Multi-field coupling fatigue test device and method for high-temperature superconducting strip

Abstract

The invention discloses a multi-field coupling fatigue test device and method for a high-temperature superconducting tape, and belongs to the field of superconducting tape fatigue tests.The multi-field coupling fatigue test device for the high-temperature superconducting tape comprises a fatigue testing machine, and a test container used for providing a low-temperature field is arranged in a test area of the fatigue testing machine; a clamp assembly used for fixing a sample to be tested is arranged in the experiment container, the clamp assembly is connected with a current assembly used for providing an electric field, and a magnet assembly used for providing a magnetic field is arranged in the experiment container. According to the multi-field coupling fatigue test device and method for the high-temperature superconducting strip, the limitation of an existing test means is broken through, and a reliable experimental platform and application value are provided for mechanical property research and service life evaluation of superconducting materials and other low-temperature service materials.

Description

Technical Field

[0001] This invention relates to the field of fatigue testing technology for superconducting tapes, and in particular to a multi-field coupling fatigue testing device and method for high-temperature superconducting tapes. Background Technology

[0002] Materials often operate in complex multiphysics environments during actual service, and these environmental conditions directly impact their mechanical properties, structural stability, and service life. Taking high-temperature superconducting materials as an example, in major engineering applications such as high-field magnets, particle accelerators, nuclear fusion devices, and power transmission systems, they must simultaneously withstand thermal stress under cryogenic conditions, electromagnetic forces generated by current loading, strong magnetic fields, and repeated superposition of cyclic mechanical loads. These multiple factors coexist and couple with each other, significantly influencing the material's mechanical response and fatigue damage evolution. Therefore, how to realistically reproduce the multiphysics-magnetic-mechanical-cryogenic multi-field coupled fatigue environment under laboratory conditions has become a key scientific and technological problem in studying the mechanical properties and fatigue behavior of superconducting materials and other cryogenic service materials. Most existing fatigue performance testing methods are limited to single-field loading or finite-field coupling conditions.

[0003] Existing low-temperature fatigue testing machines typically only control the temperature of the specimen and fixture through high and low temperature environmental chambers and rely on hydraulic servo systems to apply cyclic mechanical loads. This fails to effectively reflect the stress and fatigue damage characteristics of superconducting materials during actual service. The following significant shortcomings remain: 1. Lack of current loading function: Existing low-temperature fatigue testing machines do not have an independent current loading module, so they cannot apply current to the sample during fatigue testing. Therefore, they cannot truly reflect the electromagnetic effect brought about by current conduction in superconducting materials under service conditions.

[0004] 2. Lack of magnetic field loading function: The existing device is not equipped with an external magnetic field loading system, which cannot provide stable and controllable magnetic field conditions for the sample in a low-temperature environment. Therefore, it is difficult to simulate the electromagnetic force exerted on superconducting materials in an electromagnetic environment, especially during fatigue loading, and its influence on fatigue damage and crack evolution behavior.

[0005] 3. Difficulty in achieving multi-physics field coupling testing: Due to the lack of electric and magnetic field loading methods, existing low-temperature fatigue testing machines can only achieve dual-field coupling of low temperature and mechanics, but cannot achieve comprehensive fatigue loading of multiple physical fields such as electric, magnetic, mechanical and low temperature, thus limiting the study of fatigue performance of typical superconducting materials such as YBCO under complex service conditions.

[0006] The root cause of the above defects is that the original design of existing technologies is mainly aimed at the low-temperature fatigue performance research of conventional materials such as metals and alloys, and has not been optimized for special materials such as superconducting materials that operate in multiple fields of electric, magnetic, mechanical and low temperature. Summary of the Invention

[0007] The purpose of this invention is to provide a multi-field coupled fatigue testing device and method for high-temperature superconducting tapes, so as to overcome the limitations of existing testing methods and provide a reliable experimental platform and application value for the mechanical property research and life assessment of superconducting materials and other low-temperature service materials.

[0008] To achieve the above objectives, this invention provides a multi-field coupling fatigue testing device for high-temperature superconducting tapes, comprising a fatigue testing machine, an experimental container for providing a low-temperature field in the test area of ​​the fatigue testing machine, a clamp assembly for fixing the sample to be tested inside the experimental container, the clamp assembly being connected to a current assembly for providing an electric field, a magnet assembly for providing a magnetic field inside the experimental container, an extensometer being mounted on the sample to be tested, a lifting platform being mounted at the bottom of the experimental container, and a digital image correlation (DIC) measurement system for monitoring the experiment on the sample to be tested being mounted outside the fatigue testing machine; the magnet assembly includes symmetrical permanent magnets located on both sides of the sample to be tested, the symmetrically arranged permanent magnets being separated by a magnet frame; the current assembly includes current lines connected to the clamp assembly, the current lines being synchronously connected to the drive shaft of the fatigue testing machine via an adjusting bracket to achieve synchronous movement of the current lines and the drive shaft, a force sensor being mounted at the connection between the adjusting bracket and the drive shaft of the fatigue testing machine; two fixing clamps are mounted on the sample to be tested along its length, each fixing clamp being connected to a voltage lead, the voltage lead being connected to the fatigue testing machine via an anti-displacement structure.

[0009] Preferably, the fatigue testing machine has a base below the test area, support columns around the test area, and a crossbeam above the test area.

[0010] Preferably, the experimental container is a low-temperature Dewar jar, and the experimental container is provided with an observation window for monitoring the sample to be tested, and the clamp assembly is located directly above the experimental container.

[0011] Preferably, the clamping assembly includes an upper clamp located above and a lower clamp located below, the lower clamp being connected to the fatigue testing machine crossbeam via a support column.

[0012] Preferably, the upper clamp is connected to the drive shaft of the fatigue testing machine via low-temperature resin.

[0013] Preferably, the upper clamp and the lower clamp are connected to the current source via current lines.

[0014] Preferably, the anti-displacement structure includes a resin column wrapped around the voltage lead, and the resin column is rigidly connected to the crossbeam of the fatigue testing machine.

[0015] Preferably, the relative position of the permanent magnet is adjusted by using 3D printed magnet frames of different thicknesses. The permanent magnet is connected to one end of the adjustment bracket via an adjustment clamp one, and an adjustment clamp two is hinged to the other end of the adjustment bracket. The adjustment clamp two is connected to the lower clamp, and the adjustment clamp one and the adjustment bracket are connected by a universal joint.

[0016] Preferably, the fatigue testing machine, lifting platform, current source, nanovoltmeter, extensometer, digital image correlation (DIC) measurement system, and control computer are connected.

[0017] This invention also provides a method for multi-field coupling fatigue testing of high-temperature superconducting tapes, comprising the following steps: Step 1, Equipment Preparation and System Initialization: Turn on the power to the fatigue testing machine and the control computer, start the control software through the control computer, and set the initial parameters of force and displacement to zero. Step 2, Sample installation: Place the sample to be tested between the upper and lower clamps, and adjust the positions of the upper and lower clamps to clamp and fix the sample to be tested. Step 3, Current introduction: Connect the output terminal of the current source to the upper clamp and the lower clamp respectively through current lines; Step 4, Magnetic field loading: The permanent magnets are placed in the experimental area of ​​the sample to be tested. A 3D printed magnet frame of appropriate thickness is selected in advance to determine the spacing between the permanent magnets. The position of one permanent magnet, the magnet frame and the sample to be tested is adjusted and fixed by the adjustment frame. Then the other permanent magnet is closed. Step 5, Voltage Lead Arrangement: Two voltage leads are clamped along the length of the experimental section in the middle of the sample to be tested for four-point voltage measurement. Step 6, connect the extensometer: Connect the extensometer to the sample to be tested, and position the extensometer away from the permanent magnet and voltage leads; Step 7, Low-temperature refrigeration: The position of the cryogenic Dewar container filled with liquid nitrogen is raised by a lifting platform, so that the liquid nitrogen gradually immerses the sample to be tested. Step 8, Apply current: Turn on the nanovoltmeter and current source in sequence to adjust and control the applied current; Step 9, fatigue loading: The loading curve, cyclic parameters and target fatigue cycle number of the fatigue testing machine are set in the control software. The fatigue testing machine is started and a preset cyclic mechanical load is applied to the test sample in the magnetic field environment. At the same time, a current of a set amplitude is applied, thereby constructing a fatigue test environment with coupling of electric-magnetic-force-low temperature multi-physics fields. Step 10, Critical Current Degradation Measurement: After completing the preset number of fatigue cycles, the experiment is paused, the load on the fatigue testing machine is reduced to zero, the current is reduced to zero, and then the critical current of the sample is measured using the four-point method, and its degradation during the fatigue process is recorded. Step 11, End of Experiment and Sample Processing: The experiment is terminated when the final preset number of fatigue cycles is reached or when the test sample undergoes fatigue fracture. Then, the current source and nanovoltmeter are turned off, the cryogenic Dewar jar is lowered, and the test sample is taken out after it returns to room temperature. The permanent magnet is removed, and the fatigue testing machine is turned off. Step 12, Image Monitoring: The CCD camera in the digital image correlation (DIC) measurement system is activated, and the CCD camera is aimed at the observation window of the cryogenic Dewar jar to record the initiation and propagation of cracks in the sample under test in real time during the fatigue test. At the same time, the local strain field distribution is obtained through the extensometer.

[0018] Therefore, the present invention employs the above-mentioned multi-field coupling fatigue testing device and method for high-temperature superconducting tapes, which has the following beneficial effects: 1. Achieving multi-field coupled loading: This invention integrates current loading function into the fixture assembly and configures an external permanent magnet, enabling the sample to withstand the effects of current and magnetic field at liquid nitrogen temperature, while simultaneously superimposing hydraulic cyclic mechanical load, thereby realizing coupled fatigue test of electric-magnetic-force-low temperature multi-physics field, breaking through the limitation of existing low temperature fatigue testing machines that cannot perform current and magnetic field loading. 2. Closer to actual service environment: By conducting fatigue tests under multi-physics field conditions, this invention can more realistically simulate the actual service state of superconducting materials such as YBCO in complex electromagnetic-mechanical environments, providing experimental basis for the study of their fatigue life and damage mechanism; 3. Experimental results verify the effectiveness: By comparing the difference in fatigue life under the same mechanical loading conditions with and without current, the device of the present invention can effectively capture the influence of the electromagnetic environment on the fatigue performance of materials, which proves the functional reliability of the device and also reflects its application value in studying the electro-magnetic-mechanical-low temperature coupling effect. 4. Social and economic benefits: This invention provides an advanced experimental method for evaluating the service performance of superconducting materials, and can provide design and life prediction basis for engineering applications such as high-temperature superconducting cables and superconducting magnets, which has important social and economic significance.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1This is a schematic diagram of the overall structure of an embodiment of the high-temperature superconducting tape multi-field coupling fatigue testing device of the present invention; Figure 2 This is a schematic diagram of the magnet assembly and voltage lead structure in an embodiment of the high-temperature superconducting tape multi-field coupling fatigue testing device of the present invention; Figure 3 This is a top view of the permanent magnet in an embodiment of the high-temperature superconducting tape multi-field coupling fatigue testing device of the present invention; Figure 4 This is a schematic diagram of the sample monitoring in an embodiment of the high-temperature superconducting tape multi-field coupling fatigue testing device of the present invention.

[0021] In the diagram: 1. Low-temperature Dewar jar; 2. Upper clamp; 3. Lower clamp; 4. Base; 5. Support column; 6. Support column; 7. Low-temperature resin; 8. Crossbeam; 9. Drive shaft; 10. Current line; 11. Permanent magnet; 12. Lifting platform; 13. Digital image correlation (DIC) measurement system; 14. Magnet frame; 15. Observation window; 16. Voltage lead; 17. Adjustment clamp one; 18. Adjustment bracket; 19. Adjustment clamp two; 20. Fixing clamp; 21. Adjustment bracket; 22. Extensometer; 23. Sample to be tested; 24. Control computer. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout.

[0023] It should be noted that the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such as a process, method, system, product, or server that includes a series of steps or units, not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, products, or devices.

[0024] Similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0025] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0026] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0027] Example: like Figure 1 , Figure 2 As shown, the high-temperature superconducting tape multi-field coupling fatigue testing device of the present invention includes a fatigue testing machine, which is an Instron 8802 hydraulic servo fatigue testing machine. Below the test area of ​​the fatigue testing machine is a fatigue testing machine base 4, around the test area are support columns 5, and above the test area is a fatigue testing machine crossbeam 8. The fatigue testing machine is connected to a control computer 24, which adjusts the experimental parameters via software.

[0028] The fatigue testing machine's test area is equipped with an experimental container, a cryogenic Dewar jar 1, to provide a low-temperature field. Inside the experimental container is a clamp assembly for fixing the test sample 23. The clamp assembly is located directly above the cryogenic Dewar jar 1, which is raised via a lifting platform 12 at its bottom to immerse the test sample 23. The cryogenic Dewar jar 1 has an observation window 15 for monitoring the test sample 23. The clamp assembly includes an upper clamp 2 and a lower clamp 3. The lower clamp 3 is connected to the fatigue testing machine's crossbeam 8 via a support column 6. The upper clamp 2 is connected to the fatigue testing machine's drive shaft 9 via cryogenic resin 7. The lower clamp 3 remains stationary, with pressure provided by the upper clamp 2. During the test, the test sample 23 and the clamp assembly are placed together in the cryogenic Dewar jar 1, which is maintained at a stable low temperature of approximately 77K using liquid nitrogen cooling.

[0029] The clamp assembly is connected to a current component for providing an electric field, and a magnet assembly for providing a magnetic field is installed inside the experimental container. The current component includes a current line 11 connected to the clamp assembly. The current line 11 is synchronously connected to the drive shaft 9 of the fatigue testing machine via an adjusting bracket 21, enabling synchronous movement between the current line 11 and the drive shaft 9. By synchronously connecting the current line 11 to the drive shaft 9, the additional force introduced by the up-and-down movement of the drive shaft 9 while the current line 11 remains relatively stationary during fatigue loading can be effectively eliminated, avoiding interference from the current line 11 to the force sensor, thereby ensuring the accuracy of experimental load measurement and the reliability of experimental results. A force sensor is installed at the connection point between the adjusting bracket 21 and the drive shaft 9 of the fatigue testing machine. This connection position is above the force sensor to avoid direct interference with the force sensor measurement. The upper clamp 2 and the lower clamp 3 are respectively connected to the current source 9 via current lines 10.

[0030] like Figure 2 , Figure 3 As shown, the magnet assembly includes symmetrical permanent magnets 11 located on both sides of the sample 23 to be tested. The symmetrically arranged permanent magnets 11 are separated by a magnet frame 14. The sample 23 to be tested is located within the magnetic field formed by the permanent magnets 11 after they are energized. The permanent magnets 11 are connected to one end of the adjustment bracket 18 via an adjustment clamp 17. The other end of the adjustment bracket 18 is hinged to an adjustment clamp 19, which is connected to the lower clamp 3. The adjustment clamp 17 and the adjustment bracket 18 are connected by a universal joint. By using 3D-printed magnet frames 14 of different thicknesses to adjust the relative position of the permanent magnets 11, the magnetic field strength can be controlled. The sample 23 to be tested is placed within the magnetic field region formed by the permanent magnets 11 and is always in an adjustable external magnetic field environment during the experiment.

[0031] Two fixing clips 20 are provided along the length of the sample 23 to be tested. Voltage leads 16 are connected to the fixing clips 20 respectively. The voltage leads 16 are connected to the fatigue testing machine through an anti-displacement structure. The anti-displacement structure includes a resin column wrapped around the voltage lead 16 (the voltage lead 16 is placed in molten resin and allowed to solidify). The resin column is rigidly connected to the crossbeam 8 of the fatigue testing machine. The voltage lead 16 used to measure the voltage of the sample 23 is fixed with resin and rigidly connected to the crossbeam 8 of the fatigue testing machine, thereby effectively suppressing the lead displacement caused by shaking during the experiment, reducing the influence of the induced voltage generated by the cutting magnetic field on the voltage measurement results, and ensuring the stability and measurement accuracy of the voltage signal.

[0032] One end of the sample 23 is connected to the upper clamp 2 of the Instron 8802 hydraulic servo fatigue testing machine, and the other end is connected to the lower clamp 3. The sample forms a closed loop with the current source through the conductive upper clamp 2 and lower clamp 3, and is located in the magnetic field region and in a low-temperature environment. The Instron 8802 hydraulic servo fatigue testing machine is used to provide accurate mechanical loading. The clamp assembly has been modified to have a current loading function and can be connected to an external DC (AC) current source through the current line 10, thereby realizing the current-carrying fatigue test of the sample 23.

[0033] like Figure 4 As shown, a digital image correlation (DIC) measurement system 13 for monitoring the test sample 23 is installed on the outside of the fatigue testing machine, and an extensometer 22 is installed on the test sample 23. The fatigue testing machine, lifting platform 12, current source, nanovoltmeter, extensometer 22, digital image correlation (DIC) measurement system 13 and control computer 24 are connected by existing electrical connections.

[0034] In the experiment, the YBCO superconducting tape sample (sample 23) was first fixed in the upper clamp 2 and lower clamp 3, and liquid nitrogen was injected to lower the temperature to 77K. Then, cyclic tensile and compressive fatigue loads were applied using an Instron 8802 hydraulic servo fatigue testing machine, while a constant current was applied to the YBCO superconducting tape sample through a current source, and an external constant magnetic field was applied through a permanent magnet 11. This loading process was carried out under the combined effects of low temperature, current, magnetic field, and mechanical cycles, simulating the actual service state of the YBCO superconducting material under the coupling conditions of electro-magnetic-mechanical-low temperature multiphysics fields. The specific experimental steps are as follows: Step 1, Equipment Preparation and System Initialization: Turn on the power supply of the fatigue testing machine and the control computer 24, start the control software through the control computer 24, and reset the initial parameters such as force and displacement to zero to ensure that the equipment is in a stable standby state.

[0035] Step 2, Installation of sample 23 to be tested: The sample 23 to be tested is placed between the upper clamp 2 and the lower clamp 3, and the positions of the upper clamp 2 and the lower clamp 3 are adjusted to clamp and fix the sample 23 to be tested, ensuring that the force is uniform and that the axis of the sample 23 to be tested is consistent with the loading direction.

[0036] Step 3, Current introduction: The output terminal of the current source 9 is connected to the upper clamp 2 and the lower clamp 3 respectively through the current line 10. The upper clamp 2 is connected to the transmission shaft 9 to ensure that the upper current line 11 does not affect the experimental stability during the fatigue loading process, thereby realizing a stable current path in the sample 23 to be tested.

[0037] Step 4, Magnetic field loading: The permanent magnet 11 is placed in the experimental area of ​​the sample 23 to be tested. A 3D printed magnet frame 14 of appropriate thickness is selected in advance to determine the spacing of the permanent magnets 11. The position of one of the permanent magnets 11, the magnet frame 14 and the sample 23 to be tested are adjusted and fixed by adjusting the first adjustment frame (at this time, the second adjustment clamp 19 is fixed on the lower clamp 3, and only the position of the first adjustment frame needs to be adjusted). Then the other permanent magnet 11 is closed so that the direction and strength of the magnetic field formed meet the experimental requirements.

[0038] Step 5, Arrange voltage lead 16: Two voltage leads 16 are clamped along the length of the experimental section in the middle of the sample 23. When coupled with a magnetic field, the voltage leads 16 are spaced approximately 6 cm apart along the length to avoid the influence of the magnetic field on the voltage measurement (when not coupled with a magnetic field, a spacing of approximately 2 cm can be used). The voltage leads 16 are fixed with resin to reduce induced voltage interference caused by their movement in the magnetic field and liquid nitrogen environment. This arrangement is used for four-point voltage measurement, effectively avoiding the influence of contact resistance on the test results.

[0039] Step 6, connect extensometer 22: Connect the extensometer 22 to the sample 23 to be tested. The position of the extensometer 22 is set to be offset from the permanent magnet 11 and the voltage lead 16.

[0040] Step 7, Low-temperature refrigeration: The position of the cryogenic Dewar jar 1 containing liquid nitrogen is raised by the lifting platform 12, so that the liquid nitrogen gradually immerses the sample 23 to be tested and maintains it for at least 30 minutes to ensure that the temperature of the sample 23 to be tested is sufficiently stable in the liquid nitrogen temperature range. Step 8, Apply current: Turn on the nanovoltmeter and current source in sequence to adjust and control the applied current, ensuring that the current loading process and V-I curve test function operate normally.

[0041] Step 9, fatigue loading: The loading curve, cyclic parameters, and target number of fatigue cycles of the fatigue testing machine are set in the control software, and displacement protection and mechanical protection functions are enabled at the same time to ensure that the equipment can be stopped in time when fatigue failure occurs. Then the fatigue testing machine is started to apply a preset cyclic mechanical load to the test sample 23 in the magnetic field environment, and a current of a set amplitude is applied simultaneously to construct a fatigue test environment with multi-physics field coupling of electric-magnetic-force-low temperature.

[0042] Step 10, Critical Current Degradation Measurement: After completing the preset number of fatigue cycles, the experiment was paused, the load on the fatigue testing machine was reduced to zero, and the current was reduced to zero. Then, the critical current of the sample 23 was measured using the four-point method, and its degradation during the fatigue process was recorded.

[0043] Step 11, End of Experiment and Processing of Sample 23: When the final preset number of fatigue cycles is reached or the test sample 23 experiences fatigue fracture, the experiment is terminated; then the current source and nanovoltmeter are turned off, the low-temperature Dewar jar 1 is lowered, and the test sample 23 is taken out after it returns to room temperature; then one of the permanent magnets 11 is removed, and the other permanent magnet 11 and its magnet frame 14 are removed, and finally the fatigue testing machine is turned off.

[0044] Step 12, Image Monitoring: Before implementing image monitoring, the permanent magnet of the magnet assembly needs to be removed first, and then the CCD camera in the digital image correlation (DIC) measurement system 13 is activated. The CCD camera is aimed at the observation window 15 of the cryogenic Dewar jar 1 to record the initiation and propagation of cracks in the sample 23 under test in real time during the fatigue test. At the same time, the local strain field distribution is obtained through the extensometer 22, providing high-precision images and strain data for crack evolution and fatigue failure analysis.

[0045] In the experiments of this embodiment, the fatigue life of YBCO superconducting materials under current-carrying and non-current-carrying conditions was compared. The results show that, under the same cyclic mechanical load and magnetic field conditions, the fatigue life of the current-carrying sample is significantly lower than that of the non-current-carrying sample. For example, under the condition of applying a 90A (0.5Ic) current and an external magnetic field, the fatigue life of the YBCO tape decreases by approximately 35% compared to the non-current state. This indicates that the combined effect of current and magnetic field accelerates crack tip propagation and shortens the material life. These results fully verify that the device of this invention can effectively realize electro-magnetic-mechanical-low-temperature multi-field coupled fatigue experiments and accurately reflect the damage characteristics of superconducting materials under actual service environments.

[0046] In summary, this invention aims to overcome the limitations of existing fatigue testing equipment and proposes a simple and easy-to-implement multi-field coupled fatigue testing device and method for high-temperature superconducting tapes. It can simultaneously apply cyclic mechanical loads, currents, and magnetic fields in a low-temperature environment to meet the needs of mechanical property characterization, fatigue behavior research, and life assessment of superconducting materials and other low-temperature service materials under complex working conditions, and provide reliable technical support for related engineering applications.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A multi-field coupling fatigue testing device for high-temperature superconducting tapes, comprising a fatigue testing machine, characterized in that: The fatigue testing machine's test area includes an experimental container for providing a low-temperature field. Inside the container is a clamp assembly for fixing the sample to be tested. The clamp assembly is connected to a current assembly for providing an electric field. Inside the container is a magnet assembly for providing a magnetic field. An extensometer is mounted on the sample to be tested. A lifting platform is located at the bottom of the container. A digital image correlation (DIC) measurement system for monitoring the sample's operation is located outside the fatigue testing machine. The magnet assembly includes symmetrical permanent magnets located on both sides of the sample, separated by a magnet frame. The current assembly includes current lines connected to the clamp assembly. These current lines are synchronously connected to the fatigue testing machine's drive shaft via an adjusting bracket, enabling synchronized movement between the current lines and the drive shaft. A force sensor is located at the connection between the adjusting bracket and the drive shaft. Two clamps are positioned along the sample's length, each connected to a voltage lead. These voltage leads are connected to the fatigue testing machine via an anti-displacement structure.

2. The high-temperature superconducting tape multi-field coupled fatigue testing device according to claim 1, characterized in that: Below the test area of ​​the fatigue testing machine is the base of the fatigue testing machine, around the test area are supporting columns, and above the test area is the crossbeam of the fatigue testing machine.

3. The high-temperature superconducting tape multi-field coupling fatigue testing device according to claim 2, characterized in that: The experimental container is a low-temperature Dewar flask, with an observation window for monitoring the sample to be tested. The clamp assembly is located directly above the experimental container.

4. The high-temperature superconducting tape multi-field coupling fatigue testing device according to claim 2, characterized in that: The clamping assembly includes an upper clamp located at the top and a lower clamp located at the bottom, with the lower clamp connected to the fatigue testing machine beam via a support column.

5. The high-temperature superconducting tape multi-field coupled fatigue testing device according to claim 4, characterized in that: The upper clamp is connected to the drive shaft of the fatigue testing machine via low-temperature resin.

6. The high-temperature superconducting tape multi-field coupled fatigue testing device according to claim 5, characterized in that: The upper and lower clamps are connected to the current source via current lines.

7. The high-temperature superconducting tape multi-field coupled fatigue testing device according to claim 1, characterized in that: The anti-displacement structure includes a resin column wrapped around the voltage lead, which is rigidly connected to the crossbeam of the fatigue testing machine.

8. The high-temperature superconducting tape multi-field coupled fatigue testing device according to claim 4, characterized in that: The relative position of the permanent magnet is adjusted by using 3D-printed magnet frames of different thicknesses. The permanent magnet is connected to one end of the adjustment bracket via adjustment clamp one, and adjustment clamp two is hinged to the other end of the adjustment bracket. Adjustment clamp two is connected to the lower clamp, and adjustment clamp one and adjustment bracket are connected by universal joint.

9. The high-temperature superconducting tape multi-field coupled fatigue testing device according to claim 1, characterized in that: The fatigue testing machine, lifting platform, current source, nanovoltmeter, extensometer, digital image correlation (DIC) measurement system, and control computer are connected.

10. A method for multi-field coupled fatigue testing of high-temperature superconducting tapes, employing the multi-field coupled fatigue testing apparatus for high-temperature superconducting tapes as described in any one of claims 1-9, characterized in that, Includes the following steps: Step 1, Equipment Preparation and System Initialization: Turn on the power to the fatigue testing machine and the control computer, start the control software through the control computer, and set the initial parameters of force and displacement to zero. Step 2, Sample installation: Place the sample to be tested between the upper and lower clamps, and adjust the positions of the upper and lower clamps to clamp and fix the sample to be tested. Step 3, Current introduction: Connect the output terminal of the current source to the upper clamp and the lower clamp respectively through current lines; Step 4, Magnetic field loading: The permanent magnets are placed in the experimental area of ​​the sample to be tested. A 3D printed magnet frame of appropriate thickness is selected in advance to determine the spacing between the permanent magnets. The position of one permanent magnet, the magnet frame and the sample to be tested is adjusted and fixed by the adjustment frame. Then the other permanent magnet is closed. Step 5, Voltage Lead Arrangement: Two voltage leads are clamped along the length of the experimental section in the middle of the sample to be tested for four-point voltage measurement. Step 6, connect the extensometer: Connect the extensometer to the sample to be tested, and position the extensometer separately from the permanent magnet and voltage leads; Step 7, Low-temperature refrigeration: The position of the cryogenic Dewar container filled with liquid nitrogen is raised by a lifting platform, so that the liquid nitrogen gradually immerses the sample to be tested. Step 8, Apply current: Turn on the nanovoltmeter and current source in sequence to adjust and control the applied current; Step 9, fatigue loading: The loading curve, cyclic parameters and target fatigue cycle number of the fatigue testing machine are set in the control software. The fatigue testing machine is started and a preset cyclic mechanical load is applied to the test sample in the magnetic field environment. At the same time, a current of a set amplitude is applied, thereby constructing a fatigue test environment with coupling of electric-magnetic-force-low temperature multi-physics fields. Step 10, Critical Current Degradation Measurement: After completing the preset number of fatigue cycles, the experiment is paused, the load on the fatigue testing machine is reduced to zero, the current is reduced to zero, and then the critical current of the sample is measured using the four-point method, and its degradation during the fatigue process is recorded. Step 11, End of Experiment and Sample Processing: The experiment is terminated when the final preset number of fatigue cycles is reached or when the test sample undergoes fatigue fracture. Then, the current source and nanovoltmeter are turned off, the cryogenic Dewar jar is lowered, and the test sample is taken out after it returns to room temperature. The permanent magnet is removed, and the fatigue testing machine is turned off. Step 12, Image Monitoring: The CCD camera in the digital image correlation (DIC) measurement system is activated, and the CCD camera is aimed at the observation window of the cryogenic Dewar jar to record the initiation and propagation of cracks in the sample under test in real time during the fatigue test. At the same time, the local strain field distribution is obtained through the extensometer.

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