A device for detecting micron-level cracks in in-pile materials under high temperature and high pressure

Abstract

This invention proposes a device for detecting micron-level cracks in in-pile materials under high temperature and high pressure, comprising a sealing head, a gas pipeline, a top cover, an outer sleeve, a double-layer corrugated pipe, a bottom cover, a CT sample block, a pressure sensor placement device, and a force-bearing rod. The double-layer corrugated pipe is connected to the gas pipeline, and a sealing head is installed on the gas pipeline. A top cover is installed between the first corrugated pipe and the gas pipeline. One end of the second corrugated pipe is connected to the force-bearing rod, and a bottom cover is installed between the second corrugated pipe and the force-bearing rod. The force-bearing rod is provided with a detection end fixing hole and a space. The CT sample block is located in the space, and the pressure sensor placement device is installed on the CT sample block. This application can simulate the load under actual application conditions and directly detect the size of the sample crack by reducing the DC potential, with an accuracy of micron-level. All parameter signals are transmitted to the host computer for display via serial communication, and parameters such as crack size changes, device temperature, device pressure, and excitation signal magnitude are monitored in real time.

Description

Technical Field

[0001] This invention belongs to the field of crack detection of in-core environmental materials under high temperature and high pressure conditions in nuclear radiation environments, specifically a device for detecting micron-level cracks in in-core materials under high temperature and high pressure conditions. Background Technology

[0002] With the increasing number of nuclear power plants being built, their safety has become paramount. Research indicates that most nuclear accidents are caused by nuclear leaks from nuclear reactors and pressure vessels. Among these, fatigue failure of critical mechanical equipment such as nuclear power pressure vessels is a major safety hazard.

[0003] In the containers of nuclear radiation reactors, the materials, welding materials, and processes used in different welded parts are all different. The welded structure not only has unstable mechanical properties, but also has residual stress during welding as well as metallurgical defects such as cracks, porosity, and inclusions. In particular, when components are in a high-temperature and high-pressure water environment for a long time, the weld joints are prone to become weak points where cracks can grow and defects can occur. Therefore, in the actual operation of nuclear power plants, stress corrosion cracking (SCC) is a representative example. The reduction in the design life and safety performance of nuclear power equipment caused by SCC is a problem that we urgently need to solve.

[0004] The sudden and insidious nature of SCC crack propagation poses a significant threat to the safety, economy, and service life of nuclear power plants. To date, domestic research on stress corrosion cracking of materials under irradiation conditions has been based on post-reactor irradiation tests. The results obtained represent a final measure of the cumulative changes in the material's physical environment, mechanical properties, and microstructure. This approach fails to determine the synergistic effect between the in-reactor irradiation environment and SCC influencing factors, as well as the process evolution closely related to time, stress load, and irradiation environment.

[0005] This invention relates to a device capable of simulating and observing the crack evolution process in an in-reactor irradiation environment. Through a high-temperature, high-pressure device, it conducts research on online measurement technology for SCC crack propagation during irradiation tests, and develops a standardized device and system for online SCC crack propagation measurement, capable of detecting micron-level crack lengths under nuclear radiation environments. The device includes the following structures: a double-layer bellows, a force load transfer mechanism, a pre-fabricated crack CT sample, a pressure sensor, a gas pipeline, a fixing washer, a high-temperature pressure adapter block, a central guide rod, a central rod guide end cap, a welded threaded head, a support ring, a tightening nut M4, and a single-layer sleeve. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a device for detecting micron-level cracks in in-pile materials under high temperature and pressure. This device can fully simulate the high temperature and pressure environment under nuclear radiation. Through a material tension control unit and a loading mechanism, a constant tensile or compressive force is applied to the material under test, simulating the load under actual application conditions. The size of the crack in the sample can be directly detected through Direct Current Potential Drop (DCPD), with an accuracy down to the micron level. All parameter signals are transmitted to a host computer for display via serial communication, allowing real-time monitoring of changes in crack size, device temperature, device pressure, and the magnitude of the excitation signal. The host computer interface is simple and user-friendly.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A device for detecting micron-level cracks in in-pile materials under high temperature and high pressure, characterized in that it comprises a sealing head, a gas pipeline, a top cover, a double-layer corrugated pipe, a bottom cover, a CT sample block, a pressure sensor placement device, and a force-bearing rod. The double-layer corrugated pipe includes a first corrugated pipe and a second corrugated pipe, which are connected and fixed together. One end of the first corrugated pipe is connected to the gas pipeline, and a sealing head is installed on the gas pipeline. A top cover is installed between the first corrugated pipe and the gas pipeline. One end of the second corrugated pipe is connected to the force-bearing rod, and a bottom cover is installed between the second corrugated pipe and the force-bearing rod. The force-bearing rod has a detection end fixing hole and a space. The CT sample block is located in the space on the force-bearing rod. The CT sample block has a rectangular structure with pre-fabricated cracks from its top to its middle. A first excitation section and a second excitation section are provided on the CT sample block. A first voltage detection section and a second voltage detection section are located within the pre-fabricated cracks. Excitation wires are connected to the first and second excitation sections, and detection wires are connected to the first and second voltage detection sections. The excitation wires and detection wires do not interfere with each other. The excitation wires and detection wires are led out through a gas pipeline to acquire data for display on a host computer. When gas is injected or deflated through the gas pipeline, the first and second bellows push the CT sample block to generate pressure, thus creating a load force on the sample. The sample can then be excited and detected using the excitation wires and detection wires.

[0009] The pressure sensor placement device is installed on the CT sample block. A pressure sensor is installed on the pressure sensor placement device. The pressure sensor placement device also has a fixing hole. A thermocouple is installed in the fixing hole. The detection end of the thermocouple is fixed in the detection end fixing hole. The thermocouple and the pressure sensor do not interfere with each other. A thermocouple wire is connected to the thermocouple. The thermocouple wire is led out through a gas pipeline to acquire data and display it on the host computer.

[0010] In the above structure: This invention proposes a device for detecting micron-level cracks in in-pile materials under high temperature and high pressure, including a sealing head, a gas pipeline, a top cover, a double-layer corrugated pipe, a bottom cover, a CT sample block, a pressure sensor placement device, and a force-bearing rod. The sealing head is used to seal the gas pipeline. The gas pipeline can not only be used for filling and defilling gas, but also to extract the excitation signal (two excitation lines), voltage signal (two detection lines), and thermocouple (two thermocouple wires) from the CT sample block, thereby acquiring data for display on a host computer.

[0011] The top cover at the front end and the bottom cover at the rear end are used to seal the gas pipeline with the first bellows and the second bellows with the load-bearing rod, ensuring the airtightness of the device and providing more comprehensive protection for the entire device. It can protect the internal components from the influence of the external environment, such as dust, moisture, and corrosive gases in the air. When welding the top cover, both ends are fully welded.

[0012] A double-walled bellows is a type of metal pipe with a corrugated shape, typically made of materials such as stainless steel or copper. The first and second bellows act as a connecting device, transmitting external loads to the regulating system. When an external load is applied to the first and second bellows, the medium (nitrogen) inside both bellows experiences a corresponding pressure change, which is then transmitted to other parts of the system, thus regulating the load. The elastic deformation of the two bellows is highly sensitive to pressure changes, allowing for precise adjustment and control of the load.

[0013] The CT sample block has a rectangular structure with a pre-fabricated crack from its upper end to the middle. The CT sample block has a first excitation section and a second excitation section, and a first voltage detection section and a second voltage detection section are located within the pre-fabricated crack. Excitation wires are connected to the first and second excitation sections, and detection wires are connected to the first and second voltage detection sections. The excitation and detection wires connected to the CT sample block need to be bent 90° to the left or right to prevent interference. The excitation and detection wires are led out through a gas pipeline, and the acquired data is displayed on a host computer. When the gas is inflated or deflated through the gas pipeline, the first and second corrugated pipes push the CT sample block to generate pressure, thus creating a load force on the sample. The sample can then be excited and detected by the excitation and detection wires.

[0014] The CT (Compacted Tension) specimen, also known as a compacted tensile specimen, is one of the standard specimen shapes used to study the crack propagation behavior and fracture toughness of materials. It is rectangular and has a central notch or pre-existing crack.

[0015] In the device of the present invention, a first excitation unit, a second excitation unit, a first voltage detection unit, and a second voltage detection unit are respectively provided on the CT sample block. The excitation signal is passed into the first excitation unit and the second excitation unit, and a constant current is passed in. The voltage is set to 1V and the current is set to 1A. The DC voltage source is in constant current mode. The voltage magnitude is detected by the first voltage detection unit and the second voltage detection unit. According to the DCPD algorithm, when the current passing through the sample is constant, the voltage across the crack on the sample will increase with the increase of the crack length. The crack value can be obtained by the magnitude of the voltage.

[0016] The load-bearing rod is used to install and fix the CT sample block and the thermocouple detection end, enabling the CT sample block to better withstand loads. A pre-crack is created at the pre-crack location using a slow wire EDM method, with a minimum crack length of 5µm and a maximum crack length of 6mm.

[0017] The pressure sensor placement device is installed on the CT sample block. A pressure sensor is installed on the pressure sensor placement device. The thermocouple can be placed in the opening of the pressure sensor without interfering with its use. The detection end of the thermocouple is fixed in the detection end fixing hole. A thermocouple wire is connected to the thermocouple. The thermocouple wire is led out through the gas pipeline and the acquired data is displayed on the host computer.

[0018] This device is used in conjunction with the patent "A High-Pressure Gas Regulation System Based on Stress Corrosion Cracking". The first and second connecting seats on the patent correspond to tooling in different environments. Taking the second connecting seat as an example, the four holes are for charging and decharging the two layers of the bellows. The two small holes at 0° and 90° clockwise are for charging the inner layer of the bellows, and the small hole at 180° clockwise is for charging the outer layer. The other hole is for collecting waste materials from the entire device. For detailed information on the high-pressure gas regulation system, please refer to the patent "A High-Pressure Gas Regulation System Based on Stress Corrosion Cracking". The first connecting seat is used to charge another set of tooling.

[0019] To ensure the sealing of the electric heating element, thermocouple, and signal cable, this invention adds a sealing element, which mainly consists of a sealing head connector, a sealing head gasket, a sealing head sealing pad, a sealing head gland, and a sealing head nut.

[0020] The sealing head gasket includes a Teflon sealing ring, which is located between the connector and the sealing head to provide additional sealing and protection. It fills the gap between the contact surfaces, ensuring a tight seal. There are eight 3.5mm through holes on the ring with radii of 50mm and 57mm.

[0021] It also includes a retaining washer, which is located between the joint and the sealing head to provide additional sealing and protection. It fills the gap between the contact surfaces, ensuring a tight seal.

[0022] These sealing heads and their components effectively protect the internal electric heating elements, thermocouples, and signal cables, ensuring the required airtightness in the gas environment testing apparatus. This design prevents interference from the external environment, provides stable testing conditions, and ensures accurate measurements and data acquisition.

[0023] As a preferred technical solution of the present invention, it further includes an outer tube, which has an opening and includes a shell wall and a shell cover. The first corrugated pipe is installed in the opening, and the shell cover is connected to the top cover.

[0024] In the above structure: In order for the device to operate normally in an atmospheric environment, by placing the entire device under the cover of the extended outer tube, the inside of the first bellows can be protected from the influence of the external environment, such as dust, moisture, corrosive gases in the air.

[0025] As a preferred embodiment of the present invention, it further includes a first end cap, a second end cap, and a central guide rod. The first end cap is installed at one end of the first corrugated pipe, the end of the central guide rod is fixed on the first end cap, the second corrugated pipe is sleeved on the central guide rod, and the second end cap is installed at the end of the second corrugated pipe.

[0026] In the above structure: the first end cap is used to install the central guide rod, and the second bellows is installed and fixed through the central guide rod and the second end cap.

[0027] As a preferred embodiment of the present invention, it further includes a sealing end cap, which is installed on the opening of the outer sleeve, and the sealing end cap is provided with a through hole, through which the central guide rod passes.

[0028] In the above structure: a sealing end cap is installed on the opening of the outer tube, which can achieve a seal between the outer tube and the second corrugated tube to prevent air leakage.

[0029] As a preferred technical solution of the present invention: the gas pipeline includes a stainless steel pipe and a sample outlet, the top cover includes a first concentric circular pipe and a second concentric circular pipe, the first concentric circular pipe and the second concentric circular pipe are respectively provided with mounting through holes, the stainless steel pipe and the sample outlet are respectively installed in the mounting through holes, and the excitation line and the detection line are respectively located in the sample outlet.

[0030] In the above structure: the stainless steel tube is used to realize the inflation and deflation of the device; the top cover is composed of two concentric first concentric circular tubes and second concentric circular tubes; the stainless steel tube and the sample outlet are respectively installed in the mounting through hole; the sample outlet is used to realize the lead-out of the excitation line and the detection line, so as to facilitate data acquisition.

[0031] As a preferred technical solution of the present invention: the force-bearing rod includes a force-bearing block and a connecting block. The force-bearing block includes two concave first force-bearing blocks and a second force-bearing block. The first force-bearing block and the second force-bearing block are connected by the connecting block. The first force-bearing block and the second force-bearing block are respectively provided with a first connecting hole and a second connecting hole. The detection end fixing hole is opened on the connecting block. The empty space is the gap between the first force-bearing block and the second force-bearing block. The concave surface on the first force-bearing block and the second force-bearing block is a plane.

[0032] As a preferred technical solution of the present invention: the CT sample block is provided with a first sample fixing hole and a second sample fixing hole, the first sample fixing hole and the second sample fixing hole are fixed in the first connecting hole and the second connecting hole by a sample fixing device and are located in the open space, the plane is used to place the sample, and the length of the plane is determined by the size of the sample.

[0033] In the above structure: the force-bearing rod includes a force-bearing block and a connecting block. The force-bearing block includes two concave first force-bearing blocks and a second force-bearing block. The first force-bearing block and the second force-bearing block are connected by the connecting block. The first sample fixing hole and the second sample fixing hole on the CT sample block are connected to the first connecting hole and the second connecting hole by gaskets, respectively. The main part of the CT sample block is placed in the open space. The detection end of the thermocouple is placed through the detection end fixing hole. The length of the plane is determined by the size of the sample.

[0034] As a preferred technical solution of the present invention: the pressure sensor placement device further includes a first base column, a first fixing hole, a second fixing hole, a second base column, and a chassis. The pressure sensor is placed on the chassis, and the first and second base columns are used for support. The signal lines of the pressure sensor are led out through the first fixing hole and the second fixing hole, respectively.

[0035] In the above structure: the first and second base columns provide support and are 20mm in length. The first and second fixing holes are for leading out the signal wire of the pressure sensor and are M4 in size. The pressure sensor is placed on the chassis and has a diameter of 16mm, allowing for perfect placement of the pressure sensor on the chassis. The first fixing hole has a completely symmetrical structure and is 3.4mm in size, which can fix the pressure sensor at the bottom of the entire device, ensuring that the pressure sensor is not moved. There are four symmetrical second fixing holes on opposite sides for fixing the device from the left and right.

[0036] As a preferred technical solution of the present invention, it further includes a main control device, which is connected to the host computer via an RS422 module. The main control device includes a K-type thermocouple detection circuit, a current commutation circuit, and a main control chip. The K-type thermocouple detection circuit and the current commutation circuit are driven by the main control chip to realize the measurement of thermocouples and the elimination of thermoelectric potential. The pressure sensor is connected to the main control chip to realize the acquisition of pressure data.

[0037] In the above structure, the main control device integrates the measurement of K-type thermocouples, the data acquisition of pressure sensors, the implementation of DCPD algorithm, and the implementation of voltage and current excitation signals.

[0038] K-type thermocouple detection circuit: IN0 and IN1 are used as differential inputs, filtered by C204 and C206 respectively, and the differential input terminals are pulled up to 3.3V by R206 and R212. The resistance of R206 and R212 is 10MΩ. This chip is driven by SPI2.

[0039] The current commutation circuit consists of four solid-state relays: U601, U602, U603, and U604. It uses a ULN2003 chip (U600) as the driver to improve load-carrying capacity; this chip is suitable for driving high-speed, high-power systems. The current commutation module eliminates the influence of thermoelectric potential on test parameters. It operates on a 5V power supply and utilizes two I / O ports of the main control chip: PB6 and PB7.

[0040] PB6 and PB7 are connected to IN1 and IN2 to control the high and low levels of U600. The No.1 I / O port of the four relays is pulled high by 5V. One output port of ULN2003 is connected to the No.2 port of U601 and U603 (1C), and the other output port of ULN2003 is connected to the No.2 port of U602 and U604 (2C), thus completing the circuit connection of the solid-state relay control terminal.

[0041] The fourth I / O port of U601 and U602 is connected together to I+, and the fourth I / O port of U603 and U604 is connected together to I-. The third I / O port of U601 and U604 is connected together to I1+, which is the current inflow terminal of the CT sample. The third I / O port of U602 and U603 is connected together to I1-, which is the current outflow terminal of the CT sample. The direction of the current can be controlled by controlling the high and low levels of PB6 and PB7. When PB6 is high and PB7 is low, IC1 outputs high and IC2 outputs low. U601 and U603 are disconnected because the voltage difference between their two input pins is less than 0.5V, while U602 and U604 are closed because the voltage difference between their two input pins is less than 4.5V. When current I+ flows in, U601 is disconnected and U602 is closed. Therefore, the current flows into the CT sample through U602 and back to I- through U604. When PB6 is low and PB7 is high, the situation is reversed. The current flows into the CT sample through U601 and back to I- through U603.

[0042] The pressure display box shows the current pressure and temperature within the fixture; the crack algorithm sets parameters for the relationship between various voltages and crack values, defining different relationships for different crack lengths; the voltage and current excitation signal box sets the excitation magnitude, allowing settings for voltage, current, overvoltage, and overcurrent; the control box allows selection to enable or disable output, which takes effect upon clicking "OK"; the wire frame displays the voltage detected on the CT sample block, and the crack value can be calculated using the formulas in the crack algorithm. Real-time voltage and crack values ​​are displayed as curves on the voltage and crack curves, respectively.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] I. This invention is a detection device integrating mechanical design, hardware circuit design, software driving, and host computer development. It includes: the design of a double-layer bellows, a force load transmission mechanism, a pre-fabricated crack CT sample block, the placement and design of a pressure sensor, the installation of thermocouples, the setting of DC power supply parameters, the reading of nanovoltmeter data, the conversion of real-time voltage to crack value, current commutation settings, ADS1220 chip driving, RS485 sensor driving, RS232 instrument communication, and the implementation of RS422 communication. It is a complete system, ready to use upon startup.

[0045] Second, this invention can fully simulate the high temperature and high pressure environment under nuclear radiation. Through the material tension control unit and the loading mechanism, a constant tension or pressure is applied to the material under test to simulate the load under actual application conditions. The size of the crack in the sample can be directly detected by the DC potential reduction method with an accuracy of micrometer level.

[0046] Third, the present invention features a double-layer corrugated pipe design, which uses four electric ball valves to achieve inflation and deflation. Electric valve No. 1 controls the inflation of the outer layer, electric valves No. 2 and No. 3 control the inflation of the inner layer, and electric ball valve No. 4 deflates the pipe. The deflation device also provides exhaust gas treatment.

[0047] IV. Sealing Design of the Device: To ensure the sealing of the electric heating element, thermocouple, and signal cable, a sealing head is added. The sealing head structure mainly consists of a sealing head connector, a sealing head gasket, a sealing head sealing pad, a sealing head gland, and a sealing head nut. This design prevents interference from the external environment, provides stable test conditions, and ensures accurate measurement and data acquisition.

[0048] Fifth, the hardware of this invention has a high degree of integration, with all functions concentrated on a 10cm*10cm circuit board. The CT sample can be directly connected to the circuit board, and the circuit can withstand a maximum current of 5A. Within the current carrying capacity of the CT sample, the current commutation circuit on the hardware can perfectly meet the commutation requirements.

[0049] VI. Voltage and crack values ​​are displayed in real-time as line graphs, providing a clear view of crack length growth. The applied excitation (current, voltage, overcurrent, and overvoltage) can be viewed on the host computer, and the voltage value will change in real time when the excitation magnitude is altered during the experiment. Attached Figure Description

[0050] Figure 1 This is the system overview diagram of the present invention;

[0051] Figure 2 This is a schematic diagram of the overall structure of the present invention;

[0052] Figure 3 This is a schematic diagram of a load-bearing rod structure;

[0053] Figure 4 This is a schematic diagram of the external structure of the present invention;

[0054] Figure 5 This is a schematic diagram of the outer tube structure;

[0055] Figure 6 This is a schematic diagram of the AA end face of the present invention;

[0056] Figure 7 This is a schematic diagram of the cross-sectional structure of a double-layer corrugated pipe;

[0057] Figure 8 This is a schematic diagram of the gas pipeline structure;

[0058] Figure 9 This is a schematic diagram of a high-pressure gas regulation system based on stress corrosion cracking.

[0059] Figure 10 This is a schematic diagram of the pressure sensor placement device.

[0060] Figure 11 This is a schematic diagram of the support ring structure;

[0061] Figure 12 This is a schematic diagram of the Teflon sealing ring structure;

[0062] Figure 13 This is a schematic diagram of the fixed washer structure;

[0063] Figure 14 This is a schematic diagram of the CT sample block structure;

[0064] Figure 15 This is a circuit connection diagram for a type K thermocouple;

[0065] Figure 16 This is a connection diagram of the current commutation circuit;

[0066] Figure 17 This is the circuit connection diagram for the RS232 module;

[0067] Figure 18 This is a screenshot of the host computer monitoring interface.

[0068] List of reference numerals in the attached diagram:

[0069] 1. Sealing head; 2. Gas pipeline; 3. Top cover; 31. Mounting through hole; 32. First concentric tube; 33. Second concentric tube; 34. Stainless steel tube; 35. Sample outlet; 4. Outer tube; 41. Opening; 42. Shell wall; 43. Shell cover; 44. Sealing end cover; 45. First end cover; 46. First corrugated tube; 5. Double-layer corrugated tube; 51. Second end cover; 52. Central guide rod; 53. Second corrugated tube; 6. Bottom cover; 7. Sample fixing device; 8. CT sample block; 81. First excitation unit; 82. First voltage detection unit; 83. Second voltage detection unit 84. Second excitation part; 85. First sample fixing hole; 86. Second sample fixing hole; 87. Pre-crack; 9. Pressure sensor placement device; 91. First base column; 92. First fixing hole; 93. Second fixing hole; 94. Second base column; 95. Base plate; 96. Lead-out hole; 10. Force rod; 101. First connecting hole; 102. Detection end fixing hole; 103. Plane; 104. Open space; 105. Second connecting hole; 106. First force block; 107. Second force block; 108. Connecting block; 11. First connecting seat; 12. Second connecting seat. Detailed Implementation

[0070] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0071] like Figure 1-18 As shown, this invention proposes a device for detecting micron-level cracks in in-pile materials under high temperature and high pressure, comprising a sealing head 1, a gas pipeline 2, a top cover 3, a double-layer corrugated pipe 5, a bottom cover 6, a CT sample block 8, a pressure sensor placement device 9, and a force-bearing rod 10. The double-layer corrugated pipe 5 includes a first corrugated pipe 46 and a second corrugated pipe 53, which are connected and fixed together. One end of the first corrugated pipe 46 is connected to the gas pipeline 2, and the sealing head 1 is installed on the gas pipeline 2. The top cover 3 is installed between the first corrugated pipe 46 and the gas pipeline 2. One end of the second corrugated pipe 53 is connected to the force-bearing rod 10, and the bottom cover 6 is installed between the second corrugated pipe 53 and the force-bearing rod 10. The force-bearing rod 10 is provided with a detection end fixing hole 102 and a space 104. The CT sample block 8 is located in the space 10 on the force-bearing rod 10. In section 04, the CT sample block 8 has a rectangular structure with a pre-fabricated crack 87 extending from its upper end to its middle. The CT sample block 8 has a first excitation part 81 and a second excitation part 84. A first voltage detection part 82 and a second voltage detection part 83 are provided in the pre-fabricated crack 87. Excitation wires are connected to the first excitation part 81 and the second excitation part 84, and detection wires are connected to the first voltage detection part 82 and the second voltage detection part 83. The excitation wires and detection wires do not interfere with each other. The excitation wires and detection wires are led out through the gas pipeline 2 to acquire data for display on the host computer. When the gas is filled or defilled through the gas pipeline 2, the first corrugated pipe 46 and the second corrugated pipe 53 push the CT sample block 8 to generate pressure, which generates a load force on the sample. At this time, the sample can be excited and detected by the excitation wires and detection wires.

[0072] The pressure sensor placement device 9 is installed on the CT sample block 8. A pressure sensor is installed on the pressure sensor placement device 9. The pressure sensor placement device 9 also has a fixing hole. A thermocouple is installed in the fixing hole. The detection end of the thermocouple is fixed in the detection end fixing hole 102. The thermocouple and the pressure sensor do not interfere with each other. A thermocouple wire is connected to the thermocouple. The thermocouple wire is led out through the gas pipeline 2 and the acquired data is displayed on the host computer.

[0073] It also includes an outer tube 4, which has an opening 41 and includes a shell wall 42 and a shell cover 43. The first corrugated tube 46 is installed in the opening 41, and the shell cover 43 is connected to the top cover 3.

[0074] It also includes a first end cap 45, a second end cap 51, and a central guide rod 52. The first end cap 45 is installed at one end of the first corrugated pipe 46, the end of the central guide rod 52 is fixed on the first end cap 45, the second corrugated pipe 53 is sleeved on the central guide rod 52, and the second end cap 51 is installed at the end of the second corrugated pipe 53.

[0075] It also includes a sealing end cap 44, which is installed on the opening 41 of the outer sleeve 4. The sealing end cap 44 is provided with a through hole, and the central guide rod passes through the sealing end cap 44.

[0076] The gas pipeline 2 includes a stainless steel pipe 34 and a sample outlet 35. The top cover 3 includes a first concentric circular pipe 32 and a second concentric circular pipe 33. The first concentric circular pipe 32 and the second concentric circular pipe 33 are respectively provided with mounting through holes 31. The stainless steel pipe 34 and the sample outlet 35 are respectively installed in the mounting through holes 31. The excitation line and the detection line are respectively located in the sample outlet 35.

[0077] The force-bearing rod 10 includes a force-bearing block and a connecting block 108. The force-bearing block includes two concave first force-bearing blocks 106 and second force-bearing blocks 107. The first force-bearing blocks 106 and second force-bearing blocks 107 are connected by the connecting block 108. The first force-bearing blocks 106 and second force-bearing blocks 107 are respectively provided with a first connecting hole 101 and a second connecting hole 105. The detection end fixing hole 102 is opened on the connecting block 108. The gap 104 is the gap between the first force-bearing blocks 106 and second force-bearing blocks 107. The concave surfaces on the first force-bearing blocks 106 and second force-bearing blocks 107 are planes 103.

[0078] The CT sample block 8 is provided with a first sample fixing hole 85 and a second sample fixing hole 86. The first sample fixing hole 85 and the second sample fixing hole 86 are fixed in the first connecting hole 101 and the second connecting hole 105 by the sample fixing device 7 and are located in the open space 104. The plane 103 is used to place the sample, and the length of the plane 103 is determined by the size of the sample.

[0079] The pressure sensor placement device 9 further includes a first base post 91, a first fixing hole 92, a second fixing hole 93, a second base post 94, and a chassis 95. The pressure sensor is placed on the chassis 95. The first base post 91 and the second base post 94 are used for support. The signal line of the pressure sensor is led out through the first fixing hole 92 and the second fixing hole 93, respectively.

[0080] It also includes a main control device, which is connected to the host computer via an RS422 module. The main control device includes a K-type thermocouple detection circuit, a current commutation circuit, and a main control chip. The K-type thermocouple detection circuit and the current commutation circuit are driven by the main control chip to realize the measurement of thermocouples and the elimination of thermoelectric potential. The pressure sensor is connected to the main control chip to realize the acquisition of pressure data.

[0081] This invention proposes a device for detecting micron-level cracks in in-pile materials under high temperature and high pressure, comprising a sealing head 1, a gas pipeline 2, a top cover 3, a double-layer corrugated pipe 5, a bottom cover 6, a CT sample block 8, a pressure sensor placement device 9, and a force-bearing rod 10. The sealing head 1 is used to seal the gas pipeline 2. The gas pipeline 2 can not only be used to charge and depressurize, but also to extract the excitation signal (two excitation lines), voltage signal (two detection lines), and thermocouple (two thermocouple wires) of the CT sample block 8, thereby acquiring data for display on the host computer.

[0082] The top cover 3 at the front end and the bottom cover 6 at the rear end are used to achieve the sealing treatment between the gas pipeline 2 and the first corrugated pipe 46, and the second corrugated pipe 53 and the force rod 10, which ensures the airtightness of the device and provides more comprehensive protection for the entire device. It can protect the internal components from the influence of the external environment, such as dust, moisture, and corrosive gases in the air. When welding the top cover 3, the two ends are fully welded.

[0083] The double-walled bellows 5 is a corrugated metal pipe, typically made of materials such as stainless steel or copper. The first bellows 46 and the second bellows 53 act as a connecting device, transmitting external load forces to the regulating device. When an external load force is applied to the first bellows 46 and the second bellows 53, the medium (nitrogen) inside the two bellows experiences a corresponding pressure change, which is then transmitted to other parts of the device, thereby regulating the load force. The elastic deformation of the two bellows is highly sensitive to pressure changes, enabling precise adjustment and control of the load force.

[0084] The CT sample block 8 has a rectangular structure with a pre-fabricated crack 87 extending from its upper end to its middle. The CT sample block 8 has a first excitation section 81 and a second excitation section 84. A first voltage detection section 82 and a second voltage detection section 83 are located within the pre-fabricated crack 87. Excitation wires are connected to the first excitation section 81 and the second excitation section 84, and detection wires are connected to the first voltage detection section 82 and the second voltage detection section 83. The excitation wires and detection wires connected to the CT sample block 8 need to be bent 90° to the left or right to prevent interference. The excitation wires and detection wires are led out through the gas pipeline 2, acquiring data for display on the host computer. When the gas is filled or deflated through the gas pipeline 2, the first corrugated pipe 46 and the second corrugated pipe 53 push the CT sample block 8 to generate pressure, thus generating a load force on the sample. The sample can then be excited and detected by the excitation wires and detection wires.

[0085] The CT (Compacted Tension) specimen, also known as a compacted tensile specimen, is one of the standard specimen shapes used to study the crack propagation behavior and fracture toughness of materials. It is rectangular with a central notch or pre-existing crack.

[0086] In the device of the present invention, a first excitation unit 81, a second excitation unit 84, a first voltage detection unit 82, and a second voltage detection unit 83 are respectively provided on the CT sample block. The excitation signal is passed into the first excitation unit 81 and the second excitation unit 84, and a constant current is passed in. The voltage is set to 1V and the current is set to 1A. The DC voltage source is in constant current mode. The voltage magnitude is detected by the first voltage detection unit 82 and the second voltage detection unit 83. According to the DCPD algorithm, when the current passing through the sample is constant, the voltage across the crack on the sample will increase with the increase of the crack length. The crack value can be obtained by the magnitude of the voltage.

[0087] The force-bearing rod 10 is used to install and fix the CT sample block 8 and the thermocouple detection end. The force-bearing rod 10 enables the CT sample block 8 to better withstand load forces. A pre-crack is pre-induced at the pre-crack 87 by slow wire cutting. The minimum crack length is 5 μm and the maximum crack length is 6 mm.

[0088] The pressure sensor placement device 9 is installed on the CT sample block 8. A pressure sensor is installed on the pressure sensor placement device 9. The thermocouple can be placed in the opening 41 of the pressure sensor without interfering with its use. The detection end of the thermocouple is fixed in the detection end fixing hole 102. A thermocouple wire is connected to the thermocouple. The thermocouple wire is led out through the gas pipeline 2 and the data is acquired and displayed on the host computer.

[0089] This device is used in conjunction with the patent "A High-Pressure Gas Regulation System Based on Stress Corrosion Cracking". The first connecting seat 11 and the second connecting seat 12 on the patent correspond to tooling in different environments. Taking the second connecting seat 12 as an example, the four holes are used to charge and de-charge the two interlayers of the two bellows. The two small holes at 0° and 90° clockwise are for charging the inner interlayer of the bellows, and the small hole at 180° clockwise is for charging the outer interlayer. The other hole is for collecting waste materials from the entire device. For detailed information on the high-pressure gas regulation system, please refer to the patent "A High-Pressure Gas Regulation System Based on Stress Corrosion Cracking". The first connecting seat 11 is used to charge another set of tooling.

[0090] To ensure the sealing of the electric heating element, thermocouple, and signal cable, this invention adds a sealing element. The sealing element mainly consists of a sealing head 1 connector, a sealing head 1 washer, a sealing head 1 gasket, a sealing head 1 gland, and a sealing head 1 nut.

[0091] The sealing head 1 gasket includes a Teflon sealing ring, which is located between the connector and sealing head 1 to provide additional sealing and protection. It fills the gap between the contact surfaces, ensuring a tight seal. There are eight 3.5mm through holes on the ring with radii of 50mm and 57mm.

[0092] It also includes a retaining washer, located between the connector and sealing head 1, to provide additional sealing and protection. It fills the gap between the contact surfaces, ensuring a tight seal.

[0093] These sealing heads 1 and their components effectively protect the internal electric heating elements, thermocouples, and signal cables, ensuring the required airtightness in the gas environment testing apparatus. This design prevents interference from the external environment, provides stable testing conditions, and ensures accurate measurements and data acquisition.

[0094] In order for the device to operate normally in an atmospheric environment, the first bellows 46 can be protected from the influence of the external environment, such as dust, moisture, and corrosive gases in the air, by placing the entire device under the cover of the extended outer tube 4.

[0095] The first end cap 45 is used to install the central guide rod 52, and the second bellows 53 is installed and fixed through the central guide rod 52 and the second end cap 51.

[0096] A sealing end cap 44 is installed on the opening 41 of the outer tube 4, which can achieve a seal between the outer tube 4 and the second corrugated tube 53 to prevent air leakage.

[0097] The stainless steel tube 34 is used to charge and de-charge the device. The top cover 3 is composed of two concentric first concentric circular tubes 32 and second concentric circular tubes 33. The stainless steel tube 34 and the sample outlet 35 are respectively installed in the mounting through hole 31. The sample outlet 35 is used to bring out the excitation line and the detection line for easy data acquisition.

[0098] The force-bearing rod 10 includes a force-bearing block and a connecting block 108. The force-bearing block includes two concave first force-bearing blocks 106 and second force-bearing blocks 107. The first force-bearing blocks 106 and second force-bearing blocks 107 are connected by the connecting block 108. The first sample fixing hole 85 and the second sample fixing hole 86 on the CT sample block 8 are respectively connected to the first connecting hole 101 and the second connecting hole 105 through gaskets. The main part of the CT sample block 8 is placed in the open space 104. The detection end of the thermocouple is placed through the detection end fixing hole 102. The length of the plane 103 is determined by the size of the sample.

[0099] The first base post 91 and the second base post 94 provide support and are 20mm in length. The first fixing hole 92 and the second fixing hole 93 are for leading out the signal wire of the pressure sensor and are M4 in size. The pressure sensor is placed on the chassis 95 and has a diameter of 16mm, which allows for a perfect placement of the pressure sensor on the chassis 95. The first fixing hole 92 has a completely symmetrical structure and is 3.4mm in size, which can fix the pressure sensor at the bottom of the entire device and ensure that the pressure sensor is not moved. There are four symmetrical second fixing holes 93 on both sides for fixing the device from the left and right.

[0100] The main control unit integrates the measurement of K-type thermocouples, the data acquisition of pressure sensors, the implementation of DCPD algorithms, and the implementation of voltage and current excitation signals.

[0101] K-type thermocouple detection circuit: IN0 and IN1 are used as differential inputs, filtered by C204 and C206 respectively, and the differential input terminals are pulled up to 3.3V by R206 and R212. The resistance of R206 and R212 is 10MΩ. This chip is driven by SPI2.

[0102] The current commutation circuit consists of four solid-state relays: U601, U602, U603, and U604. It uses a ULN2003 chip (U600) as the driver to improve load-carrying capacity; this chip is suitable for driving high-speed, high-power systems. The current commutation module eliminates the influence of thermoelectric potential on test parameters. It operates on a 5V power supply and utilizes two I / O ports of the main control chip: PB6 and PB7.

[0103] PB6 and PB7 are connected to IN1 and IN2 to control the high and low levels of U600. The IO ports of the four relays are pulled high by 5V. One output port of ULN2003 is connected to port 2 of U601 and U603 (1C), and the other output port of ULN2003 is connected to port 2 of U602 and U604 (2C), thus completing the circuit connection of the solid-state relay control terminal.

[0104] The fourth I / O port of U601 and U602 is connected together to I+, and the fourth I / O port of U603 and U604 is connected together to I-. The third I / O port of U601 and U604 is connected together to I1+, which is the current inflow terminal of the CT sample. The third I / O port of U602 and U603 is connected together to I1-, which is the current outflow terminal of the CT sample. The direction of the current can be controlled by controlling the high and low levels of PB6 and PB7. When PB6 is high and PB7 is low, IC1 outputs high and IC2 outputs low. U601 and U603 are disconnected because the voltage difference between their two input pins is less than 0.5V, while U602 and U604 are closed because the voltage difference between their two input pins is less than 4.5V. When current I+ flows in, U601 is disconnected and U602 is closed. Therefore, the current flows into the CT sample through U602 and back to I- through U604. When PB6 is low and PB7 is high, the situation is reversed. The current flows into the CT sample through U601 and back to I- through U603.

[0105] The pressure display box shows the current pressure and temperature within the fixture; the crack algorithm sets parameters for the relationship between various voltages and crack values, defining different relationships for different crack lengths; the voltage and current excitation signal box sets the excitation magnitude, allowing settings for voltage, current, overvoltage, and overcurrent; the control box allows selection to enable or disable output, which takes effect upon clicking "OK"; the wire display box shows the voltage detected on CT sample block 8, and the crack value can be calculated using the formulas in the crack algorithm. Real-time voltage and crack values ​​are displayed as curves on the voltage curve and crack curve, respectively.

[0106] The present invention is compared with the prior art as follows:

[0107] I. Most existing crack detection systems are designed for non-destructive or destructive testing under normal conditions. However, the device of this invention can perform micron-level crack detection under high temperature and high pressure conditions in nuclear radiation environments. It has high detection accuracy, can operate at a maximum pressure of 10 MPa, and a maximum temperature of 400 degrees Celsius, with stable and reliable results.

[0108] Second, existing crack detection systems can only measure pre-existing cracks when the experimental testing equipment is stable and reliable. However, the device of this invention, in conjunction with "A High-Pressure Gas Regulation System Device Based on Stress Corrosion Cracking", can simulate and observe the crack evolution process in the in-reactor irradiation environment, conduct research on online measurement technology of SCC crack propagation during irradiation tests, and develop a standardized device and system for online measurement of SCC crack propagation.

[0109] Third, in existing crack detection devices, the CT sample is usually placed in an exposed position. The device of this invention is equipped with high temperature and high pressure resistant tooling, and the sample is detected in a closed space, which can shield a lot of noise interference.

[0110] Fourth, existing crack detection devices use either non-destructive or destructive methods for detection. The device of this invention, by adding a current conversion module through the DC potential drop method, eliminates the influence of thermoelectric potential and can effectively improve accuracy.

[0111] Fifth, existing crack detection systems generally lack complex circuit designs and do not reflect the temperature and pressure conditions of the device. The device of this invention collects data from thermocouples and pressure sensors through the main control circuit and packages it for display on the host computer.

[0112] VI. Existing crack detection systems rarely have a host computer display interface. All parameter signals are transmitted to the host computer for display via serial communication, which monitors parameters such as crack size changes, device temperature, device pressure, and excitation signal magnitude in real time. The host computer operation interface is simple and user-friendly.

[0113] VII. Existing crack detection systems typically use a fatigue tensile testing machine to create pre-cracks 87. In contrast, the device of this invention creates pre-cracks 87 using a slow wire cutting machine. The crack length can be controlled within 1µm, resulting in high crack precision and good performance.

[0114] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A device for detecting micron-level cracks in in-pile materials under high temperature and high pressure, characterized in that: The system includes a sealing head (1), an air passage pipe (2), a top cover (3), a double-layer corrugated pipe (5), a bottom cover (6), a CT sample block (8), a pressure sensor placement device (9), and a force-bearing rod (10). The double-layer corrugated pipe (5) includes a first corrugated pipe (46) and a second corrugated pipe (53). The first corrugated pipe (46) and the second corrugated pipe (53) are connected and fixed. One end of the first corrugated pipe (46) is connected to the air passage pipe (2). (2) A sealing head (1) is installed on it. A top cover (3) is installed between the first corrugated pipe (46) and the gas pipeline (2). One end of the second corrugated pipe (53) is connected to a force-bearing rod (10). A bottom cover (6) is installed between the second corrugated pipe (53) and the force-bearing rod (10). The force-bearing rod (10) is provided with a detection end fixing hole (102) and a space (104). The CT sample block (8) is located in the space (104) on the force-bearing rod (10). In this design, the CT sample block (8) has a rectangular structure with pre-fabricated cracks (87) from its upper end to its middle. The CT sample block (8) is provided with a first excitation part (81) and a second excitation part (84). A first voltage detection part (82) and a second voltage detection part (83) are provided in the pre-fabricated cracks (87). Excitation wires are connected to the first excitation part (81) and the second excitation part (84), and detection wires are connected to the first voltage detection part (82) and the second voltage detection part (83). The excitation wires and detection wires do not interfere with each other. The excitation wires and detection wires are led out through the gas pipeline (2) to acquire data and display it on the host computer. When the gas is filled or defilled through the gas pipeline (2), the first corrugated pipe (46) and the second corrugated pipe (53) push the CT sample block (8) to generate pressure. At this time, a load force can be generated on the sample. At this time, the sample can be excited and detected by the excitation wires and detection wires. The pressure sensor placement device (9) is installed on the CT sample block (8). The pressure sensor is installed on the pressure sensor placement device (9). The pressure sensor placement device (9) also has a fixing hole. A thermocouple is installed in the fixing hole. The detection end of the thermocouple is fixed in the detection end fixing hole (102). The thermocouple and the pressure sensor do not interfere with each other. A thermocouple wire is connected to the thermocouple. The thermocouple wire is led out through the gas pipeline (2) to obtain data and display it on the host computer. The force-bearing rod (10) includes a force-bearing block and a connecting block (108). The force-bearing block includes two concave first force-bearing blocks (106) and second force-bearing blocks (107). The first force-bearing blocks (106) and second force-bearing blocks (107) are connected by the connecting block (108). The first force-bearing blocks (106) and second force-bearing blocks (107) are respectively provided with a first connecting hole (101) and a second connecting hole (105). The detection end fixing hole (102) is opened on the connecting block (108). The gap (104) is the gap between the first force-bearing blocks (106) and second force-bearing blocks (107). The concave surfaces on the first force-bearing blocks (106) and second force-bearing blocks (107) are flat surfaces (103). The CT sample block (8) is provided with a first sample fixing hole (85) and a second sample fixing hole (86). The first sample fixing hole (85) and the second sample fixing hole (86) are fixed in the first connecting hole (101) and the second connecting hole (105) by the sample fixing device (7) and are located in the open space (104). The plane (103) is used to place the sample, and the length of the plane (103) is determined by the size of the sample.

2. The device for detecting micron-level cracks in in-pile materials under high temperature and high pressure according to claim 1, characterized in that: It also includes an outer tube (4), which has an opening (41) and includes a shell wall (42) and a shell cover (43). The first corrugated tube (46) is installed in the opening (41), and the shell cover (43) is connected to the top cover (3).

3. The device for detecting micron-level cracks in in-pile materials under high temperature and high pressure according to claim 2, characterized in that: It also includes a first end cap (45), a second end cap (51), and a central guide rod (52). The first end cap (45) is installed on one end of the first corrugated pipe (46), the end of the central guide rod (52) is fixed on the first end cap (45), the second corrugated pipe (53) is sleeved on the central guide rod (52), and the second end cap (51) is installed on the end of the second corrugated pipe (53).

4. The device for detecting micron-level cracks in in-pile materials under high temperature and high pressure according to claim 3, characterized in that: It also includes a sealing end cap (44), which is installed on the opening (41) of the outer sleeve (4). The sealing end cap (44) has a through hole, and the central guide rod passes through the sealing end cap (44).

5. The device for detecting micron-level cracks in in-pile materials under high temperature and high pressure according to claim 1, characterized in that: The gas pipeline (2) includes a stainless steel pipe (34) and a sample outlet (35). The top cover (3) includes a first concentric circular pipe (32) and a second concentric circular pipe (33). The first concentric circular pipe (32) and the second concentric circular pipe (33) are respectively provided with mounting through holes (31). The stainless steel pipe (34) and the sample outlet (35) are respectively installed in the mounting through holes (31). The excitation line and the detection line are respectively located in the sample outlet (35).

6. The device for detecting micron-level cracks in in-pile materials under high temperature and high pressure according to claim 1, characterized in that: The pressure sensor placement device (9) further includes a first base column (91), a first fixing hole (92), a second fixing hole (93), a second base column (94), and a chassis (95). The pressure sensor is placed on the chassis (95). The first base column (91) and the second base column (94) are used for support. The signal lines of the pressure sensor are led out through the first fixing hole (92) and the second fixing hole (93), respectively.

7. The device for detecting micron-level cracks in in-pile materials under high temperature and high pressure according to claim 1, characterized in that: It also includes a main control device, which is connected to the host computer via an RS422 module. The main control device includes a K-type thermocouple detection circuit, a current commutation circuit, and a main control chip. The K-type thermocouple detection circuit and the current commutation circuit are driven by the main control chip to realize the measurement of thermocouples and the elimination of thermoelectric potential. The pressure sensor is connected to the main control chip to realize the acquisition of pressure data.

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