A method for calculating a three-dimensional woven ceramic matrix composite fatigue prediction model

Abstract

The application discloses a kind of three-dimensional weaving ceramic matrix composite fatigue prediction model calculation methods, comprising: by the analysis of SiC / SiC fiber bundle composite fatigue test results, the remaining stiffness degradation law of fiber bundle composite is obtained;Establish the RVE model in line with the microstructure of three-dimensional weaving CMC, and it is carried out periodic grid division and the application of periodic boundary condition;The fiber bundle remaining stiffness degradation model is substituted into three-dimensional weaving CMC RVE model and carries out finite element calculation, and the fatigue life of three-dimensional weaving CMC material under arbitrary peak fatigue cycle load, the remaining stiffness degradation curve is predicted in combination with three-dimensional Hashin failure criterion.This application comprehensively considers the influence of various damage forms of ceramic matrix composite under fatigue load and different temperature environment to SiC / SiC fiber bundle composite material, so that the prediction result can better adapt to actual working environment.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of reliability evaluation of aviation composites, and particularly relates to a three-dimensional woven ceramic matrix composite fatigue prediction model calculation method. BACKGROUND

[0002] The upgrading of aero-engines promotes the application of new materials such as high-temperature alloy materials and composite materials in engineering. The materials used for the structure of the hot end part of a high thrust-to-weight ratio aero-engine need to have high specific strength, high specific modulus, high-temperature resistance, oxidation resistance and long service life, and the traditional nickel-based high-temperature alloy material has been difficult to meet the use requirements under the current design conditions. Under this background, the high-temperature resistant material applied to the hot end part is of great significance to improve the overall performance of the engine. In recent years, scholars at home and abroad have gradually shifted their research focus to ceramic matrix composites (CMCs) which exhibit excellent mechanical properties in super-high temperature environments. Due to their excellent high-temperature resistance, corrosion resistance and wear resistance, CMCs are considered as ideal materials for the hot end parts of future aero-engines.

[0003] The fatigue failure of the internal structural parts of an aero-engine may cause disastrous consequences, and therefore the fatigue life of the structural parts has become a key indicator that needs special attention in the design, use and maintenance of aero-engines. How to ensure that the CMC structure can still safely and reliably perform its mechanical properties under long-term vibration fatigue load has become a core problem in the dynamic strength design of CMC structures. Therefore, it is of great significance to study and establish a scientific and reasonable fatigue prediction model for improving the reliability and safety of engine parts.

[0004] Common CMC structures can be divided into three types according to the weaving structure type of their preforms, namely unidirectional, two-dimensional woven and three-dimensional woven. Unidirectional CMCs only have the ability to bear load in the fiber direction, and are less used in engineering practice and more used in material performance research. Two-dimensional woven CMCs are woven by two directions of yarns, and although they have a certain load-bearing capacity between layers, they are prone to delamination and cannot be used to make curved parts. Three-dimensional woven CMCs connect each layer through yarns, have excellent interlayer performance and strong shear resistance and impact resistance, and can be used to manufacture various rotary parts, and have been widely used in practical engineering. However, there is currently no special fatigue prediction method for three-dimensional woven CMCs. SUMMARY

[0005] The application aims to provide a three-dimensional woven ceramic matrix composite material fatigue prediction model calculation method, which considers the influence of different temperature environments on SiC / SiC fiber bundle composites, so that the prediction results can better adapt to the actual working environment, especially in high-temperature or extreme environment engineering applications; and can greatly reduce the calculation complexity and time consumption while ensuring the prediction accuracy, improve the simulation efficiency, and have high engineering application value.

[0006] To achieve the above technical purposes, the technical scheme adopted by the application is:

[0007] A three-dimensional woven ceramic matrix composite material fatigue prediction model calculation method, the method comprising the following steps:

[0008] S1, carrying out tensile test of SiC / SiC fiber bundle composites under different temperature environments to obtain the tensile strength of fiber bundle CMCs;

[0009] S2, based on the tensile strength of fiber bundle CMCs, carrying out tensile-tensile fatigue test of SiC / SiC fiber bundle composites under different temperature environments;

[0010] S3, processing the force-displacement data obtained by the fatigue test, calculating the residual stiffness curve of fiber bundle CMCs through the ratio of maximum test force to maximum displacement, and carrying out regularization processing, adopting a unified function relationship to fit the change rule of the normalized residual stiffness of fiber bundle composites with cycle number, and obtaining the residual stiffness degradation model of fiber bundle composites;

[0011] S4, establishing an RVE finite element model of three-dimensional woven CMCs, carrying out periodic grid division on the RVE finite element model and assigning material properties;

[0012] S5, applying the fatigue failure criterion to judge whether the model unit is failed or not, and counting the number and distribution of failed units; according to the unit failure result, judging whether the overall structure is failed or not, when the failed units form a complete fracture surface, considering that the structure loses the carrying capacity, ending the process, otherwise, turning to step S6;

[0013] S6, if the structure is not failed, for the unfailed units, calculating the residual stiffness thereof under the action of cyclic load by using the residual stiffness degradation model of fiber bundle composites; for the failed units, reducing the stiffness thereof, and reassigning the material properties according to the updated calculation results;

[0014] S7, repeating step S5 and step S6, iteratively calculating until the structure is failed, and outputting the distribution of structure failure units, the number of fatigue cycles experienced, and the stiffness degradation curve results.

[0015] As one of the preferred examples, in step S3, the fiber bundle composite remaining stiffness degradation model is:

[0016]

[0017] In the formula, E min (N) represents the remaining stiffness of SiC / SiC fiber bundle composite after N times of fatigue cycle load and internal damage, E min (0) represents the initial stiffness of the material, and a' and b' are material-related coefficients at different temperatures.

[0018] As one of the preferred examples, step S4 further comprises:

[0019] A three-dimensional braided CMCs geometric model conforming to the microstructure of the three-dimensional braided CMCs is established, periodic meshing and periodic boundary conditions are applied, and an RVE finite element model of the three-dimensional braided CMCs is constructed.

[0020] As one of the preferred examples, in step S4, the geometric parameter relationship of the three-dimensional braided CMCs RVE model satisfies the following conditions:

[0021]

[0022] In the formula, α is the surface braiding angle of the RVE model, γ is the internal braiding angle, W is the square width of the bottom edge of the RVE model, and h model is the height of the RVE model; the fiber bundle cross section is an octagon inscribed in an ellipse, L1 and L2 are the lengths of the edges of the octagon, and a and b are the long semi-axis and short semi-axis of the inscribed ellipse of the fiber bundle cross section.

[0023] As one of the preferred examples, in step S4, the periodic displacement field applied to the RVE model satisfies the following conditions:

[0024] u j+ -u j- =ε - (x j+ -x j- )=ε - Δx j

[0025] In the formula, u represents the node displacement; the superscripts j+ and j- represent the jth group of relative parallel planes of the RVE model; ε - represents the full-field average strain of the RVE model; x represents the absolute position of the relative parallel plane in the x direction; and Δx j represents the distance of the jth group of relative parallel planes in the x direction.

[0026] As one of the preferred examples, in step S4, the constraint equation for three pairs of parallel planes of the three-dimensional woven CMC RVE model is:

[0027]

[0028] Wherein, U, V, W are the displacements of the nodes in x, y, z directions, the subscripts I, J, K, M, N, O represent the nodes on the corresponding plane; the subscripts A, B, C, D, E, F, G, H represent the vertices of the RVE model; The average strain of the RVE model is represented by b, which is the short half axis length of the fiber bundle cross section, and h is the height of the RVE model.

[0029] As one of the preferred examples, in step S5, the residual stiffness and residual strength are introduced into the three-dimensional Hashin failure criterion as the fatigue failure criterion for the three-dimensional woven SiC / SiC composite material unit fatigue analysis, and the expression of the fatigue failure criterion is as follows:

[0030] The fiber tensile failure expression is:

[0031]

[0032] The fiber compression failure expression is:

[0033]

[0034] The matrix tensile failure expression is:

[0035]

[0036] The matrix compression failure expression is:

[0037]

[0038] The fiber and matrix shear failure expression is:

[0039]

[0040] In the formula, σ m The principal stress in the m direction is represented by m=1, 2, 3; σ pq The shear stress of the material acting on the positive p plane pointing to the q axis is represented by p=1, 2, 3, q=1, 2, 3; the subscripts T and C represent the tensile and compression states respectively; X(N), Y(N) represent the longitudinal and transverse strengths of the fiber bundle composite material when the fatigue cycle number is N; S pq (N) represents the shear strength of the material when the fatigue cycle number is N.

[0041] Compared with the prior art, the beneficial effects of the present application are as follows:

[0042] Firstly, the three-dimensional braided ceramic matrix composite fatigue prediction model calculation method of the present application comprehensively considers various damage forms of the ceramic matrix composite under fatigue load and the influence of different temperature environments on the SiC / SiC fiber bundle composite material, can calculate the fatigue life of the material under any peak fatigue cyclic load and the residual stiffness degradation curve, so that the prediction result can better adapt to the actual working environment, especially in high temperature or extreme environment engineering applications.

[0043] Secondly, the three-dimensional braided ceramic matrix composite fatigue prediction model calculation method of the present application establishes a three-dimensional braided RVE model, which can reduce the calculation complexity and time consumption while ensuring the prediction accuracy, improve the simulation efficiency, and has high engineering application value.

[0044] Thirdly, the three-dimensional braided ceramic matrix composite fatigue prediction model calculation method of the present application can be used to replace the mechanical behavior response of yarns in various braided CMC structures under various complex loads. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 is the residual stiffness degradation curve of the embodiment of the present application; wherein (a) corresponds to room temperature 25℃, (b) corresponds to high temperature 1100℃;

[0046] Figure 2 is the three-dimensional braided CMC fiber bundle space topological geometric relationship of the embodiment of the present application;

[0047] Figure 3 is the three-dimensional braided CMC internal fiber bundle cross-sectional shape of the embodiment of the present application;

[0048] Figure 4 is the three-dimensional braided CMC RVE model of the embodiment of the present application;

[0049] Figure 5 is the periodic boundary condition of the three-dimensional braided CMC RVE model of the embodiment of the present application;

[0050] Figure 6 is the three-dimensional braided CMC fatigue prediction stiffness degradation result of the embodiment of the present application; wherein (a) corresponds to room temperature 325MPa, (b) corresponds to room temperature 310MPa, (c) corresponds to high temperature 160MPa, (d) corresponds to room temperature 130MPa, (e) corresponds to room temperature 120MPa;

[0051] Figure 7 is the three-dimensional braided ceramic matrix composite fatigue prediction model calculation method flowchart of the embodiment of the present application. DETAILED DESCRIPTION

[0052] Embodiments of the present application will be described in further detail below with reference to the drawings.

[0053] Referring to Figure 7 The embodiment of the present application discloses a three-dimensional woven ceramic matrix composite fatigue prediction model calculation method, which comprises the following steps:

[0054] S1, a tensile test of SiC / SiC fiber bundle composite material under different temperature environments is carried out, and the tensile strength of the fiber bundle CMCs is obtained.

[0055] S2, based on the tensile strength of the fiber bundle CMCs, a tensile-tensile fatigue test of SiC / SiC fiber bundle composite material under different temperature environments is carried out.

[0056] S3, the force-displacement data obtained by the fatigue test is processed, the residual stiffness curve of the fiber bundle CMCs is calculated by the ratio of the maximum test force to the maximum displacement, and the normalization processing is carried out.

[0057] S4, an RVE finite element model of three-dimensional woven CMCs is established, the model is periodically meshed and material properties are assigned.

[0058] S5, whether the model unit fails is judged by applying the fatigue failure criterion, the number and distribution of the failed units are counted, and whether the overall structure fails is judged according to the unit failure result, when the failed units form a complete fracture surface, it is considered that the structure loses the carrying capacity.

[0059] S6, if the structure does not fail, the residual stiffness of the unfailed unit under the action of cyclic load is calculated by using the residual stiffness degradation model of the fiber bundle composite material, the stiffness of the failed unit is reduced, and the material properties are revalued according to the updated calculation result, and the iteration calculation is carried out until the structure fails, and the distribution of the structure failure units, the number of fatigue cycles experienced, the stiffness degradation curve and other results are output.

[0060] Step 1, a tensile test of SiC / SiC fiber bundle composite material under normal temperature and high temperature 1100℃ oxygen-free environment is carried out, and the tensile strength of the fiber bundle CMCs under different temperature environments is obtained.

[0061] Step 2, based on the tensile strength of the fiber bundle CMCs, a tensile-tensile fatigue test of SiC / SiC fiber bundle composite material under normal temperature and high temperature 1100℃ oxygen-free environment is carried out.

[0062] Step 3, the force-displacement data obtained by the fatigue test is processed, the ratio between the maximum test force and the maximum displacement is calculated, the residual stiffness curve of the fiber bundle CMCs is obtained, and the normalization processing is carried out to eliminate the influence of the dispersion of the material.

[0063] To further describe the attenuation law of the residual stiffness of fiber bundle composite material with the number of fatigue cycles, a unified function relationship can be used to fit it, which is shown in formula 1:

[0064]

[0065] In the formula, E min (N) represents the residual stiffness of SiC / SiC fiber bundle composite material after internal damage after N times of fatigue cycle load, E min (0) indicates the initial stiffness of the material, and a' and b' are the coefficients related to the material at different temperatures.

[0066] Step 4, the yarns carrying load in the three-dimensional woven SiC / SiC composite material have mechanical properties consistent with those of the SiC / SiC fiber bundle composite material. The RVE finite element model of the three-dimensional woven CMCs is established, the model is periodically meshed and the material properties are assigned.

[0067] The established RVE model of three-dimensional woven CMCs is shown in formula 2:

[0068]

[0069] In the formula, α is the surface weaving angle of the RVE model, γ is the internal weaving angle, W is the square width of the RVE model bottom edge, h model is the RVE model height; considering the real form of the fiber bundle inside the material, at the same time, in order to simplify the calculation, the fiber bundle cross section is regarded as an inscribed ellipse octagon, the long semi-axis of the inscribed ellipse of the fiber bundle cross section is a, the short semi-axis is b, and the side length of the octagon is L1 and L2 respectively.

[0070] The periodic displacement field of the RVE model is shown in formula 3:

[0071] u j+ -u j- =ε - (x j+ -x j- )=ε - Δx j (3);

[0072] In the formula, u represents node displacement; superscript j+ and j- represent the jth group of relative parallel planes of the RVE model; ε - represents the full-field average strain of the RVE model; x represents the absolute position of the relative parallel plane in x direction; Δx j represents the distance of the jth group of relative parallel planes along x direction.

[0073] For the three pairs of parallel faces of the RVE model, the constraint equations are shown in equation 4:

[0074]

[0075] where U, V, W are the displacements of the nodes in x, y, z directions, respectively, and the subscripts I, J, K, M, N, O represent the nodes on the corresponding faces; the subscripts A, B, C, D, E, F, G, H represent the vertices of the RVE model; where <ε> is the average strain of the RVE model, b is the length of the short semi-axis of the fiber bundle cross section, and h is the height of the RVE model.

[0076] Step 5: Apply the fatigue failure criterion to determine whether the model unit fails, and count the number and distribution of failed units; according to the unit failure result, determine whether the overall structure fails, when the failed units form a complete fracture surface, it is considered that the structure loses the carrying capacity.

[0077] The three-dimensional Hashin failure criterion is used as the fatigue failure criterion of the three-dimensional braided SiC / SiC composite material unit, and the three-dimensional Hashin static strength failure criterion is shown in equations (5) to (9):

[0078] Fiber tensile failure (σ1>0):

[0079]

[0080] Fiber compression failure (σ1<0):

[0081]

[0082] Matrix tensile failure (σ2>0):

[0083]

[0084] Matrix compression failure (σ2<0):

[0085]

[0086] Matrix-fiber shear failure (σ1<0):

[0087]

[0088] where σ m is the principal stress in the m direction, m=1, 2, 3; S pq (N) is the shear strength when the material fatigue cycle number is N, p=1, 2, 3, q=1, 2, 3.

[0089] Based on the static strength failure criterion, the residual stiffness and residual strength are introduced to develop a failure criterion for fatigue analysis, which is shown in equations (10) to (14).

[0090] Fiber tensile failure:

[0091]

[0092] Fiber compressive failure:

[0093]

[0094] Matrix tensile failure:

[0095]

[0096] Matrix compressive failure:

[0097]

[0098] Fiber and matrix shear failure:

[0099]

[0100] where σ m are the principal stresses in the m direction, m = 1, 2, 3; σ pq is the shear stress of the material acting on the positive p face pointing to the q axis, p = 1, 2, 3, q = 1, 2, 3; the subscripts T and C represent the tensile and compressive states, respectively; X(N), Y(N) are the longitudinal and transverse strengths of the fiber bundle composite material when the fatigue cycle number is N; S pq (N) is the shear strength of the material when the fatigue cycle number is N.

[0101] Step 6: If the structure has not failed, the residual stiffness degradation model of the fiber bundle composite material is used to calculate the residual stiffness of the unfailed unit under cyclic loading; for the failed unit, the stiffness is reduced, and the material properties are revalued according to the updated calculation results.

[0102] Through iterative calculation, the failure process of each unit in the structure is continuously monitored until the entire structure fails. The final output includes the distribution of failed units, the number of fatigue cycles experienced, the stiffness degradation curve of each unit, and other data.

[0103] Examples

[0104] 1. Tensile tests of SiC / SiC fiber bundle composites under different temperature environments are carried out to obtain the tensile strength of fiber bundle CMCs.

[0105] 2. Based on the tensile strength of fiber bundle CMCs, the tension-tension fatigue test of SiC / SiC fiber bundle CMCs is carried out under different temperature environments.

[0106] 3. The force-displacement data obtained from the fatigue test is processed to calculate the ratio between the maximum test force and the maximum displacement, and the residual stiffness curve of the fiber bundle CMCs is obtained. The normalization processing is carried out to eliminate the influence of material dispersion. In order to further describe the attenuation law of the residual stiffness of fiber bundle CMCs with the number of fatigue cycles, a unified function relationship can be used to fit it, as shown in the following formula. Figure 1

[0107] 4. The mechanical properties of the yarns carrying the load in the three-dimensional woven SiC / SiC composite material are consistent with those of the SiC / SiC fiber bundle composite material. Referring to the spatial topological geometric relationship of the RVE model of three-dimensional woven CMCs, the RVE model of three-dimensional woven CMCs is established. The spatial topological geometric relationship of the RVE model of three-dimensional woven CMCs is shown in the following figure. Figure 2 The cross-sectional shape of the fiber bundle inside the three-dimensional woven CMCs is shown in the following figure. Figure 3 The established RVE model is shown in the following figure. Figure 4

[0108] The model is periodically meshed and assigned with material properties, and the periodic boundary condition is applied. The periodic boundary condition is shown in the following figure. Figure 5

[0109] 5. The fatigue failure criterion is used to judge whether the model element fails or not, and the number and distribution of failed elements are counted. According to the element failure result, it is judged whether the overall structure fails or not. When the failed elements form a complete fracture surface, it is considered that the structure loses the carrying capacity.

[0110] The three-dimensional Hashin failure criterion is used as the fatigue failure criterion for the elements of three-dimensional woven SiC / SiC composite material. Based on the static strength failure model of this criterion, the residual stiffness and residual strength are introduced to develop a failure criterion suitable for fatigue analysis.

[0111] 6. If the structure does not fail, the residual stiffness of the unfailed elements under cyclic loading is calculated using the residual stiffness degradation model of fiber bundle composite material. For the failed elements, the stiffness is reduced, and the material properties are revalued according to the updated calculation results.

[0112] Through iterative calculation, the failure process of each element in the structure is continuously monitored until the entire structure fails. The final output includes the distribution of failed elements, the number of fatigue cycles experienced, the stiffness degradation curve of each element, etc. The calculated stiffness degradation curve is shown in the following figure. Figure 6 ​​​​

[0113] It is known from Figure 6 that the simulation results are in good agreement with the test results as a whole, but the deviation is large in the initial stage. This is because the material damage evolution speed is fast and the stiffness drops rapidly in the initial stage of fatigue loading, but the analysis step length is fixed in the calculation process, which fails to accurately capture the rapid change of material damage in real time, resulting in a certain error with the test results. With the continuous action of fatigue load, the material damage gradually tends to be stable, and the agreement of the simulation results with the test results is obviously improved. Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product.

[0114] Therefore, the present application can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage media, etc.) embodying computer-readable program code. The solutions in the embodiments of the present application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0115] The present application is described with reference to flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing apparatus to produce a machine, so that the instructions running through the processor of the computer or other programmable data processing apparatus generate a means for implementing the functions specified in the flowcharts and / or block diagrams. Figure 1 The means for implementing each flow or multiple flows and / or blocks Figure 1 The means for implementing each flow or multiple flows and / or blocks

[0116] These computer program instructions can also be stored in a computer-readable memory capable of guiding a computer or other programmable data processing apparatus to work in a specific manner, so that the instructions stored in the computer-readable memory produce a product including instruction means, which implements the functions specified in the flowcharts and / or block diagrams. Figure 1 The means for implementing each flow or multiple flows and / or blocks Figure 1 The means for implementing each flow or multiple flows and / or blocks

[0117] These computer program instructions can also be loaded into a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flowcharts and / or blocks Figure 1 one or more flowcharts and / or blocks

[0118] Although preferred embodiments of the application have been described herein, it will be apparent to those skilled in the art that various modifications can be made within the scope of the application without departing from the spirit of the application. Accordingly, it is intended that all such possible modifications be included within the scope of the application as described in the following claims. In compliance with the statute, the application has been described in language more or less specific to structural

[0119] Obviously, numerous modifications and variations of the present application are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims and their equivalents, the application can be practiced otherwise than as specifically described.

Claims

1. A method for calculating a three-dimensional woven ceramic matrix composite fatigue prediction model, characterized by, The method comprises the following steps: S1, carrying out tensile test of SiC / SiC fiber bundle composite material under different temperature environments to obtain tensile strength of fiber bundle CMCs; S2, based on the tensile strength of fiber bundle CMCs, carrying out SiC / SiC fiber bundle composite material tension-tension fatigue test under different temperature environments; S3, processing force-displacement data obtained by the fatigue test, calculating residual stiffness curve of fiber bundle CMCs through the ratio of maximum test force and maximum displacement, and carrying out regularization processing, adopting a unified function relationship to fit the change rule of normalized residual stiffness of fiber bundle composite material with cycle number, and obtaining residual stiffness degradation model of fiber bundle composite material; S4, establishing RVE finite element model of three-dimensional braided CMCs, carrying out periodic grid division on the RVE finite element model and assigning material properties; S5, judging whether the model unit is failed or not by applying fatigue failure criterion, and counting the number and distribution of failed units; judging whether the overall structure is failed or not according to the unit failure result, when the failed units form a complete fracture surface, it is considered that the structure loses the carrying capacity, the process is ended, otherwise, step S6 is entered; S6, if the structure is not failed, calculating the residual stiffness of the unfailed unit under the action of cyclic load by using the residual stiffness degradation model of fiber bundle composite material; for the failed unit, the stiffness is reduced, and the material properties are revalued according to the updated calculation result; S7, repeating step S5 and step S6, and iteratively calculating until the structure is failed, and outputting the distribution of structure failure units, the number of fatigue cycles experienced and the stiffness degradation curve result; Step S4 further comprises: A three-dimensional braided CMCs geometric model conforming to the microstructure of three-dimensional braided CMCs is established, and periodic grid division and periodic boundary conditions are applied to the geometric model to construct the RVE finite element model of three-dimensional braided CMCs; In step S4, the geometric parameter relationship of the three-dimensional braided CMCs RVE model satisfies the following conditions: In the formula, α is the surface braiding angle of the RVE model, γ is the internal braiding angle, W is the square width of the bottom edge of the RVE model, and h model is the RVE height; the fiber bundle cross section is an octagon inscribed in an ellipse, L1 and L2 are the lengths of the octagon, and a and b are the long half axis and short half axis of the inscribed ellipse of the fiber bundle cross section; In step S4, the periodic displacement field applied to the RVE model satisfies the following conditions: u j+ -u j- = ε - (x j+ -x j- ) = ε - Δx j where u represents the nodal displacement; superscripts j+ and j- represent the jth set of relative parallel faces of the RVE model; ε - represents the full-field average strain of the RVE model; x represents the absolute position of the relative parallel faces in the x direction; Δx j represents the distance of the jth set of relative parallel faces along the x direction; In step S4, the constraint equation of the three pairs of parallel planes of the three-dimensional braided CMCs RVE model is: Where U, V, W are the displacements of the nodes in x, y, z directions, and the subscripts I, J, K, M, N, O represent the nodes on the corresponding surface; the subscripts A, B, C, D, E, F, G, H represent the vertices of the RVE model; Where <ε> represents the average strain of the RVE model, b is the length of the short semi-axis of the cross section of the fiber bundle, and h is the height of the RVE model.

2. The method of claim 1, wherein the method is used to calculate the fatigue life of a three-dimensional braided ceramic matrix composite material. In step S3, the residual stiffness degradation model of the fiber bundle composite material is: where E min (N) represents the residual stiffness of the SiC / SiC fiber bundle composite after the internal damage caused by N times of fatigue cycle load, E min (0) indicates the initial stiffness of the material, and a' and b' are the coefficients related to the material at different temperatures.

3. The method of claim 1, wherein the method is a method of calculating a fatigue life prediction model of a three-dimensional woven ceramic matrix composite material, characterized by, In step S5, the residual stiffness and residual strength are introduced into the three-dimensional Hashin failure criterion as the fatigue failure criterion for the fatigue analysis of the three-dimensional braided SiC / SiC composite material unit, and the expression of the fatigue failure criterion is as follows: The fiber tensile failure expression is: The fiber compression failure expression is: The matrix tensile failure expression is: The matrix compression failure expression is: The fiber and matrix shear failure expression is: where σ m denotes the principal stress in the m direction, m = 1, 2, 3; σ pq denotes the shear stress of the material acting on the positive p face directed to the q axis, p = 1, 2, 3, q = 1, 2, 3; the subscripts T, C represent the tensile and compression states, respectively; X(N), Y(N) represent the longitudinal and transverse strengths of the fiber bundle composite material when the fatigue cycle number is N; S pq (N) represents the shear strength when the fatigue cycle number of the material is N.

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