Method and device for testing mechanical property of small punch of reactor structure material

Abstract

The invention discloses a small punch mechanical property testing method and device for a reactor structure material, and belongs to the technical field of inspection after irradiation. Starting a load applying module, pressing the punch at a preset pressing rate, recording the load applied to the sample by the punch and the displacement of the punch to form a first relation curve, and stopping pressing until the load is reduced to be below a preset threshold value; analyzing the first relation curve to obtain the yield strength and tensile strength of the corresponding material of the sample; the method comprises the following steps: preprocessing a plurality of samples at a plurality of different preset temperatures, starting a load applying module to form a first relation curve, and calculating normalized fracture absorption energy of the first relation curve corresponding to all the samples at each preset temperature, forming a second relation curve by taking the preset temperature as a horizontal axis and the average value of the normalized fracture absorption energy of all the samples at each preset temperature as a longitudinal axis; and analyzing the second relation curve to obtain the standard ductile-brittle transition temperature of the corresponding material of the sample.

Description

Technical Field

[0001] This application relates to the field of post-irradiation testing technology, and in particular to a method and apparatus for testing the mechanical properties of a small punch rod for reactor structural materials. Background Technology

[0002] In the field of nuclear energy, reactor structural materials are the core foundation for ensuring the long-term safe and stable operation of reactors, and their mechanical properties directly determine the service life and safety boundaries of the reactor. These materials are subjected to complex conditions of high temperature, radiation, and corrosion for extended periods, and their mechanical properties degrade over time, potentially leading to structural failure. Therefore, accurate characterization and long-term monitoring of their mechanical properties are key research directions in the field of nuclear safety.

[0003] Currently, the industry's testing of the mechanical properties of reactor structural materials still primarily relies on conventional mechanical testing methods such as tensile testing. While these methods can obtain core parameters such as yield strength, tensile strength, and impact toughness, they have significant limitations in practical applications. Conventional mechanical tests have strict standards for specimen size and shape. Taking the most widely used tensile test as an example, according to standards such as GB / T228.1, standard tensile specimens for metallic materials must have a parallel section length of not less than 20 mm, a cross-sectional diameter of not less than 5 mm, or a rectangular cross-sectional thickness of 3 mm. In some scenarios, specific transition arc radii and total length requirements must also be met. Furthermore, material sampling of in-service reactor structures must be done without compromising structural integrity, and is limited by structural design thickness and safety protection regulations during operation. Especially for older reactors that have been in service for more than 30 years, the structural materials themselves have already experienced a certain degree of performance degradation. If large-volume cutting and sampling are performed to meet the specimen size requirements of conventional tests, it may not only disrupt the original stress balance of the structure but also directly induce new safety hazards. The conflict between the large-size sample requirements of conventional tests and the safety sampling restrictions of in-service structures has significantly limited the applicability of conventional mechanical testing methods in the performance evaluation of in-service reactor structural materials, making it difficult to meet the technical requirements for safety monitoring throughout the entire life cycle of nuclear facilities.

[0004] To overcome this technological bottleneck, the industry has gradually shifted its research focus to small-sample testing technology in recent years to minimize the impact of sampling on the safety of in-service structures. Among these technologies, small punch testing has become an important direction for solving the challenges of evaluating the performance of materials in in-service reactors due to its outstanding advantages: it only requires millimeter-sized disc samples with a diameter of 5-10 mm and a thickness of 0.1-1 mm, and the sample size is less than 1 / 50 of that of conventional tensile test samples. Test samples can be obtained from the surface of in-service components or repaired areas without damaging the integrity of the main reactor structure, perfectly meeting the needs of minimally invasive sampling and safety assessment of in-service structures. Summary of the Invention

[0005] In view of this, this application provides a method and apparatus for testing the mechanical properties of small punches for reactor structural materials. By optimizing the sample pretreatment process, simultaneously acquiring and deeply analyzing load-displacement data, and establishing a statistical analysis model for fracture energy absorption at multiple temperature points, the core mechanical parameters of reactor structural materials under small sample conditions can be accurately characterized, providing scientific and efficient technical support for the performance evaluation and safety early warning of in-service reactor structural materials.

[0006] According to one aspect of this application, a method for testing the mechanical properties of small punches for reactor structural materials is provided, comprising: Pre-treat the sample to a preset temperature; The load application module is activated to drive the punch rod to move towards the sample and apply pressure at a preset pressing rate. At the same time, the load data applied to the sample by the punch rod and the displacement data generated by the pressing of the punch rod are recorded in real time. A first relationship curve is formed based on the load data and the displacement data. The pressing continues until the load data drops below the preset load threshold, and the pressing action of the punch rod is stopped. Analyze the first relationship curve to obtain the yield strength and tensile strength of the reactor structural material corresponding to the sample; The steps of pre-treating the sample and starting the load application module to form a first relationship curve are performed on multiple samples at multiple different preset temperatures. The normalized fracture absorption energy corresponding to the first relationship curve of all samples at each preset temperature is calculated. A second relationship curve is formed with the preset temperature as the horizontal axis and the average normalized fracture absorption energy of all samples at each preset temperature as the vertical axis. The second relationship curve was analyzed to obtain the standard ductile-brittle transition temperature of the reactor structural material corresponding to the sample.

[0007] Optionally, the pretreatment of the sample to a preset temperature includes: Fix the sample; The fixed sample is heated or cooled to bring the sample temperature to the preset temperature, and then kept at the preset temperature for no less than 10 minutes.

[0008] Optionally, during the process of heating or cooling the fixed sample and holding it at a preset temperature, the punch is placed in the central region of the sample and kept in contact with the surface of the sample.

[0009] Optionally, the analysis of the first relationship curve to obtain the yield strength and tensile strength of the reactor structural material corresponding to the sample includes: Extract the curve segment whose displacement value is less than the sample thickness from the first relationship curve, and perform linear fitting on the initial elastic deformation segment and the transition segment close to yield in the curve segment to obtain two fitted straight lines; The load value corresponding to the intersection of the two fitted straight lines is determined as the yield load, and the maximum value of the load in the first relationship curve is determined as the tensile load. Based on the linear relationship between the preset standard tensile test results and the small punch test results, the yield load is converted into the yield strength of the reactor structural material corresponding to the specimen, and the tensile load is converted into the tensile strength of the reactor structural material corresponding to the specimen.

[0010] Optionally, the normalized fracture absorption energy of the sample conforms to the formula: ; In the formula, This represents the normalized fracture absorbed energy of the sample. The energy absorbed during the fracture of the sample. The maximum load in the first relationship curve corresponding to the sample; The fracture absorption energy of the sample conforms to the formula: ; In the formula, The energy absorbed during the fracture of the sample. Let be the functional expression of the first relationship curve. This refers to the displacement corresponding to the load decreasing to 80% of the maximum load in the first relationship curve. The first relationship curve and the displacement axis are related by the displacement from... arrive The area enclosed by the interval.

[0011] Optionally, the analysis of the second relationship curve to obtain the standard ductile-brittle transition temperature of the reactor structural material corresponding to the sample includes: The second relationship curve is fitted using the hyperbolic tangent function to obtain the fitted curve; Determine the minimum value of the low-temperature plateau region and the maximum value of the high-temperature plateau region of the normalized fracture absorbed energy in the fitted curve, and calculate the median value between the minimum value of the low-temperature plateau region and the maximum value of the high-temperature plateau region; The temperature point in the fitted curve where the normalized fracture absorbed energy equals the median value is determined as the ductile-brittle transition temperature of the small punch test of the material corresponding to the sample. Based on the linear relationship between the preset standard impact test results and the small punch test results, the ductile-brittle transition temperature of the small punch test is converted into the standard ductile-brittle transition temperature of the corresponding material of the sample.

[0012] Optionally, the method further includes: After the load drops below the preset threshold and the downward pressure on the punch stops, the punch continues to move downward by 2mm to 3mm.

[0013] According to another aspect of this application, a small punch mechanical property testing device for reactor structural materials is provided, comprising: A hot and cold environment stage is provided, the stage surface of which is provided with a bearing area for bearing the sample. The hot and cold environment stage includes a cooling unit, a heating unit and a temperature control unit. The cooling unit delivers a low-temperature medium to the bearing area through a booster pump to achieve low-temperature environment control. The heating unit adjusts the output power through a heating element to achieve high-temperature environment control. The temperature control unit monitors the temperature of the bearing area in real time through a temperature sensor and adjusts the cooling unit and the heating unit according to the monitoring results to make the sample temperature reach and maintain at a preset temperature. A loading fixture includes a lower mold, a gasket, and a clamping module. The lower mold is fixed to the bearing area of ​​the hot and cold environment stage. The top of the lower mold has a concentrically arranged gasket groove and a sample groove. The bottom of the sample groove has a first through hole with rounded edges. The size of the gasket groove is adapted to the gasket. The gasket has a double-ear structure and a second through hole in the middle. The second through hole is concentric with the sample groove and is used for a punch to pass through and align with the center of the sample. The clamping module has a frame structure and a third through hole in the middle. The third through hole is concentric with the second through hole. The clamping module is connected to the lower mold and is used to clamp and fix the gasket and the sample sequentially. The load application module includes a punch and a drive unit. The drive unit is used to drive the punch to pass through the third through hole and the second through hole in sequence at a preset pressing rate and then press down on the sample. The drive unit also collects the load data applied by the punch and the displacement data generated by the pressing down of the punch in real time.

[0014] Optionally, the diameter of the third through hole of the clamping module is the same as the diameter of the second through hole of the gasket; the diameter of the first through hole of the lower mold is larger than the diameter of the second through hole.

[0015] Optionally, the punch has a hemispherical indenter near the pressure application end of the sample.

[0016] By utilizing the above technical solutions, the small-pump mechanical property testing method and apparatus for reactor structural materials provided in this application, in terms of test adaptability, relies on a hot and cold environment stage and a dedicated loading fixture to accurately achieve temperature control and stable clamping of small-volume samples, adapting to the characteristic of low induced radioactivity in irradiated samples, and solving the industry problem of high radioactivity and difficulty in testing large-size samples after irradiation; in terms of test data reliability, by applying a load at a constant preset pressing rate, simultaneously collecting load-displacement data to form a first relationship curve, and combining the stopping criterion of the load dropping to 50% of the maximum load and the sampling optimization of pressing down 2mm~3mm after stopping, the entire mechanical response of the sample from elastic deformation to fracture failure is completely and accurately captured. Then, the yield load is obtained through double linear fitting, and the maximum load is extracted as the tensile load. By combining material-specific linear relationships, yield strength and tensile strength are calculated with high data accuracy and strong logic. From the perspective of the completeness of performance evaluation, through multi-temperature point and multi-sample testing, normalized fracture absorption energy is calculated and a second relationship curve is formed. Then, the ductile-brittle transition temperature of the small punch test is determined by fitting a hyperbolic tangent function, and finally converted into the standard ductile-brittle transition temperature, realizing a comprehensive evaluation of the material's strength and ductile-brittle properties. From the perspective of engineering practicality, the entire method has a compact operation process and a high degree of modularity. In radioactive environments, it can shorten operation time and reduce personnel radiation dose. Moreover, the parts are easy to process and have low cost, which can be widely used in post-irradiation inspection technology in the nuclear energy field. It provides key data support for the structural integrity evaluation and remaining service life prediction of reactor pressure vessels, and combines efficiency, safety and economy.

[0017] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 A flowchart illustrating a method for testing the mechanical properties of a small punch rod for reactor structural materials, provided in an embodiment of this application, is shown. Figure 2 This paper illustrates a first relationship curve diagram provided by an embodiment of this application. Detailed Implementation

[0019] The present application will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present application can be combined with each other.

[0020] This embodiment provides a method for testing the mechanical properties of small punches used in reactor structural materials. See [link to relevant documentation]. Figure 1 As shown, the method includes: Step S101: Pre-treat the sample to a preset temperature.

[0021] The method for testing the mechanical properties of small punches for reactor structural materials provided in this application can be applied to fields such as nuclear energy, and specifically to post-irradiation testing technology. When conducting small punch sample tests on post-irradiated reactor structural materials, the samples are first pretreated to a preset temperature. Here, the sample refers to a test specimen obtained from the post-irradiated reactor structural material that meets the specific specifications for small punch testing.

[0022] Among them, the sample can be pretreated to a preset temperature using a small punch test device consisting of a hot and cold environment stage and a loading fixture.

[0023] Specifically, the loading fixture includes a clamping module, gaskets, and a lower mold for fixing the sample. The hot and cold environment stage includes a heating system, a cooling system, and a temperature measurement system for heating or cooling the fixed sample to achieve a preset temperature. In practical applications, the sample can be placed in the sample slot of the lower mold and clamped by the clamping module and gaskets to prevent displacement during temperature adjustment. Then, based on the preset temperature required for the test, if heating is needed, the heating wire of the heating system heats the bearing area of ​​the sample in the hot and cold environment stage. Thermocouples measure the temperature and provide feedback control to ensure the bearing area temperature matches the preset temperature. If cooling is needed, the booster pump of the cooling system compresses liquid nitrogen from the liquid nitrogen tube into the bearing area, controlling the liquid nitrogen flow rate and heating wire power to achieve the preset temperature.

[0024] Here, the specimen must be held at the preset temperature for at least 10 minutes. This ensures, on the one hand, that the specimen is fully heated or cooled, completely eliminating any potential temperature gradients within the specimen and preventing uneven deformation due to localized temperature differences, which could affect the accuracy of the mechanical response during subsequent load application. On the other hand, holding the specimen for 10 minutes or more allows its overall temperature to be stably maintained at the preset temperature, creating a uniform and constant temperature environment. This provides a stable temperature basis for applying loads at a constant rate, accurately recording load-displacement curves, and accurately obtaining mechanical parameters such as yield load, tensile load, and fracture energy absorption. It effectively avoids deviations in test data caused by temperature fluctuations or unevenness, ensuring the reliability of the final mechanical performance analysis results.

[0025] Furthermore, throughout the pretreatment process, the punch is placed in the central region of the specimen and kept in contact with the specimen surface. On the one hand, the contact between the punch and the specimen forms a physical shield, reducing heat exchange between the specimen and the external environment during heating or cooling. This prevents the specimen temperature from deviating from the preset value due to heat loss or additional heat absorption, and helps the hot and cold environment stage better maintain the specimen temperature stability, ensuring temperature control accuracy. On the other hand, positioning the punch in the central region of the specimen allows for the early determination of the application point of subsequent loads, ensuring that the direction of the force applied is aligned with the specimen center when the load is applied. This avoids uneven stress on the specimen due to load eccentricity, thereby preventing distortion of the subsequently recorded load-displacement curve and laying the foundation for accurately obtaining mechanical parameters such as yield load and tensile load.

[0026] Step S201: Start the load application module, drive the punch to move towards the sample and apply pressure at a preset pressing rate, and simultaneously record the load data applied to the sample by the punch and the displacement data generated by the pressing of the punch in real time. Based on the load data and displacement data, form a first relationship curve, and continue to press down until the load data drops below the preset load threshold, and stop the pressing action of the punch.

[0027] In this embodiment, after the sample has completed pretreatment and reached a preset temperature and stabilized, the load application module is activated. The load application module drives the punch rod to move towards the sample and apply pressure at a preset pressing rate of 0.2 mm / min to 2 mm / min. Here, the preset pressing rate is preferably 0.5 mm / min.

[0028] During the load application phase, the punch passes through the punch action hole pre-drilled between the clamping module and the shim in the loading fixture, precisely acting on the specimen pre-fixed in the specimen slot of the lower mold of the loading fixture. Simultaneously, the clearance through-hole in the lower mold provides necessary space for the punch to continuously press down, effectively preventing mechanical interference between the punch and the lower mold and ensuring the smoothness of the load application process. During this process, the load data applied to the specimen by the punch and the displacement data generated during the punch's downward pressing can be collected and recorded in real time using the data acquisition module of the test system or the data acquisition function integrated into the load application module. After acquisition, the two sets of data are correlated one-to-one along the time dimension. After data processing, a first relationship curve is generated with load as the vertical axis and displacement as the horizontal axis. This first relationship curve is the load-displacement curve used for subsequent mechanical property analysis in this test, which can fully reflect the mechanical response characteristics of the specimen from deformation under stress to gradual failure.

[0029] Specifically, during the load application and data acquisition process, the data acquisition module supporting the test system, or the data acquisition function integrated in the load application module itself, will monitor the current load data in real time. When it is detected that the current load data drops to a certain specific value, the system will control the punch rod to stop pressing down. This specific value is the load threshold preset for the test, and its specific definition is 50% of the maximum load presented in the first relationship curve. Taking the load dropping to 50% of the maximum load as the criterion for the punch rod to stop, on the one hand, it can ensure that the specimen has completely experienced the full-stage mechanical response from elastic deformation, plastic deformation to fracture failure, avoiding missing test data due to premature stop and being unable to fully reflect the mechanical properties of the specimen; on the other hand, it can prevent damage to device components such as loading fixtures and punch rods caused by excessive pressing down of the punch rod, or the generation of meaningless redundant data, ensuring the safety of the test device and the validity of the data. Finally, through this criterion, the mechanical behavior of the specimen throughout the process can be accurately captured, providing complete and reliable load-displacement curve data support for subsequent analysis of key mechanical parameters such as yield strength and fracture energy absorption.

[0030] Further, after the load drops below the preset threshold and the punch rod stops pressing down, the punch rod is continuously driven to move downward by 2 mm to 3 mm. Thus, it can ensure that the fractured specimen is completely separated from the specimen groove of the lower die, avoiding the specimen being stuck in the specimen groove due to residual deformation stress or minor adhesion after fracture, solving the problem of difficult removal of small-sized specimens after fracture, and improving the operational convenience of specimen recovery or subsequent observation after the test.

[0031] Step S301: Analyze the first relationship curve to obtain the yield strength and tensile strength of the reactor structural material corresponding to the specimen.

[0032] In this embodiment, data analysis is performed on the first relationship curve formed in step S201. First, the curve segment with a displacement less than the specimen thickness is extracted, and two straight lines are fitted on this curve segment. One straight line corresponds to the load-displacement relationship in the elastic deformation stage of the specimen, and the other straight line corresponds to the change trend of the load-displacement relationship after the specimen starts to undergo plastic deformation. The force value on the load-displacement curve corresponding to the ordinate of the intersection of the two straight lines is the yield load of the specimen. At the same time, in the entire first relationship curve, the maximum value of the load data is found, and this maximum value is the tensile load of the specimen. Subsequently, using the linear relationship established in advance through experiments between the corresponding standard tensile test results and the small punch test results, the obtained yield load and tensile load are respectively substituted into this linear relationship, and the yield strength and tensile strength of the reactor structural material corresponding to the specimen are estimated through mathematical calculations.

[0033] Among them, referring to Figure 2 shown in Figure 2 is the graph of the first relationship curve. From Figure 2As can be seen, the curve exhibits a relatively stable slope in its initial stage, corresponding to the elastic deformation stage of the specimen (e.g., the region from the origin to near point A). During this stage, the load and displacement have an approximately linear relationship, consistent with the characteristics of elastic deformation. A straight line can be fitted to this portion to represent the load-displacement relationship during the elastic deformation stage. As the displacement increases, the curve slope changes, entering the plastic deformation stage (the region after point A). Another straight line is fitted to the curve segment after the onset of plastic deformation to reflect the changing trend of the load-displacement relationship after plastic deformation. The force value corresponding to the intersection of the two fitted straight lines is the yield load of the specimen (which can be represented by...). Figure 2 (The force value at the ordinate of point A). Although not shown in the entire first relationship curve, the load data has a maximum value, which is the tensile load of the specimen. Then, based on the linear relationship between the standard tensile test results and the small punch test results established through prior experiments, the obtained yield load and tensile load are substituted into this linear relationship, and the yield strength and tensile strength of the reactor structural material corresponding to the specimen can be estimated through calculation. It is understandable that the linear relationship between the standard tensile test results and the small punch test results differs for different materials. In this embodiment, given the specimen material, the linear relationship between the standard tensile test results and the small punch test results corresponding to the test material can be determined by querying a database established through numerous matching tests on that material.

[0034] Here, the aforementioned analytical method first identifies the inflection point from elastic deformation to plastic deformation by linearly fitting the portion of the first relationship curve where the displacement is less than the specimen thickness, thereby obtaining the yield load. Then, the maximum load is directly extracted from the entire first relationship curve as the tensile load. This process follows the deformation laws of material mechanics, providing reliable basic load data for subsequent strength conversion. Subsequently, using the linear relationship established beforehand between standard tensile test and small punch test results for the test material, the obtained yield load and tensile load are substituted into the conversion, successfully transforming the load parameters obtained from the small punch test into commonly used yield strength and tensile strength indices in engineering. This method utilizes small-volume specimens, solving the problem of difficulty in testing large-size specimens after irradiation due to high radioactivity. Furthermore, the conversion process is simple and efficient, and the obtained yield strength and tensile strength data are accurate and reliable, meeting the practical needs of the engineering field for evaluating the strength performance of reactor structural materials.

[0035] Step S401: Perform pretreatment on multiple samples at multiple different preset temperatures, start the load application module to form a first relationship curve, calculate the normalized fracture absorption energy corresponding to the first relationship curve of all samples at each preset temperature, and form a second relationship curve with the preset temperature as the horizontal axis and the average normalized fracture absorption energy of all samples at each preset temperature as the vertical axis.

[0036] In this embodiment, several different preset temperatures are first determined. For reactor structural materials such as low-alloy ferritic steel, a preset temperature point can be set every 10°C, starting from -196°C. At each preset temperature point, three samples of the same specifications are selected, and the pretreatment operation in step S101 and the load application operation in step S201 are performed on each sample. Then, for the first relationship curve of each sample, its fracture absorption energy is calculated by integrating the curve segment before the load drops to 80% of the maximum load; then, the fracture absorption energy is divided by the maximum load in the first relationship curve of that sample to obtain the normalized fracture absorption energy of each sample. For each preset temperature point, the average value of the normalized fracture absorption energy of the three samples at that temperature is calculated. Finally, a second relationship curve is plotted with the preset temperature as the horizontal axis and the average value of the normalized fracture absorption energy corresponding to each temperature point as the vertical axis. Here, the second relationship curve refers to the normalized fracture absorption energy-test temperature curve.

[0037] The normalized fracture absorption energy of the sample conforms to the formula: ; In the formula, The normalized fracture energy absorbed by the sample. The energy absorbed during the fracture of the sample. The maximum load in the first relationship curve corresponding to the specimen; The fracture absorption energy of the sample conforms to the formula: ; In the formula, The energy absorbed during the fracture of the sample. Let be the functional expression of the first relationship curve. This represents the displacement corresponding to the load decreasing to 80% of the maximum load in the first relationship curve. The first relationship curve and the displacement axis are as follows: displacement from arrive The area enclosed by the interval.

[0038] Here, multiple samples are tested at various preset temperatures. By averaging the results from multiple trials, potential random errors in individual sample testing are effectively reduced, improving the reliability and representativeness of the normalized fracture absorption energy data at each temperature point. This ensures that the resulting second relationship curve accurately reflects the material's fracture performance changes at different temperatures. In practical applications, for low-alloy ferritic steels, temperature points are set every 10°C starting from -196°C. This temperature range covers the material's likely temperature range from low to room temperature, comprehensively capturing the fracture absorption energy changes under different temperature conditions. This provides comprehensive data support for subsequent analysis of the ductile-brittle transition temperature. The resulting second relationship curve visually presents the correlation between temperature and normalized fracture absorption energy, laying a clear data foundation for further obtaining the ductile-brittle transition temperature. Furthermore, the entire process is standardized and the data processing logic is rigorous, ensuring the accuracy and usability of the curve.

[0039] Step S501: Analyze the second relationship curve to obtain the standard ductile-brittle transition temperature of the reactor structural material corresponding to the sample.

[0040] In this embodiment, when performing mathematical analysis on the second relationship curve formed in step S401, a hyperbolic tangent function is used to fit the curve. By adjusting the function parameters, the fitted curve is made to coincide as closely as possible with the actual data points of the second relationship curve. After fitting, the minimum value of the low-temperature plateau region and the maximum value of the normalized fracture absorption energy in the fitted curve are determined. The median value of these two values ​​is calculated, and the temperature point corresponding to the normalized fracture absorption energy in the fitted curve equal to this median value is defined as the ductile-brittle transition temperature of the material corresponding to the sample in the small impact test. Subsequently, using the linear relationship between the standard impact test results and the small impact test results established in advance through experiments, the obtained ductile-brittle transition temperature of the small impact test is substituted into this relationship, and the standard ductile-brittle transition temperature of the reactor structural material corresponding to the sample is estimated through mathematical conversion. This standard ductile-brittle transition temperature is equivalent to the ductile-brittle transition temperature obtained by conventional standard impact tests and can be effectively used to evaluate the ductile-brittle characteristics and fracture resistance of materials at different temperatures.

[0041] Here, the hyperbolic tangent function is used to fit the second relationship curve. This function can better describe the nonlinear law of normalized fracture absorption energy changing with temperature during the transition from ductile to brittle state of the reactor structural material corresponding to the sample. Compared with other fitting methods, it can more accurately capture the transition trend and characteristic points of the curve, thereby accurately determining the ductile-brittle transition temperature of the small impact test, and providing accurate intermediate parameters for the subsequent conversion of the standard ductile-brittle transition temperature. By using the linear relationship between the standard impact test and the small impact test results, the results obtained from the small impact test are successfully converted into the engineering-acceptable standard ductile-brittle transition temperature. This achieves the goal of obtaining key ductile-brittle transition performance indicators of reactor structural materials through small-volume irradiated samples, and solves the problem that it is difficult to obtain the ductile-brittle transition temperature of irradiated materials through conventional standard impact tests. This standard ductile-brittle transition temperature can be directly used to evaluate the safety and reliability of reactor structural materials at different service temperatures, providing important key performance data for the structural integrity evaluation and remaining service life prediction of reactor pressure vessels, and has significant engineering practical value.

[0042] By applying the technical solution of this embodiment, from the perspective of test adaptability, relying on the hot and cold environment stage and the special loading fixture, the temperature control and stable clamping of small-volume samples can be accurately achieved, adapting to the characteristic of low induced radioactivity of irradiated samples, and solving the industry problem of high radioactivity and difficulty in testing large-size samples after irradiation. From the perspective of test data reliability, by applying load at a constant preset pressing rate, load-displacement data are collected simultaneously to form the first relationship curve. Combined with the stopping criterion of the load dropping to 50% of the maximum load and the sampling optimization of pressing down 2mm~3mm after stopping, the mechanical response of the sample from elastic deformation to fracture failure is completely and accurately captured. Then, the yield load is obtained by double linear fitting, the maximum load is extracted as the tensile load, and the material-specific linear relationship is combined to obtain the yield load. The method calculates yield strength and tensile strength with high data accuracy and strong logic. From the perspective of comprehensive performance evaluation, it calculates normalized fracture absorption energy and forms a second relationship curve through multi-temperature point and multi-sample testing. Then, it determines the ductile-brittle transition temperature of the small punch test by fitting a hyperbolic tangent function, and finally converts it to the standard ductile-brittle transition temperature, achieving a comprehensive evaluation of material strength and ductile-brittle properties. From an engineering practicality perspective, the entire method has a compact operation process and a high degree of modularity. In radioactive environments, it can shorten operation time and reduce personnel radiation dose. Furthermore, the components are easy to process and have low cost, making it widely applicable to post-irradiation inspection technology in the nuclear energy field. It provides key data support for the structural integrity evaluation and remaining service life prediction of reactor pressure vessels, combining efficiency, safety, and economy.

[0043] Furthermore, as Figure 1 In a specific implementation of the method, this application provides a small punch mechanical property testing device for reactor structural materials, the device comprising: The hot and cold environment stage has a support area on its platform for supporting the sample. The hot and cold environment stage includes a cooling unit, a heating unit, and a temperature control unit. The cooling unit delivers a low-temperature medium to the support area through a booster pump to achieve low-temperature environment control. The heating unit adjusts the output power through heating elements to achieve high-temperature environment control. The temperature control unit monitors the temperature of the support area in real time through a temperature sensor and adjusts the cooling unit and heating unit based on the monitoring results to ensure that the sample temperature reaches and is maintained at the preset temperature. The loading fixture includes a lower mold, a gasket, and a clamping module. The lower mold is fixed to the bearing area of ​​the hot and cold environment stage. The top of the lower mold has a concentrically arranged gasket groove and a sample groove. The bottom of the sample groove has a first through hole with rounded edges. The size of the gasket groove is adapted to the gasket. The gasket has a double-ear structure and a second through hole in the middle. The second through hole is concentric with the sample groove and is used for the punch to pass through and align with the center of the sample. The clamping module has a frame structure and a third through hole in the middle. The third through hole is concentric with the second through hole. The clamping module is connected to the lower mold and is used to clamp and fix the gasket and the sample in sequence. The load application module includes a punch and a drive unit. The drive unit is used to drive the punch to pass through the third through hole and the second through hole in sequence at a preset pressing rate and press down on the sample. It also collects the load data applied by the punch and the displacement data generated by the pressing down of the punch in real time.

[0044] The reactor structural material small punch mechanical property testing device provided in this application embodiment, in terms of temperature control accuracy, the hot and cold environment stage, through the linkage of the cooling unit, heating unit and temperature control unit, can accurately regulate the temperature of the bearing area, ensuring that the sample is stably maintained at the preset temperature, meeting the requirements of different test temperatures, and providing a uniform and constant temperature environment for subsequent mechanical property testing; in terms of sample fixation and precise load application, the loading fixture, through the concentric design of the sample groove, gasket groove and double-ear structure gasket and frame-shaped clamping module of the lower mold, can achieve stable sample clamping, while ensuring that the punch is accurately aligned with the center of the sample, avoiding load eccentricity, and the rounded corner design of the edge of the first through hole at the bottom of the sample groove can reduce stress concentration, and the connection structure between the lower mold and the clamping module further improves the clamping stability; in terms of data acquisition reliability, the driving unit of the load application module can drive the punch to apply the load at a preset pressing rate and simultaneously collect load and displacement data, providing real-time and accurate raw data for generating the first relationship curve and subsequent analysis of mechanical parameters. The overall device has a compact structure and high functional integration, which is suitable for the testing needs of small-volume irradiated samples. It not only solves the safety and convenience problems of irradiated sample testing, but also ensures the reliability of test data through the precise cooperation of each module, providing stable and efficient hardware support for the evaluation of the mechanical properties of reactor structural materials.

[0045] The cooling unit, which uses a booster pump to deliver cryogenic media such as liquid nitrogen, is used to regulate the low-temperature environment of the bearing area. The heating unit, which adjusts the output power of the heating wire, is used to regulate the high-temperature environment of the bearing area. The temperature control unit, which uses thermocouples to measure the temperature of the bearing area in real time, controls the cooling and heating units based on the temperature measurement results to ensure that the sample temperature is stable at the preset value. The first through hole at the bottom of the sample groove on the lower mold, which is the clearance through hole reserved in the middle of the lower mold mentioned earlier, provides space for the punch to press down. The second through hole in the middle of the gasket and the third through hole in the middle of the clamping module together constitute the punch action hole in the loading fixture mentioned earlier, which allows the punch to pass through and ensures that the punch acts accurately on the sample. The drive unit in the load application module can be a servo motor drive system, a stepper motor drive system, or a hydraulic drive system to achieve stable pressing of the punch at a preset pressing rate.

[0046] Specifically, in step S101, the compliant sample is placed in the sample slot of the lower mold of the loading fixture. The sample is connected to the lower mold via a frame-shaped clamping module, and the double-eared gasket and sample are sequentially clamped and fixed to ensure the sample is stable and concentric with the second through hole of the gasket and the third through hole of the clamping module. Subsequently, the hot and cold environment stage is activated, and its temperature control unit monitors the temperature of the bearing area in real time via thermocouples. If low-temperature control is required, the booster pump is controlled to deliver the low-temperature medium to the bearing area; if high-temperature control is required, the output power of the heating wire is adjusted. Ultimately, the sample temperature reaches and is maintained at the preset temperature, while the punch remains in contact with the center of the sample during this process to assist in temperature control. In step S201, the load is applied. The module's drive unit drives the punch rod at a preset pressing rate of 0.5 mm / min, allowing it to pass through the third through hole of the clamping module and the second through hole of the gasket in sequence before precisely pressing down on the sample. Simultaneously, the load data applied by the punch rod and the displacement data generated by the pressing are collected in real time to form the first relationship curve. The pressing stops when the load drops to 50% of the maximum load. The punch rod can be driven to move down another 2 mm to 3 mm to facilitate sample removal. The curve analysis and performance conversion involved in steps S301, S401, and S501 are all based on the accurate temperature data and load-displacement data collected by the device, ultimately achieving efficient and accurate testing of the mechanical properties of reactor structural materials.

[0047] In some possible embodiments disclosed in this application, the diameter of the third through hole of the clamping module is the same as the diameter of the second through hole of the gasket; the diameter of the first through hole of the lower mold is larger than the diameter of the second through hole.

[0048] In this embodiment, on the one hand, the third through hole and the second through hole have the same diameter and always remain concentric, providing a regular and uniform through channel for the punch. This prevents the punch from shifting or getting stuck when passing through the two through holes due to the difference in diameter, ensuring that the punch is always precisely aligned with the center of the sample along the preset path. This further ensures the stability of the force direction when applying loads, preventing uneven force on the sample due to load eccentricity, and thus avoiding distortion of the first relationship curve. This lays the foundation for accurately obtaining data such as yield load and tensile load. On the other hand, the diameter of the first through hole in the lower die is larger than that of the second through hole. The dual-hole diameter provides ample clearance for the punch's downward pressing process, preventing mechanical interference between the punch and the lower die. It also accommodates the minor deformation or fragment drop that may occur after the sample breaks. Furthermore, it is compatible with the operation of the punch continuing to move down 2mm~3mm after the pressing stops to separate the sample, ensuring sufficient movement space for the punch in this step to smoothly separate the broken sample from the lower die. This improves the convenience of sample recovery after the test. Moreover, the overall hole diameter design is highly matched with the functions of each component of the device, further optimizing the smoothness and reliability of the test process.

[0049] Here, taking a punch radius of 0.5mm as an example: the diameter of the first through hole of the lower die can be designed to be 1.5mm, and the diameter of the second through hole of the gasket and the third through hole of the clamping module can both be designed to be 1mm.

[0050] Furthermore, in order to reduce mechanical interference during the punching process and avoid stress concentration damage to components or samples, a chamfer can be added to the edge of the upper port of the first through hole of the lower die to disperse the local stress of fragments after sample breakage or when the punch moves downward, prevent cracks from appearing at the edge of the first through hole of the lower die due to stress concentration, and at the same time avoid sharp edges from causing secondary damage to the separated samples, thereby improving the integrity of the sample recovery after the test.

[0051] In some possible embodiments disclosed in this application, a hemispherical indenter is provided near the pressure application end of the punch rod on the sample. Here, the hemispherical indenter is the punch of the punch rod.

[0052] In this embodiment, on the one hand, the hemispherical structure ensures that the contact between the punch and the specimen remains at a point, avoiding load dispersion due to excessive contact area. This ensures that the applied load is concentrated on the central region of the specimen, further reducing the risk of load eccentricity and guaranteeing that the load data in the first relationship curve accurately reflects the stress state of the specimen. On the other hand, compared to sharp or flat indenters, the curved surface structure of the hemispherical indenter disperses local stress at the contact point, preventing premature damage to the specimen surface due to stress concentration at the moment of contact between the indenter and the specimen. This avoids interfering with the normal mechanical response process of the specimen from elastic deformation to plastic deformation, ensuring that the test can fully capture the true fracture failure characteristics of the specimen. At the same time, the rounded structure of the hemispherical indenter reduces the frictional resistance between the punch and the second through hole of the pad and the third through hole of the clamping module when the punch is pressed down, reducing wear on the edges of the indenter or through holes, extending the service life of the device components, ensuring the smoothness of the punch movement process, and further improving the stability of the test operation and the accuracy of the data.

[0053] It will be readily understood by those skilled in the art that the aforementioned advantageous methods can be freely combined and superimposed without conflict.

[0054] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the protection scope of this application.

Claims

1. A method for testing the mechanical properties of a small punch rod for reactor structural materials, characterized in that, include: Pre-treat the sample to a preset temperature; The load application module is activated to drive the punch rod to move towards the sample and apply pressure at a preset pressing rate. At the same time, the load data applied to the sample by the punch rod and the displacement data generated by the pressing of the punch rod are recorded in real time. A first relationship curve is formed based on the load data and the displacement data. The pressing continues until the load data drops below the preset load threshold, and the pressing action of the punch rod is stopped. Analyze the first relationship curve to obtain the yield strength and tensile strength of the reactor structural material corresponding to the sample; The steps of pre-treating the sample and starting the load application module to form a first relationship curve are performed on multiple samples at multiple different preset temperatures. The normalized fracture absorption energy corresponding to the first relationship curve of all samples at each preset temperature is calculated. A second relationship curve is formed with the preset temperature as the horizontal axis and the average normalized fracture absorption energy of all samples at each preset temperature as the vertical axis. The second relationship curve was analyzed to obtain the standard ductile-brittle transition temperature of the reactor structural material corresponding to the sample.

2. The method according to claim 1, characterized in that, The pretreatment of the sample to a preset temperature includes: Fix the sample; The fixed sample is heated or cooled to bring the sample temperature to the preset temperature, and then kept at the preset temperature for no less than 10 minutes.

3. The method according to claim 2, characterized in that, During the process of heating or cooling the fixed sample and holding it at a preset temperature, the punch is placed in the central area of ​​the sample and kept in contact with the surface of the sample.

4. The method according to claim 1, characterized in that, The analysis of the first relationship curve to obtain the yield strength and tensile strength of the reactor structural material corresponding to the sample includes: Extract the curve segment whose displacement value is less than the sample thickness from the first relationship curve, and perform linear fitting on the initial elastic deformation segment and the transition segment close to yield in the curve segment to obtain two fitted straight lines; The load value corresponding to the intersection of the two fitted straight lines is determined as the yield load, and the maximum value of the load in the first relationship curve is determined as the tensile load. Based on the linear relationship between the preset standard tensile test results and the small punch test results, the yield load is converted into the yield strength of the reactor structural material corresponding to the specimen, and the tensile load is converted into the tensile strength of the reactor structural material corresponding to the specimen.

5. The method according to claim 1, characterized in that, The normalized fracture absorption energy of the sample conforms to the formula: ； In the formula, This represents the normalized fracture absorbed energy of the sample. The energy absorbed during the fracture of the sample. The maximum load in the first relationship curve corresponding to the sample; The fracture absorption energy of the sample conforms to the formula: ； In the formula, The energy absorbed during the fracture of the sample. Let be the functional expression of the first relationship curve. This refers to the displacement corresponding to the load decreasing to 80% of the maximum load in the first relationship curve. The first relationship curve and the displacement axis are related by the displacement from... arrive The area enclosed by the interval.

6. The method according to claim 1, characterized in that, The analysis of the second relationship curve to obtain the standard ductile-brittle transition temperature of the reactor structural material corresponding to the sample includes: The second relationship curve is fitted using the hyperbolic tangent function to obtain the fitted curve; Determine the minimum value of the low-temperature plateau region and the maximum value of the high-temperature plateau region of the normalized fracture absorbed energy in the fitted curve, and calculate the median value between the minimum value of the low-temperature plateau region and the maximum value of the high-temperature plateau region; The temperature point in the fitted curve where the normalized fracture absorbed energy equals the median value is determined as the ductile-brittle transition temperature of the small punch test of the material corresponding to the sample. Based on the linear relationship between the preset standard impact test results and the small punch test results, the ductile-brittle transition temperature of the small punch test is converted into the standard ductile-brittle transition temperature of the corresponding material of the sample.

7. The method according to claim 1, characterized in that, Also includes: After the load drops below the preset threshold and the downward pressure on the punch stops, the punch continues to move downward by 2mm to 3mm.

8. A device for testing the mechanical properties of a small punch rod for reactor structural materials, characterized in that, include: A hot and cold environment stage is provided, the stage surface of which is provided with a bearing area for bearing the sample. The hot and cold environment stage includes a cooling unit, a heating unit and a temperature control unit. The cooling unit delivers a low-temperature medium to the bearing area through a booster pump to achieve low-temperature environment control. The heating unit adjusts the output power through a heating element to achieve high-temperature environment control. The temperature control unit monitors the temperature of the bearing area in real time through a temperature sensor and adjusts the cooling unit and the heating unit according to the monitoring results to make the sample temperature reach and maintain at a preset temperature. A loading fixture includes a lower mold, a gasket, and a clamping module. The lower mold is fixed to the bearing area of ​​the hot and cold environment stage. The top of the lower mold has a concentrically arranged gasket groove and a sample groove. The bottom of the sample groove has a first through hole with rounded edges. The size of the gasket groove is adapted to the gasket. The gasket has a double-ear structure and a second through hole in the middle. The second through hole is concentric with the sample groove and is used for a punch to pass through and align with the center of the sample. The clamping module has a frame structure and a third through hole in the middle. The third through hole is concentric with the second through hole. The clamping module is connected to the lower mold and is used to clamp and fix the gasket and the sample sequentially. The load application module includes a punch and a drive unit. The drive unit is used to drive the punch to pass through the third through hole and the second through hole in sequence at a preset pressing rate and then press down on the sample. The drive unit also collects the load data applied by the punch and the displacement data generated by the pressing down of the punch in real time.

9. The apparatus according to claim 8, characterized in that, The diameter of the third through hole of the clamping module is the same as the diameter of the second through hole of the gasket; the diameter of the first through hole of the lower mold is larger than the diameter of the second through hole.

10. The apparatus according to claim 8, characterized in that, The punch has a hemispherical indenter at the pressure application end near the sample.

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