Method for predicting high temperature and complex stress of ceramic matrix composite material based on strain control damage evolution

Abstract

The invention discloses a method for predicting high-temperature and complex stress of a ceramic-based composite material based on strain control damage evolution, and belongs to the technical field of stress prediction of ceramic-based composite materials. The method comprises the following steps: determining material high-temperature performance degradation conditions according to temperature; the total strain (mechanical strain and thermal strain) of the material is calculated, and then based on a three-dimensional failure criterion of strain control, six damage initial criterion equations including stretching and compression in the warp direction, the weft direction and the out-of-plane direction are constructed; establishing an evolution model of damage coefficients by introducing a coupling mechanism of damage factors in different directions; combining a multi-linear constitutive relation of the ceramic matrix composite material to construct a rigidity degradation matrix, and realizing rigidity adjustment of the failure unit; and finally deducing a stress-strain relation equation to complete stress prediction of the material under the conditions of high temperature and complex load. The prediction method provided by the invention can accurately predict the complex stress state of the ceramic matrix composite material under the combined action of the high temperature and the mechanical load.

Description

Technical Field

[0001] This application belongs to the field of stress prediction technology for ceramic composite materials, specifically relating to a method for predicting high-temperature and complex stresses in ceramic matrix composite materials based on strain-controlled damage evolution. Background Technology

[0002] Ceramic matrix composites (CMCs), with their excellent high-temperature resistance, high specific strength, and low density, have become key structural materials for extreme environments such as hot-end components of aero-engines, thermal protection systems of aerospace vehicles, high-performance braking devices, and nuclear energy equipment. However, these materials inevitably suffer from microstructural defects during preparation and service, including pores, non-uniform fiber bundle weaving, and discrete interfacial bonding strength, leading to significant nonlinear mechanical behavior under high temperature and multiaxial complex stress conditions. Specifically, the coupling effect of thermal stress and mechanical load can induce multiple damage mechanisms such as fiber bundle fracture, matrix cracking, interfacial debonding, and pore evolution, and there are strong interactions between the various damage modes, forming a multiaxial coupled failure process.

[0003] Currently, the mechanical property analysis of ceramic matrix composites mainly relies on macroscopic finite element simulation methods, which have limitations in three aspects: Simplification defects: Traditional models treat materials as isotropic or equivalent homogeneous units, ignoring the scale effect of microstructures such as fiber-matrix interfaces and pore distribution on mechanical properties, leading to prediction errors in local stress concentration and damage initiation locations; Lack of load coupling: Existing methods often treat thermal strain and mechanical strain in isolation, failing to construct a dynamic coupling model between the two, making it difficult to accurately describe the strain energy release law under the combined action of thermal and mechanical loads at high temperatures; Limitations in damage evolution: Damage criteria often adopt linear degradation assumptions or empirical parameter corrections, failing to reflect the cumulative effects of nonlinear damage such as progressive fiber breakage and interface delamination, resulting in significant differences between the predicted material failure modes and the actual failure process.

[0004] Current technologies lack dedicated prediction tools for complex high-temperature stress states (such as thermo-mechanical cyclic loading and multi-axial stress combinations). Engineering applications still rely on experimental calibration and safety factor amplification, which limits the effectiveness of ceramic matrix composites in lightweight and high-reliability design. Therefore, developing a prediction method capable of simultaneously analyzing multi-scale structural features, thermo-mechanical coupling effects, and nonlinear damage evolution is of significant theoretical and engineering value for improving the service safety of such materials in extreme environments. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a stress prediction method applicable to ceramic matrix composites under high temperature and complex stress states. This method constructs a strain-controlled damage evolution mechanism by combining the thermal expansion behavior of materials with multilinear constitutive relations, thereby achieving accurate prediction of damage initiation, evolution, and stress-strain relationships.

[0006] In one aspect of this application, a method for predicting high-temperature and complex stresses in ceramic matrix composites based on strain-controlled damage evolution is provided, comprising the following steps:

[0007] S1: Determine the current performance parameters of ceramic matrix composites based on high-temperature performance degradation relationships;

[0008] S2: Calculate the total strain in all directions based on the thermal expansion criterion and mechanical load, where the total strain includes mechanical strain and thermal strain;

[0009] S3: Establish a three-dimensional failure criterion for strain control, and define the damage initiation criteria for warp tension, warp compression, weft tension, weft compression, out-of-plane tension, and out-of-plane compression; the warp direction is along the fiber direction of the ceramic matrix composite material, the weft direction is perpendicular to the fiber direction, and the out-of-plane direction is along the thickness direction of the ceramic matrix composite material.

[0010] S4: Based on the constitutive relations of tensile / compression / shear failure, construct a damage evolution model that couples damage factors in different directions, and calculate the damage factors;

[0011] S5: Constructing the anisotropic stiffness degradation matrix C based on multilinear constitutive relations and damage factors. d ;

[0012] S6: Couple damage evolution with strain control criteria, establish a stress-strain relationship model, and output prediction results for complex stress states. The stress-strain relationship model includes:

[0013]

[0014]

[0015] Among them, M,C d ,ε m α and ΔT represent the damage operator, damage stiffness matrix, total strain matrix, coefficient of thermal expansion, and temperature increment, respectively, and S and S d These represent the original compliance matrix and the damaged compliance matrix, respectively.

[0016] In one implementation, the high-temperature performance degradation relationship in step S1 includes: fiber bundle fracture stress degradation rate D yarn and model load-bearing capacity degradation rate D model ;

[0017] The fiber bundle fracture stress degradation rate D yarn for:

[0018] D yarn =0.002059·T-2.793443

[0019] Where T represents the temperature of the ceramic matrix composite material, in °C;

[0020] The model's load-bearing capacity degradation rate D model for:

[0021] D model =1.000385·D yarn +0.016487.

[0022] In one implementation, the total strain ε in step S2 is expressed as mechanical strain ε t and thermal strain ε T Linear superposition yields:

[0023] ε=ε t +ε T =ε t +αΔT;

[0024] Where ε is the total strain, ε t For mechanical strain, ε T Let α be the thermal strain, α be the coefficient of thermal expansion, and ΔT be the temperature change.

[0025] In one implementation, the damage initiation criterion in step S3 is based on an extension of the Hashin criterion and satisfies:

[0026] The criterion for initiating radial stretching is:

[0027]

[0028] The criterion for initiating meridional compression is:

[0029]

[0030] The criterion for initiating latitudinal stretching is:

[0031]

[0032] The latitudinal compression initiation criterion is:

[0033]

[0034] The out-of-plane stretching initiation criterion is:

[0035]

[0036] The out-of-plane compression initiation criterion is:

[0037]

[0038] In one embodiment, in step S4, the constitutive relations of the fiber bundle tension and compression of the ceramic matrix composite material are as follows:

[0039] ε 11 >0,

[0040]

[0041] ε 11 <0,

[0042]

[0043] The constitutive relations of the ceramic matrix composite matrix under tension and compression are as follows:

[0044] ε 22 ,ε 33 >0,

[0045]

[0046] ε 22 ,ε 33 <0,

[0047]

[0048] The constitutive relation of the ceramic matrix composite matrix shear is as follows:

[0049] γ<0 or γ>0,

[0050]

[0051] In one implementation, the anisotropic stiffness degradation matrix in step S5 is: C d =[S d ] -1 =[MS] -1 ; where S and S d Let represent the original compliance matrix and the damage compliance matrix, respectively, and M represent the damage operator matrix.

[0052] In one implementation, step S6 includes integrating the damage initiation criterion, stiffness degradation matrix, and total strain data, simulating the damage evolution path through strain control criteria, and outputting stress-strain relationship curves.

[0053] The beneficial effects of this application are as follows:

[0054] This application presents a method for stress prediction of ceramic matrix composites under high temperature and complex stress conditions. It can accurately combine the combined effects of high temperature performance degradation, thermal strain and mechanical strain. By constructing a strain-controlled damage evolution mechanism and multilinear constitutive relations, the damage prediction process of the material is optimized, providing an accurate prediction method for the mechanical properties of ceramic matrix composites under high temperature conditions. Attached Figure Description

[0055] Figure 1 This is a flowchart illustrating the prediction method of this application;

[0056] Figure 2 The figures represent the thermal stress at different temperatures in this application; where a is the thermal stress cloud diagram for cooling from 1100℃ to 20℃, b is the thermal stress cloud diagram for heating from 1100℃ to 1350℃, and c is the thermal stress cloud diagram for heating from 1100℃ to 1600℃.

[0057] Figure 3 The diagram shows the simulated fracture evolution process at 1350℃; where a is the stress cloud diagram of the bearing meridional fiber bundle, b is the stress cloud diagram of the composite matrix, and c is the stress cloud diagram of the complete composite model.

[0058] Figure 4 The diagram shows the simulated fracture evolution process at 1600℃; where a is the stress cloud diagram of the bearing meridional fiber bundle, b is the stress cloud diagram of the composite matrix, and c is the stress cloud diagram of the complete composite model.

[0059] Figure 5 The load-displacement curves are from a numerical simulation at 1350℃.

[0060] Figure 6 The load-displacement curves are from a numerical simulation at 1600℃.

[0061] Figure 7 The three-dimensional reconstruction models of the specimens under different loads at 1600℃ are shown below; where a is the reconstruction model of the specimen at 0N, b is the reconstruction model of the test section at 0N, c is the reconstruction model of the test section at 100N, d is the reconstruction model of the test section at 200N, e is the reconstruction model of the test section at 500N, and f is the reconstruction model of the test section at fracture.

[0062] Figure 8 Three-dimensional reconstruction images of fracture load and specimen fracture surface at different high temperatures of 1350℃, 1600℃ and 1800℃;

[0063] Figure 9 Comparison of fracture test and simulation results at 1350℃;

[0064] Figure 10The figures show a comparison between simulation and experiment at 1600℃; where a is a comparison between the experimental 200N and simulated 248N models, b is a comparison between the experimental 500N and simulated 519N models, and c is a comparison between the experimental fracture and simulated fracture models. Detailed Implementation

[0065] The technical solution of this application will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are only some embodiments of this application, not all embodiments, and are only used to illustrate this application, and should not be regarded as limiting the scope of this application. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0066] In one embodiment, a method for predicting high-temperature and complex stresses in ceramic matrix composites based on strain-controlled damage evolution is provided. First, the high-temperature performance degradation of the material is determined based on temperature. The total strain (mechanical strain and thermal strain) of the material is calculated. Then, based on a strain-controlled three-dimensional failure criterion, six damage initiation criterion equations are constructed, including tensile and compressive stresses in the meridional, latitudinal, and out-of-plane directions. An evolution model of the damage factors is established by introducing a coupling mechanism of damage factors in different directions. Combining the multilinear constitutive relation of the ceramic matrix composite, a stiffness degradation matrix is ​​constructed to adjust the stiffness of the failure elements. Finally, the stress-strain relationship equation is derived to complete the stress prediction of the material under high-temperature and complex loading conditions. A flowchart of the calculation method is provided. Figure 1 Specifically, this can be achieved through the following steps:

[0067] S1: Determine the current performance parameters of ceramic matrix composites based on the high-temperature performance degradation relationship.

[0068] The properties of materials degrade due to the evolution of microstructure at high temperatures. For temperature conditions exceeding the bearing temperature limit, a functional relationship is established between the fiber bundle fracture stress degradation rate, the model bearing capacity degradation rate, and temperature to assess the degradation of the fracture strength of the material matrix and fiber bundle.

[0069] Specifically, temperature T is related to the fiber bundle fracture stress degradation rate (D). yarn The relationship between them is:

[0070] D yarn =0.002059·T-2.793443;

[0071] Understandably, D yarn It may be a negative value, which indicates that the degradation is not obvious at lower temperatures. In this application, the formula is mainly for high-temperature degradation (exceeding the load-bearing temperature limit). In practical applications, it is necessary to ensure that T is within the effective range.

[0072] The fiber bundle fracture stress degradation rate (D) yarn Mapping this to the overall model yields the model carrying capacity degradation rate (D). model ), fiber bundle fracture stress degradation rate (D yarn ) and model carrying capacity degradation rate (D model The relationship between them is:

[0073] D model =1.000385·D yarn +0.016487;

[0074] Among them, D model The value represents the degradation rate of the model's maximum load-bearing capacity; T represents the temperature at which the ceramic matrix composite material is located, in °C; D yarn This indicates the degradation rate of the fiber bundle fracture stress.

[0075] Based on the above two functional relationships, the fiber bundle fracture stress degradation rate D can be calculated according to the temperature T of the ceramic matrix composite material. yarn Then, the degradation rate D of the model's maximum bearing capacity is further calculated. model This allows for the evaluation and prediction of the performance of ceramic matrix composites at high temperatures, providing a theoretical basis for material design, use, and performance optimization.

[0076] S2: Calculate the total strain ε in all directions based on the thermal expansion criterion and mechanical load. The total strain includes the mechanical strain ε. t and thermal strain ε T .

[0077] Specifically, the total strain of a unit is calculated by the sum of mechanical strain and thermal strain. Mechanical loads generate mechanical strain, and temperature loads generate thermal strain. The combined effect of mechanical loads and temperature loads is the high-temperature application load of ceramic matrix composites.

[0078] ε=ε t +ε T =ε t +αΔT;

[0079] Where ε is the total strain, which is the combined degree of deformation of the material under the combined effects of mechanical and thermal forces; ε t Mechanical strain reflects deformation caused solely by mechanical load; ε T α represents thermal strain, reflecting the effect of temperature change on material deformation; α is the coefficient of thermal expansion, reflecting the rate of change of thermal strain of the material under unit temperature change; ΔT is the amount of temperature change.

[0080] S3: Establish a three-dimensional failure criterion for strain control, and define the damage initiation criteria for meridional tension, meridional compression, latitudinal tension, latitudinal compression, out-of-plane tension, and out-of-plane compression.

[0081] Specifically, six failure modes are defined based on the Hathin criterion, coupling the strain in the load-bearing direction with the strain in the shear direction to form a three-dimensional damage initiation condition. These six failure modes include warp tension, warp compression, weft tension, weft compression, out-of-plane tension, and out-of-plane compression. The warp direction is along the fiber direction of the ceramic matrix composite, the weft direction is perpendicular to the fiber direction, and the out-of-plane direction is along the thickness direction of the ceramic matrix composite.

[0082] Warp / weft stretching pattern along the fiber direction (ε) 11 >0):

[0083]

[0084] Warp / weft compression pattern along fiber direction (ε 11 <0):

[0085]

[0086] warp / weft stretching pattern perpendicular to the fiber direction (ε) 22 >0):

[0087]

[0088] Warp / weft compression pattern perpendicular to the fiber direction (ε 22 <0):

[0089]

[0090] Out-of-plane warp / weft stretching pattern (ε) 33 >0):

[0091]

[0092] Out-of-plane warp / weft compression and extrusion mode (ε) 33 <0):

[0093]

[0094] in, The initial strain for tensile damage in the fiber direction. The initial strain for compressive damage in the fiber direction. The tensile damage initiation strain is perpendicular to the fiber direction. The initiation strain for compressive damage is perpendicular to the fiber direction. The initial strain for out-of-plane tensile damage in the Z direction is... The initial strain for out-of-plane compressive damage in the Z direction is... The shear damage initiation strain is defined as the strain along the fiber direction and in the plane perpendicular to the fiber direction. The shear damage initiation strain is defined as the shear damage initiation strain in the fiber direction and the out-of-plane plane. ε is the shear damage initiation strain perpendicular to the fiber direction and the out-of-plane plane. 11 ε is the strain in the fiber direction. 22 ε is the strain perpendicular to the fiber direction. 33 ε represents the strain in the out-of-plane direction. 12 ε represents the shear strain along the fiber direction and perpendicular to the fiber direction. 13 Shear strain ε in the fiber direction and out-of-plane direction 23 This represents the shear strain perpendicular to both the fiber direction and the out-of-plane direction.

[0095] S4: Based on the constitutive relations of tensile / compression / shear failure, a damage evolution model coupling damage factors in different directions is constructed, and the damage factors are calculated to accurately describe the damage development of ceramic matrix composites under stress.

[0096] Specifically, based on the failure modes of ceramic matrix composites, the constitutive relationships and failure modes of tensile, compressive, and shear failures are established, and the calculation equations for damage factors are developed.

[0097] d1 to d6 represent damage factors under different damage modes: d1 represents the damage factor during the stretching and compression process of the fiber direction (warp or weft yarn), d2 represents the damage factor of the matrix during the stretching and compression process, d3 represents the damage factor during the out-of-plane stretching and compression process, d4 represents the damage factor during the in-plane shearing process, d5 represents the damage factor during the out-of-plane shearing process, and d6 represents the damage factor during the cross-shearing process.

[0098] Constitutive relations of fiber bundle tension and compression: The calculation process of damage factor d1 is shown in the following formula:

[0099] When ε 11 When >0 (stretch condition),

[0100]

[0101] Where d1 represents the damage factor during the stretching and compression process in the fiber direction (warp or weft), ε 11 ε is the fiber-direction strain. int ε1 is the critical strain corresponding to the occurrence of tunnel cracks, ε2 is the critical strain corresponding to the occurrence of matrix cracking, ε3 is the critical strain corresponding to the occurrence of fiber tensile fracture, and σ mc For the matrix cracking stress, σ sa For the saturation stress of the matrix crack, σ ft For fiber fracture stress, ε ft This represents the fiber fracture strain.

[0102] When ε 11 When <0 (compression case),

[0103]

[0104] Where, ε fc This represents the critical strain at which fiber compression fracture occurs.

[0105] Constitutive relations of matrix under tension and compression: The calculation process of damage factors d2 and d3 is shown in the following formula.

[0106] When ε 22 ,ε 33 When >0 (matrix tensile condition),

[0107]

[0108] Where, ε 2233 This represents ε corresponding to d2 or d3. 22 or ε 33 d2 represents the strain in the 22 or 33 direction, d3 represents the damage factor of the matrix during tension and compression, and d3 represents the damage factor during out-of-plane tension and compression.

[0109] When ε 22 ,ε 33 When <0 (matrix compression condition),

[0110]

[0111] Where d2 represents the damage factor of the matrix during tension and compression, d3 represents the damage factor during out-of-plane tension and compression, and ε fc This represents the critical strain at which fiber compression fracture occurs.

[0112] Shear constitutive relations: The calculation process for damage factors d4, d5, and d6 is shown in the following formula:

[0113] When γ<0 or γ>0

[0114]

[0115] Where d4 represents the damage factor of the in-plane shear process, d5 represents the damage factor of the out-of-plane shear process, d6 represents the damage factor of the cross-shear process, γ represents the shear strain, and γ represents the damage factor of the cross-shear process. int The critical strain corresponding to shear yielding, γ f The ultimate strain τ at shear fracture y Shear yield stress, τ b Shear fracture stress.

[0116] The parameters required for various damage evolution models are obtained through material experiments (such as uniaxial tensile, compression, and shear tests). During actual material stress processes, strain values ​​in all directions, including the strain ε along the fiber direction, are monitored in real time. 11 Strain ε perpendicular to the fiber direction 22 out-of-plane strain ε 33 And shear strain γ, etc. Based on the monitored strain values ​​and the corresponding applicable conditions, the appropriate damage evolution model formula is selected, and the damage factor in each direction is calculated.

[0117] S5: Constructing the anisotropic stiffness degradation matrix C based on multilinear constitutive relations and damage factors. d .

[0118] Specifically, an anisotropic stiffness degradation matrix C is constructed based on multilinear constitutive relations. d By dynamically adjusting the matrix parameters through damage factors, the stiffness of the failed element is progressively degraded, simulating the mechanical behavior of ceramic matrix composites during the damage process.

[0119] C d It can be done through C d =[S d ] -1 =[MS] -1 calculate;

[0120] Among them, S and S d Let M represent the original compliance matrix and the damage compliance matrix, respectively; M represents the damage operator.

[0121]

[0122] Stiffness degradation matrix C d Specifically, the form is as follows:

[0123]

[0124] Among them, C ij =C ji This matrix is ​​a symmetric matrix, reflecting the stiffness characteristics of the material in different directions;

[0125] Δ=1-(1-d1)(1-d2)ν 12 ν 21 -(1-d1)(1-d3)ν 13 ν 31 -(1-d2)(1-d3)ν 23 ν 32 -2(1-d1)(1-d2)(1-d3)ν 12 ν 23 ν 31 ;

[0126] C 11 =(1-d1)E1-(1-d1)(1-d2)(1-d3)E1ν 23 ν 32 ;

[0127] C 22 =(1-d2)E2-(1-d1)(1-d2)(1-d3)E2ν 13 ν 31 ;

[0128] C 33 =(1-d3)E3-(1-d1)(1-d2)(1-d3)E3ν 12 ν 21 ;

[0129] C 23 =(1-d2)(1-d3)E3ν 23 +(1-d1)(1-d2)(1-d3)E3ν 13 ν 21 ;

[0130] C 13 =(1-d1)(1-d3)E3ν 13 +(1-d1)(1-d2)(1-d3)E3ν 12 ν 23 ;

[0131] C 12 =(1-d1)(1-d2)E2ν 12 +(1-d1)(1-d2)(1-d3)E2ν 13 ν 32 ;

[0132] C 44 =(1-d4)G 23 ;

[0133] C 55 =(1-d5)G 31 ;

[0134] C 66 =(1-d6)G 12 ;

[0135] Where E1 represents the elastic modulus in the fiber direction, E2 represents the elastic modulus perpendicular to the fiber direction, and E3 represents the elastic modulus in the out-of-plane direction. 12 The ratio of Poisson's ratio along the fiber direction to that perpendicular to the fiber direction, v 13 The Poisson's ratio, v, represents the ratio of the fiber direction to the out-of-plane direction. 21 The ratio of Poisson's ratio perpendicular to the fiber direction to the fiber direction, v23 V represents the Poisson's ratio perpendicular to the fiber direction and the out-of-plane direction. 31 The ratio of Poisson's ratio in the out-of-plane direction to that in the fiber direction, v 32 G represents the Poisson's ratio in the out-of-plane direction and perpendicular to the fiber direction. 12 G represents the shear modulus in the fiber direction and perpendicular to the fiber direction. 23 G represents the shear modulus perpendicular to the fiber direction and the out-of-plane direction. 31 This represents the shear modulus in the fiber direction and the out-of-plane direction.

[0136] During implementation, damage factors in various directions are obtained to determine the basic mechanical parameters of the material, such as the elastic modulus E. i Shear modulus G ij Compared to Poisson's ratio v ij These parameters can be obtained through materials experiments. Substituting the damage factor and material parameters into the above formula, Δ and C are calculated sequentially. d Each element in the matrix will be used to calculate C. d The matrix is ​​applied to the constitutive model of the material to update its stiffness properties, simulating the material's mechanical behavior under the current damage state. As the damage progresses, the above steps are repeated to achieve a gradual degradation of stiffness.

[0137] S6: Couple damage evolution and strain control criteria, establish a stress-strain relationship model, and output prediction results for complex stress states.

[0138] The damage initiation criterion in step S3 is used to determine the material's damage initiation status. If damage initiation occurs, the anisotropic stiffness degradation matrix constructed in step S5 based on multilinear constitutive relations and damage factors is used. Taking into account the total material strain calculated in step S2 based on thermal expansion criteria and mechanical loads, the damage evolution process is coupled with the strain control criterion to establish a stress-strain relationship model. This model is then used to calculate and analyze the stress state of ceramic matrix composites under high temperature and complex stress.

[0139]

[0140] Where, ε m The strain matrix is ​​represented by σ; the original stress is represented by σ. This indicates the stress after damage and thermal strain adjustment.

[0141] Ultimately, this will enable the prediction of stress state of ceramic matrix composites under high temperature and complex stress conditions.

[0142] Experimental Example

[0143] 1) Based on the performance degradation formula at high temperature, determine the performance parameters of the fiber bundle and matrix at the simulated temperature, and input the microscopic fiber bundle performance parameters, including matrix tensile and compressive cracking stress, out-of-plane shear cracking stress, fiber bundle damage initiation stress, fiber bundle crack saturation stress, fiber bundle fracture stress, fiber bundle shear fracture stress, fiber bundle and matrix elastic modulus, fiber bundle and matrix thermal expansion coefficient, Poisson's ratio, etc. For specific parameters, refer to Table 1-3.

[0144] Table 1 Elastic parameters of SiC / SiC fiber bundles

[0145]

[0146] Table 2 SiC matrix parameters

[0147]

[0148] Table 3 Damage parameters of SiC / SiC fiber bundles

[0149]

[0150] 2) Obtain the micro-geometric information of the test specimen by scanning electron microscopy, including the length of the major axis of the fiber bundle, the length of the minor axis, the spacing, the number and quantity of warp and weft fiber bundle layers, etc., establish a two-dimensional braided micro-model consistent with the test specimen, and introduce pore structure into the model in combination with the observation results of scanning electron microscopy, so as to achieve the matching of the model and the test specimen in terms of size and pore distribution, which is used to support the micro-modeling and pore effect introduction in the method of this application.

[0151] 3) Apply temperature loads (from room temperature to the test temperature) and displacement loads to the established mesoscopic model, calculate thermal and mechanical strains to obtain the total strain, and use six damage initiation criteria to determine the element damage status. If damage occurs, the model enters the stiffness degradation process. Through this process, the total stress state, including thermal and mechanical stresses, is calculated, and reference thermal stress diagrams for the cooling and heating processes are obtained. Figure 2 The simulation can output damage factor cloud maps of the tensile direction (d1) at 1350℃ and 1600℃, fully demonstrating the damage evolution process. (Reference) Figure 3 and Figure 4 (Red indicates a damage factor of 1, meaning the element has failed). Extract the load-displacement curves at the two temperatures for reference. Figure 5 and Figure 6The material's load-bearing process during the simulation can be divided into four stages: the first stage is the linear stage, where the load-displacement curve shows a linear relationship, and microcracks begin to appear inside the material; the second stage is the matrix cracking stage, where the matrix cracks and reaches crack saturation in multiple regions sequentially; the third stage is the fiber bundle load-bearing stage, where the fiber bundles become the main load-bearing structure, and the cracks within the bundles gradually saturate; the fourth stage is the fracture stage, where the latitudinal fiber bundles fracture at the overlapping areas, ultimately leading to the overall failure of the material. The failure loads simulated at 1350℃ and 1600℃ are 1076N and 525N, respectively.

[0152] 4) Conduct in-situ high-temperature tensile tests (1350℃ and 1600℃), and compare the test results with the calculation results. Refer to the three-dimensional reconstruction model of the specimen under different loads at 1600℃. Figure 7 The failure loads at 1350℃ and 1600℃ are 1065N and 507N, respectively. (Reference) Figure 8 The results show that the calculated damage evolution process (initial cracks at the specimen boundary and pores → matrix tunneling cracks → microcrack saturation within the fiber bundles → fiber fracture at the lap joint of the meridional fiber bundles) is consistent with experimental observations. Figure 9 and Figure 10 The failure load errors at 1350℃ and 1600℃ were 1.03% and 3.55%, respectively, verifying the prediction accuracy and applicability of the method in this application under high temperature and complex stress conditions.

[0153] Although the embodiments of this application have been described above in conjunction with the accompanying drawings, this application is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of this application, and these are all within the scope of protection of this application.

Claims

1. A method for predicting high temperature and complex stress of ceramic matrix composites based on strain-controlled damage evolution, characterized in that, Comprise: S1: determining the current performance parameters of the ceramic matrix composite material based on the high-temperature performance degradation relationship; S2: calculating the total strain in each direction based on the thermal expansion criterion and mechanical load, the total strain including mechanical strain and thermal strain; S3: establishing a three-dimensional strain-controlled failure criterion, defining the damage initiation criteria for longitudinal tensile, longitudinal compression, transverse tensile, transverse compression, out-of-plane tensile and out-of-plane compression; the longitudinal direction is along the fiber direction of the ceramic matrix composite material, the transverse direction is perpendicular to the fiber direction, and the out-of-plane direction is along the thickness direction of the ceramic matrix composite material; S4: constructing a damage evolution model coupled with different direction damage factors according to the constitutive relationship of tensile, compression and shear failure, and calculating the damage factors; S5: Constructing the anisotropic stiffness degradation matrix C based on the multi-linear constitutive relation and the damage factor d ; S6: coupling damage evolution and strain-controlled criterion, establishing a stress-strain relationship model, and outputting the prediction results of complex stress state, the stress-strain relationship model comprising: where M, C d , ε m , α and ΔT represent the damage operator, the stiffness degradation matrix, the strain matrix, the thermal expansion coefficient and the temperature increment, respectively, and S and S d denote the original and damaged flexibility matrices, respectively.

2. The prediction method of claim 1, wherein, The high-temperature performance degradation relationship in step S1 includes: fiber bundle breaking stress degradation rate D yarn and model bearing capacity degradation rate D model ; The fiber bundle stress degradation rate D yarn is: D yarn = 0.002059 T - 2.793443 Wherein, T represents the temperature of the ceramic matrix composite material, unit: ℃; The model carrying capacity degradation rate D model is: D model = 1.000385 · D yarn + 0.016487.

3. The prediction method of claim 1, wherein, The total strain in each direction in step S2 is obtained by linear superposition of mechanical strain and thermal strain: ε = ε t + ε T = ε t + αΔT; where ε is the total strain, ε t is the mechanical strain, ε T is the thermal strain, a is the thermal expansion coefficient, and ΔΤ is the temperature change.

4. The prediction method of claim 1, wherein, The damage initiation criterion in step S3 is based on the Hashin criterion expansion: The longitudinal tensile initiation criterion is: The longitudinal compression initiation criterion is: The transverse tensile initiation criterion is: The transverse compression initiation criterion is: The out-of-plane tensile initiation criterion is: The out-of-plane compression initiation criterion is: wherein, is the tensile damage initiation strain in the fiber direction, is the compressive damage initiation strain in the fiber direction, is the tensile damage initiation strain normal to the fiber direction, is the compressive damage initiation strain normal to the fiber direction, is the out-of-plane tensile damage initiation strain in the Z-direction, is the out-of-plane compressive damage initiation strain in the Z-direction, is the shear damage initiation strain in the fiber direction and in the plane normal to the fiber direction, is the shear damage initiation strain in the fiber direction and in the plane of the out-of-plane direction, is the shear damage initiation strain normal to the fiber direction and in the plane of the out-of-plane direction, 11 is the strain in the fiber direction, ε 22 is the strain normal to the fiber direction, ε 33 is the strain in the out-of-plane direction, ε 12 is the shear strain in the fiber direction and normal to the fiber direction, ε 13 is the shear strain in the fiber direction and in the out-of-plane direction, ε 23 is the shear strain normal to the fiber direction and in the out-of-plane direction.

5. The prediction method of claim 4, wherein, In step S4, the constitutive relationship of fiber bundle tensile and compression of the ceramic matrix composite material is: ε 11 > 0, where d1 represents a damage factor in the fiber direction (warp or weft) during stretching and compression, ε 11 is the fiber direction strain, ε int is the critical strain corresponding to the occurrence of a tunnel crack, ε2 is the critical strain corresponding to the occurrence of matrix cracking, ε3 is the critical strain corresponding to the occurrence of fiber tensile fracture, σ mc is the matrix cracking stress, σ sa is the matrix crack saturation stress, σ ft is the fiber fracture stress, ε ft is the fiber fracture strain; ε 11 <0, where ε fc is the critical strain corresponding to the fiber compression fracture; The constitutive relationship of matrix tensile and compression of the ceramic matrix composite material is: ε 22 ,ε 33 >0, wherein ε 2233 represents ε 22 or ε 33 , i.e. the strain in the 22 or 33 direction, d2 represents the damage factor during tensile and compressive processes in the matrix; d3 represents the damage factor during out-of-plane tensile and compressive processes; ε 22 ,ε 33 <0, The constitutive relationship of shear of the ceramic matrix composite material is: γ<0 or γ>0, where d4 represents a damage factor of the in-plane shear process, d5 represents a damage factor of the out-of-plane shear process, d6 represents a damage factor of the cross-shear process, γ is the shear strain, γ int the critical strain corresponding to the shear yield, γ f the limit strain corresponding to the shear break, τ y the shear yield stress, τ b the shear break stress.

6. The prediction method of claim 1, wherein, The anisotropic stiffness degradation matrix in step S5 is: d = [S d ] -1 = [MS] -1 ; wherein S and S d represent the original and damaged compliance matrices, respectively, and M represents the damage operator matrix.

7. The prediction method of claim 1, wherein, Step S6 includes integrating damage initiation criterion, stiffness degradation matrix and total strain data, simulating damage evolution path through strain-controlled criterion, and outputting stress-strain relationship curve.

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