A method for predicting coupled damage mechanical properties of ceramic matrix composites

Abstract

The present invention discloses a method for predicting the coupled damage mechanical properties of ceramic matrix composite materials. Aiming at the multi-scale characteristics and tension and shear coupled loading characteristics of ceramic matrix composite materials, a set of mechanical properties prediction methods considering coupled damage is established. First, the initial microscopic performance parameters of the composite material are input, and then the RVE model is established. Through fiber bundle damage simulation and decoupling analysis, the homogenized fiber bundle initial damage and damage evolution model is established. On this basis, the original microscopic material performance parameters are corrected through uniaxial tensile test, and finally the corrected microscopic material performance parameters are used to calculate the mechanical properties of the material under complex loads. The present invention is suitable for calculating the mechanical properties of ceramic matrix composite materials with different preforms, deposition processes, and material components, and improves the accuracy of mechanical property prediction of composite materials.

Description

Technical Field

[0001] The invention belongs to the field of aerospace composite materials, and in particular relates to a method for predicting coupled damage mechanical properties of ceramic-based composite materials. Background Art

[0002] Ceramic-based composite materials represented by C / SiC and SiC / SiC have the advantages of high temperature resistance, low density and good high-temperature mechanical properties, which make them have broad application prospects in the fields of re-entry vehicle thermal protection structure and aero-engine hot end components. Ceramic-based composite components are subjected to the combined effects of aerodynamic loads, thermal loads, centrifugal loads, etc. during operation, and component failure is controlled by complex loads. To carry out scheme design and failure analysis of ceramic-based composite thermal structural parts, it is necessary to analyze the multi-scale damage mechanism of ceramic-based composite materials under complex loads, and on this basis, establish a coupled damage mechanical property prediction method to accurately predict the nonlinear damage process of the material under the combined effects of tension and shear loads, and provide a basis for the application of ceramic-based composite materials in thermal structural parts in the aerospace field.

[0003] Predicting the mechanical properties of ceramic matrix composites based on multi-scale methods is a current research hotspot, but there are few methods that consider multiaxial load coupling damage and there are still some problems in the existing multi-scale performance prediction methods. First, although the multi-scale method simplifies the complexity of the model to a certain extent by using some macroscopic phenomenological parameters to characterize the evolution of microscopic damage, there are still some mesoscopic parameters that are inevitable, such as fiber and matrix modulus, and the in-situ performance of CMC components will be attenuated due to the influence of the preparation process, which is somewhat different from the performance of pure components. Secondly, CMC preparation defects have a great influence on the mechanical properties of materials. At present, most of the pore defects are described in a random distribution in the representative volume element (RVE) modeling process, while the geometry and distribution characteristics of defects at different scales in actual materials are different, not all randomly distributed. Finally, the existing constitutive models that consider CMC coupling damage mostly directly use traditional macroscopic phenomenological models, only changing the phenomenological parameters in the model, while different materials have great differences in component properties, weaving structures, defect forms, etc., resulting in the existing macroscopic mechanical constitutive models in the form of determined formulas. It is difficult to guarantee the accuracy of describing the mechanical properties of different materials. Therefore, it is necessary to establish a performance prediction method that takes coupling damage into account for different ceramic matrix composites. Summary of the invention

[0004] The purpose of the present invention is to overcome the above defects and provide a method for predicting the coupled damage mechanical properties of ceramic matrix composite materials. Aiming at the multi-scale characteristics of ceramic matrix composite materials and the characteristics of tension and shear coupling loading, a set of mechanical property prediction methods considering coupled damage is established. First, the initial microscopic performance parameters of the composite material are input, and then the RVE model is established. Through fiber bundle damage simulation and decoupling analysis, the homogenized fiber bundle initial damage and damage evolution model are established, and the fiber bundle initial damage criterion and damage evolution model are assigned to the fiber bundle unit in the woven structure RVE model. On this basis, the uniaxial tensile mechanical properties of the material are calculated and the original microscopic material performance parameters are corrected by comparing with the uniaxial tensile test results. Finally, the corrected microscopic material performance parameters are used to calculate the mechanical properties of the material under complex loads. The present invention is suitable for the calculation of mechanical properties of ceramic matrix composites with different preforms, deposition processes, and material components, and improves the accuracy of mechanical property prediction of composite materials.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] A method for predicting coupled damage mechanical properties of ceramic matrix composite materials comprises the following steps:

[0007] (1) Determine the initial microscopic performance parameters of the composite material;

[0008] (2) Establishing the fiber bundle RVE model and the braided structure RVE model;

[0009] (3) Based on the initial microscopic performance parameters of the composite material and the fiber bundle RVE model, fiber bundle damage simulation and decoupling analysis are performed to obtain the fiber bundle initial damage criterion and damage evolution model;

[0010] (4) Assigning the fiber bundle initial damage criterion and damage evolution model to the fiber bundle unit in the braided structure RVE model;

[0011] (5) Predicting the uniaxial tensile mechanical properties using the initial mesoscopic performance parameters of the composite material and the RVE model of the woven structure, comparing the uniaxial tensile prediction results with the uniaxial tensile test results, and correcting the initial mesoscopic performance parameters of the composite material based on the comparison results to obtain the corrected mesoscopic performance parameters;

[0012] (6) The coupled damage mechanical properties of the braided structure composite materials under complex loads are predicted using the modified micro-performance parameters, the fiber bundle RVE model, and the woven structure RVE model.

[0013] Furthermore, the microscopic performance parameters include the matrix modulus E m , fiber modulus E f , interface normal modulus E i1 , interface tangent modulus Ei2 , matrix Poisson's ratio μ m , fiber Poisson's ratio μ f , fiber radius R f , pure fiber strength S f , fiber strength reduction factor D f , interface strength S i , matrix strength distribution factor m, matrix fracture energy γ m , interface debonding energy G, interface debonding energy coefficient a, fiber volume fraction V of fiber bundle f , stiffness reduction factor d, fiber bundle saturated matrix crack spacing L sat Or micro-scale matrix strength S m ;

[0014] Furthermore, in the step (2), the fiber bundle RVE model is established based on the ABAQUS platform, including fiber units, matrix units and interface layer Cohesive units; the modeling size of the fiber bundle RVE model is obtained by electron microscope scanning;

[0015] In the step (2), the woven structure RVE model is established based on the UG platform, and the model includes pore defects; the modeling size, shape and distribution characteristics of the pore defects are obtained by electron microscope scanning.

[0016] Furthermore, the internal pores of the fiber bundles in the RVE model of the woven structure are described by a mathematical random distribution method, and the shape and distribution characteristics of the pores in the woven structure are described by a geometric modeling method.

[0017] Furthermore, in step (3), the steps of performing fiber bundle damage simulation and decoupling analysis based on the initial microscopic performance parameters of the composite material and the fiber bundle RVE model to obtain the fiber bundle initial damage criterion and damage evolution model include:

[0018] (31) According to the matrix modulus E in the initial microscopic performance parameters of the composite material m , fiber modulus E f , interface normal modulus E i1 , interface tangent modulus E i2 , matrix Poisson's ratio μ m , fiber Poisson's ratio μ f , fiber radius R f , Pure fiber strength S f , fiber strength preparation reduction factor D f , interface strength S i , matrix strength distribution factor m, matrix fracture energy γ m , interface debonding energy G, interface debonding energy coefficient a, fiber volume fraction V of fiber bundle f , stiffness reduction factor d, fiber bundle saturated matrix crack spacing Lsat and fiber bundle RVE model, establish the failure criteria of matrix and fiber in fiber bundle, and describe the damage process of interface;

[0019] (32) The fiber bundle is homogenized into a two-dimensional structure including longitudinal and transverse directions, wherein the longitudinal direction is the direction along the fibers in the fiber bundle, and the transverse direction is any direction perpendicular to the fibers in the fiber bundle. The transverse microscopic performance parameters are controlled by the in-plane equivalent strain. Based on the homogenized structure of the fiber bundle, the initial damage criterion and damage evolution model of the fiber bundle are obtained according to the failure criteria of the matrix and fibers in the fiber bundle and the damage process of the interface.

[0020] Furthermore, in the step (31), the failure criterion of the matrix in the fiber bundle is when the maximum tensile principal stress at the matrix unit integration point is greater than the matrix strength S′ of the unit m Failure occurs when

[0021] S′ m =σ0[-ln(1-μ)] 1 / m

[0022]

[0023]

[0024] E c =E f V f +E m (1-V f )

[0025] Among them, σ0 is the matrix characteristic strength, the random number μ∈(0,1), m is the matrix strength distribution factor, τ i is the interface shear stress, E c is the fiber bundle modulus, γ m is the matrix fracture energy, V f is the fiber volume fraction of the fiber bundle, E f is the fiber modulus, R f is the fiber radius, E m is the matrix modulus, L sat is the matrix crack spacing;

[0026] The failure criterion of the fiber in the fiber bundle is that failure occurs when the maximum principal stress at the fiber unit integration point is greater than the in-situ fiber strength; the in-situ fiber strength is determined by the pure fiber strength S f Reduction factor D for fiber strength f Multiply them together to get;

[0027] The damage of the fiber bundle interface is described by the Traction-Separation mechanical constitutive model of the ABAQUS cohesive element.

[0028] Furthermore, in step (32), the fiber bundle initial damage criterion is as follows:

[0029]

[0030] Among them, F L is the longitudinal state parameter, F M is the lateral state parameter; ε L is the longitudinal tensile strain, ε M is the lateral equivalent strain, ε2 and ε3 are the tensile and compressive strains in the first and second transverse directions, respectively. 23 represents the shear strain in the first and second transverse directions; γ LM are the longitudinal and transverse equivalent shear strains, γ 12 and γ 13 They are all fiber bundle shear strains; 1 represents the longitudinal direction, 2 and 3 represent the first and second transverse directions that are perpendicular to each other, respectively; and are the longitudinal initial damage strain, transverse initial damage strain and shear initial damage strain of the fiber bundle, respectively, obtained according to the failure criteria of the matrix and fiber in the fiber bundle and the damage process of the interface obtained in step (31);

[0031] A and B are the lateral fitting coefficient and shear fitting coefficient, respectively, which are obtained by fitting the numerical simulation results under different proportions of lateral load and shear load.

[0032] Furthermore, in the step (32), based on the homogenized structure of the fiber bundle, the method for obtaining the damage evolution model according to the failure criteria of the matrix and the fiber in the fiber bundle and the damage process of the interface is:

[0033] (321)Definition d i-j F L or F M The damage parameter of mechanical properties in the i direction caused by E i-j F L or F M The residual homogenization modulus of the fiber bundle RVE model in the i direction is caused by is the original modulus of the fiber bundle RVE model in the i direction before damage, i = LL, MM or LM, representing the longitudinal, transverse and shear directions, respectively, j = L or M, representing the longitudinal or transverse directions;

[0034] (322) The numerical simulation of the fiber bundle RVE model under different loading conditions yielded the F L and F M The value of , and the residual modulus in the longitudinal, transverse and shear directions are obtained at the same time, and the damage parameter d is obtained according to the residual modulusi-j The different loading states include different loading directions and different loading loads;

[0035] According to F L and F M The value of the damage parameter d i-j The damage parameter d is obtained by numerical fitting. i-j Follow F L or F M The changing law of and material damage stiffness matrix, that is, the damage evolution model.

[0036] Furthermore, in step (32), the damage parameter d i-j Follow F L or F M The changing law formula is:

[0037]

[0038] Among them, F j Indicates F L or F M , A0~A n are the fitting coefficients, n=1, 2, 3, ..., the value of n makes the R-square value of the numerical fitting greater than the preset R-square value, and the preset R-square value corresponds to the preset accuracy.

[0039] Furthermore, the material damage stiffness matrix is:

[0040]

[0041] in, C 11 , C 12 , C 13 ……C 66 is the stiffness matrix coefficient.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) The present invention establishes RVE models with different characteristics according to the matrix defect characteristics. The uniformly distributed small pores are described by a mathematical random distribution method, and the woven structure scale pores with certain shapes and distribution characteristics are described by a geometric modeling method. Compared with the existing methods, the matrix defect characteristics of different scales are described more accurately.

[0044] (2) The present invention establishes a multi-scale coupled damage mechanical properties prediction method, in which a direct connection between microscopic performance parameters with practical physical significance and macroscopic coupled damage mechanical properties of materials is established. The influence of microscopic parameters of materials on macroscopic damage properties can be studied by changing the microscopic parameters of materials, thereby optimizing material properties.

[0045] (3) Before calculating the material coupling damage performance, the present invention corrects the original input mesoscopic performance parameters by comparing the test under uniaxial tensile load with the numerical calculation based on the influence mechanism of the material mesoscopic performance parameters on the macroscopic performance, thereby improving the calculation accuracy and avoiding the problem that some mesoscopic parameters are difficult to measure;

[0046] (4) The present invention adopts the microscopic finite element method to simulate the damage evolution process of the fiber bundle, and establishes the initial damage and damage evolution model after the fiber bundle is homogenized based on the decoupling method and numerical fitting, thereby avoiding the problem of inaccurate description of material properties by the existing traditional macroscopic phenomenological model, thereby ensuring the accuracy of material performance calculation;

[0047] (5) The present invention is applicable to the prediction of coupled damage mechanical properties of ceramic matrix composites with different material components, preform structures, and matrix deposition processes. The present invention compares the prediction results with the experimental data to verify the accuracy of the method. The prediction error of the elastic modulus and failure strength in each direction (uniaxial stretching, eccentric 15° stretching, eccentric 30° stretching, eccentric 45° stretching) of 2D woven SiC / SiC ceramic matrix composites by chemical vapor deposition process is within 7%. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Schematic diagram of fiber bundle structure;

[0049] Figure 2 This is a flow chart for predicting coupled damage mechanical properties of the present invention;

[0050] Figure 3 A schematic diagram of measurement parameters for modeling the two-dimensional braided microstructure of the present invention;

[0051] Figure 4 The fiber bundle RVE model of the present invention;

[0052] Figure 5 The two-dimensional braided structure RVE model of the present invention;

[0053] Figure 6 This is a schematic diagram of longitudinal shear and transverse equivalent strain data points at the initial failure of the present invention;

[0054] Figure 7 It is a schematic diagram of data points showing changes in damage parameters along with state parameters of the present invention. DETAILED DESCRIPTION

[0055] The following detailed description of the present invention will make the features and advantages of the present invention more clear and explicit.

[0056] The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise noted.

[0057] According to the bearing environment and material damage mechanism of ceramic-based composite components in the aerospace and aviation fields, ceramic-based composite components are subjected to the combined effects of aerodynamic loads, thermal loads, centrifugal loads, etc. during operation, and component failure is controlled by complex multi-axial loads. Considering that the macroscopic mechanical properties of the material are cross-controlled by various microscopic damage mechanisms such as matrix cracking, interface debonding, and fiber pull-out, and are also related to various factors such as material component performance, preparation defects, and complex loads, the scheme design and failure analysis of ceramic-based composite thermal structural parts need to accurately predict the nonlinear damage process of the material under the combined effects of multi-axial loads, especially tensile and shear loads. All multi-scale numerical simulation methods need to be used to simulate the progressive damage process of fiber bundles and braided structures under tensile and shear loads, and obtain the mechanical properties of the material based on the homogenization theory. The numerical analysis results are compared with the experimental data to verify the accuracy of the simulation analysis model and method. The present invention finally forms a set of coupled damage mechanical property prediction methods and processes suitable for ceramic-based composite materials, providing technical support for design and analysis work in related fields.

[0058] like Figure 2 The figure shows the implementation process of a method for predicting coupled damage mechanical properties of ceramic matrix composite materials of the present invention. The present invention first inputs a set of initial microscopic performance parameters of ceramic matrix composite materials and measures multi-scale RVE modeling parameters by electron microscope scanning; secondly, fiber bundle and woven structure RVE models are established respectively according to the material characteristics of different scales observed by electron microscope; fiber bundle damage simulation and decoupling analysis are carried out to establish the homogenized initial damage criterion and damage evolution model of fiber bundle; the initial damage criterion and damage evolution model of fiber bundle are assigned to the fiber bundle unit in the woven structure RVE model, and on this basis, the damage mechanical properties of the material under uniaxial tensile load are calculated and compared with the uniaxial tensile test results, and the initial microscopic material performance parameters are corrected; then, the mechanical properties of the material under complex loads are calculated; finally, an eccentric tensile test can be carried out to verify the accuracy of the calculation results.

[0059] The specific implementation of the method for predicting coupled damage mechanical properties of ceramic matrix composite materials of the present invention is as follows:

[0060] 1) Input the initial material parameters, including the matrix modulus Em , fiber modulus E f , interface normal modulus E i1 , interface tangent modulus E i2 , matrix Poisson's ratio μ m , fiber Poisson's ratio μ f , fiber radius R f , Pure fiber strength S f , fiber strength preparation reduction factor D f , interface strength S i , matrix strength distribution factor m, matrix fracture energy γ m , interface debonding energy G, interface debonding energy coefficient a, fiber volume fraction V of fiber bundle f , stiffness reduction factor d, fiber bundle saturated matrix crack spacing L sat , micro-scale matrix strength S m .

[0061] 2) The fiber bundle RVE model is established based on the ABAQUS software platform, including fiber units, matrix units, and interface layer cohesive units. The modeling dimensions are obtained by electron microscope scanning.

[0062] 3) The RVE model of the woven structure is established based on the UG modeling platform. The modeling size is obtained by electron microscope scanning. The model contains pore defects with certain shapes and distribution characteristics.

[0063] 4) According to the initial microscopic performance parameters of the composite material: matrix modulus E m , fiber modulus E f , interface normal modulus E i1 , interface tangent modulus E i2 , matrix Poisson's ratio μ m , fiber Poisson's ratio μ f , fiber radius R f , Pure fiber strength S f , fiber strength preparation reduction factor D f , interface strength S i , matrix strength distribution factor m, matrix fracture energy γ m , interface debonding energy G, interface debonding energy coefficient a, fiber volume fraction V of fiber bundle f , stiffness reduction factor d, fiber bundle saturated matrix crack spacing L sat , micro-scale matrix strength S m The fiber bundle scale fiber and matrix unit damage simulation and the micro-weaving scale fiber bundle and matrix unit damage simulation are implemented based on the USDFLD subroutine of the ABAQUS software platform, as described in steps 5) to 11);

[0064] 5) The maximum principal stress criterion is used to judge the failure of the matrix in the fiber bundle, where the maximum tensile principal stress σ1 of the matrix unit integration point in the fiber bundle is greater than the matrix strength S′ in the fiber bundle. m When failure occurs, when defining the material strength of each integration point in the USDFLD subroutine, a random number μ is first generated, μ∈(0,1), then the matrix strength S′ in the fiber bundle at this point m :

[0065] S′ m =σ0[-ln(1-μ)] 1 / m (1)

[0066]

[0067]

[0068] Where σ0 represents the matrix characteristic strength, τ i represents the interfacial shear stress, E c represents the fiber bundle modulus, m is the matrix strength distribution factor, which is calculated from the mixing ratio, and the meanings of the other symbols have been introduced in step 1).

[0069] E c =E f V f +E m (1-V f ) (4)

[0070] 6) The interface within the fiber bundle is characterized by the zero-thickness cohesive unit in ABAQUS. According to the interface normal modulus E i1 , interface tangent modulus E i2 , interface strength S i , interface debonding energy G, interface debonding energy coefficient a, and the interface damage process are described by the Traction-Separation mechanical constitutive model of the ABAQUS cohesive unit.

[0071] 7) The maximum principal stress criterion is used for the fibers in the fiber bundle. Failure occurs when the maximum principal stress at the fiber unit integration point is greater than the in-situ fiber strength. The in-situ strength of the fiber is determined by the pure fiber strength S f Multiply the fiber strength to prepare the reduction factor D f get.

[0072] 8) Schematic diagram of fiber bundle is as attached Figure 1As shown, direction 1 is the longitudinal fiber direction, and directions 2 and 3 are perpendicular to the transverse direction of the fiber, and directions 2 and 3 are perpendicular to each other. The fiber bundle is a transversely isotropic material. It is believed that the material parameters in the plane formed by directions 2 and 3 are controlled by the equivalent stress and strain in the plane. The fiber bundle is simplified into a two-dimensional structure of longitudinal L and transverse M. The damage evolution of related parameters in the transverse plane is controlled by the equivalent strain in the plane.

[0073]

[0074] ε M represents the equivalent strain in the transverse plane of the fiber bundle, ε2 and ε3 represent the tensile and compressive strains in the transverse directions 2 and 3 (i.e., the first transverse direction and the second transverse direction), and ε 23 Represents the shear strain in 2 and 3 directions.

[0075] 9) The initial damage criterion after homogenizing the fiber bundle in the braided structure scale is as shown in formula (6). When the state parameter F L When the state parameter F is greater than 1, the fiber bundle is damaged longitudinally. M When it is greater than 1, the fiber bundle is damaged transversely. The parameters A and B in the formula are obtained by fitting the numerical simulation results of the fiber bundle RVE model under transverse and shear loads of different proportions.

[0076]

[0077]

[0078] where ε L represents the longitudinal tensile strain, ε M represents the lateral equivalent strain, γ LM represents the longitudinal and transverse equivalent shear strains, γ 12 and γ 13 represents the fiber bundle shear strain, and They are the initial damage strain in the longitudinal direction, the initial damage strain in the transverse direction and the initial damage strain in the shear direction of the fiber bundle, which are obtained according to the failure criteria of the matrix and fiber in the fiber bundle and the damage process of the interface;

[0079] 10) In the braided structure scale, after the initial failure of the fiber bundle, the damage evolution in all directions is affected by F L 、F M Two state parameters are controlled and the damage parameter is defined as shown in formula (8).

[0080]

[0081] Among them, d i-j Indicates F L or F MThe damage parameters of the mechanical properties in the i direction are as follows: i = LL, MM, LM, representing the longitudinal, transverse and shear directions, respectively, and j = L, M. i-j F L or F M The residual homogenization modulus of the fiber bundle RVE model in the i direction is caused by is the original modulus of the fiber bundle in the i direction before damage in the RVE model.

[0082] 11) The residual modulus in each direction is obtained by numerical simulation of the fiber bundle model under different loading conditions, and the damage parameter d is obtained by numerical fitting. i-j With the state parameter F L or F M The change law of and material damage stiffness matrix, that is, the damage evolution model formula. Damage parameter d i-j With the state parameter F L or F M The changing law formula of is a piecewise function form, in which the non-constant part is fitted by the exponential form of formula (9). By increasing the number of terms in the brackets of formula (9), the R-square value of the numerical fitting is greater than 0.95 (this value can be adjusted according to the prediction accuracy).

[0083]

[0084] Where i = LL, MM, LM, respectively represent the longitudinal, transverse and shear directions, j = L, M. Get the damage parameter d i-j With the state parameter F L or F M After the change law formula of , the material damage stiffness matrix is ​​obtained as shown in formula (10).

[0085]

[0086]

[0087] The USDFLD subroutine based on ABAQUS assigns the above model to the fiber bundle unit in the RVE model of the woven structure. The maximum principal stress criterion is used to judge the matrix failure of the matrix unit in the woven structure. The maximum tensile principal stress of the matrix unit integration point is greater than the micro-scale matrix strength S m Failure occurs when the sample is subjected to a certain load, and the mechanical properties of ceramic matrix composites under tension and shear loads can be simulated.

[0088] 12) By comparing the uniaxial tensile test results with the predicted results, the initial input parameters are corrected, and the corrected parameters are used as input to calculate the coupled damage mechanical properties of the material under tension and shear load conditions.

[0089] The applicable fields of the present invention actually include all fields of aerospace that use ceramic-based composite materials, such as the field of aircraft engines.

[0090] Embodiment 1:

[0091] The specific method of the present invention comprises the following steps:

[0092] 1) Input the original mesoscopic performance parameters, including matrix modulus, fiber modulus, interface normal modulus, interface tangential modulus, matrix Poisson's ratio, fiber Poisson's ratio, fiber radius, pure fiber strength, fiber strength preparation reduction factor, interface strength, matrix strength distribution factor, matrix fracture energy, interface debonding energy, interface debonding energy coefficient, fiber volume fraction of fiber bundle, stiffness reduction factor, fiber bundle saturated matrix crack spacing, and mesoscopic matrix strength.

[0093] 2) Use scanning electron microscopy to observe the structural characteristics of materials at different scales and the dimensional parameters required to establish the RVE model. For example, the dimensional parameters required to be measured for modeling two-dimensional woven ceramic matrix composites are as follows: Figure 3 As shown, it includes the fiber bundle cross-sectional spacing p, the fiber bundle weaving structure cross-sectional height h, the fiber bundle cross-sectional height t, the fiber bundle cross-sectional width w (excluding the matrix), and the fiber bundle cross-sectional width s (including the matrix).

[0094] 3) Establish the RVE models of fiber bundle and woven structure respectively, where the fiber bundle RVE model is as follows: Figure 4 As shown in Figure 1, it includes fiber units, matrix units and interface layer units. The model structure is determined by the fiber volume fraction. The two-dimensional woven RVE model (taking the two-dimensional structure as an example) is as follows: Figure 5 As shown, it includes fiber bundles, matrix, and pore defects. The model structure is determined by the microscopic size parameters observed by electron microscope. The small pores in the fiber bundle are described by mathematical random distribution method, and the pores with certain geometric and distribution characteristics in the woven structure are described by geometric modeling method.

[0095] 4) Carry out fiber bundle damage simulation and decoupling analysis based on the fiber bundle RVE model, obtain the residual modulus in each direction, and obtain the damage parameter with the state parameter F L or F M The data points for fitting the initial damage criterion are shown in the figure below: Figure 6 The data points when fitting the damage evolution model are shown in Figure 7 shown.

[0096] 5) Carry out mechanical property calculations of braided structural materials under uniaxial tensile loads, and by comparing the uniaxial tensile test results with the predicted results, correct the initial microscopic performance parameters, and use the corrected parameters as input to calculate the coupled damage mechanical properties of the material under tension and shear load conditions.

[0097] 6) An eccentric tensile test can be carried out to verify the accuracy of the calculation results. For example, in the present invention, 15°, 30°, and 45° eccentric tensile tests are carried out to verify the prediction results of the damage mechanical properties of the two-dimensional woven ceramic matrix composite material by the CVI process as shown in Table 1.

[0098] Table 1 Comparison between calculation results and experiments of two-dimensional woven ceramic matrix composites

[0099]

[0100] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

[0101] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for predicting coupled damage mechanical properties of ceramic matrix composite materials, characterized in that: The following steps are included: (1) Determine the initial microscopic performance parameters of the composite material; (2) Establishing the fiber bundle RVE model and the braided structure RVE model; (3) Based on the initial microscopic performance parameters of the composite material and the fiber bundle RVE model, fiber bundle damage simulation and decoupling analysis are performed to obtain the fiber bundle initial damage criterion and damage evolution model; (4) Assigning the fiber bundle initial damage criterion and damage evolution model to the fiber bundle unit in the braided structure RVE model; (5) Predicting the uniaxial tensile mechanical properties using the initial mesoscopic performance parameters of the composite material and the RVE model of the woven structure, comparing the uniaxial tensile prediction results with the uniaxial tensile test results, and correcting the initial mesoscopic performance parameters of the composite material based on the comparison results to obtain the corrected mesoscopic performance parameters; (6) The coupled damage mechanical properties of the braided structure composite materials under complex loads were predicted by using the modified micro-performance parameters, fiber bundle RVE model and braided structure RVE model; In the step (2), the fiber bundle RVE model is established based on the ABAQUS platform, including fiber units, matrix units and interface layer cohesive units; the modeling size of the fiber bundle RVE model is obtained by electron microscope scanning; In the step (2), the woven structure RVE model is established based on the UG platform, and the model contains pore defects; the modeling size, shape and distribution characteristics of the pore defects are obtained by electron microscope scanning; The internal pores of the fiber bundles in the RVE model of the woven structure are described by mathematical random distribution method, and the shape and distribution characteristics of the pores in the woven structure are described by geometric modeling method; In the step (3), the steps of performing fiber bundle damage simulation and decoupling analysis based on the initial microscopic performance parameters of the composite material and the fiber bundle RVE model to obtain the fiber bundle initial damage criterion and the damage evolution model include: (31) Based on the initial microscopic performance parameters of the composite material and the RVE model of the fiber bundle, the failure criteria of the matrix and fiber in the fiber bundle are established, and the damage process of the interface is described; (32) The fiber bundle is homogenized into a two-dimensional structure including longitudinal and transverse directions, wherein the longitudinal direction is the direction along the fibers in the fiber bundle, and the transverse direction is any direction perpendicular to the fibers in the fiber bundle. The transverse microscopic performance parameters are controlled by the in-plane equivalent strain. Based on the homogenized structure of the fiber bundle, the initial damage criterion and damage evolution model of the fiber bundle are obtained according to the failure criteria of the matrix and fibers in the fiber bundle and the damage process of the interface.

2. A method for predicting coupled damage mechanical properties of ceramic matrix composite materials according to claim 1, characterized in that: In the step (1), the microscopic performance parameters include the matrix modulus E m , fiber modulus E f , interface normal modulus E i1 , interface tangent modulus E i2 , matrix Poisson's ratio μ m , fiber Poisson's ratio μ f , fiber radius R f , pure fiber strength S f , fiber strength reduction factor D f , interface strength S i , matrix strength distribution factor m, matrix fracture energy γ m , interface debonding energy G, interface debonding energy coefficient a, fiber volume fraction V of fiber bundle f , stiffness reduction factor d, fiber bundle saturated matrix crack spacing L sat Or micro-scale matrix strength S m .

3. A method for predicting coupled damage mechanical properties of ceramic matrix composite materials according to claim 1, characterized in that: In the step (31), the failure criterion of the matrix in the fiber bundle is when the maximum tensile principal stress at the matrix unit integration point is greater than the matrix strength S' of the unit m Failure occurs when S′ m =σ0[-ln(1-μ)] 1 / m E c =E f V f +E m (1-V f ) Among them, σ0 is the matrix characteristic strength, the random number μ∈(0,1), m is the matrix strength distribution factor, τ i is the interface shear stress, E c is the fiber bundle modulus, γ m is the matrix fracture energy, V f is the fiber volume fraction of the fiber bundle, E f is the fiber modulus, R f is the fiber radius, E m is the matrix modulus, L sat is the matrix crack spacing; The failure criterion of the fiber in the fiber bundle is that failure occurs when the maximum principal stress at the fiber unit integration point is greater than the in-situ fiber strength; the in-situ fiber strength is determined by the pure fiber strength S f Reduction factor D for fiber strength f Multiply them together to get; The damage of the fiber bundle interface is described by the Traction-Separation mechanical constitutive model of the ABAQUS cohesive element.

4. A method for predicting coupled damage mechanical properties of ceramic matrix composite materials according to claim 1, characterized in that: In the step (32), the fiber bundle initial damage criterion is as follows: Among them, F L is the longitudinal state parameter, F M is the lateral state parameter; ε L is the longitudinal tensile strain, ε M is the lateral equivalent strain, ε2 and ε3 are the tensile and compressive strains in the first and second transverse directions, respectively. 23 represents the shear strain in the first and second transverse directions; γ LM are the longitudinal and transverse equivalent shear strains, γ 12 and γ 13 They are all fiber bundle shear strains; 1 represents the longitudinal direction, 2 and 3 represent the first and second transverse directions that are perpendicular to each other, respectively; and are the longitudinal initial damage strain, transverse initial damage strain and shear initial damage strain of the fiber bundle, respectively, obtained according to the failure criteria of the matrix and fiber in the fiber bundle and the damage process of the interface obtained in step (31); A and B are the lateral fitting coefficient and shear fitting coefficient, respectively, which are obtained by fitting the numerical simulation results under different proportions of lateral load and shear load.

5. A method for predicting coupled damage mechanical properties of ceramic matrix composite materials according to claim 4, characterized in that: In the step (32), the method for obtaining the damage evolution model based on the homogenized structure of the fiber bundle, according to the failure criteria of the matrix and the fiber in the fiber bundle and the damage process of the interface is: (321)Definition d i-j F L or F M The damage parameter of mechanical properties in the i direction caused by E i-j F L or F M The residual homogenization modulus of the fiber bundle RVE model in the i direction is caused by is the original modulus of the fiber bundle RVE model in the i direction before damage, i = LL, MM or LM, representing the longitudinal, transverse and shear directions, respectively, j = L or M, representing the longitudinal or transverse directions; (322) The numerical simulation of the fiber bundle RVE model under different loading conditions yielded the F L and F M The value of , and the residual modulus in the longitudinal, transverse and shear directions are obtained at the same time, and the damage parameter d is obtained according to the residual modulus i-j The different loading states include different loading directions and different loading loads; According to F L and F M The value of the damage parameter d i-j The damage parameter d is obtained by numerical fitting. i-j Follow F L or F M The changing law of and material damage stiffness matrix, that is, the damage evolution model.

6. A method for predicting coupled damage mechanical properties of ceramic matrix composite materials according to claim 5, characterized in that: In the step (32), the damage parameter d i-j Follow F L or F M The changing law formula is: Among them, F j Indicates F L or F M , A0~A n are the fitting coefficients, n=1, 2, 3, ..., the value of n makes the R-square value of the numerical fitting greater than the preset R-square value, and the preset R-square value corresponds to the preset accuracy.

7. A method for predicting coupled damage mechanical properties of ceramic matrix composite materials according to claim 6, characterized in that: The material damage stiffness matrix is: in, C 11 , C 12 , C 13 ……C 66 is the stiffness matrix coefficient.

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