SiC / SiC composite vane oxidation life prediction method

Abstract

The application discloses a SiC / SiC composite material blade oxidation life prediction method, relates to the turbine blade oxidation technical field, and is used for solving the technical problems that the accuracy of life prediction of the prior art for actual service structural parts is low, and the oxidation life prediction of the turbine blade structure cannot be adapted. The blade oxidation life prediction method comprises the following steps: a blade model of SiC / SiC composite material is established; the channel type of the blade model is determined, and the diffusion coefficient model of the gas in each channel is established; the oxygen concentration distribution in the channel at any time is determined; the channel parameter threshold value is set, the oxidation calculation of the channel is completed, the elastic modulus of the matrix and the fiber after oxidation is obtained, and then the elastic modulus matrix of the fiber bundle composite material is calculated; the unit cell model is re-established according to the oxidation condition to obtain the elastic modulus matrix of the unit cell and the stress condition of each unit, the degradation of the fiber and the matrix in the unit when stretched or compressed in different directions is judged, the failed units are marked, and the oxidation life of the blade is obtained.

Description

Technical Field

[0001] This invention relates to the field of aero-engine blade oxidation technology, and more specifically, to a method for predicting the oxidation life of SiC / SiC composite blades. Background Technology

[0002] SiC / SiC composite materials maintain excellent mechanical properties even at high temperatures. They are widely used in hot-end components of aero-engines, especially engine blades. In actual service environments, engine blades made of this material are subjected to the impact of high-temperature airflow, centrifugal force during rotation, and oxidation under the combustion gas medium, which seriously affects their actual service performance and greatly reduces the service life of the blades.

[0003] In predicting the oxidation life of materials, existing technologies only consider the mixing and diffusion within crack channels when calculating gas diffusion, ignoring the change in diffusion mode due to the filling of diffusion channels. They do not clearly define the shape of pore channels in oxygen and establish reaction kinetic equations for pore oxidation. The failure criteria considered are too simple, resulting in inaccurate life prediction. Furthermore, they do not consider the influence of the flow field on the temperature field, force field, and chemical field. Therefore, they cannot be applied to the structure of turbine blades, and the accuracy of life prediction for actual service structural components is low. Summary of the Invention

[0004] The purpose of this invention is to provide a method for predicting the oxidation life of SiC / SiC composite blades, addressing the technical problems of low accuracy in predicting the life of actual service structural components in existing technologies, and their inability to adapt to the oxidation life prediction of turbine blade structures. In view of this, this invention achieves this through the following solution.

[0005] This invention provides a method for predicting the oxidation life of SiC / SiC composite blades, comprising:

[0006] Establish a blade model of SiC / SiC composite material;

[0007] Determine the channel type of the blade model and establish a diffusion coefficient model for the gas in each channel;

[0008] The gas diffusion coefficient model of the unit cell in the channel is determined based on the diffusion coefficient model, and the oxygen concentration distribution in the channel at any given time is determined.

[0009] Based on the oxidation process of the channel, an oxidation model is established in different directions within the channel. Channel parameter thresholds are set, and the oxidation calculation of the channel is completed based on the oxidation model and the parameter thresholds. The elastic modulus of the matrix and fiber after oxidation is obtained.

[0010] The elastic modulus matrix of the fiber bundle composite material is calculated based on the elastic modulus of the matrix and fibers after oxidation.

[0011] The elastic modulus matrix of the unit cell is obtained based on the elastic modulus of the fiber bundle composite material. The stress condition of the unit cell is obtained based on the stress condition of the unit cell. The degradation of the fiber and matrix under tension or compression in different directions in the unit cell is determined based on the elastic modulus matrix and the failure criterion. When the failure units accumulate and cause the overall aging of any part of the blade, the corresponding time is the oxidation life of the blade.

[0012] Compared with existing technologies, the oxidation lifetime prediction method for SiC / SiC composite blades of the present invention is used to predict the oxidation lifetime of SiC / SiC composite blades. This technical solution establishes a diffusion coefficient model for the gas within each channel, thus fully considering the changes in multiple diffusion modes caused by the continuous healing process of the channels when determining the oxygen concentration distribution within the channels at any given time. This is more accurate than the oxygen concentration distribution obtained by considering only a single diffusion mode. In other words, the distribution of oxidation products obtained after the oxidation calculation is more accurate. Furthermore, the influence of different types of channels on the blade is considered in the process of establishing the diffusion coefficient model for the gas within the channels. The oxidation calculation of the channels takes into account oxidation models in different directions within the channels, obtaining the elastic modulus of the matrix and fibers after oxidation. The elastic modulus matrix of the fiber bundle composite material is calculated at a microscopic level. The elastic modulus matrix of the unit cell and the stress state of the macroscopic unit are obtained through unit cell modeling and calculation. Based on the elastic modulus matrix and failure criteria, the degradation of fibers and matrix in the macroscopic unit under tension or compression in different directions can be judged, allowing for more accurate failure criteria and thus accurate prediction of the blade's oxidation lifetime. For example, the failure criterion can be the 3D Hasin failure criterion. The above-described technical solution of this invention solves the technical problems of low accuracy in predicting the lifespan of actual service structural components and its inability to adapt to the oxidation lifespan prediction of turbine blade structures in existing technologies.

[0013] Furthermore, in the SiC / SiC composite blade oxidation life prediction method of the present invention, the elastic modulus matrix of the unit cell is obtained based on the elastic modulus of the fiber bundle composite material, the stress condition of the unit cell is obtained based on the stress condition of the unit cell, and the degradation of the fiber and matrix under tension or compression in different directions in the unit cell is determined based on the elastic modulus matrix and the failure criterion, including:

[0014] Based on the obtained unit stress conditions, failure criteria are used to determine the degradation of fibers and matrix in the unit under tension or compression in different directions. Failed units are marked to determine the failure of macroscopic components. If macroscopic components do not fail, the degraded parameters are used as new material properties and the calculation is repeated.

[0015] Furthermore, in the SiC / SiC composite blade oxidation life prediction method of the present invention, the channel types include crack channels and pore channels; and / or,

[0016] The diffusion coefficient models for the gas in each channel include the mixed diffusion coefficient model, the Knudsen diffusion coefficient model, and the Fick diffusion coefficient model.

[0017] Furthermore, in the SiC / SiC composite blade oxidation life prediction method of the present invention, the diffusion coefficient model of the crack channel is transformed from a mixed diffusion coefficient model to a Knudsen diffusion coefficient model during the continuous healing process; and / or,

[0018] The mixed diffusion coefficient model of the crack channel is determined by the following formula:

[0019] ;

[0020] in, R is the mixed-type diffusion coefficient of the crack channel. g Let T be the gas constant and T be the temperature. Here, m and b0 represent the stress value, respectively, and the Weibull modulus and Weibull matrix cracking characteristic strength, respectively. The average saturation crack spacing. Let e ​​be the molecular diffusion volume, e be the crack width, and e0 be the crack width at room temperature under no force. v is the fiber's elastic modulus. m This represents the volume fraction of the matrix. , These are the coefficients of thermal expansion of the matrix and the fiber, respectively. The difference between ambient temperature and crack healing temperature is given by P, where P is the gas pressure and M is the molar mass of the mixture of the two diffusing gases. The average molar mass, Pi The temperature at which the crack heals. for molar mass of a substance It is either CO or CO2.

[0021] Furthermore, in the SiC / SiC composite blade oxidation life prediction method of the present invention, the Knudsen-type diffusion coefficient model of the crack channel is determined by the following formula:

[0022] ;

[0023] in, The Knudsen-type diffusion coefficient of the crack channel, The density of the crack. The temperature at which the crack heals. Pi Let e ​​be the molar mass of oxygen, and e0 be the crack width at room temperature under no force. v is the fiber's elastic modulus. m This represents the volume fraction of the matrix. , These are the coefficients of thermal expansion of the matrix and the fiber, respectively. Here, m and b0 represent the stress value, respectively, and the Weibull modulus and Weibull matrix cracking characteristic strength, respectively. R is the difference between ambient temperature and crack healing temperature. g Let T be the gas constant and T be the temperature.

[0024] Furthermore, in the SiC / SiC composite blade oxidation life prediction method of the present invention, the diffusion coefficient model is transformed from a Fick-type diffusion coefficient model to a mixed-type diffusion coefficient model, and then to a Knudsen-type diffusion coefficient model during the continuous healing process of the pore channels; and / or,

[0025] The Fick-type diffusion coefficient model of the pore channel is determined by the following formula:

[0026] ;

[0027] in, The Fick-type diffusion coefficient of the pore channels. Where is temperature, and P is gas pressure. The volume of molecular diffusion. Here is the molar mass of oxygen. It is CO or CO2. for The molar mass of a substance.

[0028] Furthermore, in the SiC / SiC composite blade oxidation life prediction method of the present invention, the Knudsen-type diffusion coefficient model of the pore channels is determined by the following formula:

[0029] ;

[0030] in, The Knudsen type diffusion coefficient of the pore channels. Pi The gas constant is For temperature, This represents the molar mass of oxygen.

[0031] And / or,

[0032] The mixing-type diffusion coefficient model of the pore channels is determined by the following formula:

[0033] ;

[0034] in, The mixing-type diffusion coefficient of the pore channels. The Fick-type diffusion coefficient of the pore channels. The Knudsen-type diffusion coefficient represents the pore channel.

[0035] And / or,

[0036] The gas diffusion coefficient model of the unit cell is determined by the following formula:

[0037] ;

[0038] in, The gas diffusion coefficient of a single cell. Let be the area of ​​the crack channel. The area of ​​the pore channels. The gas diffusion coefficient of the crack channel. The gas diffusion coefficient of the pore channel. This represents the area of ​​a single cell.

[0039] Furthermore, in the method for predicting the oxidation life of SiC / SiC composite blades of the present invention, during the process of determining the oxygen concentration distribution in the channel at any given time, the oxygen concentration at any given time is determined by the following formula:

[0040] = ;

[0041] in, Porosity The gas diffusion coefficient of a single cell. The reaction rate constant is... The activation energy of the reaction. The reaction temperature, For the reaction rate, Oxygen concentration, For time, Indicates the x-axis direction.

[0042] Furthermore, in the SiC / SiC composite blade oxidation lifetime prediction method of the present invention, in the process of establishing oxidation models in different directions within the channel based on the oxidation process of the channel, the oxidation models in different directions within the channel include:

[0043] Oxygen diffusion in the transverse direction of crack channels and oxidation models of the SiC matrix; oxygen diffusion in the longitudinal direction of crack channels and oxidation models of the SiC matrix; oxygen diffusion through the pyrolytic carbon layer after corrosion and oxidation models of the SiC matrix above and SiC fibers below the pyrolytic carbon layer; and / or,

[0044] The parameter thresholds include the characteristic length of the pore channel and the crack width of the crack channel.

[0045] Furthermore, in the SiC / SiC composite blade oxidation life prediction method of the present invention, the elastic modulus of the fiber bundle composite material in the unit cell is determined by the following formula:

[0046] ;

[0047] in, The axial elastic modulus of the oxidized fiber bundle composite material is given. The crack width is half the width of the crack after oxidation, and L is the crack spacing. The length consumed at the pyrolysis carbon interface. This refers to the fiber debonding length. This represents the elastic modulus of the fiber after oxidation. This represents the volume fraction of the oxidized fiber. This is the average elastic modulus.

[0048] It should be noted that the elastic modulus and stress conditions of the unit cell are calculated by applying boundary conditions and the volume uniformity rule to the oxidized unit cell model. Attached Figure Description

[0049] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0050] Figure 1 This is a schematic diagram of the oxidation process of the channel in Embodiment 3 of the present invention;

[0051] Figure 2 This is a schematic diagram of the interface of the oxidation application in Embodiment 3 of the present invention;

[0052] Figure 3 This is a schematic diagram of the velocity field, temperature field, and force field distribution in the calculation example of this invention;

[0053] Figure 4 This is a schematic diagram of the crack width distribution during the oxidation process in the example of this invention at times of 200h, 500h, 750h and 1000h;

[0054] Figure 5This is a schematic diagram showing the distribution of the thickness of the oxidation product during the oxidation process at times of 200h, 500h, 750h, and 1000h in the example of this invention.

[0055] Figure 6 This is a schematic diagram of the unit failure distribution under time periods of 50, 100, 200, 500, 800, and 1000 hours in the examples of this invention;

[0056] Figure 7 This is a flowchart of the oxidation calculation in Embodiment 3 of the present invention;

[0057] Figure 8 This is a flowchart of the failure judgment process in Embodiment 3 of the present invention;

[0058] Figure 9 This is a flowchart illustrating the development process of the oxidation application in Embodiment 3 of the present invention. Detailed Implementation

[0059] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0060] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0061] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. "Several" means one or more, unless otherwise explicitly specified.

[0062] In predicting the oxidation life of materials, existing technologies only consider the mixing and diffusion within crack channels when calculating gas diffusion, ignoring the change in diffusion mode due to the filling of diffusion channels. They do not clearly define the shape of pore channels in oxygen and establish reaction kinetic equations for pore oxidation. The failure criteria considered are too simple, resulting in inaccurate life prediction. Furthermore, they do not consider the influence of the flow field on the temperature field, force field, and chemical field. Therefore, they cannot be applied to the structure of turbine blades, and the accuracy of life prediction for actual service structural components is low.

[0063] To address the technical problem, this invention provides a method for predicting the oxidation life of SiC / SiC composite blades, comprising:

[0064] Establish a blade model of SiC / SiC composite material;

[0065] Determine the channel type of the blade model and establish a diffusion coefficient model for the gas in each channel;

[0066] The gas diffusion coefficient model of the unit cell in the channel is determined based on the diffusion coefficient model, and the oxygen concentration distribution in the channel at any given time is determined.

[0067] Based on the oxidation process of the channel, an oxidation model is established in different directions within the channel. Channel parameter thresholds are set, and the oxidation calculation of the channel is completed based on the oxidation model and the parameter thresholds. The elastic modulus of the matrix and fiber after oxidation is obtained.

[0068] The elastic modulus matrix of the fiber bundle composite material is calculated based on the elastic modulus of the matrix and fibers after oxidation.

[0069] The elastic modulus matrix of the unit cell is obtained based on the elastic modulus of the fiber bundle composite material. The stress condition of the unit cell is obtained based on the stress condition of the unit cell. The degradation of the fiber and matrix under tension or compression in different directions in the unit cell is determined based on the elastic modulus matrix and the failure criterion. When the failure units accumulate and cause the overall aging of any part of the blade, the corresponding time is the oxidation life of the blade.

[0070] Using the above technical solution, the SiC / SiC composite blade oxidation lifetime prediction method of the present invention is used to predict the oxidation lifetime of SiC / SiC composite blades. This technical solution establishes a diffusion coefficient model for the gas within each channel, and thus, in determining the oxygen concentration distribution within the channel at any given time, fully considers the changes in multiple diffusion modes caused by the continuous healing process of the channel. This is more accurate than the oxygen concentration distribution obtained by considering only a single diffusion mode. In other words, the oxidation product distribution obtained after the following oxidation calculation is more accurate. Furthermore, in establishing the diffusion coefficient model for the gas within the channel, the influence of different types of channels on the blade is also considered. In the oxidation calculation of the channel, oxidation models in different directions within the channel are considered, and the elastic modulus of the matrix and fibers after oxidation is obtained. The elastic modulus matrix of the fiber bundle composite material is calculated at a microscopic level. Through unit cell modeling and calculation, the elastic modulus matrix of the unit cell and the stress state of the macroscopic unit are obtained. Based on the elastic modulus matrix and failure criteria, in judging the degradation of fibers and matrix in the macroscopic unit under tension or compression in different directions, a more accurate failure criterion can be used, thereby accurately predicting the oxidation lifetime of the blade. For example, the failure criterion can be the 3D Hasin failure criterion. The above-described technical solution of this invention solves the technical problems of low accuracy in predicting the lifespan of actual service structural components and its inability to adapt to the oxidation lifespan prediction of turbine blade structures in existing technologies.

[0071] To better understand the present invention, the following specific embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0072] Example 1

[0073] This embodiment provides a method for predicting the oxidation life of SiC / SiC composite blades, including:

[0074] S100, establish a blade model of SiC / SiC composite material, set the working conditions of the blade, and obtain the temperature field and force field distribution;

[0075] S200, determine the channel type of the blade model, which is a crack channel and a pore channel, and establish a diffusion coefficient model for the gas in each channel;

[0076] S300, determine the gas diffusion coefficient model of the unit cell in the channel according to the diffusion coefficient model, and determine the oxygen concentration distribution in the channel at any time.

[0077] S400: Based on the oxidation process of the channel, establish oxidation models in different directions within the channel, set channel parameter thresholds, including the characteristic length of the pore channel and the crack width of the crack channel, complete the oxidation calculation of the channel based on the oxidation model and the parameter thresholds, and obtain the elastic modulus of the matrix and fiber after oxidation.

[0078] S500: Based on the elastic modulus, boundary conditions, and uniformity rules of the fiber bundle composite material, obtain the elastic modulus matrix of the unit cell and the stress condition of the unit. Calculate the elastic modulus matrix of the overall component according to the periodicity rule. Use failure criteria to determine the degradation of the unit fiber and matrix under tension or compression in different directions. Use the degraded parameters as new material properties to re-determine the model failure. Mark the failed units. When the accumulation of failed units leads to overall aging of any part of the blade, the corresponding time is the oxidation lifetime of the blade. If the blade does not fail, use the degraded parameters as new material properties to re-calculate the oxidation.

[0079] Example 2

[0080] This embodiment provides a method for predicting the oxidation life of SiC / SiC composite blades, including:

[0081] S100, establish a blade model of SiC / SiC composite material, set the working conditions of the blade, and obtain the temperature field and force field distribution;

[0082] S200, determine the channel type of the blade model, which is a crack channel and a pore channel, and establish a diffusion coefficient model for the gas in each channel;

[0083] During the continuous healing process of the crack channel, the diffusion coefficient model of the crack channel is transformed from a mixed diffusion coefficient model to a Knudsen-type diffusion coefficient model. The mixed diffusion coefficient model of the crack channel is determined by the following formula:

[0084] ;

[0085] Furthermore, ;

[0086] in, R is the mixed-type diffusion coefficient of the crack channel. g Let T be the gas constant and T be the temperature. Here, m and b0 represent the stress value, respectively, and the Weibull modulus and Weibull matrix cracking characteristic strength, respectively. The average saturation crack spacing. Let e ​​be the molecular diffusion volume, e be the crack width, and e0 be the crack width at room temperature under no force. v is the fiber's elastic modulus. m This represents the volume fraction of the matrix. , These are the coefficients of thermal expansion of the matrix and the fiber, respectively. The difference between ambient temperature and crack healing temperature is given by P, where P is the gas pressure and M is the molar mass of the mixture of the two diffusing gases. The average molar mass, Pi The temperature at which the crack heals. for molar mass of a substance It is CO or CO2;

[0087] The Knudsen-type diffusion coefficient model of the crack channel is determined by the following formula:

[0088] ;

[0089] in, The Knudsen-type diffusion coefficient of the crack channel, The density of the crack. The temperature at which the crack heals. Pi Let e ​​be the molar mass of oxygen, and e0 be the crack width at room temperature under no force. v is the fiber's elastic modulus. m This represents the volume fraction of the matrix. , These are the coefficients of thermal expansion of the matrix and the fiber, respectively. Here, m and b0 represent the stress value, respectively, and the Weibull modulus and Weibull matrix cracking characteristic strength, respectively. R is the difference between ambient temperature and crack healing temperature. g Let T be the gas constant and T be the temperature.

[0090] Statistical analysis shows that pore channels in 2D SiC / SiC materials are mainly distributed in the matrix and between fiber bundles. When establishing a unit cell model, the pores are distributed in the orthogonal region of the fiber bundles. Assuming that their shape is elliptical cylinder, after discretization by thresholding the CT image, they are fitted to elliptical cylinders and the pore feature length is statistically analyzed. The pore feature length d is classified according to the channel length determined by the three diffusion modes (Knudsen, Fick, and mixed diffusion) to obtain the proportion. According to the proportion, several pores are generated in the unit cell and the major and minor semi-axes of the pores are recorded.

[0091] Since the cross-section is an ellipse, the governing equation is:

[0092] ;

[0093] Where x and y represent the x-coordinate and y-coordinate values ​​of any point on the ellipse, Let be the length of the semi-major axis of the ellipse. is the length of the minor semi-axis of the ellipse;

[0094] Furthermore, for the characteristic length of the pore, d=Max(a,b), it means that d will be assigned the larger value between a and b, which is the length of the major semi-axis of the ellipse. is the length of the minor semi-axis of the ellipse;

[0095] For the characteristic length d of the crack, it is assumed to be equal to the width e of the crack;

[0096] It should be noted that the initial diffusion patterns of the pores inside a unit cell differ due to their initial size. As the size of the same pore changes over time, its diffusion pattern will also differ from its initial state. Specifically, as the pores heal, the diffusion coefficient model changes from the Fick-type diffusion coefficient model to the mixed diffusion coefficient model, and then to the Knudsen-type diffusion coefficient model. Therefore, when calculating the diffusion coefficient of a unit cell, it is necessary to consider all the internal pores and pay attention to their updates.

[0097] The Fick-type diffusion coefficient model of the pore channel is determined by the following formula:

[0098] ;

[0099] in, The Fick-type diffusion coefficient of the pore channels. Where is temperature, and P is gas pressure. The volume of molecular diffusion. Here is the molar mass of oxygen. It is CO or CO2. for The molar mass of a substance;

[0100] The Knudsen-type diffusion coefficient model of the pore channel is determined by the following equation:

[0101] ;

[0102] in, The Knudsen type diffusion coefficient of the pore channels. Pi The gas constant is For temperature, This represents the molar mass of oxygen.

[0103] The mixing-type diffusion coefficient model of the pore channels is determined by the following formula:

[0104] ;

[0105] in, The mixing-type diffusion coefficient of the pore channels. The Fick-type diffusion coefficient of the pore channels. The Knudsen-type diffusion coefficient represents the pore channel.

[0106] S300, determine the gas diffusion coefficient model of the unit cell in the channel according to the diffusion coefficient model, and determine the oxygen concentration distribution in the channel at any time.

[0107] The gas diffusion coefficient model for a single cell is determined by the following equation:

[0108] ;

[0109] in, The gas diffusion coefficient of a single cell. Let be the area of ​​the crack channel. The area of ​​the pore channels. The gas diffusion coefficient of the crack channel. The gas diffusion coefficient of the pore channel. The area of ​​a single cell;

[0110] In determining the oxygen concentration distribution within the channel at any given time, the oxygen concentration at any given time is determined by the following formula:

[0111] = ;

[0112] in, Porosity The gas diffusion coefficient of a single cell. The reaction rate constant is... The activation energy of the reaction. The reaction temperature, For the reaction rate, Oxygen concentration, For time, Indicates the x-axis direction;

[0113] S400: Based on the oxidation process of the channel, establish oxidation models in different directions within the channel, set channel parameter thresholds, including the characteristic length of the pore channel and the crack width of the crack channel, complete the oxidation calculation of the channel based on the oxidation model and the parameter thresholds, and obtain the elastic modulus of the matrix and fiber after oxidation.

[0114] In the process of establishing oxidation models in different directions within the channel based on the oxidation process of the channel, the oxidation models in different directions within the channel include: an oxidation model of oxygen diffusion in the transverse direction of the crack channel and oxidation of the SiC matrix; an oxidation model of oxygen diffusion in the longitudinal direction of the crack channel and oxidation of the SiC matrix; and an oxidation model of oxygen diffusion after the pyrolytic carbon layer is etched away and reaction with the SiC matrix above and below the pyrolytic carbon layer. The parameter thresholds include the characteristic length of the pore channel and the crack width of the crack channel.

[0115] S500: Based on the elastic modulus of the fiber bundle composite material, boundary conditions, and uniformity rules, obtain the elastic modulus matrix of the unit cell and the stress condition of the unit. Calculate the elastic modulus matrix of the overall component according to the periodicity rule. Use failure criteria to determine the degradation of the unit fiber and matrix under tension or compression in different directions. Use the degraded parameters as new material properties to re-determine the model failure. Mark the failed units. When the accumulation of failed units causes overall aging of any part of the blade, the corresponding time is the oxidation lifetime of the blade. If the blade does not fail, use the degraded parameters as new material properties to re-calculate the oxidation.

[0116] The elastic modulus of the fiber bundle composite material in the unit cell is determined by the following formula:

[0117] ;

[0118] in, The axial elastic modulus of the oxidized fiber bundle composite material is given. The crack width is half the width of the crack after oxidation, and L is the crack spacing. The length consumed at the pyrolysis carbon interface. This refers to the fiber debonding length. This represents the elastic modulus of the fiber after oxidation. This represents the volume fraction of the oxidized fiber. It is the average elastic modulus;

[0119] It should be noted that the elastic modulus matrix of the unit cell and the stress state in the element are calculated by modeling the unit cell, inputting the elastic modulus of the fiber bundle composite material, applying boundary conditions and homogeneity rules, and using MATLAB programming.

[0120] Example 3

[0121] This embodiment provides a method for predicting the oxidation life of SiC / SiC composite blades, including:

[0122] S100, establish a blade model of SiC / SiC composite material;

[0123] In this step, the blade tip is selected. The external flow field consists of high-temperature, high-pressure gas produced by the combustion of combustion gases and air in the combustion chamber. Since the calculation of the blade's oxidation resistance is required, only oxygen enters the blade and reacts with it. Therefore, the gas in the flow field is simplified to high-temperature, high-pressure air. A cuboid is chosen as the approximation for the flow field domain. The data is imported into COMSOL, and the flow-solid-thermal-mechanical coupling is set. The gas inlet and gas outlet ends of the fluid domain are defined, along with the inlet velocity and temperature at the inlet end. The turbine speed is set to apply centrifugal force. The blade is represented by the black area, and the flow field by the blue area. This allows for the calculation of the magnitude and distribution of the temperature and force fields within the blade.

[0124] S200, determine the channel type of the blade model, which is a crack channel and a pore channel, and establish a diffusion coefficient model for the gas in each channel;

[0125] In this step, the channel types are selected as crack channels and pore channels. During the healing process of crack channels, the diffusion coefficient model is transformed from a mixed diffusion coefficient model to a Knudsen-type diffusion coefficient model. Similarly, during the healing process of pore channels, the diffusion coefficient model is transformed from a Fick-type diffusion coefficient model to a mixed diffusion coefficient model, and then back to a Knudsen-type diffusion coefficient model. The mixed diffusion coefficient model of crack channels is determined by the following formula:

[0126] ;

[0127] Furthermore, the crack width is:

[0128] ;

[0129] in, R is the mixed-type diffusion coefficient of the crack channel. g Here, T is the gas constant, and T is the temperature (calculated by software). Here, m is the stress value, and b0 is the Weibull modulus and the characteristic strength of cracking in the Weibull matrix, respectively. m is taken as 3, and b0 as 155 MPa. The average saturation crack spacing is taken as 0.235 mm. The molecular diffusion volume is taken as 16.6. In the initial stage of the reaction, when diffusion affects the reaction rate, it is CO2. B Take 26.9cm 3 / mol, when the reaction affects the reaction rate It is CO, at this time B Take 18.9cm 3 / mol, e is the crack width, and e0 is the crack width at room temperature under no force. For the fiber's elastic modulus, take 155 GPa, v m The matrix volume fraction is taken as 0.65. , The coefficients of thermal expansion for the matrix and fiber are respectively taken as 4.5*10. -6 / ℃ and 3.2*10 -6 / ℃, The difference between ambient temperature and crack healing temperature (calculated by software), P is the gas pressure, and M is the mixed molar mass of the two diffusing gases. The average molar mass, Pi The temperature at which the crack heals. for molar mass of a substance For CO or CO2, in the above formula , , v m , The values ​​will vary depending on the blade material; only the parameter values ​​for the example are given here.

[0130] The Knudsen-type diffusion coefficient model for crack channels is determined by the following equation:

[0131] ;

[0132] in, The Knudsen-type diffusion coefficient of the crack channel, The density of the crack. The temperature at which the crack heals. Pi Let e ​​be the molar mass of oxygen, and e0 be the crack width at room temperature under no force. v is the fiber's elastic modulus. m This represents the volume fraction of the matrix. , These are the coefficients of thermal expansion of the matrix and the fiber, respectively. Here, m and b0 represent the stress value, respectively, and the Weibull modulus and Weibull matrix cracking characteristic strength, respectively. R is the difference between ambient temperature and crack healing temperature. g Let T be the gas constant and T be the temperature.

[0133] Statistical analysis shows that pore channels in 2D SiC / SiC materials are mainly distributed in the matrix and between fiber bundles. When establishing a unit cell model, the pores are distributed in the orthogonal region of the fiber bundles. Assuming that their shape is elliptical cylinder, after discretization by thresholding the CT image, they are fitted to elliptical cylinders and the pore feature length is statistically analyzed. The pore feature length d is classified according to the channel length determined by the three diffusion modes (Knudsen, Fick, and mixed diffusion) to obtain the proportion. According to the proportion, several pores are generated in the unit cell and the major and minor semi-axes of the pores are recorded.

[0134] Since the cross-section is an ellipse, the governing equation is:

[0135] ;

[0136] Where x and y represent the x-coordinate and y-coordinate values ​​of any point on the ellipse, Let be the length of the semi-major axis of the ellipse. is the length of the minor semi-axis of the ellipse;

[0137] Furthermore, for the characteristic length of the pore, d=Max(a,b), it means that d will be assigned the larger value between a and b, which is the length of the major semi-axis of the ellipse. is the length of the minor semi-axis of the ellipse;

[0138] For the crack length d, it is assumed to be equal to the crack width e;

[0139] It should be noted that the initial diffusion patterns of the pores inside a unit cell differ due to their initial size. The diffusion patterns of the same pore will also differ as the pore size changes over time: as the pores heal, the diffusion coefficient model changes from the Fick-type diffusion coefficient model to the mixed diffusion coefficient model, and then to the Knudsen-type diffusion coefficient model. Therefore, when calculating the diffusion coefficient of a unit cell, all internal pores need to be taken into account and their updates need to be monitored.

[0140] The Fick-type diffusion coefficient model of the pore channel is determined by the following formula:

[0141] ;

[0142] in, The Fick-type diffusion coefficient of the pore channels. Where is temperature, and P is gas pressure. The volume of molecular diffusion. Here is the molar mass of oxygen. It is CO or CO2. for The molar mass of a substance;

[0143] The Knudsen-type diffusion coefficient model of the pore channel is determined by the following equation:

[0144] ;

[0145] in, The Knudsen type diffusion coefficient of the pore channels. Pi The gas constant is For temperature, This represents the molar mass of oxygen.

[0146] The mixing-type diffusion coefficient model of the pore channels is determined by the following formula:

[0147] ;

[0148] in, The mixing-type diffusion coefficient of the pore channels. The Fick-type diffusion coefficient of the pore channels. The Knudsen-type diffusion coefficient represents the pore channel.

[0149] As described above, this embodiment determines the channel types of the blade model as crack channels and pore channels. For the different diffusion modes mentioned above, whether it is a crack channel or a pore channel, the judgment criterion is the same:

[0150] For Knudsen-type diffusion, d < 0.1 ;

[0151] For mixed diffusion, there is 0.1 <d<100 ;

[0152] For Fick-type diffusion, d > 100 ;

[0153] In the process of judging the above diffusion methods, Let d be the mean free path of the molecules, and d be the diameter of the channel. For crack channels, d is determined by the crack width; for pore channels, d is determined by the major and minor semi-axes of the elliptical cross-section of the pore (assuming the pore is cylindrical at the fiber bundle scale). In this embodiment, considering the filling of diffusion channels due to the oxidation of SiC to SiO2, the value of d is continuously updated and adjusted accordingly. Values ​​are compared;

[0154] S300, determine the gas diffusion coefficient model of the unit cell in the channel according to the diffusion coefficient model, and determine the oxygen concentration distribution in the channel at any time.

[0155] The gas diffusion coefficient model for a single cell is determined by the following equation:

[0156] ;

[0157] in, The gas diffusion coefficient of a single cell. Let be the area of ​​the crack channel. This represents the area of ​​the pore channel (i.e., the area of ​​the ellipse). The gas diffusion coefficient of the crack channel. The gas diffusion coefficient of the pore channel. The area of ​​a single cell;

[0158] Furthermore, by combining mass transfer and reaction kinetics, the oxygen concentration distribution in the plain-weave SiC / SiC composite material can be obtained for the next step of oxidation simulation. Specifically, N units are divided along the thickness direction. The relationship between reaction and diffusion follows the law of conservation of mass, that is, the change in gas is equal to the interpolation of the amount of gas diffusing into the reaction gas, as shown in the following formula:

[0159] ;

[0160] because: ;

[0161] because: ;

[0162] From this, we can obtain the partial differential equation:

[0163] = ;

[0164] in, Porosity The gas diffusion coefficient of a single cell. The reaction rate constant is... The activation energy of the reaction. The reaction temperature, For the reaction rate, Oxygen concentration, For time, This is the direction of oxygen diffusion. This refers to the flux of oxygen flowing into the system. The crack channel diffusion coefficient;

[0165] All the above quantities are input as variables into the COMSOL software. The partial differential equation is calculated by the coefficient form partial differential equation. Parameters such as boundary zero flux boundary, initial value boundary, absorption coefficient, and mass coefficient are set for real-time calculation to obtain the oxygen concentration distribution in the channel at any time.

[0166] S400: Based on the oxidation process of the channel, establish oxidation models in different directions within the channel, set channel parameter thresholds, including the characteristic length of the pore channel and the crack width of the crack channel, complete the oxidation calculation of the channel based on the oxidation model and the parameter thresholds, and obtain the elastic modulus of the matrix and fiber after oxidation.

[0167] In this step, during the process of establishing oxidation models in different directions within the channel based on the oxidation process of the channel, the oxidation models in different directions within the channel include: an oxidation model of oxygen diffusion in the transverse direction of the crack channel and its oxidation with the SiC matrix; an oxidation model of oxygen diffusion in the longitudinal direction of the crack channel and its oxidation with the SiC matrix; and an oxidation model of oxygen diffusion after the pyrolytic carbon layer is corroded and its reaction with the SiC matrix above and below the pyrolytic carbon layer. Specifically:

[0168] Please see Figure 1 Idealizing the fiber bundle and the matrix enclosing the fiber bundle as a cylinder, a half-section view is drawn. Figure 1 In the middle, r m r f , lr, and r represent the distances from the fiber axis to the lower boundary of the SiC matrix oxidation and the upper boundary of the SiC fiber oxidation, respectively. r is the x-direction length where the reaction is maximized. c denoted as , where is the distance from the fiber axis to the matrix surface, e is the crack width, SiCMatrix represents the SiC matrix, PyC Interphase represents the pyrolytic carbon layer, SiC Fiber represents the SiC fiber, and dx is the small change in the x-direction.

[0169] Based on reaction kinetics and mass transfer, equations and the law of conservation of mass are established. The amount of oxygen diffused in is equal to the amount of oxygen consumed in the reaction. Assuming that the crack in the crack channel is a longitudinal crack, oxygen passes through the matrix to reach the pyrolytic carbon layer, reacts with the pyrolytic carbon to generate CO2 or CO, causing the pyrolytic carbon to oxidize and corrode laterally. After the pyrolytic carbon layer is consumed, it continues to diffuse and react with the SiC fiber.

[0170] The diffusion of oxygen in the lateral direction of the crack channel and the oxidation model of the SiC matrix are determined by the following equation:

[0171] ;

[0172] Furthermore, the thickness of SiO2 is:

[0173] ;

[0174] Where 'a' represents the amount of oxygen required to generate 1 mol of SiO2. Let S be the circumferential length of SiO2 in the x-direction, and S be the cross-sectional area for gas flow. Let be the initial oxygen concentration, and z be the thickness of SiO2, which follows a parabolic form. and These are the parabolic constant and oxygen concentration under 0.1 MPa pure oxygen conditions. The density of SiO2, The molar mass of SiO2; This refers to the oxygen concentration at this location. The diffusion coefficient is the diffusion coefficient for mixed diffusion. The parabolic velocity constant is... This represents the ratio of carbon to oxygen in the carbon-oxygen reaction equation. Indicates the x-axis direction. For time;

[0175] The diffusion of oxygen in the longitudinal direction of the crack channel and the oxidation model of the SiC matrix are determined by the following equation:

[0176] ;

[0177] Furthermore:

[0178] ;

[0179] in, The distance from the matrix surface to the fiber center. For the parameters of the matrix parabola, The parabolic exponent of the matrix, Oxygen concentration, The crack width is... The density of SiO2, The molar mass of SiO2 The thickness of SiO2, The y-axis coordinate is This represents the initial oxygen concentration. for molar mass, for density, The thickness of SiO2, for thickness, The diffusion coefficient is... This represents the amount of oxygen required to generate 1 mol of SiO2 in the matrix. It is the oxygen concentration corresponding to the parabolar constant under pure oxygen conditions of 0.1 MPa. Pi This represents the ratio of the product to oxygen in the reaction equation between carbon and oxygen.

[0180] Apply boundary conditions to the above equation: =c0 (y=0);

[0181] The oxidation model of oxygen diffusion through corrosion of the pyrolytic carbon layer, reaction with the SiC matrix above the pyrolytic carbon layer, and reaction with the SiC fibers below the pyrolytic carbon layer is determined by the following equation:

[0182] ;

[0183] Where, r m r f These represent the distances from the fiber axis to the lower boundary of the SiC matrix oxidation and the upper boundary of the SiC fiber oxidation, respectively. and The distances from the fiber axis to the initial SiC matrix boundary and the initial upper boundary of the SiC fiber are denoted as . This refers to the oxygen concentration per unit cell. Oxygen concentration, The diffusion coefficient is... This represents the ratio of products to oxygen in the reaction equation of carbon and oxygen. This represents the amount of oxygen required to generate 1 mol of SiO2 in the matrix. The density of SiO2, and For the parabolic parameters of the matrix and fiber, The parabolic velocity constant of the matrix is ​​. The value represents the oxygen concentration corresponding to the parabolar constant under pure oxygen conditions of 0.1 MPa. The molar mass of SiO2 The thickness of SiO2 after substrate oxidation. This represents the amount of oxygen required to generate 1 mol of SiO2 in the fiber. Let be the parabolic speed constant of the fiber. This represents the thickness of SiO2 after fiber oxidation. Pi Indicates the x-axis direction;

[0184] The above equation has three boundary conditions, namely:

[0185] (1) At the interface between pyrolytic carbon and the matrix, at x=0, the oxygen concentration flowing in the y direction should be equal to the oxygen concentration flowing out in the x direction, that is, the oxygen concentration at this position does not change. At this time, we have:

[0186] ;

[0187] Where, r c dz represents the distance from the fiber axis to the matrix surface, y represents the y-axis, dz represents the thickness variation, e is the crack width, and r is the distance from the fiber axis to the matrix surface. m r fThese represent the distances from the fiber axis to the lower boundary of the SiC matrix oxidation and the upper boundary of the SiC fiber oxidation, respectively. Oxygen concentration, Pi;

[0188] (2) When oxygen pyrolyzes carbon in the x direction, the maximum distance lr that it can reach should be the same as the amount of oxygen consumed in the pyrolysis of carbon. If they are equal, then:

[0189] ;

[0190] in, This represents the ratio of products to oxygen in the reaction equation of carbon and oxygen. This refers to the gas concentration within a single cell. This represents the amount of oxygen consumed in the carbon pyrolysis reaction. Let be the diffusion coefficient of oxygen in the crack. The oxygen concentration is represented by x, which indicates the x-axis direction.

[0191] Oxygen consumption for carbon pyrolysis reaction We obtain it from the following formula:

[0192] = = ;

[0193] in, This represents the amount of oxygen consumed in the carbon pyrolysis reaction. The reaction rate constant is... Where is the oxygen concentration, p is the reaction index, and D is the oxygen diffusion coefficient in the crack. Let T be the gas constant and T be the temperature.

[0194] (3) At the interface between pyrolytic carbon and fiber matrix, x=0, y= At position 0, oxygen has completely reacted with pyrolytic carbon and only reacts with the fiber, causing it to thicken. Therefore: ;

[0195] in, The x-axis length is the length at which oxygen can reach maximum reaction in the pyrolytic carbon layer. Let be the oxygen diffusion coefficient in the crack. The oxygen concentration per unit cell. This represents the ratio of products to oxygen in the reaction equation of carbon and oxygen. Pi Oxygen concentration, The density of SiO2, This represents the amount of oxygen required to generate 1 mol of SiO2 in the fiber. For the parameters of the fiber parabola, r f This represents the distance from the fiber axis to the upper boundary of the SiC fiber oxidation process. The value represents the oxygen concentration corresponding to the parabolar constant under pure oxygen conditions of 0.1 MPa. Let be the parabolic speed constant of the fiber. This represents the thickness of SiO2 after fiber oxidation. The molar mass of SiO2;

[0196] When oxygen reacts with PyC along the x-direction, the length along the x-direction where the reaction reaches its maximum is defined as lr. Therefore:

[0197] ;

[0198] Where lr is the length in the x-direction that maximizes the reaction. The molar mass of pyrolytic carbon. The density of pyrolytic carbon, Oxygen concentration, This represents the initial oxygen concentration. This represents the ratio of products to oxygen in the reaction equation of carbon and oxygen. The diffusion coefficient is... This represents the number of moles of carbon consumed to produce 1 mol of oxygen. For time, Indicates the x-axis direction;

[0199] Substitute the above partial differential equations into the distributed ordinary differential equations in the COMSOL software for calculation, and solve for lr by setting parameters such as source terms and mass coefficients;

[0200] Furthermore, in this embodiment, the oxidation is uniform circumferential oxidation in all directions around the pores, and the oxidation rate is controlled by the diffusion-reaction equation. After oxidation, the pores will be filled by SiO2 generated by the matrix. Therefore, uniform oxidation results in:

[0201] ;

[0202] in, The ratio coefficient, The length of the major semi-axis of the pores before oxidation. The length of the minor semi-axis of the pores before oxidation. The thickness of SiO2 before oxidation. The length of the major semi-axis of the pores after oxidation. The length of the minor semi-axis of the pores after oxidation. The thickness of SiO2 after oxidation;

[0203] After obtaining the above ratio coefficient Then, the area of ​​the ellipse after shrinking (after oxidation). and volume They are respectively:

[0204] ;

[0205] h;

[0206] in, This represents the area of ​​the reduced ellipse. Pi The ratio coefficient, The length of the major semi-axis of the pores before oxidation. The length of the minor semi-axis of the pores before oxidation. The length of the major semi-axis of the pores after oxidation. The length of the minor semi-axis of the pores after oxidation. The height of the pore;

[0207] Furthermore, the length of the major semi-axis of the oxidized pores... and the length of the minor half-axis In subsequent loops, the pore diffusion type is reassessed, and a new unit cell diffusion coefficient is calculated.

[0208] Furthermore, new porosity and crack width can also be obtained:

[0209] New porosity: ;

[0210] in, The porosity after oxidation. The porosity before oxidation. This represents the volume after oxidation. This is the volume before oxidation;

[0211] New crack width: ;

[0212] in, The width of the crack after oxidation. The crack width before oxidation. This represents the change in thickness.

[0213] Furthermore, the changes in pore morphology, porosity, and crack width will cause changes in the diffusion coefficient. Therefore, the updated pore parameters, porosity, crack width, fiber and matrix volume fractions, and elastic modulus are re-introduced into step S200. Steps S200, S300, and S400 are iterated continuously until the set channel size critical value is reached. At this point, the oxygen channel is considered completely closed, and oxidation is complete. Please refer to [link to relevant documentation]. Figure 7The determination of complete closure of the oxygen channel can be achieved by calculating the concentration distribution of the gas (oxygen) within the channel. For example, in... Figure 7 During the oxidation process, the shape parameters of the pores, such as porosity and crack width, change. Based on the changes in the pore characteristic length d and crack width e, the calculation ends when a set threshold is met, and the oxygen concentration is obtained. When the set threshold is not met, the parameters are updated according to the diffusion coefficient model (diffusion coefficient change), and the gas (oxygen) concentration distribution is recalculated. This process is repeated, and the calculation returns to the initial changes in the pore characteristic length d and crack width e to determine whether the set threshold is met. The calculation result is obtained when the threshold is met. In particular, the calculation will also stop if the set time is reached but the threshold is not reached.

[0214] S500: Based on the elastic modulus, boundary conditions, and uniformity rules of the fiber bundle composite material, obtain the elastic modulus matrix of the unit cell and the stress state of the element. Calculate the elastic modulus matrix of the overall component according to the periodicity rule. Use failure criteria to determine the degradation of the unit fiber and matrix under tension or compression in different directions. Use the degraded parameters as new material properties to re-determine model failure. Mark the failed elements. When the accumulation of failed elements leads to overall aging of any part of the blade, the corresponding time is the oxidation lifetime of the blade. If the blade does not fail, use the degraded parameters as new material properties to re-calculate oxidation. Specifically:

[0215] First, the modulus after oxidation is calculated. A unit cell is selected as the research object, and the elastic modulus of the matrix and fiber after oxidation is calculated according to the mixing law:

[0216] ;

[0217] ;

[0218] in, and These are the moduli of the fiber and the matrix after oxidation, respectively. and These are the pre-oxidation moduli of the fiber and matrix, respectively, with E0 being the modulus of SiO2. and These represent the volume fractions of the matrix and fibers after oxidation, respectively. When cracks act as oxygen channels, both the SiC matrix and fibers oxidize to SiO2. However, when pores act as oxygen channels, only the oxidation of the matrix is ​​considered. Therefore, the volume fraction of the oxidized fibers can be obtained separately. and the volume fraction of the matrix after oxidation ;

[0219] Furthermore, the volume fraction of the oxidized fiber is: ;

[0220] in, This represents the volume fraction of the fiber after oxidation. This represents the volume of the fiber after oxidation. This refers to the volume increase resulting from fiber oxidation. This represents the fiber volume before oxidation.

[0221] Further, the volume fraction of the matrix after oxidation: ;

[0222] in, This represents the volume fraction of the matrix after oxidation. This represents the volume of the matrix after oxidation. This represents the volume increase resulting from the oxidation of the matrix. This represents the absolute value of the volume change after pore oxidation. This represents the volume of the matrix before oxidation.

[0223] The fiber bundle, the pyrolytic carbon layer, and the outer matrix are treated as a cylinder, and these three parts are combined to form a fiber bundle composite material.

[0224] Furthermore, the axial elastic modulus of the fiber bundle composite is calculated:

[0225] ;

[0226] ;

[0227] Furthermore, = / 2;

[0228] = + ;

[0229] Where m and b0 are the Weibull modulus and the Weibull matrix cracking characteristic strength, respectively. In this embodiment, m=3 and b0=155MPa are taken as values. The saturated average crack spacing L can be obtained by experimental observation of the matrix crack spacing. sat It is 0.235mm. The axial elastic modulus of the oxidized fiber bundle composite material is given. The crack width is half the width of the crack after oxidation, and L is the crack spacing. The length consumed at the pyrolysis carbon interface. This refers to the fiber debonding length. This represents the elastic modulus of the fiber after oxidation. This represents the volume fraction of the oxidized fiber. This represents the volume fraction of the oxidized matrix. Elastic modulus of the oxidized matrix The average elastic modulus, The width of the crack after oxidation;

[0230] get Afterwards, Other components in the elastic modulus matrix of fiber bundle composites can be obtained by proportional reduction. The specific reduction process is as follows:

[0231] ;

[0232] ;

[0233] in, Let i be the elastic modulus in the i-direction of the fiber bundle composite material after elastic oxidation. The axial elastic modulus of the fiber bundle composite material after elastic oxidation. The axial elastic modulus of the fiber bundle composite material before oxidation. The elastic modulus in the i-direction of the fiber bundle composite material before oxidation is given. The shear modulus of the fiber bundle composite material in various elastic directions after oxidation is given. The shear modulus of the fiber bundle composite material in all directions before oxidation;

[0234] Based on the pore parameters of the oxidized elliptical cylindrical shape, the unit cell model before oxidation is updated by inputting the pore parameters after oxidation into the unit cell model, thereby establishing the actual oxidized unit cell model.

[0235] The elastic modulus matrix of the oxidized fiber bundle composite material was used as a parameter of the yarn material in the unit cell for calculation. Boundary conditions were applied and homogenized using the finite element method in COMSOL and MATLAB: First, the unit cell model was discretized into multiple elements, then homogenized, and forced boundary conditions were applied to calculate the stress and elastic modulus matrix of each element in the unit cell. Finally, element failure was determined according to the failure criteria. The failure determination process is detailed in [link to relevant documentation]. Figure 8 ,exist Figure 8 In the process, oxidation calculations are performed first, followed by calculations of the residual elastic modulus of the fiber and matrix. After calculating the micromechanical model, it is determined whether the element has failed. If failure occurs, a reduction is applied according to the coefficient, and the micromechanical model is calculated again to determine whether the component has failed. If failure occurs, the component lifetime is output, completing the calculation process. If no failure occurs, the process returns to the beginning and repeats the oxidation calculation. It should be noted that in... Figure 8 In this process, when the judgment unit is not in failure, the micromechanical calculation is performed directly without the need for coefficient reduction.

[0236] Furthermore, in this embodiment, the failure criterion for the element is the Hashin criterion, and the elastic modulus degradation method of the instantaneous unloading model is used to degrade the fibers and matrix of the element. The failure criterion and coefficient reduction method are as follows:

[0237] (1) During longitudinal stretching ( , (Normal stress of the element in the x-direction)

[0238] ;

[0239] Among them, X T Tensile strength in the fiber direction. This is the stress value. ij These are the components in the flexibility matrix. Through elastic modulus get, The coefficients are between 0 and 1;

[0240] (2) During transverse stretching ( , The element is subjected to normal stress in the y-direction. (For an element subjected to normal stress in the z-direction).

[0241] ;

[0242] Among them, Y T This represents the tensile strength in the matrix direction. ij These are stress values ​​other than the normal stress values ​​in the x, y, and z directions. ij These are the components in the compliance matrix;

[0243] (3) During lateral compression ( , The element is subjected to normal stress in the y-direction. (For an element subjected to normal stress in the z-direction)

[0244] ;

[0245] Among them, Y C The compressive strength is in the matrix direction. This is the stress value. ij These are the components in the flexibility matrix. ij For stress values ​​in other directions; for ij i=1, 2, 3; j=1, 2, 3; for ij , i=1, 2, 3, that is ii（i=1，2，3） These are the normal stress values ​​in the x, y, and z directions;

[0246] (4) During longitudinal compression ( <0, (For an element subjected to normal stress in the x-direction).

[0247] ;

[0248] Among them, X C The compressive strength is in the fiber direction. The normal stress of the element in the x-direction;

[0249] Furthermore, during the degradation process of the fiber and matrix, any element that satisfies any one of the expressions for longitudinal tension, transverse tension, transverse compression, and transverse compression is considered to be in failure and is marked.

[0250] Furthermore, the degraded parameters will be used as new material element properties to re-evaluate model failure; specifically:

[0251] When the matrix element fails:

[0252] ;

[0253] ;

[0254] ;

[0255] ;

[0256] ;

[0257] ;

[0258] When a fiber unit fails:

[0259] ;

[0260] ;

[0261] ;

[0262] ;

[0263] ;

[0264] ;

[0265] In the above process, COMSOL, as mentioned above, uses the degraded parameters as new material properties to re-determine model failure during the output process, marks the failed units, and when the accumulation of failed units causes the overall aging of any part of the blade, the corresponding time is the oxidation life of the blade.

[0266] It should be noted that in the above process of this embodiment, all parameters should be placed in the software (the aforementioned COMSOL software), all variables should be used as global variables, initial values ​​should be used as global constants, and partial differential equations should be calculated using the partial differential equation solving module in the software. Furthermore, based on the above technical solution of the present invention, an oxidation application program can be designed, and the above process of this embodiment can be completed using an oxidation application program; for example, please refer to... Figure 9 The development flowchart for oxidation applications is as follows: Figure 9 As shown, specifically, modeling is performed based on a blade model. After modeling, solid mechanics, solid-solid heat transfer, fluid mechanics, and oxidation numerical analysis are conducted. During these analyses, material and environmental parameters need to be assigned. For numerical solutions, the analysis domain needs to be meshed. After assigning parameters and meshing, multiphysics coupling and oxidation numerical solutions are performed. The results are then analyzed to identify patterns in the material oxidation process. Based on the analysis results and the identified patterns, an oxidation application program (software development) is developed, which includes algorithm design, code writing, and software testing. Ultimately, a material oxidation application program with practical application value is developed. For another example, please refer to [link to example]. Figure 2 Oxidation applications may include the following main components:

[0267] Parameter setting area: Used for inputting material properties and boundary conditions. Users can set relevant physical parameters. This invention divides parameter input into three categories. The first category is material parameters, including matrix elastic modulus, matrix volume fraction, fiber elastic modulus, porosity, and mechanical parameters of composite materials such as E1, E2, E3, G12, G23, and G13. The second category is environmental parameters, such as the gas temperature at the gas inlet, the gas flow rate at the gas inlet, and the blade rotation speed during operation. This invention uses sliders and knobs to control gas temperature, gas velocity, and rotation speed. Users only need to slide the sliders to control the temperature and speed. The temperature is set in the range of 900~1600K, with precise adjustment steps of 1K; the speed is set from 0~1000m / s, with precise adjustment down to 1m / s. The rotation speed can be adjusted from 0~30000 rpm in 100 rpm intervals using the knobs. Finally, this invention includes a time step button to calculate the oxidation status at a set time. The slider and knob will change graphically in real time according to the values ​​set by the user.

[0268] The simulation control area includes drawing geometry, mesh generation, starting calculation, drawing temperature field, drawing fluid velocity field, drawing stress distribution, drawing oxidation product distribution map, drawing crack width distribution, and drawing failure cloud map. Users can control the simulation process through simple button operations and monitor the simulation progress in real time.

[0269] Results display area: Displays real-time simulation results. Users can view simulation results from different perspectives and color plots for easy observation and analysis. Currently, the view can zoom in and out, scale to window size, switch to default view, switch to planar view (supporting XY, YZ, and ZX planes), enable / disable wireframe rendering, enable / disable grid, enable / disable coordinate system display, and automatically save and print screenshots of the results.

[0270] Calculation example

[0271] Using the aforementioned oxidation application, with the inlet velocity set to 500 m / s, the inlet temperature set to 1200 K, and the rotational speed selected to be 17000 r / min, the calculated flow field velocity field, temperature field, and force field distribution diagrams are shown below. Figure 3 As shown. Figure 3 In the diagram, the top two figures show the flow field, the bottom left figure shows the temperature field, and the bottom right figure shows the force field.

[0272] Figure 4 The crack width distribution diagrams at 200h, 500h, 750h, and 1000h show that as oxidation progresses, crack channels are continuously filled, and crack widths decrease. Areas with large crack widths, high temperatures, and high gas concentrations (near the gas inlet) exhibit rapid oxidation. A faster oxidation rate leads to a faster decrease in crack width and a smaller crack width. As the crack width decreases, it becomes more difficult for oxygen to enter the interior through the channels, resulting in a continuously decreasing equivalent diffusion coefficient. This slows down the rate of crack width reduction in the later stages. The crack density changes by orders of magnitude in the first 200h, while in the following 800h, the changes are all of the same order of magnitude with a decreasing rate of change. Over the entire timeframe, the difference in crack width across the entire outer surface diminishes because the oxidation rate decreases in areas that initially oxidize rapidly, and is even overtaken by areas that initially oxidize more slowly. As the crack density decreases, the way gas diffuses within the crack also changes.

[0273] Figure 5The distribution diagrams show the thickness of oxidation products at 200h, 500h, 750h, and 1000h, respectively, which can represent the distribution of oxidation products. Although there are obvious signs of oxidation on the outer surface at 200h, the thickness of oxidation products on the side closer to the gas inlet is significantly greater than that on the side farther away. It can also be seen that the thickness of oxidation products increases faster at the beginning, and then the rate of change of thickness decreases as the channel is filled.

[0274] Figure 6 The diagram shows the failure distribution of elements over time periods of 50, 100, 200, 500, 800, and 1000 hours. Element 1 is defined as the element that fails. Figure 6 The red area represents failure, which is helpful to assume that most of the blades have failed by 500 hours, and the predicted lifespan is 500 hours.

[0275] In the description of the above embodiments, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0276] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for predicting the oxidation life of SiC / SiC composite blades, characterized in that, include: A blade model of SiC / SiC composite material is established. The blade model selects the tip part of the blade. The external flow field is the high-temperature and high-pressure gas generated after the combustion of combustion gas and air in the combustion chamber. The gas in the flow field is simplified to high-temperature and high-pressure air. The blade model is imported into COMSOL to set the flow field fluid-solid-thermal-mechanical coupling and define the gas inlet end and gas outlet end of the fluid domain. The channel types of the blade model are determined, and diffusion coefficient models for the gas within each channel are established. The channel types include crack channels and pore channels. The diffusion coefficient models for the gas within each channel include a mixed diffusion coefficient model, a Knudsen diffusion coefficient model, and a Fick diffusion coefficient model. During the continuous healing process, the diffusion coefficient model of the crack channel is transformed from a mixed diffusion coefficient model to a Knudsen diffusion coefficient model, and the diffusion coefficient model of the pore channel is transformed from a Fick diffusion coefficient model to a mixed diffusion coefficient model, and then to a Knudsen diffusion coefficient model. The gas diffusion coefficient model of the unit cell in the channel is determined based on the diffusion coefficient model, and the oxygen concentration distribution in the channel at any given time is determined. Oxidation models in different directions within the channel are established based on the oxidation process of the channel. Channel parameter thresholds are set, and oxidation calculations of the channel are completed based on the oxidation models and parameter thresholds. The elastic moduli of the matrix and fibers after oxidation are obtained. The oxidation models in different directions within the channel include oxidation models of oxygen diffusion in the transverse direction of the crack channel and oxidation of the SiC matrix, oxidation models of oxygen diffusion in the longitudinal direction of the crack channel and oxidation of the SiC matrix, and oxidation models of oxygen diffusion after the pyrolytic carbon layer is etched away and reaction with the SiC matrix above and below the pyrolytic carbon layer. The parameter thresholds include the characteristic length of the pore channel and the crack width of the crack channel. The elastic modulus matrix of the fiber bundle composite material is calculated based on the elastic modulus of the matrix and fibers after oxidation. Based on the obtained unit stress conditions, failure criteria are used to determine the degradation of fibers and matrix in the unit under tension or compression in different directions. Failed units are marked to determine the failure of macroscopic components. If macroscopic components do not fail, the degraded parameters are used as new material properties for re-cyclic calculation. When the accumulation of failed units causes overall aging of any part of the blade, the corresponding time is the oxidation life of the blade.

2. The method for predicting the oxidation life of SiC / SiC composite blades according to claim 1, characterized in that, The mixed diffusion coefficient model of the crack channel is determined by the following formula: ； in, The mixed-type diffusion coefficient of the crack channel. R g The gas constant is T For temperature, This is the stress value. m and b 0 For Weibull modulus and Weibull matrix cracking characteristic strength, The average saturation crack spacing. Let e ​​be the molecular diffusion volume, e be the crack width, and e0 be the crack width at room temperature under no force. v is the fiber's elastic modulus. m This is the volume fraction of the matrix. , These are the coefficients of thermal expansion of the matrix and the fiber, respectively. This represents the difference between the ambient temperature and the crack healing temperature. P For gas pressure, M The molar mass of the mixture of the two diffusing gases. The average molar mass, Pi The temperature at which the crack heals. for molar mass of a substance It is either CO or CO2.

3. The method for predicting the oxidation life of SiC / SiC composite blades according to claim 2, characterized in that, The Knudsen-type diffusion coefficient model of the crack channel is determined by the following formula: ； in, The Knudsen-type diffusion coefficient of the crack channel, The density of the crack. The temperature at which the crack heals. Pi Let e ​​be the molar mass of oxygen, and e0 be the crack width at room temperature under no force. v is the fiber's elastic modulus. m This is the volume fraction of the matrix. , These are the coefficients of thermal expansion of the matrix and the fiber, respectively. This is the stress value. m and b 0 For Weibull modulus and Weibull matrix cracking characteristic strength, This represents the difference between the ambient temperature and the crack healing temperature. R g The gas constant is T For temperature.

4. The method for predicting the oxidation life of SiC / SiC composite blades according to claim 3, characterized in that, The Fick-type diffusion coefficient model of the pore channel is determined by the following formula: ； in, The Fick-type diffusion coefficient of the pore channels. For temperature, P For gas pressure, The volume of molecular diffusion. Here is the molar mass of oxygen. It is CO or CO2. for The molar mass of a substance.

5. The method for predicting the oxidation life of SiC / SiC composite blades according to claim 4, characterized in that, The Knudsen-type diffusion coefficient model of the pore channel is determined by the following equation: ； in, The Knudsen type diffusion coefficient of the pore channels. Pi The gas constant is For temperature, Here is the molar mass of oxygen. And / or, The mixing-type diffusion coefficient model of the pore channels is determined by the following formula: ； in, The mixing-type diffusion coefficient of the pore channels. The Fick-type diffusion coefficient of the pore channels. The Knudsen-type diffusion coefficient represents the pore channel. And / or, The gas diffusion coefficient model of the unit cell is determined by the following formula: ； in, The gas diffusion coefficient of a single cell. Let be the area of ​​the crack channel. The area of ​​the pore channels. The gas diffusion coefficient of the crack channel. The gas diffusion coefficient of the pore channel. This represents the area of ​​a single cell.

6. The method for predicting the oxidation life of SiC / SiC composite blades according to claim 5, characterized in that, In determining the oxygen concentration distribution within the channel at any given time, the oxygen concentration at any given time is determined by the following formula: = ； in, Porosity The gas diffusion coefficient of a single cell. The reaction rate constant is... The activation energy of the reaction. The reaction temperature, For the reaction rate, Oxygen concentration, For time, Indicates the x-axis direction.

7. The method for predicting the oxidation life of SiC / SiC composite blades according to claim 6, characterized in that, The elastic modulus of the fiber bundle composite material in the unit cell is determined by the following formula: ； in, The axial elastic modulus of the oxidized fiber bundle composite material is given. This is half the width of the crack after oxidation. L Crack spacing, The length consumed at the pyrolysis carbon interface. This refers to the fiber debonding length. This represents the elastic modulus of the fiber after oxidation. This represents the volume fraction of the oxidized fiber. This is the average elastic modulus.

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