Method for modeling interface of rivet connection unit of oxidized ceramic matrix composite

Abstract

The invention belongs to the field of aero-engines, and provides an oxidized ceramic matrix composite rivet connection unit interface modeling method which comprises the following steps: performing a rivet ejection test on an oxidized test piece to obtain a load-displacement curve; according to all the load-displacement curves, cohesion model parameters under the designed oxidation time are obtained; according to the initial ejection strength, adopting a Weibull distribution model to determine the ejection strength of the CMCs rivet connection interface unit; and establishing a cohesion interface model according to the ejection strength and the initial fracture energy. According to the method, by analyzing the residual strength and the damage process of the CMCs rivet connection structure after oxidation, the problem that a method for analyzing the residual strength of the CMCs rivet connection structure after oxidation is lacked is solved, and support is provided for development and application of the CMCs complex structure of an advanced aero-engine.

Description

Technical Field

[0001] The present invention belongs to the field of aero-engines and relates to a method for interfacial modeling of a ceramic matrix composite rivet connection unit after oxidation. Background Art

[0002] With the rapid development of advanced aircraft, aero-engines, as the "heart" of the aircraft, are facing huge challenges. Ceramic matrix composites (CMCs) bring great potential benefits to aero-engines in terms of weight, temperature resistance, and performance improvement due to their high specific strength, high specific stiffness, good corrosion resistance, and excellent ultra-high temperature performance, and have become one of the key technologies for the development of advanced aero-engines.

[0003] At present, there is an urgent need for the research and application of CMCs in typical components such as the outer ring of the aero-engine turbine, turbine blades, combustion chambers, and heat shields. Among them, the complex structure and harsh loads of turbine blades pose challenges to the process preparation of CMCs turbine blades. Chemical vapor infiltration (CVI) is one of the earlier developed CMCs preparation processes in China. For the process form that can be connected by the same type of CMCs rivets for complex structures, this process form has stronger adaptability to complex structures, but at the same time brings new problems to the structural design and strength design of CMCs rivet connections.

[0004] In a high-temperature air oxidation environment, oxidizing gases diffuse into the material interior from the pores of CMCs, react with the interface, fibers, and matrix to generate oxidation products, which will reduce the material performance. Among them, due to the structures such as the pores on the outer surface of CMCs rivets, the pores on the opening surface of the CMCs multiple connection structure, and the local pores at the connection interface of the CMCs rivet connection unit, the connection efficiency of the CMCs rivet connection unit is prone to decrease in a high-temperature oxidation environment, and there is currently a lack of a modeling and analysis method for the interface of CMCs rivet connection units after oxidation in engineering, which brings difficulties to the remaining strength of CMCs rivet connection structures after oxidation. Summary of the Invention

[0005] In order to evaluate and assess the remaining strength of CMCs rivet connection structures after oxidation, the present invention discloses a method for interfacial modeling of a ceramic matrix composite rivet connection unit after oxidation, and the method includes the following steps: S1. Oxidize a plurality of CMCs rivet connection specimens at multiple oxidation times to obtain specimens after oxidation, and perform a rivet push-out test on the specimens after oxidation to obtain a load-displacement curve; S2. According to all the load-displacement curves, obtain the cohesive model parameters at the designed oxidation time, and the cohesive model parameters include the initial push-out strength and the initial fracture energy; S3. Determine the ejection strength of the CMCs rivet connection interface unit using the Weibull distribution model according to the initial ejection strength; S4. Establish a cohesive interface model based on the ejection strength and the initial fracture energy.

[0006] Further, in the above step S2, according to all the load-displacement curves, obtain the cohesive model parameters at the designed oxidation time, and the cohesive model parameters include the initial ejection strength and the initial fracture energy, including: S21. Calculate the rivet ejection strength of each oxidized specimen at each oxidation time according to the shear area of the rivet and the maximum load in each load-displacement curve; S22. Solve the first fitting polynomial of the ejection strength and oxidation time constructed according to all the rivet ejection strengths, and solve the second fitting polynomial of the fracture energy and oxidation time constructed according to all the load-displacement curves; S23. Calculate the initial ejection strength at the designed oxidation time according to the first fitting polynomial, and calculate the initial fracture energy at the designed oxidation time according to the second fitting polynomial.

[0007] Even further, in the above step S22, solving the first fitting polynomial of the ejection strength and oxidation time constructed according to all the rivet ejection strengths, and solving the second fitting polynomial of the fracture energy and oxidation time constructed according to all the load-displacement curves, includes: S221. Calculate the mean value of the ejection strength of all the rivet ejection strengths at each oxidation time, and solve the first fitting parameters by solving the first fitting polynomial of the ejection strength and oxidation time constructed according to all the mean values of the ejection strength and their corresponding oxidation times; S222. Calculate the mean value of the fracture energy at each oxidation time by calculating all the load-displacement curves at each oxidation time, and solve the second fitting parameters by solving the second fitting polynomial of the fracture energy and oxidation time constructed according to all the mean values of the fracture energy and their corresponding oxidation times.

[0008] Preferably, the expression of the first fitting polynomial is , and the expression of the second fitting polynomial is , where is the mean value of the ejection strength, t is the oxidation time, and a, b, and c are all the first fitting parameters, is the mean value of the fracture energy, and A, B, and C are all the second fitting parameters.

[0009] Preferably, there are at least 3 oxidation times.

[0010] Further, in the above step S3, determining the ejection strength of the CMCs rivet connection interface unit using the Weibull distribution model according to the initial ejection strength includes: S31. Performing mesh division on the finite element model of the CMCs rivet connection specimen to obtain the number of meshes; S32. Using the Weibull distribution model to generate random strengths with the same quantity as the number of meshes according to the initial ejection strength, where all the random strengths follow a two-parameter Weibull distribution, and taking the shape parameter of the two-parameter Weibull as the ejection strength of the CMCs rivet connection interface unit.

[0011] Further, in the above step S4, establishing a cohesive interface model according to the ejection strength and the initial fracture energy includes: S41. Using finite element software to establish a finite element model of the CMCs rivet and a finite element model of the CMCs structural body respectively, and selecting the area where the CMCs rivet is connected to the CMCs structural body on the finite element model of the CMCs rivet and the finite element model of the CMCs structural body to establish a cohesive model; S42. Assigning the ejection strength and the initial fracture energy to the cohesive model, and applying boundary conditions and loads to complete interface modeling.

[0012] Furthermore, in the above step S41, the cohesive model is a bilinear cohesive model or an exponential cohesive model, and the boundary conditions and loads include displacement, temperature, and force.

[0013] The method of the present invention is a cohesive interface modeling method considering random strength in an oxidation environment. This method takes into account engineering applicability, obtains the relationship between ejection strength, fracture energy, and oxidation time through parameter fitting; considers the randomness of interface bonding strength using the Weibull distribution model; and establishes a cohesive interface model considering random strength after oxidation of CMCs rivet connection through finite element analysis software, laying a foundation for the strength design and evaluation of complex CMCs structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0015] Figure 1 It is a flowchart of the interface modeling method for the oxidized ceramic matrix composite rivet connection unit disclosed in the embodiments of the present invention; Figure 22D-CVI SiC disclosed in the embodiments of the present invention f / SiC rivet connection unit, room temperature ejection test load-displacement curve after different oxidation times; Figure 3 2D-CVI SiC disclosed in the embodiments of the present invention f / SiC rivet connection unit, fitting curve of ejection strength and oxidation time; Figure 4 2D-CVI SiC disclosed in the embodiments of the present invention f / SiC rivet connection unit, fitting curve of ejection fracture energy and oxidation time; Figure 5 2D-CVI SiC disclosed in the embodiments of the present invention f / SiC rivet connection unit, bonding strength distribution after oxidation at 1200 °C for 80 h; Figure 6 2D-CVI SiC disclosed in the embodiments of the present invention f / SiC rivet connection structure finite element model. Detailed implementation manners

[0016] The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0017] The following specific examples illustrate the implementation manners of the present application. Those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The present application can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, without conflict, the following embodiments and the features of the embodiments can be combined with each other. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts belong to the scope of protection of the present application.

[0018] The embodiments of the present invention disclose an interface modeling method for a ceramic matrix composite rivet connection unit after oxidation. This method considers engineering applicability, and uses the parameter fitting method to obtain the relationship between the bonding strength, fracture energy of the CMCs rivet connection unit and the oxidation test; the Weibull distribution model is used to consider the randomness of the interface bonding strength; finally, based on commercial finite element analysis software, a cohesive interface model considering random strength after oxidation of the CMCs rivet connection is established, laying a foundation for the strength design and evaluation of complex CMCs structures. Specifically, referring to Figure 1 as shown, the method includes the following steps: S1. Oxidize multiple CMCs rivet connection specimens at multiple oxidation times respectively to obtain oxidized specimens, and conduct a rivet ejection test on the oxidized specimens to obtain a load-displacement curve; S2. According to all the load-displacement curves, obtain the cohesive force model parameters at the designed oxidation time, and the cohesive force model parameters include the initial ejection strength and the initial fracture energy; S3. Determine the ejection strength of the CMCs rivet connection interface element according to the initial ejection strength by using the Weibull distribution model; S4. Establish a cohesive force interface model according to the ejection strength and the initial fracture energy.

[0019] Further, when implementing the above step S1, at least 3 oxidation times are selected, and corresponding oxidation temperatures can be set for each oxidation time. By conducting an ejection test on the oxidized specimens after oxidation, the load-displacement curves of each oxidized specimen can be obtained, and then the variation law of the bonding performance of the CMCs rivet connection interface with the oxidation time can be obtained. The rivet ejection strengths at other oxidation times can be obtained by interpolation according to the existing test results.

[0020] Further, in the above step S2, according to all the load-displacement curves, obtain the cohesive force model parameters at the designed oxidation time, and the cohesive force model parameters include the initial ejection strength and the initial fracture energy, including: S21. Calculate the rivet ejection strength of each oxidized specimen at each oxidation time according to the rivet shear area and the maximum load in each load-displacement curve; S22. Solve the first fitting polynomial of the ejection strength and the oxidation time constructed according to all the rivet ejection strengths, and solve the second fitting polynomial of the fracture energy and the oxidation time constructed according to all the load-displacement curves; S23. Calculate the initial ejection strength at the designed oxidation time according to the first fitting polynomial, and calculate the initial fracture energy at the designed oxidation time according to the second fitting polynomial.

[0021] Furthermore, in the above step S22, solving the first fitting polynomial of the ejection strength and the oxidation time constructed according to all the rivet ejection strengths, and solving the second fitting polynomial of the fracture energy and the oxidation time constructed according to all the load-displacement curves, includes: S221. Calculate the mean value of the ejection strengths of all the rivet ejection strengths at each oxidation time, and solve the first fitting polynomial of the ejection strength and the oxidation time constructed according to all the mean values of the ejection strengths and their corresponding oxidation times to obtain the first fitting parameter; S222. Calculate the mean fracture energy at each oxidation time from all the load-displacement curves at each oxidation time. Solve for the second fitting parameters of the constructed second fitting polynomial of fracture energy versus oxidation time based on all the mean fracture energies and their corresponding oxidation times.

[0022] Preferably, the expression of the first fitting polynomial is , and the expression of the second fitting polynomial is , where is the mean ejection strength, t is the oxidation time, and a, b, and c are all the first fitting parameters. is the mean fracture energy, and A, B, and C are all the second fitting parameters.

[0023] In specific implementation, the parameters that need to be determined for the cohesive force model usually include the initial stiffness, ejection strength, and fracture energy. These parameters are related to the material direction and are used to characterize the opening mode crack (Type I), slip mode crack (Type II), and tear mode crack (Type III). The failure of the CMCs rivet connection unit under complex loads is usually a mixed type. For the cohesive strength (σ IC , σ IIC and σ IIIC ), the Type I ejection strength σ IC can take the value of the material tensile strength. Assume that the Type II ejection strength σ IIC and the Type III ejection strength σ IIIC are the same as the mean ejection strength , σ IIC =σ IIIC= . Obtain the relationship between the bonding strength of the CMCs rivet connection and the oxidation time by fitting according to the method of steps S21 - S23.

[0024] For the fracture energy (G IC , G IIC and G IIIC ), it is the strain energy release rate that resists crack propagation, corresponding to the unit area under the load-displacement curve. Among them, the Type I fracture energy G IC can be obtained through a single-edge notch fracture toughness test. Define the mean fracture energy as the Type II fracture energy G IIC , and the Type III fracture energy G IIIC is the same as the mean fracture energy G IIC , that is, G IIC =G IIIC . The material load-displacement curve can calculate the area enclosed under the curve, that is, obtain G IIC and G IIIC .

[0025] Further, in the above step S3, determining the ejection strength of the CMCs rivet connection interface unit according to the initial ejection strength by using the Weibull distribution model includes: S31. Performing mesh division on the finite element model of the CMCs rivet connection specimen to obtain the number of meshes; S32. Using the Weibull distribution model to generate random strengths with the same number as the number of meshes according to the initial ejection strength, where all the random strengths follow the two-parameter Weibull distribution, and taking the shape parameter of the two-parameter Weibull as the ejection strength of the CMCs rivet connection interface unit.

[0026] Further, in the above step S4, establishing the cohesive interface model according to the ejection strength and the initial fracture energy includes: S41. Respectively establishing a finite element model of the CMCs rivet and a finite element model of the CMCs structural body by using finite element software, and selecting the area where the CMCs rivet is connected to the CMCs structural body on the finite element model of the CMCs rivet and the finite element model of the CMCs structural body to establish a cohesive model; S42. Assigning the ejection strength and the initial fracture energy to the cohesive model, and applying boundary conditions and loads to complete the interface modeling.

[0027] Furthermore, in the above step S41, the cohesive model is a bilinear cohesive model or an exponential cohesive model, and the boundary conditions and loads include displacement, temperature, force, etc.

[0028] The present invention takes the ejection test piece of 15 2D-CVI SiC f / SiC rivet connection units as an example to illustrate the above method in detail: Step (1): The ejection strengths at room temperature after oxidizing for 0 h (i.e., not oxidized), 50 h, and 100 h at 1200 °C are shown in Table 1 below, and the load-displacement curves are as Figure 2 shown.

[0029] Table 1: Ejection strength of 2D-CVI SiC f / SiC rivet connection unit

[0030] Step (2): The fitting results of the ejection strengths of the 2D-CVI SiC f / SiC rivet connection unit before oxidation and after oxidation at 1200 °C are as Figure 3 shown, and the fitting result is as the following formula (1): (1) Wherein, σpin is the mean value of the ejection strength, MPa; t is the oxidation time, h.

[0031] Step (3): According to the load-displacement curve, calculate the fracture energy of the 2D-CVI SiC f / SiC rivet connection unit before oxidation and after oxidation at 1200°C G IIC , and the calculation results are shown in Table 2 below. The fitting results of the fracture energy are as Figure 4 shown, and the fitting result is as follows in Equation (2): (2) where G IIC is the mean value of the fracture energy, kN / mm; t is the oxidation time, h.

[0032] Table 2: Fracture energy G IIC Calculation results (unit kN / mm)

[0033] Step (4): Calculate the ejection strength of the 2D-CVI SiC f / SiC rivet connection unit after oxidation at 1200°C for 80 h. According to Equation (1) and Equation (2), when t = 80 h, σ pin = 154.1 MPa, G IIC = 3879.9 N / mm.

[0034] Step (5): Considering that during the failure process of the 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 , and the geometric parameter refers to the performance distribution of the CMCs matrix and is temporarily taken as 4. The bonding strength distribution of the 2D-CVI SiC f / SiC rivet connection is as Figure 5 shown.

[0035] Step (6): Establish a calculation model for the 2D-CVI SiC f / SiC rivet connection under a bending load after oxidation at 1200°C for 80 h. The established finite element model and interface model are as Figure 6 shown.

[0036] The method of the present invention is a cohesive interface modeling method considering random strength in an oxidation environment. This method takes into account engineering applicability, and obtains the relationships between the ejection strength, fracture energy and oxidation time through parameter fitting; the randomness of the interface bonding strength is considered by the Weibull distribution model; a cohesive interface model considering random strength after oxidation of CMCs rivet connections is established through finite element analysis software, laying a foundation for the strength design and evaluation of complex CMCs structures.

[0037] In this embodiment, a computer device is provided, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the above-mentioned arbitrary interface modeling method for ceramic matrix composite rivet connections after oxidation is implemented.

[0038] Specifically, the computer device can be a computer terminal, a server or a similar computing device.

[0039] In this embodiment, a computer-readable storage medium is provided, and the computer-readable storage medium stores a computer program for executing the above-mentioned arbitrary interface modeling method for ceramic matrix composite rivet connections after oxidation.

[0040] Specifically, computer-readable storage media include permanent and non-permanent, removable and non-removable media, and information storage can be implemented 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 technologies, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassette tapes, magnetic disk storage or other magnetic storage devices, or any other non-transmission media that can be used to store information accessible by a computing device. As defined herein, computer-readable storage media do not include transitory computer-readable media, such as modulated data signals and carrier waves.

[0041] Obviously, those skilled in the art should understand that the various modules or steps of the above embodiments of the present invention can be implemented by a general-purpose computing device. They can be concentrated on a single computing device or distributed over a network composed of multiple computing devices. Optionally, they can be implemented by program code executable by the computing device. Thus, they can be stored in a storage device and executed by the computing device. And in some cases, the steps shown or described can be executed in a different order than here, or they can be separately fabricated into individual integrated circuit modules, or multiple modules or steps among them can be fabricated into a single integrated circuit module for implementation. In this way, the embodiments of the present invention are not limited to any specific combination of hardware and software.

[0042] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the embodiments of the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for interface modeling of a ceramic matrix composite rivet connection unit after oxidation, characterized in that Comprising: Oxidizing a plurality of CMCs riveted joint specimens at multiple oxidation times respectively to obtain oxidized specimens, and performing a rivet ejection test on the oxidized specimens to obtain a load-displacement curve; According to all the load-displacement curves, obtaining cohesive force model parameters at a designed oxidation time, the cohesive force model parameters including an initial ejection strength and an initial fracture energy; Determining the ejection strength of the CMCs riveted joint interface element by using a Weibull distribution model according to the initial ejection strength; Establishing a cohesive force interface model according to the ejection strength and the initial fracture energy.

2. The interface modeling method of the oxidized ceramic matrix composite rivet connection unit according to claim 1, characterized in that According to all the load-displacement curves, obtaining cohesive force model parameters at a designed oxidation time, the cohesive force model parameters including an initial ejection strength and an initial fracture energy, comprising: Calculating the rivet ejection strength of each oxidized specimen at each oxidation time according to the rivet shear area and the maximum load in each load-displacement curve; Solving a first fitting polynomial of the ejection strength and the oxidation time constructed according to all the rivet ejection strengths, and solving a second fitting polynomial of the fracture energy and the oxidation time constructed according to all the load-displacement curves; Calculating the initial ejection strength at the designed oxidation time according to the first fitting polynomial, and calculating the initial fracture energy at the designed oxidation time according to the second fitting polynomial.

3. The interface modeling method of the ceramic matrix composite rivet connection unit after oxidation according to claim 2, wherein, Solving a first fitting polynomial of the ejection strength and the oxidation time constructed according to all the rivet ejection strengths, and solving a second fitting polynomial of the fracture energy and the oxidation time constructed according to all the load-displacement curves, comprising: Calculating the average ejection strength of all the rivet ejection strengths at each oxidation time, and solving a first fitting parameter of the ejection strength and the oxidation time constructed according to all the average ejection strengths and their corresponding oxidation times; Calculating the average fracture energy at each oxidation time by using all the load-displacement curves at each oxidation time, and solving a second fitting parameter of the fracture energy and the oxidation time constructed according to all the average fracture energies and their corresponding oxidation times.

4. The interface modeling method of the oxidized ceramic matrix composite rivet connection unit according to claim 3, characterized in that, The expression of the first fitting polynomial is , and the expression of the second fitting polynomial is , where is the mean value of the ejection strength, t is the oxidation time, and a, b, and c are all the first fitting parameters is the mean value of the fracture energy, and A, B, and C are all the second fitting parameters 5. The method for interfacial modeling of a ceramic matrix composite rivet connection unit after oxidation according to any one of claims 1 to 4, characterized in that, There are at least 3 oxidation times.

6. The interface modeling method of the oxidized ceramic matrix composite rivet connection unit according to claim 1, characterized in that, Determining the ejection strength of the CMCs riveted joint interface element by using a Weibull distribution model according to the initial ejection strength, comprising: Performing mesh division on the finite element model of the CMCs riveted joint specimen to obtain the number of meshes; Generating random strengths with the same number as the number of meshes according to the initial ejection strength by using a Weibull distribution model, wherein all the random strengths obey a two-parameter Weibull distribution, and taking the shape parameter of the two-parameter Weibull as the ejection strength of the CMCs riveted joint interface element.

7. The interface modeling method of the ceramic matrix composite rivet connection unit according to claim 1, wherein Establishing a cohesive force interface model according to the ejection strength and the initial fracture energy, comprising: The finite element models of CMCs rivets and the finite element model of the main body of the CMCs structure are established by using finite element software respectively. An cohesive model is established for the area where the CMCs rivets are connected to the main body of the CMCs structure on the finite element model of the CMCs rivets and the finite element model of the main body of the CMCs structure; The ejection strength and the initial fracture energy are assigned to the cohesive model, and the boundary conditions and loads are applied to complete the interface modeling.

8. The interface modeling method of the oxidized ceramic matrix composite rivet connection unit according to claim 7, characterized in that The cohesive model is a bilinear cohesive model or an exponential cohesive model, and the boundary conditions and loads include displacement, temperature and force.

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