Method and device for testing fatigue crack growth rate of metal material based on temperature gradient change

Abstract

The invention discloses a method and device for testing the fatigue crack growth rate of a metal material based on temperature gradient change, and relates to the technical field of metal material detection. Mounting a constant low-temperature component and a constant high-temperature component close to two ends of the sample respectively; pasting a plurality of thermocouples on the middle surface of the sample; a magnetic powder dynamic moving assembly is installed on the surface of the sample, and a constant-temperature state is given to magnetic powder; loading a bidirectional tension-compression fatigue testing machine along the through hole of the sample; a thermal imager is arranged far away from the parallel sample, and a thermal imaging image is shot; according to the data, the fatigue crack growth rate of the sample at the corresponding temperature is obtained; according to the method, the fatigue crack growth rate of the metal material can be rapidly tested, meanwhile, the temperature gradient is formed in the sample, the influence of the temperature on the crack growth rate can be obtained in different temperature areas, the device required by the whole test is simple in structure, low in cost and convenient to load and disassemble, and the whole efficiency of the test is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material detection, and in particular relates to a method and device for testing the fatigue crack growth rate of a metal material based on temperature gradient changes. Background Art

[0002] Fatigue is a phenomenon in which cracks slowly form inside a material during long-term use due to stress in different directions and internal defects of the material, and gradually expand until the material fails.

[0003] It is well known that metal fatigue failure is one of the main causes of failure in engineering structures and machinery. The complete process of fatigue in metal materials is the process of crack formation under the action of cyclic stress, crack expansion, and ultimately reaching the critical size required for fracture. Therefore, the fatigue mechanism of metal materials includes the mechanism of crack initiation and stable expansion in metal materials under the action of alternating stress. Therefore, it is necessary to accurately analyze the initiation and stable expansion of cracks in order to accurately monitor the fatigue life of the material and fully analyze the metal fatigue failure process. The commonly used test method is to evaluate the fatigue performance and remaining life of metal materials through experiments such as real-time measurement of crack extension length under metal fatigue alternating loads. The specimen forms currently specified by international standards mainly include three-point bending specimens and compact tensile specimens. Usually, the expansion of metal fatigue cracks develops along the direction of the pre-existing crack, which can accurately measure the crack length and crack growth rate.

[0004] Monitoring crack initiation and expansion using traditional microscope observation and replication methods requires manual operation, which is not only inefficient but also easily affected by subjective factors of the inspectors. It can neither guarantee the efficiency and accuracy requirements of the inspection nor meet the requirements of the experiment.

[0005] In response to the above problems, Chinese patent CN201510225456.2 discloses an observation system for fatigue crack propagation in metal materials, which belongs to the field of experimental observation systems. An observation system for fatigue crack propagation in metal materials, comprising an in-situ biaxial tension and compression fatigue testing machine, a camera, a fixed bracket and a computer; the camera is suspended and fixed above the in-situ biaxial tension and compression fatigue testing machine by a fixed bracket, and the fixed bracket has horizontal and vertical adjustment functions; the computer is connected to the camera and is used to store the test process captured by the camera. Although the above-mentioned disclosed technology has changed the traditional manual measurement operation, it directly uses a camera to shoot and record. In the later computer image processing, since there is no mark in the image, there are still deficiencies in efficiency and accuracy after the test observation based on the above method. Summary of the Invention

[0006] The purpose of the present invention is to provide a method and device for testing the fatigue crack growth rate of metal materials based on temperature gradient changes. This method can quickly test and obtain the fatigue crack growth rate of metal materials. At the same time, combined with the formation of a temperature gradient inside the specimen, the influence of temperature on the crack growth rate can be obtained in different temperature zones. The device required for the overall test is simple in structure, low in cost, easy to load and unload, and effectively improves the overall efficiency of the test.

[0007] To achieve the above object, the present invention provides the following technical solutions: The specific steps include: S1. Prepare the specimen. The specimen is an H-shaped structure with symmetrical perforations at both ends and prefabricated cracks added to the sides of the specimen. S2. Install a constant low temperature component and a constant high temperature component near both ends of the specimen; S3. Paste several thermocouples on the middle surface of the specimen. The pasting positions extend along the length of the specimen and are pasted at equal intervals. The pasting interval of the thermocouples is set according to the position of the prefabricated crack in step 1, specifically 10 to 30 mm. S4. Install a magnetic powder dynamic moving assembly on the sample surface and give the magnetic powder a constant temperature state; S5. Load the biaxial tension and compression fatigue testing machine along the perforation of the specimen, open the constant low temperature component and the constant high temperature component, and start the tensile device; S6. Set up a thermal imager at a distance from the parallel specimen and take thermal images every 1-3 minutes while recording the crack initiation load and specimen fracture load. S7. Obtain the fatigue crack growth rate of the sample at the corresponding temperature based on the crack initiation position, the temperature data recorded by the thermocouple, and the crack growth length data inside the thermal imaging image at different times.

[0008] In the present invention, since the crack propagation of the metal specimen will propagate perpendicularly to the load direction after initiation during fatigue testing, a temperature gradient will be formed inside the specimen in a direction perpendicular to the crack propagation direction, and multiple thermocouples are set to monitor the temperature values ​​in different length sections of the specimen. The crack propagation temperature in this length section is quantitative, and its crack propagation rate can be observed. Compared with the crack propagation rate in other length sections, the crack propagation rate of the specimen at different temperatures can be obtained based on the temperature trapezoidal value as a variable.

[0009] Preferably, the method for obtaining the fatigue crack growth rate in step S7 includes: obtaining the moving position of the magnetic powder based on two thermal imaging images within the interval time, obtaining the change in crack growth length based on the moving position, and obtaining the change rate based on the change length within the change time, which is the crack growth rate, wherein the thermal imaging image is divided into multiple areas according to the placement position of the thermocouple, and each thermocouple corresponds to one of the areas.

[0010] For specimens loaded with low constant temperature and high constant temperature, the thermal imaging image shows different temperature gradient areas. After the crack is generated and during the expansion process, the specimen with a temperature higher than the overall specimen temperature enters the crack. Therefore, the position of the magnetic powder can be visually marked in the thermal imaging image, and the end point of the crack extension can be visually displayed. Combining different thermal imaging images at intervals, its change rate can be obtained. At the same time, different temperature gradient areas are directly monitored by thermocouples to obtain temperature data. Therefore, the crack expansion rate can be obtained in different temperature areas, and the fatigue crack expansion test results of metal materials can be obtained quickly and accurately.

[0011] Preferably, the magnetic powder used in the magnetic powder dynamic moving component in step S4 is manganese ferrite nano magnetic powder or iron oxide nano magnetic powder.

[0012] Among them, the type of magnetic powder is disclosed, which is nano-level magnetic powder. Since the spatial size of crack expansion is generally at the micron level, the use of nano-sized magnetic powder can ensure that the magnetic powder can smoothly enter the crack.

[0013] The present invention also provides a device for testing the fatigue crack growth rate of metal materials based on temperature gradient changes, which is applied to the above-mentioned testing method, including a specimen, wherein the two ends of the specimen are detachably connected to a constant low-temperature component and a constant high-temperature component, and the two sides of the middle of the specimen are detachably connected to a magnetic powder dynamic movement component, and the constant low-temperature component and the constant high-temperature component each include two relatively connected dielectric carrier frames.

[0014] Preferably, a U-shaped rod is fixedly inserted into the interior of one of the medium carrier frames, and a threaded end is provided at the end of the U-shaped rod passing through the medium carrier frame, and a through hole is provided inside the other medium carrier frame for the threaded end of the U-shaped rod to pass through, and a locking nut is threadedly connected to the end of the threaded end. A conduit is fixedly inserted into one end of the medium carrier frame fixedly connected to the U-shaped rod, and a telescopic rubber plate is fixed on the side, and the width of the telescopic rubber plate is smaller than the width of the medium frame.

[0015] Preferably, a spring is fixed to the end of the locking nut facing the medium carrier frame, and a pad is fixed to the end of the spring away from the locking nut, and both the spring and the pad are sleeved outside the threaded end.

[0016] Preferably, the magnetic powder dynamic movement component includes a first fixed frame and a second fixed frame, the first fixed frame and the second fixed frame are respectively installed on both sides of the sample, and connecting ear plates are fixed at both ends of the first fixed frame and the second fixed frame. The first fixed frame and the second fixed frame are fixed by connecting ear plate screws. The first fixed frame is used for placing magnetic powder, and an opening is provided at the top of the frame, a rubber plug is installed inside the opening, a heating rod is provided on one side of the opening and is plugged into the top of the first fixed frame, and a conductive coil is provided inside the second fixed frame.

[0017] Preferably, a bearing seat is fixed to the first fixed frame away from the sample side, the bearing seats are symmetrically arranged, and a rotating shaft is rotatably connected inside the bearing seat. One end of the rotating shaft extends into the interior of the first fixed frame, and a flexible cloth strip is fixed to the side of the extended end. Several flexible cloth strips are provided along the circumferential direction of the rotating shaft. A servo motor is connected to the other end of the rotating shaft. A mounting seat is fixed to the bottom of the two servo motors, and the servo motor screws are fixed inside the mounting seat. A fixed cover is connected to the outside of the two mounting seats, and a heat dissipation mesh groove is provided on the side of the fixed cover.

[0018] Preferably, a metal rod is inserted in the middle of the second fixing frame, a conductive coil is wound around the outside of the metal rod, two ends of the conductive coil are connected to a power supply module, and the power supply module is screwed onto the side of the second fixing frame.

[0019] In summary, the beneficial technical effects of the present invention are as follows: a temperature gradient is formed inside the sample by using a low constant temperature component and a high constant temperature component, thereby forming different temperature zones. For samples loaded with low constant temperature and high constant temperature, they appear as gradient zones with different temperatures in the thermal imaging image. After the crack is generated and during its expansion, the dynamic movement of the magnetic powder is utilized. Since the magnetic powder with a temperature higher than that of the entire sample enters the crack, the position of the magnetic powder can be visually marked in the thermal imaging image, and the end point of the length of the crack expansion can be visually displayed. Combined with different thermal imaging images at intervals, its rate of change can be obtained. At the same time, different temperature gradient zones are directly monitored by thermocouples to obtain temperature data. Therefore, the crack expansion rate can be obtained inside different temperature zones, and the test results of the influence of temperature on the crack expansion rate can also be obtained, and the fatigue crack expansion test results of metal materials can be obtained quickly and accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification, but do not constitute a limitation of the present invention. In the accompanying drawings: Figure 1 This is a flow chart of a method for testing fatigue crack growth rate of metal materials based on temperature gradient change according to this embodiment; Figure 2 This is a schematic diagram of a sample installation state of a device for testing fatigue crack growth rate of metal materials based on temperature gradient change in this embodiment; Figure 3 This is a device for testing the fatigue crack growth rate of metal materials based on temperature gradient changes in this embodiment. Figure 2 Explosion diagram of Figure 4 This is a device for testing the fatigue crack growth rate of metal materials based on temperature gradient changes in this embodiment. Figure 3 Schematic diagram from another perspective; Figure 5This is a device for testing the fatigue crack growth rate of metal materials based on temperature gradient changes in this embodiment. Figure 4 A in the middle is an enlarged schematic diagram; Figure 6 This is a schematic diagram of the sample structure of a device for testing the fatigue crack growth rate of metal materials based on temperature gradient changes in this embodiment.

[0021] In the figure: 1. Sample; 2. Thermocouple; 3. Dielectric carrier frame; 4. U-shaped rod; 5. Threaded end; 6. Through hole; 7. Locking nut; 8. Conduit; 9. Telescopic rubber plate; 10. Spring; 11. Pad; 12. First fixed frame; 13. Second fixed frame; 14. Connecting ear plate; 15. Opening; 16. Rubber plug; 17. Heating rod; 18. Conductive coil; 19. Rotating shaft; 20. Flexible cloth strip; 21. Servo motor; 22. Mounting seat; 23. Bearing seat; 24. Fixing cover; 25. Heat dissipation mesh slot; 26. Metal rod; 27. Power supply module; 28. Prefabricated crack. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below with reference to the accompanying drawings.

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] See also Figure 1-6 , the present invention provides a technical solution: In this embodiment, a specific structure of an apparatus for testing the fatigue crack growth rate of a metal material based on temperature gradient changes is provided, specifically including a sample 1, wherein both ends of the sample 1 are detachably connected to a constant low-temperature component and a constant high-temperature component, and both sides of the middle of the sample 1 are detachably connected to a magnetic powder dynamic movement component, and the constant low-temperature component and the constant high-temperature component each include two relatively connected dielectric carrier frames 3.

[0025] A U-shaped rod 4 is fixedly inserted into the interior of one of the medium carrier frames 3, and a threaded end 5 is provided at the end of the U-shaped rod 4 passing through the medium carrier frame 3. A through hole 6 is provided inside the other medium carrier frame 3 for the threaded end 5 of the U-shaped rod 4 to pass through, and a locking nut 7 is threadedly connected to the end of the threaded end 5 passing through. A guide tube 8 is fixedly inserted at one end of the medium carrier frame 3 fixedly connected to the U-shaped rod 4, and a telescopic rubber plate 9 is fixed on the side. The width of the telescopic rubber plate 9 is smaller than the width of the medium frame. The medium carrier frame 3 is installed on both sides of the sample 1 and is arranged near both ends of the sample 1. By placing the medium carrier frame 3 with the U-shaped rod 4 on the surface of the sample 1, the other medium carrier frame 3 is inserted into the U-shaped rod 4 along its through hole 6. The two medium carrier frames 3 are threadedly fixed by a locking spring 10, and at the same time, the two medium carrier frames 3 are in contact with each other through a retractable rubber plate 9, thereby increasing the sealing of the connection between the two. At the same time, the retractable rubber plate 9 is smaller than , further improving the stability of its contact. At the same time, a spring 10 is fixed to the end of the locking nut 7 facing the medium carrier frame 3, and a pad 11 is fixed to the end of the spring 10 away from the locking nut 7. The spring 10 and the pad 11 are both sleeved on the outside of the threaded end 5. By utilizing the retractability of the spring 10, samples 1 of different thicknesses can be placed between the two medium carrier frames 3, and at the same time, its tensile property is improved to avoid damage to the medium carrier frame 3 due to the impact after the sample 1 breaks during fatigue testing.

[0026] The medium frame is connected to a conduit 8, which can be connected to the supply of cold medium or hot medium. In this embodiment, liquid nitrogen is used as the cold medium for low constant temperature, and hot water is used as the hot medium for high constant temperature. The temperature can be provided in the range of 40°C-80°C. By loading the above-mentioned cold medium and hot medium at both ends of the sample 1, a temperature gradient can be formed in the length direction of the sample 1.

[0027] Specifically, the magnetic powder dynamic movement assembly includes a first fixed frame 12 and a second fixed frame 13. The first fixed frame 12 and the second fixed frame 13 are respectively installed on both sides of the sample 1. Connecting ear plates 14 are fixed at both ends of the first fixed frame 12 and the second fixed frame 13. The first fixed frame 12 and the second fixed frame 13 are fixed with screws through the connecting ear plates 14. The first fixed frame 12 is used to place magnetic powder. An opening 15 is provided at the top of the first fixed frame. A rubber plug 16 is installed inside the opening 15. A heating rod 17 is provided on one side of the opening 15 and is plugged into the top of the first fixed frame 12. A conductive coil 18 is provided inside the second fixed frame 13. The first fixed frame 12 and the second fixed frame 13 are fixed by bolts. Bolts are inserted into the connecting ear plates 14 and are tightened and installed by nuts. The length of the bolts can be changed according to the thickness of the sample 1.

[0028] A bearing seat 23 is fixed to the side of the first fixed frame 12 away from the sample 1. The bearing seat 23 is symmetrically arranged. A rotating shaft 19 is rotatably connected inside the bearing seat 23. One end of the rotating shaft 19 extends into the interior of the first fixed frame 12. A flexible cloth strip 20 is fixed to the side of the extended end. Several flexible cloth strips 20 are provided along the circumferential direction of the rotating shaft 19. A servo motor 21 is connected to the other end of the rotating shaft 19. A mounting seat 22 is fixed to the bottom of the two servo motors 21. The servo motors 21 are screwed inside the mounting seat 22. A fixing cover 24 is connected to the outside of the two mounting seats 22. A heat dissipation mesh slot 25 is provided on the side of the fixing cover 24.

[0029] A metal rod 26 is inserted in the middle of the second fixed frame 13 , and the conductive coil 18 is wound around the outside of the metal rod 26 . Both ends of the conductive coil 18 are connected to power supply modules 27 , which are screwed onto the side of the second fixed frame 13 .

[0030] Magnetic powder is added to the inside of the first fixed frame 12. After the servo motor 21 is driven, the servo motor 21 drives the rotating shaft 19 to rotate. After the rotating shaft 19 rotates, the flexible cloth strip 20 on its side is driven to rotate, stirring the magnetic powder inside the first fixed frame 12 so that it remains in a suspended state to avoid sedimentation. At the same time, the first fixed frame 12 is made of plastic material to avoid adhesion of magnetic powder. A conductive coil 18 is set inside the second fixed frame 13. The conductive coil 18 is wound around the outside of the metal rod. After the conductive coil 18 is energized by the power supply module 27, the structure of the conductive coil and the metal rod can be The second fixed frame 13 generates a magnetic field, thereby adsorbing the magnetic powder. At the same time, the magnetic powder can be given a surface temperature by the heating rod 17 in the first fixed frame 12. After the magnetic powder is adsorbed, it moves toward the side of the sample 1. After a crack is generated on the surface of the sample 1, the magnetic powder enters the crack. Due to the tortuous path inside the crack, the magnetic powder inevitably adheres to the inside of the crack, and the magnetic powder gives a surface temperature. The position of the magnetic powder can be fully presented in the thermal imaging image. During the interval period, the length of the crack expansion during the interval period can be obtained through the position of the magnetic powder displayed on different thermal imaging images.

[0031] The temperature of the magnetic powder is higher than the temperature provided by the high constant temperature component.

[0032] The test was conducted using a biaxial tension and compression fatigue testing machine and a conventional thermal imager. The following operating steps were used: S1. Prepare the specimen. The specimen has an H-shaped structure with symmetrical perforations at both ends. Prefabricated cracks are added to the sides of the specimen. The spacing between the prefabricated cracks is 10 mm. S2. Install a constant low temperature assembly and a constant high temperature assembly near both ends of the specimen. Secure the constant low temperature assembly and the constant high temperature assembly with locking nuts, keeping the internal expansion and contraction rubber plates in a compressed state to ensure sealing and prevent internal temperature leakage. S3. Paste several thermocouples on the middle surface of the specimen. The pasting positions extend along the length of the specimen and are pasted at equal intervals. The pasting positions of the thermocouples correspond to the positions of the prefabricated cracks, and the intervals are all 10 mm. S4. Install a magnetic powder dynamic moving assembly on the sample surface and give the magnetic powder a constant temperature state; S5. Load the biaxial tension and compression fatigue testing machine along the perforation of the specimen, open the constant low temperature component and the constant high temperature component, and start the tensile device; S6. Set up a thermal imager at a distance from the parallel specimen and take thermal images every 1 minute while recording the crack initiation load and specimen fracture load. S7. Based on the crack initiation position, the temperature data recorded by the thermocouple, and the crack extension length data within the thermal imaging images at different times, the movement position of the magnetic powder can be obtained based on the two thermal imaging images within the interval time. The change in the crack extension length is obtained based on the movement position. Based on the change in length within the change time, the change rate is obtained, which is the crack extension rate. The thermal imaging image is divided into multiple areas according to the placement of the thermocouples, and each thermocouple corresponds to one of the areas.

[0033] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0034] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for testing the fatigue crack growth rate of metal materials based on temperature gradient changes, characterized in that: The specific steps include: S1. Prepare a sample (1), wherein the sample (1) is an H-shaped structure, symmetrical perforations are provided at both ends of the sample (1), and prefabricated cracks are added to the side of the sample; S2, installing a constant low temperature component and a constant high temperature component near both ends of the sample (1); S3, affixing a plurality of thermocouples (2) on the middle surface of the sample (1), with the pasting positions extending along the length direction of the sample (1) and pasting at equal intervals. The pasting interval of the thermocouples (2) is set according to the position of the prefabricated crack in step 1, specifically 10 to 30 mm; S4, installing a magnetic powder dynamic moving assembly on the surface of the sample (1) and giving the magnetic powder a constant temperature state; S5, loading the biaxial tension and compression fatigue testing machine along the perforation of the specimen (1), opening the constant low temperature component and the constant high temperature component, and starting the tensile device; S6. Set up a thermal imager at a distance from the parallel specimen (1), take thermal imaging images every 1-3 minutes, and simultaneously record the crack initiation load and the fracture load of the specimen (1); S7. Obtain the fatigue crack growth rate of the sample (1) at the corresponding temperature based on the crack initiation position, the temperature data recorded by the thermocouple (2), and the crack growth length data inside the thermal imaging image at different times.

2. The method according to claim 1, characterized in that The method for obtaining the fatigue crack growth rate in step S7 includes: obtaining the moving position of the magnetic powder based on two thermal imaging images within an interval time, obtaining the change in crack growth length based on the moving position, and obtaining the change rate based on the change in length within the change time, which is the crack growth rate, wherein the thermal imaging image is divided into multiple areas according to the placement position of the thermocouple (2), and each thermocouple (2) corresponds to one of the areas.

3. The method according to claim 1, characterized in that The magnetic powder used in the magnetic powder dynamic moving component in step S4 is manganese ferrite nano magnetic powder or iron oxide nano magnetic powder.

4. A device for testing the fatigue crack growth rate of metal materials based on temperature gradient changes, applied to the method of claim 1, characterized in that: The invention comprises a sample (1), wherein both ends of the sample (1) are detachably connected to a constant low temperature component and a constant high temperature component, and both sides of the middle of the sample (1) are detachably connected to a magnetic powder dynamic movement component, and the constant low temperature component and the constant high temperature component each comprise two relatively connected medium carrier frames (3).

5. The device according to claim 4, characterized in that A U-shaped rod (4) is fixedly inserted into one of the medium carrier frames (3), and a threaded end (5) is provided at the end of the U-shaped rod (4) passing through the medium carrier frame (3). A through hole (6) is provided inside the other medium carrier frame (3) for the threaded end (5) of the U-shaped rod (4) to pass through, and a locking nut (7) is threadedly connected to the end of the threaded end (5) passing through. A guide tube (8) is fixedly inserted into one end of the medium carrier frame (3) fixedly connected to the U-shaped rod (4), and a telescopic rubber plate (9) is fixed on the side, and the width of the telescopic rubber plate (9) is smaller than the width of the medium frame.

6. The device according to claim 5, characterized in that A spring (10) is fixed to the end of the locking nut (7) facing the medium carrier frame (3), and a pad (11) is fixed to the end of the spring (10) away from the locking nut (7). Both the spring (10) and the pad (11) are sleeved outside the threaded end (5).

7. The device according to claim 4, characterized in that The magnetic powder dynamic moving component comprises a first fixed frame (12) and a second fixed frame (13). The first fixed frame (12) and the second fixed frame (13) are respectively installed on both sides of the sample (1). Connecting ear plates (14) are fixed at both ends of the first fixed frame (12) and the second fixed frame (13). The first fixed frame (12) and the second fixed frame (13) are fixed by screws of the connecting ear plates (14). The first fixed frame (12) is used for placing magnetic powder. An opening (15) is provided at the top of the first fixed frame. A rubber plug (16) is installed inside the opening (15). A heating rod (17) plugged into the top of the first fixed frame (12) is provided on one side of the opening (15). A conductive coil (18) is provided inside the second fixed frame (13).

8. The device according to claim 7, characterized in that A bearing seat (23) is fixed on the side of the first fixed frame (12) away from the sample (1). The bearing seats (23) are symmetrically arranged. A rotating shaft (19) is rotatably connected inside the bearing seat (23). One end of the rotating shaft (19) extends into the interior of the first fixed frame (12). A flexible cloth strip (20) is fixed on the side of the extending end. Several flexible cloth strips (20) are provided along the circumferential direction of the rotating shaft (19). A servo motor (21) is connected to the other end of the rotating shaft (19). A mounting seat (22) is fixed to the bottom of the two servo motors (21). The servo motors (21) are screwed into the interior of the mounting seat (22). The two mounting seats (22) are externally connected to a fixing cover (24). A heat dissipation mesh slot (25) is provided on the side of the fixing cover (24).

9. The device according to claim 7, characterized in that A metal rod (26) is inserted into the middle of the second fixed frame (13), a conductive coil (18) is wound around the outside of the metal rod (26), two ends of the conductive coil (18) are connected to a power supply module (27), and the power supply module (27) is screwed onto the side of the second fixed frame (13).

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