A compact tensile specimen crack length in-situ monitoring system for harsh corrosive environments and methods of use thereof

Abstract

The present application relates to the field of crack propagation test of stress corrosion, corrosion fatigue and fracture toughness, and particularly relates to a system for in-situ monitoring of crack length of compact tension specimen in harsh corrosion environment and a use method thereof. Two short sides of a T-shaped connecting assembly are fixed at both sides of a center crack opening of a CT specimen, a long side head of the T-shaped connecting assembly is inserted into a through hole on one side of a turning block, a displacement transmission rod is clamped by a separated ohmic clamp on the other side of the turning block, an inductive core on the upper end of the displacement transmission rod is threadedly connected to a LVDT inserted into a high-temperature and high-pressure kettle cover, a spacer is threadedly and tightly sealed on the high-temperature and high-pressure kettle cover, a water cooling jacket is arranged outside the spacer, the LVDT is connected to the upper end of the spacer through a thread and a sealing washer, and the LVDT is connected to a data collector. The present application uses the flexibility method to obtain a relationship expression between the opening displacement of the crack opening of the CT specimen and the crack length, so that the crack length of the CT specimen in the harsh corrosion environment can be monitored in-situ.

Description

Technical Field

[0001] This invention relates to the field of crack propagation testing, including stress corrosion, corrosion fatigue, and fracture toughness. Specifically, it relates to an in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments and its usage method. Specifically, it relates to a linear variable differential pressure displacement sensor (LVDT) system for in-situ real-time monitoring of crack length of compact tensile (CT) specimens in harsh corrosive environments such as high-temperature and high-pressure water and high-temperature liquid lead-bismuth eutectic. Background Technology

[0002] Nuclear power plant structural materials typically operate in harsh corrosive environments (such as high-temperature liquid lead-bismuth eutectic and high-temperature, high-pressure water). Their stress corrosion cracking and corrosion fatigue crack propagation rates are key concerns for damage tolerance design, safety assessment, and life management in nuclear power plants. High-temperature components in nuclear power plants are frequently subjected to the combined effects of various load conditions and service environments, including fatigue, stress corrosion, creep, and creep-fatigue, which can lead to cracking from pre-existing manufacturing defects or deformation damage. Taking lead-cooled fast reactors as an example, structural materials subjected to stress in a high-temperature liquid lead-bismuth environment may undergo liquid metal embrittlement (LME), triggering rapid crack propagation and posing significant safety hazards to the equipment. Crack propagation rate is a crucial parameter for evaluating the corrosion fatigue (CF) performance and LME susceptibility of structural materials. Due to the harsh, opaque, and conductive physical properties of liquid lead-bismuth, conventional monitoring techniques cannot monitor the crack length of CT samples in a high-temperature liquid lead-bismuth environment. Therefore, developing a new technology that can accurately monitor crack length in situ in a high-temperature liquid lead-bismuth environment is of great significance for the design, research and development and application of lead-cooled fast reactors. This will accelerate the understanding and accumulation of basic data on the crack length (CF), fracture toughness and LME sensitivity of candidate structural materials in a high-temperature liquid lead-bismuth environment. Summary of the Invention

[0003] The purpose of this invention is to provide an in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments and its usage method. This system can accurately monitor the crack propagation length of CT specimens in harsh corrosive environments in real time, providing technical support for research on fatigue crack propagation, stress corrosion cracking, and fracture toughness of pressurized water reactor and lead-cooled fast reactor structural materials in high-temperature, high-pressure water and high-temperature liquid lead-bismuth environments.

[0004] The technical solution of this invention is:

[0005] A system for in-situ monitoring of crack length in compact tensile specimens in harsh corrosive environments is disclosed. Two T-shaped connecting components have their vertical short sides bolted to the upper and lower sides of the central horizontal crack opening of the CT specimen. The horizontal long side of the T-shaped connecting components is inserted into a cuboid-shaped through-hole in a steering block, fitting tightly with it. The center of the cylindrical through-hole of the ohmic clamp on one side of the steering block corresponds precisely to the center hole of the linear variable differential pressure displacement sensor above the lid of the high-temperature and high-pressure reactor. The horizontal long side of the T-shaped connecting components is tightly fixed to the cuboid-shaped through-hole in the steering block by two bolts. One end of a vertical displacement transmission rod passes through the cylindrical through-hole of the ohmic clamp on one side of the steering block and is fixed to the ohmic clamp on one side of the steering block by two bolts. The end of the displacement transmission rod is connected to an induction core. All components are installed together and the bolts are tightened to form a "connecting assembly." The "connecting assemblies" on the upper and lower sides of the central crack opening of the CT specimen have the same structure.

[0006] The upper end of the displacement transmission rod passes through the horizontal high-temperature and high-pressure reactor lid and extends to the center hole of the spacer. The spacer is installed on the through hole of the high-temperature and high-pressure reactor lid by a threaded hard seal. The linear variable differential pressure displacement sensor is connected to the top of the spacer by threads and a sealing gasket. The linear variable differential pressure displacement sensor is located above the high-temperature and high-pressure reactor lid.

[0007] The aforementioned in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments has an induction core connected to the end of a displacement transmission rod that extends into the central hole of a linear variable differential pressure displacement sensor. A gap is left between the displacement transmission rod and the through hole of the high-temperature and high-pressure reactor lid, allowing the displacement transmission rod to pass through the through hole of the high-temperature and high-pressure reactor lid without friction, and the induction core to pass through the central hole of the linear variable differential pressure displacement sensor without friction. There is no contact between the displacement transmission rod and the high-temperature and high-pressure reactor lid, or between the induction core and the linear variable differential pressure displacement sensor.

[0008] The aforementioned in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments features a water-cooled jacket installed on the outside of the spacer, through which the linear variable differential pressure displacement sensor is cooled.

[0009] The aforementioned in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments uses a linear variable differential pressure displacement sensor connected to a data acquisition unit via a circuit. The linear variable differential pressure displacement sensor senses the displacement of the sensing core and sends a corresponding signal. The displacement of the "connection component" is displayed by the data acquisition unit, which can further transmit the real-time displacement of the crack opening of the CT specimen.

[0010] The aforementioned in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments features a T-type connecting assembly that is an integral combination of a vertical short side with a threaded hole and a horizontal long side in the shape of a cuboid plate. Bolts pass through the threaded holes on the vertical short side and connect to the CT specimen, allowing the T-type connecting assembly to be installed in conjunction with the CT specimen.

[0011] The aforementioned in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments includes a T-shaped connecting component that corresponds one-to-one with a steering block. One side of the steering block has a horizontal rectangular through-hole and two threaded holes perpendicular to the rectangular through-hole. The horizontal long side of the T-shaped connecting component is inserted into the rectangular through-hole, and a bolt passes through the threaded hole to fix it to the horizontal long side. An ohmic clamp is installed on the other end of the steering block, with two symmetrical horizontal threaded holes on the other end. The ohmic clamp has a horizontal through-hole corresponding to the threaded hole, forming a one-to-one correspondence and coaxial connection between the through-hole and the threaded hole. A bolt passes through the through-hole and the threaded hole to fix it to the steering block. At the center of the joint between the other end of the steering block and the ohmic clamp, a cylindrical through-hole is vertically opposite to the other end, and a displacement transmission rod is inserted into the cylindrical through-hole.

[0012] The aforementioned in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments includes a T-shaped connecting component and a displacement transmission rod that are respectively installed in conjunction with a steering block to adjust the alignment and perpendicularity of the displacement transmission rod with the linear variable differential pressure displacement sensor on the high-temperature and high-pressure reactor lid.

[0013] The specific steps for using the in-situ crack length monitoring system for compact tensile specimens in harsh corrosive environments are as follows:

[0014] (1) Install the CT sample on the fixture, fix the short side of the T-type connecting component on both sides of the central crack opening of the CT sample, insert the long side of the T-type connecting component into the cuboid through hole of the steering block, adjust the position of the steering block on the head of the long side of the T-type connecting component so that the cylindrical through hole of the ohm clamp on one side of the steering block is exactly below the through hole of the high temperature and high pressure vessel cover, and then fix the T-type connecting component and the steering block tightly to form a firm fit installation.

[0015] (2) The spacer, water cooling jacket and linear variable differential pressure displacement sensor are sealed and installed on the high temperature and high pressure vessel lid. The water cooling jacket is circulated with cooling water to change the working environment of the linear variable differential pressure displacement sensor on the high temperature and high pressure vessel lid to a normal temperature environment.

[0016] (3) Connect the signal output line of the linear variable differential pressure displacement sensor to the data acquisition unit to monitor and acquire the value output by the linear variable differential pressure displacement sensor;

[0017] (4) Pass one end of the displacement transmission rod through the ohmic clamp on one side of the steering block, connect the end of the displacement transmission rod to the induction core and insert it into the induction coil of the linear variable differential pressure displacement sensor above the high temperature and high pressure vessel lid, adjust the position of the induction core to make it near the zero point, tighten the bolts to make the ohmic clamp stably hold the displacement transmission rod, tighten all the bolts to form a "connection assembly", and the displacement transmission rod and the induction core have no contact with the high temperature and high pressure vessel lid, the spacer, or the linear variable differential pressure displacement sensor.

[0018] The method of using the in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments involves pre-fabricating a crack in a CT specimen in air using a fatigue testing machine and measuring the crack length using an optical microscope. Simultaneously, a linear variable differential pressure displacement sensor is used to monitor the crack opening displacement. The relationship between the crack opening displacement and the crack length is obtained by fitting using the compliance method.

[0019] a / W=C0+C1U x + C2U x 2 + C3U x 3 + C4U x 4 + C5U x 5 (1)

[0020] 1 / U x = (BEV) x / P) 1 / 2 +1 (2)

[0021] Where a is the crack length (mm), W is the specimen width (mm), C0-C5 are fitting constants, B is the specimen thickness (mm), E is Young's modulus (GPa), V is displacement (mm), P is load (kN), and U x V represents the transformation function. x The crack opening displacement is expressed in mm. In harsh corrosive environments, the crack length of CT specimens in harsh corrosive environments is monitored in situ in real time by measuring the crack opening displacement of CT specimens and combining it with the above relationship expression.

[0022] The method of using the in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments involves installing and adjusting the position of the induction core, zeroing it, and monitoring the crack opening displacement of CT specimens in high-temperature liquid lead-bismuth eutectic or high-temperature and high-pressure water in real time. The linear variable differential pressure displacement sensor is designed to withstand pressures of 10-30 MPa, and the displacement transmission rod is made of non-magnetic, high-temperature resistant material, ensuring long-term stable operation in normal temperature and high-pressure environments.

[0023] The design concept of this invention is:

[0024] This invention mounts an LVDT displacement sensor above the lid of a high-temperature, high-pressure autoclave. By connecting a water-cooling jacket to the autoclave lid, the LVDT system is placed in a normal-temperature working environment. The induction core is connected to the upper end of the displacement transmission rod, avoiding direct contact with the high-temperature liquid lead-bismuth. A level gauge monitors the liquid lead-bismuth level to prevent it from entering the LVDT system. The displacement transmission rod is made of alumina ceramic material, which is resistant to high temperatures and has minimal deformation, effectively improving the accuracy of displacement transmission. The working principle of the LVDT displacement sensor is as follows: the induction core generates displacement through the "connecting component" and the displacement transmission rod; the induction coil responds and generates a signal, indicating the crack opening displacement of the CT sample. This technology for monitoring the crack propagation length of CT samples in a harsh high-temperature liquid lead-bismuth environment successfully avoids the physical properties of high temperature, opacity, and high conductivity of the liquid lead-bismuth environment, effectively monitoring the crack propagation length of CT samples in a high-temperature lead-bismuth environment in situ.

[0025] The advantages and beneficial effects of this invention are:

[0026] 1. This invention fixes the short side of a T-shaped connecting assembly to both ends of the central crack opening of a CT sample, and connects the long side of the T-shaped connecting assembly to a displacement transmission rod with a through-hole steering block, forming a "connecting assembly" to transmit the crack opening displacement of the CT sample. Circulating cooling water is used to impede heat transfer from inside the reactor to outside, converting the LVDT working environment to a normal temperature environment. The LVDT is connected to a spacer, senses the displacement of the sensing core, and emits a corresponding signal, which is displayed by a connected data acquisition device. Through the connection of these components, an LVDT system for in-situ real-time monitoring of the crack opening displacement of CT samples in harsh corrosive environments is formed. This system can accurately monitor the length of fatigue crack propagation in CT samples in harsh corrosive environments in real time.

[0027] 2. The LVDT system of the present invention accurately transmits the crack opening displacement of the CT sample through the "connection component"; ensures that the LVDT is in a suitable working environment through the spacer and water cooling jacket; senses the displacement of the sensing core through the high-precision LVDT and sends out the corresponding displacement signal to accurately display the crack opening displacement of the CT sample; successfully avoids the physical properties of liquid lead-bismuth eutectic, such as high temperature, harshness, easy conductivity and opacity.

[0028] 3. The LVDT system of the present invention is ingeniously designed and easy to operate. It can realize in-situ real-time accurate monitoring of the displacement of crack opening in CT specimens in existing high-temperature liquid lead-bismuth eutectic environment and high-temperature and high-pressure water corrosion fatigue test device, which greatly improves the monitoring accuracy of corrosion fatigue crack propagation length. Attached Figure Description

[0029] Figure 1This is a structural diagram of the in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments, and a schematic diagram of its installation in a high-temperature and high-pressure autoclave. In the diagram: 1. CT specimen; 2. T-shaped connecting assembly; 3. Steering block; 4. Displacement transmission rod; 5. High-temperature and high-pressure autoclave lid; 6. Water-cooled jacket; 7. Spacer; 8. Induction core; 9. Linear variable differential pressure displacement sensor; 10. Sealing gasket; 11. Data acquisition unit; 19. Crack opening.

[0030] Figure 2(a)-Figure 2(b) Figure 2(a) is a front view; Figure 2(b) is a top view. In the figures, 2 represents the T-shaped connecting component (21 is the vertical short side, 22 is the horizontal long side); and 12 represents the threaded hole.

[0031] Figures 3(a)-3(b) Figure 3(a) is a front view; Figure 3(b) is a top view. In the figures, 3 is the steering block; 13 is the threaded hole (M3); 14 is the cuboid through hole; 15 is the threaded hole (M4); 16 is the ohm clip; 17 is the through hole; and 18 is the cylindrical through hole.

[0032] Figure 4 This figure shows the experimental accuracy verification of an in-situ real-time monitoring system for crack length in CT samples under harsh corrosive environments (high-temperature liquid lead-bismuth eutectic and high-temperature, high-pressure water). In the figure, the horizontal axis BEV / P represents the normalized compliance, and the vertical axis a / W represents the normalized crack length. Detailed Implementation

[0033] like Figure 1 As shown in Figure 3, the LVDT system for in-situ real-time monitoring of crack opening displacement in CT specimens under harsh corrosive environments (such as high-temperature liquid lead-bismuth eutectic or high-temperature high-pressure water) mainly includes: CT specimen 1, T-type connecting assembly 2, steering block 3, displacement transmission rod 4, water-cooled jacket 6, spacer 7, induction core 8, sealing gasket 10, linear variable differential pressure displacement sensor 9 (LVDT), and data acquisition unit 11. The specific structure is as follows:

[0034] like Figure 1 , Figure 2(a)-Figure 2(b) , Figures 3(a)-3(b)As shown, the vertical short sides 21 of the two T-shaped connecting components 2 are fixed to the upper and lower sides of the central horizontal crack opening 19 of the CT sample 1 with bolts (M2.5). The T-shaped connecting components are stably fixed to the CT sample 1 by bolts (M2.5) and can be taken out as needed, which is convenient and quick. The head of the horizontal long side 22 of the T-shaped connecting component 2 is inserted into the cuboid through hole 14 in the steering block 3 and fits tightly with the cuboid through hole 14. The position of the ohm clip 16 on one side of the steering block 3 is adjusted so that the center of the cylindrical through hole 18 (M6) of the ohm clip on one side of the steering block 3 corresponds exactly to the center hole of the linear variable differential pressure displacement sensor 9 (LVDT) above the high temperature and high pressure vessel cover 5. The head of the horizontal long side 22 of the T-shaped connecting component 2 is tightly fixed to the cuboid through hole 14 in the steering block 3 by two bolts (M2.5). One end of the vertical displacement transmission rod 4 (M6) passes through the cylindrical through hole 18 of the ohm clip 16 on one side of the steering block 3. The displacement transmission rod 4 (M6) is fixed to the ohm clip on one side of the steering block 3 by two bolts (M3). The end of the displacement transmission rod 4 (M6) is connected to the induction core 8. The components are installed together and the bolts are tightened to form a "connecting assembly". The "connecting assemblies" on both sides of the central crack 19 of CT sample 1 have the same structure.

[0035] The upper end of the displacement transmission rod 4 (M6) passes through the horizontal high-temperature and high-pressure reactor lid 5 and extends to the center hole of the spacer 7. The spacer 7 is installed on the through hole of the high-temperature and high-pressure reactor lid 5 by a threaded hard seal. The linear variable differential pressure displacement sensor 9 is connected to the top of the spacer 7 by threads and a sealing gasket 10. A water-cooling jacket 6 is installed on the outside of the spacer 7, so that the LVDT system above the high-temperature and high-pressure reactor lid 5 can avoid the harsh high-temperature and corrosive environment and operate in a normal temperature environment. The linear variable differential pressure displacement sensor 9 is located above the high-temperature and high-pressure reactor lid 5 and is cooled by the water-cooling jacket 6. The linear variable differential pressure displacement sensor 9 is connected to the data acquisition unit 11 through a circuit. The induction core 8 connected to the end of the displacement transmission rod 4 (M6) extends into the central hole of the linear variable differential pressure displacement sensor 9. A gap is left between the displacement transmission rod 4 (M6) and the through hole of the high-temperature and high-pressure reactor cover 5, so that the displacement transmission rod 4 (M6) can pass through the through hole of the high-temperature and high-pressure reactor cover 5 without friction, and the induction core 8 can pass through the central hole of the linear variable differential pressure displacement sensor 9 without friction. There is no contact between the displacement transmission rod 4 (M6) and the high-temperature and high-pressure reactor cover 5, and between the induction core 8 and the linear variable differential pressure displacement sensor 9. The linear variable differential pressure displacement sensor 9 senses the displacement of the induction core 8 and sends a corresponding signal. The displacement of the "connection component" is displayed by connecting to the data acquisition unit 11, which can further transmit the real-time displacement of the opening of the CT sample crack 19.

[0036] A CT specimen was pre-cracked in air using a fatigue testing machine, and the crack length was measured using an optical microscope. Simultaneously, the crack opening displacement was monitored using an LVDT (Low Voltage Detector). The relationship between the crack opening displacement and the crack length was obtained by fitting the relationship using the compliance method.

[0037] a / W=C0+C1U x + C2U x 2 + C3U x 3 + C4U x 4 + C5U x 5 (1)

[0038] 1 / U x = (BEV) x / P) 1 / 2 +1 (2)

[0039] Where a is the crack length (mm), W is the specimen width (mm), C0-C5 are fitting constants (dimensionless, obtained by nonlinear curve fitting), B is the specimen thickness (mm), E is Young's modulus (GPa), V is displacement (mm), P is load (kN), and U... x V represents the transformation function (dimensionless). x The crack opening displacement is expressed in mm. In harsh corrosive environments, the crack length of CT specimens in harsh corrosive environments is monitored in situ in real time by measuring the crack opening displacement of CT specimens and combining it with the above relationship expression.

[0040] like Figure 2(a)-Figure 2(b) As shown, the T-type connecting assembly 2 is an integral combination structure of a vertical short side 21 with a threaded hole 12 and a rectangular plate-shaped horizontal long side 22. The bolt (M2.5) passes through the threaded hole 12 on the vertical short side 21 and connects with the CT sample 1, so that the T-type connecting assembly 2 and the CT sample 1 can be installed together.

[0041] like Figures 3(a)-3(b)As shown, the T-shaped connecting assembly 2 corresponds one-to-one with the steering block 3. One side of the steering block 3 has a horizontal rectangular through hole 14 and two threaded holes 13 perpendicular to the rectangular through hole 14. The horizontal long side 22 of the T-shaped connecting assembly 2 is inserted into the rectangular through hole 14, and a bolt (M2.5) passes through the threaded holes 13 and is fixedly connected to the horizontal long side 22. An ohm clamp 16 is installed on the other end of the steering block 3. Two horizontal threaded holes 15 are symmetrically opened on the other end of the steering block 3. The ohm clamp 16 has openings that correspond to the... The horizontal through hole 17 corresponding to the threaded hole 15 is coaxially connected to the threaded hole 15. The bolt (M3) passes through the through hole 17 and the threaded hole 15 and is fixedly connected to the steering block 3. A cylindrical through hole 18 is opened vertically at the center of the docking point between the other end of the steering block 3 and the ohm clamp 16 (a semi-cylindrical through hole is opened at the other end of the steering block 3 and a semi-cylindrical through hole is opened in the ohm clamp 16, and the two semi-cylindrical through holes are opposite to each other to form a cylindrical through hole 18). The displacement transmission rod 4 is inserted into the cylindrical through hole 18.

[0042] In this invention, the T-shaped connecting component 2 and the displacement transmission rod 4 are respectively installed in conjunction with the steering block 3 to adjust the alignment and perpendicularity of the displacement transmission rod 4 (M6) and the linear variable differential pressure displacement sensor 9 on the high temperature and high pressure vessel cover 5.

[0043] like Figure 1 As shown in Figure 3, the installation steps of the in-situ real-time monitoring system for crack length of CT specimens in harsh corrosive environments according to the present invention are as follows:

[0044] (1) Install the CT sample 1 on the fixture, fix the short side of the T-type connecting component 2 on both sides of the central crack opening 19 of the CT sample 1, insert the long side of the T-type connecting component 2 into the cuboid through hole 14 of the steering block 3, adjust the position of the steering block 3 on the head of the long side of the T-type connecting component 2 so that the cylindrical through hole 18 of the ohm clip 16 on one side of the steering block 3 is exactly below the through hole of the high temperature and high pressure vessel cover 5, and then fix the T-type connecting component 2 and the steering block 3 tightly to form a firm fit installation;

[0045] (2) The spacer 7, the water cooling jacket 6 and the linear variable differential pressure displacement sensor 9 are sealed and installed on the high temperature and high pressure vessel cover 5. The water cooling jacket 6 is circulated with cooling water to change the working environment of the linear variable differential pressure displacement sensor 9 on the high temperature and high pressure vessel cover 5 to a normal temperature environment.

[0046] (3) Connect the signal output line of the linear variable differential pressure displacement sensor 9 to the data acquisition unit 11 to monitor and acquire the output value of the linear variable differential pressure displacement sensor 9; wherein, the data acquisition unit 11 is a conventional data acquisition product that matches the linear variable differential pressure displacement sensor 9, such as: consisting of a controller, a computer and fatigue testing machine software.

[0047] (4) Pass one end of the displacement transmission rod 4 (M6) through the ohmic clamp 16 on one side of the steering block 3. Connect the end of the displacement transmission rod 4 (M6) to the induction core 8 and insert it into the induction coil of the linear variable differential pressure displacement sensor 9 above the high temperature and high pressure vessel cover 5. Adjust the position of the induction core 8 so that it is near the zero point. Tighten the bolt (M3) to make the ohmic clamp 16 stably hold the displacement transmission rod 4 (M6). Tighten all bolts to form a "connection assembly". The displacement transmission rod 4 (M6) and the induction core 8 have no contact with the high temperature and high pressure vessel cover 5, the spacer 7, or the linear variable differential pressure displacement sensor 9.

[0048] Through the above-described installation and adjustment of the induction core position, the system is zeroed and can monitor the crack opening displacement of CT samples in high-temperature liquid lead-bismuth eutectic or high-temperature, high-pressure water in real time. The LVDT is internally designed to withstand pressures of 10–30 MPa, and the displacement transmission rod is made of non-magnetic, high-temperature resistant material, enabling long-term stable operation in ambient temperature and high-pressure environments.

[0049] The in-situ real-time monitoring system for crack length of CT specimens in harsh corrosive environments of the present invention is applicable to CT specimens of any size and is suitable for low-melting-point liquid metal environments such as liquid metal lead-bismuth eutectic, lead, bismuth, sodium, mercury and gallium.

[0050] The present invention will be further described in detail below through embodiments.

[0051] Example

[0052] In the precision calibration test, an LVDT system was installed to monitor the crack length of CT specimens in harsh corrosive environments in real time. The monitored crack length was 0.25 mm.

[0053] like Figure 4 The diagram shows the compliance relationship between crack opening displacement and crack length. (From...) Figure 4 It can be seen that the LVDT system designed in this invention can accurately monitor the crack opening displacement of CT specimens, thereby enabling in-situ real-time monitoring of the crack length of CT specimens in harsh corrosive environments (such as 350℃ high-temperature liquid lead-bismuth eutectic and 250℃, 4MPa high-temperature high-pressure water).

[0054] ​The results of the embodiments show that, in this invention, the short side of the T-shaped connecting assembly is fixed to both sides of the central crack in the CT sample, and the long side of the T-shaped connecting assembly passes through the through hole of the steering block. An ohmic clamp on one side of the steering block holds the displacement transmission rod, and one end of the displacement transmission rod is connected to the induction core of the LVDT. The perpendicularity and alignment of the displacement transmission rod and the LVDT system are adjusted, and then the corresponding bolts are tightened. Through the above installation and adjustment of the induction core position, and after zeroing, the crack length of the CT sample in harsh corrosive environments (such as high-temperature liquid lead-bismuth eutectic and high-temperature high-pressure water) can be monitored in situ in real time.

Claims

1. A compact tensile specimen crack length in-situ monitoring system for harsh corrosive environments, characterized in that, The harsh corrosive environment is either high-temperature liquid lead-bismuth eutectic or high-temperature, high-pressure water. The displacement transmission rod is made of non-magnetic, high-temperature resistant alumina ceramic material. A level gauge is used to monitor the liquid lead-bismuth level to prevent it from entering the linear variable differential pressure displacement sensor system. The vertical short sides of the two T-shaped connecting components are bolted to the upper and lower sides of the central horizontal crack opening of the CT sample. The horizontal long side head of the T-shaped connecting component is inserted into the cuboid through hole in the steering block and fits tightly with the cuboid through hole. The center of the cylindrical through hole of the ohmic clamp on one side of the steering block is directly above the center of the through hole. At the center hole of the linear variable differential pressure displacement sensor above the high-temperature and high-pressure reactor lid, the horizontal long side head of the T-shaped connecting assembly is tightly fixed to the cuboid through hole in the steering block by two bolts; one end of the vertical displacement transmission rod passes through the cylindrical through hole of the ohmic clamp on one side of the steering block, and the other end of the displacement transmission rod is fixed to the ohmic clamp on one side of the steering block by two bolts, and the end of the displacement transmission rod is connected to the induction core; the components are installed together and the bolts are tightened to form a "connecting assembly". The "connecting assemblies" on the upper and lower sides of the central crack opening of the CT sample have the same structure. The T-type connecting assembly is an integrated structure consisting of a vertical short side with threaded holes and a horizontal long side in the shape of a cuboid plate. Bolts pass through the threaded holes on the vertical short side and connect to the CT sample, allowing the T-type connecting assembly to be installed in conjunction with the CT sample. The T-type connecting assembly and the displacement transmission rod are respectively installed in conjunction with the steering block to adjust the alignment and perpendicularity of the displacement transmission rod with the linear variable differential pressure displacement sensor on the high-temperature and high-pressure reactor lid. The upper end of the displacement transmission rod passes through the horizontal high-temperature and high-pressure reactor cover and extends to the center hole of the partition sleeve. The partition sleeve is installed on the through hole of the high-temperature and high-pressure reactor cover by a threaded hard seal. The linear variable differential pressure displacement sensor is connected to the top of the partition sleeve by threads and sealing gaskets. The linear variable differential pressure displacement sensor is located above the high-temperature and high-pressure reactor cover. A water-cooled jacket is installed on the outside of the partition. The linear variable differential pressure displacement sensor is cooled by the water-cooled jacket. The water-cooled jacket is filled with circulating cooling water, which changes the working environment of the linear variable differential pressure displacement sensor on the high-temperature and high-pressure reactor lid to a normal temperature environment.

2. The in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments according to claim 1, characterized in that, The induction iron core connected to the end of the displacement transmission rod extends into the central hole of the linear variable differential pressure displacement sensor. There is a gap between the displacement transmission rod and the through hole of the high-temperature and high-pressure vessel lid, so that the displacement transmission rod can pass through the through hole of the high-temperature and high-pressure vessel lid without friction, and the induction iron core can pass through the central hole of the linear variable differential pressure displacement sensor without friction. There is no contact between the displacement transmission rod and the high-temperature and high-pressure vessel lid, and between the induction iron core and the linear variable differential pressure displacement sensor.

3. The in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments according to claim 1, characterized in that, The linear variable differential pressure displacement sensor is connected to the data acquisition unit via a line. The linear variable differential pressure displacement sensor senses the displacement of the sensing iron core and sends out a corresponding signal. The displacement of the "connection component" is displayed by the data acquisition unit, and it can further transmit the real-time displacement of the crack opening of the CT sample.

4. The in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments according to claim 1, characterized in that, The T-shaped connecting assembly corresponds one-to-one with the steering block. One side of the steering block has a horizontal rectangular through hole and two threaded holes perpendicular to the rectangular through hole. The horizontal long side of the T-shaped connecting assembly is inserted into the rectangular through hole, and the bolt passes through the threaded hole and is fixedly connected to the horizontal long side. An ohmic clamp is installed at the other end of the steering block. Two horizontal threaded holes are symmetrically opened at the other end of the steering block. The ohmic clamp has a horizontal through hole corresponding to the threaded hole. The through hole and the threaded hole are one-to-one and coaxially connected. The bolt passes through the through hole and the threaded hole and is fixedly connected to the steering block. At the center of the joint between the other end of the steering block and the ohmic clamp, a cylindrical through hole is opened vertically opposite to the other end. The displacement transmission rod is inserted into the cylindrical through hole.

5. A method of using the in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments as described in any one of claims 1 to 4, characterized in that, The specific steps are as follows: (1) Install the CT sample on the fixture, fix the short side of the T-type connecting component on both sides of the central crack opening of the CT sample, insert the long side of the T-type connecting component into the cuboid through hole of the steering block, adjust the position of the steering block on the head of the long side of the T-type connecting component so that the cylindrical through hole of the ohm clamp on one side of the steering block is exactly below the through hole of the high temperature and high pressure vessel cover, and then fix the T-type connecting component and the steering block tightly to form a firm fit installation; (2) The spacer, water cooling jacket and linear variable differential pressure displacement sensor are sealed and installed on the lid of the high temperature and high pressure vessel. Circulating cooling water is circulated in the water cooling jacket to change the working environment of the linear variable differential pressure displacement sensor on the lid of the high temperature and high pressure vessel to a normal temperature environment. (3) Connect the signal output line of the linear variable differential pressure displacement sensor to the data acquisition unit, monitor and acquire the output value of the linear variable differential pressure displacement sensor; (4) Pass one end of the displacement transmission rod through the ohmic clamp on one side of the steering block, connect the end of the displacement transmission rod to the induction core and insert it into the induction coil of the linear variable differential pressure displacement sensor above the high temperature and high pressure vessel lid, adjust the position of the induction core to make it near the zero point, tighten the bolts to make the ohmic clamp stably hold the displacement transmission rod, tighten all the bolts to form a "connection assembly", and the displacement transmission rod and the induction core have no contact with the high temperature and high pressure vessel lid, the spacer, or the linear variable differential pressure displacement sensor.

6. The method of using the in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments according to claim 5, characterized in that, A CT specimen was pre-cracked in air using a fatigue testing machine, and the crack length was measured using an optical microscope. Simultaneously, a linear variable differential pressure displacement sensor was used to monitor the crack opening displacement. The relationship between the crack opening displacement and the crack length was obtained by fitting using the compliance method. a / W=C0+C1U x + C2U x 2 + C3U x 3 + C4U x 4 + C5U x 5 (1) 1 / U x =(BEV x / P) 1 / 2 +1 (2) Where a is the crack length (mm); W is the specimen width (mm); C0-C5 are fitting constants; B is the specimen thickness (mm); E is Young's modulus (GPa); V is displacement (mm); P is load (kN); U x V represents the transformation function; x The crack opening displacement is expressed in mm. In harsh corrosive environments, the crack length of CT specimens is monitored in situ in real time by measuring the crack opening displacement of CT specimens and combining it with the above relationship expression.

7. The method of using the in-situ monitoring system for crack length of compact tensile specimens in harsh corrosive environments according to claim 5, characterized in that, By installing and adjusting the position of the induction core, the sensor is zeroed out and can monitor the crack opening displacement of CT samples in high-temperature liquid lead-bismuth eutectic or high-temperature and high-pressure water in real time. The linear variable differential pressure displacement sensor is designed to withstand pressures of 10-30 MPa, and the displacement transmission rod is made of non-magnetic, high-temperature resistant material, which can operate stably for a long time in a normal temperature and high pressure environment.

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