Corrosion test device and method for fluctuation load stress of grillage spring

Abstract

The invention discloses a grid spring fluctuation load stress corrosion test device and method. The device comprises a high-pressure kettle; an environment control system; the loading system comprises a loading tester and a loading pair, and the loading pair is used for applying constant deformation and fluctuation load to the grillage spring; the loading tester controls the loading pair to move in the high-pressure kettle until the loading pair is in contact with the grillage spring; the contact point measuring system comprises a constant voltage source and a first signal acquisition device, constant voltage is applied to the grillwork spring and the loading pair through the constant voltage source, and the first signal acquisition device monitors current abrupt change and determines a loading starting point; according to the integrity measuring 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 collecting device monitors changes of electric signals at the two ends of the grillwork spring in real time and determines the complete state of the grillwork spring. According to the invention, accurate identification of the loading starting point of the grillage spring and real-time monitoring of the integrity state in the high-pressure environment are realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of service performance evaluation of nuclear power key component materials, and particularly relates to a grid spring fluctuating load stress corrosion test device and a manufacturing method. BACKGROUND

[0002] As a core functional component of a nuclear fuel assembly, the grid spring realizes precise clamping and positioning of fuel rods through cooperation with the rigid protrusions of the strip, and the structural integrity thereof is directly related to the safety of the operation of a nuclear reactor. In actual service, the component not only bears the constant deformation constraint after assembly, but also needs to superimpose dynamic loads such as core hydraulic excitation and flow-induced vibration, and is prone to stress corrosion cracking (SCC) failure in a high-temperature and high-pressure water environment, so the research on the failure mechanism thereof has important engineering significance for nuclear power safety guarantee.

[0003] The thickness of the grid spring is usually less than 1 mm, the width is less than 5 mm, and the grid spring has a special arc-shaped structure, and conventional standard test methods are mainly designed for large-size samples, so it is difficult to realize precise loading of the small load of the grid spring. SUMMARY

[0004] Based on the deficiencies of the prior art, the grid spring fluctuating load stress corrosion test device and method provided by the application can realize accurate identification of the loading starting point of the grid spring and real-time monitoring of the integrity state of the grid spring in a high-pressure environment.

[0005] The application provides a grid spring fluctuating load stress corrosion test device, which comprises: A high-pressure kettle is used to simulate a high-temperature and high-pressure water environment of a nuclear power primary loop and contains the grid spring. An environment control system is connected to the high-pressure kettle and is used to control the environmental parameters of the high-pressure kettle. A loading system comprises a loading test machine and a loading pair, and the loading pair is used to apply constant deformation and fluctuating load to the grid spring; the loading test machine moves in the high-pressure kettle until it contacts the grid spring by controlling the loading pair. A contact point measurement system comprises a constant voltage source and a first signal acquisition device, and the constant voltage source applies a constant voltage to the grid spring and the loading pair, and the first signal acquisition device monitors current mutation to determine the loading starting point. An integrity measurement system comprises a constant current source, a current reversing device and a second signal acquisition device; the constant current source provides a stable direct current, the current reversing device switches the current direction at a preset frequency, and the second signal acquisition device monitors the change of the electrical signal at both ends of the grid spring in real time to determine the integrity state of the grid spring.

[0006] In some embodiments, the loading system converts the local stress of the specific position of the grid spring into the spring deformation amount through finite element mechanics modeling, and forms the loading parameters of the loading testing machine, which are used to control the loading pair.

[0007] In some embodiments, the loading parameters include loading waveform, frequency, and stress ratio.

[0008] In some embodiments, the grid spring is installed in an electrically insulated structure, and the loading pair and the spring are separated by a ceramic or polymer insulating piece.

[0009] In some embodiments, the frequency of the current reversing device switching the current direction is 0.1-10 Hz.

[0010] In some embodiments, the first signal acquisition device is an ammeter and a first wire, and the first wire is connected to one end of the grid spring and the loading pair, respectively. The second signal acquisition device is a voltmeter and a second wire, and a multi-channel signal instrument, the second wire is connected to both ends of the grid spring, and the wire leading end is located outside the autoclave, and the multi-channel signal instrument is connected to the processor for real-time recording and analysis of the voltage signal.

[0011] In a second aspect, the present application provides a grid spring fluctuating load stress corrosion test method, comprising: Fixing the grid spring in the autoclave and closing the autoclave; Injecting the medium through the environment control system, adjusting the environmental parameters to the preset range, and maintaining the stability of the medium composition; Applying controlled loading to the grid spring through the loading system, applying constant voltage between the grid spring and the loading pair through the constant voltage source, and determining the threshold value, and the first signal acquisition device real-time monitors the current value; Controlling the loading pair to move towards the grid spring, until the loading pair contacts the grid spring and the current value exceeds the current threshold value, determining the loading starting point; Applying constant current through the constant current source and switching the current direction through the current reversing device at a preset frequency, and the second signal acquisition device intermittently monitors the voltage value at both ends of the grid spring; Comparing the real-time voltage value with the initial voltage value to determine the integrity of the grid spring.

[0012] In some embodiments, comparing the real-time voltage value with the initial voltage value to determine the integrity of the grid spring comprises: Recording the initial voltage value, and comparing the real-time voltage value with the initial voltage value; the initial voltage value is the voltage signal when the small-size metal sample is complete; During the test, the loading system is paused for voltage measurement and real-time voltage value is continuously collected and compared with the initial voltage value; and each time the voltage value is measured, the loading system is paused for loading; 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, and the corresponding loading condition and environmental parameters are recorded.

[0013] In some embodiments, further comprising: According to the loading waveform, frequency and environmental parameters corresponding to the structural damage, a stress corrosion inducing mechanism model is established.

[0014] In some embodiments, the current threshold is determined according to the conductivity of the liquid or gas medium in the autoclave.

[0015] The present application provides a lattice spring fluctuating load stress corrosion test device and method, which can apply constant deformation and fluctuating load to the lattice spring under high temperature and high pressure water environment, and accurately identify the loading starting point through the contact point measurement system to avoid starting judgment error. At the same time, the integrity measurement system monitors the voltage change between the two ends of the lattice spring in real time through the constant current source and the current reversing device, which can timely judge the integrity state of the lattice spring, realize the intuitive judgment of the structural damage, and improve the accuracy and reliability of the test. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The structure diagram of the lattice spring fluctuating load stress corrosion test device provided by the present application is shown in the figure; Figure 2 The flowchart of the lattice spring fluctuating load stress corrosion test method provided by the present application is shown in the figure; In the figure: 1, autoclave; 2, loading testing machine; 3, loading pair; 4, lattice spring; 5, constant voltage source; 6, ammeter; 7, displacement sensor; 8, prompting device; 9, constant current source; 10, current reversing device; 11, multi-channel signal instrument; 12, voltmeter. DETAILED DESCRIPTION

[0017] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention, in conjunction with the accompanying drawings. It should be understood that the described embodiments are only some of the embodiments of the present invention, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and in no way limits the present invention, its application, or use. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to be protected by the present invention. Unless otherwise specified, the relative arrangement of components and steps, expressions, and numerical values ​​described 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 drawings are not drawn to scale. Technologies, methods, and devices known to persons of ordinary skill in the relevant art may not be discussed in detail, but, where appropriate, such technologies, 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 illustrative and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0018] The present application provides a grid spring fluctuating load stress corrosion test device, which can achieve accurate identification of the grid spring loading starting point and real-time monitoring of the integrity status under high pressure environment.

[0019] Specifically, such as Figure 1 Figure 2 shows a schematic diagram of the structure of a fluctuating load stress corrosion test apparatus for a grid spring 4. This apparatus is used for mechanical loading and in-situ monitoring of grid spring 4 components in the high-temperature, high-pressure water service environment of a nuclear power plant. The apparatus comprises 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, high-pressure water environment of a nuclear power plant's primary circuit and houses the grid spring 4. The environmental control system is connected to the autoclave 1 and controls its environmental parameters. The loading system comprises a loading tester 2 and a loading pair 3. The loading pair 3 applies constant deformation and fluctuating loads to the grid spring 4. The loading tester 2 controls the loading pair 3's movement within the autoclave 1 until it contacts the grid spring 4. The contact point measurement system comprises 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 fluctuations to determine the loading starting point. The integrity measurement system includes a constant current source 9, a current reversing device 10 and a second signal acquisition device; the constant current source 9 provides a stable DC current, the current reversing 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 of the grid spring 4.

[0020] In the present application, the lattice spring 4 is an elongated elastic member applied in a nuclear power assembly, usually made of high-performance alloy material, with small size, high flexibility, corrosion resistance and other characteristics. It is usually a strip or sheet-shaped elastic element that provides stable pre-tightening force or cushioning performance through its own elastic deformation. Because its working environment is usually high temperature and high pressure, strong corrosive medium, such as the nuclear power primary loop water environment, and the load level during loading is low, the mechanical response signal of the lattice spring 4 is easily covered by the frictional resistance of the loading system, and it is difficult to accurately identify the loading starting point through the traditional force sensor. At the same time, due to the thin-walled structure of the lattice spring 4, local yielding, stress corrosion crack initiation and expansion and other micro-damages may occur after loading, and its service life is significantly affected by the stress corrosion coupling effect.

[0021] The autoclave 1 is made of alloy material with excellent corrosion resistance, preferably stainless steel or nickel-based alloy, and the material selection and structure design are carried out according to the specific test medium and temperature, pressure requirements. The autoclave body of the autoclave 1 is in a cylindrical structure, matched with a disc type cover, connected by bolts and cooperated with sealing rings or metal sealing pads to form a reliable sealing structure, which can realize high pressure environment sealing in liquid or gas medium.

[0022] In order to adapt to the harsh working conditions of high temperature and high pressure water environment in nuclear power, the pressure resistance grade of the autoclave 1 can be designed to 10MPa~30MPa, and the temperature resistance range can reach 50℃ to 400℃, and can be extended accordingly according to the experimental requirements. The autoclave body is provided with medium inlet and outlet, pressure detection port and temperature sensing port, which can realize fluid circulation, pressure regulation and temperature control with the external environment control system, to ensure the long-term stability of the medium composition and physical parameters in the autoclave. At the same time, the autoclave body structure is subjected to finite element strength checking, which can withstand the internal pressure load under the action of high pressure fluid and ensure that there is no plastic deformation or sealing failure under multiple cyclic loading, thereby providing a stable and repeatable high pressure test environment for the controllable loading of the lattice spring 4.

[0023] The environment control system is connected with the autoclave 1, which is used to build a high temperature and high pressure corrosion environment simulating the actual service conditions of the lattice spring 4, and is suitable for various corrosion test requirements, including high temperature and high pressure water environment, superheated steam environment and other special working conditions in nuclear power system. The environment control system can select water solution as the working medium according to the test requirements, and accurately regulate the temperature, pressure and chemical composition of the test environment to ensure the test repeatability and environmental stability.

[0024] The environment control system can adjust the solute concentration, dissolved gas content, pH value and conductivity of the solution. During the long-term loading test, the environment control system can realize dynamic adjustment and real-time monitoring of the medium composition and physical parameters, so as to ensure that the internal environment of the autoclave 1 always maintains in the preset range, meeting the experimental requirements of in-situ controllable loading of the lattice spring 4.

[0025] The loading starting point refers to the moment when the loading pair 3 first contacts the sample and starts to apply stress or strain to the sample. The traditional method takes the force value mutation as the basis for judgment, but the cage spring 4 cannot accurately determine the force value signal due to the influence of friction.

[0026] The loading system includes a loading testing machine 2 arranged 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 through a force transmission connecting rod. The loading testing machine 2 has multiple loading modes such as constant stress, constant strain, and fluctuating loading, which can meet the multi-working condition loading requirements of the cage spring 4 in a high temperature and high pressure environment. Generally, the loading pair 3 is a detachable structure, which is used to directly contact the cage spring 4 and apply axial compressive stress. The loading pair 3 is coupled with the loading testing machine 2 through a force transmission connecting rod, and accurately transmits the force generated by the loading testing machine 2 to the specified position of the cage spring 4 during the loading process. The surface of the loading pair 3 is preferably made of electrically conductive and corrosion-resistant materials such as zirconium alloy, and the corresponding geometric profile is designed according to the structure and size of the cage spring 4 to ensure that the force application mode is representative.

[0027] The force value of the force transmission connecting rod is low during the loading process, but the loading testing machine 2 can compensate for the influence of the friction of the force transmission connecting rod through displacement closed-loop control. The force value applied by the force transmission connecting rod to the cage spring 4 is small, which will not cause the deformation of the force transmission connecting rod, and will not affect the accurate control of the loading testing machine 2 on the force transmission connecting rod and the loading pair 3. The overall loading process can maintain high precision and improve the accuracy of the loading starting point judgment.

[0028] Before loading, the loading system converts the target stress of the key parts of the cage spring 4 into the displacement of the loading pair 3 through finite element mechanics modeling. The loading testing machine 2 controls the position according to the displacement value, thereby improving the accuracy of stress control and ensuring that a good comparable loading stress field is obtained on the cage spring 4 samples of different sizes and different elastic moduli. The loading parameters include loading frequency, loading waveform, stress ratio, etc.

[0029] To avoid electrical signal interference, ceramic or polymer insulating gaskets are arranged between the loading pair 3 and the cage spring 4 to achieve mechanical loading while ensuring electrical isolation. During the loading process, the loading testing machine 2 controls the loading pair 3 to move slowly at a set speed, and cooperates with the contact point measurement system to determine the loading starting point synchronously. Once the loading starts, the loading testing machine 2 continuously applies fluctuating load or constant load to the cage spring 4 according to the preset loading path, thereby realizing the simulation of the in-situ corrosion stress process of the spring.

[0030] In order to avoid the interference of the grid spring 4 with the loading pair 3, the grid spring 4 is installed in an electrically insulated structure, and the loading pair 3 is separated from the spring by a ceramic or polymer insulating piece. In some embodiments, a clamp can be provided to fix the grid spring 4 in the clamp through the insulating piece, and the clamp as a whole has sufficient mechanical strength and rigidity, and the deformation amount is negligible during the entire experiment, which will not interfere with the mechanical response of the sample.

[0031] The contact point measurement system includes a constant voltage source 5 and a first signal acquisition device. The constant voltage source 5 connects the grid spring 4 and the loading pair 3, and is used to continuously apply a constant voltage during loading; the first signal acquisition device monitors the current signal in the loading circuit in real time.

[0032] The constant voltage source 5 is arranged outside the autoclave 1, and is electrically connected to the loading pair 3 and the grid spring 4 through wires, so as to continuously apply a constant voltage during loading. The output voltage range of the constant voltage source 5 is generally 0.01-1V, which does not affect the micro properties of the metal sample while measuring the electrical signal. The first signal acquisition device includes a first wire and an ammeter 6, and the first wire is fixed on the grid spring 4 and the loading pair 3 by welding or pressure connection, and the connection position is selected at a position that does not affect the loading force, so as to avoid the interference of the difference in medium conductivity on the electrical signal detection.

[0033] The ammeter 6 and the constant voltage source 5 are connected in series in the circuit, and the current change between the loading pair 3 and the metal sample is monitored in real time, and the sampling frequency can reach more than 1kHz, so as to ensure that the transient current mutation signal can be captured during loading. When the loading pair 3 has not yet contacted the grid spring 4, the circuit is in an open state, and the current value is close to zero; as the loading pair 3 gradually approaches and first contacts the grid spring 4, the circuit is turned on, and the current changes suddenly. The ammeter 6 identifies the mutation and compares it with the current threshold value, and once the current increases suddenly exceeds the current threshold value, it can be judged that the loading pair 3 has contacted the grid spring 4, and then the loading starting point is determined. This determination process does not depend on the load on the sample, and can effectively overcome the distortion problem of the force value signal caused by the friction of the transmission connecting rod.

[0034] In order to facilitate the prompt of the loading starting point, the contact point measurement system can work with a prompter, which can prompt the operator through sound and light signals through the prompt device 8 when the loading starting point is determined, so as to ensure the accuracy and repeatability of the loading control. At the same time, the displacement of the loading pair 3 at this time is recorded by the displacement sensor 7, which provides an initial reference for the subsequent loading path.

[0035] The setting of the current threshold is determined according to the conductivity characteristics of the medium in the autoclave 1 and the actual application of the grid spring 4. For air or gas environment, since the medium has very low conductivity, the circuit is completely open before the loading vice 3 contacts the sample, so the current threshold can be set to 100-10000 times the open circuit current of the signal acquisition device, that is, the starting point can be determined. For water-based solution and other media with strong conductivity, there may be a small leakage current in the circuit when the loading vice 3 does not contact the grid spring 4, and the contact current threshold can be set to 10-1000 times the open circuit current to ensure accuracy. For newly developed tests, it is appropriate to determine the law of current signal change with distance by combining simulation and pre-experiment to determine the best threshold range.

[0036] The electric signal measurement system is used for real-time or intermittent monitoring of the integrity change of the grid spring 4 during the loading process, including a constant current source 9 and a current reversing device 10, 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 change of the grid spring 4 is determined according to the change of the voltage value during the loading process.

[0037] The second signal acquisition device is a voltmeter 12 and a second wire, a multi-channel signal instrument 11, the second wire is connected to both ends of the grid spring 4 respectively, and the wire leading end is located outside the autoclave 1, the multi-channel signal instrument 11 is connected to a processor for real-time recording and analysis of voltage signals. The second wire is connected to both ends of the grid spring 4 respectively; the multi-channel signal acquisition instrument is used for synchronous recording of voltage value, loading displacement signal and environmental parameters. The constant current source 9 provides a stable constant direct current, which flows through the grid spring 4 through the wire; the voltmeter 12 is used for measuring the voltage value and small change of the metal sample at both ends, and transmitting the voltage value to the multi-channel signal acquisition instrument and being recorded and processed by the processor. The current reversing device 10 can switch the current direction at a frequency of 1Hz, which is used to eliminate the influence of contact resistance heating on the stability of the voltage signal, so that the measurement result is more accurate and reliable. In this application, the current reversing device 10 is generally selected at a frequency of about 0.1-10Hz according to the influence of the wire connection part of the grid spring 4, including material type and connection method, etc. to prevent the interference of contact resistance heating on local voltage change.

[0038] In the embodiment, the electrical signal measurement system first determines the accurate starting point of loading through the contact point measurement system. Since the grid spring 4 is a small-size low-rigidity metal component, the force value it bears during loading is extremely small, and the traditional method based on sudden change of force value cannot accurately identify the starting point of loading. Therefore, by applying a constant voltage between the loading pair 3 and the grid spring 4 and monitoring the sudden change of current by using the first signal acquisition device, the starting point of loading can be accurately identified when the sample first contacts, avoiding misjudgment caused by friction interference, thereby providing a reliable reference for subsequent loading control.

[0039] After the starting point of loading is determined, the integrity monitoring stage is entered. A stable current is provided by the constant current source 9, and the current direction is alternately switched by the current reversing device 10. The second signal acquisition device intermittently monitors the voltage change across the grid spring 4, and continuously compares the real-time voltage with the initial value. When the voltage deviates beyond the threshold value, it indicates that the structural integrity of the sample has changed. 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, thereby improving the accuracy and reliability of corrosion fracture behavior research.

[0040] In actual operation, the following grid spring 4 fluctuating load stress corrosion test method is adopted: Step S1, fixing the grid spring 4 in the autoclave 1 and closing the autoclave 1; Step S2, injecting medium by the environment control system, adjusting the environmental parameters to the preset range, and maintaining the stability of the medium composition; Step S3, applying controlled loading to the grid spring 4 by the loading system, applying a constant voltage by the constant voltage source 5 and determining the threshold value, and monitoring the current value in real time by the first signal acquisition device; Step S4, controlling 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 value, which is determined as the starting point of loading; Step S5, applying a constant current by the constant current source 9 and switching the current direction at a preset frequency by the current reversing device 10, and intermittently monitoring the voltage value across the grid spring 4 by the second signal acquisition device; Step S6, comparing the real-time voltage value with the initial voltage value to determine the integrity state of the grid spring 4.

[0041] During the stress corrosion test of the grid spring 4, the determination of the loading starting point is performed first, and then the complete state monitoring is performed, and the order of the two cannot be exchanged. Through the contact point measurement system, a constant voltage is applied in the early stage of loading, and the signal acquisition device is used to monitor the current jump, so that the time when the loading pair 3 and the grid spring 4 first contact can be accurately determined. This time point marks the starting point of mechanical loading, and also provides the reference state required for integrity monitoring, which is used to record the initial voltage value. If the loading starting point is not detected first, the initial voltage value may be collected before loading or in the unstable stage of loading, which cannot reflect the complete state of the sample, thereby affecting the voltage comparison result and leading to inaccurate fracture determination. Therefore, the loading starting point detection must be completed first, and then the integrity monitoring is performed, to ensure that the change of the electric signal reflects the true physical process and improves the accuracy and repeatability of the test data.

[0042] To ensure the sensitivity of the electric signal detection, the grid spring 4 is installed in the autoclave 1 by an electrically insulated manner, to ensure that the current only forms a loop through the grid spring 4, and will not flow through the metal components of the autoclave 1 and the loading system. The loading system applies a controlled load to the grid spring 4, and the second signal acquisition device pauses the loading at each voltage measurement to avoid introducing noise interference to the electric signal acquisition during the test process. During the test process, the stress is applied by the loading system and the voltage value is collected.

[0043] After the determination of the loading starting point is completed, the initial voltage value of the grid spring 4 in the complete state is recorded first, and the distribution characteristics of the initial voltage value, including the average value and the standard deviation, are obtained. The initial voltage value is the voltage signal of the grid spring 4 in the complete state. During the loading test process, the second signal acquisition device intermittently measures the voltage value between the two ends of the sample, and compares it with the distribution characteristics of the initial voltage value. When the voltage value significantly deviates from the initial value for a continuous period of time, it is considered that the integrity of the sample has changed.

[0044] During the test process, the loading system applies stress or strain according to the preset loading path, and the electric signal measurement system continuously collects the real-time voltage value between the two ends of the grid spring 4. At each measurement of the real-time voltage value, the loading system pauses the loading to avoid the mechanical noise introduced by the loading to interfere with the voltage signal measurement. The real-time voltage value is compared with the initial voltage value to determine the integrity state of the sample.

[0045] The change of the voltage value is mainly caused by the change of the cross-sectional area of the grid spring 4. When the spring is partially cracked, the crack will cause the cross-sectional area of the conductive path to decrease, and the conductive path will become narrow, so that the resistance at this position increases. Under the condition of constant current, according to Ohm's law, the increase of the resistance will cause the voltage signal to rise correspondingly, and an identifiable mutation feature is formed. When the grid spring 4 is completely cracked, the conductive path of the metal body is cut off, and the current is forced to pass through a medium such as high-temperature and high-pressure water or gas from one piece of metal to another, that is, a metal-medium-metal conductive mode is formed. Because the conductivity of the medium is much lower than that of the metal, the overall resistance rises sharply, so under the condition that the output of the constant current source 9 does not change, the voltage signal at both ends of the system will rise significantly, and the system is in a completely cracked state. This electrical signal response characteristic can be used to judge the structural integrity of the spring in real time.

[0046] When the real-time voltage value deviates from the average value, the integrity has changed, and the greater the deviation, the higher the damage degree. The standard deviation threshold includes a first threshold and a second threshold. When the amplitude of the real-time voltage value deviating from the initial average value exceeds the first threshold and is not greater than the second threshold, it is determined that the grid spring 4 is partially cracked; when the amplitude of the real-time voltage value deviating from the initial average value exceeds the second threshold, it is determined that the grid spring 4 is completely cracked. The first threshold is 3-5 times the standard deviation of the initial voltage signal, and the second threshold is 10-100 times the standard deviation of the initial voltage signal. Through the determination standard of the standard deviation threshold, the grid spring 4 in the complete state, the partially cracked state or the completely cracked state can be distinguished sensitively, and the loading condition and the environmental parameter at that time are recorded, so that the whole process of the change of the structural integrity of the sample can be accurately captured.

[0047] The conductivity of the environmental medium has a certain influence on the degree of signal change. When the conductivity of the medium is good, even if the sample has cracks or gaps, the medium can still conduct the cracks and gaps, so that the change of the voltage signal is small; when the conductivity of the medium is poor or non-conductive, once the sample is cracked, the circuit is broken, and the change of the voltage signal is more significant. Therefore, the present application can judge the integrity state of the grid spring 4 according to the deviation degree of the voltage signal, and further distinguish whether the sample is in the complete, partially cracked or completely cracked state according to the deviation range, so that the structural integrity of the sample in the high-pressure environment can be monitored sensitively.

[0048] Further comprising: Step S7, establishing a stress corrosion inducing mechanism model according to the loading waveform, the frequency and the environmental parameter corresponding to the structural damage.

[0049] In the actual test process, after the identification of the loading starting point of the grid spring 4 and the whole process of electrical signal monitoring, the test data can be further statistically summarized and correlated analyzed in combination with different loading waveforms, loading frequencies and environmental parameters, and the typical working condition information corresponding to different damage characteristics is extracted. On this basis, mathematical modeling or machine learning method can be used to establish a stress corrosion induced mechanism model to describe the coupling rule of loading stress and environmental factors on the crack initiation, propagation and final fracture process of the grid spring 4, thereby providing data support and theoretical basis for subsequent material life prediction, service safety evaluation and corrosion-resistant structure optimization design.

[0050] The above only describes some embodiments of the present application. For ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the protection scope of the present application.

Claims

1. Grid spring fluctuating load stress corrosion test device, characterized in that: include: Autoclave, used to simulate the high-temperature and high-pressure water environment of a nuclear power primary circuit and to house grid springs; Environmental control system, connected to the autoclave, used to regulate the environmental parameters of the autoclave; The loading system includes a loading tester and a loading pair, wherein the loading pair is used to apply a constant deformation and a fluctuating load to the grid spring; the loading tester 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 the current mutation to determine the loading starting point. The integrity measurement system includes a constant current source, a current reversing device, and a second signal acquisition device; the constant current source provides a stable direct current, the current reversing 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 status of the grid spring.

2. The grid spring fluctuating load stress corrosion test device according to claim 1, characterized in that: The loading system converts the local stress at a specific position of the grid spring into spring deformation through finite element mechanics modeling to form loading parameters of the loading tester, and the loading parameters are used to control the loading pair.

3. The grid spring fluctuating load stress corrosion testing device according to claim 2, characterized in that: The loading parameters include loading waveform, frequency, and stress ratio.

4. The grid spring fluctuating load stress corrosion testing device according to claim 3, characterized in that: The grid spring is installed in an electrically insulating structure, and the loading pair and the spring are isolated by ceramic or polymer insulation.

5. The grid spring fluctuating load stress corrosion testing device according to claim 3, characterized in that: The frequency of switching the current direction of the current reversing device is 0.1~10Hz.

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

7. Grid spring fluctuating load stress corrosion test method, characterized in that: include: securing the grid spring in an autoclave and closing the autoclave; Inject the medium through the environmental control system, adjust the environmental parameters to the preset range, and maintain the stability of the medium composition; Applying a controlled load to the grid spring through a loading system, applying a constant voltage between the grid spring and the loading pair through a constant voltage source and determining a threshold, and monitoring the current value in real time by a first signal acquisition device; Controlling the loading pair to move toward the grid spring until the loading pair contacts the grid spring and the current value exceeds a current threshold, determining it as a loading starting point; A constant current is applied by a constant current source and a current reversing device switches the current direction at a preset frequency, and a second signal acquisition device intermittently monitors the voltage value at both ends of the grid spring; The real-time voltage value is compared with the initial voltage value to determine the integrity state of the grid spring.

8. The grid spring fluctuating load stress corrosion test method according to claim 7, characterized in that: Comparing the real-time voltage value with the initial voltage value to determine the integrity of the grid spring includes: 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 measurement and continuously collects real-time voltage values, which are compared with the initial voltage values; and each time the voltage value is measured, the loading system pauses loading; When the real-time voltage value deviates from the average value and exceeds the standard deviation threshold, the integrity of the small-size metal sample changes, and the corresponding loading conditions and environmental parameters are recorded.

9. The grid spring fluctuating load stress corrosion test method according to claim 7, characterized in that: Also includes: A stress corrosion induction mechanism model was established based on the loading waveform, frequency and environmental parameters corresponding to the structural damage.

10. The grid spring fluctuating load stress corrosion test method according to claim 7, characterized in that: The current threshold is determined according to the conductivity of the liquid or gas medium in the autoclave.

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