the thermal properties of C / SiC materials has not considered the effect of fiber oxidation. The formula can calculate the thermal conductivity of C / SiC materials before oxidation, but because the established formula fails to consider the oxygen characteristics of the fibers, it cannot predict the equivalent thermal conductivity of C / SiC materials after fiber oxidation.

[0004] So far, researchers have conducted a lot of research on the oxidation behavior of C / SiC composites. Unfortunately, no researchers have yet introduced the characteristics of the oxidation microstructure changes into the thermal analysis model to obtain the thermal conductivity of C / SiC materials after oxidation. Therefore, a method is needed to obtain the equivalent thermal conductivity of unidirectional carbon fiber toughened ceramic matrix composites under the conditions of oxidation temperature and oxidation time. Summary of the invention

[0005] Purpose of the invention: The present invention provides a method for estimating the thermal conductivity of carbon fiber-reinforced ceramic-based composite materials under high-temperature oxidation, which can predict the thermal conductivity of the material under different oxidation temperatures and oxidation times.

[0006] Technical solution: The method for estimating the thermal conductivity of carbon fiber toughened ceramic matrix composite materials under high temperature oxidation according to the present invention comprises the following steps:

[0007] (1) Based on the microscopic scanning electron microscope photos of unidirectional fiber-reinforced C / SiC ceramic matrix composites, the basic geometric characteristics of unidirectional fiber-reinforced C / SiC ceramic matrix composites were obtained, and the RVE model of unidirectional fiber-reinforced C / SiC ceramic matrix composites was established;

[0008] (2) calculating the geometric change characteristics of the fiber and the interface after oxidation, i.e., the oxidation notch depth δ, according to the oxidation kinetics principle; and introducing the oxidation notch depth δ characteristics into the RVE model established in step (1) to obtain a modified RVE model capable of oxidation characteristics;

[0009] (3) Divide the modified RVE model obtained in step (2) into five characteristic regions along the fiber axis; wherein regions I and V are composed of fibers, interface layers and matrix; regions II and IV are composed of fibers, oxidation notches and matrix; and region III is composed of fibers, oxidation notches and cracks; establish an equivalent axial thermal resistance for each characteristic region, connect the axial thermal resistances of the five regions in series to obtain the overall axial thermal resistance network of the material, and solve the axial thermal resistance network to obtain the axial thermal conductivity prediction formula of the material;

[0010] (4) The regional division of the modified RVE model is consistent with step (3). When establishing the thermal resistance network, the equivalent lateral thermal resistance is established for each region. Then, the lateral thermal resistances of the five regions are connected in parallel to obtain the overall lateral thermal resistance of the material. Then, the thermal resistance network is solved to obtain the prediction formula of the lateral thermal conductivity of the material.

[0011] Furthermore, the basic geometric features include the length, width and height dimensions of the characteristic unit, the fiber diameter, the crack size and the interface layer thickness.

[0012] Furthermore, the axial thermal resistance network in step (3) is composed of five equivalent thermal resistances connected in series, each of which is composed of three basic thermal resistances connected in parallel, and each thermal resistance reflects the structural characteristics of the corresponding region; wherein the axial thermal resistance of regions I and V reflects the combined thermal resistance characteristics of the fiber, matrix and interface layer; the axial thermal resistance of regions II and IV reflects the combined thermal resistance characteristics of the fiber, matrix and oxidation notch; and the axial thermal resistance of region III reflects the thermal resistance characteristics of the combination of fiber, matrix crack and oxidation notch.

[0013] Furthermore, the axial thermal conductivity formula of the material in step (3) is:

[0014]

[0015]

[0016]

[0017] The axial length of region I is L r =(LL e ) / 2,L e is the width of the oxidation notch, R m,I ,R i,I ,R fa,I are the axial thermal resistances of the matrix, interface layer and fiber in region I, r f is the radius of the fiber, λ m is the thermal conductivity of the matrix, λ i is the thermal conductivity of the interface layer, λ fa is the axial thermal conductivity of the fiber;

[0018] Axial thermal resistance R in region I ea,I By connecting R m,I ,R i,I ,R fa,I get:

[0019]

[0020]

[0021] Axial thermal resistance R in region V ea,V for:

[0022]

[0023] For Region II:

[0024]

[0025]

[0026]

[0027] Among them, R m,Ⅱ ,R i,Ⅱ ,R fa,Ⅱ are the axial thermal resistances of the matrix, interface layer and fiber in region II, respectively, gas is the thermal conductivity of the oxidation notch;

[0028] The axial equivalent thermal resistance of area II is connected in parallel with R m,Ⅱ ,R i,Ⅱ ,R fa,Ⅱ get:

[0029]

[0030]

[0031] Axial thermal resistance R in region V ea,Ⅳ for:

[0032]

[0033] For Region III:

[0034]

[0035]

[0036] Among them, R fa,Ⅲ is the axial thermal resistance of the fiber in region III, R gas,Ⅲ is the axial thermal resistance of oxidation notches and cracks in region III;

[0037] Axial thermal resistance R in region III ea,Ⅲ By connecting R gas,Ⅲ ,R fa,Ⅲ get:

[0038]

[0039]

[0040] Axial thermal resistance R of RVE model ea By connecting R ea,I ,R ea,Ⅱ ,R ea,Ⅲ ,R ea,Ⅳ ,R ea,V get:

[0041] R ea =R ea,I +R ea,Ⅱ +R ea,Ⅲ +R ea,Ⅳ +R ea,V

[0042] Axial thermal conductivity λ of the RVE model ea By R ea Find:

[0043]

[0044] Furthermore, the implementation process of step (4) is as follows:

[0045] The transverse thermal resistance network is composed of five equivalent thermal resistances in parallel, and each equivalent thermal resistance reflects the structural characteristics of the corresponding area; among them, the transverse thermal resistance of areas I and V reflects the combined thermal resistance characteristics of the fiber, matrix and interface layer; the transverse thermal resistance of areas II and IV reflects the combined thermal resistance characteristics of the fiber, matrix and oxidation notch; the transverse thermal resistance of area III reflects the thermal resistance characteristics of the combination of fiber, matrix crack and oxidation notch;

[0046] Transverse thermal resistance R of RVE model etBy connecting R et,I ,R et,Ⅱ ,R et,Ⅲ ,R et,Ⅳ ,R et,V get:

[0047]

[0048] For regions Ⅰ, Ⅱ, Ⅳ and V, which are composed of three-phase materials, the lateral thermal resistance is calculated by the following formula:

[0049]

[0050] Among them, α=η~π / 2, η=sin -1 (r f / (r f +d i )).λ ft is the transverse thermal conductivity of the fiber;

[0051]

[0052] Among them, θ=γ~π / 2, γ=sin -1 (r(r f +d i -δ) / (r f +d i ));

[0053] Region III is composed of two-phase materials, and its lateral thermal resistance is calculated by the following formula:

[0054]

[0055] In summary, the lateral thermal conductivity of the RVE model can be calculated through the thermal resistance network:

[0056]

[0057] Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects: the present invention can predict the thermal conductivity of materials under different oxidation temperature and oxidation time conditions; and provide basic thermal physical properties (thermal conductivity) parameters for the thermal design of ceramic-based hot end components in high-temperature service environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 The scanning electron microscope images of a unidirectional fiber-reinforced C / SiC ceramic matrix composite material; (a) is a microstructure diagram of the C / SiC ceramic matrix composite material, and (b) is a schematic diagram of oxidation notches;

[0059] Figure 2Schematic diagram of the RVE model of unidirectional fiber-reinforced C / SiC ceramic matrix composites with oxidation characteristics; (a) schematic diagram of the RVE model, (b) schematic diagram of the cross section in the RVE model, (c) simplified schematic diagram of the oxidation notch;

[0060] Figure 3 This is the schematic diagram of the axial thermal resistance network of the RVE model;

[0061] Figure 4 Schematic diagram of the lateral thermal resistance network of the RVE model, including: (a) cross-sectional diagram of region I, (b) cross-sectional diagram of region II, and (c) cross-sectional diagram of the RVE model. DETAILED DESCRIPTION

[0062] The present invention is further described in detail below with reference to the accompanying drawings.

[0063] The present invention provides a method for calculating the equivalent thermal conductivity of a unidirectional carbon fiber toughened ceramic matrix composite material. First, the geometric structure characteristics of the material when oxidized are obtained to establish an RVE model of the material after oxidation. Then, based on the principle of the thermal resistance network method, a material thermal resistance network containing oxidation characteristics is established, and the thermal conductivity of the material is obtained by solving; specifically, the following steps are included:

[0064] Step 1: According to the microscopic scanning electron microscope photos of the unidirectional fiber-toughened C / SiC ceramic matrix composites, the basic geometric characteristics of the unidirectional fiber-toughened C / SiC ceramic matrix composites are obtained, including: the length, width and height dimensions of the characteristic unit, the fiber diameter, the crack size and the interface layer thickness; according to the geometric characteristics, a representative unit model (RVE model) of the unidirectional fiber-toughened C / SiC ceramic matrix composites is established.

[0065] like Figure 1 As shown in Figure 1, the unidirectional fiber-reinforced C / SiC ceramic matrix composite consists of a carbon phase (fiber and interface phase) and a SiC matrix. When the C / SiC-UFRC is cooled from processing temperature to room temperature, the extensive mismatch in thermal expansion coefficients of the carbon phase (fiber and interface phase) and the SiC matrix leads to cracks embedded in the matrix and perpendicular to the fiber axis, as shown in Figure 1. Figure 1 (a) As shown. When oxygen diffuses into the carbon phase through the crack, an oxidation reaction occurs when the carbon contacts oxygen. The oxygen concentration near the crack tip is the highest, causing the carbon fiber to be consumed at the fastest rate. As the gas concentration decreases, the oxidation rate of the fiber away from the crack tip decreases, thus forming an arc-shaped oxidation gap on the fiber, as shown in Figure 1. Figure 1 (b) as shown.

[0066] Step 2: According to the principle of oxidation kinetics, the geometric change characteristics of the fiber and the interface after oxidation, namely the oxidation notch depth δ, are calculated; and the oxidation notch depth δ characteristics are introduced into the RVE model established in step 1 to obtain a modified RVE model capable of oxidation characteristics.

[0067] based on Figure 1 Based on the microstructure photograph shown in the figure, a modified RVE model including oxidation features was established. Figure 2 As shown in (a), the length of the RVE model is L, the width of the RVE model is H, and the width of the matrix crack is h c , whose distance from the side of the RVE model is L C , the width of the T interface layer is d i , the diameter of the fiber is D f , the volume fraction of the fiber is V f , the depth of the oxidation notch is δ. Figure 2 (b) It can be seen that the geometry of the oxidation gap is irregular. The irregular geometry makes it difficult to establish the thermal resistance network. Therefore, the oxidation gap is simplified while keeping the volume of the oxidation gap unchanged. The simplified oxidation gap is a regular annular column with a cross section as shown in Figure 2 (c), where the depth of the oxidation notch is kept constant at δ and the width is L e .

[0068] Step 3: Divide the modified RVE model obtained in step 2 into five characteristic regions along the fiber axis; establish the equivalent axial thermal resistance for each region, and then connect the axial thermal resistances of the five regions in series to obtain the overall axial thermal resistance of the material, and then solve the thermal resistance network to obtain the axial thermal conductivity prediction formula of the material.

[0069] The modified RVE model is divided into five special regions along the fiber axis, such as Figure 3 As shown in the figure, the first and fifth regions are composed of fibers, interface layer and matrix. The second and fourth regions are composed of fibers, oxidation notches (air) and matrix, and the third region is composed of fibers, oxidation notches (air) and cracks (air). The axial thermal resistance network is shown in the figure. Figure 3 As shown in the figure, the thermal resistance network is composed of five equivalent thermal resistances in series, each of which is composed of three basic thermal resistances in parallel, and each thermal resistance reflects the structural characteristics of the corresponding area. The axial thermal resistance of regions I and V reflects the combined thermal resistance characteristics of the fiber, matrix and interface layer, the axial thermal resistance of regions II and IV reflects the combined thermal resistance characteristics of the fiber, matrix and oxidation notch, and the axial thermal resistance of region III reflects the thermal resistance characteristics of the combination of fiber, matrix crack and oxidation notch.

[0070] According to the thermal resistance network, the axial thermal conductivity formula of the material can be obtained:

[0071]

[0072]

[0073]

[0074] Among them, the axial length of region I is L r =(LL e ) / 2,L e is the width of the oxidation notch, R m,I ,R i,I ,R fa,I are the axial thermal resistances of the matrix, interface layer and fiber in region I, respectively. f is the radius of the fiber. m is the thermal conductivity of the matrix. i is the thermal conductivity of the interface layer. fa is the axial thermal conductivity of the fiber.

[0075] Axial thermal resistance R in region I ea,I By connecting R m,I ,R i,I ,R fa,I get:

[0076]

[0077]

[0078] Region V has a similar physical structure to Region I. Therefore, the axial thermal resistance R ea,V for:

[0079]

[0080] For Region II:

[0081]

[0082]

[0083]

[0084] Among them, R m,Ⅱ ,R i,Ⅱ ,R fa,Ⅱ are the axial thermal resistances of the matrix, interface layer and fiber in region II respectively. gas is the thermal conductivity of the oxidation notch.

[0085] The axial equivalent thermal resistance of region II can be obtained by connecting R m,Ⅱ ,R i,Ⅱ ,R fa,Ⅱ get:

[0086]

[0087]

[0088] Region IV has a similar physical structure to Region II. Therefore, the axial thermal resistance R of Region V is ea,Ⅳ for:

[0089]

[0090] For Region III:

[0091]

[0092]

[0093] Among them, R fa,Ⅲ is the axial thermal resistance of the fiber in region III, R gas,Ⅲ is the axial thermal resistance of oxidation notches and cracks in region III.

[0094] Axial thermal resistance R of region III ea,Ⅲ By connecting R gas,Ⅲ ,R fa,Ⅲ get:

[0095]

[0096]

[0097] Axial thermal resistance R of RVE model ea By connecting R ea,I ,R ea,Ⅱ ,R ea,Ⅲ ,R ea,Ⅳ ,R ea,V get:

[0098] R ea =R ea,I +R ea,Ⅱ +R ea,Ⅲ +R ea,Ⅳ +R ea,V

[0099] Axial thermal conductivity λ of the RVE model ea It can be done through R ea Find:

[0100]

[0101] Step 4: The regional division of the modified RVE model is consistent with step (3). However, when establishing the thermal resistance network, the equivalent lateral thermal resistance is established for each region, and then the lateral thermal resistances of the five regions are connected in parallel to obtain the overall lateral thermal resistance of the material. Then, the thermal resistance network is solved to obtain the prediction formula of the lateral thermal conductivity of the material.

[0102] The lateral thermal resistance network is as follows Figure 4 As shown in (c), the lateral thermal resistance network is composed of five equivalent thermal resistances in parallel, and each equivalent thermal resistance reflects the structural characteristics of the corresponding area. The lateral thermal resistance of regions I and V reflects the combined thermal resistance characteristics of the fiber, matrix and interface layer. Its geometric structure diagram Figure 4 (a) shows that the lateral thermal resistance of regions II and IV reflects the combined thermal resistance characteristics of the fiber, matrix and oxidation notch. Figure 4 As shown in (b), the lateral thermal resistance of region III reflects the thermal resistance characteristics of the combination of fibers, matrix cracks and oxidation notches.

[0103] Transverse thermal resistance R of RVE model et By connecting R et,I ,R et,Ⅱ ,R et,Ⅲ ,R et,Ⅳ ,R et,V get:

[0104]

[0105] For regions Ⅰ, Ⅱ, Ⅳ and V, they are all composed of three-phase materials. Their lateral thermal resistance can be calculated by the following formula:

[0106]

[0107] Where α=η~π / 2, η=sin -1 (r f / (r f +d i )),like Figure 4 As shown in (a), ft is the transverse thermal conductivity of the fiber.

[0108]

[0109] Among them, θ=γ~π / 2, γ=sin -1 (r(r f +d i -δ) / (r f +d i )),like Figure 4 (b) as shown.

[0110] Region III is composed of two-phase materials. Its lateral thermal resistance can be calculated by the following formula:

[0111]

[0112] In summary, the lateral thermal conductivity of the RVE model can be calculated through the thermal resistance network:

[0113]

[0114] In this embodiment, the length of the RVE model is L = 20 μm. The width of the RVE model is H = 9.8 μm. The width of the matrix crack is h c = 0.32 μm, and its distance from the side of the RVE model is L C =10μm. The width of the interface layer is d i = 0.2 μm. The diameter of the fiber is D f =14μm. The volume fraction of the fiber is V f =0.4. The depth of the oxidation notch is δ=1.76 μm. The oxidation time is 10 hours and the oxidation temperature is 700°C.

[0115] The basic thermal conductivity parameters of unidirectional fiber-reinforced C / SiC ceramic matrix composites include: axial thermal conductivity of the fiber λ fa =40W / (m·K), transverse thermal conductivity of the fiber λ fa =4W / (m·K); thermal conductivity of the matrix λ m =17W / (m·K); thermal conductivity of the interface layer λ i =25W / (m·K); thermal conductivity of air λ fa =0.0267W / (m·K).

[0116] By substituting the above basic parameters into the equivalent thermal conductivity prediction method of the unidirectional fiber-reinforced C / SiC ceramic matrix composite material after oxidation established in this patent, the equivalent thermal conductivity of the material can be obtained.

[0117] For the axial thermal conductivity, the axial thermal resistance network constructed by the present invention is used to calculate the equivalent thermal conductivity of the material oxidized at 700°C for 10 hours to be 23.93W / (m·K), while the axial thermal conductivity of the material calculated by the traditional method (without considering the oxidation of the material) is 26.5W / (m·K). The error between the two is as high as 10.74%. It can be seen that the method of the present invention can more accurately predict the thermal conductivity of the material after oxidation.

[0118] For the transverse thermal conductivity, using the transverse thermal resistance network constructed by the patent of this article, the above equation can be used to calculate the transverse equivalent thermal conductivity of the material oxidized at 700°C for 10 hours to be 11.52W / (m·K), while the traditional method (without considering material oxidation) calculates the transverse thermal conductivity of the material to be 14.7W / (m·K). The error between the two is as high as 27.6%. It can be seen that the method of the present invention can more accurately predict the thermal conductivity of the material after oxidation. In summary, the present invention can more accurately predict the thermal conductivity of the material after oxidation. In the prediction of the axial thermal conductivity of the material, the prediction accuracy is improved by 10.74% compared with the existing method; in the prediction of the transverse thermal conductivity of the material, the prediction accuracy is improved by 27.6%.

Claims

1. A method for estimating thermal conductivity of carbon fiber toughened ceramic matrix composites under high temperature oxidation, characterized in that: The following steps are involved: (1) Based on the microscopic scanning electron microscope photos of unidirectional fiber-reinforced C / SiC ceramic matrix composites, the basic geometric characteristics of unidirectional fiber-reinforced C / SiC ceramic matrix composites were obtained, and the RVE model of unidirectional fiber-reinforced C / SiC ceramic matrix composites was established; (2) calculating the geometric change characteristics of the fiber and the interface after oxidation, i.e., the oxidation notch depth δ, according to the oxidation kinetics principle; and introducing the oxidation notch depth δ characteristics into the RVE model established in step (1) to obtain a modified RVE model capable of oxidation characteristics; (3) Divide the modified RVE model obtained in step (2) into five characteristic regions along the fiber axis; wherein regions I and V are composed of fibers, interface layers and matrix; regions II and IV are composed of fibers, oxidation notches and matrix; and region III is composed of fibers, oxidation notches and cracks; establish an equivalent axial thermal resistance for each characteristic region, connect the axial thermal resistances of the five regions in series to obtain the overall axial thermal resistance network of the material, and solve the axial thermal resistance network to obtain the axial thermal conductivity prediction formula of the material; (4) The regional division of the modified RVE model is consistent with step (3). When establishing the thermal resistance network, the equivalent lateral thermal resistance is established for each region. Then, the lateral thermal resistances of the five regions are connected in parallel to obtain the overall lateral thermal resistance of the material. Then, the thermal resistance network is solved to obtain the prediction formula of the lateral thermal conductivity of the material.

2. The method for estimating thermal conductivity of carbon fiber toughened ceramic matrix composite materials under high temperature oxidation according to claim 1, characterized in that: The basic geometric features include the length, width and height dimensions of the characteristic unit, the fiber diameter, the crack size and the interface layer thickness.

3. The method for estimating thermal conductivity of carbon fiber toughened ceramic matrix composite materials under high temperature oxidation according to claim 1, characterized in that: The axial thermal resistance network in step (3) is composed of five equivalent thermal resistances connected in series, each of which is composed of three basic thermal resistances connected in parallel, and each thermal resistance reflects the structural characteristics of the corresponding region; wherein the axial thermal resistance of regions I and V reflects the combined thermal resistance characteristics of the fiber, matrix and interface layer; the axial thermal resistance of regions II and IV reflects the combined thermal resistance characteristics of the fiber, matrix and oxidation notch; and the axial thermal resistance of region III reflects the thermal resistance characteristics of the combination of fiber, matrix crack and oxidation notch.

4. The method for estimating thermal conductivity of carbon fiber toughened ceramic matrix composite materials under high temperature oxidation according to claim 1, characterized in that: The axial thermal conductivity formula of the material in step (3) is: The axial length of region I is L r =(LL e ) / 2,L e is the width of the oxidation notch, R m,I ,R i,I ,R fa,I are the axial thermal resistances of the matrix, interface layer and fiber in region I, r f is the radius of the fiber, λ m is the thermal conductivity of the matrix, λ i is the thermal conductivity of the interface layer, λ fa is the axial thermal conductivity of the fiber; Axial thermal resistance R in region I ea,I By connecting R m,I ,R i,I ,R fa,I get: Axial thermal resistance R in region V ea,V for: For Region II: Among them, R m,Ⅱ ,R i,Ⅱ ,R fa,Ⅱ are the axial thermal resistances of the matrix, interface layer and fiber in region II, respectively, gas is the thermal conductivity of the oxidation notch; The axial equivalent thermal resistance of area II is connected in parallel with R m,Ⅱ ,R i,Ⅱ ,R fa,Ⅱ get: Axial thermal resistance R in region V ea,Ⅳ for: For Region III: Among them, R fa,Ⅲ is the axial thermal resistance of the fiber in region III, R gas,Ⅲ is the axial thermal resistance of oxidation notches and cracks in region III; Axial thermal resistance R in region III ea,Ⅲ By connecting R gas,Ⅲ ,R fa,Ⅲ get: Axial thermal resistance R of RVE model ea By connecting R ea,I ,R ea,Ⅱ ,R ea,Ⅲ ,R ea,Ⅳ ,R ea,V get: R ea =R ea,I +R ea,Ⅱ +R ea,Ⅲ +R ea,Ⅳ +R ea,V Axial thermal conductivity λ of the RVE model ea By R ea Find:

5. The method for estimating thermal conductivity of carbon fiber toughened ceramic matrix composite materials under high temperature oxidation according to claim 1, characterized in that: The implementation process of step (4) is as follows: The transverse thermal resistance network is composed of five equivalent thermal resistances in parallel, and each equivalent thermal resistance reflects the structural characteristics of the corresponding area; among them, the transverse thermal resistance of areas I and V reflects the combined thermal resistance characteristics of the fiber, matrix and interface layer; the transverse thermal resistance of areas II and IV reflects the combined thermal resistance characteristics of the fiber, matrix and oxidation notch; the transverse thermal resistance of area III reflects the thermal resistance characteristics of the combination of fiber, matrix crack and oxidation notch; Transverse thermal resistance R of RVE model et By connecting R et,I ,R et,Ⅱ ,R et,Ⅲ ,R et,Ⅳ ,R et,V get: For regions Ⅰ, Ⅱ, Ⅳ and V, which are composed of three-phase materials, the lateral thermal resistance is calculated by the following formula: Among them, α=η~π / 2, η=sin -1 (r f / (r f +d i )).λ ft is the transverse thermal conductivity of the fiber; Where, θ=γ~π / 2,γ=sin -1 (r(r f +d i -d) / (r f +d i )); Region III is composed of two-phase materials, and its lateral thermal resistance is calculated by the following formula: In summary, the lateral thermal conductivity of the RVE model can be calculated through the thermal resistance network:

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