Four-point bending stress corrosion test fixture for irradiation sample in high-temperature molten salt environment and test method thereof

Abstract

The invention discloses a four-point bending stress corrosion test fixture for an irradiation sample in a high-temperature molten salt environment and a test method of the four-point bending stress corrosion test fixture. The fixture comprises a main stretching rod, a kettle cover, a position deviation adjuster, a counter-force frame, four secondary stretching rods, a counter-force plate, a loading block support, a sample table, a positioning pin, a loading block and a fixing pin, a reverse stretching mode is adopted, a main stretching rod is pulled upwards through a servo stretching machine, a secondary stretching rod, a sample table and a sample are sequentially driven to move upwards, the sample is subjected to counter-acting force of a loading block in the upward moving process, the lower surface is bent, and tensile stress is generated; therefore, the material cracking research of the sample under the joint coupling of irradiation, high-temperature molten salt corrosion and stress is realized. According to the method, the limitation of an existing research scheme is broken through, the relationship between the sample surface stress and the applied load is established by adopting a four-point bending method and combining finite element analysis, the stress of a sample irradiation surface is strictly controlled, the research of multi-environment coupling is realized, and the period of experimental research and the cost of a single experiment are reduced.

Description

Technical Field

[0001] This invention relates to the study of material performance degradation in the field of nuclear energy materials research involving multi-environment coupling, and particularly to a four-point bending stress corrosion test fixture and its test method for irradiated samples in a high-temperature molten salt environment. Background Technology

[0002] Key structural materials in molten salt reactors operate under harsh environments characterized by high temperatures, radiation, corrosion, and stress. The combined effects of these multiple factors easily degrade the alloy's properties, significantly threatening the reactor's operational safety. Currently, no mature and effective technical solutions have been developed for addressing the coupled effects of radiation, high-temperature molten salt corrosion, and stress. The following are some potential research pathways:

[0003] 1) Samples are prepared using neutron irradiation, and multi-environment coupling studies are conducted in a molten salt environment. Thanks to the large penetration depth of neutron irradiation, alloys can be processed into standard-sized mechanical samples, enabling relevant tests to be performed on conventional tensile testing machines. However, this approach suffers from problems such as long irradiation cycles, high costs, and strong sample radioactivity, leading to increased experimental management difficulties and persistently high overall research costs.

[0004] 2) Ion irradiation is used instead of neutron irradiation, and the samples are immersed in a molten salt environment after irradiation. Although this method can couple irradiation with high-temperature molten salt corrosion, it does not introduce stress factors, making it difficult to explore the mechanism of stress on alloy performance degradation and failing to meet the core requirements of multi-environment coupling research.

[0005] 3) Constructing an in-situ experimental system at the ion accelerator terminal to achieve simultaneous coupling of ion irradiation, high-temperature molten salt corrosion, and stress. However, no such dedicated facility has yet been built in China. This approach requires first constructing a dedicated beamline on the ion accelerator, and then investing heavily in building a molten salt environment simulation system and stress application device adapted to the beamline, with overall construction costs reaching several million yuan. Furthermore, the experiment is highly dependent on the ion accelerator's time resources, is difficult to operate, and has extremely high costs per experiment, making widespread application difficult.

[0006] Therefore, it is necessary to develop a stress corrosion testing method that is suitable for small-sized ion-irradiated samples, enables precise coupling of irradiation-high-temperature molten salt corrosion-stress, and is low-cost and easy to operate. Summary of the Invention

[0007] The purpose of this invention is to provide a four-point bending stress corrosion test fixture and its test method for irradiated samples in a high-temperature molten salt environment, thereby solving the problems of existing technologies that are difficult to achieve effective coupling research of irradiation, high-temperature molten salt corrosion and stress, and have problems such as long experimental cycle, high cost, high operation difficulty or imperfect function.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] According to a first aspect of the present invention, a four-point bending stress corrosion test fixture for irradiated samples in a high-temperature molten salt environment is provided, comprising: a main tension rod, a vessel lid, a position deviation adjuster, a reaction frame, four secondary tension rods, a reaction plate, a loading block holder, a sample stage, positioning pins, a loading block, and fixing pins; wherein, the reaction frame is installed at the bottom of the vessel lid, the reaction plate is horizontally fixed below the reaction frame, the loading block holder is installed at the bottom of the reaction plate, and the loading block is detachably installed in the loading block holder by fixing pins, with a pre-existing gap between the loading block and the loading block holder; the sample stage is drivenly connected to the main tension rod through the four secondary tension rods, and the secondary tension rods are connected to the sample stage by a positioning step. The flat-head structure is matched, and the four secondary tension rods are kept at the same height through the connecting block; the positioning pins are symmetrically arranged on both sides of the sample stage for precise sample positioning; the position deviation adjuster adopts a cylindrical pin structure and is set between the main tension rod and the connecting rod, providing freedom in the YZ plane; the reverse tensioning method is adopted, and the main tension rod is pulled upward by the servo tensioning machine, which in turn drives the secondary tension rods, the sample stage and the sample to move upward in sequence. During the upward movement, the sample is subjected to the reaction force of the loading block and the lower surface bends, generating tensile stress, thereby realizing the study of material cracking of irradiated samples under the combined coupling of irradiation, high temperature molten salt corrosion and stress.

[0010] Preferably, the loading block has a cuboid head and a top that gradually tapers away from the head. The top has two circular contact points with a diameter of 2 mm, and the center-to-center distance between the two circular contact points is 2 mm. The cuboid head is detachably connected to the loading block holder by a fixing pin, and a gap is reserved between the cuboid head and the loading block holder, which allows the loading block to have rotational freedom around the fixing pin. The circular contact points are used to contact the surface of small-sized samples to transfer loads. The rotational freedom is adapted to sample thickness deviations or tension axis eccentricity to ensure uniform contact between the two circular contact points and the upper surface of the sample.

[0011] Preferably, the sample stage includes: symmetrically arranged protrusions on both sides and a recessed portion in the middle. A rectangular groove is provided in the center of the recessed portion, and the two ends of the rectangular groove are connected to the recessed portion by arc segments. The arc segments form two-point contact with the lower surface of the sample, and the circular contact points form two-point contact with the upper surface of the sample, which together constitute a four-point bending clamp for the sample.

[0012] Preferably, each of the protrusions on the sample stage is provided with a through hole for positioning, through which a positioning pin passes to clamp the sample. The positioning pin controls the forward distance by rotating synchronously, so that the center of the sample is precisely aligned with the midpoint of the line connecting the two circular contact points of the loading block, thereby realizing continuous tracking testing of the sample corrosion surface.

[0013] Preferably, the position deviation adjuster includes an adjuster body, a connecting block, and an adjuster pin. The adjuster body has a rectangular side slot along its side for the connecting block to enter. The adjuster body has a through central hole in its middle. The adjuster body has a first pin hole, and the connecting block has a second pin hole in its middle. The connecting block is fitted into the central hole, and the first pin hole and the second pin hole are aligned. The adjuster pin passes through the first and second pin holes to form a flexible connection between the connecting block and the adjuster body that can rotate at a small angle in the YZ plane.

[0014] Preferably, the upper and lower sides of the adjuster body are respectively provided with an upper external threaded hole and an lower external threaded hole for fixed connection with the main tension rod and the connecting rod to transfer load. The upper external threaded hole is reserved for a small translation space. The inner side of the connecting block, below the second pin hole, is provided with a lower internal threaded hole, which is also reserved for a small translation space. The flexible connection achieved by the adjuster body, connecting block, main tension rod, connecting rod and adjuster pin allows the position deviation adjuster to compensate for contact deviation caused by sample thickness deviation, indenter corrosion or tension shaft eccentricity, ensuring uniform contact between the two circular contact points of the loading block and the upper surface of the small sample in the four-point bend test, and adapting to the stress corrosion test scenario in the high temperature molten salt environment.

[0015] According to a second aspect of the present invention, a method for four-point bending stress corrosion testing of a sample irradiated in a high-temperature molten salt environment is provided, comprising the following steps:

[0016] 1) Prepare small-sized four-point bend samples, and perform grinding and electrochemical polishing on the sample surface;

[0017] 2) The sample prepared in step 1) is subjected to ion irradiation treatment;

[0018] 3) Fix the irradiated sample to the sample stage of the fixture using positioning pins, so that the center of the sample is aligned with the middle position of the two circular contact points of the loading block;

[0019] 4) In the glove box, put the molten salt into the pure nickel crucible and seal it. Transfer it to the vessel body and fix it. After sealing the vessel body, evacuate and introduce high-purity Ar gas to establish a micro-positive pressure environment.

[0020] 5) Heat the vessel to bring the molten salt to the set temperature and stabilize it, then adjust the position of the vessel lid to immerse the sample in the liquid molten salt;

[0021] 6) By driving the main tensile rod with a servo tensile machine and combining the functional relationship between load and sample surface stress obtained from finite element analysis, a fixed load is applied to generate bending tensile stress in the sample, thereby realizing the coupled test of irradiation-high temperature molten salt corrosion-stress.

[0022] 7) After the test, while the molten salt is still in a liquid state, lift the lid of the vessel and remove the sample stage and sample from the molten salt.

[0023] Preferably, in step 2), the sample is placed on an ion irradiation terminal, and different types of ion irradiation, irradiation energy and flux rate are selected according to different experimental requirements.

[0024] Preferably, in step 4), the vacuum level is controlled at 1×10⁻⁶. 3 Pa, high-purity Ar gas purity ≥99.999%, the pressure of the micro-positive pressure environment inside the reactor is 1-5 bar; the molten salt temperature stabilization time in step 5) is 10-20 minutes.

[0025] Preferably, in step 6), the finite element analysis pre-establishes the corresponding functional relationship between the applied load and the surface stress of the sample irradiation surface. A fixed load is applied by a servo tensile machine to achieve precise control of the sample surface stress and avoid stress relaxation under high temperature conditions.

[0026] It should be understood that the four-point bend method is a standard test method recommended by ASTM and GB, but the design of the test fixture varies significantly under different test scenarios. When applying the four-point bend method to small-sized samples, several technical problems often arise that require specific solutions. The four-point bend test fixture and method designed in this invention are specifically designed for small-sized samples and have the following significant advantages:

[0027] 1) Sample centering control is achieved: Since the surface morphology of the fixed area needs to be continuously observed during the test, the position of the support point in each test must be consistent with the previous one. For this purpose, the present invention designs a pair of positioning pins symmetrically arranged on both sides. By rotating the positioning pins on both sides forward by the same distance, the precise fixation of the sample position is achieved.

[0028] 2) Stable contact at the support points is maintained: The distance between the two upper support points is only 2mm. If there is a thickness deviation in the sample or the tension axis is offset from the central axis, the two-point support can easily become a single-point support. To address this, the present invention designs a dual compensation mechanism: The first compensation is a loading block fixing pin, which connects the loading block and the base, and a gap (<1mm) is reserved between the top of the loading block and the base to provide a degree of rotational freedom for the loading block; the second compensation is a position deviation adjuster, which uses a cylindrical pin design to avoid uneven force distribution on the four-point bending sample due to eccentricity of the main tension rod.

[0029] 3) This invention solves the problem of contact state changes caused by loading block corrosion: Molten salt is highly corrosive and easily causes corrosion of the two-point supported loading block, changing the original line contact to surface contact and affecting test accuracy. Based on the structural design of the position adjuster, this invention enables convenient replacement of corroded loading blocks, ensuring test reliability.

[0030] 4) Solves the problems of molten salt sealing and support frame corrosion: The strong corrosiveness of molten salt makes sealing extremely difficult, and the support frame is easily damaged by corrosion. This invention adopts an inverted tensioning method, which requires only a small amount of molten salt to completely immerse the test sample, while eliminating the need for complex sealing of the molten salt, and controlling the corrosion range below the loading block, significantly reducing most of the corrosion loss of the support frame;

[0031] 5) Precise control of sample stress is achieved: Due to the extremely small sample size, the bending displacement required to obtain a specific stress is at the micrometer level. However, in a high-temperature molten salt environment, the measurement accuracy of micrometer-level deformation is extremely poor, making it difficult to adjust the sample surface stress by controlling the displacement of the loading block. To address this, this invention employs the finite element analysis method to pre-establish the functional relationship between the applied load and the sample surface stress. During the experiment, a fixed load is applied using a tensile testing machine, thus achieving precise control of the surface stress of the four-point bend sample.

[0032] This invention uses ion irradiation to simulate the damage caused by neutron irradiation to alloys. However, due to the size limitations of the ion irradiation terminal, the size of the ion-irradiated samples is only on the millimeter scale, making it impossible to process them into standard-sized tensile samples for related research. Furthermore, the damage layer of the ion-irradiated samples is shallow, making it difficult to precisely control the surface stress using traditional tensile methods. Therefore, this invention specifically designs a four-point bending fixture suitable for ion-irradiated samples. Combined with finite element analysis, it establishes the correspondence between the sample surface stress and the applied load, enabling precise control of the stress in the irradiated layer of the sample, thereby achieving multi-environment coupling research of irradiation, high-temperature molten salt corrosion, and stress.

[0033] In summary, the four-point bending stress corrosion test fixture and its test method for irradiated samples in a high-temperature molten salt environment provided by the present invention adopt an inverted tensile design, which can ensure that the sample is completely immersed in the molten salt environment to meet the test requirements, and can significantly reduce the amount of molten salt consumed in a single test, effectively avoid the reaction plate and reaction frame from being corroded by molten salt, and eliminate the need for complex sealing of the molten salt. After the test, the sample stage and sample can be directly removed while the molten salt is still in a liquid state, avoiding the molten salt from adhering to the sample surface after cooling and solidification, thus reducing the difficulty of sample removal and the risk of surface damage. At the same time, by using the relationship between the applied load and the stress function of the sample surface constructed by finite element analysis, combined with the loading of the tensile machine, the magnitude and range of surface stress of small-sized samples can be precisely controlled. The lower surface of the sample can be stably bent by pulling the upper tensile rod. Furthermore, this method does not rely on neutron irradiation, significantly reducing experimental costs from several million yuan to tens of thousands of yuan. At the same time, by replacing conventional strain control with load control, it effectively avoids the stress relaxation problem of samples under high-temperature conditions and supports timed detection of sample surface conditions, fully meeting the needs of material performance research under irradiation-high-temperature molten salt corrosion-stress coupling conditions. Attached Figure Description

[0034] Figure 1 This is a four-point bending stress corrosion test fixture provided according to a preferred embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the individual structure of the position deviation adjuster;

[0036] Figure 3 This is a schematic diagram of the connecting plate's individual structure;

[0037] Figure 4 A schematic diagram of the individual structure of this tension rod;

[0038] Figure 5 This is a schematic diagram of the assembly of the loading block and the loading tray;

[0039] Figure 6 This is a schematic diagram of the sample stage structure, where A is a vertical cross-sectional view and B is a horizontal cross-sectional view.

[0040] The meanings of the reference numerals in the attached figures are as follows:

[0041] 1. Main tension rod; 2. Kettle lid; 3. Position deviation adjuster; 4. Reaction frame; 5. Connecting rod; 6. Connecting plate; 7. Secondary tension rod; 8. Reaction plate; 9. Fastening screw; 10. Loading support; 11. Sample; 12. Sample stage; 13. Positioning screw; 14. Loading block; 15. Fixing pin; 31. Adjuster body; 32. Connecting block; 61. Threaded hole; 71. Large end; 72. Middle section; 73. Threaded section; 74. Positioning step; 101. Threaded hole; 121. Protrusion; 122. Recess; 123. Rectangular groove; 124. Arc section; 125. Through hole; 126. Threaded hole; 141. Cuboid head; 142. Top; 143. Circular contact point; 144. Threaded hole; 311. Rectangular side slot; 312. Center hole; 313. First pin hole; 314. Upper external threaded hole; 315. Lower external thread; 321. Second pin hole; 322. Lower internal threaded hole. Detailed Implementation

[0042] The present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, the techniques used in the embodiments are conventional practices in the art, or experimental methods recommended by the instrument manufacturer. Unless otherwise specified, the reagents and materials used in the embodiments are commercially available.

[0043] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. 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 limitations on this invention.

[0044] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0045] Example 1: A four-point bending stress corrosion test fixture for samples irradiated in a high-temperature molten salt environment

[0046] like Figure 1The image shows a four-point bending stress corrosion test fixture according to a preferred embodiment of the present invention, comprising: a main tension rod 1, a vessel lid 2, a position deviation adjuster 3, a reaction frame 4, four secondary tension rods 7, a reaction plate 8, a loading block support 10, a sample stage 12, a positioning pin 13, a loading block 14, and a fixing pin 15. Detailed structural description is as follows:

[0047] The reaction frame 4 is installed at the bottom of the vessel cover 2. The reaction plate 8 is horizontally fixed below the reaction frame 4 by fastening screws 9. The loading block support 10 is installed at the bottom of the reaction plate 8. The loading block 14 is detachably installed in the loading block support 10 by fixing pins 15, and a certain gap is reserved between the loading block 14 and the loading block support 10. The sample stage 12 is connected to the main tension rod 1 by four secondary tension rods 7. The secondary tension rods 7 and the sample stage 12 are connected by a flat-head structure with positioning steps, and the four secondary tension rods 7 are kept at the same height by the connecting plate 6. The positioning pins 13 are symmetrically arranged on both sides of the sample stage 12 for precise positioning of the sample 11. The position deviation adjuster 3 adopts a cylindrical pin structure and is set between the main tension rod 1 and the connecting rod 5 to provide freedom in the YZ plane.

[0048] The fixture adopts a reverse tensioning method. The main tensioning rod 1 is pulled upward by the servo tensioning machine, which in turn drives the secondary tensioning rod 7, the sample stage 12 and the sample 11 to move upward in sequence. During the upward movement, the sample 11 is subjected to the reaction force of the loading block 14, and the lower surface bends, generating tensile stress. This enables the study of material cracking of irradiated samples under the combined coupling of irradiation, high temperature molten salt corrosion and stress.

[0049] Combination Figure 1 , Figure 2 As shown, the position deviation adjuster 3 includes an adjuster body 31, a connecting block 32, and an adjuster pin (not shown). The adjuster body has a rectangular side slot 311 along its side for the connecting block 32 to enter. The adjuster body 31 has a through central hole 312 in the middle. The outer shell of the adjuster body has a first pin hole 313. The connecting block 32 has a second pin hole 321 in the middle. The connecting block 32 is fitted into the central hole 312, and the first pin hole 313 and the second pin hole 321 are aligned. Therefore, when the adjuster pin passes through the first and second pin holes 313 and 321, the connecting block 32 can be connected to the adjuster body 31, thereby forming a flexible connection that can rotate at a small angle in the YZ plane.

[0050] Furthermore, the upper and lower sides of the adjuster body 31 are respectively provided with an upper external threaded hole 314 and an lower external thread 315, which are used to fix and connect with the main tension rod 1 and the connecting rod 5 to transmit load. The upper external threaded hole 314 is provided with a small translation space for adjustment. The inner side of the connecting block 32, below the second pin hole 321, is provided with an inner lower threaded hole 322, which is also provided with a small translation space for adjustment. Therefore, through the flexible connection achieved by the adjuster body 31, the connecting block 32, the main tension rod 1, the connecting rod 5 and the adjuster pin, the position deviation adjuster can compensate for the contact deviation caused by sample thickness deviation, indenter corrosion or tension shaft eccentricity, and ensure that the two circular support points 143 at the bottom of the loading block 14 are in uniform contact with the small sample in the four-point bend test, which is suitable for stress corrosion test scenarios in high temperature molten salt environment.

[0051] Combination Figure 3 , Figure 4 As shown, the secondary tension rod 7 is a one-piece rod-shaped structure, consisting of a large end 71, a middle section 72, and a threaded section 73. A positioning step 74 is provided between the middle section 72 and the threaded section 73. Therefore, the secondary tension rod 7 passes through the threaded hole 126 on the sample stage 12, the threaded hole on the reaction plate 8, and then through the threaded hole 61 on the connecting plate 6. It is connected by bolt threads. Under the action of the positioning step 74, the four secondary tension rods 7 can maintain the same height.

[0052] like Figure 5 As shown, the loading block holder 10 has a threaded hole 101 for mounting to the bottom of the reaction plate 8 with screws. The loading block 14 has a cuboid head 141 and a top 142 that gradually narrows from the cuboid head 141 away from the head. The cuboid head 141 has a threaded hole 144, and the top 142 has two circular contact points 143 with a diameter of 2 mm. The center distance between the two circular contact points 143 is 2 mm. The cuboid head 141 is detachably connected to the loading block holder 10 by a fixing pin 15, and a gap is reserved between the cuboid head and the loading block holder 10. This gap allows the loading block 14 to have a degree of rotational freedom about the fixing pin 15. The circular contact points 143 are used to contact the surface of small-sized samples to transfer load. This degree of rotational freedom is adapted to sample thickness deviation or tension axis eccentricity to ensure that the two circular contact points 143 are always in uniform contact with the upper surface of the sample 11.

[0053] like Figure 6As shown in Figures A and B, the sample stage 12 includes: symmetrically arranged protrusions 121 on both sides and a recessed portion 122 in the middle. A rectangular groove 123 is provided in the center of the recessed portion, and the two ends of the rectangular groove 123 are connected to the recessed portion 122 by a rounded segment 124. Therefore, when the sample 11 is placed above the rectangular groove 123, the rounded segment 124 forms a two-point contact with the lower surface of the sample 11. Combined with the two-point contact formed between the two circular contact points 143 on the loading block 14 and the upper surface of the sample 11, a four-point bending clamp is formed on the sample.

[0054] Each protrusion of the sample stage 12 is provided with a through hole 125 for positioning, which is used to pass through the positioning pin 13 to clamp the sample 11. The positioning pin 13 controls the forward distance by synchronous rotation, so that the center of the sample 11 is precisely aligned with the midpoint of the line connecting the two circular contact points 143 of the loading block 14, so as to realize continuous tracking test of the sample corrosion surface.

[0055] Example 2: A four-point flexural stress corrosion test method for irradiated samples in a high-temperature molten salt environment.

[0056] In this embodiment, the four-point bending stress corrosion test fixture provided in Example 1 is used to perform a four-point bending stress corrosion test on an irradiated sample in a high-temperature molten salt environment. The method specifically includes the following steps:

[0057] 1) Samples were prepared using wire cutting technology (initial dimensions 10×6.5×1.1mm). 3 The sample was then sanded to a 4000# grit using sandpaper to achieve a final thickness of 1 mm. The sanded sample was then placed in a prepared perchloric acid-methanol solution and electrochemically polished at -20°C to obtain a smooth surface. Afterward, the electrochemically polished sample was placed in an ion irradiation terminal, and the appropriate ion irradiation type, energy, and flux rate were selected according to experimental requirements to complete the ion irradiation treatment.

[0058] 2) After ion irradiation, place the sample 11 prepared in step 1) on the sample stage 12 and position it using the positioning screws 13 on both sides of the sample stage 12: rotate the positioning screws 13 synchronously forward from the same initial position, and ensure that the center of the sample 11 is precisely aligned with the center of the two circular contact points 143 of the loading block 14 by precisely controlling the number of rotations of the screws. Start the servo stretching machine and drive the main stretching rod 1 to move upward, applying a preload of 10N to the sample 11 to ensure that the upper surface of the sample 11 is in full contact with the two circular contact points 143 of the loading block 14, thus temporarily fixing the sample; then rotate and remove the positioning screws 13 on both sides to prevent them from corroding in the subsequent high-temperature molten salt environment.

[0059] 3) Inside the glove box, load the prepared molten salt into a pure nickel crucible and seal it. Then, quickly transfer the crucible to the fixing slot inside the vessel and secure it. Activate the vessel lid lifting device to move the vessel lid 2 and sample stage 12 downwards simultaneously, allowing the sample stage 12 to enter the vessel body without contacting the solid molten salt. Seal the vessel body and perform vacuum treatment until the vacuum degree reaches 1×10⁻⁶. -3 After Pa, high-purity Ar gas (purity > 99.999%) is introduced into the reactor to establish a 3 bar micro-positive pressure protective atmosphere. The heating system is started, and after the molten salt temperature rises to the set experimental temperature and stabilizes for 15 minutes, the reactor lid 2 is moved vertically downwards an appropriate distance to ensure that the sample 11 is completely immersed in the liquid molten salt. Finally, according to the experimental purpose, load or strain control is performed using a servo tensile machine, thereby realizing a multi-environment coupling study of irradiation-high-temperature molten salt corrosion-stress, significantly reducing experimental costs. After the experiment, while the molten salt is still liquid, the reactor lid 2 is moved upwards to lift the sample stage 12 out of the high-temperature molten salt, preventing the molten salt from adhering to the sample surface after cooling and solidification. This reduces the cumbersome sampling operation and the risk of damage to the sample surface.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. All simple and equivalent changes and modifications made in accordance with the claims and description of this application fall within the protection scope of the claims of this patent. All aspects not described in detail in this invention are conventional technical content.

Claims

1. A four-point bending stress corrosion test fixture for samples irradiated in a high-temperature molten salt environment, characterized in that, include: The main tension rod (1), the vessel lid (2), the position deviation adjuster (3), the reaction frame (4), the connecting rod (5), the connecting plate (6), four secondary tension rods (7), the reaction plate (8), the loading block support (10), the sample stage (12), the positioning pin (13), the loading block (14), and the fixing pin (15); among which, The reaction frame (4) is installed at the bottom of the vessel cover (2), the reaction plate (8) is horizontally fixed below the reaction frame (4), the loading block support (10) is installed at the bottom of the reaction plate (8), and the loading block (14) is detachably installed in the loading block support (10) by means of the fixing pin (15), and a gap is reserved between the loading block (14) and the loading block support (10); The sample stage (12) is connected to the main tension rod (1) via four secondary tension rods (7). The secondary tension rods (7) pass through the sample stage (12) and the reaction plate (8) in sequence, and are then connected to the connecting plate (6) by bolts. The positioning pins (13) are symmetrically arranged on both sides of the sample stage (12) for precise positioning of the sample (11). The position deviation adjuster (3) adopts a cylindrical pin structure and is set between the main tension rod (1) and the connecting rod (5) to provide freedom in the YZ plane. Using the reverse tensioning method, the main tensioning rod (1) is pulled upward by the servo tensioning machine, which in turn drives the secondary tensioning rod (7), the sample stage (12) and the sample (11) to move upward in sequence. The sample (11) is subjected to the reaction force of the loading block (14) and the lower surface bends to generate tensile stress, thereby realizing the material cracking study of the sample under the combined coupling of irradiation, high temperature molten salt corrosion and stress.

2. The four-point bending stress corrosion test fixture according to claim 1, characterized in that, The loading block (14) has a cuboid head (141) and a top (142) that gradually narrows from the cuboid head to the side away from the head. The top has two circular contact points (143) with a diameter of 2 mm and a center-to-center distance of 2 mm between the two circular contact points. The cuboid head (141) is connected to the loading block support (10) by a fixing pin (15) and a gap is reserved between them. This gap allows the loading block (14) to have a degree of rotational freedom around the fixing pin (15). The circular contact points (143) are used to contact the surface of small-sized samples to transfer load. The degree of rotational freedom is adapted to sample thickness deviation or tension axis eccentricity to ensure that the two contact points are in uniform contact with the upper surface of the sample.

3. The four-point bending stress corrosion test fixture according to claim 2, characterized in that, The sample stage (12) includes: symmetrically arranged protrusions (121) on both sides and a recessed part (122) in the middle. A rectangular groove (123) is provided in the center of the recessed part, and the two ends of the rectangular groove (123) are connected to the recessed part (122) by a circular arc segment (124). The circular arc segment (124) forms two-point contact with the lower surface of the sample (11), and combined with the two-point contact formed by the circular contact point (143) and the upper surface of the sample (11), a four-point bending clamp is formed.

4. The four-point bending stress corrosion test fixture according to claim 3, characterized in that, Each of the protrusions of the sample stage (12) is provided with a through hole (125) for positioning, which is used to pass through the positioning pin (13) to clamp the sample. The positioning pin (13) controls the forward distance by synchronous rotation, so that the center of the sample (11) is precisely aligned with the midpoint of the line connecting the two circular contact points (143) of the loading block (14), supporting continuous tracking of the corrosion surface.

5. The four-point bending stress corrosion test fixture according to claim 1, characterized in that, The position deviation adjuster (3) includes an adjuster body (31), a connecting block (32) and an adjuster pin. The adjuster body has a rectangular side slot (311) for the connecting block (32) to enter. The adjuster body (31) has a through center hole (312) in the middle. The adjuster body has a first pin hole (313). The connecting block (32) has a second pin hole (321) in the middle. The connecting block (32) is fitted into the center hole (312), and the first pin hole (313) and the second pin hole (321) are aligned. The adjuster pin passes through the first and second pin holes (313, 321) to form a flexible connection between the connecting block (32) and the adjuster body (31) that can rotate at a small angle in the YZ plane.

6. The four-point bending stress corrosion test fixture according to claim 5, characterized in that, The upper and lower sides of the adjuster body (31) are respectively provided with an upper external threaded hole (314) and an lower external threaded hole (315) for fixed connection with the main tension rod (1) and the connecting rod (5) to transmit load. The upper external threaded hole (314) is reserved with a small translation space. The inner side of the connecting block (32) and below the second pin hole is provided with an inner lower threaded hole (322), and the inner lower threaded hole (322) is reserved with a small translation space. Through the reserved small translation space, the flexible connection can compensate for the contact deviation caused by sample thickness deviation, indenter corrosion or tension shaft eccentricity.

7. A method for testing four-point flexural stress corrosion of irradiated samples in a high-temperature molten salt environment, characterized in that, Includes the following steps: 1) Prepare small-sized four-point bend samples, and perform grinding and electrochemical polishing on the sample surface; 2) The sample prepared in step 1) is subjected to ion irradiation treatment; 3) Fix the irradiated sample (11) onto the sample stage (12) of the fixture as described in any one of claims 1-6 using positioning pins (13), so that the center of the sample is aligned with the middle position of the two circular contact points (143) of the loading block (14); 4) In the glove box, put the molten salt into the pure nickel crucible and seal it. Transfer it to the vessel body and fix it. After sealing the vessel body, evacuate and introduce high-purity Ar gas to establish a micro-positive pressure environment. 5) Heat the vessel to bring the molten salt to the set temperature and stabilize it, and adjust the position of the vessel lid so that the sample (11) is immersed in the liquid molten salt; 6) Drive the main tension rod (1) through the servo tensioning machine, and combine the functional relationship between the load and the surface stress of the sample obtained by finite element analysis to apply a fixed load to generate bending tensile stress in the sample, so as to realize the coupled test of irradiation-high temperature molten salt corrosion-stress. 7) After the test, while the molten salt is still in a liquid state, lift the lid (2) and remove the sample stage (12) and sample (11) from the molten salt.

8. The test method according to claim 7, characterized in that, In step 2), the sample is placed on the ion irradiation terminal, and different types of ion irradiation, irradiation energy and flux rate are selected according to different experimental requirements.

9. The test method according to claim 7, characterized in that, In step 4), the vacuum level is controlled at 1×10⁻⁶. 3 Pa, high-purity Ar gas purity ≥99.999%, the pressure of the micro-positive pressure environment inside the reactor is 1-5 bar; the molten salt temperature stabilization time in step 5) is 10-20 minutes.

10. The test method according to claim 7, characterized in that, In step 6), the finite element analysis pre-establishes the corresponding functional relationship between the applied load and the surface stress of the sample irradiation surface. A fixed load is applied by a servo tensile machine to achieve precise control of the sample surface stress and avoid stress relaxation under high temperature conditions.

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