A CT-based deep imaging strain measurement device and measurement method

Abstract

This invention discloses a CT-based deep imaging strain measuring instrument and method, belonging to the field of mechanical experimental technology. The measuring instrument includes a clamping cylinder, an upper clamping part of the sample, a lower clamping part of the sample, deep imaging measurement marks, an axial loading mechanism, and a CT X-ray source and detector. The measurement method involves fixing upper and lower measuring feature balls to upper and lower pressure heads that directly contact the sample. During loading, the CT scan acquires real-time projection images of the two feature balls. Image processing algorithms are used to calculate the actual distance change between the two balls, obtaining the true axial deformation of the sample and thus the true strain. This invention eliminates interference from external structural stiffness and sealing friction on the measurement results, enabling full-process, non-contact, real-time measurement of the true strain of the sample under high and low temperature environments. It is seamlessly compatible with CT three-dimensional reconstruction, providing high-precision strain data support for rock mechanics and seepage coupling experiments.

Description

Technical Field

[0001] This invention patent relates to the field of geotechnical engineering mechanics experimental technology, specifically to a deep imaging strain measuring device and method based on CT (computed tomography) technology, which is particularly suitable for the accurate, non-contact measurement of the true strain of materials such as rocks and concrete during in-situ mechanical testing inside a CT scanner. Background Technology

[0002] In rock mechanics and geotechnical engineering testing, strain measurement of rock specimens is a core step in analyzing their mechanical properties and revealing deformation and failure mechanisms. The accuracy of real strain data directly determines the reliability of test results and has significant guiding significance for underground engineering design, oil and gas resource extraction, and geological disaster prevention and control.

[0003] Currently, strain measurement methods in rock mechanics loading processes are mainly divided into two categories: contact measurement and non-contact measurement.

[0004] Contact measurement methods (such as resistance strain gauges, contact extensometers, fiber Bragg gratings, etc.) are widely used, but they have obvious drawbacks: First, the measurement range is limited, and it can only obtain the local strain in the sensor bonding area, which cannot reflect the strain distribution of the whole sample and its interior; second, the sensor bonding will impose additional constraints on the sample surface, interfering with its natural deformation state; third, under high pressure, high temperature and large deformation conditions, the sensor is prone to falling off and being damaged, and the sealing problem of the lead wire passing through the high pressure cavity is extremely difficult to solve; fourth, it is completely unable to capture the strain evolution during the initiation and propagation of cracks inside the sample.

[0005] While non-contact measurement methods (such as traditional digital image correlation and non-contact extensometers) have solved the contact problem, they still have limitations: digital image correlation requires an optical window, cannot penetrate the thick-walled metal clamp housing, and cannot be applied to in-situ testing inside a CT scanner; while non-contact extensometers or external displacement sensors usually measure the displacement of the loading frame or hydraulic cylinder piston, which includes deformation of multiple components such as deformation of equipment structural parts and compression of seals, and cannot truly reflect the deformation of the sample itself.

[0006] CT imaging technology, as a non-destructive testing technique, acquires a series of projected images of the sample from different angles through the relative motion between the X-ray source, the sample, and the detector. These images are then reconstructed in three dimensions to obtain slices of different layers within the sample, thus achieving a clear and intuitive representation of the microstructure of rock samples, such as pores and fissures. Furthermore, it allows for dynamic scanning throughout the loading process without damaging or interfering with the sample's deformation. Currently, CT technology has been applied to characterize the internal structure and damage characteristics of rocks. Some studies have attempted to combine CT images with rock deformation analysis, but these are mostly used only for qualitative observation of internal fissure changes. A systematic and accurate method for quantitatively measuring true strain has not yet been developed. Problems exist, including insufficient image preprocessing accuracy, mismatch between strain calculation models and rock deformation characteristics, and difficulty in controlling measurement errors. Therefore, it cannot meet the demand for accurate measurement of true strain in rock mechanics experiments. Summary of the Invention

[0007] The present invention aims to overcome the shortcomings of the prior art and provide a CT-based deep imaging strain measuring instrument and measurement method to solve the technical problems that the existing strain measurement technology cannot measure the true deformation of the sample in real time and accurately under CT scanning environment, and is easily affected by external factors such as the stiffness of the equipment structure and the friction of the sealing parts.

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

[0009] A CT-based deep imaging strain measuring device includes:

[0010] The clamping cylinder has a test cavity inside and openings at both the top and bottom ends that communicate with the test cavity;

[0011] The sample clamping part is detachably and sealingly installed in the upper opening of the clamping cylinder;

[0012] The sample clamping part is detachably and sealingly installed in the lower end opening of the clamping cylinder;

[0013] The deep imaging measurement mark includes an upper measurement feature head and a lower measurement feature head. The upper measurement feature head is mounted on the upper clamping part of the sample, and the lower measurement feature head is mounted on the lower clamping part of the sample. The upper measurement feature head and the lower measurement feature head are arranged opposite each other in the axial direction.

[0014] An axial loading mechanism, connected to the lower part of the clamping cylinder, is used to apply an axial mechanical load to the test sample;

[0015] The CT X-ray source and CT detector are symmetrically arranged on both sides of the outer side of the clamping cylinder, and are used to acquire projected images containing the upper and lower measuring feature heads in real time.

[0016] Furthermore, the sample clamping part includes a threaded cap, an upper sealing end cap, and a sample upper pressure head; the threaded cap is threadedly connected to the upper opening of the clamping device cylinder, the upper sealing end cap is inserted into the threaded cap, the sample upper pressure head is connected to the bottom surface of the upper sealing end cap, and the upper measuring feature head is mounted on the sample upper pressure head; the outer wall of the upper sealing end cap at the contact point with the clamping device cylinder is provided with a first sealing groove, and a first sealing ring is embedded in the first sealing groove.

[0017] Furthermore, the lower clamping part of the sample includes a lower sealing end cap and a lower pressing head of the sample; the lower pressing head of the sample is connected to the top surface of the lower sealing end cap, the lower sealing end cap is inserted into the lower opening of the clamping device cylinder, and the lower measuring feature head is installed on the lower pressing head of the sample; the outer wall of the lower sealing end cap at the contact point with the clamping device cylinder is provided with a second sealing groove, and a second sealing ring is embedded in the second sealing groove.

[0018] Furthermore, the axial loading mechanism is a hydraulic cylinder, including a cylinder body, a piston, and a push rod; the upper part of the cylinder body is sealed to the lower part of the clamping cylinder body, the piston is movably disposed in the cylinder body, and the push rod is connected to the top surface of the piston and abuts against the lower clamping part of the sample; a first hydraulic oil inlet is provided on one side of the lower part of the cylinder body for inputting hydraulic oil and pushing the piston upward, and a second hydraulic oil inlet is provided on the top surface of the cylinder body for inputting hydraulic oil and pushing the piston downward.

[0019] Furthermore, the lower part of the clamping cylinder is provided with a medium inlet communicating with the test chamber, and the upper part is provided with a medium outlet communicating with the test chamber, for providing a stable environmental fluid to the test chamber.

[0020] Furthermore, the piston, the push rod, the lower sealing end cap, the lower sample pressure head, the upper sample pressure head, and the upper sealing end cap are provided with coaxial displacement fluid channels at their centers; the bottom surface of the piston is provided with a displacement fluid inlet communicating with its internal displacement fluid channel, and the top surface of the upper sealing end cap is provided with a displacement fluid outlet communicating with its internal displacement fluid channel.

[0021] Furthermore, a third sealing ring is provided at the joint between the piston and the push rod, the joint between the push rod and the lower sealing end cap, and the joint between the lower sealing end cap and the lower pressure head of the sample; a fourth sealing ring is provided at the joint between the upper pressure head of the sample and the upper sealing end cap.

[0022] Furthermore, the deep imaging measurement mark is at least one of spherical, needle-shaped, or cylindrical, and its material is a metal or alloy with stronger X-ray imaging capability than the sample and clamp material.

[0023] A CT-based method for measuring deep radiographic strain, using the aforementioned measuring instrument, includes the following steps:

[0024] S1: Installation steps: Place the test sample in the test cavity of the clamping cylinder, clamp and fix it by the upper clamping part and the lower clamping part of the sample, and install the deep development measurement mark;

[0025] S2: The medium is injected into the test chamber through the medium inlet and flows out from the medium outlet to create a high-temperature and high-pressure environment that simulates formation stress in the test chamber;

[0026] S3: Initial State Calibration Steps: Activate the CT X-ray source and CT detector, acquire the projection images of the upper and lower measurement feature heads in the initial state, and calculate and record the initial distance L between them using an image processing algorithm. o ;

[0027] S4: Loading Measurement Step: The axial loading mechanism is activated to apply an axial load to the test sample. During the loading process, the CT X-ray source and CT detector acquire dynamic projection images of the upper and lower measurement feature heads in real time, and calculate the dynamic distance L between them in real time. i ;

[0028] S5: Steps for calculating dependent variable: Calculate dynamic distance L i With initial distance L o The difference ΔL = L i - L o The difference ΔL is the actual deformation of the test sample in the axial direction. Based on the actual deformation and the original gauge length of the test sample, the actual strain of the sample is calculated.

[0029] Furthermore, the image processing algorithms in steps S3 and S4 include: denoising, binarizing and segmenting the projected image, extracting edges, identifying the centroid coordinates of the upper and lower measurement feature heads, and calculating the actual physical distance by combining the pixel distance between the two centroids with the system calibration coefficient.

[0030] Furthermore, the measurement method also includes a CT reconstruction scanning step: when it is necessary to reconstruct the test sample in three dimensions, the deformation of the sample is kept constant by the axial loading mechanism, and a CT scan is performed to obtain an image of the internal three-dimensional structure of the sample under the deformation state.

[0031] Furthermore, the measurement method is applicable to the measurement of strain when performing compression, tension, or creep mechanical experiments on the test sample.

[0032] Furthermore, the measurement method is applicable to high-temperature and high-pressure rock mechanics experiments with an ambient temperature ≥150℃ and / or a confining pressure ≥70MPa.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] (1) This invention directly installs the deep imaging measurement mark on the upper and lower pressure heads that directly contact and apply force to the sample. The measured displacement change is completely equivalent to the compression or tensile deformation of the sample itself. This measurement result completely eliminates the influence of the elastic deformation and connection gaps of all external structural components such as the external clamping cylinder, sealing end cap, loading piston and even equipment frame. For the first time, it realizes accurate and direct measurement of the "true deformation" of the sample in a CT environment.

[0035] (2) The entire measurement process is a non-contact optical (X-ray) measurement. The measurement mark is located inside the sealed cavity and no lead wires are required. The circulation loop formed by the medium inlet and medium outlet makes it naturally suitable for extremely harsh testing environments such as high temperature (≥150℃), high pressure (≥70MPa) and chemically corrosive fluids, which is completely unattainable by traditional strain gauges and extensometers.

[0036] (3) During the loading process, the CT X-ray source and detector can work continuously to capture the position changes of the feature markers in real time with the set time resolution, thereby drawing a complete stress-strain curve without missing any critical deformation or damage moments.

[0037] (4) The measurement process and the CT scanning process of the present invention do not interfere with each other. When it is necessary to obtain the internal three-dimensional structure of the sample, it is only necessary to pause the loading and maintain the displacement to perform a high-precision scan. After the scan, the loading can be resumed immediately, realizing the acquisition of mechanical data and internal structural evolution images "on the same machine, on the same axis, and simultaneously".

[0038] (5) By setting up coaxial displacement fluid channels, seepage experiments can be carried out at the same time as strain measurement, providing a powerful tool for studying rock mechanical behavior under stress-strain-seepage coupling conditions. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the measuring device of the present invention;

[0040] Figure 2 for Figure 1 A schematic diagram after the axial loading mechanism has been removed.

[0041] Figure 3 This is a schematic diagram showing the sample clamped by the upper clamping part and the lower clamping part of the sample.

[0042] Figure 4This is a block diagram illustrating the measurement method in this invention.

[0043] In the figure: 1-Threaded gland, 2-Upper sealing end cap, 3-Sample upper pressure head, 4-Test sample, 5-Sample lower pressure head, 6-Lower sealing end cap, 7-Upper measuring feature head, 8-Lower measuring feature head, 9-Clamping cylinder, 10-CT controller, 11-CT X-ray source, 12-Media inlet, 13-Media outlet, 14-Cylinder, 15-Piston, 16-Push rod, 17-First hydraulic oil inlet, 18-Second hydraulic oil inlet, 19-First sealing ring, 20-Second sealing ring, 21-Third sealing ring, 22-Fourth sealing ring, 23-Displacement fluid channel, 24-Displacement fluid inlet, 25-Displacement fluid outlet. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Example 1

[0046] Please see Figures 1-3 This embodiment provides a CT-based deep imaging strain measuring device.

[0047] The core of this measuring instrument is the in-situ dedicated core holder body 9, which has a hollow test cavity with openings at both the top and bottom. A threaded cap 1 is threadedly connected to the upper opening of the body 9, and an upper sealing end cap 2 is inserted into and pressed tightly by the threaded cap 1. A first sealing groove is provided on the outer wall of the upper sealing end cap 2 where it contacts the inner wall of the body 9, and a first sealing ring 19 is embedded in the first sealing groove to achieve a seal. The sample upper pressure head 3 is fixed to the bottom surface of the upper sealing end cap 2 by threads or a tight fit. These components together constitute the sample upper clamping part.

[0048] The lower sealing end cap 6 is inserted into the lower opening of the main body 9. A second sealing groove is provided on the outer wall where it contacts the inner wall of the main body 9. A second sealing ring 20 is embedded in the second sealing groove to achieve a sliding seal between the sample pressing head 6 and the clamping cylinder 9. The sample pressing head 5 is fixed to the top surface of the lower sealing end cap 6. Together, they constitute the sample lower clamping part.

[0049] The test sample 4 is clamped between the upper indenter 3 and the lower indenter 5.

[0050] The upper measuring feature head 7 is fixed to the upper pressure head 3 of the sample by thread or embedding. The lower measuring feature head 8 is fixed to the lower pressure head 5 of the sample in the same way. The two feature heads are positioned opposite each other in the annular area formed by the sample and the clamping cylinder. The material is high-density tungsten steel or other metals or alloys with strong X-ray imaging ability to form clear, high-contrast bright spots in CT images.

[0051] The CT beam source 11 and the CT detector 10 are located on the left and right sides of the main body 9 of the holder, respectively. Their beams can penetrate the entire holder and clearly image the two feature heads.

[0052] The axial loading mechanism is a double-acting hydraulic cylinder. The upper end of the cylinder body 14 is sealed and connected to the lower part of the clamping body 9. The piston 15 is built into the cylinder body 14, and the push rod 16 at its top passes through the top cover of the cylinder body and abuts against the bottom surface of the lower sealed end cover 6. A first hydraulic oil inlet 17 is provided on one side of the lower part of the cylinder body 14, and a second hydraulic oil inlet 18 is provided on the top surface of the cylinder body 14. Oil entering through the first hydraulic oil inlet 17 can push the piston 15 and the push rod 16 to move upward, realizing the compression loading of the sample; oil entering through the second hydraulic oil inlet 18 can make the piston return.

[0053] A through-flow displacing fluid channel is formed at the center of the piston 15, push rod 16, lower sealing end cap 6, sample lower pressure head 5, sample upper pressure head 3, and upper sealing end cap 2. The bottom surface of the piston 15 has a displacing fluid inlet 24 communicating with its internal displacing fluid channel, and the top surface of the upper sealing end cap 2 has a displacing fluid outlet 25 communicating with its internal displacing fluid channel. This channel is used to introduce displacing fluid during percolation experiments.

[0054] To ensure that the displacement fluid does not leak under high pressure, a third sealing ring 21 is provided at the joint between piston 15 and push rod 16, the joint between push rod 16 and lower sealing end cap 6, and the joint between lower sealing end cap 6 and sample lower pressure head 5; a fourth sealing ring 22 is provided at the joint between sample upper pressure head 3 and upper sealing end cap 2.

[0055] In addition, the lower part of the clamp body 9 is provided with a medium inlet 12 communicating with the test chamber, and the upper part is provided with a medium outlet 13 communicating with the test chamber. High-pressure and high-temperature confining pressure medium (such as hydraulic oil or simulated pore fluid) is injected into the test chamber through the medium inlet 12, and the medium flows out from the medium outlet 13 to form a circulation loop, thereby providing a stable environment for the test chamber to simulate formation stress and temperature field.

[0056] Example 2

[0057] This embodiment provides a method for measuring the true strain of a rock sample using the above-mentioned measuring instrument, including the following specific steps:

[0058] Step 1: Sample Installation and Initial Preparation

[0059] Place the prepared standard cylindrical rock specimen 4 on the lower indenter 5, and slowly lower the upper indenter 3 to ensure good contact between it and the upper end face of the specimen. Tighten the threaded cap 1 to provide initial preload.

[0060] Step 2: Establishing a high-temperature and high-pressure environment and initial zero-point calibration

[0061] A pre-set confining pressure medium (e.g., confining pressure 70 MPa, temperature 150 °C) is continuously injected into the test chamber through the medium inlet 12. The medium flows out from the medium outlet 13, forming a circulation loop, so that the environmental parameters in the test chamber are stabilized at the target value, thereby simulating the formation stress field and temperature field conditions required for rock mechanics tests.

[0062] Then, a small initial preload (e.g., 2-5 kN) is applied via the axial loading mechanism 14 to bring the sample to a hydrostatic pressure state. Next, the CT X-ray source 11 and detector 10 are activated, and the scanning parameters (voltage, current, exposure time) are adjusted. By moving the stage or adjusting the position of the clamp, the projections of the upper measuring feature head 7 and the lower measuring feature head 8 are positioned in the center of the detector's field of view, and the line connecting them is perpendicular to the detector plane, to obtain optimal resolution and image contrast.

[0063] An initial projection image is acquired. The image is then processed using image processing algorithms: First, Gaussian filtering and median filtering are used to remove noise; second, Otsu's method is used for image binarization segmentation to separate the two high-brightness feature head regions from the background (rock sample and metal gripper); then, the Canny edge detection algorithm is used to extract the contours of the two feature heads, and a circle is fitted using the least squares method to calculate the pixel coordinates of the centers of the two feature heads; the Euclidean distance (in pixels) between the centers of the two feature heads is calculated; the system is calibrated using a standard sphere or block of known size to obtain the pixel equivalent k (mm / pixel). The initial physical distance L is then calculated. o =D_pixel×k. The system records this distance as the zero-point displacement.

[0064] Step 3: Dynamic loading and real-time strain measurement

[0065] High-pressure oil is injected into the first hydraulic oil inlet 17 at a set rate (e.g., 0.1 mm / min) through the hydraulic control system, pushing the piston 15 and push rod 16 upward to apply axial compression loading to the sample 4.

[0066] Throughout the loading process, the CT X-ray source 11 and detector 10 continuously acquire projected images at fixed time intervals (e.g., 10 frames per second). For each frame, the image processing and distance calculation algorithm in step 2 is repeated to obtain the distance L_t at the current moment in real time.

[0067] The control system calculates the current absolute deformation ΔL_t = L_t - L in real time. o Simultaneously, the system acquires axial load sensor data F_t and calculates the axial stress σ_t of the specimen. The system then plots and displays the stress-strain curve (σ_t - ΔL_t / original gauge length of the specimen) in real time.

[0068] Step 4: Interrupt loading for 3D reconstruction

[0069] When loading reaches a critical point (such as before or after the stress peak) or according to the predetermined plan, the control system switches to "hold" mode and precisely controls the cylinder pressure through the servo valve to keep the displacement of push rod 16 (i.e. the deformation amount ΔL_t of the specimen) constant.

[0070] In this stable state, a complete CT rotational scan procedure is initiated (typically a 360-degree or 180-degree rotation, acquiring thousands of projected images). After the scan is completed, the computer reconstructs a high-precision internal 3D image of the sample during this deformation stage (including the evolution of pores and cracks) based on these projected images.

[0071] After the 3D reconstruction is completed, the control system immediately exits the "hold" mode, restores the previous loading rate, and continues the experiment.

[0072] Step 5: Seepage Test

[0073] When a seepage experiment is required, during the loading or holding phase, a pre-pressurized displacing fluid is injected into the displacing fluid channel through the displacing fluid inlet 24. The displacing fluid flows through the coaxial channel 25 centered on the piston 15, push rod 16, lower sealing end cap 6, sample lower pressure head 5, test sample 4, sample upper pressure head 3, and upper sealing end cap 2, and finally flows out from the displacing fluid outlet 25. By measuring the displacing fluid flow rate and pressure difference, combined with real-time strain data, the rock mechanical behavior under stress-strain-seepage coupling conditions can be studied.

[0074] Step 6: Data Processing and Mechanical Parameter Calculation

[0075] After the experiment, a complete stress-strain curve was obtained. Since ΔL_t directly originates from the characteristic spherical displacement and does not contain any system deformation, it represents the true strain of the specimen. Based on this true strain data, key mechanical parameters such as the specimen's elastic modulus E (the slope of the elastic segment of the stress-strain curve), Poisson's ratio (if radial strain is measured simultaneously), yield strength, and compressive strength can be accurately calculated. By combining the three-dimensional reconstructed images from different stages, a quantitative correlation model between "local microstructure evolution and macroscopic true strain" can be established.

[0076] Through the above description of specific embodiments, those skilled in the art can clearly understand that the present invention provides an innovative, reliable, and high-precision CT-based deep imaging strain measurement scheme, which effectively solves a long-standing technical problem in the field.

[0077] It should be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0078] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A CT-based deep imaging strain measuring device, characterized in that, include: The clamping cylinder (9) has a test cavity inside and has openings at the top and bottom ends that communicate with the test cavity; The sample clamping part is detachably and sealedly installed in the upper opening of the clamping cylinder (9); The sample clamping part is detachably and sealedly installed in the lower end opening of the clamping cylinder (9); The deep development measurement mark includes an upper measurement feature head (7) and a lower measurement feature head (8). The upper measurement feature head (7) is mounted on the upper clamping part of the sample, and the lower measurement feature head (8) is mounted on the lower clamping part of the sample. The upper measurement feature head (7) and the lower measurement feature head (8) are arranged opposite to each other in the axial direction. An axial loading mechanism, connected to the lower part of the clamping cylinder (9), is used to apply an axial mechanical load to the test sample; The CT X-ray source (11) and CT detector (10) are symmetrically arranged on both sides of the outer side of the clamping cylinder (9) for real-time acquisition of projection images containing the upper measuring feature head (7) and the lower measuring feature head (8).

2. The CT-based deep imaging strain measuring device according to claim 1, characterized in that, The sample clamping part includes a threaded cap (1), an upper sealing end cap (2), and a sample upper pressure head (3); the threaded cap (1) is threadedly connected to the upper opening of the clamping device cylinder (9), and the upper sealing end cap (2) is inserted into the threaded cap (1), and the upper sealing end cap (2) is pressed tightly into the clamping device cylinder (9) by the threaded cap (1); the sample upper pressure head (3) is connected to the bottom surface of the upper sealing end cap (2), and the upper measuring feature head (7) is installed on the sample upper pressure head (3); the outer wall of the upper sealing end cap (2) at the contact point with the clamping device cylinder (9) is provided with a first sealing groove, and a first sealing ring (19) is embedded in the first sealing groove.

3. The CT-based deep imaging strain gauge according to claim 2, characterized in that, The sample lower clamping part includes a lower sealing end cap (6) and a sample lower pressure head (5); the sample lower pressure head (5) is connected to the top surface of the lower sealing end cap (6), the lower sealing end cap (6) is inserted into the lower end opening of the clamping device cylinder (9), and the lower measuring feature head (8) is installed on the sample lower pressure head (5); the outer wall of the contact point between the lower sealing end cap (6) and the clamping device cylinder (9) is provided with a second sealing groove, and a second sealing ring (20) is embedded in the second sealing groove.

4. The CT-based deep imaging strain measuring device according to claim 3, characterized in that, The axial loading mechanism is a hydraulic cylinder, including a cylinder body (14), a piston (15), and a push rod (16); the upper part of the cylinder body (14) is sealed and connected to the lower part of the clamping cylinder (9); the piston (15) is movably disposed in the cylinder body (14); the push rod (16) is connected to the top surface of the piston (15) and abuts against the lower clamping part of the sample; a first hydraulic oil inlet (17) is provided on one side of the lower part of the cylinder body (14) for inputting hydraulic oil and pushing the piston upward; a second hydraulic oil inlet (18) is provided on the top surface of the cylinder body (14) for inputting hydraulic oil and pushing the piston downward.

5. A CT-based deep imaging strain gauge according to claim 1, characterized in that, The lower part of the clamping cylinder (9) is provided with a medium inlet (12) communicating with the test chamber, and the upper part is provided with a medium outlet (13) communicating with the test chamber, for providing a stable environmental fluid to the test chamber.

6. A CT-based deep imaging strain gauge according to claim 1, characterized in that, The deep imaging measurement mark is at least one of spherical, needle-shaped, or cylindrical, and its material is a metal or alloy with stronger X-ray imaging ability than the sample and clamp material.

7. A CT-based deep imaging strain measuring device according to claim 4, characterized in that, The piston (15), the push rod (16), the lower sealing end cap (6), the sample lower pressure head (5), the sample upper pressure head (3), and the upper sealing end cap (2) are provided with a coaxial displacement liquid channel (23) at their center; the bottom surface of the piston (15) is provided with a displacement liquid inlet (24) communicating with its internal displacement liquid channel, and the top surface of the upper sealing end cap (2) is provided with a displacement liquid outlet (25) communicating with its internal displacement liquid channel. A third sealing ring (21) is provided at the joint between the piston (15) and the push rod (16), the joint between the push rod (16) and the lower sealing end cap (6), and the joint between the lower sealing end cap (6) and the sample lower pressure head (5); a fourth sealing ring (22) is provided at the joint between the sample upper pressure head (3) and the upper sealing end cap (2).

8. A CT-based method for measuring deep visible strain, characterized in that, Using the measuring instrument according to any one of claims 1-7, the steps include: S1: Installation steps: Place the test sample (4) in the test cavity of the clamping cylinder (9), clamp and fix it by the upper clamping part and the lower clamping part of the sample, and install the deep development measurement mark. S2: The medium is injected into the test chamber through the medium inlet and flows out from the medium outlet to create a high-temperature and high-pressure environment that simulates formation stress in the test chamber; S3: Initial state calibration steps: Start the CT X-ray source (11) and CT detector (10), acquire the projection images of the upper measurement feature head (7) and the lower measurement feature head (8) in the initial state, and calculate and record the initial distance L between them through image processing algorithm. o ; S4: Loading Measurement Step: The axial loading mechanism is activated to apply an axial load to the test sample (4). During the loading process, the dynamic projection images of the upper measurement feature head (7) and the lower measurement feature head (8) are acquired in real time by the CT X-ray source (11) and the CT detector (10), and the dynamic distance L between them is calculated in real time. i ; S5: Steps for calculating dependent variable: Calculate dynamic distance L i With initial distance L o The difference ΔL = L i - L o The difference ΔL is the actual deformation of the test sample (4) in the axial direction. Based on the actual deformation and the original gauge length of the test sample (4), the actual strain of the sample is calculated.

9. A method for measuring deep imaging strain based on CT according to claim 8, characterized in that, The image processing algorithms in steps S3 and S4 include: denoising, binarizing and segmenting the projected image, extracting edges, identifying the centroid coordinates of the upper measurement feature head (7) and the lower measurement feature head (8), and calculating the actual physical distance by combining the pixel distance between the two centroids with the system calibration coefficient.

10. A CT-based deep imaging strain measurement method according to claim 9, characterized in that, It also includes a CT reconstruction scanning step: when it is necessary to reconstruct the test sample (4) in three dimensions, the deformation of the sample is kept constant by the axial loading mechanism, and a CT scan is performed to obtain the three-dimensional structural image of the sample under the deformation state.

Images