Method for predicting, regulating and controlling residual stress of thermal structure of large integral ceramic matrix composite
By establishing a curing and pyrolysis model of the thermal structure of ceramic matrix composite materials, predicting and controlling residual stress, the problem of not considering the impact of the curing process in the prior art is solved, and low-cost and efficient process stress optimization and precise control are achieved.
Patent Information
- Application Number
- CN202510640546.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-19
- Publication Date
- 2025-08-15
AI Technical Summary
When establishing a thermal structure process stress control model of the integrated ceramic matrix composite, the existing technology failed to consider the impact of the ceramic precursor curing process on the process stress, resulting in inaccurate residual stress prediction, and the traditional process optimization method is costly, which limits the widespread application of large integrated ceramic matrix composite materials.
By establishing thermal structure curing and pyrolysis models of ceramic matrix composites, the total strain increment and equivalent stress increment of ceramic precursors are predicted, combined with curing and multiple rounds of pyrolysis processes, the residual stress is predicted and regulated, including adjusting geometric characteristics and process parameters to optimize the process scheme.
Low-cost and efficient process stress optimization for different fiber/matrix materials and thermal structure geometry is achieved, improving the accuracy of residual stress prediction and process control accuracy, and reducing manufacturing costs.
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Figure CN120493550A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of advanced manufacturing of composite material structures, and in particular relates to a method for predicting and controlling residual stress of a large-scale integral ceramic-based composite material thermal structure. Background Art
[0002] The high-performance, precise, integral forming technology for large, monolithic ceramic-based composite thermal structures directly determines the high performance, reliability, and even development success of these structures. Using accurate, reasonable, and efficient process mechanics models to predict and control thermal structure residual stresses is a key step in minimizing the application risks of aircraft thermal structures during service and maximizing their comprehensive thermal performance advantages and potential. Among them, the precursor infusion and pyrolysis process (PIP) is a near-net-shape preparation method for CMC thermal structures. It gradually increases the density of the ceramic matrix through repeated cycles of ceramic precursor infiltration and pyrolysis. This process can better control the matrix composition and microstructure, as well as the net-shape manufacturing of complex monolithic components, and has important applications in the manufacturing of high-temperature, monolithic thermal structures for aerospace. However, the process stresses generated during the precursor pyrolysis process severely restrict the application and advancement of large-scale, monolithic CMC thermal structures, and even the development of high-performance thermal structures.
[0003] However, during the PIP process, if Figure 1 As shown, both the curing and pyrolysis processes of the ceramic precursor lead to residual stresses in the matrix, ultimately causing pores and cracks in the CMC. If not predicted and controlled, this can lead to unpredictable catastrophic failure during the subsequent use of the thermal structure, resulting in unnecessary losses. Furthermore, the optimal processing conditions vary for different fiber / matrix materials and thermal structure geometries, necessitating repeated optimization. Because CMC parts typically have low production volumes, traditional process optimization methods result in high manufacturing costs, limiting their widespread industrial application. Therefore, establishing an analytical model for the PIP process can help reduce process optimization time and costs.
[0004] In summary, the high-temperature forming process of large-scale, monolithic ceramic-matrix composite thermal structures is extremely complex and lacks accurate quantitative analysis methods. Existing modeling methods for controlling process stress in monolithic ceramic-matrix composite thermal structures have the following main shortcomings: They fail to consider the impact of the "curing" process on process stress during the PIP process. Traditional models generally assume that the ceramic precursor after curing and before pyrolysis is in a stress-free state, and process stress prediction begins with pyrolysis after curing. However, in reality, the series of compositional evolutions, chemical shrinkage, and thermal stresses that occur during the curing process generate non-negligible process stresses. Furthermore, existing technical experience in forming ceramic-matrix composite wing and rudder thermal structures lacks effective control of forming process stresses, making it unable to meet the demanding manufacturing precision and quality requirements of the new generation of large-scale, monolithic ceramic-matrix composite thermal structures. This has become a bottleneck technology that urgently needs to be overcome in the design and manufacture of thermal structures for new aircraft. Summary of the Invention
[0005] In response to the problems existing in the prior art, the present invention proposes a method for predicting and controlling the residual stress of the thermal structure of a large-scale integral ceramic-based composite material. The purpose is to solve the problem that the prior art does not consider the influence of the ceramic precursor curing process on the process stress when establishing the thermal structure process stress control model of the integral ceramic-based composite material.
[0006] The present invention proposes the following technical solutions to solve the technical problems:
[0007] A method for predicting and controlling residual stress of a large-scale integral ceramic matrix composite thermal structure is characterized by comprising the following steps:
[0008] Step 1: Prediction of residual stress based on the effect of the ceramic precursor curing process on process stress, specifically including the following steps:
[0009] 1) Establish a thermal structural curing model for ceramic matrix composites;
[0010] 2) Establish a thermal structure pyrolysis model of ceramic matrix composites;
[0011] 3) obtaining the total strain increment and equivalent stress increment of the ceramic precursor;
[0012] 4) Predict the final residual stress of the thermal structure of ceramic matrix composites;
[0013] Step 2: Residual stress control based on the influence of the ceramic precursor curing process on the process stress, specifically including the following process:
[0014] 1) Based on the comparison between the predicted residual stress and the target residual stress, the residual stress is controlled by adjusting the geometric features of the input geometric model at a certain coordinate (x, y, z);
[0015] 2) By adjusting the curing process parameters and pyrolysis process parameters, the process parameters are optimized to achieve the purpose of reducing residual stress.
[0016] Furthermore, the establishment of the thermal structure curing model of the ceramic matrix composite material in the step 1) is as follows: Under a certain curing process temperature field T(x, y, z, t), the curing kinetic equation can be expressed as:
[0017]
[0018] In the formula, the known number is: A can be obtained through experiments α 、E α , n1 and the universal gas constant R, A α represents the curing reaction frequency factor, E α represents the activation energy of the curing reaction, n1 is the curing reaction order; the unknowns are: absolute temperature T, curing degree α and curing rate dα / dt, among which absolute temperature T is the independent variable, and curing degree α and curing rate dα / dt are dependent variables.
[0019] Furthermore, the step 1 process 2) of establishing a thermal structure pyrolysis model of ceramic matrix composite materials is specifically as follows: for a given pyrolysis process temperature field T(x, y, z, t), the pyrolysis kinetic equation can be expressed as:
[0020]
[0021] In the formula, the known number is A which can be obtained through experiments r 、E r and n2 and the universal gas constant R, A r represents the pyrolysis reaction frequency factor, E r represents the activation energy of the pyrolysis reaction, n2 is the pyrolysis reaction order; the unknowns are absolute temperature T, ceramic conversion degree r and ceramic conversion rate dr / dt, among which absolute temperature T is the independent variable, and ceramic conversion degree r and ceramic conversion rate dr / dt are dependent variables.
[0022] Furthermore, the total strain increment and equivalent stress increment of the ceramic precursor obtained in step 1 process 3) are specifically as follows:
[0023] ① The incremental linear elastic model is used to describe the strain of the precursor during the curing and pyrolysis process. The total strain increment of the precursor is described as follows:
[0024] Δε=Δε e +Δε th +Δε ch (3)
[0025] Among them, the known number is: Δε e , Δεth and Δε ch , respectively elastic strain, thermal strain and chemical shrinkage strain increments: elastic strain increment Δε e is a function of the applied load, which is a known input; the thermal strain increment Δε th =βΔT is a function of ΔT, β is the thermal expansion coefficient, which is a known number; chemical strain increment Δε ch Satisfy Δε during the curing process ch =ηΔα, which is a function of Δα; Δε is satisfied during the pyrolysis process ch =ηΔr, which is a function of Δr and a known number.
[0026] ②The equivalent stress increment can be expressed as follows:
[0027] Δσ=CΔε (4)
[0028] Among them, the left side of the equal sign in formula (4) is the total residual stress increment during the PIP process, the right side of the equal sign Δε is the known number obtained in formula (3), and C is the elastic stiffness matrix, which evolves with the process. The residual stress during the PIP process can be obtained by integrating formula (4).
[0029] Furthermore, the specific steps of predicting the final residual stress of the thermal structure of the ceramic matrix composite material in step 1 process 4) are as follows:
[0030] ① Obtain the curing residual stress field during the curing process;
[0031] ② The residual stress generated during the solidification process is used as the initial stress field input for multiple rounds of pyrolysis to obtain the final residual stress prediction.
[0032] Furthermore, the residual stress of the curing process in step 1 (4) is obtained as follows:
[0033] 1) Input the geometric model of the curing process;
[0034] 2) Apply the same load boundary conditions as the actual working condition to the geometric model. At this time, the increase in load leads to the generation of elastic strain increment Δε e ;
[0035] 3) Apply temperature boundary conditions T(t) to the geometric model according to the curing process temperature. At this time, the temperature change produces a thermal expansion strain increment Δε th ;
[0036] 4) Update and determine the curing degree field size α, the curing degree α changes to produce chemical shrinkage strain increment Δε ch ;
[0037] 5) Update the matrix properties. Changes in matrix properties lead to updates in the stiffness C matrix.
[0038] 6) Elastic strain increment Δε e , thermal expansion strain increment Δε th , chemical shrinkage strain increment Δε ch and the stiffness matrix C as input to update the curing residual stress field;
[0039] 7) Determine whether the curing process is completed. If the curing process is not completed, return to process 2) and continue to iterate the curing residual stress field. If the curing process is completed, continue to process 8).
[0040] 8) The solidified residual stress field will be passed as input to the subsequent multiple rounds of pyrolysis simulation.
[0041] Furthermore, in step 1, process 4) link ②, the residual stress generated during the solidification process is used as the initial stress field input for multiple rounds of pyrolysis to obtain the final residual stress prediction, as follows:
[0042] 1) Input the geometric model of the pyrolysis process, which is the same as the geometric model of the solidification process;
[0043] 2) Apply the same load boundary conditions as the actual working condition to the geometric model. At this time, the increase in load leads to the generation of elastic strain increment Δε e ;
[0044] 3) Apply the temperature boundary condition T(t) to the geometric model according to the pyrolysis process temperature. At this time, the temperature change generates the thermal expansion strain increment Δε ch
[0045] 4) Update and determine the ceramic conversion field size r. The change of ceramic conversion r produces a chemical shrinkage strain increment Δε ch ;
[0046] 5) Update the matrix components and properties. Changes in matrix components and properties lead to updates in the stiffness matrix C.
[0047] 6)Δε e , Δε ch , Δε th and C as input to update the pyrolysis residual stress field;
[0048] 7) Determine whether the current round of pyrolysis is complete. If it is complete, proceed to step 8). If not, return to step 2) and start a new round of pyrolysis.
[0049] 8) Determine whether the pyrolysis rounds are sufficient. If so, proceed to step 9). If not, return to step 2).
[0050] 9) Output residual stress prediction results.
[0051] Furthermore, in the step 2 process 1), the residual stress is controlled by adjusting the geometric features of the input geometric model at a certain coordinate (x, y, z). The geometric model is divided into three types: control of the microstructure and composition of the preform, control of the geometric features of the thermal structure, and control of the surface curvature; the preform is a geometric frame of woven fibers inside a large integral ceramic-based composite material; the thermal structure is a large ceramic-based composite material prepared by a PIP process based on the preform; the surface curvature refers to the curvature feature of the geometric shape of the large ceramic-based composite material.
[0052] Furthermore, the regulation of the microscopic structure and composition of the preform is specifically as follows: at the microscopic level, the residual stress is regulated by adjusting the uniform distribution and volume fraction of the fibers; at the microscopic level, the residual stress is regulated by adjusting the weaving or laying method of the fiber bundles, the spatial distribution and volume fraction of the fiber bundles; the regulation of the geometric characteristics of the thermal structure: by adjusting the geometric shape, size, thickness and symmetry of the thermal structure, the optimal geometric characteristics are found to regulate the residual stress; the regulation of the surface curvature: the change in curvature may change the location of stress concentration, and the residual stress distribution under different curvatures is obtained by adjusting the surface, thereby regulating the appropriate surface curvature.
[0053] Furthermore, the residual stress control method based on process parameters in step 2 is specifically as follows:
[0054] 1) By adjusting the curing temperature curve T(t) and the pyrolysis temperature curve T(t), such as the heating gradient and the isothermal dwell time, the curing rate dα / dt and the pyrolysis rate dr / dt are controlled to ensure uniform curing and ceramic conversion and reduce residual stress caused by local unevenness; the temperature curve T(t) is an independent variable that affects the curing degree α(x, y, z, t) and the ceramic conversion degree r(x, y, z, t).
[0055] 2) For multiple rounds of pyrolysis, the pyrolysis temperature, heating rate, and holding time are set in stages; the pyrolysis temperature, heating rate, and holding time are all included in the temperature curve T(t), thereby finding the optimal process route to achieve the purpose of regulating residual stress.
[0056] Advantages and effects of the present invention
[0057] 1. This invention fully considers the effects of curing and multiple cycles of pyrolysis on residual stresses, establishing a more comprehensive model for predicting thermal process stresses in monolithic ceramic matrix composites. This method allows for cost-effective and efficient optimization of PIP process solutions for different fiber / matrix materials and thermal structure geometries, achieving optimal control of process stresses.
[0058] 2. Since the present invention takes into account the influence of the curing process on the residual stress, the predicted process stress generated by the PIP process can be closer to the actual situation and therefore more accurate;
[0059] 3. Since the present invention takes into account the curing and multiple rounds of pyrolysis processes that mainly generate process stress in the PIP process, it can change the process parameters in these processes based on experimental data, and then optimize the process plan to achieve the purpose of controlling process stress. Compared with traditional process optimization methods that result in higher manufacturing costs, this helps to reduce process time and cost. BRIEF DESCRIPTION OF THE DRAWINGS
[0060] Figure 1 This is a schematic diagram of the PIP process flow;
[0061] Figure 2 This is a flow chart of the process residual stress prediction and control method of the present invention;
[0062] Figure 3 This is a flow chart of residual stress prediction in the process of the present invention;
[0063] Figure 4 This is a flow chart of residual stress control in the process of the present invention. DETAILED DESCRIPTION
[0064] The innovation of the present invention is: First, the degree of solidification α and the total strain increment Δε are organically combined, and the total strain increment Δε=Δε in formula (3) e +Δε th +Δε ch In the description of ch Satisfy Δε during the curing process ch =ηΔα, which is a function of Δα; Δε is satisfied during the pyrolysis process ch =ηΔr, which is a function of Δr. Therefore, the total strain increment takes into account both the curing degree increment Δα and the conversion degree increment Δr. Second, the residual stress generated during the curing process is used as the initial stress field input for multiple rounds of pyrolysis to obtain the final residual stress prediction. Figure 3 As shown in the figure, the input to the geometric model during the pyrolysis process is not only the load conditions, but also the previously obtained curing residual stress field, that is, the Δε obtained during the pyrolysis process. th , Δε ch , Δε e are affected by the residual stress field during the solidification process, or in other words, the Δε obtained during the pyrolysis process th , Δε ch , Δε e Δε including the curing process th , Δε ch , Δε eThird, the prediction of residual stress based on the influence of the ceramic precursor curing process on process stress is organically combined with the residual stress control based on the influence of the ceramic precursor curing process on process stress. Prediction comes first, followed by control. Accurate prediction leads to accurate control. Because the influence of residual stress during the curing process is taken into account when predicting residual stress, the control stage can achieve an accurate control target.
[0065] Based on the above invention principle, the present invention designs a method for predicting and controlling the residual stress of the thermal structure of a large-scale integral ceramic matrix composite material. Figure 2-4 As shown, its characteristics are: comprising the following steps:
[0066] Step 1: Prediction of residual stress based on the effect of the ceramic precursor curing process on process stress, specifically including the following steps:
[0067] Supplementary Note 1 :
[0068] The difference between the present invention and the prior art is that the residual stress prediction in the prior art does not take into account the residual stress generated during the curing process, but only considers the residual stress of the pyrolysis process. The difference between step 1 of the present invention and the prior art is that the residual stress prediction of the present invention is a prediction of the residual stress that takes into account the influence of the ceramic precursor curing process on the process stress. Therefore, the following processes 1), 2), 3), and 4) are all designed around the residual stress generated during the curing process.
[0069] 1) Establish a thermal structural curing model for ceramic matrix composites;
[0070] Specifically, under a certain curing process temperature field T(x, y, z, t), the curing kinetics equation can be expressed as:
[0071]
[0072] In the formula, the known number is: A can be obtained through experiments α 、E α , n1 and the universal gas constant R, A α represents the curing reaction frequency factor, E α represents the activation energy of the curing reaction, n1 is the curing reaction order; the unknowns are: absolute temperature T, curing degree α and curing rate dα / dt, among which absolute temperature T is the independent variable, and curing degree α and curing rate dα / dt are dependent variables.
[0073] 2) Establish a thermal structure pyrolysis model of ceramic matrix composites; the details are as follows:
[0074] For a given pyrolysis process temperature field T(x,y,z,t), the pyrolysis kinetic equation can be expressed as:
[0075]
[0076] In the formula, the known number is A which can be obtained through experiments r 、E r and n2 and the universal gas constant R, A r represents the pyrolysis reaction frequency factor, E r represents the activation energy of the pyrolysis reaction, n2 is the pyrolysis reaction order; the unknowns are absolute temperature T, ceramic conversion degree r and ceramic conversion rate dr / dt, among which absolute temperature T is the independent variable, and ceramic conversion degree r and ceramic conversion rate dr / dt are dependent variables.
[0077] 3) Obtaining the total strain increment and equivalent stress increment of the ceramic precursor; specifically as follows:
[0078] ① The incremental linear elastic model is used to describe the strain of the precursor during the curing and pyrolysis process. The total strain increment of the precursor is described as follows:
[0079] Δε=Δε e +Δε th +Δε ch (7)
[0080] Among them, the known number is: Δε e , Δε th and Δε ch , respectively elastic strain, thermal strain and chemical shrinkage strain increments: elastic strain increment Δε e is a function of the applied load, which is a known input; the thermal strain increment Δε th =βΔT is a function of ΔT, β is the thermal expansion coefficient, which is a known number; chemical strain increment Δε ch Satisfy Δε during the curing process ch =ηΔα, which is a function of Δα; Δε is satisfied during the pyrolysis process ch =ηΔr, which is a function of Δr and a known number.
[0081] ②The equivalent stress increment can be expressed as follows:
[0082] Δσ=CΔε (8)
[0083] Among them, the left side of the equal sign in formula (4) is the total residual stress increment during the PIP process, the right side of the equal sign Δε is the known number obtained in formula (3), and C is the elastic stiffness matrix, which evolves with the process. The residual stress during the PIP process can be obtained by integrating formula (4).
[0084] Supplementary Note 2 :
[0085] First, the left side of formula (3) is the total strain increment. It can be seen that the chemical strain increment Δε ch Satisfy Δε during the curing process ch =ηΔα, that is, the total strain increment includes the stress caused by the curing degree increment;
[0086] Second, formula (4) is the equivalent stress increment, that is, the predicted residual stress. Since the total strain increment takes into account the curing degree increment Δα, the equivalent stress increment also includes the residual stress of the curing process.
[0087] 4) If Figure 3 As shown in the figure, the final residual stress of the thermal structure of ceramic matrix composites is predicted; the specific steps are as follows:
[0088] Supplementary Note 3:
[0089] The following method for predicting the final residual stress of a ceramic matrix composite thermal structure is divided into two steps. The present invention differs from the prior art in that the curing residual stress field is calculated first, followed by the total predicted stress. The prior art predicts residual stresses, not the curing residual stress field, but only the residual stresses from the pyrolysis process.
[0090] ① Obtain the curing residual stress field during the curing process; the details are as follows:
[0091] 1) Input the geometric model of the curing process;
[0092] 2) Apply the same load boundary conditions as the actual working condition to the geometric model. At this time, the increase in load leads to the generation of elastic strain increment Δε e ;
[0093] 3) Apply temperature boundary conditions T(t) to the geometric model according to the curing process temperature. At this time, the temperature change produces a thermal expansion strain increment Δε th ;
[0094] 4) Update and determine the curing degree field size α, the curing degree α changes to produce chemical shrinkage strain increment Δε ch ;
[0095] 5) Update the matrix properties. Changes in matrix properties lead to updates in the stiffness C matrix.
[0096] 6) Elastic strain increment Δε e , thermal expansion strain increment Δε th , chemical shrinkage strain increment Δε ch and the stiffness matrix C as input to update the curing residual stress field;
[0097] 7) Determine whether the curing process is completed. If the curing process is not completed, return to process 2) and continue to iterate the curing residual stress field. If the curing process is completed, continue to process 8).
[0098] 8) The solidified residual stress field will be passed as input to the subsequent multiple rounds of pyrolysis simulation.
[0099] ② The residual stress generated during the solidification process is used as the initial stress field input for multiple rounds of pyrolysis to obtain the final residual stress prediction. The details are as follows:
[0100] 1) Input the geometric model of the pyrolysis process, which is the same as the geometric model of the solidification process;
[0101] 2) Apply the same load boundary conditions as the actual working condition to the geometric model. At this time, the increase in load leads to the generation of elastic strain increment Δε e ;
[0102] 3) Apply the temperature boundary condition T(t) to the geometric model according to the pyrolysis process temperature. At this time, the temperature change generates the thermal expansion strain increment Δε ch
[0103] 4) Update and determine the ceramic conversion field size r. The change of ceramic conversion r produces a chemical shrinkage strain increment Δε ch ;
[0104] 5) Update the matrix components and properties. Changes in matrix components and properties lead to updates in the stiffness matrix C.
[0105] 6)Δε e , Δε ch , Δε th and C as input to update the pyrolysis residual stress field;
[0106] 7) Determine whether the current round of pyrolysis is complete. If it is complete, proceed to step 8). If not, return to step 2) and start a new round of pyrolysis.
[0107] 8) Determine whether the pyrolysis rounds are sufficient. If so, proceed to step 9). If not, return to step 2).
[0108] 9) Output residual stress prediction results.
[0109] Step 2: Residual stress control based on the influence of the ceramic precursor curing process on the process stress, specifically including the following process:
[0110] Supplementary Note 4:
[0111] The difference between the present invention and the prior art is that the residual stress control is based on the residual stress prediction including the residual stress generated during the solidification process.
[0112] 1) Based on the comparison between the predicted residual stress and the target residual stress, the residual stress is controlled by adjusting the geometric features of the input geometric model at a certain coordinate (x, y, z);
[0113] This geometric model is divided into three categories: the regulation of the microstructure and composition of the preform, the regulation of the geometric characteristics of the thermal structure, and the regulation of the surface curvature. The preform is the geometric framework of the woven fibers inside the large-scale monolithic ceramic matrix composite material; the thermal structure is the large-scale ceramic matrix composite material prepared and formed by the PIP process based on the preform; and the surface curvature refers to the curvature characteristics of the geometric shape of the large-scale ceramic matrix composite material.
[0114] The regulation of the microscopic structure and composition of the preform is specifically as follows: at the microscopic level, the residual stress is regulated by adjusting the uniform distribution and volume fraction of the fibers; at the microscopic level, the residual stress is regulated by adjusting the weaving or laying method of the fiber bundles, the spatial distribution and volume fraction of the fiber bundles; the regulation of the geometric characteristics of the thermal structure: by adjusting the geometric shape, size, thickness and symmetry of the thermal structure, the optimal geometric characteristics are found to regulate the residual stress; the regulation of the surface curvature: the change in curvature may change the location of stress concentration, and the residual stress distribution under different curvatures is obtained by adjusting the surface, thereby regulating to obtain a suitable surface curvature.
[0115] 2) By adjusting the curing process parameters and pyrolysis process parameters, the process parameters are optimized to achieve the purpose of reducing residual stress. Specifically:
[0116] ① By adjusting the curing temperature curve T(t) and the pyrolysis temperature curve T(t), such as the heating gradient and the isothermal residence time, the curing rate dα / dt and the pyrolysis rate dr / dt are controlled to make the curing and ceramic conversion occur uniformly and reduce the residual stress caused by local unevenness; the temperature curve T(t) is an independent variable that affects the curing degree α(x, y, z, t) and the ceramic conversion degree r(x, y, z, t).
[0117] ② For multiple rounds of pyrolysis, the pyrolysis temperature, heating rate, and holding time are set in stages; the pyrolysis temperature, heating rate, and holding time are all included in the temperature curve T(t), thereby finding the optimal process route to achieve the purpose of regulating residual stress.
[0118] It should be emphasized that the above specific embodiments are merely explanations of the present invention and are not limitations of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the above embodiments as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.
Claims
1. A method for predicting and controlling residual stress in thermal structures of large-scale monolithic ceramic matrix composite materials, characterized by: The following steps are involved: Step 1: Prediction of residual stress based on the effect of ceramic precursor curing process on process stress. The following processes are included: 1) Establish a thermal structural curing model for ceramic matrix composites; 2) Establish a thermal structure pyrolysis model of ceramic matrix composites; 3) obtaining the total strain increment and equivalent stress increment of the ceramic precursor; 4) Predict the final residual stress of the thermal structure of ceramic matrix composites; Step 2: Residual stress control based on the influence of the ceramic precursor curing process on the process stress, specifically including the following process: 1) Based on the comparison between the predicted residual stress and the target residual stress, the residual stress is regulated by adjusting the geometric features of the input geometric model at a certain coordinate (x, y, z); 2) By adjusting the curing process parameters and pyrolysis process parameters, the process parameters are optimized to achieve the purpose of reducing residual stress.
2. The method for predicting and controlling residual stress of thermal structure of large-scale monolithic ceramic matrix composite materials according to claim 1, characterized in that: The step 1) of establishing a thermal structure curing model of ceramic matrix composite materials is as follows: Under a certain curing process temperature field T (x, y, z, t), the curing kinetic equation can be expressed as: In the formula, the known number is: A can be obtained through experiments α 、E α , n1 and the universal gas constant R, A α represents the curing reaction frequency factor, E α represents the activation energy of the curing reaction, n1 is the curing reaction order; the unknowns are: absolute temperature T, curing degree α and curing rate dα / dt, among which absolute temperature T is the independent variable, and curing degree α and curing rate dα / dt are dependent variables.
3. The method for predicting and controlling residual stress of thermal structure of large-scale monolithic ceramic matrix composite materials according to claim 1, characterized in that: The step 1 process 2) of establishing a thermal structure pyrolysis model of ceramic matrix composite materials is as follows: for a given pyrolysis process temperature field T (x, y, z, t), the pyrolysis kinetic equation can be expressed as: In the formula, the known number is A which can be obtained through experiments r 、E r and n2 and the universal gas constant R, A r represents the pyrolysis reaction frequency factor, E r represents the activation energy of the pyrolysis reaction, n2 is the pyrolysis reaction order; the unknowns are absolute temperature T, ceramic conversion degree r and ceramic conversion rate dr / dt, among which absolute temperature T is the independent variable, and ceramic conversion degree r and ceramic conversion rate dr / dt are dependent variables.
4. The method for predicting and controlling residual stress of thermal structure of large-scale monolithic ceramic matrix composite materials according to claim 1, characterized in that: The total strain increment and equivalent stress increment of the ceramic precursor in step 1 process 3) are obtained as follows: ① The incremental linear elastic model is used to describe the strain of the precursor during the curing and pyrolysis process. The total strain increment of the precursor is described as follows: No = No e +No th +No ch (3) Among them, the known number is: Δε e , Δε th and Δε ch , respectively elastic strain, thermal strain and chemical shrinkage strain increments: elastic strain increment Δε e is a function of the applied load, which is a known input; the thermal strain increment Δε th =βΔT is a function of ΔT, β is the thermal expansion coefficient, which is a known number; chemical strain increment Δε ch Satisfy Δε during the curing process ch =ηΔα, which is a function of Δα; Δε is satisfied during the pyrolysis process ch =ηΔr, a function of Δr, which is a known number; ②The equivalent stress increment can be expressed as follows: Δσ=CΔε (4) Among them, the left side of the equal sign in formula (4) is the total residual stress increment during the PIP process, the right side of the equal sign Δε is the known number obtained in formula (3), and C is the elastic stiffness matrix, which evolves with the process. The residual stress during the PIP process can be obtained by integrating formula (4).
5. The method for predicting and controlling residual stress of thermal structure of large-scale monolithic ceramic matrix composite materials according to claim 4, characterized in that: The specific steps of predicting the final residual stress of the thermal structure of the ceramic matrix composite material in step 1 process 4) are as follows: ① Obtain the curing residual stress field during the curing process; ② The residual stress generated during the solidification process is used as the initial stress field input for multiple rounds of pyrolysis to obtain the final residual stress prediction.
6. The method for predicting and controlling residual stress of thermal structure of large-scale monolithic ceramic matrix composite materials according to claim 4, characterized in that: The residual stress of the curing process in step 1 (4) is obtained as follows: 1) Input the geometric model of the curing process; 2) Apply the same load boundary conditions as the actual working condition to the geometric model. At this time, the increase in load leads to the generation of elastic strain increment Δε e ; 3) Apply temperature boundary conditions T(t) to the geometric model according to the curing process temperature. At this time, the temperature change produces a thermal expansion strain increment Δε th ; 4) Update and determine the curing degree field size α, the curing degree α changes to produce chemical shrinkage strain increment Δε ch ; 5) Update the matrix properties. Changes in matrix properties lead to updates in the stiffness C matrix. 6) Elastic strain increment Δε e , thermal expansion strain increment Δε th , chemical shrinkage strain increment Δε ch and the stiffness matrix C as input to update the curing residual stress field; 7) Determine whether the curing process is completed. If the curing process is not completed, return to step 2) and continue to update and iterate the curing residual stress field. If the curing process is complete, continue with process 8); 8) The solidified residual stress field will be passed as input to the subsequent multiple rounds of pyrolysis simulation.
7. The method for predicting and controlling residual stress of thermal structure of large-scale monolithic ceramic matrix composite materials according to claim 4, characterized in that: In step 1, process 4) (2), the residual stress generated during the solidification process is used as the initial stress field input for multiple rounds of pyrolysis to obtain the final residual stress prediction, as follows: 1) Input the geometric model of the pyrolysis process, which is the same as the geometric model of the solidification process; 2) Apply the same load boundary conditions as the actual working condition to the geometric model. At this time, the increase in load leads to the generation of elastic strain increment Δε e ; 3) Apply the temperature boundary condition T(t) to the geometric model according to the pyrolysis process temperature. At this time, the temperature change generates the thermal expansion strain increment Δε ch 4) Update and determine the ceramic conversion field size r. The change of ceramic conversion r produces a chemical shrinkage strain increment Δε ch ; 5) Update the matrix components and properties. Changes in matrix components and properties lead to updates in the stiffness matrix C. 6)Δε e , Δε ch , Δε th and C as input to update the pyrolysis residual stress field; 7) Determine whether the current round of pyrolysis is complete. If it is complete, proceed to step 8). If not, return to step 2) and start a new round of pyrolysis. 8) Determine whether the pyrolysis rounds are sufficient. If so, proceed to step 9). If not, return to step 2). 9) Output residual stress prediction results.
8. The method for predicting and controlling thermal structural residual stress of a large-scale monolithic ceramic matrix composite material according to claim 1, characterized in that: In the step 2 process 1), the residual stress is controlled by adjusting the geometric features of the input geometric model at a certain coordinate (x, y, z). The geometric model is divided into three types: control of the microstructure and composition of the preform, control of the geometric features of the thermal structure, and control of the surface curvature; the preform is a geometric frame of woven fibers inside a large integral ceramic-based composite material; the thermal structure is a large ceramic-based composite material prepared by the PIP process based on the preform; the surface curvature refers to the curvature characteristics of the geometric shape of the large ceramic-based composite material.
9. The method for predicting and controlling thermal structural residual stress of a large-scale monolithic ceramic matrix composite material according to claim 4, characterized in that: The regulation of the microscopic structure and composition of the preform is specifically as follows: at the microscopic level, the residual stress is regulated by adjusting the uniform distribution and volume fraction of the fibers; at the microscopic level, the residual stress is regulated by adjusting the weaving or laying method of the fiber bundles, the spatial distribution and volume fraction of the fiber bundles; the regulation of the geometric characteristics of the thermal structure: by adjusting the geometric shape, size, thickness and symmetry of the thermal structure, the optimal geometric characteristics are found to regulate the residual stress; the regulation of the surface curvature: the change in curvature may change the location of stress concentration, and the residual stress distribution under different curvatures is obtained by adjusting the surface, thereby regulating to obtain a suitable surface curvature.
10. The method for predicting and controlling residual stress of thermal structure of large-scale monolithic ceramic matrix composite materials according to claim 1, characterized in that: The residual stress control method based on process parameters in step 2 is specifically as follows: 1) by adjusting the curing temperature curve T(t) and the pyrolysis temperature curve T(t), such as the temperature ramp and the isothermal dwell time, controlling the curing rate dα / dt and the pyrolysis rate dr / dt, so that the curing and ceramic conversion occur uniformly and the residual stress caused by local unevenness is reduced; the temperature curve T(t) is an independent variable that affects the curing degree α(x, y, z, t) and the ceramic conversion degree r(x, y, z, t); 2) For multiple rounds of pyrolysis, the pyrolysis temperature, heating rate, and holding time are set in stages; the pyrolysis temperature, heating rate, and holding time are all included in the temperature curve T(t), thereby finding the optimal process route to achieve the purpose of regulating residual stress.