Method and system for predicting creep-fatigue life of welded component based on multi-material constraint effect

Abstract

The invention discloses a welded component creep-fatigue life prediction method and system based on a multi-material constraint effect, and relates to the technical field of crack propagation and life prediction of high-temperature structural materials. Respectively obtaining a nonlinear relationship between the normalized creep-fatigue rate and the normalized constraint parameter of the homogeneous material under different holding time and the reference working condition, and a linear relationship between the mismatch condition and the normalized creep-fatigue rate and the normalized constraint parameter of the homogeneous material under the same holding time; and through coupling the nonlinear relationship and the linear relationship, predicting the creep-fatigue crack growth rate of the welding joint at different mismatch levels under different holding time. According to the method, the creep-fatigue crack propagation residual life of the welding joint under different holding time and working conditions can be efficiently predicted, and accurate residual life evaluation on the welding component under complex working conditions is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of crack propagation and life prediction of high-temperature structural materials, and in particular to a method and system for predicting the creep-fatigue life of welded components based on multi-material constraint effects. Background Art

[0002] Currently, an increasing number of thermal and nuclear power plants are operating under extreme operating conditions exceeding 600°C and 25 MPa. Furthermore, with the large-scale development and integration of renewable energy into the grid, thermal and nuclear power plants are facing demands for flexible power generation and deep peak load regulation. These changes are subjecting high-temperature components (such as steam pipes, reheaters, and superheaters) to long-term combined creep-fatigue stress. Since most of these high-temperature components are welded structures, they are highly susceptible to creep-fatigue damage. Typically, different regions of welded joints (such as the base metal, weld, and heat-affected zone) exhibit differences in high-temperature mechanical properties, introducing a property mismatch at the joint. Furthermore, complex local metallurgical behavior occurs in various regions during welding, making cracks or crack-like defects more likely to form. These defects often serve as initiation sources for creep-fatigue cracks. Consequently, welded joints are often considered the weakest link in high-temperature structures. A deeper understanding of the creep-fatigue crack growth characteristics and creep-fatigue damage distribution of welded joints is crucial for assessing the residual life of welded joints and ensuring the safe service life of high-temperature welded components.

[0003] In the traditional prediction of creep-fatigue crack growth behavior, a relatively simple creep-fatigue linear superposition damage model is usually used to simulate the crack growth behavior. However, a large number of studies have shown that under high-temperature cyclic loading, creep damage and fatigue damage interact and significantly affect the crack growth behavior. In addition, traditional creep-fatigue life prediction methods mostly use simplified material models, ignoring the performance differences between different material regions in the weld joint (such as base metal, weld and heat-affected zone). However, the material property differences between the base metal, weld metal and heat-affected zone in actual weld joints, especially the creep and fatigue behavior differences under high temperature conditions, often lead to significant differences in crack growth rate and life. The main deficiency of the existing technology is that it fails to consider the material property mismatch effect in the weld joint area and generally fails to accurately reflect the creep-fatigue interactive damage behavior of different weld joint areas. Summary of the Invention

[0004] In order to solve the above problems, the purpose of the present invention is to provide a creep-fatigue life prediction technology for welded components based on multi-material constraint effects, aiming to enable accurate remaining life assessment of welded components under complex working conditions.

[0005] To achieve the above technical objectives, the present application provides a method for predicting the creep-fatigue life of welded components based on the multi-material constraint effect, comprising the following steps:

[0006] (1) Construction of multiaxial creep-fatigue damage model:

[0007] Based on existing creep damage and fatigue damage models, a new creep-fatigue damage model is constructed by combining multiaxial creep ductility and cyclic plastic strain. This model comprehensively considers the ductile behavior of materials under multiaxial creep conditions, especially the nonlinear cumulative effects of plastic strain and cyclic loading on creep damage at high temperatures. The creep damage calculation method is as follows:

[0008]

[0009]

[0010] Among them, σ m / σ e is the stress triaxiality, σ i (i=1-3) represents the principal stress, is the multiaxial creep ductility, is the equivalent creep strain rate, ε f represents the uniaxial creep ductility, and n represents the dimensionless creep stress hardening exponent.

[0011] Therefore, the creep damage at any time is:

[0012]

[0013] In the above formula, A is the creep constant.

[0014] The fatigue damage calculation method is as follows:

[0015]

[0016] Where dω f / dN is the accumulated fatigue damage in each cycle; E, S1, S2, v are material parameters; Δε p is the plastic strain variation range within each cycle, σ e is the Mises equivalent stress, R v represents the stress triaxiality coefficient, ω represents the total creep-fatigue damage, and v represents the Poisson's ratio of the material.

[0017] Δε p The relationship between the peak stress in each cycle can be calculated using the following formula:

[0018]

[0019] Among them, σmin and Δσ are the minimum stress and stress range, respectively; K' and n' are material parameters obtained from high-temperature low-cycle fatigue tests. The total fatigue damage accumulated until cycle j can be calculated by the following formula:

[0020]

[0021] Where j represents the number of fatigue cycles currently experienced, represents the accumulated fatigue damage in the i-th cycle, represents the fatigue damage accumulated until the jth cycle;

[0022] In addition to creep damage and fatigue damage, this model also considers the nonlinear damage accumulation process caused by creep-fatigue interaction:

[0023]

[0024] Where ω represents the total creep-fatigue damage, ω c represents the creep damage size, ω f Indicates the size of fatigue damage;

[0025] (2) Introduction of material mismatch effect and characterization of constraint state:

[0026] Using double mismatch factor MF W and MF HAZ To describe the creep performance mismatch effect between BM-HAZ-WS multi-materials in welded joints:

[0027]

[0028] Among them, A w , A b , A HAZ are the creep constants of WS zone, BM zone and HAZ zone respectively, n w , n b , n HAZ Respectively The creep index of WS zone, BM zone and HAZ zone is adjusted by MF W and MF HAZ Welded joints under different mismatch conditions.

[0029] Subsequently, based on the above creep-fatigue damage model and performance mismatch construction method, the constraint state of the crack tip of the welded structure with crack defects under different combinations is calculated. A new constraint parameter under creep-fatigue load is proposed. Calculate the restraint state:

[0030]

[0031] Among them, (C t ) avgrepresents the high-temperature fracture parameter, σ0 is the yield stress, the unit is MPa; is the creep strain rate corresponding to the yield stress, in h -1 ;I n is a dimensionless function related to n, where n is the dimensionless creep stress hardening exponent; L is the characteristic length; σ m Represents the hydrostatic pressure: σ ii (i=1,2,3) is the normal stress in the three perpendicular directions of the micro unit; σ m (r,0) is the hydrostatic pressure at a certain distance r from the crack tip in the mismatched weld joint, in MPa; (r,0) is the hydrostatic pressure at a certain distance r from the crack tip in the homogeneous material state, in MPa; r is the distance from the crack front study point to the crack tip, in mm.

[0032] (3) Prediction of creep-fatigue crack growth rate of welded joints under different holding times and different mismatch conditions:

[0033] First, the relationship between the crack growth rate and the constraint parameter of the homogeneous material under different holding times is established. t ) avg -(da / dt) avg There is a linear relationship between them, so the following relationship exists:

[0034]

[0035] Where D0 and Φ0 are coefficients obtained by nonlinear regression; and D0 and Φ0 are coefficients of creep-fatigue crack growth rate under the corresponding holding time of homogeneous material. (C t ) avg It is a high-temperature fracture parameter with the unit of MPa.mm / h. It can be obtained by calculating the load line displacement or crack tip opening displacement according to relevant standards.

[0036] Then the relationship between the holding time and the coefficients D0 and Φ0 is established:

[0037] D=A1*exp(t h / A2)+A3

[0038] φ=B1*exp(t h / B2)+B3

[0039] Among them, A1, A2, A3, B1, B2, and B3 are all related parameters obtained through nonlinear fitting. Based on the above relationship, the relationship between the normalized creep-fatigue rate and the normalized constraint parameter of the homogeneous material under different holding times can be constructed:

[0040]

[0041] Where A, B, and C are the relevant parameters obtained by nonlinear fitting. is the creep-fatigue crack growth rate under different holding times, is the creep-fatigue crack growth rate under the reference holding time, is the creep-fatigue constraint level of the homogeneous material under different holding time, is the creep-fatigue constraint level of the homogeneous material under reference holding time.

[0042] Secondly, the relationship between the normalized creep-fatigue rate and the normalized constraint parameter of the homogeneous material under the same holding time is established:

[0043]

[0044] in, is the creep-fatigue crack growth rate in the weld joint under mismatch conditions, in mm / h; is the creep-fatigue crack growth rate in a homogeneous material specimen, in mm / h; C1 is the fitting coefficient, which is determined by the mismatching conditions of the welded component.

[0045] Finally, based on the nonlinear relationship between the normalized creep-fatigue rate and the normalized constraint parameter of the homogeneous material and the homogeneous material under the reference working condition at different holding times, and the linear relationship between the normalized creep-fatigue rate and the normalized constraint parameter of the mismatch condition and the homogeneous material under the same holding time, the two are coupled to obtain a prediction method for the creep-fatigue crack growth rate of welded joints with different mismatch levels at different holding times:

[0046]

[0047] Combined (C t ) avg -(da / dt) avg There is a linear relationship between them, and the above formula can be rewritten as:

[0048]

[0049] The present invention discloses the following technical effects:

[0050] This paper proposes an innovative method that takes into account creep-fatigue constraint effects and the prediction of creep-fatigue crack growth rates, enabling accurate assessment of the crack growth behavior and damage evolution of welded components under creep-fatigue loading in high-temperature environments. This method combines multiaxial creep ductility with cyclic plastic strain effects under creep-fatigue loading conditions. Through the finite element method and precise calculation of material constants, the creep-fatigue crack growth rate and its evolution path can be rapidly determined under different operating conditions, enabling a comprehensive analysis of the damage process.

[0051] In addition, the present invention also proposes a creep-fatigue life prediction method for welded components based on the multi-material constraint effect, especially for multi-material welded structures with weld zone, heat-affected zone and parent material. This method obtains the material constraint parameters under specific mismatch conditions and holding time conditions. The values ​​and related fitting coefficients can be used to predict the crack growth rate under corresponding conditions based on the normalized creep-fatigue crack growth rate. Furthermore, combined with the mean creep-fatigue crack growth rate calculated by the damage model and the component ligament length, the present invention can effectively predict the residual creep-fatigue crack growth life of welded joints under different holding times and operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0053] Figure 1 This is a schematic diagram of the method flow of the present invention;

[0054] Figure 2 This is a schematic diagram of the CT sample used in the present invention;

[0055] Figure 3 To compare the crack growth results calculated using the creep-fatigue damage model proposed in this invention with the experimental results;

[0056] Figure 4 Comparison of life expectancy calculated for the creep-fatigue damage model with experimental results;

[0057] Figure 5 Comparison of the crack growth rate calculated for the creep-fatigue damage model with experimental results;

[0058] Figure 6 Schematic diagram of different creep performance combinations of three-material welded joints under mismatch conditions;

[0059] Figure 7 is the typical HAZ center crack under different mismatch conditions (C t ) avg -(da / dt) avg curve

[0060] Figure 8 is the relationship between the fitting parameters D, Φ and the holding time;

[0061] Figure 9 is the constraint level of the HAZ center crack tip under different mismatch conditions value;

[0062] Figure 10 The relationship between the normalized creep-fatigue crack growth rate and the normalized constraint parameter of the homogeneous material is shown using the data under creep conditions as a reference;

[0063] Figure 11 is the normalized creep-fatigue crack growth rate and The fitting curve of

[0064] Figure 12 For different mismatch conditions and different holding times Calculation results of the three-parameter CFCG rate correlation method. DETAILED DESCRIPTION

[0065] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of this application.

[0066] like Figures 1-12As shown, the present invention provides a novel high-temperature creep-fatigue crack growth behavior and life prediction method. This method considers the effects of material mismatch and creep-fatigue interaction on crack growth behavior in multi-material welded joints. This method is suitable for predicting the creep-fatigue life of welded components subjected to high-temperature service conditions, such as steam pipes, reheaters, and superheaters. In particular, it accurately assesses the creep-fatigue crack growth rate of welded joints while considering the effects of material mismatch and different hold times. By introducing a nonlinear creep-fatigue damage model and incorporating the effects of material mismatch in multiple regions of the welded joint, this method improves on traditional prediction methods and enables accurate remaining life assessment of welded components under complex operating conditions.

[0067] Example: In one embodiment of the present invention, a method for predicting creep-fatigue crack growth behavior and life of high-temperature welded components considering the material constraint effect is provided. The specific process of the prediction method is shown in the attached figure. Figure 1 As shown, it includes the following steps:

[0068] (1) Construction of multiaxial creep-fatigue damage model:

[0069] Based on existing creep damage and fatigue damage models, a new creep-fatigue damage model was constructed by combining multiaxial creep ductility and cyclic plastic strain. This model comprehensively considers the ductile behavior of materials under multiaxial creep conditions, especially the nonlinear cumulative effects of plastic strain and cyclic loading on creep damage at high temperatures.

[0070] (a) The creep damage calculation method is as follows:

[0071]

[0072] Among them, σ m / σ e is the stress triaxiality, σ i (i=1-3) represents the principal stress, is the multiaxial creep ductility, is the equivalent creep strain rate, ε f represents the uniaxial creep ductility, and n represents the dimensionless creep stress hardening exponent.

[0073] Therefore, the creep damage at any time is:

[0074]

[0075] (b) The fatigue damage calculation method is as follows:

[0076]

[0077] Where dω f / dN is the accumulated fatigue damage in each cycle; E, S1, S2, v are material parameters; Δε p is the plastic strain variation range within each cycle, σ e is the Mises equivalent stress, R v represents the stress triaxiality coefficient, ω represents the total creep-fatigue damage, and v represents the Poisson's ratio of the material.

[0078] Δε p The relationship between the peak stress in each cycle can be calculated using the following formula:

[0079]

[0080] Among them, σ min and Δσ are the minimum stress and stress range, respectively; K' and n' are material parameters obtained from high-temperature low-cycle fatigue tests. The total fatigue damage accumulated until cycle j can be calculated by the following formula:

[0081]

[0082] Where j represents the number of fatigue cycles currently experienced, represents the accumulated fatigue damage in the i-th cycle, represents the fatigue damage accumulated until the jth cycle;

[0083] (c) In addition to creep damage and fatigue damage, this model also considers the nonlinear damage accumulation process caused by creep-fatigue interaction:

[0084]

[0085] Where ω represents the total creep-fatigue damage, ω c represents the creep damage size, ω f Indicates the size of fatigue damage;

[0086] In this embodiment, G115 new high-temperature heat-resistant steel is selected as the finite element and experimental control object. The material properties of G115 steel at 650°C are shown in Table 1 below.

[0087] Table 1

[0088]

[0089] CT specimens were selected to carry out creep-fatigue damage model verification. The specimen dimensions are shown in the attached diagram. Figure 2As shown in the figure, a finite element CT model of a cracked G115 steel specimen was constructed. Two symmetrical loading pin holes were placed in the specimen body, one above the other. The notch and pre-existing crack were located at the specimen center, with the pre-existing crack located at the notch tip. Loads were applied to the crack tip using the pin holes to simulate high-temperature creep-fatigue experiments. After setting the loading boundary conditions and material property parameters, the damage model was imported into Abaqus using the USDFLD subroutine written in Fortran to verify the creep-fatigue damage model.

[0090] The finite element simulation results are shown in the attached Figure 3 As shown in the figure, the crack extension morphology calculated by the damage model proposed in this invention is very similar to the experimental results. Figure 4 and attached Figure 5 The expected life and crack growth rate calculated by the damage model under different holding times show little deviation from the experimental results, and the predicted life is distributed within the range of 1.3 times the error band, which proves the effectiveness and accuracy of the creep-fatigue damage model proposed in this invention, and can better describe the creep-fatigue crack progressive growth and damage behavior of metal materials in high temperature environments.

[0091] (2) Introduction of material mismatch effect and characterization of constraint state:

[0092] With reference to the width and creep performance differences of different areas in the actual welded joint, the corresponding finite element calculation model is constructed, such as Figure 6 As shown. This example uses the central crack of the heat-affected zone as an example to carry out the calculation. In order to obtain different mismatch degrees in the weld joint, the creep properties of the HAZ area are fixed and unchanged, and the creep properties of the surrounding weld and base material are systematically changed. At the same time, the width of the heat-affected zone can also be changed. Using the double mismatch factor MF W and MF HAZ To describe the creep performance mismatch effect between BM-HAZ-WS multi-materials in welded joints:

[0093]

[0094] Among them, A w , A b , A HAZ are the creep constants of WS zone, BM zone and HAZ zone respectively, n w , n b , n HAZ Respectively The creep index of WS zone, BM zone and HAZ zone is adjusted by MF W and MF HAZ Welded joints under different mismatch conditions.

[0095] Subsequently, based on the above creep-fatigue model and performance mismatch construction method, the constraint state of the crack tip of the welded structure with crack defects under different combinations is calculated. A new constraint parameter under creep-fatigue load is proposed. Calculate the restraint state:

[0096]

[0097] Among them, (C t ) avg represents the high-temperature fracture parameter, σ0 is the yield stress, the unit is MPa; is the creep strain rate corresponding to the yield stress, in h -1 ;I n is a dimensionless function related to n, where n is the dimensionless creep stress hardening exponent; L is the characteristic length; σ m Represents the hydrostatic pressure: σ ii (i=1,2,3) is the normal stress in the three perpendicular directions of the micro unit; σ m (r,0) is the hydrostatic pressure at a certain distance r from the crack tip in the mismatched weld joint, in MPa; (r,0) is the hydrostatic pressure at a certain distance r from the crack tip in the homogeneous material state, in MPa; r is the distance from the crack front study point to the crack tip, in mm.

[0098] In this example (C t ) avg Take 2E-6MPa.mm / h, σ0 take 267MPa, I n Take 4.58, Take 6.44E-4h-1. The calculation results are as follows Figure 7 As shown. Figure 7 It can be seen that in different (C t ) avg Under the same load holding time, the same mismatched material combination has the corresponding The values ​​are the same.

[0099] (3) Prediction of creep-fatigue crack growth rate of welded joints under different holding times and different mismatch conditions:

[0100] (a) Determination of creep-fatigue crack growth rate of corresponding homogeneous materials at different holding times by finite element method and creep-fatigue crack growth rates under various mismatch conditions of welded joints Since in the double logarithmic coordinate system (C t ) avg -(da / dt)avg There is a linear relationship between Figure 8 ), so the following relationship exists:

[0101]

[0102] Where D0 and φ0 are the coefficients of creep-fatigue crack growth rate under the corresponding holding time of homogeneous material. (C t ) avg It is a high temperature fracture parameter, with the unit of MPa.mm / h, which can be obtained by calculating the load line displacement or crack tip opening displacement according to relevant standards. t ) avg -(da / dt) avg Curves such as Figure 8 .

[0103] (b) Then construct the holding time t h The relationship between the coefficients D0 and φ0:

[0104] D=A1*exp(t h / A2)+A3

[0105] φ=B1*exp(t h / B2)+B3

[0106] Among them, A1, A2, A3, B1, B2, and B3 are all related parameters obtained through nonlinear fitting. The relationship under different holding times is as follows: Figure 9 In this embodiment, the values ​​of A1, A2, A3, B1, B2, and B3 are -1.1340, 1157.663, 1.721, -0.668, 632.911, and 0.757, respectively.

[0107] (c) Based on the above relationship, the relationship between the normalized creep-fatigue rate and the normalized constraint parameter of the homogeneous material under different holding times can be constructed:

[0108]

[0109] Where A, B, and C are the relevant parameters obtained by nonlinear fitting. is the creep-fatigue crack growth rate under different holding times, is the creep-fatigue crack growth rate under the reference holding time, is the creep-fatigue constraint level of the homogeneous material under different holding times, is the creep-fatigue constraint level of the homogeneous material under the reference holding time. In this example, the extended results under creep load are selected as reference, and the constructed correlation results are as follows: Figure 10 The coefficients A, B, and C obtained by fitting in this embodiment are 2.27×10-8 , 12.67 and 2.04. The above relationship shows that as long as the constraint state of the homogeneous material under creep conditions is determined Then we can use the load-independent constraint parameters The normalized CFCG rate of homogeneous material at any holding time is calculated using the relationship.

[0110] (d) By Figure 8 It can be seen that the CFCG rate under different mismatch conditions shows a rate relationship with the homogeneous material results, and the change in crack growth rate is related to the constraint state. Therefore, the relationship between the normalized creep-fatigue rate of the homogeneous material and the normalized constraint parameter under the same holding time can be constructed:

[0111]

[0112] in, is the creep-fatigue crack growth rate in the weld joint under mismatch conditions, in mm / h; is the creep-fatigue crack growth rate in the homogeneous material sample, in mm / h; C1 is the fitting coefficient, which is determined by the mismatching working conditions of the welded components. In this embodiment, the fitting coefficient C1 is -1.103. The results calculated using the above formula are as follows: Figure 11 shown.

[0113] (e) Finally, based on the nonlinear relationship between the normalized creep-fatigue rate and the normalized constraint parameter of the homogeneous material at different holding times and the linear relationship between the normalized creep-fatigue rate and the normalized constraint parameter of the homogeneous material at the same holding time, the two are coupled to obtain a prediction method for the creep-fatigue crack growth rate of welded joints with different mismatch levels at different holding times:

[0114]

[0115] The first term represents the change in creep-fatigue crack growth rate caused by the change in holding time, and the second term represents the change in creep-fatigue crack growth rate caused by material constraint. Combined with the double logarithmic coordinate system (C t ) avg -(da / dt) avg The linear relationship between them can be rewritten as:

[0116]

[0117] The above formula shows that when the constraint level and crack growth rate of the specimen under the reference holding time are determined, as long as the constraint change caused by the holding time is determined and material constraints The CFCG rate of any component under mismatch conditions can be obtained, that is, The three-parameter CFCG rate correlation method can be used to analyze the change of holding time and material constraint coupling of actual welded components. Figure 12 As shown. It can be seen that the data points under all mismatch conditions are basically located on the 45° straight line. This shows that and constraint parameters There is a good linear relationship between them, which will greatly facilitate the engineering application of the three-parameter correlation method.

[0118] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0119] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0120] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A creep-fatigue life prediction method for welded components based on multi-material constraint effect, characterized in that: The following steps are involved: (1) Construct a multiaxial creep-fatigue nonlinear damage model, comprehensively consider the multiaxial creep ductility, cyclic plastic strain and their interaction of the material, and establish mathematical expressions for creep damage, fatigue damage and their nonlinear interaction terms respectively; (2) Introducing the material performance mismatch effect, by setting the double mismatch factor MF W and MF HAZ Characterize the creep performance differences between the weld zone, heat-affected zone and base material, and establish a multi-material creep performance mismatch model; (3) Using new constraint parameters based on creep-fatigue loads Combined with the stress distribution state in the crack tip area, the constraint level of the crack tip under different mismatch conditions is calculated; (4) Under the same holding time, a linear relationship between the normalized creep-fatigue rate and the normalized constraint parameter between the mismatched welded joint and the homogeneous material is established; (5) Under different holding times, the nonlinear relationship between the normalized creep-fatigue rate and the normalized constraint parameter between the homogeneous material under different holding times and the homogeneous material under reference working conditions is constructed; (6) By coupling the nonlinear relationship and the linear relationship, the creep-fatigue crack growth rate of welded joints with different mismatch levels under different holding times is predicted.

2. The method according to claim 1, characterized in that The creep-fatigue damage model is calculated using the following formula: The calculation method of creep damage is as follows: Among them, σ m / σ e is the stress triaxiality, σ i (i=1-3) represents the principal stress, is the multiaxial creep ductility, is the equivalent creep strain rate, ε f represents the uniaxial creep ductility, n represents the dimensionless creep stress hardening exponent; The creep damage at any time is: In the above formula, A is the creep constant; The fatigue damage calculation method is as follows: Where dω f / dN is the accumulated fatigue damage in each cycle; E, S1, S2, v are material parameters; Δε p is the plastic strain variation range within each cycle, σ e is the Mises equivalent stress, R v represents the stress triaxiality coefficient, ω represents the total creep-fatigue damage, and v represents the Poisson's ratio of the material; Δε p The relationship between the peak stress in each cycle can be calculated using the following formula: Among them, σ min and Δσ are the minimum stress and stress range, respectively; K' and n' are the material parameters obtained from high-temperature low-cycle fatigue tests; Then the total fatigue damage accumulated until cycle j can be calculated by the following formula: Where j represents the number of fatigue cycles currently experienced, represents the accumulated fatigue damage in the i-th cycle, represents the fatigue damage accumulated until the jth cycle; In addition to creep damage and fatigue damage, the nonlinear damage accumulation process caused by creep-fatigue interaction is: Where ω represents the total creep-fatigue damage, ω c represents the creep damage size, ω f Indicates the size of fatigue damage.

3. The method according to any one of claims 1 to 2, characterized in that The method for characterizing the creep performance mismatch between different regions of the welded joint is: Using double mismatch factor MF W and MF HAZ To describe the creep performance mismatch effect between BM-HAZ-WS multi-materials in welded joints: Among them, A w , A b , A HAZ are the creep constants of WS zone, BM zone and HAZ zone respectively, n w , n b , n HAZ Represent the creep index of WS zone, BM zone and HAZ zone respectively. W and MF HAZ Welded joints under different mismatch conditions.

4. The method according to any one of claims 1 to 3, characterized in that The constraint parameter Defined as: Among them, (C t ) avg represents the high-temperature fracture parameter, σ0 is the yield stress, the unit is MPa; is the creep strain rate corresponding to the yield stress; I n is a dimensionless function related to n, where n is the dimensionless creep stress hardening exponent; L is the characteristic length; σ m Represents the hydrostatic pressure: σ ii (i=1,2,3) is the normal stress in the three perpendicular directions of the micro unit; σ m (r,0) is the hydrostatic pressure at a certain distance r from the crack tip in the mismatched weld joint; is the hydrostatic pressure at a certain distance r from the crack tip in the homogeneous material state; r is the distance from the crack front study point to the crack tip.

5. The method according to any one of claims 1 to 4, characterized in that Under the same holding time, the linear relationship between the normalized creep-fatigue rate and the normalized constraint parameter between the mismatched welded joint and the homogeneous material is: in, is the creep-fatigue crack growth rate in the weld joint under mismatch conditions; is the creep-fatigue crack growth rate in the homogeneous material specimen; C1 is the fitting coefficient, which is determined by the mismatch condition of the welded component.

6. The method according to any one of claims 1 to 5, characterized in that Under different holding times, the nonlinear relationship between the normalized creep-fatigue rate and the normalized constraint parameter between the homogeneous material under different holding times and the homogeneous material under the reference working condition is: Where A, B, and C are the relevant parameters obtained by nonlinear fitting. is the creep-fatigue crack growth rate under different holding times, is the creep-fatigue crack growth rate under the reference holding time, is the creep-fatigue constraint level of the homogeneous material under different holding time, is the creep-fatigue constraint level of the homogeneous material under reference holding time.

7. The method according to any one of claims 1 to 6, characterized in that The final prediction model for creep-fatigue crack growth rate of welded joints with different mismatch levels under different holding times is:

8. The method according to any one of claims 1 to 7, a method and system for predicting creep-fatigue life of welded components based on multi-material constraint effect, characterized in that: include: Data analysis module: used to calculate the crack growth rate and crack tip restraint level of welded components and homogeneous materials based on the multiaxial creep-fatigue damage model and mismatch conditions; Relationship building module: used to establish linear and nonlinear relationships between normalized creep-fatigue crack growth rate and normalized constraint parameters; The prediction module is used to predict the crack growth rate of the target welded component under different holding times and mismatch conditions based on the established relationship coupling calculation results.

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