CN113408181B - Method for predicting oxidation life of ceramic matrix composite structure - Google Patents
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- 238000007254 oxidation reaction Methods 0.000 title claims abstract description 88
- 230000003647 oxidation Effects 0.000 title claims abstract description 83
- 239000011153 ceramic matrix composite Substances 0.000 title claims abstract description 71
- 238000000034 method Methods 0.000 title claims abstract description 50
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 36
- 239000001301 oxygen Substances 0.000 claims abstract description 36
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 31
- 238000009940 knitting Methods 0.000 claims abstract description 11
- 230000008569 process Effects 0.000 claims abstract description 11
- 230000006378 damage Effects 0.000 claims abstract description 8
- 238000000265 homogenisation Methods 0.000 claims abstract description 7
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- 235000010948 carboxy methyl cellulose Nutrition 0.000 claims abstract 14
- 229920006184 cellulose methylcellulose Polymers 0.000 claims abstract 14
- 238000012710 chemistry, manufacturing and control Methods 0.000 claims abstract 14
- 239000011159 matrix material Substances 0.000 claims description 39
- 239000000835 fiber Substances 0.000 claims description 37
- 239000000463 material Substances 0.000 claims description 24
- 239000002131 composite material Substances 0.000 claims description 14
- 238000009792 diffusion process Methods 0.000 claims description 13
- 230000008878 coupling Effects 0.000 claims description 7
- 238000010168 coupling process Methods 0.000 claims description 7
- 238000005859 coupling reaction Methods 0.000 claims description 7
- 238000009941 weaving Methods 0.000 claims description 7
- 239000007789 gas Substances 0.000 claims description 6
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 claims description 5
- 229910004298 SiO 2 Inorganic materials 0.000 claims description 4
- 238000006243 chemical reaction Methods 0.000 claims description 4
- 230000000737 periodic effect Effects 0.000 claims description 4
- 239000011148 porous material Substances 0.000 claims description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 3
- 229920001410 Microfiber Polymers 0.000 claims description 3
- 229910052799 carbon Inorganic materials 0.000 claims description 3
- 239000003658 microfiber Substances 0.000 claims description 3
- 238000002156 mixing Methods 0.000 claims description 3
- 230000000750 progressive effect Effects 0.000 claims description 3
- 239000012495 reaction gas Substances 0.000 claims description 3
- 239000000126 substance Substances 0.000 claims description 3
- 238000012935 Averaging Methods 0.000 claims description 2
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- 230000001105 regulatory effect Effects 0.000 description 15
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- 230000001186 cumulative effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000004792 oxidative damage Effects 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
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Abstract
The invention relates to a method for predicting the oxidation life of a ceramic matrix composite structure, which comprises the following steps: establishing a macroscopic model of the CMCs structural member according to working conditions and calculating temperature and stress distribution in the CMCs structural member through finite elements; calculating the oxygen concentration distribution inside each unit in the CMCs structural member based on a homogenization method; calculating microscopic oxidation morphology parameters inside each unit in the CMCs structural member based on the oxidation dynamics model; calculating the mesomechanical performance parameters of each unit of the CMCs structural member; calculating the mechanical parameters of each knitting unit; the mechanical parameters include cell residual strength; determining stress distribution of the oxidized macroscopic structure; the oxidation life of the structure is predicted. The invention simulates the evolution process of oxidation damage and unit failure of the structural member from the angles that each region in the structural member is oxidized to different degrees under the complex environment, and realizes the prediction of the oxidation life of the CMCs structure level under different working conditions.
Description
Technical Field
The invention belongs to the field of ceramic matrix composite materials, and particularly relates to a method for predicting the oxidation life of a ceramic matrix composite structure.
Background
Ceramic Matrix Composites (CMCs) have broad application prospects in the field of high-performance aeroengine hot-end components due to excellent mechanical properties at high temperatures. A great amount of oxidizing gas exists in the service environment of the hot end component, and the CMCs structure can generate oxidation reaction with oxygen at high temperature to fail. Predicting the oxidation life of CMCs structural members of an engine is one of the important issues that CMCs structural designs need to address.
In order to reliably apply the ceramic matrix composite to engineering practice, many scholars at home and abroad develop researches on life prediction of the ceramic matrix composite. Currently, most of the existing methods are fatigue life prediction, such as: the fatigue life prediction method (CN 105760605A) of the ceramic matrix composite with the complex woven structure discloses a prediction method of a fatigue life curve of the ceramic matrix composite with the complex woven structure, the fatigue life prediction method (CN 111507038A) of the ceramic matrix composite with the complex woven structure discloses a prediction method of the fatigue life of a ceramic matrix composite structural member under the high-temperature and variable-load environment, and the prediction research on the oxidation life of the structural grade of the ceramic matrix composite under the environment of 'heat-force-oxygen' coupling is not disclosed.
The traditional method is mainly based on a microscopic model to study the fatigue life of CMCs material level and structural level, but CMCs structural members face complex service environments in aeroengines, including high temperature, stress, oxidation and other factors. The literature indicates that oxidative damage to CMCs is one of the important factors affecting its strength and life. Therefore, it is necessary to provide a method for predicting the oxidation life of a ceramic matrix composite structure to reflect the problem of the influence of the distribution of oxidation damage on the strength of the structural member, so as to predict the oxidation life of the structural member of CMCs.
Disclosure of Invention
The invention provides a method for predicting the oxidation life of a ceramic matrix composite structure, aiming at the blank in the technical field and the defects in the prior art, and aims to solve the problem of predicting the oxidation life of the ceramic matrix composite structure in a high-temperature-stress-oxidation coupling environment.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
an oxidation life prediction method of a ceramic matrix composite structure comprises the following steps:
step 1: establishing a macroscopic model of the CMCs structural member according to working conditions and calculating temperature and stress distribution in the CMCs structural member through finite elements;
step 2: according to the temperature and stress distribution in the step 1, calculating the oxygen concentration distribution inside each unit in the CMCs structural member based on a homogenization method;
step 3: according to the calculation result of the oxygen concentration distribution in the step 2, calculating the microscopic oxidation morphology parameters inside each unit in the CMCs structural member based on the oxidation dynamics model;
step 4: calculating the mesomechanical performance parameters of each unit of the CMCs structural member according to the mesooxidative morphology parameters obtained in the step 3;
step 5: calculating the mechanical property parameters of each woven unit cell according to the mesoscopic mechanical property parameters obtained in the step 4; the mechanical property parameters comprise unit residual strength;
step 6: determining stress distribution after oxidation of a macroscopic structure, redefining mechanical property parameters of the woven single cells obtained in the step 5 as material parameters after oxidation of each unit in a macroscopic model, and performing finite element calculation on the macroscopic model of the CMCs structural member in a 'heat-force-oxygen' coupling environment again to obtain stress distribution and unit stress in the oxidized structure;
step 7: predicting the oxidation life of the structural member, comparing the unit stress obtained in the step 6 with the unit residual strength obtained in the step 5, if the unit stress is larger than the unit residual strength, considering the unit to be invalid, if the invalid unit is accumulated to form a through invalid unit group, considering the structure to be invalid, otherwise, increasing the oxidation time to continuously adjust the diffusion-oxidation process in the structural member, repeating the steps until the structure is invalid, wherein the oxidation time is the natural oxidation life of the CMCs structure under the working condition.
Further, in the step 2, according to the law of conservation of energy, the relationship between diffusion and oxidation kinetics in the oxidation process is described by using a partial differential equation as follows:
wherein phi is the porosity of CMCs, c A Is oxygen concentration, D eff Weaving equivalent diffusion coefficient of unit cell for each unit, R A For the reaction rate, x is the diffusion distance, t is the time, and the above equation is solved by finite difference method to obtain the oxygen concentration of each unit in the structure.
Further, taking the calculation result in the step 2 as the oxygen concentration in the pores of the unit internal braid cells; part of the oxygen propagates to the fiber interface through the matrix cracks, accompanied by oxidation of the matrix at the crack channels to SiO 2 The oxide layer and PyC interface is consumed, and the oxide layer thicknesses of the matrix and the fiber are respectively expressed as:
wherein z is m 、z f The oxide layer thickness of the matrix and the oxide layer thickness of the fiber are shown respectively,respectively represent parabolic rate constants of the matrix and the component materials of the fiber under 100KPa pure oxygen in oxidation, c * Represents the oxygen concentration, p, at oxidation of a constituent material under 100kPa pure oxygen m 、p f Respectively the indexes of the matrix and the fiber; pyC interface consumption length l r The following formula is used for calculation:
wherein b is the number of moles of carbon consumed per mole of oxygen,is a mixed diffusion coefficient, M C Is C molar mass ρ C For C density->Representing the oxygen concentration gradient within the crack, c 0 For the crack tip oxygen concentration, α is the ratio of the amounts of the substances of the reaction gas to the product gas.
Further, in the step 4, the axial residual stiffness E of the fiber bundle composite material after oxidation is according to a micro-mechanics model 1 ' is:
wherein l d Length d is the interfacial debonding length e Is half of the width of the crack of the matrix, L is the average crack spacing of the matrix, v f For the fiber volume content, E' f 、E' m 、E' c Respectively representing the elastic modulus of the oxidized fiber, matrix and fiber bundle composite material, and calculating by using a mixing ratio formula:
wherein E is f 、E m Initial modulus of elasticity, E, of the fibers and matrix, respectively o Is an oxidation product SiO 2 Modulus of elasticity, v m V for initial matrix volume content f (x)、v m (x) The volume contents of the fiber and the matrix at a certain position x in the oxidation zone are respectively expressed, and the residual rigidity of the fiber bundle composite material after oxidation in the rest direction is calculated according to the equal proportion folding method.
Further, in the step 5, mechanical performance parameters of the micro fiber bundle composite material are used as material parameters of yarn units in unit cell dimensions of a macroscopic model, a standard homogenization process is adopted, and macroscopic stress of the knitting units is defined by a volume average methodMacroscopic strain->
Where V is the unit cell volume, σ and ε are the microscopic stresses and strains of the units in the unit cell model,
according to the elastic constitutive relation of the materials, applying 6 groups of periodic boundary conditions to the weaving unit, carrying out finite element analysis, calculating stress and strain distribution in the periodic boundary conditions, combining a calculation formula of macroscopic stress and macroscopic strain to obtain stress-strain responses of a plurality of groups of materials, and finally solving a flexibility matrix [ S ] ij ]：
According to the definition of the compliance matrix:
wherein E represents elastic modulus, G represents shear modulus, v represents Poisson's ratio, subscripts 1, 2, 3 respectively correspond to warp, weft and thickness directions of the knitting unit, equivalent elastic modulus of the knitting unit in each direction is calculated according to the group of formulas, and residual strength of the knitting unit is calculated through progressive damage analysis.
Further, based on the equal strain assumption and stiffness averaging method, the elastic constitutive relationship of the material is expressed as:
in the formula, subscripts 1, 2, 3 correspond to the warp direction, the weft direction, and the thickness direction in the knitting unit, respectively.
According to the oxidation life prediction method of the ceramic matrix composite structure, local material performance degradation caused by nonuniform oxidation degree in the CMCs structure under the 'heat-force-oxygen' coupling environment is considered, and the processes of oxidation failure and strength degradation of the internal units of the CMCs structure after reaction diffusion interaction are simulated based on a diffusion theory and an oxidation dynamics theory, so that a reference basis is provided for CMCs structure design. The invention simulates the evolution process of oxidation damage and unit failure from the angles that each area inside the structural member is oxidized to different degrees under the complex environment, integrates the coupling evolution of gas concentration distribution, component material consumption oxidation and mechanical property degradation in the CMCs, and realizes the oxidation life prediction of the CMCs structure level under different working conditions.
Drawings
FIG. 1 is a flow chart of the method of the present invention.
Figure 2 is a graph of the cumulative process of failure cells of CMCs conditioning sheet models in a "heat-force-oxygen" coupled environment.
Detailed Description
The invention will now be described in further detail with reference to the accompanying drawings.
Based on the initial conditions of the actual working conditions, taking a CMCs regulating sheet as an example, the oxidation life of the CMCs regulating sheet is analyzed by adopting the method.
Step 1: and establishing a macroscopic geometric model of the regulating plate, applying linearly-changing temperature and pressure load on the inner side of the regulating plate, applying constant load on the outer side of the regulating plate, and calculating temperature and stress distribution in the regulating plate through finite elements.
Step 2: and (3) determining the oxygen concentration at each point of the regulating sheet based on a homogenization method according to the temperature field and the stress field in the step (1). The relationship between diffusion and oxidation kinetics during oxidation can be described by partial differential equations according to the law of conservation of mass:
wherein phi is the porosity of CMCs, c A Is oxygen concentration, t is time, D eff Weaving equivalent diffusion coefficient of unit cell for each unit, R A Is the reaction rate. And solving the above equation by adopting a finite difference method to obtain the oxygen concentration at each point inside the CMCs regulating sheet along the gas transmission direction.
Step 3: and (3) according to the concentration calculation result in the step (2), calculating the oxidation morphology at each point in the regulating sheet based on the oxidation kinetic model. Wherein, the calculation result of the step 2 is taken as the oxygen concentration in the pores of the unit internal weaving unit, and the yarn matrix around the pores is uniformly oxidized at first. Another part of oxygen is diffused to the fiber interface through the crack of the matrix, and SiO is generated along with the oxidation of the matrix and the fiber at the crack channel 2 The oxide layer and the PyC interface are consumed. Wherein, the thickness of the oxide layer of the matrix and the fiber is expressed as:
wherein z is m 、z f The oxide layer thickness of the matrix and the oxide layer thickness of the fiber are shown respectively,respectively represent parabolic rate constants of the matrix and the component materials of the fiber under 100KPa pure oxygen in oxidation, c * For oxygen concentration, p m 、p f The indices of matrix and fiber, respectively. PyC interface consumption length l r The calculation can be performed with the following formula:
wherein b is the number of moles of carbon consumed per mole of oxygen,is a mixed diffusion coefficient, M C Is C molar mass ρ C For C density->Representing the oxygen concentration gradient within the crack, c 0 For the crack tip oxygen concentration, α is the ratio of the amounts of the substances of the reaction gas to the product gas.
Step 4: and (3) calculating the degradation condition of the microscopic mechanical property at each point according to the microscopic oxidation morphology parameters at each point obtained by calculation in the step (3). According to the mesomechanical model, the axial residual rigidity of the fiber bundle composite material after oxidation is as follows:
wherein, I d Length d is the interfacial debonding length e Is half of the width of the crack of the matrix, L is the average crack spacing of the matrix, v f For the volume content of the fiber, E f '、E c ' represents the elastic modulus of the oxidized fiber and fiber bundle composite material respectively, and can be calculated by using a mixing rate formula:
the residual stiffness of the fiber bundle composite material after oxidation in the rest direction can be calculated according to an equal proportion folding method. Wherein, the initial material parameters of the fiber bundle composite are listed in the following table:
TABLE 1 parameters of SiC/SiC fiber bundle composites
Step 5: and (3) calculating the mechanical property degradation condition of the woven unit cells at each point of the regulating sheet model according to the mesoscopic mechanical property parameters obtained by calculation in the step (4). Taking the mechanical property calculation result of the micro fiber bundle composite material as the material parameter of the yarn unit in the unit cell scale of the macro regulating sheet model, adopting a standard homogenization process, and defining the macro stress and the macro strain of the weaving unit cell by a volume average method:
solving a flexibility matrix according to the elastic constitutive relation of the material:
definition by the compliance matrix:
ν 12 ＝-S 12 ·E 1 ,ν 13 ＝-S 13 ·E 1 ,ν 23 ＝-S 23 ·E 2
the equivalent elastic modulus of each single cell in each direction can be calculated, and the residual strength of each single cell can be calculated through progressive damage analysis.
Step 6: the stress distribution of the CMCs conditioning sheet after oxidation was determined. And (3) redefining the mechanical parameter calculation result of the woven unit in the step (5) as the oxidized material parameters of each unit in the macroscopic model, and carrying out finite element calculation on the macroscopic model of the CMCs regulating sheet under the working condition of the example again to obtain the stress distribution condition in the oxidized regulating sheet.
Step 7: the oxidation life of CMCs regulator sheets is predicted. And (3) performing failure judgment on each unit in the regulating sheet according to the maximum stress failure criterion, comparing the unit stress calculated in the step (6) with the unit residual strength calculated in the step (5), if the unit stress exceeds the unit residual strength, considering the unit to fail, marking out failed units, and recording the number of the failed units. If the failure units accumulate to form a penetrating failure unit group, the structure is considered to be invalid; otherwise, increasing the oxidation time, continuing the oxidation process in the regulating sheet, and repeating the steps until the structure fails. Fig. 2 shows a damage accumulation process of a failure unit caused by strength degradation after oxidation of a material in the CMCs conditioner sheet, wherein the failure unit of the CMCs conditioner sheet model is continuously expanded along the axial direction and the thickness direction along with the increase of oxidation time, when the oxidation time reaches 1200h, the failure unit almost covers the whole plane, and the increase rate of the failure unit becomes very small thereafter, so that the oxidation life of the CMCs conditioner sheet after being subjected to coupling damage such as 'high temperature-stress-oxidation' in this example can be predicted to be 1200h. In this embodiment, the oxidation life of CMCs structural members may be predicted by analyzing the structural members of different geometric models under different conditions according to given temperature and load conditions.
The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above examples, and all technical solutions belonging to the concept of the present invention belong to the protection scope of the present invention. It should be noted that modifications and adaptations to the invention without departing from the principles thereof are intended to be within the scope of the invention as set forth in the following claims.
Claims (6)
1. The method for predicting the oxidation life of the ceramic matrix composite structure is characterized by comprising the following steps of:
step 1: establishing a macroscopic model of the CMCs structural member according to working conditions and calculating temperature and stress distribution in the CMCs structural member through finite elements;
step 2: according to the temperature and stress distribution in the step 1, calculating the oxygen concentration distribution inside each unit in the CMCs structural member based on a homogenization method;
step 3: according to the calculation result of the oxygen concentration distribution in the step 2, calculating the microscopic oxidation morphology parameters inside each unit in the CMCs structural member based on the oxidation dynamics model;
step 4: calculating the mesomechanical performance parameters of each unit of the CMCs structural member according to the mesooxidative morphology parameters obtained in the step 3;
step 5: calculating the mechanical property parameters of each woven unit cell according to the mesoscopic mechanical property parameters obtained in the step 4; the mechanical property parameters comprise unit residual strength;
step 6: determining stress distribution after oxidation of a macroscopic structure, redefining mechanical property parameters of the woven single cells obtained in the step 5 as material parameters after oxidation of each unit in a macroscopic model, and performing finite element calculation on the macroscopic model of the CMCs structural member in a 'heat-force-oxygen' coupling environment again to obtain stress distribution and unit stress in the oxidized structure;
step 7: predicting the oxidation life of the structural member, comparing the unit stress obtained in the step 6 with the unit residual strength obtained in the step 5, if the unit stress is larger than the unit residual strength, considering the unit to be invalid, if the invalid unit is accumulated to form a through invalid unit group, considering the structure to be invalid, otherwise, increasing the oxidation time to continuously adjust the diffusion-oxidation process in the structural member, repeating the steps until the structure is invalid, wherein the oxidation time is the natural oxidation life of the CMCs structure under the working condition.
2. The method for predicting the oxidation life of a ceramic matrix composite structure according to claim 1, wherein in the step 2, according to the law of conservation of energy, the relationship between diffusion and oxidation kinetics in the oxidation process is described by using a partial differential equation as follows:
wherein phi is the porosity of CMCs, c A Is oxygen concentration, D eff Weaving equivalent diffusion coefficient of unit cell for each unit, R A For the reaction rate, x is the diffusion distance, t is the time, and the above equation is solved by finite difference method to obtain the oxygen concentration of each unit in the structure.
3. The method for predicting the oxidation life of a ceramic matrix composite structure according to claim 1, wherein in the step 3, the calculation result in the step 2 is used as the oxygen concentration in the pores of each unit internal braid cell; part of the oxygen propagates to the fiber interface through the matrix cracks, accompanied by oxidation of the matrix at the crack channels to SiO 2 The oxide layer and PyC interface is consumed, and the oxide layer thicknesses of the matrix and the fiber are respectively expressed as:
wherein z is m 、z f The oxide layer thickness of the matrix and the oxide layer thickness of the fiber are shown respectively,respectively represent parabolic rate constants of the matrix and the component materials of the fiber under 100KPa pure oxygen in oxidation, c * Represents the oxygen concentration, p, at oxidation of a constituent material under 100kPa pure oxygen m 、p f Respectively the indexes of the matrix and the fiber; pyC interface consumption length l r The following formula is used for calculation:
wherein b is the number of moles of carbon consumed per mole of oxygen,is a mixed diffusion coefficient, M C Is C molar mass ρ C For C density->Representing the oxygen concentration gradient within the crack, c 0 For the crack tip oxygen concentration, α is the ratio of the amounts of the substances of the reaction gas to the product gas.
4. The method for predicting oxidation life of ceramic matrix composite structure according to claim 1, wherein in step 4, the axial residual stiffness E 'of the fiber bundle composite after oxidation is based on a micro-mechanical model' 1 The method comprises the following steps:
wherein l d Length d is the interfacial debonding length e Is half of the width of the crack of the matrix, L is the average crack spacing of the matrix, v f For the fiber volume content, E' f 、E′ m 、E′ c Respectively representing the elastic modulus of the oxidized fiber, matrix and fiber bundle composite material, and calculating by using a mixing ratio formula:
E′ f ＝E f v f (x)+E o (1-v f (x))
E′ m ＝E m v m (x)+E o (1-v m (x))，
E′ c ＝E′ m v m +E′ f v f
wherein E is f 、E m Initial modulus of elasticity, E, of the fibers and matrix, respectively o Is oxidized byProduct SiO 2 Modulus of elasticity, v m V for initial matrix volume content f (x)、v m (x) The volume contents of the fiber and the matrix at a certain position x in the oxidation zone are respectively expressed, and the residual rigidity of the fiber bundle composite material after oxidation in the rest direction is calculated according to the equal proportion folding method.
5. The method for predicting the oxidation life of a ceramic matrix composite structure according to claim 4, wherein in said step 5, the mechanical property parameters of the micro fiber bundle composite are used as the material parameters of the yarn units in the unit cell scale of the macro model, and the macro stress of the knitting units is defined by a volume average method by adopting a standard homogenization processMacroscopic strain->
Where V is the unit cell volume, σ and ε are the microscopic stresses and strains of the units in the unit cell model,
according to the elastic constitutive relation of the materials, applying 6 groups of periodic boundary conditions to the weaving unit, carrying out finite element analysis, calculating stress and strain distribution in the periodic boundary conditions, combining a calculation formula of macroscopic stress and macroscopic strain to obtain stress-strain responses of a plurality of groups of materials, and finally solving a flexibility matrix [ S ] ij ]：
According to the definition of the compliance matrix:
wherein E represents elastic modulus, G represents shear modulus, v represents Poisson's ratio, subscripts 1, 2, 3 respectively correspond to warp, weft and thickness directions of the knitting unit, equivalent elastic modulus of the knitting unit in each direction is calculated according to the group of formulas, and residual strength of the knitting unit is calculated through progressive damage analysis.
6. The method for predicting the oxidation life of a ceramic matrix composite structure of claim 5, wherein the elastic constitutive relationship of said material based on the equal strain assumption and stiffness averaging method is expressed as:
in the formula, subscripts 1, 2, 3 correspond to the warp direction, the weft direction, and the thickness direction in the knitting unit, respectively.
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