Method for regulating and controlling damage of protective material under force-heat-oxygen coupling condition

Abstract

The invention discloses a method for regulating and controlling damage of a protective material under a force-heat-oxygen coupling condition, and belongs to the technical field of aerospace, and the method comprises the following steps: S1, constructing a force-heat-oxygen coupling constitutive model of the protective material in a high-temperature, stress and oxidation environment; s2, defining diffusion coefficients of oxygen molecules in the matrix material and the fiber material, taking the diffusion coefficients as functions of damage factors, introducing parameters related to the oxidation degree, and establishing a corresponding constitutive model based on the parameters; s3, developing a finite element calculation program based on a Galerkin method and a Newton-Rafson iteration format; and S4, designing protective materials with different crack characteristics, carrying out modeling simulation by utilizing a force-heat-oxygen coupling model, and analyzing the influence of the crack characteristics on the failure behavior of the protective materials. According to the method for regulating and controlling the damage of the protective material under the force-heat-oxygen coupling condition, the force-heat-oxygen coupling effect is combined, and the damage behavior of the protective material under the action of oxidation and mechanical stress can be accurately described.

Description

Technical Field

[0001] The present invention relates to the field of aerospace technology, and in particular to a method for regulating and controlling damage of protective materials under conditions of force, heat and oxygen coupling. Background Art

[0002] High-temperature structural materials operating in extreme environments, such as aircraft engine nozzles and spacecraft heat protection components, face extremely harsh oxidation and thermomechanical load conditions. These materials must have excellent oxidation resistance, mechanical properties and chemical stability to ensure their long-term reliable use under high temperature and high pressure. The failure of high-temperature structural materials often leads to serious catastrophic consequences. Therefore, it is particularly important to study how to enhance the stability and reliability of these materials under extreme conditions. Among these materials, silicon carbide reinforced carbon-based (C / SiC) composites have become one of the indispensable candidate materials in the aerospace field due to their excellent high temperature resistance, low density and oxidation resistance.

[0003] The outstanding advantage of C / SiC composites is that they can maintain low density and high strength at high temperatures, while having good oxidation resistance. However, in high-temperature oxidizing environments, a protective oxide layer (such as SiO2) is generated on the surface of these materials to slow down the oxidation process. The presence of these oxide layers usually helps to improve the material's oxidation resistance, but its effectiveness depends largely on the integrity and stability of the oxide layer. When the material is subjected to thermal stress or mechanical load, cracks inevitably form on the surface or inside the material. These cracks provide channels for the rapid diffusion of oxidants, resulting in increased local oxidation and reducing the overall oxidation resistance of the material. The formation and expansion of the oxide layer is often accompanied by the accumulation of local stress. The geometry and distribution of the cracks have a key influence on this stress accumulation and the integrity of the oxide layer.

[0004] Existing studies have shown that the presence of cracks causes local stress accumulation in the generation of oxides, which may further promote crack propagation and even lead to structural failure of the material. The interaction between the oxide layer and the crack area is not only a thermo-mechanical problem, but also a typical multi-physics field coupling problem. This complex coupling relationship makes the prediction of the mechanical properties and life of the material extremely complex and difficult, especially under the combined effects of high temperature, variable stress field and oxidizing environment. Therefore, understanding the formation and evolution of cracks and their impact on the oxidation behavior of materials is crucial for designing high-temperature structural materials with better oxidation resistance.

[0005] In actual application environments, high-temperature structural materials are often faced with the simultaneous effects of thermal stress and mechanical loads. The interaction between these multiple factors may cause crack propagation, oxide layer peeling, and even material failure. However, how the geometric parameters of cracks, such as crack width, depth, spacing, and inclination angle, affect the oxidation behavior and stress evolution of materials is still a difficult problem that has not been fully solved. Especially in high-temperature oxidation environments, there is still a lack of systematic and in-depth research on the specific effects of crack geometry on oxidation-induced stress distribution and crack propagation behavior. Solving this problem will help reveal the degradation mechanism of materials in extreme environments and provide a scientific basis for the design optimization of materials. Summary of the invention

[0006] The purpose of the present invention is to provide a method for regulating damage of protective materials under mechanical, thermal and oxygen coupling conditions, which can significantly characterize the oxidation path, stress evolution and mechanical damage mode, and promote the transformation and application of protective materials in aerospace connection structures under mechanical, thermal and oxygen coupling conditions.

[0007] To achieve the above object, the present invention provides a method for regulating damage of protective materials under mechanical, thermal and oxygen coupling conditions, comprising the following steps:

[0008] S1. Construct a mechanical-thermal-oxygen coupled constitutive model of protective materials under high temperature, stress and oxidation environment;

[0009] S2. Define the diffusion coefficient of oxygen molecules in the matrix material and the fiber material, and use it as a function of the damage factor, introduce parameters related to the degree of oxidation, and establish the corresponding constitutive model based on the parameters;

[0010] S3. Develop finite element calculation procedures based on Galerkin method and Newton-Raphson iteration format;

[0011] S4. Design protective materials with different crack characteristics, use the force-heat-oxygen coupling model for modeling and simulation, and analyze how crack characteristics affect the failure behavior of protective materials.

[0012] Preferably, the deformation of the matrix of the protective material in S1 conforms to the isotropic small deformation assumption, and the deformation of the fiber material of the protective material conforms to the transversely isotropic small deformation assumption.

[0013] Preferably, in S1, the high temperature is 800-1300°C, the oxygen concentration is constant, and the applied stress causes mechanical damage to the matrix and fiber material of the protective material. The force-heat-oxygen coupling constitutive model includes the damage caused by oxidation and the damage caused by mechanical loading. The damage caused by oxidation and the damage caused by mechanical loading affect the failure of the protective material.

[0014] Preferably, in S1, in the mechanical-thermal-oxygen coupled constitutive model, O2 molecules diffuse along microcracks in the matrix and carbon fibers, and the diffusion coefficient of O2 molecules is a simple function of the damage factor;

[0015] The mechanical-thermal-oxygen coupling constitutive model is:

[0016]

[0017] Where k is m or f, m is the matrix, f is the fiber; ε k is the strain, σ k is stress, is the flexibility tensor including oxidation and mechanical damage, is the stiffness tensor of the flexibility matrix including oxidation and mechanical damage, d k is the damage factor caused by mechanical damage, is the maximum matrix or fiber concentration, c k is the concentration of the matrix or fiber at a certain moment.

[0018] Preferably, in S2, the diffusion coefficient of O2 molecules in the matrix and the carbon fiber material is a function of the damage factor. It is considered that the O2 molecules diffuse along the outer surface of the silicon carbide matrix and the microcracks, and chemical reactions occur; the O2 molecules diffuse to the outer surface of the fiber bundle, diffuse along the carbon fibers and the fiber cracks, and chemical reactions occur;

[0019] The functional relationship of the diffusion coefficient is:

[0020]

[0021] in, is the diffusion coefficient of oxygen molecules, is the diffusion coefficient of oxygen molecules in air environment, is the maximum matrix or fiber concentration, c c is the matrix or fiber concentration at a certain moment.

[0022] Preferably, in S2, the parameter related to the degree of oxidation is When the matrix or fiber is intact, d k =0, indicating that O2 molecules cannot diffuse in; when When the material is oxidized, oxidation damage occurs and O2 molecules diffuse into the material. <d m <1, the material is mechanically damaged, O2 molecules diffuse into the material, and d k is the damage factor of the matrix caused by mechanical damage, the mass conservation of C atoms and O2 molecules, and the mass conservation equation of C atoms and O2 molecules in differential form is:

[0023]

[0024] Where ξ is the oxidation reaction rate, c k is the matrix or fiber concentration at a certain moment, is the concentration of O2 molecules at a certain moment, R is the oxidation rate coefficient, Among them, Q ξ is the activation energy of the chemical reaction, R0 is the rate constant, R g is the ideal gas constant and T is the absolute temperature.

[0025] Preferably, the specific operation of S3 is: based on the finite element calculation program of the Galerkin method and the Newton-Raphson iterative format, a user-defined single program based on ABAQUS is developed, each node has five degrees of freedom, the backward Euler difference method is used to realize time discretization, and the Newton-Raphson iterative solution is used at each time step; at the unit scale, the equivalent integral form of the basic equation is:

[0026]

[0027] Where L is the differential operator, σ is the stress vector, w1, w2 and w3 are the weight functions corresponding to the three basic control equations, is the concentration of O2 molecules at a certain moment, R is the oxidation rate coefficient, is the diffusion coefficient of oxygen molecules, Ω is the integration area, t is the time phase, is the gradient operator.

[0028] Preferably, in S4, the protective material having different crack characteristics is a protective material having crack set characteristics with different crack widths, crack depths, crack spacings and crack inclinations.

[0029] Preferably, in S4, analyzing how crack characteristics affect the failure behavior of protective materials is specifically as follows: based on the simulation results, specifically analyzing the oxide acoustic field and stress evolution of cracks with different initial crack characteristics under initial boundary conditions such as force-heat-oxygen.

[0030] Therefore, the present invention adopts the above-mentioned protective material damage control method under the conditions of force, heat and oxygen coupling, which has the following beneficial effects:

[0031] (1) The present invention provides a more realistic and reliable method for simulating the behavior of protective materials by considering the chemical, thermodynamic and mechanical coupling effects in an oxidizing environment. This method not only helps to predict the performance and life of protective materials in high-temperature aerobic environments, but also can provide strong support for material design and manufacturing.

[0032] (2) The present invention solves the deficiencies in the prior art and, based on experimental research and numerical analysis methods, realizes the high-temperature oxidation behavior and thermal-mechanical-oxygen coupling failure mechanism of protective materials used in aerospace.

[0033] (3) It can significantly characterize the oxidation path, stress evolution and mechanical damage mode, and promote the transformation and application of protective materials in aerospace connection structures under thermal-oxidative coupling conditions.

[0034] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a flow chart of Example 1 of the method for controlling damage of protective materials under the conditions of force, heat and oxygen coupling of the present invention;

[0036] Figure 2 It is a schematic diagram of the model oxidation reaction, initial boundary conditions and loading conditions of Example 1 of the protective material damage control method under the conditions of force, heat and oxygen coupling of the present invention;

[0037] Figure 3 It is the stress evolution and oxide domain growth at key points under different crack spacings in Example 1 of the method for controlling damage of protective materials under mechanical, thermal and oxygen coupling conditions of the present invention. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0039] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0040] The present invention provides a method for regulating and controlling damage of protective materials under mechanical, thermal and oxygen coupling conditions, comprising the following steps:

[0041] S1. Construct a force-heat-oxygen coupling constitutive model of protective materials under high temperature, stress and oxidation environment; the matrix deformation of the protective material conforms to the isotropic small deformation assumption, and the deformation of the fiber material of the protective material conforms to the transverse isotropic small deformation assumption.

[0042] The high temperature is 800-1300℃, the oxygen concentration is constant, and the applied stress causes mechanical damage to the matrix and fiber material of the protective material. The force-heat-oxygen coupling constitutive model includes the damage caused by oxidation and the damage caused by mechanical loading. The damage caused by oxidation and the damage caused by mechanical loading affect the failure of the protective material.

[0043] In the mechanical-thermal-oxygen coupled constitutive model, O2 molecules diffuse along microcracks in the matrix and carbon fibers, and the diffusion coefficient of O2 molecules is a simple function of the damage factor;

[0044] The mechanical-thermal-oxygen coupling constitutive model is:

[0045]

[0046] Where k is m or f, m is the matrix, f is the fiber; ε k is the strain, σ k is stress, is the flexibility tensor including oxidation and mechanical damage, is the stiffness tensor of the flexibility matrix including oxidation and mechanical damage, d k is the damage factor caused by mechanical damage, is the maximum matrix or fiber concentration, c k is the concentration of the matrix or fiber at a certain moment.

[0047] The stiffness tensor of the compliance matrix including oxidation and mechanical damage is:

[0048]

[0049] in, is the maximum matrix or fiber concentration, ck is the matrix or fiber concentration at a certain moment, d k is the damage factor caused by mechanical damage, E k is the elastic modulus of the material, is the initial damage compliance tensor.

[0050] S2. Define the diffusion coefficient of oxygen molecules in the matrix material and fiber material, and use it as a function of the damage factor, introduce parameters related to the degree of oxidation, and establish the corresponding constitutive model based on the parameters.

[0051] The diffusion coefficient of O2 molecules in the matrix and carbon fiber material is a function of the damage factor. It is believed that O2 molecules diffuse along the outer surface of the silicon carbide matrix and the microcracks, and chemical reactions occur; O2 molecules diffuse to the outer surface of the fiber bundle, diffuse along the carbon fibers and the fiber cracks, and chemical reactions occur.

[0052] The functional relationship of the diffusion coefficient is:

[0053]

[0054] in, is the diffusion coefficient of oxygen molecules, is the diffusion coefficient of oxygen molecules in air environment, is the maximum matrix or fiber concentration, c cis the matrix or fiber concentration at a certain moment.

[0055] The parameters related to the degree of oxidation are When the matrix or fiber is intact, d k =0, indicating that O2 molecules cannot diffuse in; when When the material is oxidized, oxidation damage occurs and O2 molecules diffuse into the material. <d m <1, the material is mechanically damaged, O2 molecules diffuse into the material, and d k is the damage factor of the matrix caused by mechanical damage, the mass conservation of C atoms and O2 molecules, and the mass conservation equation of C atoms and O2 molecules in differential form is:

[0056]

[0057] Where ξ is the oxidation reaction rate, c k is the matrix or fiber concentration at a certain moment, is the concentration of O2 molecules at a certain moment, R is the oxidation rate coefficient, Among them, Q ξ is the activation energy of the chemical reaction, R0 is the rate constant, R g is the ideal gas constant and T is the absolute temperature.

[0058] S3. Develop a finite element calculation program based on the Galerkin method and the Newton-Raphson iterative format. The specific operations are as follows: Based on the Galerkin method and the Newton-Raphson iterative format, develop a user-defined single program based on ABAQUS. Each node has five degrees of freedom. The backward Euler difference method is used to achieve time discretization. Newton-Raphson iteration is used to solve at each time step. At the unit scale, the equivalent integral form of the basic equation is:

[0059]

[0060]

[0061] Where L is the differential operator, σ is the stress vector, w1, w2 and w3 are the weight functions corresponding to the three basic control equations, is the concentration of O2 molecules at a certain moment, R is the oxidation rate coefficient, is the diffusion coefficient of oxygen molecules, Ω is the integration area, t is the time phase, is the gradient operator.

[0062] S4. Design protective materials with different crack characteristics, use the force-heat-oxygen coupling model for modeling and simulation, analyze how crack characteristics affect the failure behavior of protective materials, and analyze how crack characteristics affect the failure behavior of protective materials. Specifically: According to the simulation results, analyze the evolution of oxide acoustic field and stress of cracks with different initial crack characteristics under the initial boundary conditions of force-heat-oxygen, etc.

[0063] The protective material with different crack characteristics is a protective material with crack set characteristics of different crack widths, crack depths, crack spacings and crack inclinations.

[0064] Example 1

[0065] Carbon fiber monofilaments coated with silicon carbide matrix are the most basic components in protective materials. During the preparation of protective materials, silicon carbide matrix is ​​deposited on the surface of carbon fiber by chemical vapor infiltration (CVI) process, and then a micro-composite material of silicon carbide matrix coated with carbon fiber monofilaments is formed. Based on the real physical morphology, a simplified calculation model with annular geometric defects was established, and the modeling process was implemented by ABAQUS finite element software.

[0066] like Figure 1 As shown, the present invention provides a method for regulating damage of protective materials under mechanical, thermal and oxygen coupling conditions, comprising the following steps:

[0067] S1. Construct a coupled constitutive model of mechanics, thermal and oxidation for protective materials under high temperature, stress and oxidation environments.

[0068] High temperature oxidation is an environment with a temperature range of 800℃-1300℃ and a constant oxygen concentration. The mechanical-thermal-oxygen coupled constitutive model includes the damage caused by oxidation and the damage caused by mechanical loading. Oxidation and mechanical damage will damage the matrix at the same time, making the diagonal elements in the flexibility matrix larger and gradually losing the load-bearing capacity.

[0069] In this embodiment, a model of a carbon fiber monofilament with annular defects is established, wherein the carbon fiber diameter is 6um, the matrix diameter thickness is 2um, the fiber monofilament height is 10um, and there are cracks with annular defects. The spacing between the cracks is 1.6μm, the crack depth is 0.5μm, the crack inclination angle is 90°, and there are different crack widths, which are 0.1μm, 0.3μm, and 0.5μm. Figure 2 The displacement on the right side of the figure is constrained in the x-axis direction, and a tensile load is applied in the x-direction on the left side. At the same time, an O2 boundary condition is applied around the initial crack. The material parameters of the 1 / 4 carbon fiber monofilament containing annular defects are shown in Table 1, and the chemical parameters are shown in Table 2:

[0070] Table 1 Basic material parameters

[0071]

[0072] Table 2 Basic chemical parameters

[0073]

[0074] The mechanical-thermal-oxygen coupled constitutive model assumes that O2 molecules diffuse along microcracks in the matrix and fiber, and assumes that the diffusion coefficient of O2 molecules is a simple function of the damage factor.

[0075] The mechanical-thermal-oxygen coupling constitutive model is:

[0076]

[0077] Where k is m or f, m is the matrix, f is the fiber; ε k is the strain, σ k is stress, is the flexibility tensor including oxidation and mechanical damage, is the stiffness tensor of the flexibility matrix including oxidation and mechanical damage, d k is the damage factor caused by mechanical damage, is the maximum matrix or fiber concentration, c k is the concentration of the matrix or fiber at a certain moment.

[0078] The stiffness tensor of the compliance matrix including oxidation and mechanical damage is:

[0079]

[0080] in, is the maximum matrix or fiber concentration, ck is the matrix or fiber concentration at a certain moment, d k is the damage factor caused by mechanical damage, E k is the elastic modulus of the material, is the initial damage compliance tensor.

[0081] S2. Define the diffusion coefficient of oxygen molecules in the matrix material and fiber material, and use it as a function of the damage factor, introduce parameters related to the degree of oxidation, and establish the corresponding constitutive model based on the parameters.

[0082] The diffusion coefficient of oxygen molecules in the matrix and fiber materials is a function of the damage factor. It is believed that O2 molecules diffuse along the outer surface of the matrix and the microcracks, and chemical reactions occur; O2 molecules diffuse to the outer surface of the fiber bundle, diffuse along the fibers and fiber cracks, and chemical reactions occur.

[0083] The functional relationship of the diffusion coefficient is:

[0084]

[0085] in, is the diffusion coefficient of oxygen molecules, is the diffusion coefficient of oxygen molecules in air environment, is the maximum matrix or fiber concentration, c c is the matrix or fiber concentration at a certain moment.

[0086] The parameters related to the degree of oxidation are When the matrix or fiber is intact, d k =0, indicating that O2 molecules cannot diffuse in; when When the material is oxidized, oxidation damage occurs and O2 molecules diffuse into the material. <d m <1, the material is mechanically damaged, O2 molecules diffuse into the material, and d k is the damage factor of the matrix caused by mechanical damage, the mass conservation of C atoms and O2 molecules, and the mass conservation equation of C atoms and O2 molecules in differential form is:

[0087]

[0088] Where ξ is the oxidation reaction rate, c k is the matrix or fiber concentration at a certain moment, is the concentration of O2 molecules at a certain moment, R is the oxidation rate coefficient, Among them, Q ξ is the activation energy of the chemical reaction, R0 is the rate constant, R g is the ideal gas constant and T is the absolute temperature.

[0089] S3. Develop a finite element calculation program based on the Galerkin method and Newton-Raphson iterative format.

[0090] Based on the Galerkin method and Newton-Raphson iteration format, a user-defined single (UEL) program based on ABAQUS was developed, with five degrees of freedom at each node: displacement components u, v, w, C atoms and O2 molecule concentrations. The backward Euler difference method was used to achieve time discretization, and the Newton-Raphson iteration was used to solve at each time step.

[0091] At the unit scale, the equivalent integral form of the basic equations (mechanical equilibrium equations, mass conservation equations of C atoms and O2 molecules) can be written as:

[0092]

[0093] Where L is the differential operator, σ is the stress vector, w1, w2 and w3 are the weight functions corresponding to the three basic control equations, is the concentration of O2 molecules at a certain moment, R is the oxidation rate coefficient, is the diffusion coefficient of oxygen molecules, Ω is the integration area, t is the time phase, is the gradient operator.

[0094] The established UEL program is used to complete the simulation calculation of the coupled failure process, and the final calculation is completed based on the built-in algebraic equation solving algorithm in ABAQUS software. Generally speaking, multiple iterations are required at each time step until the total residual vector is zero.

[0095] S4. Design protective materials with different crack characteristics, use the force-heat-oxygen coupling model for modeling and simulation, and analyze how the crack characteristics affect the failure behavior of the protective materials. As shown in Table 3, composite materials with different crack widths were designed, and the effect of crack width on the oxide growth and stress evolution of the material was analyzed.

[0096] Table 3 Composite materials with different crack characteristics

[0097]

[0098] Figure 3 (a) is the stress-strain diagram of the fiber monofilament at different crack widths. Figure 3 (b) When the crack width is 0.50 μm, the stress change cloud diagram at the key time point, Figure 3 (c) shows the evolution of the oxide domain at the critical time point when the crack width is 0.10 μm. Figure 3 (d) shows the evolution of the oxide domain at the critical time point when the crack width is 0.30 μm. Figure 3 (e) in the figure shows the evolution of the oxide domain at critical time points when the crack width is 0.50 μm.

[0099] Figure 3 (a) shows the effect of thermal-mechanical-oxidative conditions on the mechanical properties of the material when the crack width is 0.10μm, 0.30μm and 0.50μm. Figure 3 From (a) in Figure 1, we can see that the crack width has little effect on the elastic region, and the slopes of the stress-strain curves are almost the same. Figure 3 As can be seen from the figure (b), there is an obvious concentration of stress around the crack, which may be due to the redistribution of stress due to the presence of the crack.

[0100] However, the larger the crack width, the greater the stress in the second stage, indicating that the wider the crack, the more difficult it is for oxidation and mechanical damage to propagate to the matrix-fiber interface, e.g. Figure 3 (c) Figure 3 (d) Figure 3As shown in (e), this phenomenon occurs because the high-temperature oxidation reaction on the crack surface is more active. The wider the crack, the more extensive the diffusion and distribution of the oxide in the initial oxidation stage (stage I-II), and the more obvious the oxidation effect. When the crack is wider, the oxidation products may fill the crack, hindering the further diffusion of oxygen, resulting in local stress concentration and deformation. Narrower cracks (0.10μm) produce higher local stresses near the crack tip, leading to faster entry into stage II, when "stress corrosion cracking" occurs. The smaller the crack width (0.10μm), the greater the stress before fracture at higher strain values, and the better the oxidation resistance. Narrower cracks help maintain higher material strength, thereby enhancing structural integrity under oxidizing conditions.

[0101] Therefore, the present invention adopts the above-mentioned method for regulating damage of protective materials under mechanical, thermal and oxygen coupling conditions, which can significantly characterize oxide generation, stress evolution and mechanical damage mode, and promote the transformation and application of protective materials in aerospace connection structures under mechanical, thermal and oxygen coupling conditions.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for controlling damage of protective materials under conditions of force, heat and oxygen coupling, characterized in that: The following steps are involved: S1. Construct a mechanical-thermal-oxygen coupled constitutive model of protective materials under high temperature, stress and oxidation environment; S2. Define the diffusion coefficient of oxygen molecules in the matrix material and the fiber material, and use it as a function of the damage factor, introduce parameters related to the degree of oxidation, and establish the corresponding constitutive model based on the parameters; S3. Develop finite element calculation procedures based on Galerkin method and Newton-Raphson iteration format; S4. Design protective materials with different crack characteristics, use the force-heat-oxygen coupling model for modeling and simulation, and analyze how crack characteristics affect the failure behavior of protective materials.

2. The method for controlling damage of protective materials under mechanical, thermal and oxygen coupling conditions according to claim 1, characterized in that: The deformation of the matrix of the protective material in S1 conforms to the isotropic small deformation assumption, and the deformation of the fiber material of the protective material conforms to the transverse isotropic small deformation assumption.

3. The method for controlling damage of protective materials under mechanical, thermal and oxygen coupling conditions according to claim 1, characterized in that: In S1, the high temperature is 800-1300℃, the oxygen concentration is constant, and the applied stress causes mechanical damage to the matrix and fiber material of the protective material. The force-heat-oxygen coupling constitutive model includes the damage caused by oxidation and the damage caused by mechanical loading. The damage caused by oxidation and the damage caused by mechanical loading affect the failure of the protective material.

4. The method for controlling damage of protective materials under mechanical, thermal and oxygen coupling conditions according to claim 1, characterized in that: In S1, in the mechanical-thermal-oxygen coupled constitutive model, O2 molecules diffuse along microcracks in the matrix and carbon fibers, and the diffusion coefficient of O2 molecules is a simple function of the damage factor; The mechanical-thermal-oxygen coupled constitutive model is: Where k is m or f, m is the matrix, f is the fiber; ε k is the strain, σ k is stress, is the flexibility tensor including oxidation and mechanical damage, is the stiffness tensor of the flexibility matrix including oxidation and mechanical damage, d k is the damage factor caused by mechanical damage, is the maximum matrix or fiber concentration, c k is the concentration of the matrix or fiber at a certain moment.

5. The method for controlling damage of protective materials under the conditions of force, heat and oxygen coupling according to claim 4, characterized in that: In S1, the stiffness tensor of the flexibility matrix including oxidation and mechanical damage is: in, is the maximum matrix or fiber concentration, ck is the matrix or fiber concentration at a certain moment, d k is the damage factor caused by mechanical damage, E k is the elastic modulus of the material, is the initial damage compliance tensor.

6. The method for controlling damage of protective materials under mechanical, thermal and oxygen coupling conditions according to claim 1, characterized in that: In S2, the diffusion coefficient of O2 molecules in the matrix and carbon fiber material is a function of the damage factor. It is believed that O2 molecules diffuse along the outer surface of the silicon carbide matrix and the microcracks, and chemical reactions occur; O2 molecules diffuse to the outer surface of the fiber bundle, diffuse along the carbon fiber and the fiber cracks, and chemical reactions occur; The functional relationship of the diffusion coefficient is: Among them, D O2 is the diffusion coefficient of oxygen molecules, is the diffusion coefficient of oxygen molecules in air environment, is the maximum matrix or fiber concentration, c c is the matrix or fiber concentration at a certain moment.

7. The method for controlling damage of protective materials under the conditions of force, heat and oxygen coupling according to claim 1, characterized in that: In S2, the parameters related to the degree of oxidation are When the matrix or fiber is intact, d k =0, indicating that O2 molecules cannot diffuse in; when When the material is oxidized, oxidation damage occurs and O2 molecules diffuse into the material. <d m When <1, the material is mechanically damaged, and O2 molecules diffuse into the material. k is the damage factor of the matrix caused by mechanical damage, the mass conservation of C atoms and O2 molecules, and the mass conservation equation of C atoms and O2 molecules in differential form is: Where ξ is the oxidation reaction rate, c k is the matrix or fiber concentration at a certain moment, c O2 is the concentration of O2 molecules at a certain moment, R is the oxidation rate coefficient, Among them, Q ξ is the activation energy of the chemical reaction, R0 is the rate constant, R g is the ideal gas constant and T is the absolute temperature.

8. The method for controlling damage of protective materials under the conditions of force, heat and oxygen coupling according to claim 1, characterized in that: The specific operation of S3 is: based on the Galerkin method and the Newton-Raphson iterative format of the finite element calculation program, develop a user-defined single program based on ABAQUS, each node has five degrees of freedom, the backward Euler difference method is used to achieve time discretization, and the Newton-Raphson iterative solution is used at each time step; at the unit scale, the equivalent integral form of the basic equation is: Where L is the differential operator, σ is the stress vector, w1, w2 and w3 are the weight functions corresponding to the three basic control equations, is the concentration of O2 molecules at a certain moment, R is the oxidation rate coefficient, is the diffusion coefficient of oxygen molecules, Ω is the integration area, t is the time phase, and ▽ is the gradient operator.

9. The method for controlling damage of protective materials under mechanical, thermal and oxygen coupling conditions according to claim 1, characterized in that: In S4, the protective material with different crack characteristics is a protective material with crack set characteristics of different crack widths, crack depths, crack spacings and crack inclinations.

10. The method for controlling damage of protective materials under mechanical, thermal and oxygen coupling conditions according to claim 1, characterized in that: In S4, how crack characteristics affect the failure behavior of protective materials is analyzed specifically as follows: Based on the simulation results, cracks with different initial crack characteristics are specifically analyzed under the initial boundary conditions of force-heat-oxygen, etc., and the evolution of the oxide acoustic field and stress is analyzed.

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