Effectiveness evaluation method for impact test data in material ductile-brittle transition temperature test

Abstract

The invention discloses a method for evaluating the effectiveness of impact test data in a material ductile-brittle transition temperature test, and relates to the technical field of material aging analys.The method comprises the steps that S1, a function expression of a material ductile-brittle transition curve is determined according to test data, and the material ductile-brittle transition curve comprises an upper platform area, a lower platform area and a ductile-brittle transition area; s2, calculating discreteness parameters of test data in the ductile-brittle transition region; s3, calculating the deviation of the test data in the ductile-brittle transition zone relative to the transition curve; s4, calculating an upper envelope line and a lower envelope line of a 95% confidence interval of the transformation curve according to the discreteness parameter and the deviation; and S5, judging the validity of the test data according to the upper envelope line and the lower envelope line. According to the method provided by the invention, the upper and lower envelope lines of the impact data approximate to 95% confidence interval can be given, so that the validity of the test data can be judged.

Description

Technical Field

[0001] This invention belongs to the field of material aging analysis technology, specifically relating to a method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of materials. Background Technology

[0002] The reactor pressure vessel (RPV) of a commercial nuclear power plant is typically a massive pressure-bearing structure made of ferritic steel, operating in extremely harsh environments. Due to the effects of high-energy neutrons and high temperatures, the performance of RPV materials deteriorates significantly. This degradation is primarily manifested in the shift of the transition curve towards the high-temperature region, leading to a marked increase in the material's low-temperature brittleness. Monitoring this degradation is essential to protect the safety of the RPV. Charpy impact testing is commonly used to determine the material's transition curve, enabling the monitoring and assessment of the degree of embrittlement in the reactor pressure vessel.

[0003] Generally, experiments require a series of tests at multiple temperatures, with 1-3 tests at each temperature, totaling 12-18 tests. Due to special circumstances, a small number of data points may differ significantly from others, potentially indicating outliers. If the anomalies are obvious, such as abnormal sample fracture surfaces, abnormal sample appearance, or test results significantly exceeding the normal range, the outliers can be discarded. However, most outliers lack clear characteristics, making manual determination of their necessity. In such cases, statistical methods for removing invalid data become a viable approach.

[0004] The data from the transition curve experiment exhibited a characteristic of low temperature and high temperature. Existing statistical techniques, when analyzing the low-temperature region, would give an lower boundary of the envelope below 0, such as... Figure 1 As shown. Considering that the limit value of the data should be greater than 0, and the lower envelope below 0 has no physical meaning, this invention proposes a more effective method for evaluating the validity of experimental data. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of materials. This method can provide the upper and lower envelopes of the approximately 95% confidence interval of the impact data, thereby enabling the determination of the validity of the test data.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of materials includes the following steps:

[0008] S1. Determine the functional expression of the ductile-brittle transition curve of the material based on the experimental data. The ductile-brittle transition curve of the material includes an upper plateau region, a lower plateau region, and a ductile-brittle transition region.

[0009] S2. Calculate the discrete parameters of the test data within the ductile-brittle transition zone;

[0010] S3. Calculate the deviation of the test data in the ductile-brittle transition zone from the transition curve;

[0011] S4. Based on the discrete parameters and deviations, calculate the upper and lower envelopes of the 95% confidence interval of the transition curve.

[0012] S5. Determine the validity of the test data based on the upper and lower envelopes.

[0013] Furthermore, in the method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of the material as described above, step S1 includes:

[0014] The ductile-brittle transition curve of the material is a hyperbolic tangent function with an S-shaped profile that is lower at first and higher at later. The upper plateau region is the high-temperature region corresponding to when the impact test measurement value of the S-shaped transition curve tends to stabilize. The lower plateau region is the low-temperature region corresponding to when the impact test measurement value of the S-shaped transition curve tends to stabilize. The brittle-ductile transition zone is the medium-temperature region corresponding to the middle section of the S-shaped transition curve.

[0015] The functional expression for the brittle-ductile transition curve of the material is:

[0016] (1)

[0017] In formula (1):

[0018] T represents temperature;

[0019] V(T) is the impact test measurement value corresponding to the temperature, including shear ratio, impact absorbed energy and lateral expansion value;

[0020] V upper This is the value for the platform.

[0021] V lower This is the value of the next platform.

[0022] C and D are the parameters to be fitted, and the experimental data are obtained by nonlinear fitting using formula (1).

[0023] Furthermore, in the method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of materials as described above, step S2 involves calculating the data dispersion parameter of the ductile-brittle transition zone according to EJ / T 20276-2021 "Standard for Determination of Ductile-Brittle Transition Temperature Curve of Reactor Pressure Vessel Materials". The calculation formula is:

[0024] (2)

[0025] In formula (2):

[0026] T i —The test temperature corresponding to the i-th test data;

[0027] V i —The experimental measurement value corresponding to the i-th experimental data;

[0028] n—The total number of valid test data within the ductile-brittle transition region;

[0029] ν—Degrees of freedom, equal to 2;

[0030] T(V i — The transformation temperature corresponding to the i-th experimental data on the transformation curve is obtained by inverse transformation of formula (1) as a function of the transformation temperature:

[0031] (3)

[0032] In formula (3):

[0033] arctanh — the inverse hyperbolic tangent function;

[0034] T(V) — a function of transition temperature;

[0035] V – The independent variable of the function refers to the experimentally measured value, including shear cross-sectional area, impact absorbed energy, and lateral expansion value.

[0036] Furthermore, in the method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of the material as described above, in step S3: when there is a sufficient amount of test data, the deviation is calculated using the following formula. :

[0037] (4)

[0038] In equation (4):

[0039] n—The total number of valid test data within the ductile-brittle transition region;

[0040] i — the data number used;

[0041] Y i —The impact test measurements corresponding to the i-th test data include shear cross-sectional area, impact absorbed energy, and lateral expansion value;

[0042] T i —The test temperature value corresponding to the i-th data point;

[0043] V(T) i — The impact fit value on the transition curve corresponding to the test temperature value of the i-th data point.

[0044] Furthermore, in the method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of materials as described above, step S3 involves: in the case of insufficient test data, calculating the deviation using the range method. .

[0045] Furthermore, in the method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of the material as described above, in step S4: the formula for calculating the upper envelope of the 95% confidence interval of the transition curve is:

[0046] (5)

[0047] Furthermore, in the method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of the material as described above, in step S4: the formula for calculating the lower envelope of the 95% confidence interval of the transition curve is:

[0048] (6)

[0049] Furthermore, in the method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of the material as described above, step S5 specifically involves: determining test data falling outside the upper envelope and the lower envelope as invalid data.

[0050] Compared with existing technologies, the method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of materials provided by this invention has the following beneficial effects:

[0051] The method provided by this invention first obtains the ductile-brittle transition curve of the material by fitting experimental data; then, it calculates the dispersion parameters and bias of the experimental data; finally, based on the dispersion parameters and bias, it provides the upper and lower envelopes of the approximately 95% confidence interval of the experimental data; and then, it judges the validity of the experimental data based on the positional relationship between the experimental data and the upper and lower envelopes. This method provides an algorithm for eliminating invalid data, eliminates the influence of human factors, reduces the requirements for experimental personnel, reduces the difficulty of the experiment, and the given envelopes can more effectively evaluate the validity of the experimental data. Attached Figure Description

[0052] To further illustrate the above and other advantages and features of this application, the specific embodiments of this application will be described in more detail below with reference to the accompanying drawings. The accompanying drawings, together with the following detailed description, are included in and form a part of this specification. It should be understood that these drawings only depict typical examples of this application and should not be considered as limiting the scope of this application.

[0053] Figure 1 The upper and lower boundary lines of the test data given by the existing technology in the transition temperature test;

[0054] Figure 2 This is a flowchart of a method for evaluating the validity of impact test data in a material ductile-brittle transition temperature test, provided in an embodiment of the present invention.

[0055] Figure 3 The upper and lower boundary lines for the transition temperature test data given by the method provided in this invention;

[0056] Figure 4 These are the upper and lower boundary lines of the test data determined in the examples. Detailed Implementation

[0057] Exemplary embodiments of this application will be described below with reference to the accompanying drawings. For clarity and brevity, not all features of actual implementations are described in the specification. However, it should be understood that many implementation-specific decisions must be made in the development of any such actual embodiment to achieve the developer's specific goals, such as complying with constraints related to the system and business, and these constraints may vary depending on the implementation. Furthermore, it should be understood that while development work can be very complex and time-consuming, such development work is merely a routine task for those skilled in the art who benefit from the content of this application.

[0058] It should also be noted that, in order to avoid obscuring this application with unnecessary details, only the equipment structure and / or processing steps closely related to the solution according to this application are shown in the accompanying drawings, while other details that are not closely related to this application are omitted.

[0059] The embodiments or examples disclosed below are used to implement this application. To simplify the disclosure of this application, the components and methods of specific examples are described below. Of course, they are merely examples and are not intended to limit this application.

[0060] Due to the effects of high-energy neutrons and high temperatures, the performance of RPV materials in commercial nuclear power plants undergoes significant degradation. This degradation is primarily manifested in the shift of the transition curve towards the high-temperature region, leading to a marked increase in the material's low-temperature brittleness. Testing personnel typically conduct impact tests to determine the material's transition curve, enabling the monitoring and assessment of the degree of embrittlement within the reactor pressure vessel. The test subjects are predetermined numbers of samples placed inside the reactor pressure vessel beforehand.

[0061] To remove invalid experimental data, this invention provides a method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of materials. This method can provide the upper and lower envelopes of the approximately 95% confidence interval for the impact data, thereby determining the validity of the test data based on the positional relationship between the test data and the upper and lower envelopes. The method includes the following steps:

[0062] S1. Determine the functional expression of the ductile-brittle transition curve of the material based on the experimental data. The ductile-brittle transition curve of the material includes an upper plateau region, a lower plateau region, and a ductile-brittle transition region.

[0063] like Figure 1 As shown, in the coordinate axis containing the transition curve, the horizontal axis represents the test temperature, and the vertical axis represents the impact test measurement value. The transition curve is a hyperbolic tangent function, exhibiting an S-shape with a low initial value followed by a high value. It is divided into an upper plateau region, a lower plateau region, and a ductile-brittle transition region. The upper plateau region corresponds to the high-temperature area where the impact test measurement value of the S-shaped transition curve tends to stabilize. The impact test measurement value corresponding to the upper plateau region is the upper plateau value, denoted as V. upper The lower plateau region is the low-temperature area where the impact test measurement value of the S-shaped transition curve tends to stabilize. The impact test measurement value corresponding to the lower plateau region is the lower plateau value, denoted as V. lower The ductile-brittle transition zone corresponds to the intermediate temperature region in the middle section of the S-shaped transition curve. Within this zone, the fracture mechanism of the material changes from ductile fracture to brittle fracture. In this temperature range, when subjected to impact loads, the material's behavior changes from "fracture after absorbing a large amount of energy" (ductile) to "sudden fracture after absorbing very little energy" (brittle), and the fracture surface of the specimen exhibits a mixed state of fibrous and brittle cleavage.

[0064] Test temperature, impact test measurement, maximum value V upper and minimum value V lower Satisfy the following expression:

[0065] (1)

[0066] In formula (1):

[0067] T represents temperature;

[0068] V(T) is the impact test measurement value corresponding to the temperature, including shear ratio, impact absorbed energy, and lateral expansion value;

[0069] V upper —Value on the platform;

[0070] V lower —Lower platform value;

[0071] tanh() is a hyperbolic tangent function, with an S-shaped curve that is initially low and then rises.

[0072] C and D are the parameters to be fitted.

[0073] The transition temperature test data were nonlinearly fitted using formula (1) to obtain the values ​​of parameters C and D, thereby determining the transition temperature curve and its functional expression. In the nonlinear fitting, all test data, including data within the upper plateau temperature range, data within the ductile-brittle transition region, and low absorbed energy data, should be included in the calculation.

[0074] S2. Calculate the data dispersion parameters within the ductile-brittle transition region.

[0075] EJ / T 20276-2021, "Standard for Determination of the Brittle-Ductile Transition Temperature Curve of Reactor Pressure Vessel Materials," specifies the data dispersion parameters for the brittle-ductile transition zone. The calculation formula is:

[0076] (2)

[0077] In formula (2):

[0078] S tdT —Discreteness parameters of data in the brittle-ductile transition zone;

[0079] T i —The test temperature corresponding to the i-th test data;

[0080] V i —The experimental measurement value corresponding to the i-th experimental data;

[0081] n — the total number of valid test data in the ductile-brittle transition zone. Here, valid test data refers to the remaining test data after obviously abnormal data has been manually removed.

[0082] ν—Degrees of freedom, equal to 2;

[0083] T(V i — The fitted transition temperature corresponding to the i-th experimental data can be obtained by inversely transforming formula (1) to obtain the functional form of the transition temperature:

[0084] (3)

[0085] In formula (3):

[0086] arctanh — the inverse hyperbolic tangent function;

[0087] T(V) — a function of transition temperature;

[0088] V – The independent variable of the function refers to the experimentally measured value, including shear cross-sectional area, impact absorbed energy, and lateral expansion value.

[0089] S3. Calculate the deviation of the test data in the ductile-brittle transition zone from the transition curve.

[0090] When there is a large amount of experimental data, the following formula is used for calculation:

[0091] (4)

[0092] In equation (4):

[0093] n—The total number of valid test data within the ductile-brittle transition region;

[0094] i — the data number used;

[0095] Y i —The impact test measurement value corresponding to the i-th data point, including shear cross-sectional area, impact absorbed energy, and lateral expansion value;

[0096] T i —The test temperature value corresponding to the i-th data point;

[0097] V(T) i — The impact fit value on the transition curve corresponding to the test temperature value of the i-th data point.

[0098] When data is limited, the range method is used to calculate the deviation.

[0099] S4. Calculate the upper and lower envelopes of the 95% confidence interval of the transition curve.

[0100] Transform the V in the curve function (1) upper Replace item with V upper +2*S Y Replace parameter C with C-2*S tdT The functional form of formula (1) is transformed as follows:

[0101] (5)

[0102] This is the upper boundary of the 95% confidence interval of the transformation curve, i.e., the upper envelope.

[0103] Transform the V in the curve function (1) upper Replace item with V upper -2*S Y Replace parameter C with C+2*S tdT The functional form of formula (1) is transformed as follows:

[0104] (6)

[0105] This is the lower boundary of the 95% confidence interval of the transformation curve, i.e., the lower envelope.

[0106] S5. Determine the validity of the test data based on its positional relationship with the upper and lower envelope lines. Test data falling outside the upper and lower envelope lines are considered invalid data.

[0107] Example

[0108] A VVER-1000 nuclear power plant needs to complete a monitoring test. The upper and lower boundaries were obtained by shifting the transition temperature curve vertically. Figure 1 As shown, from Figure 1 It is evident that the lower boundary is significantly below 0, indicating a data anomaly. To correct this anomaly, the method provided in this invention is used to redetermine the upper and lower envelopes, thereby enabling the validity assessment of the experimental data. The specific steps are as follows:

[0109] Step 1: Determine the transformation curve function

[0110] The set of experimental data to be evaluated is shown in Table 1 below.

[0111] Table 1 Experimental Data

[0112] Test temperature / °C Impact absorption energy obtained from the test / J 26 258 -74 15 -74 11 26 266 1 268 -24 160 -24 42 -49 51 -49 151 -49 59 -24 38 -74 10 -99 5 51 252 -26 206 -49 65

[0113] According to formula (1), the impact absorption energy test data in Table 1 are analyzed and fitted to obtain C=-25.47 and D=37.4485. Therefore, the transformation curve function form is:

[0114]

[0115] Step 2: Calculate the deviation and

[0116] Because there are only four temperature ranges available for the upper platform, the range method was used to calculate the deviation of the experimental data from the fitted transformation curve within the brittle-ductile transition region. The maximum impact energy in the upper platform section is 268, and the minimum impact energy is 252, therefore S Y =R / C=(268-252) / 2.06=7.767.

[0117] Calculated according to the provisions of EJ / T 20276-2021 :

[0118]

[0119] Step 3: Calculate the upper and lower envelope lines

[0120] Calculate the upper envelope according to formula (5):

[0121]

[0122] Calculate the lower envelope according to formula (6):

[0123]

[0124] Step 4: Determine the validity of the test data.

[0125] The fitted transition curves, upper envelope, lower envelope, and experimental data are shown in the figure. Figure 3 As shown, from Figure 3 As can be seen, all experimental data fall between the upper and lower envelopes, so all experimental data in this set are valid.

[0126] The present invention provides a method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of materials. This method involves fitting the test data to obtain the ductile-brittle transition curve of the material; then calculating the dispersion parameters and bias of the test data; finally, based on the dispersion parameters and bias, providing the upper and lower envelopes of the approximate 95% confidence interval of the test data; and then judging the validity of the test data based on the positional relationship between the test data and the upper and lower envelopes. The envelopes provided by this method can more effectively evaluate the validity of the test data.

[0127] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention is also intended to include these modifications and variations.

Claims

1. A method for evaluating the validity of impact test data in a material ductile-brittle transition temperature test, comprising the following steps: S1. Determine the functional expression of the ductile-brittle transition curve of the material based on the experimental data. The ductile-brittle transition curve of the material includes an upper plateau region, a lower plateau region, and a ductile-brittle transition region. S2. Calculate the discrete parameters of the test data within the ductile-brittle transition zone; S3. Calculate the deviation of the test data in the ductile-brittle transition zone from the transition curve; S4. Based on the discrete parameters and deviations, calculate the upper and lower envelopes of the 95% confidence interval of the transition curve. S5. Determine the validity of the test data based on the upper and lower envelopes.

2. The method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of materials according to claim 1, characterized in that, In step S1: The ductile-brittle transition curve of the material is a hyperbolic tangent function with an S-shaped profile that is lower at first and higher at later. The upper plateau region is the high-temperature region corresponding to when the impact test measurement value of the S-shaped transition curve tends to stabilize. The lower plateau region is the low-temperature region corresponding to when the impact test measurement value of the S-shaped transition curve tends to stabilize. The brittle-ductile transition zone is the medium-temperature region corresponding to the middle section of the S-shaped transition curve. The functional expression for the brittle-ductile transition curve of the material is: （1） In formula (1): T represents temperature; V(T) is the impact test measurement value corresponding to the temperature, including shear ratio, impact absorbed energy and lateral expansion value; V upper This is the value for the platform. V lower This is the value of the next platform. C and D are the parameters to be fitted, and the experimental data are obtained by nonlinear fitting using formula (1).

3. The method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of materials according to claim 2, characterized in that, In step S2: Calculate the data dispersion parameters of the brittle-ductile transition zone according to EJ / T 20276-2021 "Standard for Determination of the Brittle-Ductile Transition Temperature Curve of Reactor Pressure Vessel Materials". The calculation formula is: （2） In formula (2): T i —The test temperature corresponding to the i-th test data; V i —The experimental measurement value corresponding to the i-th experimental data; n—The total number of valid test data within the ductile-brittle transition region; ν—Degrees of freedom, equal to 2; T(V i — The transition temperature corresponding to the i-th experimental data on the transition curve is obtained by inverse transformation of formula (1) as a function of the transition temperature: （3） In formula (3): arctanh — the inverse hyperbolic tangent function; T(V) — a function of transition temperature; V – The independent variable of the function refers to the experimentally measured value, including shear cross-sectional area, impact absorbed energy, and lateral expansion value.

4. The method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of materials according to claim 3, characterized in that, In step S3: when there is enough experimental data, the deviation is calculated using the following formula. : （4） In equation (4): n—The total number of valid test data within the ductile-brittle transition region; i — the data number used; Y i —The impact test measurements corresponding to the i-th test data include shear cross-sectional area, impact absorbed energy, and lateral expansion value; T i —The test temperature value corresponding to the i-th data point; V(T) i — The impact fit value on the transition curve corresponding to the test temperature value of the i-th data point.

5. The method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of materials according to any one of claims 2-4, characterized in that, In step S3: When experimental data is insufficient, the range method is used to calculate the deviation. .

6. The method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of materials according to claim 5, characterized in that, In step S4: The formula for calculating the upper envelope of the 95% confidence interval of the transition curve is: （5）。 7. The method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of materials according to claim 6, characterized in that, In step S4: The formula for calculating the lower envelope of the 95% confidence interval of the transition curve is: （6）。 8. The method for evaluating the validity of impact test data in the ductile-brittle transition temperature test of materials according to claim 7, characterized in that, Step S5 specifically involves determining that test data falling outside the upper envelope and the lower envelope are invalid data.

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