A multi-axial fatigue test elastic sealing fixture system and test method for liquid lead-bismuth environment

Abstract

The application relates to a multi-axial fatigue test elastic sealing clamp system for a liquid lead bismuth environment, which comprises an external liquid lead bismuth pipeline unit, an oxygen concentration PLC control gas path unit and a test loading and control unit, can realize dynamic circulation flow of LBE in a tubular test piece and accurate control of oxygen concentration, can guarantee complete decoupling of sealing pre-tightening force and a stress path of the test piece, can avoid pollution of measurement data by an additional load, can automatically compensate axial deformation of the test piece in tension-compression cycle and position deviation in a clamping process, and all sealing elements can be disassembled and replaced. The method fills the blank of the existing device which cannot apply controllable oxygen concentration flowing liquid lead bismuth to the inner wall of the tubular test piece and simultaneously carry out multi-axial test by monitoring the oxygen concentration in the external LBE pipeline in real time and controlling the gas path unit in linkage, thereby maintaining a stable low-oxygen environment in the whole pre-experiment and formal test.

Description

Technical Field

[0001] This invention belongs to the field of nuclear engineering technology, specifically relating to a tensile-compression-torsional multiaxial fatigue testing system and corresponding testing method for tubular specimens in a high-temperature liquid lead-bismuth (LBE) environment. Background Technology

[0002] Liquid lead-bismuth alloy (LBE) is a key coolant and scattering target material for fourth-generation lead-cooled fast reactors and accelerator-driven subcritical systems (ADS). During actual reactor operation, structural components such as cladding tubes not only endure corrosion from high-temperature, flowing LBE, but also experience complex tensile-compressive-torsional multiaxial cyclic loads caused by thermal cycling, fluid pulsation, and mechanical vibration. Therefore, establishing a laboratory-scale testing system capable of simulating simultaneous contact of the inner and outer walls of tubular specimens with cyclic LBE and conducting multiaxial fatigue tests is of irreplaceable significance for accurately assessing material service performance and establishing life prediction models.

[0003] However, existing testing systems typically employ uniaxial loading and mostly immerse the entire specimen in the LBE tank, failing to simulate the condition where the inner wall of the casing tube contacts the flowing LBE alone. A few attempts to use hollow tubular specimens with LBE introduced inside face a series of long-standing technical challenges. First, the tubular specimen has an inner diameter of only 8-10 mm, resulting in extremely narrow internal space. This makes it impossible to directly install oxygen sensors or introduce reducing gas for oxygen concentration control in the LBE, and also makes it difficult to directly connect external LBE tubing to the specimen's inner cavity. Existing connection methods, whether rigid tubes or flexible hoses, introduce non-negligible additional axial forces or torques to the test specimen. Rigid tubes directly transmit pipeline vibration and thermal expansion stress to the specimen, severely interfering with the measurement accuracy of force sensors; while flexible hoses generate varying elastic reaction forces during tension-compression cycles, and their seals are prone to aging and failure in high-temperature LBEs. Second, to ensure the reliability of metal-to-metal contact seals (such as conical seals), a large initial preload is usually required. However, if this preload is transmitted through the specimen, it becomes part of the test load, causing the measured stress-strain curve to deviate from the true value. Furthermore, the specimen undergoes elastic or plastic axial elongation during multiaxial fatigue. Traditional rigid seals cannot adapt to this length change; the sealing surface pressure either increases sharply, leading to overload, or decreases or even disengages, causing LBE leakage. Moreover, due to the lack of an independently adjustable preload mechanism, minor positional deviations during specimen installation, length differences between different specimens, and specimen deformation during the experiment are difficult to absorb. This often requires repeated adjustments of the fixture, making the operation cumbersome and affecting the monitoring and results of the test process. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a multiaxial fatigue test elastic sealing fixture system for high-temperature liquid lead-bismuth environment. This system can realize dynamic circulation of LBE inside the tubular specimen and precise control of oxygen concentration, while ensuring complete decoupling of the sealing preload and the force path of the specimen, avoiding additional load from contaminating the measurement data, and can automatically compensate for the axial deformation of the specimen in the tension-compression cycle and the positional deviation during the clamping process. All sealing elements can be disassembled and replaced.

[0005] A test method for a multiaxial fatigue test elastic sealing fixture system for high-temperature liquid lead-bismuth environment is also provided. By real-time monitoring of the oxygen concentration in the external LBE pipeline and linkage control of the gas circuit unit, a stable low-oxygen environment is maintained throughout the pre-experiment and formal test. This fills the gap in existing devices that cannot apply controllable oxygen concentration flowing liquid lead-bismuth to the inner wall of tubular specimens and carry out multiaxial tests simultaneously.

[0006] The technical problem solved by this invention is achieved through the following technical solution: A multiaxial fatigue testing elastic sealing fixture system for liquid lead-bismuth environment includes an external liquid lead-bismuth pipeline unit, an oxygen concentration PLC control gas circuit unit, and a test loading and control unit; The external liquid lead-bismuth pipeline unit includes a liquid lead-bismuth heating storage tank, which is connected to a high-temperature liquid metal electromagnetic pump via a pipeline, and the high-temperature liquid metal electromagnetic pump is connected to an elastic sealing clamp device via a pipeline. The oxygen concentration PLC control gas circuit unit includes an oxygen concentration PLC control cabinet and an oxygen concentration sensor installed on the liquid lead-bismuth heating storage tank. The oxygen concentration sensor uses a signal line to transmit oxygen concentration data to the oxygen concentration PLC control cabinet. The oxygen concentration PLC control cabinet is connected to the oxidizing gas source and the reducing gas source through pipelines via a rotor flow meter. The test loading and control unit includes a vertical electric cylinder multiaxial fatigue testing machine, a multiaxial test tubular specimen located inside the vertical electric cylinder multiaxial fatigue testing machine, a load sensor, a strain extensometer, an induction heating coil, a K-type thermocouple, and a multi-functional control cabinet and control computer connected to the vertical electric cylinder multiaxial fatigue testing machine; the vertical electric cylinder multiaxial fatigue testing machine applies test loads and torques to the multiaxial test tubular specimen with the loading axis located in the elastic sealing clamp device via a multiaxial motor. The elastic sealing clamp device includes an upper base, a lower base, an upper clamp, a lower clamp, a liquid lead-bismuth inlet pipe, and a liquid lead-bismuth outlet pipe. The upper base is connected to the loading shaft, and a load sensor is installed below the lower base. The upper base and the lower base are fixedly connected to the upper clamp and the lower clamp, respectively. Floating sealing bases and plugs are installed between the upper base and the upper clamp, and between the lower base and the lower clamp. The tubular specimen for multiaxial testing passes through the upper base, the upper clamp, the lower base, and the lower clamp at both ends, and is connected to the liquid lead-bismuth inlet pipe rotary interface and the liquid lead-bismuth inlet pipe through a swivel joint with a corrugated pipe located on the floating sealing base. The oxygen concentration PLC control cabinet is connected to the oxygen concentration sensor signal and is connected to the oxidizing gas source and the reducing gas source through pipelines respectively. The inlet of the high-temperature liquid metal electromagnetic pump is connected to the outlet of the liquid lead-bismuth heating storage tank, and the outlet is connected to the liquid inlet of the upper base. The liquid outlet of the lower base returns to the liquid lead-bismuth heating storage tank through pipelines, forming a closed loop.

[0007] Furthermore, both the upper and lower bases are provided with a horizontal liquid inlet channel and a vertical turning channel. The outer end of the horizontal liquid inlet channel is equipped with a threaded rotary interface for connecting to an external liquid lead-bismuth pipeline, and the end of the vertical turning channel is machined with an internal threaded interface for connecting to a rotary joint with a bellows.

[0008] Furthermore, the rotary joint with bellows is seamlessly welded from a hollow threaded column and a metal vacuum bellows; wherein the metal vacuum bellows has an inner diameter of 10-15 mm, an outer diameter of 16-20 mm, a wall thickness of 0.2 mm, a free length of 12-15 mm, an axial travel of ±1.5 mm, and an axial stiffness ≤10 N. mm.

[0009] Furthermore, one end of the hollow threaded column is welded to the metal vacuum bellows, and the other end is detachably connected to the internal thread interfaces of the upper and lower bases respectively through external threads; the floating sealing base is welded to the other end of the metal vacuum bellows, and the flange end face of the plug is pressed with the corresponding end face of the floating sealing base by circumferentially distributed bolts to form a seal, and the pre-tightening force of the seal does not pass through the tubular specimen used in the multiaxial test, thus decoupling from the mechanical loading path in the test.

[0010] Furthermore, the plug consists of a flange and a cylindrical section, with a liquid lead-bismuth flow channel through hole in the center; the outer side of the cylindrical section is machined with external threads for detachable screw-in connection with the internal threads in the center of the tubular specimen clamping section for multiaxial testing.

[0011] Furthermore, the upper base and the lower base are detachably and fixedly connected to the loading shaft and the load sensor, respectively.

[0012] Furthermore, both the upper and lower clamps are hollow annular structures with anti-slip textures on their inner surfaces. The upper and lower clamps are detachably fixed to the upper and lower bases respectively by axial connecting bolts, and radial preload is applied to the tubular specimen for multiaxial testing by radial clamping bolts.

[0013] A method for conducting multiaxial fatigue tests in a liquid lead-bismuth environment using an elastic sealing fixture system for multiaxial fatigue testing, comprising the following steps: Step 1, Preliminary Experiment: (1) Connect the oxygen-controlled mixed gas inlet pipe, the oxidizing gas source, the reducing gas source to the oxygen concentration PLC control cabinet, and close the rotor flow meter and the solenoid valve for the liquid lead-bismuth inlet pipeline and the solenoid valve for the liquid lead-bismuth outlet pipeline. (2) Turn on the induction heating furnace and heat the solid lead-bismuth alloy in the liquid lead-bismuth heating tank to 180°C to melt it; (3) After the lead-bismuth alloy melts into liquid at 180 °C, the liquid lead-bismuth heating tank and the top cover are sealed with graphite gaskets and tightened with bolts. Then, the oxygen concentration sensor and the armored thermocouple are sealed with vacuum flanges and vacuum ferrule joints respectively and tightened with bolts and clamps. (4) Turn on the oxygen concentration sensor and oxygen concentration PLC control cabinet to monitor the oxygen concentration, adjust the flow rate of the rotor flow meter to 50 mL / min, introduce the mixed gas, perform the gas washing operation of liquid lead bismuth for 2 hours, and then raise the temperature to the target temperature. (5) After the gas washing is completed, the oxygen concentration in the storage tank is automatically controlled using the oxygen concentration PLC control cabinet. Step Two: Formal Experiment (1) Connect the external threaded cylindrical section of the plug to the internal thread at the center of the clamping section on both sides of the tubular specimen for multiaxial testing, and install the rotary joint with bellows and the floating sealing base. (2) Connect the plug to the corresponding floating seal base with bolts, and seal the flange with a metal copper gasket; (3) After the connection and sealing between the liquid lead-bismuth pipeline and the specimen are achieved, the upper clamp and the upper base are fixedly connected by the connecting bolts through the outer ring threaded hole. Then, the clamping bolts are pre-tightened circumferentially to press the anti-slip texture of the clamp into the tubular specimen for multiaxial testing. The axial load and circumferential torque are further ensured through slight local deformation. The connecting bolts and clamping bolts of the lower clamp are tightened in the same way to ensure that the specimen will not slip during the test. (4) First, open the solenoid valve of the liquid lead-bismuth inlet pipeline so that the liquid lead-bismuth that meets the experimental requirements flows into the high-temperature liquid metal electromagnetic pump. After the pump meets the working requirements, start the high-temperature liquid metal electromagnetic pump. After confirming that it is safe and there is no leakage, open the solenoid valve of the liquid lead-bismuth outlet pipeline. (5) After the liquid lead-bismuth circulates, start the induction heating coil and preset the specimen temperature through the control computer. Install the strain extensometer and place it close to the surface of the specimen. At the same time, connect the signal acquisition line to the fatigue test multi-functional control cabinet. (6) Set the multi-axis loading parameters and start the test.

[0014] The advantages and positive effects of this invention are: 1. The present invention provides an elastic sealing fixture system for multiaxial fatigue testing in high-temperature liquid lead-bismuth environments. It can realize dynamic circulation of LBE inside tubular specimens and precise control of oxygen concentration. At the same time, it ensures complete decoupling of the sealing preload and the force path of the specimen, avoids additional load from contaminating the measurement data, and can automatically compensate for the axial deformation of the specimen in tension-compression cycles and the positional deviation during clamping. All sealing elements can be disassembled and replaced.

[0015] 2. This invention relates to an elastic sealing fixture system for multiaxial fatigue testing in a high-temperature liquid lead-bismuth environment. The system uses a PLC to adjust the oxygen concentration in real time. An electromagnetic pump draws LBE from the storage tank, introduces it into the inner cavity of the tubular specimen used in the multiaxial test via the upper base 410, and then returns it to the storage tank from the lower base, forming a closed-loop cycle. Simultaneously, a strain controller and thermocouples, in conjunction with an induction coil, achieve strain-controlled multiaxial tension-torsion loading and precise temperature regulation of the specimen. The entire system can record the stress-strain curve in real time, completing multiaxial fatigue tests of tubular specimens under high-temperature, oxygen-controlled, and dynamic cyclic LBE conditions. Notably, this system incorporates a unique integrated elastic sealing fixture device within the upper and lower bases. This device employs a bellows and detachable flange sealing structure: the bellows serves as a flexible channel for the LBE (Limited-Earth Beam Absorption) system, its low axial stiffness isolating the additional force from the pipeline from the specimen load, completely eliminating the interference of the sealing preload on the test load. The force sensor measurement error is less than 0.5%, automatically adapting to the axial deformation of the specimen. The bellows stroke is ±1.5mm, the sealing pressure fluctuation is less than 20%, and it tolerates ±0.5mm axial deviation and ≤1° angular deviation, facilitating clamping. The flange seal preload is provided independently by the studs, without passing through the specimen, thus avoiding any impact on the experimental results. This elastic structure solves the problems of pipeline additional force interference, inability to independently control sealing preload, inability to adapt to axial deformation, and difficulty in compensating for clamping deviations in existing technologies, while also achieving modular and rapid assembly and disassembly.

[0016] 3. By maintaining the temperature at high temperature for 2 hours before the test, the oxygen concentration, temperature and strain data tend to stabilize, which effectively reduces the experimental errors caused by fluctuations in oxygen concentration, changes in strain rate and temperature drift, and improves the accuracy and reliability of the test data.

[0017] 4. The present invention provides a test method for a multiaxial fatigue test elastic sealing fixture system in a liquid lead-bismuth environment. It offers a sequentially decoupled clamping and sealing method, which operates in the fixed sequence of first connecting the elastic sealing component, then tightening the flange, then screwing the specimen in, and finally locking the fixture. This ensures that the sealing preload and the fixture clamping force do not interfere with each other, thereby improving the repeatability of the test and the reliability of the data.

[0018] 5. The present invention provides a test method for a multiaxial fatigue test elastic sealing fixture system for liquid lead-bismuth environments. It offers a method for dynamic circulation and precise oxygen control of the LBE inside a tubular specimen. By real-time monitoring of the oxygen concentration in the external LBE pipeline and linkage control of the gas path unit, a stable low-oxygen environment is maintained throughout the pre-experiment and formal test. This fills the gap in existing devices that cannot apply controllable oxygen concentration to the inner wall of a tubular specimen while simultaneously conducting multiaxial tests. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the elastic sealing fixture system for multiaxial fatigue testing in a high-temperature liquid lead-bismuth environment according to the present invention; Figure 2 This is a schematic diagram of the elastic sealing clamp device structure of the multiaxial fatigue testing elastic sealing clamp system for high-temperature liquid lead-bismuth environment of the present invention; In the picture: 100-Liquid lead-bismuth heating storage tank; 101-Liquid lead-bismuth inlet pipe; 102-Sheathed thermocouple; 103-Liquid lead-bismuth outlet pipe; 104-Oxygen-controlled mixed gas outlet pipe; 105-One-way valve; 106-Oxygen-controlled mixed gas inlet pipe; 107-Oxygen concentration sensor; 108-Induction heating furnace; 109-Oxygen concentration PLC control cabinet; 200-High temperature liquid metal electromagnetic pump; 300-Vertical electric cylinder multi-axis fatigue testing machine; 301-Multi-axis motor; 302-Loading shaft; 303-Strain extensometer; 304-Induction heating coil; 305-K-type thermocouple; 306-Load sensor; 410-Upper base; 411-Rotary joint with bellows; 412- Sealing gasket; 413-Threaded rotary interface; 414-Liquid lead-bismuth inlet pipe; 415-Base countersunk hole; 416-Floating sealing base; 417-Plug; 418-Sealing bolt; 420-Lower base; 421-Liquid lead-bismuth outlet pipe; 510-Upper clamp; 511-Connecting bolt; 512-Clamping bolt; 520-Lower clamp; 600-Tube specimen for multi-axis testing; 601-Liquid lead-bismuth flow channel; 701-Liquid lead-bismuth inlet solenoid valve; 702-Liquid lead-bismuth outlet solenoid valve; 801-Oxidizing gas source; 802-Reducing gas source; 803-Gas rotor flow meter; 900-Fatigue testing multi-functional control cabinet; 901-Control computer. Detailed Implementation

[0020] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0021] like Figure 1 , Figure 2 As shown, a multiaxial fatigue testing elastic sealing fixture system for a liquid lead-bismuth environment includes an external liquid lead-bismuth pipeline unit, an oxygen concentration PLC-controlled gas path unit, and a test loading and control unit. The oxygen concentration PLC-controlled gas path unit controls the oxygen concentration and temperature of the external liquid lead-bismuth, and the deoxygenated liquid lead-bismuth is transported to the test apparatus and the interior of the multiaxial test tubular specimen 600 via the external liquid lead-bismuth pipeline unit, simulating the operating environment of a lead-cooled fast reactor. Finally, the test loading and control unit performs multiaxial mechanical tests on the multiaxial test tubular specimen 600 under simulated operating conditions.

[0022] The external liquid lead-bismuth pipeline unit includes a liquid lead-bismuth heating storage tank 100, which is connected to a high-temperature liquid metal electromagnetic pump 200 via pipelines. The high-temperature liquid metal electromagnetic pump 200 is connected to an elastic sealing clamp device via pipelines.

[0023] The liquid lead-bismuth heating storage tank 100 and its top cover are both made of 410 stainless steel. They are sealed with tongue and groove flanges according to the parameters PN=16 and DN=65 in the standard GB / T9113-2010 "Integral Steel Pipe Flanges". The liquid lead-bismuth heating storage tank 100 includes an oxygen-controlled mixed gas inlet pipe 106 made of 410 stainless steel connected to an oxygen concentration PLC control unit, an oxygen-controlled mixed gas outlet pipe 104 with a one-way valve 105 installed at the tail, a liquid lead-bismuth outflow pipe 103 for transporting the liquid lead-bismuth alloy, and a liquid lead-bismuth inflow pipe 101. All these pipes are seamlessly welded to the liquid lead-bismuth heating storage tank. To melt and control the temperature of the lead-bismuth alloy in the storage tank, an armored thermocouple 102 is used in conjunction with an induction heater 108 equipped with the liquid lead-bismuth heating storage tank for temperature control. Furthermore, a high-temperature liquid metal electromagnetic pump 200 is used to transport the required high-temperature oxygen-controlled liquid lead-bismuth to the entire circuit.

[0024] The liquid lead-bismuth heating storage tank 100 uses armored thermocouples 102 and induction heating furnace 108 for heat input and temperature control of the liquid lead-bismuth inside the tank. A liquid lead-bismuth outlet pipe 103 and a liquid lead-bismuth inlet pipe 101 are seamlessly welded to the liquid lead-bismuth heating storage tank 100. A metal pipe connects the liquid lead-bismuth outlet pipe 103 to the liquid lead-bismuth inlet pipe solenoid valve 701, tightening the joint with clamps. The other side of the liquid lead-bismuth inlet pipe solenoid valve 701 is also connected to a high-temperature liquid metal electromagnetic pump 200 using a metal pipe. The pipe at the outlet of the high-temperature liquid metal electromagnetic pump 200 is further connected to the swivel interface of the liquid lead-bismuth inlet pipe on the side of the upper clamp, and sealed with threads. The liquid lead-bismuth pipe returns from the liquid lead-bismuth inlet pipe to the liquid lead-bismuth heating storage tank 100 via the liquid lead-bismuth outlet pipe solenoid valve 702, all connected using metal pipes and tightened with clamps at the joints.

[0025] The oxygen concentration PLC control gas circuit unit includes an oxygen concentration PLC control cabinet 109 and an oxygen concentration sensor 107 installed on the liquid lead-bismuth heating storage tank 100. The oxygen concentration sensor 107 transmits oxygen concentration data to the oxygen concentration PLC control cabinet 109 via a signal line. The oxygen concentration PLC control cabinet 109 is connected to the oxidizing gas source 801 and the reducing gas source 802 via pipelines and a rotor flow meter 803. The oxygen concentration sensor 107 is installed on the liquid lead-bismuth heating storage tank 100 via a welded CF16 vacuum flange, oxygen-free copper gasket, and bolts to monitor oxygen concentration and transmit real-time oxygen concentration data to the oxygen concentration PLC control cabinet 109 via a signal line for precise gas delivery. Furthermore, both the oxidizing gas source 801 and the reducing gas source 802 are connected to the gas solenoid valve interface on the side of the oxygen concentration PLC control cabinet 109 via gas pipes and a rotor flow meter 803, and the two gases are precisely mixed according to the PLC control program. All gas connections are tightened with clamps to prevent gas leakage. The mixed gas flows out from the mixed gas interface outlet on the other side of the oxygen concentration PLC control cabinet 109, and flows into the liquid lead-bismuth heating storage tank 100 through the controlled oxygen mixed gas inlet pipe 106. Simultaneously, a one-way valve 105 is installed to discharge the internally reacted mixed gas into the environment through the controlled oxygen mixed gas outlet pipe 104, ensuring the safety of the internal gas pressure and the stability of gas renewal. Based on the real-time monitoring of the actual oxygen concentration value by the oxygen sensor 107 and the difference between it and the set oxygen concentration, the oxygen concentration PLC control cabinet automatically controls the opening and closing of the internal liquid lead-bismuth gas path solenoid valve to achieve precise mixing of oxidizing and reducing gases. The mixture then enters the liquid lead-bismuth heating storage tank 100 through the mixed gas inlet pipe 106 via the side gas path.

[0026] The test loading and control unit includes a vertical electric cylinder multiaxial fatigue testing machine 300, a multiaxial test tubular specimen 600 located inside the vertical electric cylinder multiaxial fatigue testing machine 300, a load sensor 306, a strain extensometer 303, an induction heating coil 304, a K-type thermocouple 305, and a multi-functional control cabinet 900 and a control computer 901 connecting the vertical electric cylinder multiaxial fatigue testing machine 300. The multiaxial test tubular specimen 600 is designed according to the specimen in GB / T 40410-2021 "Methods for Axial-Torsion Strain Control in Multiaxial Fatigue Testing of Metallic Materials", and an M12 internal thread is machined axially at the center of the clamping section. Before the test, plugs 417 are installed on both sides of the clamping section of the multiaxial test tubular specimen 600. The 316L stainless steel plugs 417 are composed of a flange and a cylinder, and an 8 mm diameter through hole is machined in the center of the plug as a liquid lead-bismuth flow channel. The cylindrical section has an M12 external thread on its outer side, which mates with the internal thread at the center of the clamping section of the tubular specimen 600 for multiaxial testing, allowing for a detachable screw-in connection that enables quick replacement and prevents leakage of liquid lead and bismuth. The flange side of the plug 417 is flange-sealed with the 316L floating sealing base 416, and preloaded using four M6 bolts. To achieve connection and sealing with the upper base, the floating base 416 is seamlessly welded to the metal vacuum bellows side of the rotary joint 411 with bellows. Before clamping the tubular specimen 600 for multiaxial testing, the floating sealing base 416 is connected to the upper base via the external thread of the rotary joint 411 with bellows. The fit between the lower base 420 and the tubular specimen 600 for multiaxial testing is the same as that of the upper base, relying on the fit between the plug 417, the floating sealing base 416, and the rotary joint 411 with bellows for connection and sealing.

[0027] The vertical electric cylinder multiaxial fatigue testing machine 300 applies test loads and torques to the multiaxial test tubular specimen 600 located in the elastic sealing clamp device via a multiaxial motor 301 driving the loading shaft 302. The multiaxial test tubular specimen 600 is clamped by the elastic sealing clamp device through radial clamping bolts 512 and internal anti-slip grooves, and connected to the corresponding upper base 410 and lower base 420 through connecting bolts 511 to withstand the test set loads and torques. Further, the upper base 410 is connected to the loading shaft 302 that transmits loads and torques through a base countersunk hole 415, while the lower base 420 is connected to the bottom load sensor 306 through a base countersunk hole 415. The strain gauge 303 is fixed in the gauge length region perpendicular to the multiaxial test tubular specimen 600 by an external bracket, with the front end of the strain gauge in direct contact with the specimen; at the same time, a K-type thermocouple 305 is used to tightly adhere to the surface of the specimen. The strain and temperature data measured by the strain extensometer 303 and the K-type thermocouple 305, together with the data from the load sensor 306 of the testing machine, are transmitted to the fatigue test multi-functional control cabinet 900 via signal lines, and the test process is adjusted and monitored by the preset control program in the control computer 901.

[0028] The elastic sealing clamp device includes an upper base 410, a lower base 420, an upper clamp 510, a lower clamp 520, a liquid lead-bismuth inlet pipe 414, and a liquid lead-bismuth outlet pipe 421. The upper base 410 is connected to the loading shaft 302. A load sensor 306 is installed below the lower base 420. The upper base 410 and the lower base 420 are fixedly connected to the upper clamp 510 and the lower clamp 520, respectively. Floating sealing bases 416 and plugs 417 are installed between the upper base 410 and the upper clamp 510, and between the lower base 420 and the lower clamp 520. The tubular specimen 600 for multiaxial testing passes through the upper base 410, the upper clamp 510, the lower base 420, and the lower clamp 520 at both ends, respectively. It is connected to the liquid lead-bismuth inlet pipe rotary interface 413 and the liquid lead-bismuth inlet pipe 414 through a bellows-equipped rotary joint 411 located on the floating sealing base 416.

[0029] The upper base 410 and the lower base 420 are detachably and fixedly connected to the loading shaft 302 and the load sensor 306, respectively. The clamping feature is that the connection of the elastic sealing clamp device is completed first, and then the upper clamp 510 and the lower clamp 520 are fixed to the upper base 410 and the lower base 420 respectively by axial bolts, and finally the clamp is locked by radial bolts.

[0030] Both the upper clamp 510 and the lower clamp 520 are hollow annular structures. The inner surfaces of the clamps that contact the tubular specimen 600 used in the multiaxial test are machined with anti-slip textures. The upper clamp 510 and the lower clamp 520 are respectively clamped to the tubular specimen 600 using M6 clamping bolts 512, applying radial preload to ensure torque transmission and prevent slippage of the tubular specimen 600 during the experiment. The upper clamp 510 and the lower clamp 520 are detachably fixed to the upper base 410 and the lower base 420 respectively using connecting bolts 511.

[0031] Both the upper base 410 and the lower base 420 are equipped with a horizontal liquid inlet channel and a vertical turning channel. The outer end of the horizontal liquid inlet channel is equipped with a threaded rotary interface 413 for connecting to an external liquid lead-bismuth pipeline. The end of the vertical turning channel is machined with an internal thread interface for connecting to a rotary joint 411 with a bellows.

[0032] The rotary joint 411 with bellows is seamlessly welded from a hollow threaded post and a metal vacuum bellows; wherein the metal vacuum bellows has an inner diameter of 15 mm, an outer diameter of 18 mm, a wall thickness of 0.2 mm, a free length of 12-15 mm, an axial travel of ±1.5 mm, and an axial stiffness ≤10 N. mm, the inner cavity can be used as a delivery channel for liquid lead bismuth to buffer the geometric deviation and additional stress of the specimen caused by the preload provided between the sealing surfaces, and to maintain good alignment.

[0033] One end of the hollow threaded column is welded to the metal vacuum bellows, and the other end is detachably connected to the internal thread interfaces of the upper base 410 and the lower base 420 via external threads. The floating sealing base is welded to the other end of the metal vacuum bellows. The flange end face of the plug 417 and the corresponding end face of the floating sealing base 416 are tightened by circumferentially distributed bolts to form a seal, and the pre-tightening force of this seal does not pass through the tubular specimen 600 used in the multiaxial test, thus decoupling it from the mechanical loading path in the test. The metal vacuum bellows has low axial stiffness and flexible deformation capability, which can absorb axial position deviation (±0.5mm) and flange sealing surface angle deviation (≤1°) during the clamping process, while isolating the additional force generated by the external pipeline connection from the specimen load. The metal vacuum bellows has axial elastic expansion and contraction capability. When the specimen undergoes tensile and compressive cycles and generates axial deformation, the bellows automatically expands and contracts to maintain stable contact pressure of the sealing surface and prevent leakage of liquid lead bismuth.

[0034] The floating sealing base 416 is connected to the other side of the metal vacuum bellows using seamless welding technology. The floating sealing base 416 is connected to the upper base 410 and the lower base 420 at their centers via the external threads of a threaded joint with a bellows, thus achieving installation. A sealing gasket 412 is used to seal the flange face between the end face of the floating sealing base 416 and the plug 417, and a sealing bolt 418 is used to provide preload.

[0035] Before installing the tubular specimen 600 for multiaxial testing and the floating sealing base 416, the upper base 410 and the loading shaft 302 must be connected by bolts through the countersunk hole 415 of the base, so as to transmit the axial load and radial torque applied by the motor.

[0036] After installing the tubular specimen 600 for multi-axis testing, the solenoid valve 701 for liquid lead-bismuth inlet needs to be opened first, allowing the liquid lead-bismuth in the heating tank 100 to flow into the high-temperature liquid metal electromagnetic pump 200, provided the required level is met. Once the start-up requirements are met, the high-temperature liquid metal electromagnetic pump 200 is started, and the circuit is observed for any leakage of liquid lead-bismuth. After ensuring the circuit is safe, the solenoid valve 702 for liquid lead-bismuth outlet is opened to ensure the circuit is unobstructed.

[0037] The fatigue testing multi-functional control cabinet 900 and control computer 901 are used to set the test parameters and test scheme, and record real-time test data for subsequent processing and analysis. During the experiment, the induction heating coil 304 is activated to heat the tubular specimen 600 for multiaxial testing, and the experimental temperature of the tubular specimen 600 for multiaxial testing is monitored using a K-type thermocouple 305. The temperature data is transmitted to the fatigue testing multi-functional control cabinet 900, and the power of the induction heating coil 304 is dynamically controlled based on the comparison with the set temperature. At the same time, the strain extensometer 303 is used to collect strain data during the cyclic loading process and transmit it to the fatigue testing multi-functional control cabinet 900. The motor power is dynamically adjusted according to the set strain control test scheme, and the stress-strain curve is plotted on the control computer 901 in conjunction with the data recorded by the load sensor.

[0038] To reduce errors caused by fluctuations in oxygen concentration, strain rate, and temperature during the experiment, the test must be conducted at high temperature for 2 hours before the experiment. The oxygen concentration data on the display screen of the PLC control cabinet 109 and the temperature and strain data on the fatigue test multi-functional control cabinet 900 should be observed. Once the data is basically stable, the multi-axis tensile and torsion fatigue test can be carried out according to the test plan.

[0039] As an optional implementation, the tubular specimen 600 for multiaxial testing can be replaced with tubular specimens or round bar specimens of other specifications, which is suitable for various specimen types and loading conditions.

[0040] As an extended implementation, the modular special plug and floating sealing base structure can also be used for other types of bases and fixtures, provided that the threaded connection to the specimen or liquid lead-bismuth container is guaranteed.

[0041] As an extended implementation, the external liquid lead-bismuth unit can be transformed into other special environments and gas environments, and further meet the corresponding requirements through an external circuit.

[0042] Working principle of this invention: First, this system achieves oxygen concentration regulation and temperature control of LBE through an external liquid lead-bismuth pipeline unit and an oxygen concentration PLC control gas circuit unit. The LBE in the liquid lead-bismuth heating storage tank 100 is melted and heated to a set temperature, such as 550℃, by an induction heating furnace 108. An oxygen concentration sensor 107 monitors the oxygen concentration of the LBE in the tank in real time. The PLC control cabinet 109 automatically controls the mixing ratio of reducing gas 802 and oxidizing gas 801 based on the difference between the set value and the measured value, and introduces the mixture into the storage tank through a gas pipe 106, so that the LBE reaches the target low oxygen concentration, such as 10%. -8 wt.%. Subsequently, the high-temperature liquid metal electromagnetic pump 200 delivers the required LBE through pipelines and solenoid valve 701 to the side inlet of the upper base 410.

[0043] Inside the upper base 410, the LBE flows vertically through a horizontal channel and enters the central channel of the bellows-equipped rotary joint 411. The bellows-equipped rotary joint 411 uses a welded metal vacuum bellows with extremely low axial stiffness (≤10 N / mm). One end of the metal vacuum bellows is seamlessly welded to the floating sealing base 416, while the other end of the rotary joint is connected to the vertical flow channel of the upper base 410 via external threads. An oxygen-free copper gasket is placed between the lower end face of the floating sealing base 416 and the flange end face of the plug 417, and an initial preload seal is provided by M6 bolts. This preload is entirely borne by the bolts, without the need for a multiaxial test tubular specimen 600, and the metal vacuum bellows automatically adapts to minute angular deviations and axial positional tolerances of the flange face during preload, ensuring uniform contact of the sealing surface.

[0044] Liquid lead-bismuth flows out from the central channel of the rotary joint, passes through the floating sealing base and the 8mm diameter central through-hole of the plug, and enters the inner cavity of the tubular specimen 600 for multiaxial testing. Because the clamping section of the tubular specimen 600 has an M12 internal thread machined in its center, the external thread of the cylindrical section of the plug 417 engages with it, ensuring that the liquid lead-bismuth does not leak from the threaded connection. The liquid lead-bismuth flows downwards along the inner cavity of the specimen, and after reaching the lower base 420, it symmetrically passes through the plug 417, the floating sealing base 416, and the rotary joint 411 with a bellows, finally returning from the lower base side to the outlet via the liquid lead-bismuth outflow pipeline solenoid valve 702 to the liquid lead-bismuth heating storage tank 100, forming a complete closed loop.

[0045] During the multiaxial mechanical test loading process, the drive motor 301 applies axial tensile, compressive, and torsional loads to the tubular specimen 600 for the multiaxial test via the loading shaft 302, upper clamp 510, and lower clamp 520. At this time, the upper clamp 510 further provides frictional force between the anti-slip texture on its inner surface and the outer circular surface of the specimen clamping section through radial clamping bolts 512, and is simultaneously fixed to the upper base 410 through axial connecting bolts 511, directly transferring the load to the specimen. The metal vacuum bellows in the elastic sealing clamp device, due to its low axial stiffness, can freely extend and retract by ±1.5 mm when the tubular specimen 600 undergoes axial elongation or compression, without transferring the additional force generated by the pipe connection to the specimen. Simultaneously, the preload of the flange seal is provided by independent bolts, which does not change with specimen deformation, thus ensuring the stability of the seal. In addition, the flexibility of the metal vacuum bellows can compensate for the axial position deviation of ±0.5 mm and the angular deviation of ≤1° when the specimen is clamped, avoiding locking caused by geometric deviation during the clamping process, and facilitating the clamping of tubular specimens 600 for multiaxial testing.

[0046] Throughout the experiment, the strain extensometer 303 monitors the axial and shear strain of the gauge length of the specimen in real time, feeding the signals back to the fatigue test multi-functional control cabinet 900. The control computer 901 adjusts the motor power according to the set strain control scheme, while the load sensor 306 records stress data and plots stress-strain curves. The induction heating coil 304 and the K-type thermocouple 305 work together to maintain the specimen temperature stability. Thus, this invention realizes multiaxial fatigue testing of tubular specimens in a high-temperature, low-oxygen, flowing LBE environment, with complete decoupling of sealing and mechanical loading functions, without introducing additional interference.

[0047] A method for conducting multiaxial fatigue tests in a liquid lead-bismuth environment using an elastic sealing fixture system, comprising the following steps: Step 1, Preliminary Experiment: 1. Connect the oxygen-controlled mixed gas inlet pipe 106, the oxidizing gas source 801, and the reducing gas source 802 to the oxygen concentration PLC control cabinet 109, and close the rotor flow meter 803 and the solenoid valve 701 for the liquid lead-bismuth inlet pipeline and the solenoid valve 702 for the liquid lead-bismuth outlet pipeline. 2. Turn on the induction heating furnace 108 to heat the solid lead-bismuth alloy in the liquid lead-bismuth heating storage tank 100 to 180°C to melt it; 3. After the lead-bismuth alloy melts into a liquid state at 180 °C, the liquid lead-bismuth heating tank 100 and the top cover are sealed with graphite gaskets and tightened with bolts. Subsequently, the oxygen concentration sensor 107 and the armored thermocouple 102 are sealed with vacuum flanges and vacuum ferrule joints respectively and tightened with bolts and clamps. 4. Turn on the oxygen concentration sensor 107 and the oxygen concentration PLC control cabinet 109 to monitor the oxygen concentration. Adjust the flow rate of the rotor flow meter to 50 mL / min, introduce the mixed gas, and perform the gas washing operation of liquid lead bismuth for 2 hours. Then raise the temperature to the target temperature. 5. After the gas washing is completed, the oxygen concentration in the storage tank is automatically controlled using the oxygen concentration PLC control cabinet 109. Step Two: Formal Experiment 1. Connect the external threaded cylindrical section of the plug 417 to the internal thread at the center of the clamping section on both sides of the tubular specimen 600 for multiaxial testing, and install the rotary joint 411 with bellows and the floating sealing base 416. 2. Connect the plug 417 to the corresponding floating seal base 416 with bolts, and seal the flange with a metal copper gasket; 3. After connecting and sealing the liquid lead-bismuth pipeline with the specimen, use connecting bolts 511 to fix the upper clamp 510 to the upper base 410 through the outer threaded hole. Then, use clamping bolts 512 to pre-tighten circumferentially, pressing the anti-slip texture of the clamp into the tubular specimen 600 for multiaxial testing. This further ensures the transmission of axial load and circumferential torque through slight local deformation. Tighten the connecting bolts and clamping bolts of the lower clamp 520 in the same way to ensure that the specimen will not slip during the test. 4. First, open the solenoid valve 701 of the liquid lead-bismuth inlet pipeline to allow the liquid lead-bismuth that meets the experimental requirements to flow into the high-temperature liquid metal electromagnetic pump 200. After the pump meets the working requirements, start the high-temperature liquid metal electromagnetic pump 200. After confirming that it is safe and there is no leakage, open the solenoid valve 702 of the liquid lead-bismuth outlet pipeline. 5. After the liquid lead-bismuth circulates, start the induction heating coil 304 and preset the specimen temperature through the control computer 901. Install the strain extensometer 303, which is in close contact with the specimen surface. At the same time, connect the signal acquisition line to the fatigue test multi-functional control cabinet 900. 6. Set the multi-axis loading parameters and start the test.

[0048] Although embodiments and drawings of the present invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A multiaxial fatigue testing elastic sealing fixture system for liquid lead-bismuth environments, characterized in that: Includes an external liquid lead-bismuth pipeline unit, an oxygen concentration PLC control gas circuit unit, and a test loading and control unit; The external liquid lead-bismuth pipeline unit includes a liquid lead-bismuth heating storage tank (100), which is connected to a high-temperature liquid metal electromagnetic pump (200) via a pipeline, and the high-temperature liquid metal electromagnetic pump (200) is connected to an elastic sealing clamp device via a pipeline. The oxygen concentration PLC control gas circuit unit includes an oxygen concentration PLC control cabinet (109) and an oxygen concentration sensor (107) installed on the liquid lead-bismuth heating storage tank (100). The oxygen concentration sensor (107) transmits oxygen concentration data to the oxygen concentration PLC control cabinet (109) via a signal line. The oxygen concentration PLC control cabinet (109) is connected to the oxidation gas source (801) and the reduction gas source (802) via a pipeline and a rotor flow meter (803). The test loading and control unit includes a vertical electric cylinder multiaxial fatigue testing machine (300), a multiaxial test tubular specimen (600) located inside the vertical electric cylinder multiaxial fatigue testing machine (300), a load sensor (306), a strain extensometer (303), an induction heating coil (304), a K-type thermocouple (305), and a multi-functional control cabinet (900) and a control computer (901) connecting the vertical electric cylinder multiaxial fatigue testing machine (300); the vertical electric cylinder multiaxial fatigue testing machine (300) drives the loading shaft (302) through the multiaxial motor (301) to apply test loads and torques to the multiaxial test tubular specimen (600) located in the elastic sealing clamp device; The elastic sealing clamp device includes an upper base (410), a lower base (420), an upper clamp (510), a lower clamp (520), a liquid lead-bismuth inlet pipe (414), and a liquid lead-bismuth outlet pipe (421). The upper base (410) is connected to the loading shaft (302), and a load sensor (306) is installed below the lower base (420). The upper base (410) and the lower base (420) are fixedly connected to the upper clamp (510) and the lower clamp (520), respectively. The upper base (410) and the lower base (420) are respectively fixedly connected to the upper clamp (510) and the lower clamp (520). A floating sealing base (416) and a plug (417) are installed between the upper clamp (510) and between the lower base (420) and the lower clamp (520). The tubular specimen (600) for multiaxial testing passes through the upper base (410), the upper clamp (510), the lower base (420), and the lower clamp (520) at both ends, and is connected to the liquid lead bismuth inlet pipe rotary interface (413) and the liquid lead bismuth inlet pipe (414) through the bellows-loaded rotary joint (411) located on the floating sealing base (416). The oxygen concentration PLC control cabinet (109) is connected to the oxygen concentration sensor (107) and is connected to the oxidation gas source (801) and the reduction gas source (802) through pipelines respectively. The inlet of the high temperature liquid metal electromagnetic pump (200) is connected to the outlet of the liquid lead-bismuth heating storage tank (100), and the outlet is connected to the liquid inlet of the upper base (410). The liquid outlet of the lower base (420) returns to the liquid lead-bismuth heating storage tank (100) through pipelines, forming a closed loop.

2. The elastic sealing fixture system for multiaxial fatigue testing in a liquid lead-bismuth environment according to claim 1, characterized in that: The upper base (410) and the lower base (420) are both provided with a horizontal liquid inlet channel and a vertical turning channel. The outer end of the horizontal liquid inlet channel is equipped with a threaded rotary interface (413) for connecting to an external liquid lead-bismuth pipeline. The end of the vertical turning channel is machined with an internal thread interface for connecting to a rotary joint (411) with a bellows.

3. The elastic sealing fixture system for multiaxial fatigue testing in a liquid lead-bismuth environment according to claim 1, characterized in that: The bellows-equipped rotary joint (411) is seamlessly welded from a hollow threaded post and a metal vacuum bellows; wherein the metal vacuum bellows has an inner diameter of 10-15 mm, an outer diameter of 16-20 mm, a wall thickness of 0.2 mm, a free length of 12-15 mm, an axial travel of ±1.5 mm, and an axial stiffness of ≤10 N. mm.

4. The elastic sealing fixture system for multiaxial fatigue testing in a liquid lead-bismuth environment according to claim 3, characterized in that: One end of the hollow threaded column is welded to the metal vacuum bellows, and the other end is detachably connected to the internal thread interfaces of the upper base (410) and the lower base (420) respectively through external threads; the floating sealing base (416) is welded to the other end of the metal vacuum bellows, and the flange end face of the plug (417) is pressed with the corresponding end face of the floating sealing base (416) by circumferentially distributed bolts to form a seal, and the pre-tightening force of the seal does not pass through the tubular specimen (600) for multiaxial test, thus decoupling from the mechanical loading path in the test.

5. The elastic sealing fixture system for multiaxial fatigue testing in a liquid lead-bismuth environment according to claim 4, characterized in that: The plug (417) consists of a flange and a cylindrical section, with a liquid lead-bismuth flow channel through hole in the center; the outer side of the cylindrical section is machined with external threads for detachable screw-in connection with the internal threads in the center of the clamping section of the tubular specimen (600) for multiaxial testing.

6. The elastic sealing fixture system for multiaxial fatigue testing in a liquid lead-bismuth environment according to claim 1, characterized in that: The upper base (410) and lower base (420) are detachably and fixedly connected to the loading shaft (302) and the load sensor (306), respectively.

7. The elastic sealing fixture system for multiaxial fatigue testing in a liquid lead-bismuth environment according to claim 1, characterized in that: The upper clamp (510) and the lower clamp (520) are both hollow ring structures with anti-slip textures on their inner surfaces. The upper clamp (510) and the lower clamp (520) are detachably fixed to the upper base (410) and the lower base (420) respectively by axial connecting bolts (511), and radial preload is applied to the tubular specimen (600) for multiaxial testing by radial clamping bolts (512).

8. A method for conducting multiaxial fatigue tests in a liquid lead-bismuth environment using the elastic sealing fixture system for multiaxial fatigue testing in a liquid lead-bismuth environment as described in any one of claims 1 to 8, characterized in that: Includes the following steps: Step 1, Preliminary Experiment: (1) Connect the oxygen-controlled mixed gas inlet pipe (106), the oxidizing gas source (801), the reducing gas source (802) to the oxygen concentration PLC control cabinet (109), and close the rotor flow meter (803) and the liquid lead-bismuth inlet pipeline solenoid valve (701) and the liquid lead-bismuth outlet pipeline solenoid valve (702). (2) Turn on the induction heating furnace (108) to heat the solid lead-bismuth alloy in the liquid lead-bismuth heating tank (100) to 180°C to melt it; (3) After the lead-bismuth alloy melts into liquid at 180 °C, the liquid lead-bismuth heating tank (100) and the top cover are sealed with graphite gaskets and tightened with bolts. Then, the oxygen concentration sensor (107) and the armored thermocouple (102) are sealed with vacuum flanges and vacuum ferrule joints respectively and tightened with bolts and clamps. (4) Turn on the oxygen concentration sensor (107) and oxygen concentration PLC control cabinet (109) to monitor the oxygen concentration, adjust the flow rate of the rotor flow meter to 50 mL / min, introduce the mixed gas, perform the gas washing operation of liquid lead bismuth for 2 hours, and then raise the temperature to the target temperature. (5) After the gas washing is completed, the oxygen concentration in the storage tank is automatically controlled using the oxygen concentration PLC control cabinet (109). Step Two: Formal Experiment (1) Connect the external thread cylindrical section of the plug (417) to the internal thread at the center of the clamping section on both sides of the tubular specimen (600) for multiaxial testing, and install the rotary joint (411) with bellows and the floating sealing base (416). (2) Connect the plug (417) to the corresponding floating sealing base (416) with bolts, and seal the flange with a metal copper gasket; (3) After the connection and sealing between the liquid lead-bismuth pipeline and the specimen are achieved, the upper clamp (510) and the upper base (410) are fixedly connected by the connecting bolt (511) through the outer ring thread hole. Then, the clamping bolt (512) is used to pre-tighten the circumferentially and press the anti-slip texture of the clamp into the tubular specimen (600) for multiaxial test. The axial load and circumferential torque are further guaranteed by slight local deformation. Tighten the connecting bolts and clamping bolts of the lower clamp (520) in the same manner to ensure that the specimen will not slip during the test; (4) First, open the solenoid valve (701) of the liquid lead-bismuth inlet pipeline so that the liquid lead-bismuth that meets the experimental requirements flows into the high-temperature liquid metal electromagnetic pump (200). After the pump meets the working requirements, start the high-temperature liquid metal electromagnetic pump (200). After confirming that there is no leakage, open the solenoid valve (702) of the liquid lead-bismuth outlet pipeline. (5) After the liquid lead-bismuth circulates, start the induction heating coil (304) and preset the specimen temperature through the control computer (901). Install the strain extensometer (303) and place it close to the surface of the specimen. At the same time, connect the signal acquisition line to the fatigue test multi-functional control cabinet (900). (6) Set the multi-axis loading parameters and start the test.

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