Creep life evaluation method for component with defects based on unified defect characteristic parameter

Abstract

The present application relates to the technical field of structural safety evaluation of high-temperature pressure-bearing equipment, and provides a creep life evaluation method for a defective component based on a unified defect characteristic parameter, which comprises the following steps: conducting a high-temperature creep test on a non-defective material / structure, and obtaining creep life data under different stress levels to calibrate material parameters; using a Latin hypercube sampling method to generate N groups of representative defect samples in a three-dimensional parameter space containing defect geometric parameters, establishing a corresponding finite element model of a defective structure, simulating and obtaining creep life, simultaneously simulating and obtaining the creep life of a non-defective structure under the same load level as a benchmark, and obtaining a sample set; constructing a unified defect characteristic parameter, and establishing a linear relationship between normalized creep life and the parameter; obtaining the defect geometric characteristics of a component to be evaluated through a non-destructive testing technology, calculating the value of the unified defect characteristic C parameter, and combining the creep life of a non-defective structure under the same working condition to obtain the predicted life of the defective component.

Description

Technical Field

[0001] This invention relates to the technical field of structural safety evaluation of high-temperature pressure equipment, especially in the fields of high-end equipment manufacturing such as nuclear energy and petrochemicals, and relates to a method for evaluating the creep life of defective components based on unified defect characteristic parameters. Background Technology

[0002] With the deepening development of the high-end equipment manufacturing industry in fields such as nuclear energy, advanced thermal power, and petrochemicals, the safe operation of high-temperature pressure-bearing equipment such as nuclear reactor pressure vessels, supercritical thermal power units, and petrochemical hydrogenation reactors is facing increasingly severe challenges. These devices operate in extremely harsh environments for extended periods, accumulating fatigue, creep, and other damage, ultimately leading to fracture failure. Their structural integrity has become a core bottleneck restricting the long-term safe operation of these equipment. However, in actual manufacturing processes, limitations in casting and welding inevitably lead to the formation of volumetric defects such as porosity, shrinkage cavities, and inclusions within the components. These defects significantly disturb the local stress-strain field, severely weakening the creep bearing capacity and service life of the components.

[0003] Currently, two main technical approaches are commonly used for creep life assessment of structures with defects. The first approach is a refined method based on finite element numerical simulation. This method explicitly constructs the defect geometry in a three-dimensional model, directly simulating the impact of defects on the local stress field and damage evolution, thereby predicting creep life. This method can realistically reflect the influence of defects on local mechanical behavior, but the modeling process is complex, requiring high precision in model parameters, mesh generation, and computational convergence. The computation time for a single model is also long, making it difficult to meet the needs of rapid on-site assessment in engineering projects. The second approach is an engineering evaluation method based on fracture mechanics. This method typically treats volumetric defects as equivalent cracks and uses fracture mechanics parameters such as stress intensity factor and C* integral to predict crack initiation and propagation life. International engineering standards such as API 579-1 / ASME FFS-1, BS 7910, and the R5 assessment procedure all establish creep assessment processes for high-temperature components based on a fracture mechanics framework. These methods are mature and have strong engineering applicability, but they often simplify complex volumetric defects into ideal crack morphology based on conservative assumptions. This makes it difficult to accurately reflect the combined effects of geometric features such as defect size, shape, and spatial location, resulting in conservative evaluation results.

[0004] From a mechanical perspective, the impact of volumetric defects on creep life exhibits typical multidimensional coupling characteristics. Specifically, the size of the defect determines the effective weakening degree of the load-bearing section, the location of the defect affects the stress concentration and damage initiation site, and the shape of the defect regulates the distribution of the local stress field. Complex nonlinear coupling effects exist among the various geometric characteristic parameters, making it difficult to accurately describe the comprehensive impact of defect geometry on creep life by considering only a single parameter. Furthermore, with the rapid development of nondestructive testing technologies such as industrial CT, the three-dimensional geometric information of internal defects in components can now be acquired with high precision. However, an effective theoretical method is currently lacking for transforming the detected multidimensional defect characteristic information into input parameters that can be directly used for creep life assessment.

[0005] Therefore, it is urgent for those skilled in the art to design a prediction method that can uniformly characterize the multidimensional geometric features of defects into a single feature parameter and establish an explicit mapping relationship between this parameter and creep life, so as to achieve rapid and accurate assessment of the creep life of high-temperature service components with defects. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for evaluating the creep life of defective components based on unified defect characteristic parameters, the method comprising:

[0007] S1. Conduct high-temperature creep tests on defect-free materials / structures to obtain creep life data under different stress levels to calibrate material parameters for subsequent finite element simulations.

[0008] S2. Using the Latin hypercube sampling method, N representative defect samples are generated in a three-dimensional parameter space containing defect geometric parameters. A corresponding finite element model of the defective structure is established, and the creep life is simulated and obtained. Simultaneously, the creep life of a defect-free structure under the same load level was simulated and obtained as a benchmark. This yields the sample set;

[0009] S3, Constructing unified defect features Parameters, establishing normalized creep life and Linear relationship of parameters, and calibration of parameters. , , , ;

[0010] S4. Obtain the defect geometric features of the component to be evaluated through non-destructive testing technology and calculate the uniform defect feature C parameter value. Substitute it into the linear relationship to calculate the normalized creep life. Combine the creep life of the defect-free structure under the same working conditions to obtain the predicted life of the component with defects.

[0011] Furthermore, the defect geometric parameters mentioned in step S2 include the major axis, minor axis, and depth;

[0012] The range of values ​​for each defect geometric parameter is divided into N intervals. A sample point is randomly selected in each interval. The sample points of the three defect geometric parameters are randomly arranged and combined to form an initial sample set. The sample points are then uniformly distributed in the parameter space through iterative optimization.

[0013] The range of values ​​for the defect geometric parameters is determined based on the specimen size: defect major axis and short axis The values ​​of all values ​​are smaller than the sample radius and the defect depth. The value range is no greater than 1 / 2 of the sample diameter, and simultaneously satisfies... Geometric constraints; the number of samples N generated by Latin hypercube sampling is ≥30.

[0014] Furthermore, in step S2, based on the calibrated creep constitutive model parameters, a three-dimensional finite element model is established for each group of defect samples using finite element tools to simulate the creep life of the defect sample. Simultaneously, a defect-free structural model is established, and the baseline creep life is simulated under the same conditions. After batch calculation of N groups of defect-containing models, the creep life of each group is calculated. Divide by the reference life The normalized creep life was obtained. Finally, a complete sample set is constructed. ,in, They represent the first The major axis, minor axis, and depth of a defect sample; Indicates the first The creep lifetime ratio corresponding to each defect sample.

[0015] Furthermore, in step S3, the expression for constructing the unified defect feature C parameter is as follows:

[0016]

[0017] in, The specific area is expressed as the ratio of the area of ​​the envelope ellipse of the defect projected onto the load plane to the cross-sectional area of ​​the specimen. The ratio, ;

[0018] Relative depth is indicated by the sample diameter. The ratio of the difference in defect depth to the sample diameter, ;

[0019] Indicates the aspect ratio, which is the major axis of the defect. With short axis The ratio, ;

[0020] α and β are the power exponent parameters to be calibrated.

[0021] Furthermore, in step S3, there is a linear relationship between the normalized creep lifetime and the uniform defect characteristic parameter C, defined as:

[0022]

[0023] in, To normalize creep life, The creep life of a defective structure. The creep life of a defect-free structure under the same load level. The slope coefficient represents the linear relationship. The intercept is C. A larger C value indicates a stronger weakening effect of defects on material properties, and a higher normalized creep life. The smaller.

[0024] Furthermore, the specific steps for calibrating parameters α, β, k, and b in step S3 are as follows:

[0025] sample set Convert to dataset ;

[0026] Group N As a dataset, define a custom function form in the regression analysis software:

[0027]

[0028] The optimal values ​​of the four parameters are solved simultaneously using the nonlinear least squares method, which minimizes the sum of squared residuals between the predicted and actual values ​​of all sample points. The goodness of fit is evaluated by the coefficient of determination R².

[0029] Furthermore, step S4 specifically involves obtaining the geometric feature parameters of the defect, including the long axis of the defect, through non-destructive testing techniques. short axis ,depth and the diameter of the sample Calculate the specific area Relative depth and aspect ratio ,Will , , Substitute the C parameter into the unified defect feature calculation formula to obtain the C parameter value, and then substitute the C parameter value into the linear relationship to calculate the normalized creep life; according to the actual service conditions of the component to be evaluated, use the creep constitutive model calibrated in step (1) to calculate the creep life of the defect-free structure under the same conditions. The predicted life of a defective component can be calculated using the following formula:

[0030]

[0031] The present invention has the following beneficial effects:

[0032] (1) This invention defines the specific area Relative depth and aspect ratio Three dimensionless parameters are used to uniformly characterize the multidimensional geometric features of defects into a single feature parameter C, and an explicit linear mapping relationship between the C parameter and the normalized creep life is established. This realizes the dimensionality reduction characterization of the multidimensional features of defects, avoids the need for case-by-case finite element analysis, and can provide technical support for the rapid assessment of the creep life of defective components in high-temperature pressure-bearing equipment such as nuclear power, thermal power, and petrochemical plants.

[0033] (2) This invention proposes a unified defect feature C parameter, which overcomes the complexity of traditional methods that require consideration of the interaction of multiple defect parameters separately. The C parameter realizes the dimensionality reduction characterization of multidimensional features and can quantitatively describe the weakening effect of defects with different geometric shapes on creep life.

[0034] (3) This invention has universality and scalability. For different material systems, only the C parameter and linear relationship coefficients k and b need to be recalibrated, and the method can be extended to the life assessment of defective components of other high-temperature alloy materials.

[0035] (4) This invention has good engineering applicability, and normalized creep life can be quickly predicted using only conventional non-destructive testing techniques. This method avoids complex finite element analysis, is suitable for rapid on-site evaluation in engineering projects, and significantly improves the efficiency of evaluating the integrity of structures with defects.

[0036] (5) This invention achieves a unified representation of defect features through the C parameter, integrating multiple independent defect geometric parameters into a single dimensionless parameter. Compared with existing multivariate regression methods, it simplifies the form of the mapping relationship and improves the interpretability and engineering applicability of the model.

[0037] (6) This invention does not require complex finite element simulation. It can complete the life prediction by using only non-destructive testing parameters and simple calculations, taking into account both efficiency and accuracy. It is also adaptable to different service conditions and solves the problem of cumbersome process in traditional evaluation methods. Attached Figure Description

[0038] Figure 1 This is a flowchart of the creep life evaluation process for defective components according to the present invention.

[0039] Figure 2 This is a schematic diagram of the definition of defect geometric parameters in Example 1.

[0040] Figure 3 It is a two-dimensional scatter plot of the major axis and depth of the Latin hypercube sampling in Example 1.

[0041] Figure 4 This is a two-dimensional scatter plot of the minor axis and depth of the Latin hypercube sampling in Example 1.

[0042] Figure 5 This is a two-dimensional scatter plot of the major and minor axes of the Latin hypercube sampling in Example 1.

[0043] Figure 6 This is a scatter plot of the three-dimensional defect geometry parameters and normalized creep lifetime ratio of the Latin hypercube sampling in Example 1.

[0044] Figure 7 This is a scatter plot of C parameter and normalized creep life in Example 1.

[0045] Figure 8 This is a scatter plot verifying the fit between the predicted and actual creep life ratio values ​​in Example 1. Detailed Implementation

[0046] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. However, these embodiments are not intended to limit the present invention. Any similar structures and similar variations of the present invention should be included in the protection scope of the present invention. The commas in the present invention all indicate the relationship between and. The English letters in the present invention are case-sensitive.

[0047] This invention provides a method for evaluating the creep life of defective components based on unified defect characteristic parameters, the method comprising:

[0048] S1. Conduct high-temperature creep tests on defect-free materials / structures to obtain creep life data under different stress levels in order to calibrate material parameters (calibrate creep constitutive model parameters) for subsequent finite element simulations.

[0049] S2. Using the Latin hypercube sampling method, N representative defect samples are generated in a three-dimensional parameter space containing defect geometric parameters. A corresponding finite element model of the defective structure is established, and the creep life is simulated and obtained. Simultaneously, the creep life of a defect-free structure under the same load level was simulated and obtained as a benchmark. This yields the sample set;

[0050] The defect geometry parameters include the major axis, minor axis, and depth;

[0051] The range of values ​​for each defect geometric parameter is divided into N intervals. A sample point is randomly selected in each interval. The sample points of the three defect geometric parameters are randomly arranged and combined to form an initial sample set. The sample points are then uniformly distributed in the parameter space through iterative optimization.

[0052] The range of values ​​for the defect geometric parameters is determined based on the specimen size: defect major axis and short axis The values ​​of all values ​​are smaller than the sample radius and the defect depth. The value range is no greater than 1 / 2 of the sample diameter, and simultaneously satisfies... Geometric constraints; the number of samples N generated by Latin hypercube sampling is ≥30.

[0053] Based on the calibrated creep constitutive model parameters, a three-dimensional finite element model was established for each group of defect samples using finite element tools to simulate the creep life of the defect sample. At the same time, a defect-free structural model was established, and the baseline creep life was simulated under the same conditions. After batch calculation of N groups of defect-containing models, the creep life of each group is calculated. Divide by the reference life The normalized creep life was obtained. Finally, a complete sample set is constructed. ,in, They represent the first The major axis, minor axis, and depth of a defect sample; Indicates the first The creep lifetime ratio corresponding to each defect sample.

[0054] S3, Constructing unified defect features Parameters, establishing normalized creep life and Linear relationship of parameters, and calibration of parameters. , , , ;

[0055] Construct a unified defect feature parameter C to reduce the dimensionality of multi-dimensional defect geometric information into a single comprehensive feature, simplifying lifetime correlation modeling. The expression is as follows:

[0056]

[0057] in, , , Three dimensionless parameters are defined for the defect-based geometric features;

[0058] The specific area is expressed as the ratio of the area of ​​the envelope ellipse of the defect projected onto the load plane to the cross-sectional area of ​​the specimen. The ratio, ;

[0059] Relative depth is indicated by the sample diameter. The ratio of the difference in defect depth to the sample diameter, ;

[0060] Indicates the aspect ratio, which is the major axis of the defect. With short axis The ratio, ;

[0061] α and β are power exponent parameters to be calibrated, quantifying the nonlinear coupling effect of relative depth and aspect ratio on lifetime.

[0062] Specific area This reflects the degree of reduction in effective load-bearing area caused by defects. The larger the value, the larger the cross-sectional area occupied by the defect, the weaker the effective load-bearing capacity of the material, and the stronger the weakening effect of the defect on creep life; relative depth It reflects the distance between the defect and the sample surface. A larger aspect ratio indicates that the defect is closer to the surface, creep damage is more likely to accumulate, and the lifespan is more severely reduced; Reflecting the shape characteristics of the defect, The larger the value, the more elongated the defect is, while a defect that is close to circular ( Approaching 1) has a stronger weakening effect on creep life. The power exponents α and β are used to describe the nonlinearity of the influence of relative depth and aspect ratio on creep life, respectively, where α takes a positive value and β takes a negative value, reflecting the coupling effect of different geometric features on creep life weakening.

[0063] There is a linear relationship between the normalized creep lifetime and the uniform defect characteristic parameter C, defined as:

[0064]

[0065] in, To normalize creep life, The creep life of a defective structure. The creep life of a defect-free structure under the same load level. The slope coefficient represents the linear relationship. The intercept is C. A larger C value indicates a stronger weakening effect of defects on material properties, and a higher normalized creep life. The smaller.

[0066] The specific steps for calibrating parameters α, β, k, and b are as follows:

[0067] sample set Convert to dataset ;

[0068] Group N As a dataset, define a custom function form in the regression analysis software:

[0069]

[0070] The optimal values ​​of the four parameters are simultaneously solved using the nonlinear least squares method, minimizing the sum of squared residuals between the predicted and actual values ​​for all sample points. The goodness of fit is evaluated using the coefficient of determination R². This custom function accurately characterizes the nonlinear power-law relationship between lifetime ratio and defect geometry, with clearly defined physical meanings for the parameters. The formula accurately characterizes the influence of defect size on high-temperature creep lifetime, and the clear physical meanings of the parameters facilitate fitting and subsequent numerical simulation.

[0071] S4. Obtain the geometric features of defects in the component to be evaluated using non-destructive testing (NDT) techniques and calculate the uniform defect feature C parameter value. Substitute this value into a linear relationship to calculate the normalized creep life. Combine this with the creep life of a defect-free structure under the same working conditions to obtain the predicted life of the component with defects. Specifically, the steps are as follows: Obtain the geometric feature parameters of the defects using NDT techniques, including the defect's long axis. short axis ,depth and the diameter of the sample Calculate the specific area Relative depth and aspect ratio ,Will , , Substitute the C parameter into the unified defect feature calculation formula to obtain the C parameter value, and then substitute the C parameter value into the linear relationship to calculate the normalized creep life; according to the actual service conditions of the component to be evaluated, use the creep constitutive model calibrated in step (1) to calculate the creep life of the defect-free structure under the same conditions. The predicted life of a defective component can be calculated using the following formula:

[0072]

[0073] Example 1

[0074] This embodiment takes nuclear-grade 316H stainless steel as the research object and provides a specific implementation process for a method for evaluating the creep life of defective components based on unified defect characteristic parameters. The method for evaluating the creep life of defective components includes:

[0075] S1. Conduct high-temperature creep tests on defect-free materials / structures to obtain creep life data under different stress levels to calibrate material parameters for subsequent finite element simulations.

[0076] Following the requirements of ASTM E139-11 standard, "Standard Test Methods for Creep, Creep Failure and Stress-Failure Testing of Metallic Materials," a high-temperature creep test was conducted on an NCSJSJC0040 high-temperature creep testing machine at a set temperature of 550℃. Four stress levels—250MPa, 270MPa, 290MPa, and 310MPa—were selected. Standard cylindrical smooth specimens were used, with a gauge length of 30mm and a gauge diameter of 6mm. Before the test, the specimens were mounted on the testing machine, heated to 550℃, and held for 1 hour to ensure uniform temperature distribution, with temperature fluctuations controlled within ±2℃. Subsequently, a preset constant tensile stress was applied, and the creep strain was recorded over time until the specimen fractured. Creep life, steady-state creep rate, and creep strain data were obtained.

[0077] Based on the obtained experimental data, taking the following constitutive model as an example, the parameters of the creep constitutive model are calibrated, and its constitutive equation is:

[0078]

[0079]

[0080] in, The creep strain rate, Let M, q, A, n, and p be the damage rate, and M, q, A, n, and p be the parameters of the creep constitutive model. Equivalent stress;

[0081] After making reasonable assumptions, simplifications, and derivations of equations (5) and (6), we can obtain the expressions for steady-state creep rate and stress level, creep life and stress level, and creep strain and time:

[0082]

[0083]

[0084]

[0085] The constitutive model parameters A and n are calibrated using equation (7), the constitutive model parameters M and p are calibrated using equation (8), and the constitutive model parameter q is calibrated using equation (9).

[0086] S2, using the Latin hypercube sampling method on the long axis of the defect. short axis ,depth N representative defect samples are generated in the three-dimensional parameter space. A corresponding finite element model of the defective structure is established and the creep life is obtained through simulation. Simultaneously, the creep life of a defect-free structure under the same load level is obtained as a benchmark. , obtain sample set ;

[0087] A Latin hypercube sampling method is used to generate defect parameter combinations. This sampling method can obtain representative and uniformly distributed samples in the defect geometric parameter space. First, the range of values ​​for the defect geometric parameters is determined. In this embodiment, the defect is regularized into an ellipsoid, and its geometric features are described by three parameters: major axis... Let be the length of the semi-major axis of the ellipsoid in the plane perpendicular to the load direction, and be the length of the minor axis. The length of the minor semi-axis and the depth within the same plane. The distance from the defect center to the nearest surface of the specimen is given by the defect geometric parameters as follows: Figure 2 As shown. Given that the gauge length diameter of the test sample used in step (5) is 6 mm, and considering the feasibility and calculation accuracy of finite element modeling, the following restrictions are placed on the range of defect parameters:

[0088]

[0089]

[0090]

[0091] The constraint condition in equation (12) is used to ensure that there is sufficient material thickness between the defect edge and the sample surface to meet the requirements of the minimum element size for finite element mesh generation, and to ensure calculation accuracy and convergence.

[0092] Based on the above parameter range and constraints, an optimized hypercube sampling algorithm is used to generate 150 sets of defect parameter samples. The specific steps are as follows: First, the value range of each parameter is divided into 150 intervals. A sample point is randomly selected in each interval. The sample points of the three parameters are randomly arranged and combined to form an initial sample set. Then, the initial sample set is optimized using the maximum-minimum distance criterion. Multiple sets of candidate samples are generated through iteration. The minimum distance between all sample points in the standardized parameter space of each set of samples is calculated. The sample set with the largest minimum distance is selected as the optimal result.

[0093] For the 150 generated defect parameter samples, three-dimensional finite element numerical models were established to simulate creep life. The model geometry was consistent with the test sample, with a gauge length diameter of 6 mm and a length of 30 mm. An ellipsoidal defect was established at the center of the gauge length, and the defect geometry was determined by the parameters. Confirmed. An eight-node hexahedral reduced integral element discretization model is adopted. The mesh in the defect vicinity is refined to 0.1 mm to capture local stress gradients, while the mesh in the far field is gradually transitioned to 0.5 mm to balance computational accuracy and efficiency. The calibrated creep damage constitutive model is embedded into the finite element solver through a user-defined subroutine, using damage variables... Reaching a critical value of 0.99 is used as the failure criterion, and the corresponding cumulative time is recorded as the creep life of the defective structure. The simulated boundary conditions were: one end fully constrained, and the other end subjected to an axial tensile load of 290 MPa, at an ambient temperature of 550 °C. Simultaneously, a defect-free structure was simulated under the same conditions to obtain the baseline creep life. =422.28h. After completing all 150 simulations, the normalized creep life is obtained by dividing the creep life of each simulation by the baseline life. Finally, construct the sample set. The sample distribution is as follows Figure 3-6 As shown.

[0094] S3, construct a unified defect feature C parameter, establish a linear relationship between normalized creep life and C parameter, and calibrate parameters α, β, k, and b;

[0095] This embodiment proposes a unified defect characteristic parameter C to quantify the weakening effect of defects with different geometric shapes on creep life. The parameter C is expressed mathematically by combining the three geometric parameters of the defect (major axis...). short axis ,depth This is combined into a single dimensionless eigenvalue, thereby achieving dimensionality reduction representation of multidimensional features.

[0096] The unified defect characteristic parameter C is defined as follows:

[0097]

[0098] in, , , Three dimensionless parameters are defined for the defect-based geometric features, where α and β are power-law parameters to be calibrated. The specific definitions of the three dimensionless parameters are as follows:

[0099] Specific area is the ratio of the area of ​​the envelope ellipse of the defect projected onto the load plane to the cross-sectional area of ​​the specimen. In this embodiment .

[0100] Relative depth is the ratio of the difference between the specimen diameter and the defect depth to the specimen diameter. ,

[0101] Aspect ratio, representing the major axis of the defect. With short axis The ratio, .

[0102] Based on the specific definition of each parameter in the unified defect feature parameter C, the sample set can be... Transform into a dataset .

[0103] Based on the unified defect characteristic parameter C, a normalized creep life is established. The linear relationship between the parameter C and the parameter C is defined as follows:

[0104]

[0105] in, To normalize creep life, The creep life of a defective structure. The creep life of a defect-free structure under the same load level. The slope coefficient represents the linear relationship. This is the intercept.

[0106] 150 groups As a dataset, define a custom function form in the regression analysis software:

[0107]

[0108] The Levenberg-Marquardt nonlinear least squares optimization algorithm is used to simultaneously find the optimal values ​​of the four parameters α, β, k, and b, minimizing the sum of squared residuals between the predicted and actual values ​​for all sample points. After iterative optimization, the optimal parameter values ​​obtained after convergence are: α = 1.312, β = -0.174, k = -10.461, and b = 1.031.

[0109] Substituting the calibrated parameters into equation (3), the normalized creep life prediction values ​​for 150 samples were calculated and compared with the actual values. The goodness of fit was evaluated using the coefficient of determination R², calculated as follows:

[0110]

[0111] The calculation results show that R² = 0.9841, indicating that the established linear relationship can accurately predict the normalized creep life of defects with different geometric shapes. Furthermore, the prediction error distribution of 150 sample points shows that 92.67% of the sample points have a relative error within ±10%, proving the effectiveness of the unified defect characteristic parameter C and the accuracy of the linear relationship. The scatter plot of C parameter versus normalized creep life is shown below. Figure 7As shown in the figure, the scatter plot verifying the fit between the predicted and actual creep life ratios is as follows. Figure 8 As shown.

[0112] S4. Obtain the defect geometric features of the component to be evaluated through non-destructive testing technology and calculate the uniform defect feature C parameter value. Substitute it into the linear relationship to calculate the normalized creep life. Combine the creep life of the defect-free structure under the same working conditions to obtain the predicted life of the component with defects.

[0113] We have a 316H stainless steel sample with internal defects to be evaluated. The geometric parameters of the defects obtained through non-destructive testing are as follows: Defect major axis: =1.1 mm, = 0.75 mm, = 1.0 mm.

[0114] Based on the unified defect characteristic parameter definition established in step (3), the defect geometric parameters are substituted into formula (9) to calculate the C parameter value of the defect as 0.0607. According to the calibrated Liu-Murakami model and formula (4), the creep life of the defect-free structure at 550℃ and 290MPa is... The creep life of the defective component is 422.28h, and the creep life is calculated by formula (13).

[0115]

[0116] The calculated creep life of the defective structure is 166.8 hours.

[0117] To verify the accuracy of the predicted results, a creep test was conducted on the defective specimen at 550°C and a stress level of 290 MPa on an NCSJSJC0040 high-temperature creep testing machine according to ASTM E139-11 standard. The creep strain of the specimen was monitored in real time during the test until the specimen fractured. The actual creep life measured by the test was 180 hours.

[0118] The relative error between the actual life and the predicted life is 7.33%, which is within the acceptable range for engineering applications. This fully verifies the effectiveness and accuracy of the creep life prediction method for defective structural components based on the unified defect characteristic parameter C proposed in this invention.

[0119] In summary, this invention proposes a method for predicting the creep life of defective components based on a unified defect characteristic parameter C. This method defines the specific area... Relative depth and aspect ratio Three dimensionless parameters are used to uniformly characterize the multidimensional geometric features of defects into a single feature parameter C, and an explicit linear mapping relationship is established between parameter C and normalized creep life. This invention achieves dimensionality reduction characterization of multidimensional defect features, avoiding the need for case-by-case finite element analysis, and can provide technical support for rapid assessment of creep life of defective components in high-temperature pressure-bearing equipment such as nuclear power, thermal power, and petrochemical plants.

[0120] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

Claims

1. A method for evaluating the creep life of defective components based on unified defect characteristic parameters, characterized in that, The method includes: S1. Conduct high-temperature creep tests on defect-free materials / structures to obtain creep life data under different stress levels to calibrate material parameters for subsequent finite element simulations. S2. Using the Latin hypercube sampling method, N representative defect samples are generated in a three-dimensional parameter space containing defect geometric parameters. A corresponding finite element model of the defective structure is established, and the creep life is simulated and obtained. Simultaneously, the creep life of a defect-free structure under the same load level was simulated and obtained as a benchmark. This yields the sample set; S3, Constructing unified defect features Parameters, establishing normalized creep life and Linear relationship of parameters, and calibration of parameters. , , , ; The expression for the unified defect feature parameter C is: in, The specific area is expressed as the ratio of the area of ​​the envelope ellipse of the defect projected onto the load plane to the cross-sectional area of ​​the specimen. The ratio, ; Relative depth is indicated by the sample diameter. The ratio of the difference in defect depth to the sample diameter, ; Indicates the aspect ratio, which is the major axis of the defect. With short axis The ratio, ; α and β are the power exponent parameters to be calibrated; There is a linear relationship between the normalized creep lifetime and the uniform defect characteristic parameter C, defined as: in, To normalize creep life, The creep life of a defective structure. The creep life of a defect-free structure under the same load level. The slope coefficient represents the linear relationship. The intercept; S4. Obtain the defect geometric features of the component to be evaluated through non-destructive testing technology and calculate the uniform defect feature C parameter value. Substitute it into the linear relationship to calculate the normalized creep life. Combine the creep life of the defect-free structure under the same working conditions to obtain the predicted life of the component with defects. Specifically, this involves obtaining the geometric characteristic parameters of the defect, including the long axis of the defect, through non-destructive testing techniques. short axis ,depth and the diameter of the sample Calculate the specific area Relative depth and aspect ratio ,Will , , Substitute the C parameter into the unified defect feature calculation formula to obtain the C parameter value, and then substitute the C parameter value into the linear relationship to calculate the normalized creep life; according to the actual service conditions of the component to be evaluated, use the creep constitutive model calibrated in step (1) to calculate the creep life of the defect-free structure under the same conditions. The predicted life of a defective component can be calculated using the following formula. : 。 2. The method for evaluating the creep life of defective components based on unified defect characteristic parameters according to claim 1, characterized in that, The defect geometry parameters mentioned in step S2 include the major axis, minor axis, and depth; The range of values ​​for each defect geometric parameter is divided into N intervals. A sample point is randomly selected in each interval. The sample points of the three defect geometric parameters are randomly arranged and combined to form an initial sample set. The sample points are then uniformly distributed in the parameter space through iterative optimization.

3. The method for evaluating the creep life of defective components based on unified defect characteristic parameters according to claim 2, characterized in that, The range of values ​​for the defect geometric parameters is determined based on the sample size: defect major axis and short axis The values ​​of all values ​​are smaller than the sample radius and the defect depth. The value range is no greater than 1 / 2 of the sample diameter, and simultaneously satisfies... Geometric constraints; the number of samples N generated by Latin hypercube sampling is ≥30.

4. The method for evaluating the creep life of defective components based on unified defect characteristic parameters according to claim 1, characterized in that, In step S2, based on the calibrated creep constitutive model parameters, a three-dimensional finite element model is established for each group of defect samples using finite element tools to simulate the creep life of the defect sample. Simultaneously, a defect-free structural model is established, and the baseline creep life is simulated under the same conditions. After batch calculation of N groups of defect-containing models, the creep life of each group is calculated. Divide by the reference life , obtained the Normalized creep lifetime of a defect sample Finally, a complete sample set is constructed. ,in, They represent the first The major axis, minor axis, and depth of a defect sample; Indicates the first The creep lifetime ratio corresponding to each defect sample.

5. The method for evaluating the creep life of defective components based on unified defect characteristic parameters according to claim 1, characterized in that, The specific steps for calibrating parameters α, β, k, and b in step S3 are as follows: sample set Convert to dataset ; Group N As a dataset, define a custom function form in the regression analysis software: The optimal values ​​of the four parameters are solved simultaneously using the nonlinear least squares method, which minimizes the sum of squared residuals between the predicted and actual values ​​of all sample points. The goodness of fit is evaluated by the coefficient of determination R².

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