Lattice spring fluctuating load stress corrosion test device and method

Abstract

The present application discloses a lattice spring fluctuating load stress corrosion test device and method, comprising: an autoclave; an environment control system; a loading system, comprising a loading tester and a loading pair, the loading pair is used for applying constant deformation and fluctuating load to the lattice spring; the loading tester moves in the autoclave until contacting with the lattice spring by controlling the loading pair; a contact point measurement system, comprising a constant voltage source and a first signal acquisition device, the constant voltage source applies constant voltage to the lattice spring and the loading pair, the first signal acquisition device monitors current mutation to determine the loading starting point; an integrity measurement system, a constant current source provides stable direct current, a current reversing device switches the current direction at a preset frequency, and a second signal acquisition device monitors the electrical signal change of both ends of the lattice spring in real time to determine the integrity state of the lattice spring. The present application realizes accurate identification of the loading starting point of the lattice spring under high pressure environment and real-time monitoring of the integrity state.

Description

Technical Field

[0001] This invention belongs to the field of service performance evaluation of key nuclear power component materials, and particularly relates to a test device and manufacturing method for stress corrosion testing of grid springs under fluctuating loads. Background Technology

[0002] As a core functional component of nuclear fuel assemblies, the grid spring, in synergy with the rigid protrusions of the strips, achieves precise clamping and positioning of the fuel rods. Its structural integrity is directly related to the safe operation of the nuclear reactor. In actual service, this component not only bears the constant deformation constraints after assembly, but also needs to withstand dynamic loads such as core hydraulic excitation and flow-induced vibration. Under high temperature and high pressure water environment, it is prone to stress corrosion cracking (SCC) failure. Therefore, conducting research on its failure mechanism is of great engineering significance for ensuring nuclear power safety.

[0003] Grid springs are typically less than 1 mm thick and less than 5 mm wide, and have a special arc-shaped structure. Conventional standard test methods are mainly designed for large-size specimens, making it difficult to accurately apply small loads to grid springs. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the present invention provides a test device and method for stress corrosion testing of grid springs under fluctuating load, which can realize the accurate identification of the loading start point of grid springs and the real-time monitoring of their integrity status under high pressure.

[0005] This application provides a grid spring fluctuating load stress corrosion testing apparatus, including:

[0006] Autoclave, used to simulate the high-temperature and high-pressure water environment of the primary loop of a nuclear power plant, and to house the grid springs;

[0007] An environmental control system, connected to the autoclave, is used to regulate the environmental parameters of the autoclave.

[0008] The loading system includes a loading testing machine and a loading pair, wherein the loading pair is used to apply constant deformation and fluctuating load to the grid spring; the loading testing machine controls the loading pair to move within the autoclave until it contacts the grid spring;

[0009] The contact point measurement system includes a constant voltage source and a first signal acquisition device. The constant voltage source applies a constant voltage to the grid spring and the loading pair, and the first signal acquisition device monitors current changes to determine the loading start point.

[0010] The integrity measurement system includes a constant current source, a current commutation device, and a second signal acquisition device. The constant current source provides a stable DC current, the current commutation device switches the current direction at a preset frequency, and the second signal acquisition device monitors the changes in electrical signals at both ends of the grid spring in real time to determine the integrity state of the grid spring.

[0011] In some implementations, the loading system converts the local stress at a specific location of the lattice spring into spring deformation through finite element mechanical modeling, forming the loading parameters of the loading test machine, which are used to control the loading pair.

[0012] In some implementations, the loading parameters include the loading waveform, frequency, and stress ratio.

[0013] In some implementations, the grid spring is mounted with an electrically insulated structure, and the loading pair is isolated from the spring by a ceramic or polymer insulator.

[0014] In some embodiments, the frequency at which the current switching device switches the current direction is 0.1 to 10 Hz.

[0015] In some implementations, the first signal acquisition device is an ammeter and a first wire, the first wire being connected to the loading pair and one end of the grid spring, respectively;

[0016] The second signal acquisition device consists of a voltmeter, a second lead wire, and a multi-channel signal analyzer. The second lead wire is connected to both ends of the grid spring, and the lead wire outlet is located outside the autoclave. The multi-channel signal analyzer is connected to a processor for real-time recording and analysis of voltage signals.

[0017] Secondly, the present invention provides a method for testing stress corrosion under fluctuating loads on lattice springs, comprising:

[0018] Fix the grid spring inside the autoclave and close the autoclave;

[0019] The environmental control system injects the medium, regulates the environmental parameters to a preset range, and maintains the stability of the medium composition.

[0020] A controlled load is applied to the grid spring by a loading system, a constant voltage is applied between the grid spring and the loading pair by a constant voltage source and a threshold is determined, and the first signal acquisition device monitors the current value in real time.

[0021] The loading pair is controlled to move towards the grid spring until the loading pair contacts the grid spring and the current value exceeds the current threshold, which is determined as the loading start point;

[0022] A constant current is applied by a constant current source and the current reversing device switches the current direction at a preset frequency. The second signal acquisition device intermittently monitors the voltage value at both ends of the grid spring.

[0023] By comparing the real-time voltage value with the initial voltage value, the complete state of the grid spring is determined.

[0024] In some implementations, comparing the real-time voltage value with the initial voltage value to determine the complete state of the grid spring includes:

[0025] Record the initial voltage value and compare the real-time voltage value with the initial voltage value; the initial voltage value is the voltage signal when the small-sized metal sample is intact.

[0026] During the test, the loading system performs voltage measurements and continuously collects real-time voltage values, comparing them with the initial voltage value; and the loading system pauses loading each time a voltage value is measured.

[0027] When the real-time voltage value deviates from the average value and exceeds the standard deviation threshold, the integrity of the small-sized metal sample changes. Record the corresponding loading conditions and environmental parameters.

[0028] In some implementations, it also includes:

[0029] Based on the loading waveform, frequency, and environmental parameters corresponding to structural damage, a stress corrosion induction mechanism model is established.

[0030] In some embodiments, the current threshold is determined based on the conductivity of the liquid or gas medium inside the autoclave.

[0031] This application provides a testing apparatus and method for stress corrosion testing of lattice springs under fluctuating loads. It can apply constant deformation and fluctuating loads to lattice springs in a high-temperature, high-pressure water environment, and accurately identify the loading start point through a contact point measurement system, avoiding errors in initial judgment. Simultaneously, the integrity measurement system monitors the voltage changes across the lattice spring in real time through a constant current source and current reversing device, enabling timely judgment of its integrity status and providing a direct assessment of structural damage, thus improving the accuracy and reliability of the test. Attached Figure Description

[0032] Figure 1 A schematic diagram of the lattice spring wave load stress corrosion testing device provided by the present invention;

[0033] Figure 2 This is a schematic flowchart of the stress corrosion test method for fluctuating load on lattice springs provided by the present invention;

[0034] In the diagram: 1. High-pressure autoclave; 2. Loading test machine; 3. Loading pair; 4. Grid spring; 5. Constant pressure source; 6. Ammeter; 7. Displacement sensor; 8. Indication device; 9. Constant current source; 10. Current reversing device; 11. Multi-channel signal instrument; 12. Voltmeter. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specifically stated, the relative arrangement, expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the present invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the accompanying drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0036] This application provides a grid spring fluctuating load stress corrosion testing device, which can realize the accurate identification of the loading start point of the grid spring and the real-time monitoring of its integrity status under high pressure.

[0037] Specifically, such as Figure 1 The diagram shows a schematic of the structure of the fluctuating load stress corrosion testing device for the grid spring 4, used for mechanical loading and in-situ monitoring of the grid spring 4 component under the high-temperature and high-pressure water service environment of nuclear power plants. The device includes an autoclave 1, an environmental control system, a loading system, a contact point measurement system, and an integrity measurement system. The autoclave 1 simulates the high-temperature and high-pressure water environment of the primary loop of a nuclear power plant and houses the grid spring 4. The environmental control system is connected to the autoclave 1 and is used to regulate the environmental parameters of the autoclave 1. The loading system includes a loading testing machine 2 and a loading pair 3. The loading pair 3 applies constant deformation and fluctuating load to the grid spring 4. The loading testing machine 2 controls the movement of the loading pair 3 within the autoclave 1 until it contacts the grid spring 4. The contact point measurement system includes a constant voltage source 5 and a first signal acquisition device. The constant voltage source 5 applies a constant voltage to the grid spring 4 and the loading pair 3, and the first signal acquisition device monitors current changes to determine the loading start point. The integrity measurement system includes a constant current source 9, a current commutation device 10, and a second signal acquisition device. The constant current source 9 provides a stable DC current, the current commutation device switches the current direction at a preset frequency, and the second signal acquisition device monitors the changes in electrical signals at both ends of the grid spring 4 in real time to determine the integrity state of the grid spring 4.

[0038] In this application, the grid spring 4 is a slender elastic component used in nuclear power assemblies. It is typically made of high-performance alloy materials and features small size, high flexibility, and corrosion resistance. Generally, it is a strip-shaped or sheet-shaped elastic element that provides stable preload or buffering performance through its own elastic deformation. Because its working environment is usually high temperature, high pressure, and highly corrosive media, such as the primary loop water environment of a nuclear power plant, and the load level during loading is relatively low, the mechanical response signal of the grid spring 4 is easily masked by the frictional resistance of the loading system, making it difficult to accurately identify its loading initiation point using traditional force sensors. Simultaneously, due to the thin-walled structure of the grid spring 4, it is prone to microscopic damage such as local yielding, stress corrosion crack initiation and propagation under load, and its service life is significantly affected by stress corrosion coupling.

[0039] The autoclave 1 is made of an alloy material with excellent corrosion resistance, preferably stainless steel or nickel-based alloy. The material selection and structural design are based on the specific test medium and temperature and pressure requirements. The autoclave 1 has an overall cylindrical structure and is equipped with a disc-shaped lid. It is connected by bolts and uses sealing rings or metal gaskets to form a reliable sealing structure, which can achieve high-pressure environment sealing in liquid or gas media.

[0040] To withstand the harsh operating conditions of the high-temperature and high-pressure water environment in nuclear power plants, the pressure resistance of the autoclave 1 can be designed to range from 10MPa to 30MPa, and the temperature resistance range can reach 50℃ to 400℃, with corresponding expansions possible according to experimental requirements. The autoclave 1 is equipped with media inlet and outlet, pressure detection port, and temperature sensing port, enabling fluid circulation, pressure regulation, and temperature control through external environmental control systems, ensuring long-term stability of the composition and physical parameters of the medium inside the autoclave. Simultaneously, the autoclave structure has undergone finite element strength verification, capable of withstanding internal pressure loads under high-pressure fluid and ensuring no plastic deformation or sealing failure occurs under repeated cyclic loading, thus providing a stable and repeatable high-pressure testing environment for the controllable loading of the grid spring 4.

[0041] The environmental control system is connected to the autoclave 1 to construct a high-temperature, high-pressure corrosion environment simulating the actual service conditions of the grid spring 4. It is adaptable to various corrosion test requirements, including special operating conditions such as high-temperature, high-pressure water environments and superheated steam environments in nuclear power systems. The environmental control system can select an aqueous solution as the working medium according to the test requirements and precisely control the temperature, pressure, and chemical composition of the test environment to ensure test repeatability and environmental stability.

[0042] The environmental control system can adjust the solute concentration, dissolved gas content, pH value, and conductivity of the solution. During long-term loading tests, the environmental control system can dynamically adjust and monitor the composition and physical parameters of the medium in real time, thereby ensuring that the internal environment of the autoclave 1 is always maintained within the preset range, meeting the experimental requirements for in-situ controllable loading of the grid spring 4.

[0043] The loading start point refers to the instant when the loading pair 3 first contacts the sample and begins to apply stress or strain to it. Traditional methods use sudden changes in force as the basis for judgment, but the force signal of the grid spring 4 is overwhelmed by friction, making accurate judgment impossible.

[0044] The loading system includes a loading testing machine 2 located outside the autoclave 1 and a loading pair 3 located inside the autoclave 1. The loading testing machine 2 controls the movement of the loading pair 3 via a force transmission link. The loading testing machine 2 has multiple loading modes, including constant stress, constant strain, and fluctuating loading, which can meet the multi-condition loading requirements of the grid spring 4 under high temperature and high pressure environments. Generally, the loading pair 3 is a detachable structure used to directly contact the grid spring 4 and apply axial compressive stress. The loading pair 3 is coupled to the loading testing machine 2 via a force transmission link, accurately transmitting the force generated by the loading testing machine 2 to the designated position of the grid spring 4 during the loading process. The surface of the loading pair 3 is preferably made of a conductive and corrosion-resistant material, such as zirconium alloy, and its geometric profile is designed according to the structural dimensions of the grid spring 4 to ensure that the force application method is representative.

[0045] The force transmission link experiences a low force value during loading. However, because the loading test machine 2 can compensate for the influence of friction of the force transmission link through displacement closed-loop control, the force applied by the force transmission link to the grid spring 4 is small, which will not cause deformation of the force transmission link and will not affect the precise control of the loading test machine 2 on the force transmission link and loading pair 3. The overall loading process can maintain high precision and improve the accuracy of the loading start point judgment.

[0046] Before loading, the loading system uses finite element modeling to convert the target stress of key parts of the lattice spring 4 into the displacement of the loading pair 3. The loading testing machine 2 controls the position based on this displacement value, thereby improving the accuracy of stress control and ensuring that comparable loading stress fields are obtained on lattice spring 4 samples of different sizes and elastic moduli. Loading parameters include loading frequency, loading waveform, and stress ratio.

[0047] To avoid electrical signal interference, a ceramic or polymer insulating gasket is placed between the loading pair 3 and the grid spring 4, ensuring electrical isolation while achieving mechanical loading. During loading, the loading testing machine 2 controls the loading pair 3 to move slowly at a set speed, and simultaneously determines the loading start point in conjunction with the contact point measurement system. Once loading begins, the loading testing machine 2 continuously applies fluctuating or constant loads to the grid spring 4 according to a preset loading path, simulating the in-situ corrosion stress process of the spring.

[0048] To avoid electrical signal interference between the grid spring 4 and the loading pair 3, the grid spring 4 is installed with an electrically insulating structure, and the loading pair 3 is isolated from the spring by a ceramic or polymer insulator. In some embodiments, a clamp can be provided to fix the grid spring 4 in the clamp through an insulator. The clamp as a whole has sufficient mechanical strength and rigidity, and the deformation is negligible throughout the experiment, so it will not interfere with the mechanical response of the sample.

[0049] The contact point measurement system includes a constant voltage source 5 and a first signal acquisition device. The constant voltage source 5 is connected to the grid spring 4 and the loading pair 3, and is used to continuously apply a constant voltage during the loading process; the first signal acquisition device monitors the current signal in the loading circuit in real time.

[0050] A constant voltage source 5 is located outside the autoclave 1 and is electrically connected to the loading pair 3 and the grid spring 4 via wires, allowing a constant voltage to be continuously applied during loading. The output voltage range of the constant voltage source 5 is typically 0.01~1V, enabling electrical signal measurement without affecting the microscopic properties of the metal sample. The first signal acquisition device includes a first wire and an ammeter 6. The first wire is fixed to the grid spring 4 and the loading pair 3 by welding or crimping, with the connection position chosen to avoid interference from differences in the conductivity of the medium on the electrical signal detection.

[0051] Ammeter 6 is connected in series with the constant voltage source 5 to monitor the current change between the loading pair 3 and the metal sample in real time. The sampling frequency can reach over 1kHz, ensuring that transient current surges can be captured during the loading process. When the loading pair 3 has not yet made contact with the grid spring 4, the circuit is in an approximately open circuit state, and the current value is close to zero. As the loading pair 3 gradually approaches and makes initial contact with the grid spring 4, the circuit is closed, and the current surges. Ammeter 6 identifies this surge and compares it with a current threshold. Once the current surge exceeds the current threshold, it can be determined that the loading pair 3 has made contact with the grid spring 4, thus determining the loading start point. This determination process is independent of the load on the sample and can effectively overcome the problem of force signal distortion caused by the friction of the transmission linkage.

[0052] To facilitate the indication of the loading start point, the contact point measurement system can work in conjunction with a prompter. While determining the loading start point, the prompting device 8 provides audible and visual signals to the operator, ensuring the accuracy and repeatability of loading control. Simultaneously, the displacement sensor 7 records the displacement value of the loading attachment 3 at this time, providing an initial reference for the subsequent loading path.

[0053] The current threshold is set based on the conductivity characteristics of the medium inside the autoclave 1 and the grid spring 4 used in the actual application. For air or gas environments, due to the extremely low conductivity of the medium, the circuit is completely open before the loading pair 3 contacts the sample. Therefore, the current threshold can be set to 100 to 10,000 times the open-circuit current of the signal acquisition device to determine the starting point. For highly conductive media such as water-based solutions, there may be a small leakage current in the circuit when the loading pair 3 does not contact the grid spring 4. The contact current threshold can be set to 10 to 1,000 times the open-circuit current to ensure accurate judgment. For newly conducted experiments, it is advisable to combine simulation and pre-experimentation to determine the law of current signal variation with distance in order to clarify the optimal threshold range.

[0054] An electrical signal measurement system is used to monitor the integrity changes of the grid spring 4 in real time or intermittently during loading. It includes a constant current source 9, a current reversing device 10, and a second signal acquisition device. The constant current source 9 applies a constant current to the grid spring 4, the current reversing device 10 switches the direction of the constant current at a preset frequency, and the second signal acquisition device intermittently monitors the voltage value across the grid spring 4. The integrity changes of the grid spring 4 are determined based on the changes in the voltage value during loading.

[0055] The second signal acquisition device consists of a voltmeter 12, a second lead wire, and a multi-channel signal analyzer 11. The second lead wire is connected to both ends of the grid spring 4, with the lead-out end located outside the autoclave 1. The multi-channel signal analyzer 11 is connected to a processor for real-time recording and analysis of voltage signals. The second lead wire is connected to both ends of the grid spring 4. The multi-channel signal acquisition device is used to synchronously record voltage values, load displacement signals, and environmental parameters. A constant current source 9 provides a stable and constant DC current, which flows through the grid spring 4 via the lead wire. The voltmeter 12 is used to measure the voltage value and minute changes across the metal sample, and transmits the voltage value to the multi-channel signal acquisition device for recording and processing by the processor. The current reversing device 10 can switch the current direction at a frequency of 1Hz to eliminate the influence of contact resistance heating on the stability of the voltage signal, making the measurement results more accurate and reliable. In this application, the current reversing device 10, based on the influence of the connection between the lead wire and the grid spring 4, including factors such as material type and connection method, generally selects a frequency of approximately 0.1~10Hz in practical applications to prevent contact resistance heating from interfering with local voltage changes.

[0056] In this embodiment, the electrical signal measurement system first accurately determines the loading start point through the contact point measurement system. Since the grid spring 4 is a small-sized, low-stiffness metal component, the force it experiences during loading is extremely small, making it difficult to accurately identify the loading start point using traditional methods based on sudden force changes. Therefore, by applying a constant voltage between the loading pair 3 and the grid spring 4, and using the first signal acquisition device to monitor current changes, the loading start point can be accurately identified upon the first contact of the sample, avoiding misjudgments caused by frictional interference, thus providing a reliable reference for subsequent loading control.

[0057] After the loading start point is determined, the integrity monitoring stage begins. A stable current is provided by a constant current source 9, and the current direction is alternately switched by a current reversing device 10. A second signal acquisition device intermittently monitors the voltage changes across the grid spring 4, continuously comparing the real-time voltage with the initial value. When the voltage deviates beyond a threshold, it indicates a change in the sample's structural integrity. This method does not rely on mechanical fracture judgment and can monitor the material damage evolution process in real time under extreme environments such as high-pressure corrosion, improving the accuracy and reliability of corrosion fracture behavior research.

[0058] In practice, the following fluctuating load stress corrosion test method for grid springs is adopted:

[0059] Step S1: Fix the grid spring 4 inside the high-pressure reactor 1 and close the high-pressure reactor 1;

[0060] Step S2: Inject the medium through the environmental control system, adjust the environmental parameters to the preset range, and maintain the stability of the medium composition;

[0061] Step S3: Apply controlled loading to the grid spring 4 through the loading system, apply constant voltage through the constant voltage source 5 and determine the threshold, and monitor the current value in real time with the first signal acquisition device;

[0062] Step S4: Control the loading pair 3 to move towards the grid spring 4 until the loading pair 3 contacts the grid spring 4 and the current value exceeds the current threshold, which is determined as the loading start point;

[0063] Step S5: Apply a constant current through the constant current source 9 and the current switching device 10 switches the current direction at a preset frequency. The second signal acquisition device intermittently monitors the voltage value across the grid spring 4.

[0064] Step S6: Compare the real-time voltage value with the initial voltage value to determine the complete state of the grid spring 4.

[0065] In the fluctuating load stress corrosion test of the grid spring 4, the loading initiation point must be determined first, followed by integrity monitoring; the order of these two steps is irreversible. By applying a constant voltage during the early stages of loading using a contact point measurement system and monitoring current abrupt changes using signal acquisition equipment, the moment of initial contact between the loading pair 3 and the grid spring 4 can be accurately determined. This moment marks the starting point of the mechanical loading and also provides the baseline state required for integrity monitoring, used to record the initial voltage value. If the loading initiation point is not detected first, the initial voltage value may be collected before loading or during an unstable loading phase, failing to reflect the integrity of the sample and thus affecting the voltage comparison results, leading to inaccurate fracture determination. Therefore, the loading initiation point must be detected before integrity monitoring to ensure that changes in the electrical signal reflect the true physical process, improving the accuracy and repeatability of the test data.

[0066] To ensure the sensitivity of electrical signal detection, the grid spring 4 is electrically insulated and installed inside the autoclave 1, ensuring that current only flows through the grid spring 4 to form a circuit and does not flow through the autoclave 1 or the metal components of the loading system. A controlled load is applied to the grid spring 4 through the loading system, and the second signal acquisition device pauses loading during each voltage measurement to avoid introducing noise that could interfere with the electrical signal acquisition during the test. During the test, stress is applied through the loading system and voltage values ​​are acquired.

[0067] After determining the loading start point, the initial voltage value of the grid spring 4 in its intact state is first recorded, and the distribution characteristics of the initial voltage value, including the mean and standard deviation, are statistically analyzed. The initial voltage value is the voltage signal of the grid spring 4 when it is intact. During the loading test, the second signal acquisition device intermittently measures the voltage values ​​across the sample and compares them with the initial voltage value distribution characteristics. When the voltage value deviates significantly from the initial value over a continuous period, the integrity of the sample is considered to have changed.

[0068] During the test, stress or strain is applied according to a preset loading path using a loading system, and the real-time voltage values ​​at both ends of the grid spring 4 are continuously acquired by an electrical signal measurement system. The loading system pauses loading each time a real-time voltage value is measured to avoid mechanical noise introduced by the loading interfering with the voltage signal measurement. The real-time voltage value is compared with the initial voltage value to determine the integrity status of the sample.

[0069] The change in voltage value primarily stems from the change in the cross-sectional area of ​​the lattice spring 4. When a local crack occurs in the spring, the crack reduces the conductive cross-section, narrowing the conduction path and thus increasing the resistance at that location. Under constant current conditions, according to Ohm's law, the increase in resistance will cause a corresponding increase in the voltage signal, forming a identifiable abrupt change. When the lattice spring 4 completely breaks, the conduction path of the metal body is interrupted, and the current is forced to conduct from one section of metal to another through a medium such as high-temperature, high-pressure water or gas, forming a metal-medium-metal conduction mode. Since the conductivity of the medium is much lower than that of the metal, the overall resistance increases sharply. Therefore, with the constant current source 9 output remaining unchanged, the voltage signal across the system will spike significantly, indicating a complete break in the conduction path. This electrical signal response characteristic can be used to determine the structural integrity of the spring in real time.

[0070] When the real-time voltage value deviates from the average value, its integrity has changed; the greater the deviation, the higher the degree of damage. The standard deviation threshold includes a first threshold and a second threshold. When the real-time voltage value deviates from the initial average value by more than the first threshold but not more than the second threshold, the grid spring 4 is determined to have partially broken; when the real-time voltage value deviates from the initial average value by more than the second threshold, the grid spring 4 is determined to have completely broken. The first threshold is 3 to 5 times the standard deviation of the initial voltage signal, and the second threshold is 10 to 100 times the standard deviation of the initial voltage signal. By using the standard deviation threshold criteria, the grid spring 4 can be sensitively distinguished between an intact, partially broken, or completely broken state. Combined with the loading conditions and environmental parameters at the time, this allows for accurate capture of the entire process of changes in the sample's structural integrity.

[0071] The conductivity of the environmental medium has a certain influence on the degree of signal change. When the medium has good conductivity, even if cracks or gaps appear in the sample, the medium may still conduct through the cracks and gaps, resulting in a smaller change in the voltage signal. However, when the medium has poor conductivity or is non-conductive, once the sample cracks, the circuit is blocked, leading to a more significant change in the voltage signal. Therefore, this invention can determine the integrity status of the grid spring 4 by combining the degree of voltage signal deviation, and further distinguish whether the sample is in an intact, partially broken, or completely broken state by combining the deviation range, thereby achieving sensitive monitoring of sample integrity under high pressure.

[0072] Also includes:

[0073] Step S7: Establish a stress corrosion induction mechanism model based on the loading waveform, frequency and environmental parameters corresponding to structural damage.

[0074] In the actual test, after identifying the loading initiation point and monitoring the electrical signals throughout the entire process of the lattice spring 4, the test data can be further statistically summarized and correlated by combining different loading waveforms, loading frequencies, and environmental parameters to extract typical working condition information corresponding to different damage characteristics. Based on this, a stress corrosion induction mechanism model can be established using mathematical modeling or machine learning methods to describe the coupling effect of loading stress and environmental factors on the crack initiation, propagation, and final fracture process of the lattice spring 4. This provides data support and theoretical basis for subsequent material life prediction, service safety assessment, and corrosion-resistant structural optimization design.

[0075] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for stress corrosion testing of lattice springs under fluctuating loads, characterized in that, An apparatus for testing stress corrosion under fluctuating loads on lattice springs, the apparatus comprising: Autoclave, used to simulate the high-temperature and high-pressure water environment of the primary loop of a nuclear power plant, and to house the grid springs; An environmental control system, connected to the autoclave, is used to regulate the environmental parameters of the autoclave. The loading system includes a loading testing machine and a loading pair, wherein the loading pair is used to apply constant deformation and fluctuating load to the grid spring; the loading testing machine controls the loading pair to move within the autoclave until it contacts the grid spring; The contact point measurement system includes a constant voltage source and a first signal acquisition device. The constant voltage source applies a constant voltage to the grid spring and the loading pair, and the first signal acquisition device monitors current changes to determine the loading start point. An integrity measurement system includes a constant current source, a current commutation device, and a second signal acquisition device; the constant current source provides a stable DC current, the current commutation device switches the current direction at a preset frequency, and the second signal acquisition device monitors the changes in electrical signals at both ends of the grid spring in real time to determine the integrity state of the grid spring; the method includes: Fix the grid spring inside the autoclave and close the autoclave; The environmental control system injects the medium, regulates the environmental parameters to a preset range, and maintains the stability of the medium composition. A controlled load is applied to the grid spring by a loading system, a constant voltage is applied between the grid spring and the loading pair by a constant voltage source and a threshold is determined, and the first signal acquisition device monitors the current value in real time. The loading pair is controlled to move towards the grid spring until the loading pair contacts the grid spring and the current value exceeds the current threshold, which is determined as the loading start point; A constant current is applied by a constant current source and the current reversing device switches the current direction at a preset frequency. The second signal acquisition device intermittently monitors the voltage value at both ends of the grid spring. By comparing the real-time voltage value with the initial voltage value, the complete state of the grid spring is determined, including: Record the initial voltage value and compare the real-time voltage value with the initial voltage value; the initial voltage value is the voltage signal when the small-sized metal sample is intact. During the test, the loading system performs voltage measurements and continuously collects real-time voltage values, comparing them with the initial voltage value; and the loading system pauses loading each time a voltage value is measured. When the real-time voltage value deviates from the average value and exceeds the standard deviation threshold, the integrity of the small-sized metal sample changes. Record the corresponding loading conditions and environmental parameters.

2. The method for testing stress corrosion under fluctuating load on a lattice spring according to claim 1, characterized in that, The loading system uses finite element mechanical modeling to convert the local stress at a specific location of the lattice spring into spring deformation, forming the loading parameters of the loading test machine. These loading parameters are used to control the loading pair.

3. The method for stress corrosion testing of lattice springs under fluctuating loads according to claim 2, characterized in that, The loading parameters include the loading waveform, frequency, and stress ratio.

4. The method for stress corrosion testing of lattice springs under fluctuating loads according to claim 3, characterized in that, The grid spring is installed with an electrically insulated structure, and the loading pair and the spring are isolated by ceramic or polymer insulators.

5. The method for stress corrosion testing of lattice springs under fluctuating loads according to claim 3, characterized in that, The frequency at which the current switching device switches the current direction is 0.1~10Hz.

6. The method for testing stress corrosion under fluctuating load on a lattice spring according to claim 3, characterized in that, The first signal acquisition device consists of an ammeter and a first wire, which are respectively connected to the loading pair and one end of the grid spring. The second signal acquisition device consists of a voltmeter, a second lead wire, and a multi-channel signal analyzer. The second lead wire is connected to both ends of the grid spring, and the lead wire outlet is located outside the autoclave. The multi-channel signal analyzer is connected to a processor for real-time recording and analysis of voltage signals.

7. The method for testing stress corrosion under fluctuating load on a lattice spring according to claim 1, characterized in that, Also includes: Based on the loading waveform, frequency, and environmental parameters corresponding to structural damage, a stress corrosion induction mechanism model is established.

8. The method for stress corrosion testing of lattice springs under fluctuating loads according to claim 1, characterized in that, The current threshold is determined based on the conductivity of the liquid or gas medium inside the autoclave.

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