Fatigue loading device, system and fatigue test method for matching ct imaging system

Abstract

The embodiment of the application provides a fatigue loading device, a system and a fatigue experiment method matched with a CT imaging system. An observation window is designed on the surface of a bearing structure in the fatigue loading device, surface image acquisition during bearing of a test piece is realized, and the fatigue loading device can measure full-field deformation of a surface area of the test piece in combination with a digital image correlation method. Therefore, in the embodiment, the fatigue loading device is coupled and matched with a CT in-situ imaging system and a digital image correlation system, in-situ fatigue loading of a sample under the CT in-situ imaging system can be realized, internal three-dimensional topography is reconstructed, surface images of the test piece are collected at the same time, surface deformation of the test piece is measured in real time in combination with the digital image correlation system, and fatigue mechanical behaviors of the test piece can be studied from two angles of the surface and the interior at the same time.

Description

Technical Field

[0001] This invention relates to the fields of optical mechanics, engineering materials, and component displacement and deformation measurement technology, and particularly to a fatigue loading device, system, and fatigue testing method that is matched with a CT imaging system. Background Technology

[0002] Currently, X-ray computed tomography (CT) imaging technology is widely used in the study of the internal microstructure of materials. CT imaging not only allows for the observation of the internal microstructure of materials but also enables the integration of CT imaging systems with various loading systems to study the mechanical response and evolution of the microstructure during specimen fatigue. However, existing commercial loading platforms, when applied to CT imaging systems, often suffer from problems such as structural shielding of X-rays and excessively large device size, making it impossible to achieve in-situ measurements compatible with CT. Therefore, there is a need to develop a fatigue loading device specifically designed for CT systems.

[0003] To achieve compatibility between the fatigue loading device and the CT imaging system, the structure of the loading system needs to be modified to reduce the X-ray shielding effect and avoid affecting the CT scanning process of the sample. Furthermore, due to the limited internal space of the CT system, an open design for the load-bearing unit is difficult to implement in the design of the fatigue loading device. Therefore, a compact loading system is required, employing an integrated design of the load-bearing structure and the loading unit. When the loading unit applies a load to the sample, the load-bearing structure connected to the loading unit provides the reaction force required for the loading. In this case, the load-bearing structure is spatially located outside the sample. During CT rotation scanning, X-rays will penetrate both the load-bearing structure and the sample sequentially. Therefore, to reduce X-ray absorption by the loading system, the load-bearing structure needs to be made of a low-density material to maintain high X-ray transmittance. Thus, the load-bearing material needs both sufficient strength and stiffness to support the load of the device and high X-ray transmittance. Carbon fiber is typically a suitable material for the load-bearing structure of CT-compatible loading systems, and there are currently numerous compact CT system loading devices that utilize carbon fiber as the load-bearing structure.

[0004] However, closed loading systems using carbon fiber load-bearing structures have significant limitations: once the specimen is mounted onto the loading system, its surface condition cannot be directly observed. Furthermore, Digital Image Correlation (DIC) is a measurement technique based on image analysis and feature matching. It uses an image of the object's surface before deformation as a reference image and performs correlation analysis with the image after deformation. This allows for the search and matching of the corresponding positions of each local region of the object's surface in the images before and after deformation, obtaining the displacement of each region after deformation, and thus the overall displacement of the object's surface. The strain field can then be calculated. The DIC method offers advantages such as high efficiency and environmental robustness, and is currently widely used in the macro- and micro-deformation measurement of various materials and structures. Measuring the surface displacement of the specimen using the DIC method during fatigue loading allows for real-time analysis of fatigue damage. Combining surface deformation measurement with internal three-dimensional structural analysis is of great significance for revealing the fatigue failure mechanism of the specimen. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the technical problems in the related art.

[0006] Therefore, the purpose of this invention is to propose a fatigue loading device, system, and fatigue testing method that is matched with a CT imaging system. The fatigue loading device incorporates an observation window designed on the surface of the load-bearing structure, enabling the acquisition of surface images of the specimen under load. Furthermore, the device can measure the full-field deformation of the specimen surface area using a digital image correlation method. By coupling and matching this fatigue loading device with both a CT in-situ imaging system and a digital image correlation system, in-situ fatigue loading of the sample under CT in-situ imaging can be achieved, reconstructing its internal three-dimensional morphology. Simultaneously, surface images of the specimen are acquired, and the surface deformation is measured in real time using the digital image correlation system, allowing for the study of the specimen's fatigue mechanical behavior from both surface and internal perspectives.

[0007] To achieve the above objectives, the present invention provides a fatigue loading device for matching a CT imaging system, comprising:

[0008] Fixed frame;

[0009] A support mechanism is provided on the top of the fixed frame, including a support cover and a top cover; wherein the top cover is provided on the top of the support cover; the support cover allows X-rays to pass through, and its lower end is provided on the fixed frame through an annular sleeve; the upper end of the support cover is connected to the top cover through the annular sleeve, and an observation window is provided on the support cover for acquiring surface images of the specimen inside the support cover;

[0010] A clamping mechanism, disposed within the support cover, includes an upper clamp and a lower clamp, wherein the upper clamp is connected to the top cover; the two ends of the specimen are respectively clamped by the upper clamp and the lower clamp within the support cover and are vertically arranged, with the specimen positioned opposite the inspection window; and

[0011] The actuation mechanism includes a load sensor and a lifting screw; wherein the lower clamp is connected to the top end of the lifting screw through the load sensor, and the lifting screw is driven to reciprocate up and down to provide a cyclic tensile load, so that the specimen is subjected to a tensile load.

[0012] In some embodiments, the support cover is made of carbon fiber.

[0013] In some embodiments, both the upper clamp and the lower clamp include a clamping cavity and a wedge-shaped clamping block; wherein the wedge-shaped clamping block is used to wrap the end of the specimen, and one end of the wedge-shaped clamping block is disposed in the clamping cavity, and the other end is plugged into and movably connected to the clamping cavity when subjected to tensile load.

[0014] In some embodiments, both the upper and lower clamps contain two wedge-shaped clamps, which cooperate to wrap around the end of the specimen. The upper wedge-shaped clamp in the upper clamp has a larger cross-sectional area than its lower end, and the upper cross-sectional area of ​​the wedge-shaped clamp in the upper clamp is larger than the aperture of the clamp cavity of the upper clamp. The lower wedge-shaped clamp in the lower clamp has a smaller cross-sectional area than its lower end, and the lower cross-sectional area of ​​the wedge-shaped clamp in the lower clamp is larger than the aperture of the clamp cavity of the lower clamp.

[0015] In some embodiments, the actuating mechanism further includes a motor, a reducer, and a guide rail; wherein the lifting screw is disposed within the guide rail, and the motor drives the lifting screw to reciprocate up and down within the guide rail via the reducer.

[0016] In some embodiments, the fatigue loading device further includes a disk; the disk is disposed at the bottom of the fixed frame, and the projection of the specimen on the disk coincides with the center of the disk.

[0017] In some embodiments, an in-situ experimental system combining DIC surface deformation measurement and X-ray in-situ CT imaging is proposed, comprising,

[0018] The fatigue loading device, DIC measurement system, and CT in situ imaging system described in any of the above embodiments; wherein the disk of the fatigue loading device is placed on the rotating stage of the CT in situ imaging system, and the projection of the disk and the rotating stage in the vertical direction coincides; and the DIC measurement system is set at a position corresponding to the viewing window of the fatigue loading device.

[0019] In some embodiments, a fatigue testing method combining DIC surface deformation measurement and in-situ X-ray CT imaging is proposed. The fatigue testing of specimens using the in-situ testing system described in any of the above embodiments includes the following steps:

[0020] Prepare the specimen and install it into the fatigue loading device;

[0021] The fatigue loading device is matched and coupled with the DIC measurement system and the CT in situ imaging system; an initial tensile load is applied to the specimen and the initial surface image of the specimen under the initial tensile load is recorded as a reference image, and the internal tomographic data of the specimen in this state is recorded using the DIC measurement system; wherein the magnitude of the initial tensile load is the average load of the maximum and minimum tensile loads to be applied to the specimen.

[0022] The fatigue loading device is controlled to operate so that the specimen is subjected to cyclic tensile load, and the cyclic tensile load is stopped after reaching a preset number of times; the surface image of the specimen after being subjected to cyclic tensile load is recorded as a deformation image using the CT in situ imaging system; and it is determined whether fatigue damage has occurred in the deformation image. If so, a three-dimensional image reconstruction of the specimen is performed.

[0023] In some embodiments, it is determined whether fatigue damage has occurred in the deformation image. If not, the specimen is subjected to repeated cyclic tensile load processes until the specimen exhibits a high degree of fatigue damage.

[0024] In some embodiments, the method for preparing the specimen is to uniformly spray a white primer onto the surface of the cylindrical specimen; then spray black paint in the form of particles onto the white primer of the specimen to produce a uniformly distributed speckle pattern on the surface of the specimen, which serves as a carrier of deformation information during the calculation process of the DIC measurement system.

[0025] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0026] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 This is a schematic diagram of the structure of a fatigue loading device for a matching CT imaging system proposed in an embodiment of the present invention;

[0028] Figure 2 This is an embodiment of the present invention that includes Figure 1 A schematic diagram of the in-situ experimental system;

[0029] Figure 3 This is a schematic diagram of the upper and lower clamps according to an embodiment of the present invention;

[0030] Figure 4 This is a flowchart of a fatigue testing method combining DIC surface deformation measurement and X-ray in-situ CT imaging, as proposed in an embodiment of the present invention.

[0031] In the figure, 1. X-ray source; 2. Fatigue loading device; 3. DIC measurement system; 4. Specimen; 5. X-ray target surface; 6. Disc; 7. Rotary table; 201. Top cover; 202. Bearing cover; 203. Lower clamp; 204. Load sensor; 205. Guide rail; 206. Lifting screw; 207. Reducer; 208. Motor; 209. Fixed frame; 210. Inspection window; 211. Upper clamp; 212. Bolt; 301. Upper clamp cavity; 302. Lower clamp cavity; 303. Nut; 305. Wedge-shaped clamp. Detailed Implementation

[0032] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the invention, and should not be construed as limiting the invention. Rather, embodiments of the invention include all variations, modifications, and equivalents falling within the spirit and scope of the appended claims.

[0033] Figure 1 This is a schematic diagram of a fatigue loading device for matching a CT imaging system according to an embodiment of the present invention.

[0034] See Figure 1A fatigue loading device for a CT imaging system includes a fixed frame 209, a support mechanism, a clamping mechanism, and an actuating mechanism. The support mechanism includes a support cover 202 and a top cover 201, with the top cover 201 positioned at the top of the support cover 202. The support cover 202 is cylindrical, and to ensure high X-ray penetration and sufficient strength, it is made of carbon fiber. The carbon fiber support cover 202 allows X-rays to penetrate the support cover 202 and scan the specimen 4 within it during CT scanning in the CT in situ imaging system. The lower end of the support cover 202 is positioned above and fixedly connected to the fixed frame 209 via an annular sleeve. The upper end of the support cover 202 is also connected to the top cover 201 via an annular sleeve. The support cover 202, top cover 201, and fixed frame 209 remain relatively fixed in the vertical and horizontal directions.

[0035] A rectangular viewing window 210 is provided in the center of one side of the support cover 202. A CT in situ imaging system is set at the position opposite to the viewing window 210. The surface image of the specimen 4 inside the support cover 202 can be acquired through the viewing window. Combined with a digital image correlation measurement system such as the DIC measurement system 3, the surface deformation of the specimen 4 can be measured in real time.

[0036] In this embodiment, the clamping mechanism is disposed inside the support cover 202, including an upper clamp 211 and a lower clamp 203, wherein the upper clamp 211 and the lower clamp 203 respectively wrap around and clamp both ends of the specimen 4, so that the specimen 4 is vertically arranged inside the support cover 202, and the specimen 4 is opposite to the observation window 210; wherein the upper end of the upper clamp 211 is connected to the top cover 201 by bolts 212 and nuts 303; the lower clamp 203 is fixedly connected to the actuation mechanism.

[0037] Specifically, both the upper clamp 211 and the lower clamp 203 include a clamp cavity and a wedge-shaped clamp 305; the wedge-shaped clamp 305 is used to wrap the end of the specimen 4, and one end of it is set in the clamp cavity, while the other end is plugged into the clamp cavity when subjected to tensile load. When installing specimen 4, wedge-shaped clamps are used to wrap around the upper and lower ends of specimen 4 respectively, and they are installed in the clamp cavities of the upper clamp 211 and the lower clamp 203 (i.e., the upper clamp cavity 301 and the lower clamp cavity 302). The lower end of the lower clamp cavity 302 is connected to the load sensor 204 in the actuation mechanism by bolts 212 and nuts 303. The bearing cover 202 passes through specimen 4, upper clamp 211 and lower clamp 203, and is installed on the fixed frame 209 through an annular sleeve. Another bolt 212 is connected to the upper end of the upper clamp cavity 301. The top cover 201 passes through the bolt 212 and is installed and fixed to the upper end of the bearing cover 202 through the annular sleeve. The top cover 201 is fixed to the bolt 212 at the upper end of the upper clamp 211 by nuts 303.

[0038] The actuation mechanism in this embodiment, fixed to the bottom of the fixed frame 209, includes a motor 208, a reducer 207, the aforementioned load sensor 204, guide rail 205, and lifting screw 206. The motor 208 drives the lifting screw 206 via the reducer 207. Specifically, the reducer 207 is connected to a worm gear, which engages with a turbine and is connected to the lifting screw 206. The load sensor 204 is fixed to the top of the lifting screw 206. When the motor 208 operates, it drives the screw to reciprocate up and down within the guide rail 205 via the reducer 207, providing the cyclic tensile load for the fatigue loading device 2.

[0039] In this embodiment, when the actuating mechanism is running, the motor 208 drives the lifting screw 206 to connect with the lower clamp 203 through the reducer 207 to generate movement. The upper clamp 211 is connected to the top cover 201 of the bearing mechanism by bolts 212 and kept fixed; the top cover 201 fixes the top of the bearing cover 202 and is fixed to the fixed frame 209 at the bottom of the lifting screw 206. Therefore, when the lower clamp 203 clamps the specimen 4 and moves downwards connected to the lifting screw 206, the upper clamp 211 clamps the specimen 4 and keeps it fixed to the bearing mechanism and the fixed frame 209. The upper and lower ends of the specimen 4 are subjected to tensile loads under the combined action of the lower clamp 203 and the lower clamp 204. Therefore, the fatigue loading device 2 in this embodiment can be well matched with the CT scanning imaging system. The use of carbon fiber material with high X-ray transmittance in the bearing cover 202 will not affect the CT imaging results of the specimen 4. The fatigue loading test of the specimen 4 can be carried out under the CT system. In addition, the fatigue loading device 2 in this embodiment can also be well matched with the DIC measurement system 3. Through the setting of the viewing window 210 on the sealed bearing cover 202, the surface image of the specimen 4 inside the bearing cover 202 can be collected through the viewing window 210 and the surface image of the specimen 4 can be recorded. Combined with the DIC measurement system 3, the surface deformation field of the specimen 4 during the cyclic tensile load loading process can be measured.

[0040] It should be noted that the load sensor 204 is connected to the computer via a data cable to display the current load in real time; the motor 208 is also connected to the computer via a data cable, and the computer controls the motor 208 to apply load to the specimen 4, with a load range of 0-5kN. In addition, the fatigue loading device 2 is small in size and light in weight, and can be placed on the rotary table 7 of the CT in-situ imaging system. By using the rotary table to drive the main body of the testing machine and the specimen 4 under load to perform CT rotation scanning, the internal three-dimensional morphology of the specimen 4 can be reconstructed.

[0041] In some embodiments, there are two wedge-shaped clamping blocks 305 in both the upper clamp 211 and the lower clamp 203, and the two wedge-shaped clamping blocks 305 cooperate to wrap around the end of the specimen 4; wherein the cross-sectional area of ​​the upper end of the wedge-shaped clamping block 305 in the upper clamp 211 is larger than the cross-sectional area of ​​its lower end, and the cross-sectional area of ​​the upper end of the wedge-shaped clamping block 305 in the upper clamp 211 is larger than the aperture of the clamping cavity of the lower clamp 203; wherein the cross-sectional area of ​​the upper end of the wedge-shaped clamping block 305 in the lower clamp 203 is smaller than the cross-sectional area of ​​its lower end, and the cross-sectional area of ​​the lower end of the wedge-shaped clamping block 305 in the lower clamp 203 is larger than the aperture of the clamping cavity of the lower clamp 203.

[0042] Specific examples Figure 3 As shown; both the upper clamp 211 and the lower clamp 203 include clamp cavities and wedge-shaped clamping blocks 305; there are two wedge-shaped clamping blocks 305 in each clamp; taking the upper clamp 211 as an example: the two wedge-shaped clamping blocks 305 are respectively set on the left and right sides of the specimen 4, wrapping the end of the specimen 4. The clamp cavity is a hollow structure with a certain inner diameter and one end is open; it can be understood that the wedge-shaped clamping blocks 305 are structures with different cross-sectional areas, wherein the cross-sectional area of ​​the upper end of the wedge-shaped clamping block 305 in the upper clamp 211 is larger than the cross-sectional area of ​​its lower end, and the upper clamp 211 In section 1, the cross-sectional area of ​​the upper end of the wedge-shaped clamp 305 is larger than the aperture of the clamp cavity of the lower clamp 203. When the specimen 4 is subjected to tensile load, the lower end of the wedge-shaped clamp 305 receives tension and moves downward as a whole. As the cross-sectional area of ​​the wedge-shaped clamp 305 gradually increases from bottom to top, the pressure load of the clamp cavity on the specimen 4 gradually increases, thereby clamping the specimen 4. However, because the cross-sectional area of ​​the upper end of the wedge-shaped clamp 305 is larger than the inner diameter of the clamp cavity, one end of the wedge-shaped clamp 305 is always located inside the clamp cavity to prevent the specimen 4 from falling off. Therefore, we can extend this to the lower clamp 203, which will not be elaborated further. The wedge-shaped clamps 305 of the lower clamp 203 and the upper clamp 211 can ensure that the specimen 4 is placed in the clamp cavity. The wedge-shaped clamps 305 are connected to the specimen 4 at one end, and the other end is connected to the clamp cavity of the lower clamp 203 and the upper clamp 211 respectively in a plug-in movable connection. When the lifting screw 206 is driven to move up and down to provide a cyclic tensile load, the specimen 4 is subjected to a tensile load.

[0043] In some embodiments, the fatigue loading device 2 further includes a disk 6; the disk 6 is disposed at the bottom of the fixed frame 209, and the projection of the specimen 4 on the disk 6 coincides with the center of the disk 6.

[0044] Specifically, such as Figure 2As shown, the lower end of the fixed frame 209 is connected to the disk 6 by bolts 212 to ensure that the axis of the specimen 4 coincides with the center of the disk 6 in the clamping mechanism, that is, the projection of the specimen 4 on the disk 6 coincides with the center of the disk 6. This facilitates the direct placement of the fatigue loading device 2 on the high-precision rotating stage 7 of the CT in-situ imaging system during the matching and coupling of the fatigue loading device 2 and the CT in-situ imaging system, enabling rapid matching and coupling.

[0045] In some embodiments, an in-situ experimental system combining DIC surface deformation measurement and X-ray in-situ CT imaging is proposed, comprising,

[0046] The fatigue loading device 2, DIC measurement system 3, and CT in-situ imaging system are described in any of the above embodiments. The disk 6 of the fatigue loading device 2 is placed on the rotary table 7 of the CT in-situ imaging system, and the vertical projections of the disk 6 and the rotary table 7 coincide. The DIC measurement system 3 is positioned corresponding to the viewing window 210 of the fatigue loading device 2. In this embodiment, the diameter of the disk 6 is the same as the diameter of the rotary table 7, and they remain aligned during operation, ensuring that the axis of the specimen 4 and the center of the rotary table 7 are in the same vertical direction. When the rotary table 7 rotates, driving the fatigue loading device 2 to rotate, the specimen 4 remains rotated along its axis.

[0047] Therefore, the fatigue loading device 2 in this embodiment can be simultaneously matched with an X-ray CT imaging system and a visible light digital image correlation deformation measurement system (DIC measurement system 3) to perform internal three-dimensional structural analysis and surface deformation measurement of the specimen 4. During the fatigue experiment, real-time analysis of the residual deformation on the surface of the specimen 4 can determine the fatigue damage state of the specimen 4 and promptly identify the timing of significant fatigue damage in the specimen 4. This allows for the determination of the critical timing for CT scanning during the fatigue process of the specimen 4. By performing CT scanning reconstruction on the specimen 4 under the critical damage state, important data on the internal structural evolution of the specimen 4 during the fatigue process can be obtained.

[0048] During the fatigue test of specimen 4, the surface deformation of specimen 4 was measured in real time. Due to the scarcity of CT imaging system resources, the time allocated by the researchers was strictly limited. By combining surface deformation measurement to determine the key fatigue damage state of specimen 4 and performing CT scanning imaging on specimen 4, effective data can be obtained. This can greatly improve the efficiency of the test, make effective use of the CT imaging system time, and save manpower and material resources, which is of great significance to the research in this field.

[0049] In some embodiments, a fatigue testing method combining DIC surface deformation measurement and in-situ X-ray CT imaging is proposed, specifically as follows: Figure 4 As shown, fatigue testing using the in-situ testing system in any of the above embodiments includes the following steps:

[0050] S1: Prepare specimen 4 and install specimen 4 into fatigue loading device 2;

[0051] S2: Match and couple the fatigue loading device 2 with the DIC measurement system 3 and the CT in situ imaging system; and record the initial surface image of the specimen 4 as a reference image;

[0052] S3: Control the fatigue loading device 2 to perform up-and-down reciprocating motion so that the specimen 4 is subjected to cyclic tensile load, and stop loading the cyclic tensile load after reaching the preset number of times; and use the CT in-situ imaging system to record the surface image of the specimen 4 after being subjected to cyclic tensile load as a deformation image; perform DIC surface deformation measurement on the deformation image and the reference image, and reconstruct the internal three-dimensional structure of the specimen 4.

[0053] Specifically, the method for preparing specimen 4 in S1 is as follows: After mechanically grinding and polishing specimen 4, the surface is cleaned with anhydrous ethanol or acetone until it is clean and smooth. A thin layer of white primer is evenly sprayed onto the surface of specimen 4, completely covering the entire surface within the gauge length section of specimen 4 to ensure that the surface has no metallic luster; the gauge length section on specimen 4 can be understood as the observation area in the middle of the specimen. After the white primer on the surface of specimen 4 dries, black paint is sprayed to produce a random black speckle pattern on the surface of specimen 4. The speckles are evenly distributed on the entire surface of the gauge length section of specimen 4. After the paint dries, the speckle preparation is completed, serving as the deformation information carrier in the calculation process of DIC measurement system 3. The completed specimen 4 is installed in fatigue loading device 2, and a tensile preload is applied to specimen 4. The preload is controlled to be less than 100N according to the reading of load sensor 204.

[0054] Specifically, in S2, the disk 6 at the bottom of the fatigue loading device 2 is placed on the rotary table 7 of the CT in-situ imaging system. The position is adjusted so that the axis of the specimen 4 and the center of the rotary table 7 are in the same vertical direction. The height of the X-ray source 1 of the CT in-situ imaging system is adjusted to be consistent with the height of the gauge length section of the specimen 4. Furthermore, a three-dimensional digital image correlation measurement device, i.e., a DIC measurement system 3, is set up opposite the viewing window 210 to jointly adjust the relative spatial position of the X-ray source 1 and the X-ray target surface 5 with the fatigue loading device 2, as well as the system imaging angle, so that the gauge length section surface of the specimen 4 is clearly imaged within the imaging area. After adjustment, the position of the CT in-situ imaging system and the camera acquisition parameters are kept constant during the experiment. The computer controls the motor 208 to rotate, driving the actuation mechanism to move downwards. The lower clamp 203 applies an initial downward tensile load to the specimen 4, and the initial surface image of the specimen 4 under this initial tensile load is recorded as a reference image. The magnitude of the initial tensile load is the average load between the maximum and minimum tensile loads to be applied to the specimen 4. At the same time, the CT in-situ imaging system is activated, and the fatigue loading device 2 and the specimen 4 are rotated 360 degrees by the rotary table 7. High-energy X-rays penetrate the bearing hood 202 and the specimen 4 and are received by the detector. The computer reconstructs the internal three-dimensional structure of the specimen 4 based on the obtained tomographic data, and the internal tomographic data of the specimen 4 in this state is recorded by the DIC measurement system 3.

[0055] Specifically, in step S3, the computer controls the motor 208 to rotate cyclically, driving the actuator to reciprocate up and down. A cyclic tensile load is applied to the lower end of the specimen 4 via the lower clamp 203. After a certain number of cyclic loading cycles, the computer controls the cyclic tensile load to stop, while simultaneously maintaining the specimen 4 under an intermediate tensile load between the maximum and minimum tensile loads. Image acquisition and CT scanning are then performed to record the deformation images of the specimen 4 after a certain number of cyclic tensile load cycles. Finally, the computer analyzes the surface images of the specimen 4 after different tensile load cycles, performs image correlation calculations to obtain the residual strain field of the specimen 4 after different fatigue tensile load cycles, analyzes the overall residual deformation of the specimen 4, and determines the fatigue damage state of the specimen 4 based on whether there is significant deformation concentration within the strain field. When the residual deformation level of specimen 4 is low and uniformly distributed throughout the field, it is determined that specimen 4 has no obvious fatigue damage. Step S3 is repeated to continue applying fatigue tensile load to specimen 4 and analyze the residual deformation. When obvious strain concentration occurs in the deformation field of specimen 4, it is determined that specimen 4 has a high degree of fatigue damage. Then, the three-dimensional image reconstruction of specimen 4 is performed again. That is, the CT in situ imaging system is started and the fatigue loading device 2 and specimen 4 are rotated 360 degrees by the rotating stage 7. High-energy X-rays are used to penetrate the bearing cover 202 and specimen 4 and are received by the detector. The computer is used to reconstruct the internal three-dimensional structure of specimen 4 based on the obtained tomographic data to obtain the key internal tomographic data of specimen 4 under high fatigue damage state.

[0056] In summary, the in-situ experimental system combining DIC surface deformation measurement and X-ray in-situ CT imaging in this embodiment can perform tensile fatigue loading on various materials and simultaneously measure the surface deformation and internal three-dimensional structure of specimen 4 during the fatigue tensile load loading process. The fatigue damage state of specimen 4 can be estimated based on the surface deformation, and the key timing for tomographic imaging of specimen 4 can be determined. This provides important hardware support for studying the evolution law of internal defects and cracks in specimen 4 during fatigue.

[0057] It should be noted that in the description of this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0058] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

[0059] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0060] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An in-situ experimental system combining DIC surface deformation measurement and X-ray in-situ CT imaging, characterized in that, include, The fatigue loading device, the DIC measurement system, and the CT in situ imaging system; wherein the fatigue loading device includes a load-bearing mechanism; It is set on top of a fixed frame and includes a support cover and a top cover; wherein the top cover is set on the top of the support cover; the support cover allows X-rays to penetrate and its lower end is set on the fixed frame through an annular sleeve; the upper end of the support cover is connected to the top cover through the annular sleeve, and an observation window is opened on the support cover for acquiring surface images of the specimen inside the support cover; Clamping mechanism; It is disposed within the support cover and includes an upper clamp and a lower clamp, wherein the upper clamp is connected to the top cover; both ends of the specimen are clamped vertically within the support cover by the upper clamp and the lower clamp, respectively, and the specimen is positioned opposite the inspection window; both the upper clamp and the lower clamp include a clamp cavity and a wedge-shaped clamping block; wherein the wedge-shaped clamping block is used to wrap the ends of the specimen, and one end of the wedge-shaped clamping block is disposed within the clamp cavity, and the other end is movably connected to the clamp cavity by insertion when subjected to tensile load; The actuation mechanism includes a load sensor and a lifting screw; The lower clamp is connected to the top of the lifting screw via the load sensor. The lifting screw is driven to reciprocate up and down, providing a cyclic tensile load, thus subjecting the specimen to a tensile load; and A disc; the disc is disposed at the bottom of the fixed frame, and the projection of the specimen onto the disc coincides with the center of the disc; The disk of the fatigue loading device is placed on the rotating stage of the CT in situ imaging system, and the projection of the disk and the rotating stage in the vertical direction coincides; and the DIC measurement system is set at the position corresponding to the viewing window of the fatigue loading device.

2. The in-situ experimental system as described in claim 1, characterized in that, The support cover is made of carbon fiber.

3. The in-situ experimental system as described in claim 1, characterized in that, Both the upper and lower clamps contain two wedge-shaped clamping blocks, which cooperate to wrap around the end of the specimen. The upper wedge-shaped clamping block in the upper clamp has a larger cross-sectional area at its upper end than at its lower end, and the cross-sectional area at its upper end is larger than the aperture of the clamping cavity in the upper clamp. Similarly, the lower wedge-shaped clamping block in the lower clamp has a smaller cross-sectional area at its upper end than at its lower end, and the cross-sectional area at its lower end is larger than the aperture of the clamping cavity in the lower clamp.

4. The in-situ experimental system as described in claim 1, characterized in that, The actuating mechanism also includes a motor, a reducer, and a guide rail; wherein the lifting screw is disposed in the guide rail, and the motor drives the lifting screw to reciprocate up and down in the guide rail through the reducer.

5. A fatigue testing method combining DIC surface deformation measurement and in-situ X-ray CT imaging, characterized in that, The fatigue test of the specimen using the in-situ experimental system according to any one of claims 1-4 includes the following steps: Prepare the specimen and install it into the fatigue loading device; The fatigue loading device is matched and coupled with the DIC measurement system and the CT in situ imaging system; an initial tensile load is applied to the specimen and the initial surface image of the specimen under the initial tensile load is recorded as a reference image, and the internal tomographic data of the specimen at this time is recorded using the DIC measurement system; wherein the magnitude of the initial tensile load is the average load of the maximum and minimum tensile loads to be applied to the specimen. The fatigue loading device is controlled to operate so that the specimen is subjected to cyclic tensile load, and the cyclic tensile load is stopped after reaching a preset number of times; the surface image of the specimen after being subjected to cyclic tensile load is recorded as a deformation image using the CT in situ imaging system; and it is determined whether fatigue damage has occurred in the deformation image. If so, a three-dimensional image reconstruction of the specimen is performed.

6. The fatigue testing method as described in claim 5, characterized in that, Determine whether fatigue damage has occurred in the deformation image. If not, subject the specimen to repeated cyclic tensile load processes until the specimen exhibits a high degree of fatigue damage.

7. The fatigue testing method as described in claim 5, characterized in that, The method for preparing the specimen is to uniformly spray white primer onto the surface of the cylindrical specimen; then spray black paint in the form of particles onto the white primer of the specimen to produce a uniformly distributed speckle pattern on the surface of the specimen, which serves as the carrier of deformation information in the calculation process of the DIC measurement system.

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