An Interface Modeling Method for a Riveted Connection Unit of Oxidized Ceramic Matrix Composite Materials

Abstract

The present invention relates to the field of aeroengines and provides a method for modeling the interface of rivet-connected units in ceramic-matrix composites after oxidation. The method comprises: performing a rivet ejection test on an oxidized specimen to obtain a load-displacement curve; obtaining cohesion model parameters at a designed oxidation time based on all load-displacement curves; determining the ejection strength of the CMC rivet connection interface unit using a Weibull distribution model based on the initial ejection strength; and establishing a cohesion interface model based on the ejection strength and initial fracture energy. By analyzing the residual strength and failure process of CMC rivet connection structures after oxidation, the present invention addresses the lack of methods for analyzing the residual strength of CMC rivet connection structures after oxidation, providing support for the development and application of complex CMC structures in advanced aeroengines.

Description

Technical Field

[0001] The invention belongs to the field of aviation engines and relates to a method for modeling an interface of a rivet connection unit of an oxidized ceramic-based composite material. Background Art

[0002] With the rapid development of advanced aircraft, aircraft engines, the heart of aircraft, face significant challenges. Ceramic matrix composites (CMCs), with their high specific strength, high specific stiffness, excellent corrosion resistance, and superior ultra-high-temperature performance, offer significant potential for improving aircraft engine weight, temperature resistance, and performance, making them a key technology in the development of advanced aircraft engines.

[0003] Currently, there is an urgent need for the development and application of CMCs in typical aircraft engine components, such as turbine outer rings, turbine blades, flame tubes, and heat shields. Turbine blades, in particular, present challenges in their fabrication due to their complex structure and demanding loads. Chemical vapor deposition (CVI), one of the earliest CMC fabrication processes in China, offers greater adaptability to complex structures by allowing similar CMCs to be riveted together. However, this process also presents new challenges in the structural and strength design of CMC rivet connections.

[0004] In a high-temperature air oxidation environment, oxidizing gases diffuse through the pores of CMCs into the material, reacting with the interface, fibers, and matrix to form oxidation products, which in turn degrade the material's performance. The connection efficiency of CMC rivet joints is easily reduced in high-temperature oxidation environments due to the pores on the outer surface of the CMC rivets, the pores on the surface of the CMC double-joint structure, and the local pores at the connection interface. Currently, there is a lack of engineering modeling and analysis methods for the interface of CMC rivet joints after oxidation, which poses difficulties in determining the residual strength of CMC rivet joint structures after oxidation. Summary of the Invention

[0005] In order to evaluate and assess the residual strength of CMCs rivet connection structures after oxidation, the present invention discloses a method for modeling the interface of rivet connection units of ceramic matrix composite materials after oxidation, the method comprising the following steps:

[0006] S1. Oxidizing a plurality of CMCs rivet connection specimens at a plurality of oxidation times to obtain oxidized specimens, and performing a rivet ejection test on the oxidized specimens to obtain load-displacement curves;

[0007] S2. Obtaining cohesion model parameters under a designed oxidation time based on all the load-displacement curves, wherein the cohesion model parameters include initial ejection strength and initial fracture energy;

[0008] S3. Determine the ejection strength of the CMCs rivet connection interface unit using a Weibull distribution model based on the initial ejection strength;

[0009] S4. Establishing a cohesive interface model according to the ejection strength and the initial fracture energy.

[0010] Furthermore, in the above step S2, based on all the load-displacement curves, the cohesion model parameters under the designed oxidation time are obtained, and the cohesion model parameters include initial ejection strength and initial fracture energy, including:

[0011] S21, calculating the rivet ejection strength of each oxidized test piece at each oxidation time based on the rivet shear surface area and the maximum load in each load-displacement curve;

[0012] S22. Solving a first fitting polynomial of ejection strength and oxidation time based on all the rivet ejection strengths, and solving a second fitting polynomial of fracture energy and oxidation time based on all the load-displacement curves;

[0013] S23. Calculate the initial ejection strength under the designed oxidation time according to the first fitting polynomial, and calculate the initial fracture energy under the designed oxidation time according to the second fitting polynomial.

[0014] Furthermore, in the above step S22, based on all the rivet ejection strengths, a first fitting polynomial of ejection strength and oxidation time is solved, and based on all the load-displacement curves, a second fitting polynomial of fracture energy and oxidation time is solved, including:

[0015] S221, calculating an average ejection strength of all the rivets at each oxidation time, and solving a first fitting polynomial of ejection strength and oxidation time according to all the average ejection strengths and their corresponding oxidation times to obtain a first fitting parameter;

[0016] S222. Calculate the mean fracture energy at each oxidation time through all the load-displacement curves at each oxidation time, and solve a second fitting polynomial of fracture energy and oxidation time constructed based on all the fracture energy means and their corresponding oxidation times to obtain a second fitting parameter.

[0017] Preferably, the expression of the first fitting polynomial is , the expression of the second fitting polynomial is ,in, is the mean ejection strength, t is the oxidation time, a, b, c are the first fitting parameters, is the mean fracture energy, and A, B, and C are the second fitting parameters.

[0018] Preferably, there are at least three oxidation times.

[0019] Furthermore, in the above step S3, the ejection strength of the CMCs rivet connection interface unit is determined using a Weibull distribution model according to the initial ejection strength, including:

[0020] S31, performing mesh division on the finite element model of the CMCs rivet connection specimen to obtain a mesh number;

[0021] S32. Using a Weibull distribution model to generate random strengths equal to the number of grids based on the initial ejection strength, wherein all the random strengths obey a two-parameter Weibull distribution, and using the shape parameters of the two-parameter Weibull as the ejection strength of the CMCs rivet connection interface unit.

[0022] Furthermore, in the above step S4, a cohesive interface model is established according to the ejection strength and the initial fracture energy, including:

[0023] S41, using finite element software to establish a CMCs rivet finite element model and a CMCs structural body finite element model, respectively, and selecting the area where the CMCs rivet connects to the CMCs structural body on the CMCs rivet finite element model and the CMCs structural body finite element model to establish a cohesive force model;

[0024] S42, assigning the ejection strength and the initial fracture energy to the cohesion model, and applying boundary conditions and loads to complete interface modeling.

[0025] Furthermore, in the above step S41, the cohesion model is a bilinear cohesion model or an exponential cohesion model, and the boundary conditions and loads include displacement, temperature and force.

[0026] The method of the present invention is a cohesive interface modeling method that considers random strength in an oxidizing environment. The method takes engineering applicability into consideration and obtains the relationship between ejection strength, fracture energy, and oxidation time through a parameter fitting method. The randomness of the interface bonding strength is considered using a Weibull distribution model. Finite element analysis software is used to establish a cohesive interface model that considers random strength after oxidation of CMC rivet connections, laying a foundation for the strength design and evaluation of complex CMC structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0028] Figure 1 This is a flow chart of a method for modeling an interface of a rivet connection unit of an oxidized ceramic matrix composite material disclosed in an embodiment of the present invention;

[0029] Figure 2 2D-CVI SiC disclosed in the embodiment of the present invention f / Load-displacement curves of the ejection test of SiC rivet connection units at room temperature after different oxidation times;

[0030] Figure 3 2D-CVI SiC disclosed in the embodiment of the present invention f / Fitting curve of ejection strength and oxidation time of SiC rivet connection unit;

[0031] Figure 4 2D-CVI SiC disclosed in the embodiment of the present invention f / Fitting curve of ejection fracture energy and oxidation time of SiC rivet connection unit;

[0032] Figure 5 2D-CVI SiC disclosed in the embodiment of the present invention f Bonding strength distribution of SiC rivet connection unit after oxidation at 1200℃ for 80h;

[0033] Figure 6 2D-CVI SiC disclosed in the embodiment of the present invention f / SiC rivet connection structure finite element model. DETAILED DESCRIPTION

[0034] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0035] The following describes the embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the features of the following embodiments and embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of this application.

[0036] The embodiment of the present invention discloses a method for modeling the interface of a rivet connection unit of a ceramic matrix composite material after oxidation. The method takes into account engineering applicability and uses a parameter fitting method to obtain the relationship between the bonding strength, fracture energy and oxidation test of the CMCs rivet connection unit; the randomness of the interface bonding strength is considered using a Weibull distribution model; and finally, based on commercial finite element analysis software, a cohesive interface model of the CMCs rivet connection after oxidation is established considering the random strength, laying the foundation for the strength design and evaluation of complex CMCs structures. Specifically, see Figure 1 As shown, the method includes the following steps:

[0037] S1. Oxidizing a plurality of CMCs rivet connection specimens at a plurality of oxidation times to obtain oxidized specimens, and performing a rivet ejection test on the oxidized specimens to obtain load-displacement curves;

[0038] S2. Obtaining cohesion model parameters under a designed oxidation time based on all the load-displacement curves, wherein the cohesion model parameters include initial ejection strength and initial fracture energy;

[0039] S3. Determine the ejection strength of the CMCs rivet connection interface unit using a Weibull distribution model based on the initial ejection strength;

[0040] S4. Establishing a cohesive interface model according to the ejection strength and the initial fracture energy.

[0041] Furthermore, when implementing step S1, at least three oxidation times are selected, and a corresponding oxidation temperature can be set for each oxidation time. By performing an ejection test on the oxidized specimen, a load-displacement curve of each oxidized specimen can be obtained, and then the variation pattern of the bonding performance of the CMCs rivet connection interface with the oxidation time can be obtained. The rivet ejection strength at other oxidation times can be obtained by interpolation based on existing test results.

[0042] Furthermore, in the above step S2, based on all the load-displacement curves, the cohesion model parameters under the designed oxidation time are obtained, and the cohesion model parameters include initial ejection strength and initial fracture energy, including:

[0043] S21, calculating the rivet ejection strength of each oxidized test piece at each oxidation time based on the rivet shear surface area and the maximum load in each load-displacement curve;

[0044] S22. Solving a first fitting polynomial of ejection strength and oxidation time based on all the rivet ejection strengths, and solving a second fitting polynomial of fracture energy and oxidation time based on all the load-displacement curves;

[0045] S23. Calculate the initial ejection strength under the designed oxidation time according to the first fitting polynomial, and calculate the initial fracture energy under the designed oxidation time according to the second fitting polynomial.

[0046] Furthermore, in the above step S22, based on all the rivet ejection strengths, a first fitting polynomial of ejection strength and oxidation time is solved, and based on all the load-displacement curves, a second fitting polynomial of fracture energy and oxidation time is solved, including:

[0047] S221, calculating an average ejection strength of all the rivets at each oxidation time, and solving a first fitting polynomial of ejection strength and oxidation time according to all the average ejection strengths and their corresponding oxidation times to obtain a first fitting parameter;

[0048] S222. Calculate the mean fracture energy at each oxidation time through all the load-displacement curves at each oxidation time, and solve a second fitting polynomial of fracture energy and oxidation time constructed based on all the fracture energy means and their corresponding oxidation times to obtain a second fitting parameter.

[0049] Preferably, the expression of the first fitting polynomial is , the expression of the second fitting polynomial is ,in, is the mean ejection strength, t is the oxidation time, a, b, c are the first fitting parameters, is the mean fracture energy, and A, B, and C are the second fitting parameters.

[0050] In specific implementation, the parameters that need to be determined for the cohesive force model are usually initial stiffness, ejection strength, and fracture energy. These parameters are related to the material direction and are used to characterize opening cracks (Type I), sliding cracks (Type II), and tearing cracks (Type III). Under complex loads, the failure of CMCs rivet connection units is usually mixed. For the cohesive force strength (σ IC ,σ IIC and σ IIIC ), I-type ejection strength σ IC It can be taken as the tensile strength of the material, assuming that the type II ejection strength σ IIC and type III ejection strength σ IIIC and the mean ejection strength Same, σ IIC =σ IIIC= The relationship between the bonding strength of the CMCs rivet connection and the oxidation time is obtained by fitting the method of steps S21-S23.

[0051] For the fracture energy (G IC , G IIC and G IIIC ) is the strain energy release rate to resist crack growth, corresponding to the unit area under the load-displacement curve, where the mode I fracture energy G IC It can be obtained through the single-edge notch fracture toughness test, and the mean fracture energy is defined as the type II fracture energy G IIC , Type III fracture energy G IIIC and the mean fracture energy G IIC Same, that is, G IIC =G IIIC The material load-displacement curve can calculate the area under the curve, that is, G IIC and G IIIC .

[0052] Furthermore, in the above step S3, the ejection strength of the CMCs rivet connection interface unit is determined using a Weibull distribution model according to the initial ejection strength, including:

[0053] S31, performing mesh division on the finite element model of the CMCs rivet connection specimen to obtain a mesh number;

[0054] S32. Using a Weibull distribution model to generate random strengths equal to the number of grids based on the initial ejection strength, wherein all the random strengths obey a two-parameter Weibull distribution, and using the shape parameters of the two-parameter Weibull as the ejection strength of the CMCs rivet connection interface unit.

[0055] Furthermore, in the above step S4, a cohesive interface model is established according to the ejection strength and the initial fracture energy, including:

[0056] S41, using finite element software to establish a CMCs rivet finite element model and a CMCs structural body finite element model, respectively, and selecting the area where the CMCs rivet connects to the CMCs structural body on the CMCs rivet finite element model and the CMCs structural body finite element model to establish a cohesive force model;

[0057] S42, assigning the ejection strength and the initial fracture energy to the cohesion model, and applying boundary conditions and loads to complete interface modeling.

[0058] Furthermore, in the above step S41, the cohesion model is a bilinear cohesion model or an exponential cohesion model, and the boundary conditions and loads include displacement, temperature, force, etc.

[0059] The present invention uses 15 2D-CVI SiC f / The ejection test piece of SiC rivet connection unit is taken as an example to explain the above method in detail:

[0060] Step (1): The ejection strength at room temperature after oxidation at 1200℃ for 0h (i.e., unoxidized), 50h, and 100h is shown in Table 1 below. The load-displacement curve is shown in Figure 2 shown.

[0061] Table 1: 2D-CVI SiC f / SiC rivet connection unit ejection strength

[0062]

[0063] Step (2): 2D-CVI SiC f The ejection strength fitting results of the unoxidized and oxidized SiC rivet connection units at 1200℃ are shown in Figure 2. Figure 3 As shown, the fitting results are as follows (1):

[0064] (1)

[0065] in, σ pin is the mean ejection strength, MPa; t is the oxidation time, h.

[0066] Step (3): Calculate 2D-CVI SiC based on the load-displacement curve f / SiC rivet connection unit before oxidation and after oxidation at 1200℃ G IICThe calculation results are shown in Table 2 below, and the fracture energy fitting results are shown in Figure 4 As shown, the fitting results are as follows (2):

[0067] (2)

[0068] in, G IIC is the mean fracture energy, kN / mm; t is the oxidation time, h.

[0069] Table 2: Fracture energy G IIC Calculation results (unit: kN / mm)

[0070]

[0071] Step (4): Calculate the 2D-CVI SiC after oxidation at 1200℃ for 80h f The ejection strength of the SiC rivet connection unit is calculated according to formula (1) and formula (2). When t=80h, σ pin =154.1MPa, G IIC =3879.9N / mm.

[0072] Step (5): Considering the failure process of CMCs rivet connection unit, the rivet connection interface is mainly type II fracture, so the shape parameter of the Weibull distribution model is taken as σ pin The geometric parameters refer to the CMCs matrix performance distribution and are temporarily taken as 4, 2D-CVISiC f / SiC rivet connection bonding strength distribution Figure 5 shown.

[0073] Step (6): Building 2D-CVI SiC f The calculation model of SiC rivet connection under bending load after oxidation at 1200℃ for 80h is established. The finite element model and interface model are as follows: Figure 6 shown.

[0074] The method of the present invention is a cohesive interface modeling method that considers random strength in an oxidizing environment. The method takes engineering applicability into consideration and obtains the relationship between ejection strength, fracture energy, and oxidation time through a parameter fitting method. The randomness of the interface bonding strength is considered using a Weibull distribution model. Finite element analysis software is used to establish a cohesive interface model that considers random strength after oxidation of CMC rivet connections, laying a foundation for the strength design and evaluation of complex CMC structures.

[0075] In this embodiment, a computer device is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, any of the above-mentioned methods for modeling the interface of a rivet connection unit of a post-oxidation ceramic matrix composite material is implemented.

[0076] Specifically, the computer device may be a computer terminal, a server or a similar computing device.

[0077] In this embodiment, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores a computer program for executing any of the above-mentioned methods for modeling interfaces of rivet connection units of oxidized ceramic matrix composite materials.

[0078] Specifically, computer-readable storage media include permanent and non-permanent, removable and non-removable media that can be used to store information by any method or technology. The information can be computer-readable instructions, data structures, program modules or other data. Examples of computer-readable storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassettes, tape disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer-readable storage media does not include transitory media such as modulated data signals and carrier waves.

[0079] Obviously, those skilled in the art should understand that the various modules or steps of the above-mentioned embodiments of the present invention can be implemented using a general-purpose computing device, they can be concentrated on a single computing device, or distributed across a network composed of multiple computing devices. Alternatively, they can be implemented using program code executable by the computing device, so that they can be stored in a storage device and executed by the computing device. In some cases, the steps shown or described can be performed in a different order than herein, or they can be made into separate integrated circuit modules, or multiple modules or steps can be made into a single integrated circuit module for implementation. Thus, the embodiments of the present invention are not limited to any specific combination of hardware and software.

[0080] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for modeling the interface of a rivet connection unit of an oxidized ceramic matrix composite material, characterized in that: include: A plurality of CMCs rivet connection specimens are oxidized at various oxidation times to obtain oxidized specimens, and a rivet ejection test is performed on the oxidized specimens to obtain load-displacement curves; Obtaining cohesion model parameters at a designed oxidation time based on all the load-displacement curves, the cohesion model parameters including initial ejection strength and initial fracture energy, including: calculating the rivet ejection strength of each oxidized specimen at each oxidation time based on the rivet shear surface area and the maximum load in each load-displacement curve; solving a first fitting polynomial of ejection strength and oxidation time constructed based on all the rivet ejection strengths, and solving a second fitting polynomial of fracture energy and oxidation time constructed based on all the load-displacement curves; calculating the initial ejection strength at the designed oxidation time based on the first fitting polynomial, and calculating the initial fracture energy at the designed oxidation time based on the second fitting polynomial; Determining the ejection strength of the CMCs rivet connection interface unit using a Weibull distribution model based on the initial ejection strength, comprising: meshing a finite element model of the CMCs rivet connection specimen to obtain a number of meshes; generating random strengths equal to the number of meshes based on the initial ejection strength using the Weibull distribution model, wherein all the random strengths obey a two-parameter Weibull distribution, and using shape parameters of the two-parameter Weibull distribution as the ejection strength of the CMCs rivet connection interface unit; A cohesive interface model is established based on the ejection strength and the initial fracture energy, including: using finite element software to respectively establish a CMCs rivet finite element model and a CMCs structural body finite element model, selecting the area where the CMCs rivet and the CMCs structural body are connected on the CMCs rivet finite element model and the CMCs structural body finite element model to establish a cohesive force model; assigning the ejection strength and the initial fracture energy to the cohesive force model, and applying boundary conditions and loads to complete the interface modeling.

2. The interface modeling method of the rivet connection unit of the oxidized ceramic matrix composite material according to claim 1, characterized in that: Solving a first fitting polynomial of the ejection strength and the oxidation time according to all the rivet ejection strengths, and solving a second fitting polynomial of the fracture energy and the oxidation time according to all the load-displacement curves, including: Calculating an average ejection strength of all the rivets at each oxidation time, and solving a first fitting polynomial of ejection strength and oxidation time according to all the average ejection strengths and their corresponding oxidation times to obtain a first fitting parameter; The mean fracture energy at each oxidation time is calculated through all the load-displacement curves at each oxidation time. According to all the fracture energy means and their corresponding oxidation times, the second fitting polynomial of the fracture energy and oxidation time is solved to obtain the second fitting parameter.

3. The interface modeling method of the rivet connection unit of the oxidized ceramic matrix composite material according to claim 2, characterized in that: The expression of the first fitting polynomial is: , the expression of the second fitting polynomial is ,in, is the mean ejection strength, t is the oxidation time, a, b, c are the first fitting parameters, is the mean fracture energy, and A, B, and C are the second fitting parameters.

4. The interface modeling method of rivet connection unit of oxidized ceramic matrix composite material according to any one of claims 1 to 3, characterized in that: There are at least three oxidation times.

5. The interface modeling method of rivet connection unit of oxidized ceramic matrix composite material according to claim 1, characterized in that: The cohesion model is a bilinear cohesion model or an exponential cohesion model, and the boundary conditions and loads include displacement, temperature and force.

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