Method for determining effective length of insertion section of radioactive impact sample

Abstract

The invention belongs to the technical field of physical and chemical inspection of radioactive metal materials, and discloses a method for determining the effective length of an insertion section of a radioactive impact sample. Determining the size of a plastic deformation area of the impact broken end of the sample under different impact energy in different intervals, determining the sampling length of the insertion section of the reconstructed sample according to the size of the plastic deformation area, and finally improving the utilization rate of the radioactive impact sample. The utilization rate of the radioactive impact sample can be improved to the maximum extent, and meanwhile the overall accuracy of impact test data is improved.

Description

Technical Field

[0001] The present application belongs to the technical field of physical and chemical testing of radioactive metal materials, and in particular to a method for determining the effective length of an insertion section of a radioactive impact specimen. Background Art

[0002] To evaluate the degree of radiation embrittlement of pressure vessel materials, it is necessary to carry out impact tests at different temperatures. One test requires about 15 radioactive impact specimens to form a ductile-brittle transition temperature curve to obtain the ductile-brittle transition temperature of the pressure vessel material. There are a fixed number of radioactive impact specimens in each reactor, and each radioactive specimen cannot be used after the impact test. The overall utilization rate of the impact specimens is low. At the same time, the later unit life extension, single impact test failure or other factors may lead to insufficient number of radioactive impact specimens designed for the original reactor, affecting the subsequent regular monitoring of radiation embrittlement of pressure vessel materials. In addition, in order to improve the accuracy of the impact test data, more impact specimens need to be used for each test. In view of this situation, there is currently no relevant research and technology in China to solve the problem of insufficient number of reactor radioactive impact specimens. Therefore, it is urgent to develop a radioactive specimen reconstruction technology to improve the utilization rate of radioactive impact specimens.

[0003] Radioactive impact specimen reconstruction is a technology that reassembles and processes the tested impact specimen head into a standard impact specimen for retesting. This technology can significantly improve the efficiency of impact specimen use and obtain more impact test data. The reconstruction technology first needs to process the impact specimen head after the previous impact test into an insertion section, and then process it into a new impact specimen after welding the support section. Since the impact energy of the impact test at different temperatures is different, the impact energy of the specimen is the highest and its deformation is the largest in the upper platform temperature area of ​​the test; the impact energy in the lower platform area is the lowest and its deformation is the smallest. Only the undeformed part of the impact specimen head can be used for specimen reconstruction. Therefore, before the specimen reconstruction, it is necessary to first determine the size of the effective undeformed area in the radioactive impact specimen head to ensure that the inserted section has sufficient length. Summary of the invention

[0004] The purpose of this application is to provide a method for determining the effective length of the insertion section of a radioactive shock specimen, to guide whether subsequent shock specimens can be reconstructed, or how many specimens can be reconstructed, thereby solving the problem of insufficient radioactive shock specimens in the later stage of unit operation due to continuous consumption of radioactive shock specimens, shock test losses and other factors, and at the same time, by increasing the number of shock tests, the shock test data can be made more accurate and effective.

[0005] In order to achieve the above objectives, this application provides the following technical solutions:

[0006] The present application provides a method for determining the effective length of the insertion section of a radioactive impact specimen. The method determines the size of the plastic deformation area of ​​the specimen impact fracture under different impact energies in different intervals based on the deformation results of the radioactive impact specimen fracture in different intervals of the ductile-brittle transition temperature curve. The length of the insertion section of the reconstructed specimen is determined based on the size of the plastic deformation area, thereby ultimately improving the utilization rate of the radioactive impact specimen.

[0007] In some embodiments, the method for determining the effective length of the insertion section of the radioactive impact specimen specifically includes:

[0008] Step 1: Carry out impact tests at different temperatures on the radioactive impact specimens to obtain the ductile-brittle transition temperature curve of the specimens and the impact fracture heads under different impact energies that can be used for plastic deformation zone analysis;

[0009] Step 2: Analyze the fractured morphology of the impact specimens left by the impact test, measure the microhardness variation trend of the fractured specimens along the length direction, and obtain the plastic deformation zone information of different impact specimens;

[0010] Step 3: Use the finite element analysis method to analyze the impact test process and the size of the deformation zone of the impact specimen break to determine the effective length of the insertion section.

[0011] In some embodiments, impact fractures in different temperature ranges are obtained through impact tests, and the axial hardness change of the impact fracture is measured using a microhardness tester to obtain the hardness field distribution of the impact specimen fracture, and the position where the hardness value increases sharply is determined as the edge of the plastic zone.

[0012] In some embodiments, the measured hardness value is processed, and a hardness variation trend graph is drawn by taking four average values ​​in the longitudinal direction at the same position from the end to find the platform with the maximum plastic deformation zone at the ductile-brittle transition temperature.

[0013] In some embodiments, according to the hardness test results, a hardness distribution cloud diagram is drawn based on the plastic deformation of the upper platform sample fracture of the impact sample.

[0014] In some embodiments, for the impact specimen occurring in the ductile fracture zone of the upper platform, the GTN model based on the microvoid nucleation, growth and aggregation mechanism, which is most commonly used in studying the ductile damage fracture of metal materials, is used to perform finite element analysis simulation on the impact specimen breakage.

[0015] In some embodiments, the GTN model is as follows:

[0016] The pore volume fraction in the GTN model affects the growth, nucleation and aggregation of the material. The modified f * This is more consistent with the mutual aggregation effect of holes when the material undergoes macroscopic fracture, as shown in formula (2).

[0017]

[0018] Where: Φ represents the plastic potential, σ eq is Mises stress, σ m , σ e and σ h They represent the macro-average stress, equivalent stress and macro-hydrostatic stress of the material respectively; q1, q2 and q3 are the model correction parameters added to consider the effect of adjacent holes; f u * is a function of the pore volume fraction f; f u * is the void volume fraction when the material loses its bearing capacity; f c is the critical hole fraction when holes start to aggregate; f F is the void volume fraction at rupture.

[0019] According to the requirements of the GTN model, in addition to the inherent material parameters of the material, there are 9 undetermined parameters that need to be determined, namely q1, q2, q3, f0, f n 、f c 、f F , ε n , S N . Where f0 is the initial pore volume fraction; f n and ε n are the void volume fraction and equivalent plastic strain when void nucleation occurs, respectively; S N Refers to the standard deviation of the normal distribution of the hole nucleation. For metal materials, the values ​​of the correction parameters q1, q2, and q3 are widely recognized, that is, q1 = 1.5, q2 = 1, and q3 = 2.25.

[0020] In some embodiments, after the simulation of the impact process is completed, the data is processed by ABAQUS, the load and displacement data points of the reference point set at the center of the pendulum are exported, and the load-displacement curve of the simulated impact is drawn.

[0021] In some embodiments, the plastic deformation length of the upper platform break is determined by outputting the distance between the peripheral contour node and the fracture node.

[0022] Compared with the prior art, the method for determining the effective length of the insertion section of the radioactive impact specimen provided in the present application has the following beneficial effects:

[0023] This method can determine the size of the plastic deformation zone of the broken specimens of radioactive impact specimens at different test temperatures by analyzing the broken specimen morphology and the microhardness change trend of the broken specimens along the length direction. An analysis method for the length of the insertion section of the radioactive impact specimen is established, the length of the insertion section is determined, and the preparation conditions are established for processing and reconstructing standard impact specimens.

[0024] This method can maximize the utilization of radioactive impact specimens and improve the overall accuracy of impact test data. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for the technical description.

[0026] Figure 1 A flow chart of a method for determining the effective length of the insertion section of a radioactive impact specimen provided in this application;

[0027] Figure 2 A schematic diagram of the locations of hardness test points provided for one embodiment of the present application;

[0028] Figure 3 A hardness variation trend diagram provided for one embodiment of the present application;

[0029] Figure 4 A hardness field distribution diagram of the upper platform break provided for one embodiment of the present application;

[0030] Figure 5 A comparison chart of Charpy impact test results and simulation results provided for one embodiment of the present application;

[0031] Figure 6 A schematic diagram of simulation results provided for an embodiment of the present application. DETAILED DESCRIPTION

[0032] The following is further explained in detail through specific implementation methods.

[0033] like Figure 1 As shown, the present application provides a method for determining the effective length of the insertion section of a radioactive impact specimen. The method determines the size of the plastic deformation area of ​​the specimen under different impact energies in different intervals according to the deformation results of the radioactive impact specimen fracture in different intervals of the ductile-brittle transition temperature curve; the length of the insertion section of the reconstructed specimen is determined according to the size of the deformation area of ​​the impact fracture, thereby ultimately improving the utilization rate of the radioactive impact specimen. Specifically, it includes:

[0034] Step 1: Carry out impact tests at different temperatures on the radioactive impact specimens to obtain the ductile-brittle transition temperature curve of the specimens and the impact fracture heads under different impact energies that can be used for plastic deformation zone analysis;

[0035] Step 2: Analyze the fractured specimen morphology left by the impact test, measure the microhardness variation trend of the fractured specimen along the length direction, and obtain the plastic deformation zone information of different impact specimens;

[0036] Step 3: Use the finite element analysis method to analyze the impact test process and the size of the deformation zone of the impact specimen break to determine the effective length of the insertion section.

[0037] This method mainly includes hardness test analysis and finite element analysis.

[0038] (1) Hardness test analysis

[0039] Through the impact test, the impact fracture heads in different temperature ranges are obtained, and the axial hardness change of the impact fracture heads is measured by using a microhardness tester to obtain the hardness field distribution of the impact specimen fracture heads. The position where the hardness value increases sharply is determined as the edge of the plastic zone. The position distribution of the hardness test points is as follows: Figure 2 As shown, the hardness test starts from the broken end of the impact specimen and is tested sequentially at a certain distance to determine the size of the inserted section.

[0040] The measured hardness value is processed, and the hardness change trend diagram is drawn by taking 4 average values ​​in the longitudinal direction at the same position from the end, as shown in Figure 3 As shown, it can be found that the upper platform has the largest plastic deformation zone at the ductile-brittle transition temperature. As the test temperature increases, the plastic deformation of the impact fracture gradually increases. This is because as the impact energy increases, the strain of the material also increases. The hardness value of the impact fracture of the lower platform remains basically unchanged, and there is almost no position where the hardness suddenly increases. The hardness value of the impact fracture in the transition zone begins to change at a distance of 4.5mm (for example) from the fracture. The fracture of the upper platform shows a hardness change trend similar to that of the fracture in the transition zone, that is, it maintains a relatively stable hardness value in the elastic zone near the end of the specimen, and then a large change occurs in the hardness value at a certain position. The difference is that compared with the shorter plastic deformation area of ​​the fracture in the transition zone, the plastic deformation of the upper platform is larger. According to the hardness test results, the hardness distribution cloud map of the upper platform specimen of the impact specimen is finally drawn based on the plastic deformation, as shown in the figure. Figure 4 As shown, the length of the plastic deformation zone is about 7 mm (example). Figure 4 The values ​​of hardness distribution in are as follows:

[0041] ①240kg / mm 2 ~267kg / mm 2 ;

[0042] ②238kg / mm 2 ~257kg / mm 2 ;

[0043] ③230kg / mm 2 ~240kg / mm 2 ;

[0044] ④220kg / mm 2 ~230kg / mm 2 .

[0045] (2) Finite element analysis

[0046] The impact specimen has the largest impact absorption energy on the upper platform, and the plastic deformation is the largest. To ensure that the insertion section size of the reconstructed specimen meets the reconstruction requirements, the deformation of the upper platform area is simulated. For the impact specimen that occurs in the ductile fracture zone of the upper platform, the GTN model based on the microvoid nucleation, growth and aggregation mechanism (i.e., the Gurson model modified by Tvergaard and Needleman), which is most commonly used in the study of ductile damage fracture of metal materials, is used to perform finite element analysis simulation on the impact specimen.

[0047] The GTN model is shown in formula (1). The pore volume fraction in the GTN model affects the growth, nucleation and aggregation of the material. The modified f * This is more consistent with the mutual aggregation effect of holes when the material undergoes macroscopic fracture, as shown in formula (2).

[0048]

[0049] Where: Φ represents the plastic potential, σ eq is the Mises stress, σ m , σ e and σ h They represent the macro-average stress, equivalent stress and macro-hydrostatic stress of the material respectively; q1, q2 and q3 are the model correction parameters added to consider the effect of adjacent holes; f u * is a function of the pore volume fraction f; f u * is the void volume fraction when the material loses its bearing capacity; f c is the critical hole fraction when holes start to aggregate; f F is the void volume fraction at rupture.

[0050] According to the requirements of the GTN model, in addition to the inherent material parameters of the material, there are 9 undetermined parameters that need to be determined, namely q1, q2, q3, f0, f n 、f c 、f F , ε n , S N. Where f0 is the initial pore volume fraction; f n and ε n are the void volume fraction and equivalent plastic strain when void nucleation occurs, respectively; S N Refers to the standard deviation of the normal distribution of the hole nucleation. For metal materials, the values ​​of the correction parameters q1, q2, and q3 are widely recognized, that is, q1 = 1.5, q2 = 1, and q3 = 2.25. Based on the finite element inverse calculation method, firstly, the variable adjustment is performed for a single parameter, and then f0, f N 、f c The parameters were adjusted so that the simulation results gradually approached the experimental results, and the GTN model parameters were finally determined as shown in Table 1.

[0051] Table 1 GTN parameters

[0052] parameters <![CDATA[q1]]> <![CDATA[q2]]> <![CDATA[q3]]> <![CDATA[ε n ]]> <![CDATA[S N ]]> <![CDATA[f0]]> <![CDATA[f N ]]> <![CDATA[f c ]]> <![CDATA[f F ]]> value 1.5 1.0 2.25 0.3 0.1 0.0002 0.0011 0.10 0.12

[0053] Considering the symmetry of the impact specimen structure and load, 1 / 2 of the specimen thickness direction was selected to establish the model, and symmetric constraint boundary conditions were given at the cross section. The pendulum and anvil of the impact model were set as rigid structures, and the material density was 7.8×10 3 Kg / m3, elastic modulus is 210Gpa, Poisson's ratio is 0.3. The impact specimen is composed of C3D8R solid units, and the material density is 7.8×10 3 Kg / m3, elastic modulus is 128Gpa, Poisson's ratio is 0.28. Explicit dynamic analysis is used in the numerical simulation process, the initial velocity of the pendulum is set to 5.2m / s, the friction coefficient is set to 0.2, and the entire impact time is 0.006s. The core area of ​​the entire model, that is, the area where the Charpy impact specimen undergoes plastic deformation, is decided to set the center 15mm (example) as the core area based on the existing experimental results, and finally it is decided to set 40 layers of units in the thickness direction, that is, the unit size is 0.25mm (example). A transition area with a unit size of 1.0mm (example) is set in the area outside the core area, and the unit size of the outermost edge is set to 1.5mm (example), totaling 83,700 units, with no error units.

[0054] After the simulation of the impact process is completed, the data is processed by ABAQUS, the load and displacement data points of the reference point set at the center of the pendulum are exported, and the load-displacement curve of the simulated impact is drawn. Figure 5 As shown in the figure, the red diamond data points are derived from the pendulum reference points set in the simulation, and the black curve is the impact curve of the upper platform sample derived from the impact tester. The figure shows that the simulation results are consistent with the overall trend of the test, and the simulation effect reproduces the impact test of the material on the upper platform well. Figure 6This is a schematic diagram of the plastic deformation of the simulated upper platform impact fracture, where the arrows indicate the concentrated area of ​​plastic deformation. It can be seen that the plastic deformation on both sides of the notch is distributed symmetrically, which is consistent with the theoretical reasoning of fracture mechanics. Figure 6 It shows that the plastic deformation is the largest at the impact position of the pendulum, and its hardness value should also be the highest. According to the ABAQUS data processing results, the plastic edge shown in the plastic deformation diagram is taken as the outermost contour. By outputting the distance between the outer contour node and the fracture node, it is comprehensively determined that the plastic deformation length of the upper platform break is about 7.0mm (example). Based on the comprehensive comparison and judgment of the hardness results and the simulation results, it is finally determined that the size of the middle insertion section of the reconstructed specimen is 20mm (example).

[0055] The above description is only a specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed in the present application should be covered within the protection scope of the present application.

Claims

1. A method for determining the effective length of a radioactive impact specimen insertion section, characterized in that: According to the deformation results of radioactive impact specimens in different intervals of the ductile-brittle transition temperature curve, the size of the plastic deformation area of ​​the specimen impact fracture under different impact energies in different intervals is determined. The length of the insertion section of the reconstructed specimen is determined according to the size of the plastic deformation area, ultimately improving the utilization rate of the radioactive impact specimens.

2. The method for determining the effective length of the insertion section of the radioactive impact specimen according to claim 1 is characterized in that: Specifically include: Step 1: Carry out impact tests at different temperatures on the radioactive impact specimens to obtain the ductile-brittle transition temperature curve of the specimens and the impact fracture heads for plastic deformation zone analysis under different impact energies; Step 2: Analyze the morphology of the broken impact specimens left by the impact test, measure the microhardness variation trend of the broken specimens along the length direction, and obtain the plastic deformation zone information of different impact specimens; Step 3: Use the finite element analysis method to analyze the impact test process and the size of the deformation zone of the impact specimen break to determine the effective length of the insertion section.

3. The method for determining the effective length of the insertion section of the radioactive impact specimen according to claim 2, characterized in that: Through the impact test, the impact fracture heads in different temperature ranges were obtained. The axial hardness change of the impact fracture heads was measured using a microhardness tester. The hardness field distribution of the impact specimen fracture heads was obtained, and the position where the hardness value increased sharply was determined as the edge of the plastic zone.

4. The method for determining the effective length of the radioactive impact specimen insertion section according to claim 3 is characterized in that: The measured hardness value is processed, and the hardness variation trend diagram is drawn by taking 4 average values ​​in the longitudinal direction at the same position away from the end to find the platform with the largest plastic deformation zone at the ductile-brittle transition temperature.

5. The method for determining the effective length of the radioactive impact specimen insertion section according to claim 4, characterized in that: According to the hardness test results, the hardness distribution cloud diagram is drawn based on the plastic deformation of the upper platform specimen of the impact specimen.

6. The method for determining the effective length of the radioactive impact specimen insertion section according to claim 2, characterized in that: For the impact specimens occurring in the ductile fracture zone of the upper platform, the GTN model based on the microvoid nucleation, growth and aggregation mechanism, which is most commonly used in studying the ductile damage fracture of metal materials, was used to perform finite element analysis simulation on the impact specimen breakage.

7. The method for determining the effective length of the radioactive impact specimen insertion section according to claim 6, characterized in that: The GTN model is as follows: Where Φ represents the plastic potential, σ eq is Mises stress, σ m , σ e and σ h They represent the macro-average stress, equivalent stress and macro-hydrostatic stress of the material respectively, and q1, q2 and q3 are the model correction parameters added to consider the effect of adjacent holes; After modifying the GTN model, it is as follows: In the formula, f * is a function of the pore volume fraction f, is the void volume fraction when the material loses its bearing capacity, f c is the critical hole fraction when holes start to aggregate, f F is the void volume fraction at rupture.

8. The method for determining the effective length of the radioactive impact specimen insertion section according to claim 7, characterized in that: Determine 9 parameters to be determined, namely q1, q2, q3, f0, f n 、f c 、f F , ε n , S N , where f0 is the initial pore volume fraction, f n and ε n are the void volume fraction and equivalent plastic strain when void nucleation occurs, S N is the standard deviation of the normal distribution of hole nucleation; For metal materials, the values ​​of correction parameters q1, q2, and q3 are: q1 = 1.5, q2 = 1, q3 = 2.25; Based on the finite element inverse operation method, the variable adjustment is performed for a single parameter, and then f0, f N , fc to adjust the parameters so that the simulation results gradually approach the experimental results, and finally determine the GTN model parameters as follows: q1 = 1.5, q2 = 1, q3 = 2.25, ε n =0.3, S N =0.1, f0=0.0002, f N =0.0011, fc=0.1, f F =0.

12.

9. The method for determining the effective length of the radioactive impact specimen insertion section according to claim 6, characterized in that: After the simulation of the impact process is completed, the data is processed by ABAQUS, the load and displacement data points of the reference point set at the center of the pendulum are exported, and the load-displacement curve of the simulated impact is drawn.

10. The method for determining the effective length of the radioactive impact specimen insertion section according to claim 9, characterized in that: The plastic deformation length of the upper platform break is determined by outputting the distance between the outer contour node and the fracture node.

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