A prediction method for the strength dispersion of CMC considering the thermo-solid coupling effect

Abstract

The present invention relates to a method for predicting the strength of a composite material, in particular a CMC progressive damage strength prediction method considering thermo-solid coupling effects based on dispersion analysis. This method overcomes the drawbacks of existing methods that do not simultaneously consider the dispersion of CMC material properties and thermo-solid coupling effects by establishing an RVE geometric model of CMC, considering the dispersion of the mesoscopic structure strength of CMC, and performing thermo-solid coupling analysis on its progressive damage process under different temperature conditions. Therefore, the CMC strength dispersion analysis method considering thermo-solid coupling effects of the present invention can achieve thermo-solid coupling analysis considering the dispersion of CMC strength properties, and the method is easy to implement.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials, and particularly relates to a CMC progressive damage strength prediction method considering thermo-solid coupling effects based on dispersion analysis. Background Art

[0002] Ceramic Matrix Composites (CMC for short) are lightweight high-temperature resistant composite materials with broad application prospects at present, and are very suitable for application in hot-end components of aerospace. In order to ensure the service conditions of CMC components under various temperature conditions, more accurate strength limit prediction results of CMC are required. Since the design of CMC components is very different from that of traditional metal components, the prediction methods for their strength limits are also different. In the performance analysis of CMC, it is necessary to consider the material property dispersion caused by the structural dispersion of the composite material, and at the same time consider the characteristics of inhomogeneity and anisotropy of the CMC structural components. Therefore, it is difficult to predict the strength of CMC. In current research, a small part is for the strength prediction of CMC at room temperature under the condition of considering structural dispersion, and a small part is for the strength prediction of CMC under high-temperature conditions. However, there are few studies on the strength prediction of CMC considering the influence of material dispersion and material temperature conditions. Therefore, the accuracy of the CMC strength prediction results still needs to be improved, and the current methods are not sufficient to widely cover CMC materials with different preform structures.

[0003] Currently, comprehensively considering different temperature conditions during the service of CMC and its high degree of dispersion in structure and performance, analyzing the progressive damage process of CMC at the Representative Volume Element (RVE) scale, and predicting the stress-strain relationship and strength limit of CMC materials are important and urgently needed technical problems in this technical field. Summary of the Invention

[0004] Aiming at the deficiencies of the above-mentioned existing technologies, the present invention provides a CMC strength dispersion prediction method considering thermo-solid coupling effects.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A CMC strength dispersion prediction method considering thermo-solid coupling effects, comprising the following steps:

[0007] Step 1: Establish an analysis model: According to the actual preform geometric characteristics of CMC, combined with specific calculation requirements and simulation purposes, ignoring the microscopic inhomogeneity of the preform that has little influence on the simulation calculation, construct a CMC material RVE geometric model of the preform, which is composed of CMC composite material fiber bundles arranged in the warp and weft directions and the matrix in the fiber bundle intervals;

[0008] Step 2: Determine the initial material parameters of the model: Mesh the CMC material RVE geometric model to form fiber bundle elements and matrix elements, and assign corresponding material parameters to each fiber bundle element and matrix element;

[0009] Step 3: Thermo-solid coupling mechanical analysis: Determine the RVE temperature load distribution according to the temperature conditions, and apply periodic boundary conditions and initial external loads to the CMC material RVE geometric model for finite element analysis;

[0010] Step 4: Determine the dispersity of component properties: According to the known tensile strength distribution function of the CMC small composite material, determine the strength distribution of the fiber bundles in the CMC material. According to this distribution, give the tensile strain limit and shear strain limit of the fiber bundle elements in the CMC material RVE geometric model, and give the tensile strain limit and shear strain limit of the matrix elements in the CMC material RVE geometric model according to the strength distribution of the matrix in the CMC material. Take the tensile strain limit, shear strain limit of the fiber bundle elements and the tensile strain limit, shear strain limit of the matrix elements as the failure criteria for the fiber bundle elements and matrix elements;

[0011] Step 5: Progressive damage analysis: Judge the failure of fiber bundle elements and matrix elements according to the failure criteria of fiber bundle elements and matrix elements in Step 4, reduce the material properties of the failed fiber bundle elements and matrix elements, and then re-analyze the stress and strain of the remaining fiber bundle elements and matrix elements and judge the element failure. Repeat this process until the overall failure of the CMC material;

[0012] Step 6: Determine the material strength: Draw the stress-strain curve of the CMC material according to the finite element analysis results, and determine the material strength limit;

[0013] Step 7: Determine the material strength distribution: Use the models established in Step 1 and Step 2, repeat the multiple finite element analyses from Step 3 to Step 6, perform function fitting on the obtained RVE strength results, and determine the strength distribution of the CMC material.

[0014] To optimize the above technical solutions, the specific measures taken also include:

[0015] In the above Step 1, the actual geometric characteristics of the CMC preform are obtained based on its CT scan image. During the construction of the geometric model, its cross-sectional shape, fiber orientation and pore microstructure should be approximated under the condition of retaining the basic characteristics required for calculation to facilitate analysis.

[0016] In the above Step 2, the material parameters include elastic modulus, shear modulus and Poisson's ratio.

[0017] In the above step 3, the temperature condition is the temperature distribution at a certain point of the CMC actual preform under its working condition, and the initial external load of the RVE is a mechanical external load far less than the failure strength.

[0018] The specific method for applying periodic boundary conditions to the CMC material RVE geometric model in step 3 is as follows:

[0019]

[0020] (v x＝LC -v x＝0 ) y,z =0

[0021] (w x＝LC -w x＝0 ) y,z =0

[0022] (u y＝WC -u y＝0 ) x,z =0

[0023]

[0024] (w y＝WC -w y＝0 ) x,z =0

[0025] (u z＝HC -u z＝0 ) x,y =0

[0026] (v z＝HC -v z＝0 ) x,y =0

[0027]

[0028] where u i 、v i 、w i are the displacements of the specified point in the RVE geometric model in the X, Y, and Z orthogonal directions respectively. The specified point is represented by a subscript. For example, (u x＝LC -u x＝0 ) y,z represents the subtraction of the displacements in the X direction at (LC, 0, 0) and (0, 0, 0); are the strains of the three representative points rp1, rp2, and rp3 in the X, Y, and Z directions respectively.

[0029] The known tensile strength distribution function of the CMC small composite material in the above step 4 is the Weibull distribution function: Among them, P(σ) is the tensile strength of the small composite material, and σ, S0, and m represent the strength, scale parameter, and shape parameter of the small composite material, respectively.

[0030] In the above step 5, the element failure judgment method follows the maximum strain criterion: ε and γ are the tensile strain and shear strain of each element, respectively, and ε t and γ s are the tensile strain limit and shear strain limit of the corresponding elements, respectively.

[0031] In the above step 5, the reduction treatment of the element material properties refers to gradually reducing the stiffness of the element by percentage reduction until it reaches zero.

[0032] In the above step 7, the specific method for fitting the function to the RVE strength results obtained from the analysis to determine the strength distribution of the CMC material is as follows: fitting the multiple RVE strength results obtained from the analysis to a normal distribution by the least squares method, so as to determine the strength distribution law of the CMC material, and the distribution probability density where a and μ are different influencing factors.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] The present invention provides a method for analyzing the strength dispersion of CMC considering the thermo-solid coupling effect. By establishing the RVE geometric model of CMC, considering the dispersion of the mesoscopic structure strength of CMC, and performing thermo-solid coupling analysis on its progressive damage process under different temperature conditions, the present invention overcomes the shortcomings of the existing methods that do not consider both the dispersion of CMC material properties and the thermo-solid coupling effect at the same time. Therefore, the method for analyzing the strength dispersion of CMC considering the thermo-solid coupling effect of the present invention can realize the thermo-solid coupling analysis considering the dispersion of CMC strength performance, and the method is easy to implement. Description of the Drawings

[0035] Figure 1 is a schematic diagram of the RVE geometric model of 2.5D woven CMC material in the embodiment;

[0036] Figure 2 is a schematic diagram of the result of dividing the finite element mesh of the RVE of 2.5D woven CMC material in the embodiment;

[0037] Figure 3 is the stress-strain curve of 2.5D woven CMC in the embodiment. Among them, point A is the point corresponding to the material strength on the stress-strain curve.

[0038] The reference numerals are: 1. RVE geometric model of 2.5D woven CMC material, 2. Fiber bundle of 2.5D woven CMC material, 3. Matrix of 2.5D woven CMC material. Detailed implementation manners

[0039] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0040] The present invention provides an analysis method for the strength dispersion of CMC considering the thermo-solid coupling effect. Taking 2.5D woven CMC as an example and an implementation object, the method includes the following steps:

[0041] Step 1: Establish an analysis model. As Figure 1 shown, according to the actual preform geometric characteristics of 2.5D woven CMC, for the purpose of analyzing the overall tensile strength, ignoring some microscale inhomogeneities, a 2.5D woven CMC material RVE geometric model 1 is established. This model is composed of 2.5D woven CMC material fiber bundles 2 arranged in the warp and weft directions and the 2.5D woven CMC material matrix 3 in the fiber bundle intervals. Since there are always a large number of large-sized holes in the 2.5D woven CMC material matrix 3 of this material, the porosity between the fiber bundles is approximately 100%, and the 2.5D woven CMC material matrix 3 is the hole.

[0042] Step 2: Determine the initial material parameters of the model. Mesh the CMC material RVE geometric model, and the meshing result is as Figure 2 shown. Assign material parameters to each element, including elastic modulus, shear modulus, Poisson's ratio, etc.

[0043] Step 3: Thermo-solid coupling mechanical analysis. Determine the RVE temperature load distribution according to the temperature distribution at a certain point of the macroscopic component under its working condition, and apply periodic boundary conditions to the CMC material RVE geometric model:

[0044]

[0045] (v x＝LC -v x＝0 ) y,z = 0

[0046] (w x＝LC -w x＝0 ) y,z = 0

[0047] (u y＝WC -u y＝0 ) x,z = 0

[0048]

[0049] (w y＝WC -w y＝0) x,z = 0

[0050] (u z＝HC - u z＝0 ) x,y = 0

[0051] (v z＝HC - v z＝0 ) x,y = 0

[0052]

[0053] where u i , v i , w i are the displacements of the specified point in the RVE in the three orthogonal directions of X, Y, and Z, respectively. The specified point is represented by a subscript. For example, (u x＝LC - u x＝0 ) y,z represents the subtraction of the displacements in the X direction at (LC, 0, 0) and (0, 0, 0); are the strains of the three representative points rp1, rp2, and rp3 in the three directions of X, Y, and Z, respectively. A low-level initial mechanical external load far less than the failure strength is applied for stress-strain analysis.

[0054] Step 4: Determination of structural dispersion. According to the tensile strength distribution function of the CMC small composite material, such as the Weibull distribution function where σ, S0, and m represent the strength, scale parameter, and shape parameter of the small composite material, respectively, determine the strength distribution of the fiber bundles in the 2.5D woven CMC RVE; according to this distribution, given the failure criteria for the fiber bundle elements in the CMC material RVE geometric model, that is, the tensile strain limit and shear strain limit for each fiber bundle element. Similarly, given the strength distribution of the matrix in the 2.5D woven CMC material, the failure criteria for the matrix elements in the CMC material RVE geometric model are determined.

[0055] Step 5: Progressive damage analysis: Determine and process the element failure according to the element failure criteria in Step 4, that is, according to the element failure criteria obtained in Step 4, with the maximum strain criterion: (ε and γ are the tensile strain and shear strain of each element, respectively, and ε t and γ s are the tensile strain limit and shear strain limit of the corresponding elements, respectively) as the material failure criterion to judge whether each element fails; perform stiffness reduction processing on the material properties of the failed elements, re-conduct stress-strain analysis and element failure judgment, and repeat this process until the overall failure of the material. The stiffness reduction of the element material is carried out in the form of percentage reduction, and the material stiffness is gradually reduced to a very small value close to zero.

[0056] Step 6: Determine the material strength. Draw a material stress-strain curve based on the stress-strain results of the simulation experiment, in the form of Figure 3 , and determine the material strength according to this figure. The stress value corresponding to the end point A of the curve is the material strength value. The stress-strain curve is a curve formed by the overall stress and strain results obtained from the continuously repeated process in Step 4, and the stress at its end point is the material strength.

[0057] Step 7: Determine the material strength distribution. Continuing with the results of Step 1 and Step 2, repeat the multiple simulation experiments from Step 3 to Step 6. The operations for each repetition of the simulation experiment are the same; fit the multiple material strength results obtained from the multiple simulation experiments into a normal distribution by the least squares method, and the distribution probability density (where σ is the material strength, and a and μ are influencing factors), and determine the strength distribution law of the 2.5D woven CMC.

[0058] The above is only the preferred implementation mode of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, several improvements and refinements made without departing from the principle of the present invention should be regarded as within the protection scope of the present invention.

Claims

1. A method for predicting the strength dispersion of CMC considering the thermo-solid coupling effect, characterized in that It includes the following steps: Step 1: Establish an analysis model: According to the actual geometric characteristics of the CMC preform, combined with specific calculation requirements and simulation purposes, ignoring the mesoscopic inhomogeneity of the preform that has little impact on the simulation calculation, construct a geometric model of the CMC material RVE for the preform. This model is composed of CMC composite fiber bundles arranged in the warp and weft directions and the matrix in the intervals between the fiber bundles; Step 2: Determine the initial material parameters of the model: Mesh the geometric model of the CMC material RVE to form fiber bundle elements and matrix elements, and assign corresponding material parameters to each fiber bundle element and matrix element; Step 3: Thermo-solid coupling mechanical analysis: Determine the RVE temperature load distribution according to the temperature condition, and apply periodic boundary conditions and initial external loads to the geometric model of the CMC material RVE for finite element analysis; Step 4: Determine the dispersion of component properties: According to the known tensile strength distribution function of the CMC small composite material, determine the strength distribution of the fiber bundles in the CMC material. According to this distribution, given the tensile strain limit and shear strain limit of the fiber bundle elements in the geometric model of the CMC material RVE, and given the tensile strain limit and shear strain limit of the matrix elements in the geometric model of the CMC material RVE by the strength distribution of the matrix in the CMC material. Use the tensile strain limit, shear strain limit of the fiber bundle elements and the tensile strain limit, shear strain limit of the matrix elements as the failure criteria for the fiber bundle elements and matrix elements; Step 5: Progressive damage analysis: Judge the failure of the fiber bundle elements and matrix elements according to the failure criteria of the fiber bundle elements and matrix elements in Step 4, reduce the material properties of the failed fiber bundle elements and matrix elements, and then re-analyze the stress and strain of the remaining fiber bundle elements and matrix elements and judge the element failure. Repeat this process until the overall failure of the CMC material; Step 6: Determine the material strength: Draw the stress-strain curve of the CMC material according to the finite element analysis results and determine the material strength limit; Step 7: Determine the material strength distribution: Use the model established in Step 1 and Step 2, repeat the multiple finite element analyses from Step 3 to Step 6, perform function fitting on the RVE strength results obtained from the analysis, and determine the strength distribution of the CMC material.

2. A prediction method for the strength dispersion of CMC considering the thermosetting coupling effect according to claim 1, characterized in that, The actual geometric characteristics of the CMC preform in Step 1 are obtained based on its CT scan image. During the construction of the geometric model, its cross-sectional shape, fiber orientation, and pore mesoscopic structure should be approximated under the condition of retaining the basic characteristics required for the calculation to facilitate analysis.

3. The prediction method for the strength dispersion of CMC considering the thermo-solid coupling effect according to claim 2, wherein In Step 2, the material parameters include elastic modulus, shear modulus, and Poisson's ratio.

4. A method for predicting the strength dispersion of CMC considering the thermo-solid coupling effect according to claim 3, characterized in that In Step 3, the temperature condition is the temperature distribution at a certain point of the CMC actual preform under its working condition, and the RVE initial external load is a mechanical external load far less than the failure strength.

5. A prediction method for the strength dispersion of CMC considering the thermo-solid coupling effect according to claim 4, characterized in that The specific method of applying periodic boundary conditions to the geometric model of the CMC material RVE in Step 3 is: (v x＝LC -v x＝0 ) y,z = 0 (w x＝LC -w x＝0 ) y,z = 0 (u y＝WC -u y＝0 ) x,z = 0 (w y＝WC -w y＝0 ) x,z = 0 (u z＝HC -u z＝0 ) x,y = 0 (v z＝HC -v z＝0 ) x,y = 0 where u i , v i , w i are the displacements of the specified point in the RVE geometric model in the three orthogonal directions of X, Y, and Z, respectively. The specified point is represented by a subscript. For example, (u x＝LC - u x＝0 ) y,z represents the subtraction of the displacements in the X direction at (LC, 0, 0) and (0, 0, 0); are the strains of the three representative points rp1, rp2, and rp3 in the three directions of X, Y, and Z, respectively.

6. A prediction method for the strength dispersion of CMC considering the thermo-solid coupling effect according to claim 5, characterized in that The known tensile strength distribution function of the CMC small composite material in step 4 is the Weibull distribution function: where P(σ) is the tensile strength of the small composite material, and σ, S0, and m represent the strength, scale parameter, and shape parameter of the small composite material, respectively.

7. A prediction method for the strength dispersion of CMC considering the thermo-solid coupling effect according to claim 6, characterized in that The unit failure judgment method in step 5 follows the maximum strain criterion: ε and γ are the tensile strain and shear strain of each unit respectively, and ε t and γ s are the tensile strain limit and shear strain limit of the corresponding units respectively.

8. A method for predicting the strength dispersion of CMC considering the thermo-solid coupling effect according to claim 7, characterized in that, The reduction treatment of the element material properties in Step 5 refers to gradually reducing the stiffness of the element in a percentage reduction manner until it reaches zero.

9. A method for predicting the strength dispersion of CMC considering the thermo-solid coupling effect according to claim 8, characterized in that, In step 7, the specific method for function fitting of the RVE strength results obtained by analysis to determine the strength distribution of the CMC material is as follows: multiple RVE strength results obtained by analysis are fitted into a normal distribution by the least squares method, so as to determine the strength distribution law of the CMC material, and the distribution probability density where a and μ are different influencing factors.

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