Method for predicting oxidation life of SiC / SiC composite material blade

Abstract

The invention discloses a SiC / SiC composite material blade oxidation life prediction method, relates to the technical field of aero-engine blade oxidation, and is used for solving the technical problems that in the prior art, the accuracy of life prediction of an actual service structural part is low, and oxidation life prediction of a turbine blade structure cannot be adapted. The blade oxidation life prediction method comprises the following steps: establishing a SiC / SiC composite material blade model; determining the channel type of the blade model, and establishing a diffusion coefficient model of gas in each channel; determining oxygen concentration distribution in the channel at any moment; setting a channel parameter threshold value, completing oxidation calculation of the channel, obtaining elasticity modulus of the oxidized matrix and the fiber, and further calculating an elasticity modulus matrix of the fiber bundle composite material; and re-establishing a unit cell model according to the oxidation condition to obtain an elastic modulus matrix of the unit cells and the stress condition of each unit, judging degeneration of fibers and matrixes in the units during stretching or compression in different directions, marking failure units, and obtaining the oxidation life of the blade.

Description

Technical Field

[0001] The present invention relates to the technical field of aero-engine blade oxidation, and more specifically, to a method for predicting the oxidation life of a SiC / SiC composite blade. Background Art

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

[0003] In the process of predicting the oxidation life of materials, the existing technology only considers the mixed diffusion in the crack channel when calculating the gas diffusion and ignores the change in the diffusion mode due to the filling of the diffusion channel. It does not clarify the shape of the pore channel in oxygen and establish the reaction kinetic equation of pore oxidation. The failure criteria considered are too simple, resulting in inaccurate life prediction, and the influence of the flow field on the temperature field, force field and chemical field is not considered. Therefore, it cannot be applied to the structure of turbine blades, and the accuracy of the life prediction of actual service structural parts is low. Summary of the invention

[0004] The purpose of the present invention is to provide a method for predicting the oxidation life of SiC / SiC composite blades, which is used to solve the technical problems that the prior art has low accuracy in predicting the life of actual service structural parts and cannot adapt to the prediction of the oxidation life of turbine blade structures. In view of this, the present invention is implemented through the following scheme.

[0005] The present invention provides a method for predicting the oxidation life of a SiC / SiC composite blade, comprising:

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

[0007] Determining the channel type of the blade model and establishing a diffusion coefficient model of the gas in each channel;

[0008] 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;

[0009] According to the oxidation process of the channel, an oxidation model in different directions in the channel is established, a channel parameter threshold is set, the oxidation calculation of the channel is completed according to the oxidation model and the parameter threshold, and the elastic modulus of the matrix and the fiber after oxidation is obtained;

[0010] The elastic modulus matrix of the fiber bundle composite is calculated based on the elastic moduli of the matrix and the fiber after oxidation;

[0011] The elastic modulus matrix of the unit cell is obtained according to the elastic modulus of the fiber bundle composite material, and the stress condition of the unit is obtained according to the stress condition of the unit cell. The degradation of the fiber and the matrix when stretched or compressed in different directions in the unit is judged according to the elastic modulus matrix and the failure criterion. When the accumulation of failed units leads to overall aging of any part of the blade, the corresponding time at this time is the oxidation life of the blade.

[0012] Compared with the prior art, the oxidation life prediction method of SiC / SiC composite blades of the present invention is used to predict the oxidation life of SiC / SiC composite blades. The technical solution establishes a diffusion coefficient model of the gas in each channel, and then fully considers the changes in various diffusion modes caused by the continuous healing process of the channel in the process of determining the oxygen concentration distribution in the channel at any time, which is more accurate than the oxygen concentration distribution obtained by considering only a single diffusion mode. It can also be said that the distribution of oxidation products obtained after the following oxidation calculation is more accurate. Further, in the process of establishing the diffusion coefficient model of the gas in the channel, the influence of different types of channels on the blade is also considered. In the process of channel oxidation calculation, the oxidation model in different directions in the channel is considered, and the elastic modulus of the matrix and fiber after oxidation is obtained. The elastic modulus matrix of the fiber bundle composite material under the microscopic view is calculated, and the elastic modulus matrix of the unit cell and the stress condition of the macro unit are obtained by modeling and calculating the unit cell. According to the elastic modulus matrix and the failure criterion, in the process of judging the degradation of the fiber and matrix in the macro unit when stretched or compressed in different directions, a more accurate failure criterion can be used, and then the oxidation life of the blade is accurately predicted. By way of example, the failure criterion may be a 3D Hasin failure criterion. The above technical solution of the present invention solves the technical problems that the prior art has low accuracy in predicting the life of actual service structural parts and cannot adapt to the prediction of oxidation life of turbine blade structures.

[0013] Furthermore, in the method for predicting the oxidation life of SiC / SiC composite blades of the present invention, the elastic modulus matrix of the unit cell is obtained according to the elastic modulus of the fiber bundle composite material, the stress condition of the unit is obtained according to the stress condition of the unit cell, and the degradation of the fiber and the matrix when stretched or compressed in different directions in the unit is judged according to the elastic modulus matrix and the failure criterion, including:

[0014] According to the obtained unit stress conditions, the failure criteria are used to determine the degradation of the fiber and matrix in the unit when stretched or compressed in different directions. The failed units are marked to determine the failure of the macroscopic component. If the macroscopic component has not failed, the degraded parameters are used as new material properties for recalculation.

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

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

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

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

[0019] ;

[0020] in, is the mixed diffusion coefficient of the crack channel, R g is the gas constant, T is the temperature, is the stress value, m and b0 are the Weibull modulus and Weibull matrix crack characteristic strength, is the average saturated crack spacing, is the molecular diffusion volume, e is the crack width, e0 is the crack width at room temperature without any force acting on it, is the fiber elastic modulus, v m is the matrix volume fraction, , are the thermal expansion coefficients of the matrix and fiber, is the difference between the ambient temperature and the crack healing temperature, P is the gas pressure, M is the mixed molar mass of the two diffused gases, is the average molar mass, is the circumference of a circle, is the crack healing temperature, for The molar mass of a substance, is CO or CO2.

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

[0022] ;

[0023] in, Knudsen-type diffusion coefficient of the crack channel, is the density of the crack, is the crack healing temperature, is the circumference of a circle, is the molar mass of oxygen, e0 is the crack width at room temperature without any force acting on it, is the fiber elastic modulus, v m is the matrix volume fraction, , are the thermal expansion coefficients of the matrix and fiber, is the stress value, m and b0 are the Weibull modulus and Weibull matrix crack characteristic strength, is the difference between the ambient temperature and the crack healing temperature, R g is the gas constant and T is the temperature.

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

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

[0026] ;

[0027] in, is the Fickian diffusion coefficient of the pore channel, is the temperature, P is the gas pressure, is the molecular diffusion volume, is the molar mass of oxygen, is CO or CO2, for The molar mass of a substance.

[0028] Furthermore, in the method for predicting the oxidation life of SiC / SiC composite blades of the present invention, the Knudsen diffusion coefficient model of the pore channel is determined by the following formula:

[0029] ;

[0030] in, is the Knudsen diffusion coefficient of the pore channel, is the circumference of a circle, is the gas constant, is the temperature, is the molar mass of oxygen;

[0031] and / or,

[0032] The mixed diffusion coefficient model of the pore channel is determined by the following formula:

[0033] ;

[0034] in, is the mixed diffusion coefficient of the pore channel, is the Fickian diffusion coefficient of the pore channel, is the Knudsen diffusion coefficient of 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, is the gas diffusion coefficient of the unit cell, is the area of ​​the crack channel, is the area of ​​the pore channel, is the gas diffusion coefficient in the crack channel, is the gas diffusion coefficient of the pore channel, is the area of ​​the unit cell.

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

[0040] = ;

[0041] in, is the porosity, is the gas diffusion coefficient of the unit cell, is the reaction rate constant, is the reaction activation energy, is the reaction temperature, is the reaction rate, is the oxygen concentration, For time, Indicates the x direction of the coordinate axis.

[0042] Furthermore, in the method for predicting the oxidation life of SiC / SiC composite blades of the present invention, in the process of establishing oxidation models in different directions in the channel according to the oxidation process of the channel, the oxidation models in different directions in the channel include:

[0043] Oxidation model of oxygen diffusion in the lateral direction of the crack channel and the SiC matrix, oxidation model of oxygen diffusion in the longitudinal direction of the crack channel and the SiC matrix, oxidation model of oxygen diffusion in the eroded pyrolytic carbon layer and the reaction of the SiC matrix above the pyrolytic carbon layer and the SiC fiber below; 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 method for predicting the oxidation life of SiC / SiC composite blades 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, is the axial elastic modulus of the oxidized fiber bundle composite material, is the half width of the crack after crack oxidation, L is the crack spacing, is the consumed length of the pyrolytic carbon interface, is the fiber debonding length, is the elastic modulus of the oxidized fiber, is the volume fraction of the oxidized fiber, 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 volume uniformity law to the unit cell model after oxidation. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

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

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

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

[0053] Figure 4 Schematic diagram of crack width distribution at 200h, 500h, 750h and 1000h during the oxidation process in the example of the present invention;

[0054] Figure 5Schematic diagram of the distribution of oxidation product thickness at 200 h, 500 h, 750 h, and 1000 h during the oxidation process in the example of the present invention;

[0055] Figure 6 Schematic diagram of unit failure distribution at times of 50, 100, 200, 500, 800, and 1000 h in the example of the present invention;

[0056] Figure 7 This is a flow chart of oxidation calculation in Example 3 of the present invention;

[0057] Figure 8 This is a failure judgment flow chart in Example 3 of the present invention;

[0058] Fig. 9 This is a flow chart for developing an oxidation application in Example 3 of the present invention. DETAILED DESCRIPTION

[0059] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

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

[0061] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. The meaning of "several" is one or more, unless otherwise clearly and specifically defined.

[0062] In the process of predicting the oxidation life of materials, the existing technology only considers the mixed diffusion in the crack channel when calculating the gas diffusion and ignores the change in the diffusion mode due to the filling of the diffusion channel. It does not clarify the shape of the pore channel in oxygen and establish the reaction kinetic equation of pore oxidation. The failure criteria considered are too simple, resulting in inaccurate life prediction, and the influence of the flow field on the temperature field, force field and chemical field is not considered. Therefore, it cannot be applied to the structure of turbine blades, and the accuracy of the life prediction of actual service structural parts is low.

[0063] In order to solve the technical problem, the present invention provides a method for predicting the oxidation life of a SiC / SiC composite blade, comprising:

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

[0065] Determining the channel type of the blade model and establishing a diffusion coefficient model of the gas in each channel;

[0066] 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;

[0067] According to the oxidation process of the channel, an oxidation model in different directions in the channel is established, a channel parameter threshold is set, the oxidation calculation of the channel is completed according to the oxidation model and the parameter threshold, and the elastic modulus of the matrix and the fiber after oxidation is obtained;

[0068] The elastic modulus matrix of the fiber bundle composite is calculated based on the elastic moduli of the matrix and the fiber after oxidation;

[0069] The elastic modulus matrix of the unit cell is obtained according to the elastic modulus of the fiber bundle composite material, and the stress condition of the unit is obtained according to the stress condition of the unit cell. The degradation of the fiber and the matrix when stretched or compressed in different directions in the unit is judged according to the elastic modulus matrix and the failure criterion. When the accumulation of failed units leads to overall aging of any part of the blade, the corresponding time at this time is the oxidation life of the blade.

[0070] In the case of adopting the above technical scheme, the oxidation life prediction method of the SiC / SiC composite blade of the present invention is used to predict the oxidation life of the SiC / SiC composite blade. The technical scheme establishes a diffusion coefficient model of the gas in each channel, and then fully considers the changes in various diffusion modes caused by the continuous healing process of the channel in the process of determining the oxygen concentration distribution in the channel at any time, which is more accurate than the oxygen concentration distribution obtained by considering only a single diffusion mode. It can also be said that the distribution of oxidation products obtained after the following oxidation calculation is more accurate. Further, in the process of establishing the diffusion coefficient model of the gas in the channel, the influence of different types of channels on the blade is also considered. In the process of channel oxidation calculation, the oxidation model in different directions in the channel is considered, and the elastic modulus of the matrix and fiber after oxidation is obtained. The elastic modulus matrix of the fiber bundle composite material under the microscopic view is calculated, and the elastic modulus matrix of the unit cell and the stress condition of the macro unit are obtained by modeling and calculating the unit cell. According to the elastic modulus matrix and the failure criterion, in the process of judging the degradation of the fiber and matrix in the macro unit when stretched or compressed in different directions, a more accurate failure criterion can be used, and then the oxidation life of the blade is accurately predicted. By way of example, the failure criterion may be a 3D Hasin failure criterion. The above technical solution of the present invention solves the technical problems that the prior art has low accuracy in predicting the life of actual service structural parts and cannot adapt to the prediction of oxidation life of turbine blade structures.

[0071] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with specific embodiments, 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 a SiC / SiC composite blade, comprising:

[0074] S100, establishing a blade model of SiC / SiC composite material, setting the blade working conditions, and obtaining the temperature field and force field distribution;

[0075] S200, determining the channel type of the blade model, the channel type being a crack channel and a pore channel, and establishing a diffusion coefficient model of the gas in each channel;

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

[0077] S400, establishing oxidation models in different directions in the channel according to the oxidation process of the channel, setting channel parameter thresholds, the parameter thresholds including the characteristic length of the pore channel and the crack width of the crack channel, completing the oxidation calculation of the channel according to the oxidation model and the parameter thresholds, and obtaining the elastic modulus of the matrix and the fiber after oxidation;

[0078] S500, according to the elastic modulus and boundary conditions of the fiber bundle composite material and the uniformity law, the elastic modulus matrix of the unit cell and the stress condition of the unit cell are obtained, the elastic modulus matrix of the overall component is calculated according to the periodic law, and the failure criterion is used to judge the degradation of the unit fiber and the matrix when stretched or compressed in different directions, and the degraded parameters are used as new material properties to re-judge the model failure, and the failed units are marked. When the accumulation of failed units leads to overall aging of any part of the blade, the corresponding time at this time is the oxidation life of the blade. If the blade has not failed, the degraded parameters are used as new material properties to re-calculate the oxidation.

[0079] Example 2

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

[0081] S100, establishing a blade model of SiC / SiC composite material, setting the blade working conditions, and obtaining the temperature field and force field distribution;

[0082] S200, determining the channel type of the blade model, the channel type being a crack channel and a pore channel, and establishing a diffusion coefficient model of the gas in each channel;

[0083] Wherein, 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 diffusion coefficient model, and the mixed diffusion coefficient model of the crack channel is determined by the following formula:

[0084] ;

[0085] Further, ;

[0086] in, is the mixed diffusion coefficient of the crack channel, R g is the gas constant, T is the temperature, is the stress value, m and b0 are the Weibull modulus and Weibull matrix crack characteristic strength, is the average saturated crack spacing, is the molecular diffusion volume, e is the crack width, e0 is the crack width at room temperature without any force acting on it, is the fiber elastic modulus, v m is the matrix volume fraction, , are the thermal expansion coefficients of the matrix and fiber, is the difference between the ambient temperature and the crack healing temperature, P is the gas pressure, M is the mixed molar mass of the two diffused gases, is the average molar mass, is the circumference of a circle, is the crack healing temperature, for The molar mass of a substance, CO or CO2;

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

[0088] ;

[0089] in, Knudsen-type diffusion coefficient of the crack channel, is the density of the crack, is the crack healing temperature, is the circumference of a circle, is the molar mass of oxygen, e0 is the crack width at room temperature without any force acting on it, is the fiber elastic modulus, v m is the matrix volume fraction, , are the thermal expansion coefficients of the matrix and fiber, is the stress value, m and b0 are the Weibull modulus and Weibull matrix crack characteristic strength, is the difference between the ambient temperature and the crack healing temperature, R g is the gas constant, T is the temperature;

[0090] According to statistics, the pore channels in 2D SiC / SiC materials are mainly distributed in the matrix and between fiber bundles. When the unit cell model is established, the pores are distributed in the orthogonal region of the fiber bundles. Assuming that its shape is an elliptical cylinder, the pore characteristic length is counted after being discretized by threshold division of the CT image and fitted into an elliptical cylinder. The pore characteristic 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] Among them, x and y represent the values ​​of the horizontal and vertical coordinates of any point on the ellipse. is the length of the major semiaxis 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 of 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 pores inside the unit cell have different initial diffusion modes due to their initial sizes. As the pore size changes over time, the diffusion mode of the same pore will be different from the initial one. Specifically, the diffusion coefficient model is transformed from the Fick diffusion coefficient model to the mixed diffusion coefficient model and then to the Knudsen diffusion coefficient model during the continuous healing process. Therefore, when calculating the diffusion coefficient of the unit cell, all the pores inside need to be taken into account and their updates should be paid attention to.

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

[0098] ;

[0099] in, is the Fickian diffusion coefficient of the pore channel, is the temperature, P is the gas pressure, is the molecular diffusion volume, is the molar mass of oxygen, is CO or CO2, for The molar mass of a substance;

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

[0101] ;

[0102] in, is the Knudsen diffusion coefficient of the pore channel, is the circumference of a circle, is the gas constant, is the temperature, is the molar mass of oxygen;

[0103] The mixed diffusion coefficient model of the pore channel is determined by the following formula:

[0104] ;

[0105] in, is the mixed diffusion coefficient of the pore channel, is the Fickian diffusion coefficient of the pore channel, is the Knudsen diffusion coefficient of the pore channel;

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

[0107] The gas diffusion coefficient model of the unit cell is determined by the following formula:

[0108] ;

[0109] in, is the gas diffusion coefficient of the unit cell, is the area of ​​the crack channel, is the area of ​​the pore channel, is the gas diffusion coefficient in the crack channel, is the gas diffusion coefficient of the pore channel, is the area of ​​the unit cell;

[0110] In the process of determining the oxygen concentration distribution in the channel at any time, the oxygen concentration corresponding to any time is determined by the following formula:

[0111] = ;

[0112] in, is the porosity, is the gas diffusion coefficient of the unit cell, is the reaction rate constant, is the reaction activation energy, is the reaction temperature, is the reaction rate, is the oxygen concentration, For time, Indicates the x direction of the coordinate axis;

[0113] S400, establishing oxidation models in different directions in the channel according to the oxidation process of the channel, setting channel parameter thresholds, the parameter thresholds including the characteristic length of the pore channel and the crack width of the crack channel, completing the oxidation calculation of the channel according to the oxidation model and the parameter thresholds, and obtaining the elastic modulus of the matrix and the fiber after oxidation;

[0114] Wherein, in the process of establishing oxidation models in different directions in the channel according to the oxidation process of the channel, the oxidation models in different directions in the channel include: an oxidation model of oxygen diffusion in the lateral direction of the crack channel and the oxidation model of the SiC matrix, an oxidation model of oxygen diffusion in the longitudinal direction of the crack channel and the oxidation model of the SiC matrix, an oxidation model of oxygen diffusion in the corrosion of the pyrolytic carbon layer and the reaction of the SiC matrix above the pyrolytic carbon layer and the reaction of the SiC fiber below; the parameter threshold includes the characteristic length of the pore channel and the crack width of the crack channel;

[0115] S500, obtaining the elastic modulus matrix of the unit cell and the stress condition of the unit cell according to the elastic modulus and boundary conditions of the fiber bundle composite material and the uniformity law, calculating the elastic modulus matrix of the overall component according to the periodic law, and using the failure criterion to judge the degradation of the unit fiber and the matrix when stretched or compressed in different directions, and re-judging the model failure by using the degraded parameters as new material properties, marking the failed units, and when the accumulation of failed units leads to overall aging of any part of the blade, the corresponding time at this time is the oxidation life of the blade, and if the blade has not failed, re-calculating the oxidation by using the degraded parameters as new material properties;

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

[0117] ;

[0118] in, is the axial elastic modulus of the oxidized fiber bundle composite material, is the half width of the crack after crack oxidation, L is the crack spacing, is the consumed length of the pyrolytic carbon interface, is the fiber debonding length, is the elastic modulus of the oxidized fiber, is the volume fraction of the oxidized fiber, is the average elastic modulus;

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

[0120] Example 3

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

[0122] S100, building a blade model of SiC / SiC composite materials;

[0123] In this step, the end part of the blade is selected. The external flow field is the high-temperature and high-pressure gas generated by the combustion of the combustion gas and air in the combustion chamber. Since the antioxidant performance of the blade needs to be calculated, only oxygen enters the blade to react with it, so the gas in the flow field is simplified to high-temperature and high-pressure air. The flow field domain is approximated by a rectangular parallelepiped. Import it into COMSOL to set the flow field flow-solid-thermal-mechanical coupling, define the gas inlet end and the gas outlet end of the fluid domain, the inlet velocity and temperature of the inlet end, and set the turbine speed to apply centrifugal force to it. The blade is the black part, and the flow field is the blue part, so as to calculate the size and distribution of the temperature field and force field in the blade;

[0124] S200, determining the channel type of the blade model, the channel type being a crack channel and a pore channel, and establishing a diffusion coefficient model of the gas in each channel;

[0125] In this step, the channel type selects crack channel and pore channel. 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 diffusion coefficient model. During the continuous healing process of the pore channel, the diffusion coefficient model is transformed from a Fick diffusion coefficient model to a mixed diffusion coefficient model, and then to a Knudsen diffusion coefficient model. The mixed diffusion coefficient model of the crack channel is determined by the following formula:

[0126] ;

[0127] Furthermore, the crack width is:

[0128] ;

[0129] in, is the mixed diffusion coefficient of the crack channel, R g is the gas constant, T is the temperature (calculated by the software), is the stress value, m and b0 are the Weibull modulus and Weibull matrix crack characteristic strength, m is 3, b0 is 155Mpa, is the average saturated crack spacing, taken as 0.235 mm, is the molecular diffusion volume, take 16.6, In the initial stage of the reaction, when diffusion affects the reaction rate, it is CO2. B Take 26.9cm 3 / mol, the reaction affects the reaction rate, is CO, at this time B Take 18.9cm 3 / mol, e is the crack width, e0 is the crack width at room temperature without any force acting on it, is the fiber elastic modulus, taken as 155 GPa, v m is the matrix volume fraction, which is taken as 0.65, , are the thermal expansion coefficients of the matrix and fiber, respectively, taking 4.5*10 -6 / ℃ and 3.2*10 -6 / ℃, is the difference between the ambient temperature and the crack healing temperature (calculated by the software), P is the gas pressure, M is the mixed molar mass of the two diffused gases, is the average molar mass, is the circumference of a circle, is the crack healing temperature, for The molar mass of a substance, is CO or CO2, in the above formula , , 、v m , There will be differences due to the different blade materials, and only the parameter values ​​of the example are given here;

[0130] The Knudsen diffusion coefficient model of the crack channel is determined by the following formula:

[0131] ;

[0132] in, Knudsen-type diffusion coefficient of the crack channel, is the density of the crack, is the crack healing temperature, is the circumference of a circle, is the molar mass of oxygen, e0 is the crack width at room temperature without any force acting on it, is the fiber elastic modulus, v m is the matrix volume fraction, , are the thermal expansion coefficients of the matrix and fiber, is the stress value, m and b0 are the Weibull modulus and Weibull matrix crack characteristic strength, is the difference between the ambient temperature and the crack healing temperature, R g is the gas constant, T is the temperature;

[0133] According to statistics, the pore channels in 2D SiC / SiC materials are mainly distributed in the matrix and between fiber bundles. When the unit cell model is established, the pores are distributed in the orthogonal region of the fiber bundles. Assuming that its shape is an elliptical cylinder, the pore characteristic length is counted after being discretized by threshold division of the CT image and fitted into an elliptical cylinder. The pore characteristic 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] Among them, x and y represent the values ​​of the horizontal and vertical coordinates of any point on the ellipse. is the length of the major semiaxis 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 of 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 length d of the crack, it is assumed to be equal to the width e of the crack;

[0139] It should be noted that the pores inside the unit cell have different initial diffusion modes due to their initial sizes. The same pore will have a different diffusion mode as the pore size changes over time: the diffusion coefficient model is transformed from the Fick diffusion coefficient model to the mixed diffusion coefficient model, and then to the Knudsen diffusion coefficient model during the continuous healing process. Therefore, when calculating the diffusion coefficient of the unit cell, all the pores inside need to be taken into account and their updates need to be paid attention to.

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

[0141] ;

[0142] in, is the Fickian diffusion coefficient of the pore channel, is the temperature, P is the gas pressure, is the molecular diffusion volume, is the molar mass of oxygen, is CO or CO2, for The molar mass of a substance;

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

[0144] ;

[0145] in, is the Knudsen diffusion coefficient of the pore channel, is the circumference of a circle, is the gas constant, is the temperature, is the molar mass of oxygen;

[0146] The mixed diffusion coefficient model of the pore channel is determined by the following formula:

[0147] ;

[0148] in, is the mixed diffusion coefficient of the pore channel, is the Fickian diffusion coefficient of the pore channel, is the Knudsen diffusion coefficient of the pore channel;

[0149] As described above, this embodiment determines that the channel type of the blade model is a crack channel and a pore channel. For the above different diffusion modes, whether it is a crack channel or a pore channel, the judgment criteria are:

[0150] For Knudsen diffusion, d < 0.1 ;

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

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

[0153] In the above diffusion mode judgment process, is the molecular mean free path, d is 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 pore elliptical cross section (the pore is considered to be an elliptical column in the fiber bundle scale). In this embodiment, the filling of the diffusion channel due to the oxidation of SiC to SiO2 is taken into account, and the d value is continuously updated and continuously compared with The values ​​are compared;

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

[0155] The gas diffusion coefficient model of the unit cell is determined by the following formula:

[0156] ;

[0157] in, is the gas diffusion coefficient of the unit cell, is the area of ​​the crack channel, is the area of ​​the pore channel (i.e. the area of ​​the ellipse), is the gas diffusion coefficient in the crack channel, is the gas diffusion coefficient of the pore channel, is the area of ​​the unit cell;

[0158] Furthermore, the mass transfer and reaction kinetics are combined to obtain the oxygen concentration distribution in the plain woven SiC / SiC composite material, so as to carry out the next oxidation simulation. Specifically, N units are divided along the thickness direction, and 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 diffused inflow and the amount of reaction gas, and the formula is as follows:

[0159] ;

[0160] because: ;

[0161] because: ;

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

[0163] = ;

[0164] in, is the porosity, is the gas diffusion coefficient of the unit cell, is the reaction rate constant, is the reaction activation energy, is the reaction temperature, is the reaction rate, is the oxygen concentration, For time, is the oxygen diffusion direction, is the flux of oxygen entering, is the crack channel diffusion coefficient;

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

[0166] S400, establishing oxidation models in different directions in the channel according to the oxidation process of the channel, setting channel parameter thresholds, the parameter thresholds including the characteristic length of the pore channel and the crack width of the crack channel, completing the oxidation calculation of the channel according to the oxidation model and the parameter thresholds, and obtaining the elastic modulus of the matrix and the fiber after oxidation;

[0167] In this step, in the process of establishing oxidation models in different directions in the channel according to the oxidation process of the channel, the oxidation models in different directions in the channel include: an oxidation model of oxygen diffusion in the lateral direction of the crack channel and the SiC matrix, an oxidation model of oxygen diffusion in the longitudinal direction of the crack channel and the SiC matrix, and an oxidation model of oxygen diffusion in the corrosion of the pyrolytic carbon layer and the reaction of the SiC matrix above the pyrolytic carbon layer and the SiC fiber reaction below; specifically:

[0168] See also Figure 1 , idealize the fiber bundle and the matrix wrapping the fiber bundle as a cylinder, draw a half-section diagram, Figure 1 In, r m 、r f are 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; lr is the length in the x direction that can achieve the maximum reaction; r c is the distance from the fiber axis to the matrix surface, e is the crack width, SiCMatrix represents SiC matrix, PyC Interphase represents pyrolytic carbon layer, SiC Fiber represents SiC fiber, and dx is the small change in the x direction;

[0169] According to the reaction kinetics and mass transfer equations and the law of conservation of mass, the amount of oxygen diffused into the crack is equal to the amount of oxygen consumed by 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 in the horizontal direction. After the pyrolytic carbon layer is consumed, it continues to diffuse and react with the SiC fiber.

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

[0171] ;

[0172] Furthermore, the thickness of SiO2 is:

[0173] ;

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

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

[0176] Further:

[0177] ;

[0178] in, is the distance from the substrate surface to the fiber center, are the parameters of the base parabola, is the parabolic index of the matrix, is the oxygen concentration, is the crack width, is the density of SiO2, is the molar mass of SiO2, is the thickness of SiO2, is the y-axis coordinate, is the initial oxygen concentration, for The molar mass of for The density of is the thickness of SiO2, for The thickness of is the diffusion coefficient, The oxygen required to generate 1 mol of SiO2 in the matrix, is the oxygen concentration corresponding to the parabolic constant under 0.1MPa pure oxygen conditions, is the circumference of a circle, It is the ratio of the product to oxygen in the reaction equation of carbon and oxygen.

[0179] Apply boundary conditions to the above equation: =c0(y=0);

[0180] The oxidation model of oxygen diffusing and reacting with the SiC matrix above the pyrolytic carbon layer and the SiC fiber below the pyrolytic carbon layer is determined by the following formula: ;

[0181] Among them, r m 、r f are the distances from the fiber axis to the lower oxidation boundary of the SiC matrix and the upper oxidation boundary of the SiC fiber, respectively. and is the distance from the fiber axis to the initial SiC matrix boundary and the initial upper boundary of the SiC fiber, is the single cell oxygen concentration, is the oxygen concentration, is the diffusion coefficient, is the ratio of the product to oxygen in the reaction equation of carbon and oxygen, The oxygen required to generate 1 mol of SiO2 in the matrix, is the density of SiO2, and are the matrix and fiber parabolic parameters, is the parabolic rate constant of the matrix, is the oxygen concentration corresponding to the parabola constant under 0.1MPa pure oxygen conditions, is the molar mass of SiO2, is the thickness of SiO2 after substrate oxidation, is the oxygen required to generate 1 mol of SiO2 in the fiber, is the parabolic rate constant of the fiber, is the thickness of SiO2 after fiber oxidation, is the circumference of a circle, Indicates the x direction of the coordinate axis;

[0182] The above formula has three boundary conditions, namely:

[0183] (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:

[0184] ;

[0185] Among them, r c is the distance from the fiber axis to the substrate surface, y represents the y direction of the coordinate axis, dz represents the thickness change, e is the crack width, r m 、r f are the distances from the fiber axis to the lower oxidation boundary of the SiC matrix and the upper oxidation boundary of the SiC fiber, respectively. Oxygen concentration, is the ratio of pi;

[0186] (2) The maximum distance lr that oxygen can reach when it reacts with pyrolysis carbon in the x direction. At this time, the amount of oxygen flowing in should be equal to the amount of oxygen consumed by the pyrolysis carbon reaction. If they are equal, then:

[0187] ;

[0188] in, is the ratio of the product to oxygen in the reaction equation of carbon and oxygen, is the gas concentration in a single cell, is the oxygen consumption of the pyrolysis reaction, is the diffusion coefficient of oxygen in the crack, is the oxygen concentration, x represents the x direction of the coordinate axis;

[0189] Oxygen consumption for pyrolysis carbon reaction Obtained by the following formula:

[0190] = = ;

[0191] in, is the oxygen consumption of the pyrolysis reaction, is the reaction rate constant, is the oxygen concentration, p is the reaction index, D is the diffusion coefficient of oxygen in the crack, is the gas constant, T is the temperature;

[0192] (3) At the interface between pyrolytic carbon and fiber matrix, x=0, y= At 0, the oxygen has completely reacted with the pyrolytic carbon and only reacted with the fiber to make it thicker, then: ;

[0193] in, is the x-direction length that oxygen can reach the maximum reaction in the pyrolytic carbon layer, is the diffusion coefficient of oxygen in the crack, is the oxygen concentration in the unit cell, is the ratio of the product to oxygen in the reaction equation of carbon and oxygen, is the circumference of a circle, is the oxygen concentration, is the density of SiO2, is the oxygen required to generate 1 mol of SiO2 in the fiber, is the fiber parabola parameter, r f is the distance from the fiber axis to the upper oxidation boundary of the SiC fiber, is the oxygen concentration corresponding to the parabola constant under 0.1MPa pure oxygen conditions, is the parabolic rate constant of the fiber, is the thickness of SiO2 after fiber oxidation, is the molar mass of SiO2;

[0194] When oxygen reacts with PyC along the x direction, the x-direction length that can reach the maximum reaction is defined as lr, then:

[0195] ;

[0196] Among them, lr is the length in the x direction that can achieve the maximum reaction, is the molar mass of pyrolytic carbon, is the density of pyrolytic carbon, is the oxygen concentration, is the initial oxygen concentration, is the ratio of the product to oxygen in the reaction equation of carbon and oxygen, is the diffusion coefficient, is the number of moles of carbon consumed by 1 mol of oxygen, For time, Indicates the x direction of the coordinate axis;

[0197] The above partial differential equations are brought into the distributed ordinary differential equations in COMSOL software for calculation, and the source term, mass coefficient and other parameters are set to solve and obtain lr;

[0198] Furthermore, in this embodiment, the oxidation is uniform in all directions around the pores, and the oxidation rate is controlled by the diffusion-reaction equation. After oxidation, the pores will be filled with SiO2 generated by the matrix, and the uniform oxidation is:

[0199] ;

[0200] in, is the ratio coefficient, is the length of the long semi-axis of the pore before oxidation, is the length of the short semi-axis of the pore before oxidation, is the thickness of SiO2 before oxidation, is the length of the long semi-axis of the pore after oxidation, is the length of the short semi-axis of the pore after oxidation, is the thickness of SiO2 after oxidation;

[0201] In the above ratio coefficient After that, the area of ​​the ellipse after shrinking (oxidation) and volume They are:

[0202] ;

[0203] h;

[0204] in, is the area of ​​the reduced ellipse, is the circumference of a circle, is the ratio coefficient, is the length of the long semi-axis of the pore before oxidation, is the length of the short semi-axis of the pore before oxidation, is the length of the long semi-axis of the pore after oxidation, is the length of the short semi-axis of the pore after oxidation, is the height of the pore;

[0205] Furthermore, the length of the long semi-axis of the oxidized pore and the length of the minor semiaxis Update and re-determine the pore diffusion type in subsequent cycles and calculate the new unit cell diffusion coefficient;

[0206] Furthermore, new porosity and crack width can be obtained:

[0207] New Porosity: ;

[0208] in, is the porosity after oxidation, is the porosity before oxidation, is the volume after oxidation, is the volume before oxidation;

[0209] New crack width: ;

[0210] in, is the crack width after oxidation, is the crack width before oxidation, is the thickness variation;

[0211] Furthermore, the changes in the pore morphology, porosity and crack width will cause the change in the diffusion coefficient, that is, the updated pore parameters, porosity and crack width, volume fraction and elastic modulus of the fiber and matrix are re-introduced into the above step S200, and the steps S200, S300 and S400 are continuously iterated until the set channel size critical value is reached, then it is determined that the oxygen channel is completely closed and the oxidation is completed. Please refer to Figure 7 , in the process of determining that the oxygen channel is completely closed, this can be achieved by calculating the concentration distribution of the gas (oxygen) in the channel. For example, Figure 7In the oxidation process, the shape parameters of the pores, such as porosity and crack width, change. According to the changes in the characteristic pore length d and the crack width e, when the set threshold is met, the calculation ends 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 changes), and the gas (oxygen) concentration distribution is recalculated. The calculation is cyclically repeated and returns to the initial state again. According to the changes in the characteristic pore length d and the crack width e, it is judged whether the set threshold is met until the calculation result is obtained after the threshold is met. In particular, the calculation will be stopped when the set time is reached but the threshold is not reached.

[0212] S500, according to the elastic modulus and boundary conditions of the fiber bundle composite material and the uniformity law, the elastic modulus matrix of the unit cell and the stress condition of the unit cell are obtained, the elastic modulus matrix of the overall component is calculated according to the periodic law, and the degradation of the unit fiber and the matrix when stretched or compressed in different directions is judged by the failure criterion, and the degraded parameters are used as new material properties to re-judge the model failure, and the failed units are marked. When the accumulation of failed units leads to the overall aging of any part of the blade, the corresponding time at this time is the oxidation life of the blade. If the blade has not failed, the degraded parameters are used as new material properties to re-calculate the oxidation; specifically:

[0213] First, calculate the modulus after oxidation, select the unit cell as the research object, and calculate the elastic modulus of the oxidized matrix and fiber according to the mixing law:

[0214] ;

[0215] ;

[0216] in, and are the moduli of the fiber and matrix after oxidation, and are the moduli of fiber and matrix before oxidation, E0 is the modulus of SiO2, and are the volume fractions of the matrix and fiber after oxidation, respectively. When cracks act as oxygen channels, the SiC matrix and fiber will be oxidized to SiO2, while when pores act as oxygen channels, only the oxidation of the matrix is ​​considered. Therefore, the volume fractions of the fibers after oxidation can be obtained respectively. and the volume fraction of the matrix after oxidation ;

[0217] Furthermore, the fiber volume fraction after oxidation is: ;

[0218] in, is the fiber volume fraction after oxidation, is the fiber volume after oxidation, is the volume increase after fiber oxidation. is the fiber volume before oxidation;

[0219] Furthermore, the volume fraction of the matrix after oxidation is: ;

[0220] in, is the volume fraction of the matrix after oxidation, is the volume of the matrix after oxidation, is the volume increment after the matrix is ​​oxidized, is the absolute value of the volume change after pore oxidation, is the volume of the matrix before oxidation;

[0221] The fiber bundle, the pyrolytic carbon layer and the outer matrix are treated as a cylinder, and these three parts are combined into a fiber bundle composite material;

[0222] Furthermore, the axial elastic modulus of the fiber bundle composite material is calculated:

[0223] ;

[0224] ;

[0225] Further, = / 2;

[0226] = + ;

[0227] Wherein, m, b0 are Weibull modulus and Weibull matrix crack characteristic strength, respectively, in this embodiment, the values ​​of m=3, b0=155Mpa, and the saturated average crack spacing L can be obtained by experimental observation of matrix crack spacing. sat 0.235mm, is the axial elastic modulus of the oxidized fiber bundle composite material, is the half width of the crack after crack oxidation, L is the crack spacing, is the consumed length of the pyrolytic carbon interface, is the fiber debonding length, is the elastic modulus of the oxidized fiber, is the volume fraction of the oxidized fiber, is the volume fraction of the matrix after oxidation, The elastic modulus of the matrix after oxidation, is the average elastic modulus, is the crack width after oxidation;

[0228] get After that, The other components in the elastic modulus matrix of the fiber bundle composite material can be obtained by proportional reduction. The specific reduction process is:

[0229] ;

[0230] ;

[0231] in, is the elastic modulus of the fiber bundle composite material in the i direction after elastic oxidation, is the axial elastic modulus of the fiber bundle composite material after elastic oxidation, is the axial elastic modulus of the fiber bundle composite material before oxidation, is the elastic modulus of the fiber bundle composite material in the i direction before oxidation, is the shear modulus of elasticity in all directions of the oxidized fiber bundle composite material, is the shear modulus of elasticity in all directions of the fiber bundle composite material before oxidation;

[0232] According to the oxidation, the pore parameters of the elliptical cylinder after oxidation are brought into the unit cell to update the unit cell model before oxidation, thereby establishing the unit cell model after actual oxidation.

[0233] The elastic modulus matrix of the oxidized fiber bundle composite material is taken as the yarn material parameter in the unit cell and then brought back to the unit cell for calculation. The boundary conditions are applied and homogenized by the finite element method in COMSOL and MATLAB: First, the unit cell model is discretized into multiple units, the unit cell model is homogenized and mandatory boundary conditions are applied to it to calculate the force condition and elastic modulus matrix of each unit in the unit cell. Then, the unit failure is judged according to the failure criterion. The failure judgment process is detailed in Figure 8 ,exist Figure 8 In the calculation, the oxidation calculation is performed first, and then the residual elastic modulus of the fiber and matrix is ​​calculated. After calculating the micro-model mechanics, it is determined whether the unit has failed. When it fails, it is deducted (reduced) according to the coefficient, and the micro-model mechanics is calculated again to determine whether the component has failed. If it fails, the construction life is output to complete the calculation process. If it does not fail, it continues to return to the starting step to repeat the oxidation calculation. It should be noted that in Figure 8 In the process, when it is judged that the unit has not failed, the microscopic model mechanics is directly calculated without the need for the coefficient loss process.

[0234] Furthermore, in this embodiment, the failure criterion of the unit is the Hashin criterion, and the elastic modulus degradation method of the instantaneous unloading model is used to degrade the fiber and matrix of the unit. The failure criterion and coefficient reduction method are as follows:

[0235] (1) When longitudinally stretched ( , is the normal stress of the unit in the x-direction):

[0236] ;

[0237] Among them, X T is the tensile strength in the fiber direction, is the stress value, ij is the component in the flexibility matrix, Through the elastic modulus get, is a coefficient between 0 and 1;

[0238] (2) When stretching horizontally ( , The element is subjected to positive stress in the y direction, The element is subjected to positive stress in the z direction):

[0239] ;

[0240] Among them, Y T is the tensile strength in the matrix direction, ij is the stress value other than the normal stress value in the x, y and z directions, ij is the component in the flexibility matrix;

[0241] (3) When the horizontal compression , The element is subjected to positive stress in the y direction, The element is subjected to positive stress in the z direction):

[0242] ;

[0243] Among them, Y C is the compressive strength in the matrix direction, is the stress value, ij is the component in the flexibility matrix, ij is the stress value in other directions; ij , i=1,2,3; j=1,2,3; for ij , i=1, 2, 3, that is ii（i=1，2，3） is the normal stress value in the x, y and z directions;

[0244] (4) When longitudinally compressed ( <0, The element is subjected to positive stress in the x-direction):

[0245] ;

[0246] Among them, X C is the compressive strength in the fiber direction, is the normal stress of the unit in the x direction;

[0247] Furthermore, in the process of degradation of the fiber and the matrix, as long as any expression among longitudinal tension, transverse tension, transverse compression and transverse compression is satisfied, the corresponding unit can be considered as failed and the unit will be marked;

[0248] Furthermore, the degraded parameters will be used as new material unit properties to re-judge the model failure; specifically:

[0249] When the base element fails:

[0250] ;

[0251] ;

[0252] ;

[0253] ;

[0254] ;

[0255] ;

[0256] When a fiber unit fails:

[0257] ;

[0258] ;

[0259] ;

[0260] ;

[0261] ;

[0262] ;

[0263] In the above process, during the output process, COMSOL uses the degraded parameters as new material properties to re-judge the model failure and 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 life of the blade.

[0264] It should be noted that all parameters in the above process of this embodiment should be placed in the software (the above COMSOL software), all variables are used as global variables, initial values ​​are used as global constants, and partial differential equations are calculated using the partial differential equation solving module in the software. Further, based on the above technical solution of the present invention, an oxidation application program can be further designed, and the above process of this embodiment can be completed using the oxidation application program; for example, please refer to Fig. 9 , the development flow chart of oxidation application is as follows Fig. 9 As shown, specifically, according to the blade model, solid mechanics, solid and solid heat transfer, fluid mechanics, and oxidation numerical analysis are performed after modeling. When performing the above analysis, material parameters and environmental parameters need to be assigned. In order to perform numerical solution, the analysis area needs to be meshed. After assigning parameters and meshing, multi-physics field coupling solution and oxidation numerical solution are performed, and then the solution results are analyzed to find the laws in the material oxidation process. According to the analysis results and the laws found, the oxidation application is developed, that is, software development, which includes multiple links such as designing algorithms, writing codes, and testing software, and finally the above material oxidation application with practical application value is developed; as another example, please refer to Figure 2 , oxidation applications may include the following main parts:

[0265] Parameter setting area: used to input material properties and boundary conditions. Users can set relevant physical parameters. The present 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 rotation speed of the blade when working. The present invention uses sliders and knobs to control the gas temperature, gas speed, and rotation speed. The user only needs to slide the slider to control the temperature and speed. Here, the temperature is set within 900~1600K, and the step size that can be accurately adjusted is 1K; the speed is set to 0~1000m / s, and the precise adjustment can be 1m / s. The knob can be used to adjust the speed from 0 to 30,000 rpm, with an interval of 100 rpm. Finally, the present invention is provided with a time step button, which can calculate the oxidation situation under the set time. Sliders and knobs will change graphically in real time based on the values ​​set by the user.

[0266] Simulation control area: including drawing geometry, meshing, starting calculation, drawing temperature field, drawing fluid velocity field, drawing stress distribution, drawing oxidation product distribution map, drawing crack width distribution, drawing failure cloud map. Button users can control the simulation process through simple operations and monitor the simulation progress in real time.

[0267] Result display area: can display real-time simulation results. Users can display simulation results through different viewing angles and color maps for easy observation and analysis. Currently, the view can zoom in and out, zoom to window size, switch to default view, switch to plane view (supports XY, YZ, ZX three planes), enable / disable wireframe rendering, enable / disable grid, enable display coordinate system, and can also realize automatic result screenshot saving and printing functions.

[0268] Calculation example

[0269] Using the above oxidation application program, the inlet velocity at the inlet end is set to 500m / s, the inlet temperature is set to 1200K, and the speed is selected to 17000r / min. The calculated flow field velocity field, temperature field, and force field distribution diagram are as follows: Figure 3 shown. Figure 3 In the figure, the top two figures are flow fields, the lower left figure is the temperature field, and the lower right figure is the force field.

[0270] Figure 4 The crack width distribution diagrams for 200h, 500h, 750h, and 1000h show that as oxidation continues, the crack channel is continuously filled, the crack width continues to decrease, and the oxidation rate is fast in places with large crack width, high temperature, and high gas concentration (near the gas inlet). The faster the oxidation rate, the faster the crack width decreases, and the smaller the crack width. As the crack width decreases, it becomes more difficult for oxygen to enter the interior through the channel, and the equivalent diffusion coefficient continues to decrease, causing the subsequent crack width to decrease more slowly. The crack density in the first 200h changes by an order of magnitude, while the subsequent 800h changes by the same order of magnitude and the rate of change decreases. Over time, the difference in crack width on the entire outer surface becomes smaller, because the oxidation rate in places where oxidation starts quickly decreases or is even surpassed by places where oxidation starts slowly. As the crack density continues to decrease, the way gas diffuses in the crack will also change.

[0271] Figure 5 The distribution diagram of the oxidation product thickness at 200h, 500h, 750h, and 1000h respectively can represent the distribution of oxidation products. Although the outer surface has obvious signs of oxidation at 200h, the thickness of the oxidation product on the side away from the gas inlet is obviously greater than the thickness on the side away from the gas inlet, and it can be seen that the thickness of the oxidation product increases faster at the beginning, and then the thickness change rate decreases as the channel is filled.

[0272] Figure 6 The unit failure distribution diagram at the time of 50, 100, 200, 500, 800, and 1000 h is shown in Figure 2. The failed unit is 1. Figure 6The red area represents failure, which helps to believe that most of the blades have failed at 500 hours, so the predicted life is 500 hours.

[0273] In the description of the above embodiments, specific features, structures, materials or characteristics may be combined in a suitable manner in any one or more embodiments or examples.

[0274] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for predicting the oxidation life of SiC / SiC composite blades, characterized in that: include: Establish a blade model of SiC / SiC composite materials; Determine the channel type of the blade model and establish a diffusion coefficient model of the gas in each channel; 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; According to the oxidation process of the channel, an oxidation model in different directions in the channel is established, a channel parameter threshold is set, the oxidation calculation of the channel is completed according to the oxidation model and the parameter threshold, and the elastic modulus of the matrix and the fiber after oxidation is obtained; The elastic modulus matrix of the fiber bundle composite is calculated based on the elastic moduli of the matrix and the fiber after oxidation; The elastic modulus matrix of the unit cell is obtained according to the elastic modulus of the fiber bundle composite material, and the stress condition of the unit is obtained according to the stress condition of the unit cell. The degradation of the fiber and the matrix when stretched or compressed in different directions in the unit is judged according to the elastic modulus matrix and the failure criterion. When the accumulation of failed units leads to overall aging of any part of the blade, the corresponding time at this time is the oxidation life of the blade.

2. The method for predicting oxidation life of SiC / SiC composite blades according to claim 1, characterized in that: The elastic modulus matrix of the unit cell is obtained according to the elastic modulus of the fiber bundle composite material, the stress condition of the unit is obtained according to the stress condition of the unit cell, and the degradation of the fiber and the matrix when stretched or compressed in different directions in the unit is judged according to the elastic modulus matrix and the failure criterion, including: According to the obtained unit stress conditions, the failure criteria are used to determine the degradation of the fiber and matrix in the unit when stretched or compressed in different directions. The failed units are marked to determine the failure of the macroscopic component. If the macroscopic component has not failed, the degraded parameters are used as new material properties for recalculation.

3. The method for predicting oxidation life of SiC / SiC composite blades according to claim 2, characterized in that: The channel types include crack channels and pore channels; and / or, The diffusion coefficient models of the gas in each channel include a mixed diffusion coefficient model, a Knudsen diffusion coefficient model and a Fick diffusion coefficient model.

4. The method for predicting oxidation life of SiC / SiC composite blades according to claim 3, characterized in that: In the process of continuous healing of the crack channel, the diffusion coefficient model of the crack channel is transformed from a mixed diffusion coefficient model to a Knudsen diffusion coefficient model; and / or, The mixed diffusion coefficient model of the crack channel is determined by the following formula: ； in, is the mixed diffusion coefficient of the crack channel, R g is the gas constant, T is the temperature, is the stress value, m and b0 are the Weibull modulus and Weibull matrix crack characteristic strength, is the average saturated crack spacing, is the molecular diffusion volume, e is the crack width, e0 is the crack width at room temperature without any force acting on it, is the fiber elastic modulus, v m is the matrix volume fraction, , are the thermal expansion coefficients of the matrix and fiber, is the difference between the ambient temperature and the crack healing temperature, P is the gas pressure, M is the mixed molar mass of the two diffused gases, is the average molar mass, is the circumference of a circle, is the crack healing temperature, for The molar mass of a substance, is CO or CO2.

5. The method for predicting oxidation life of SiC / SiC composite blades according to claim 4, characterized in that: The Knudsen-type diffusion coefficient model of the crack channel is determined by the following formula: ； in, Knudsen-type diffusion coefficient of the crack channel, is the density of the crack, is the crack healing temperature, is the circumference of a circle, is the molar mass of oxygen, e0 is the crack width at room temperature without any force acting on it, is the fiber elastic modulus, v m is the matrix volume fraction, , are the thermal expansion coefficients of the matrix and fiber, is the stress value, m and b0 are the Weibull modulus and Weibull matrix crack characteristic strength, is the difference between the ambient temperature and the crack healing temperature, R g is the gas constant and T is the temperature.

6. The method for predicting oxidation life of SiC / SiC composite blades according to claim 5, characterized in that: During the continuous healing process of the pore channel, the diffusion coefficient model is transformed from a Fick-type diffusion coefficient model to a mixed diffusion coefficient model, and then to a Knudsen-type diffusion coefficient model; and / or, The Fickian diffusion coefficient model of the pore channel is determined by the following formula: ； in, is the Fickian diffusion coefficient of the pore channel, is the temperature, P is the gas pressure, is the molecular diffusion volume, is the molar mass of oxygen, is CO or CO2, for The molar mass of a substance.

7. The method for predicting oxidation life of SiC / SiC composite blades according to claim 6, characterized in that: The Knudsen diffusion coefficient model of the pore channel is determined by the following formula: ； in, is the Knudsen diffusion coefficient of the pore channel, is the circumference of a circle, is the gas constant, is the temperature, is the molar mass of oxygen; and / or, The mixed diffusion coefficient model of the pore channel is determined by the following formula: ； in, is the mixed diffusion coefficient of the pore channel, is the Fickian diffusion coefficient of the pore channel, is the Knudsen diffusion coefficient of the pore channel; and / or, The gas diffusion coefficient model of the unit cell is determined by the following formula: ； in, is the gas diffusion coefficient of the unit cell, is the area of ​​the crack channel, is the area of ​​the pore channel, is the gas diffusion coefficient in the crack channel, is the gas diffusion coefficient of the pore channel, is the area of ​​the unit cell.

8. The method for predicting oxidation life of SiC / SiC composite blades according to claim 7, characterized in that: In the process of determining the oxygen concentration distribution in the channel at any time, the oxygen concentration corresponding to any time is determined by the following formula: = ； in, is the porosity, is the gas diffusion coefficient of the unit cell, is the reaction rate constant, is the reaction activation energy, is the reaction temperature, is the reaction rate, is the oxygen concentration, For time, Indicates the x direction of the coordinate axis.

9. The method for predicting oxidation life of SiC / SiC composite blades according to claim 8, characterized in that: In the process of establishing oxidation models in different directions in the channel according to the oxidation process of the channel, the oxidation models in different directions in the channel include: Oxidation model of oxygen diffusion in the lateral direction of the crack channel and the SiC matrix, oxidation model of oxygen diffusion in the longitudinal direction of the crack channel and the SiC matrix, oxidation model of oxygen diffusion in the eroded pyrolytic carbon layer and the reaction of the SiC matrix above the pyrolytic carbon layer and the SiC fiber below; and / or, The parameter thresholds include the characteristic length of the pore channel and the crack width of the crack channel.

10. The method for predicting oxidation life of SiC / SiC composite blades according to claim 9, characterized in that: The elastic modulus of the fiber bundle composite material in the unit cell is determined by the following formula: ； in, is the axial elastic modulus of the oxidized fiber bundle composite material, is the half width of the crack after crack oxidation, L is the crack spacing, is the consumed length of the pyrolytic carbon interface, is the fiber debonding length, is the elastic modulus of the oxidized fiber, is the volume fraction of the oxidized fiber, is the average elastic modulus.

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