A synchronous CT triaxial testing method for lunar soil samples

Abstract

The present invention belongs to the technical field related to lunar soil mechanics research, and discloses a synchronous CT triaxial testing method for lunar soil samples, comprising: S1 preparing a lunar soil sample in a triaxial tester, and installing the triaxial tester after preparing the lunar soil sample on a rotating table of a CT scanning system; S2 using CT scanning to confirm the loading effect of the lunar soil sample; S3 applying confining pressure to the lunar soil sample to a preset pressure and maintaining it for a preset time; S4 using CT scanning to obtain an initial scan image of the lunar soil sample before applying axial pressure; S5 applying axial pressure to the lunar soil sample and using CT scanning to obtain a scan image, thereby achieving synchronous CT triaxial testing of the lunar soil sample. The present invention uses a step of CT scanning to confirm the loading effect, which can improve the accuracy of the test results while ensuring the accuracy of the micro-amount of real lunar soil loading, ensuring the authenticity and reliability of the test results, while avoiding repeated loading due to loading operation errors, which is conducive to reducing lunar soil loss.

Description

Technical Field

[0001] The present invention belongs to the technical field related to lunar soil mechanics research, and more specifically, relates to a synchronous CT triaxial testing method for lunar soil samples. Background Art

[0002] The mechanical properties of lunar soil primarily include compressibility and shear strength, which serve as the foundation for exploring lunar landing, lunar exploration, and lunar construction. Triaxial testing, as an important method for studying the three-dimensional deformation strength characteristics of soil and constructing soil constitutive models, is also used to study the stress-strain relationship of lunar soil. Furthermore, to fundamentally explore the microscopic mechanisms underlying the macroscopic mechanical properties of lunar soil, such as the movement of lunar soil particles, and to establish macroscopic constitutive models based on microscopic mechanisms, X-ray micro-CT imaging technology is commonly used to explore the microscopic mechanical behavior of lunar soil at the particle scale under triaxial shear.

[0003] Traditional triaxial tests on soil often rely on visual inspection to determine if the sample loading meets the requirements due to the large sample size. However, when conducting triaxial tests on real lunar soil, due to its scarcity and preciousness, only trace amounts of sample are used for testing. Therefore, the prepared specimens are often smaller, making it difficult to use traditional methods to determine if the sample loading meets the test requirements, and thus, to ensure the accuracy of the test results. Summary of the Invention

[0004] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides a synchronous CT triaxial testing method for lunar soil samples, which is used to solve the problem that the size of lunar soil samples prepared during triaxial testing is often small, making it difficult to use traditional naked eye observation methods to determine whether the sample meets the test requirements.

[0005] To achieve the above objectives, according to the present invention, a synchronous CT triaxial testing method for lunar soil samples is provided. The method is performed on a synchronous CT triaxial testing apparatus. The synchronous CT triaxial testing apparatus includes a triaxial tester and a CT scanning system. The CT scanning system includes a radiation source, a detector, and a rotating stage disposed between the radiation source and the detector. The synchronous CT triaxial testing method includes:

[0006] S1, prepare lunar soil samples in a triaxial tester, and install the triaxial tester after preparing the lunar soil samples on the rotating table of the CT scanning system;

[0007] S2, using CT scanning to confirm the loading effect of lunar soil samples;

[0008] S3: Apply confining pressure to the lunar soil sample that has been confirmed to meet the requirements through a triaxial tester to a preset pressure and maintain it for a preset time;

[0009] S4, using CT scanning to obtain the initial scanning image of the lunar soil sample before axial compression;

[0010] S5, apply axial pressure to the lunar soil sample through a triaxial tester, and use CT scanning to obtain scanning images of the lunar soil sample during the axial pressure application process, to achieve synchronous CT triaxial testing of the lunar soil sample.

[0011] According to the synchronous CT triaxial testing method for lunar soil samples provided by the present invention, preparing the lunar soil sample in the triaxial testing instrument in S1 specifically includes:

[0012] Weigh a lunar soil sample of a preset mass according to test requirements;

[0013] Use tweezers to place the permeable stone on the support column of the triaxial tester base for placing specimens. Cover the permeable stone with a layer of filter paper. Place the latex film on the support column, the permeable stone above, and the filter paper. Finally, place a rubber ring on the outside of the latex film corresponding to the support column.

[0014] Fix the sample preparation mold on the periphery of the latex film;

[0015] Apply suction to the wall of the sample making mold so that the latex film is close to the inner wall of the mold, and turn the upper part of the latex film down and put it on the upper end of the sample making mold;

[0016] The lunar soil samples were evenly packed into the latex film in layers;

[0017] After placing filter paper, permeable stone, and pressure column on the upper surface of the lunar soil sample, the latex film on the upper end of the sample preparation mold is turned up and put on the outside of the filter paper, permeable stone, and pressure column, and a rubber ring is put on the outside of the latex film corresponding to the pressure column;

[0018] Stop the suction applied to the wall of the sample preparation mold, remove the sample preparation mold, and complete the preparation of the lunar soil sample in the triaxial testing instrument.

[0019] According to the synchronous CT triaxial testing method for lunar soil samples provided by the present invention, S2 specifically includes:

[0020] Perform a CT scan on the lunar soil sample in the triaxial tester to obtain a cross-sectional grayscale image of the lunar soil sample;

[0021] Based on the distribution of sample particles and the shape of the sample edge in the cross-sectional grayscale image, determine whether the lunar soil sample is evenly distributed, whether it is in a cylindrical shape, and whether it is placed vertically. If so, the lunar soil sample meets the requirements.

[0022] According to the synchronous CT triaxial testing method for lunar soil samples provided by the present invention, S3 specifically includes:

[0023] The confining pressure loading device of the triaxial tester is used to increase the confining pressure in the pressure chamber where the lunar soil sample is located to 80-120 kPa, and maintain it for 20-40 minutes to allow the lunar soil sample to consolidate.

[0024] According to the synchronous CT triaxial testing method for lunar soil samples provided by the present invention, applying axial pressure to the lunar soil sample by the triaxial tester in S5 specifically includes:

[0025] The axial pressure loading device in the triaxial tester was controlled to press down the lunar soil sample at a speed of 0.08-0.12 mm / min, that is, axial pressure was applied to the lunar soil sample through displacement control.

[0026] According to the synchronous CT triaxial testing method for lunar soil samples provided by the present invention, S5 specifically includes:

[0027] Monitor and obtain the real-time axial stress and real-time axial strain of lunar soil samples during axial compression;

[0028] Set multiple preset strain values ​​and maximum strain values. Stop axial compression loading when the real-time axial strain of the lunar soil sample reaches the preset strain value. Use CT scanning to obtain the process scan image. Then continue axial compression loading until the maximum strain value is reached. Stop axial compression loading. Use CT scanning to obtain the termination scan image and end the test.

[0029] According to the synchronous CT triaxial testing method for lunar soil samples provided by the present invention, setting multiple predetermined strain values ​​specifically includes:

[0030] Conduct triaxial tests on simulated lunar soil samples to obtain stress-strain curves of the simulated lunar soil samples;

[0031] A reference strain value corresponding to the peak stress in the stress-strain curve, a strain value less than the reference strain value, and a strain value between the reference strain value and the maximum strain value are selected as predetermined strain values.

[0032] According to the synchronous CT triaxial testing method for lunar soil samples provided by the present invention, the CT scanning of the lunar soil samples in S2, S4 and S5 specifically includes:

[0033] During the scanning process, the rotating stage is controlled to rotate 180° counterclockwise at a constant speed. After each scan is completed, the rotating stage is controlled to rotate clockwise back to its original position and wait for the next scan.

[0034] The synchronous CT triaxial testing method for lunar soil samples provided by the present invention further includes: S6, recovering the lunar soil samples; specifically,

[0035] Remove the confining pressure and take out the lunar soil sample from the triaxial tester;

[0036] Open the storage container of the lunar soil sample, transfer the lunar soil sample into the storage container, pour the lunar soil sample wrapped in latex film into the storage container, and use a sample brush to brush the lunar soil sample on the inner wall of the latex film into the storage container, and then close the storage container.

[0037] According to the synchronous CT triaxial testing method for lunar soil samples provided by the present invention, the synchronous CT triaxial testing of the lunar soil sample in S5 specifically includes:

[0038] Analyze the test data of the triaxial tester to obtain the stress-strain relationship and shear strength of the lunar soil samples; analyze the test data of the CT scanning system to obtain information on the evolution of the internal structure of the lunar soil samples during the compression process; the shear strength of the lunar soil samples is specifically:

[0039]

[0040] Among them, τ f is the shear strength, c is the cohesion, σ is the stress, is the internal friction angle.

[0041] In general, compared with the prior art, the above technical solutions conceived by the present invention provide a synchronous CT triaxial testing method for lunar soil samples:

[0042] 1. The use of triaxial testing combined with X-ray micro-CT imaging technology can simultaneously explore the macro- and micro-mechanical properties of lunar soil samples and achieve non-destructive testing of the samples. Adding a CT scan to confirm the loading of the lunar soil samples after preparation can improve the accuracy of the test results while ensuring the accuracy of the loading of trace amounts of authentic lunar soil. This ensures the authenticity and reliability of the test results, while avoiding repeated loading due to loading errors, which helps reduce the loss of authentic lunar soil samples.

[0043] 2. Given the small size of real lunar soil samples (mm level), higher requirements must be met for controlled axial compression loading. During the experiment, displacement control was used for axial compression loading. Multiple predetermined strain values ​​were designed to design the axial compression loading process, and a maximum strain value was designed to control the end of axial compression loading. This is beneficial for maximally protecting the real lunar soil samples and minimizing sample loss.

[0044] 3. The disclosed synchronous CT triaxial testing method is suitable for testing the mechanical properties of trace samples, which can minimize sample loss and reduce sample costs to the greatest extent; it can provide technical support for mechanical property testing of samples from the moon, Mars, asteroids, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a flow chart of a synchronous CT triaxial testing method for lunar soil samples according to an embodiment of the present invention;

[0046] Figure 2 This is a schematic diagram of the installation and sample loading results of the triaxial testing instrument according to an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of a synchronous CT triaxial testing device and its principle according to an embodiment of the present invention;

[0048] Figure 4 is a schematic diagram of the Mohr circle according to an embodiment of the present invention;

[0049] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0050] 01-Data acquisition and control system; 02-Displacement sensor; 03-Pressure column; 04-Permeable stone; 05-Lunar soil sample; 06-Pressure chamber; 07-Base; 08-Confining pressure loading device; 09-Valve; 10-Rubber ring; 11-Filter paper; 12-Top cover; 13-Loading rod; 14-Load sensor; 15-Motor. DETAILED DESCRIPTION

[0051] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0052] See also Figure 1 and Figure 2 The present invention provides a synchronous CT triaxial testing method for lunar soil samples. The synchronous CT triaxial testing method is performed on a synchronous CT triaxial testing device. The synchronous CT triaxial testing device includes a triaxial tester and a CT scanning system. The CT scanning system includes a radiation source, a detector, and a rotating stage disposed between the radiation source and the detector. The synchronous CT triaxial testing method includes:

[0053] S1, prepare lunar soil samples in a triaxial tester, and install the triaxial tester after preparing the lunar soil samples on the rotating table of the CT scanning system;

[0054] S2, using CT scanning to confirm the loading effect of lunar soil samples;

[0055] S3: Apply confining pressure to the lunar soil sample that has been confirmed to meet the requirements through a triaxial tester to a preset pressure and maintain it for a preset time;

[0056] S4, using CT scanning to obtain the initial scanning image of the lunar soil sample before axial compression;

[0057] S5, apply axial pressure to the lunar soil sample through a triaxial tester, and use CT scanning to obtain scanning images of the lunar soil sample during the axial pressure application process, to achieve synchronous CT triaxial testing of the lunar soil sample.

[0058] refer to Figure 2 The triaxial tester includes a confining pressure loading device 08, an axial pressure loading device, a pressure chamber 06, a data acquisition and control system 01, and a connection support assembly, wherein the bottom of the pressure chamber 06 is connected to the base 07, the top of the pressure chamber 06 is connected to the top cover 12, a support column is connected to the base 07, the top of the support column is used to place the sample, a pressure column 03 is provided above the sample, the top surface of the pressure column 03 is in contact with the bottom surface of the loading rod 13, and the axial pressure loading device acts on the sample through the pressure column 03 to apply axial pressure to the sample;

[0059] The axial pressure loading device includes a motor 15, a linear displacement mechanism and a fixed frame. The fixed frame is connected to the top cover 12. The motor 15 and the linear displacement mechanism are installed through the fixed frame. The motor 15 is connected to the linear displacement mechanism to drive the linear displacement mechanism to move up and down. The linear displacement mechanism can move up and down under the drive of the motor 15. The moving end of the linear displacement mechanism is connected to a loading rod 13. The loading rod 13 passes through the top cover 12 and is sealed and slidably connected to the top cover 12. A load sensor 14 is provided between the loading rod 13 and the moving end of the linear displacement mechanism. The moving end of the linear displacement mechanism is also connected to a displacement sensor 02. The load sensor 14 is used to monitor the axial stress of the sample, and the displacement sensor 02 is used to monitor the axial strain of the sample.

[0060] The confining pressure loading device 08 is connected to the pressure chamber 06 through a pipeline, and a valve 09 is provided on the pipeline. The confining pressure loading device 08 may include a water pump and a pressure control element, and may also be provided with a control panel for controlling the water pressure supplied to the pressure chamber 06 and thereby controlling the confining pressure in the pressure chamber 06; the data acquisition and control system 01 includes various sensors and control elements, and also includes a data processing unit which may be a computer. The various sensors and control elements are connected to the data processing unit through connecting wires or wirelessly.

[0061] refer to Figure 3 The base 07 of the triaxial tester can be connected to the rotating table of the CT scanning system, and the rotating table can be connected to a lifting device. The height of the rotating table can be adjusted by the lifting device so that the sample in the triaxial tester is within the scanning range of the radiation light source. Figure 3 The wall of the pressure chamber 06 can be made of transparent materials such as glass to enable CT scanning.

[0062] Furthermore, the preparation of lunar soil samples in the triaxial tester in S1 specifically includes:

[0063] According to the test requirements, weigh the lunar soil sample 05 of the preset mass, i.e., the real lunar soil sample;

[0064] Use tweezers to place the permeable stone 04 on the support column of the triaxial tester base 07 for placing the sample. Cover the permeable stone 04 with a layer of filter paper 11. Put the latex film on the support column and the permeable stone 04 and filter paper 11 above. Put a rubber ring 10 on the outside of the latex film corresponding to the support column to prevent the infiltration of confining pressure water.

[0065] Fix the sample mold on the periphery of the latex film; the sample mold is composed of two parts spliced ​​together to form a structure with a cylindrical inner hole. The two parts can be placed on the periphery of the latex film first, and then the two parts are locked with bolts;

[0066] Applying suction to the wall of the sample making mold to draw a vacuum so that the latex film is closely attached to the inner wall of the mold, and then turning the upper part of the latex film down to cover the upper end of the sample making mold; an opening is provided on the wall of the sample making mold, the opening is connected to the cylindrical hole inside, and a nozzle can be connected to the opening, and applying suction to the nozzle. The suction acts on the cylindrical hole inside to draw a vacuum, thereby ensuring that the latex film is closely attached to the inner wall of the mold, and then turning the upper part of the latex film down to cover the upper end of the sample making mold;

[0067] Evenly load lunar soil sample 05 into the latex film in layers; evenly load the prepared real lunar soil sample 05 into the latex film in layers using a sample spoon;

[0068] After placing filter paper 11, permeable stone 04, and pressure column 03 on the upper surface of lunar soil sample 05, turn the latex film on the upper end of the sample preparation mold upside down and put it on the outside of filter paper 11, permeable stone 04, and pressure column 03. Put a rubber ring 10 on the outside of the latex film corresponding to the pressure column 03 to prevent the infiltration of confining pressure water; the pressure column 03 can be a stainless steel pressure column 03;

[0069] Stop the suction applied to the sample preparation mold wall, remove the sample preparation mold, and complete the preparation of the lunar soil sample in the triaxial tester. That is, suspend the suction applied to the sample preparation mold nozzle and remove the sample preparation mold.

[0070] Specifically, the lunar soil samples prepared in the triaxial testing instrument have a diameter of 2-4 mm and a height of 4-8 mm.

[0071] Before preparing the lunar soil sample in the triaxial tester, S1 also includes: selecting the rotating table and lifting device of the CT scanning system, and aligning the axis of the rotating table; then placing the data acquisition and control system 01 (microcomputer, data acquisition instrument such as sensor), confining pressure loading device 08 and connecting wires to ensure that the connecting wires of the load sensor 14, displacement sensor 02, motor 15, etc. and the water pipeline of the confining pressure loading device 08 do not block the light path when the rotating table rotates 180°.

[0072] In S1, the triaxial tester after preparing the lunar soil sample is installed on the rotating table of the CT scanning system, that is, the installation of the triaxial instrument specifically includes: first, fixing the pressure chamber 06 and the top cover 12 with bolts, and then fixing this part to the triaxial instrument base 07 with bolts, and then fixing the triaxial instrument base 07 on the rotating table, and then fixing the upper structure of the triaxial instrument, that is, the fixing frame and the axial pressure loading device to the pressure chamber 06 top cover 12 with bolts, and finally adjusting the loading rod 13 to just contact the top surface of the pressure column 03 through the motor 15; the displacement of the loading rod 13 can be controlled by the displacement sensor 02 so that the bottom surface of the loading rod 13 moves to the top surface of the pressure column 03.

[0073] After the triaxial tester is installed in place, the light source energy and detector resolution of the CT scanning system can be selected to determine the spot height.

[0074] S2 specifically includes:

[0075] Perform a CT scan on the lunar soil sample in the triaxial tester to obtain a cross-sectional grayscale image of the lunar soil sample;

[0076] Based on the distribution of sample particles and the shape of the sample edges in the cross-sectional grayscale image, it is determined whether the lunar soil sample is evenly distributed, cylindrical, and vertically placed. If all of these conditions are met, the lunar soil sample loading meets the requirements. Based on the cross-sectional grayscale image obtained by CT scanning, the distribution of sample particles and the shape of the sample edges can be visually determined to determine whether the sample loading meets the requirements.

[0077] S3 specifically includes:

[0078] The confining pressure in the pressure chamber 06 containing the lunar soil sample was increased to 80-120 kPa using the confining pressure loading device 08 of the triaxial tester and maintained for 20-40 minutes to allow the lunar soil sample to consolidate. For example, the confining pressure was applied to the target pressure of 100 kPa using the control panel of the confining pressure loading device 08, and the actual lunar soil sample was allowed to consolidate for 30 minutes.

[0079] In S5, the axial pressure applied to the lunar soil sample by the triaxial tester specifically includes:

[0080] The axial pressure loading device in the triaxial tester is controlled to press down the lunar soil sample at a speed of 0.08-0.12 mm / min, that is, axial pressure is applied to the lunar soil sample through displacement control. Controlling the speed of axial pressure loading through displacement is beneficial to avoid damage to the lunar soil caused by excessive axial pressure, and is beneficial to protecting the lunar soil.

[0081] S5 specifically includes:

[0082] Monitor and obtain the real-time axial stress and real-time axial strain of lunar soil samples during axial compression;

[0083] Set multiple preset strain values ​​and maximum strain values. Stop axial compression loading when the real-time axial strain of the lunar soil sample reaches the preset strain value. Use CT scanning to obtain the process scan image. Then continue axial compression loading until the maximum strain value is reached. Stop axial compression loading. Use CT scanning to obtain the termination scan image and end the test.

[0084] Setting multiple predetermined strain values ​​specifically includes:

[0085] Conduct triaxial tests on simulated lunar soil samples to obtain stress-strain curves of the simulated lunar soil samples;

[0086] A reference strain value corresponding to the peak stress in the stress-strain curve, a strain value less than the reference strain value, and a strain value between the reference strain value and the maximum strain value are selected as predetermined strain values.

[0087] Specifically, the predetermined strain values ​​are 2%, 5%, and 10%, with a maximum strain value of 20%. The predetermined axial strain value for the actual lunar soil sample was determined based on the stress-strain curve of the triaxial test of simulated lunar soil sample 05. This predetermined value must include the axial strain corresponding to the peak stress. Furthermore, the maximum axial strain during loading control should not exceed 20%, otherwise it will cause damage to the latex film and the actual lunar soil.

[0088] The CT scanning of lunar soil samples in S2, S4 and S5 specifically includes:

[0089] During the scanning process, the rotating stage is controlled to rotate 180° counterclockwise at a constant speed. After each scan is completed, the rotating stage is controlled to rotate clockwise back to its original position and wait for the next scan.

[0090] Furthermore, the synchronous CT triaxial testing method for lunar soil sample 05 further includes: S6, recovering lunar soil sample 05; specifically,

[0091] Remove the confining pressure and take out the lunar soil sample from the triaxial tester;

[0092] Open the storage container of lunar soil sample 05, transfer the lunar soil sample into the storage container, pour the lunar soil sample 05 wrapped in latex film into the storage container, and use a sample brush to brush the lunar soil sample 05 on the inner wall of the latex film into the storage container, and then close the storage container.

[0093] Specifically, open valve 09 to drain the water in the pressure chamber 06; remove the connecting wires, remove the triaxial instrument from the rotating table, and remove the triaxial instrument upper structure, top cover 12, and pressure chamber 06 from top to bottom; remove the rubber ring 10, use absorbent paper to absorb the residual moisture on the surface of the latex film, and carefully remove the permeable stone 04-filter paper 11-real lunar soil sample-filter paper 11-permeable stone 04-pressure column 03 wrapped in the latex film from the support column at the end of the triaxial instrument base 07, place it on the weighing paper, and use tweezers to separate the pressure column 03, permeable stone 04, and filter paper 11 from the whole; open the real lunar soil sample 05 glass bottle, transfer the lunar soil sample into the glass bottle, and then use a sample brush to gently brush the lunar soil sample remaining on the inner wall of the latex film into the glass bottle, and then tighten the glass bottle cap and wrap it with sealing film.

[0094] The synchronous CT triaxial testing of lunar soil samples in S5 specifically includes:

[0095] The test data from the triaxial tester were analyzed to obtain the stress-strain relationship and shear strength of lunar soil sample 05. The test data from the CT scanning system were analyzed to obtain information on the evolution of the internal structure of lunar soil sample 05 during the compression process. The shear strength of lunar soil sample 05 is specifically:

[0096]

[0097] Among them, τ f is the shear strength, c is the cohesion, σ is the stress, is the internal friction angle.

[0098] Specifically, after the synchronous CT triaxial test of lunar soil sample 05 is completed, the triaxial tester can obtain the deviatoric stress-axial strain curve of the real lunar soil sample; the shear strength can be calculated based on the deviatoric stress-axial strain curve; combined with the CT scanning image information, the evolution information of the internal structure of lunar soil sample 05 can be obtained, and the compression process of lunar soil sample 05 can be visualized and digitized, which is conducive to in-depth research on the mechanical properties of lunar soil.

[0099] Determining the shear strength of lunar soil sample 05 involves conducting multiple triaxial tests on the lunar soil sample, each with a different confining pressure, and obtaining multiple deviatoric stress-axial strain curves corresponding to the tests. Based on these deviatoric stress-axial strain curves, the abscissa and radius of the Mohr circles corresponding to different confining pressures are calculated. Multiple Mohr circles corresponding to different confining pressures are then plotted at corresponding locations on the shear strength-stress graph, with a common tangent line drawn between every two Mohr circles. Finally, the slopes and intercepts of these common tangent lines are calculated and averaged to determine the internal friction angle and cohesion of the lunar soil sample, thereby determining the relationship between shear strength and stress.

[0100] For example, three triaxial tests can be conducted, subjecting the lunar soil sample to three different confining pressures. Based on the deviatoric stress-axial strain curves obtained from these three tests, the shear strength indicators of the actual lunar soil sample, including the internal friction angle and cohesion, can be further determined. The confining pressure value for the actual lunar soil sample can be determined by referring to the confining pressure value set in the simulated lunar soil triaxial test.

[0101] The specific method is as follows:

[0102] First, obtain the maximum deviatoric stress value (σ1-σ3) of each deviatoric stress-axial strain curve under three different confining pressures (σ3 represents the confining pressure), where σ1 represents the maximum axial stress. Then calculate the abscissa and radius of the center of the Mohr circle corresponding to these three different confining pressures, with the ordinate of the center being 0. Then, at τ f Three Mohr circles are drawn at the corresponding positions of the -σ diagram, and a common tangent line is drawn between every two Mohr circles, such as Figure 4 Finally, we get the slopes of the three common tangent lines. and intercept (c i , i=1,2,3), take the average of the slope and intercept to get the internal friction angle of the real lunar soil sample and cohesion c.

[0103] The calculation formula is as follows:

[0104]

[0105]

[0106] Where x is the abscissa of the center of the Mohr circle, and R is the radius of the Mohr circle.

[0107] This invention discloses a synchronous CT triaxial testing method for a trace amount of authentic lunar soil sample 05. This method belongs to the technical field of authentic lunar soil mechanical property research. Its purpose is to improve the accuracy of test results while ensuring the accuracy of the loading of the trace amount of authentic lunar soil, while minimizing the loss of the authentic lunar soil sample 05. The method includes: installing a triaxial test apparatus, preparing a test sample, determining the loading effect based on a CT scan, securing the triaxial apparatus to a rotating table within the CT scanning apparatus, debugging the CT scanning apparatus, increasing the confining pressure to a target pressure using a confining pressure loading device 08, performing an initial CT scan on the test sample, controlling the application of axial pressure, stopping the loading when a predetermined value is reached, scanning the test sample again, repeating the two steps of applying axial pressure and scanning the sample until loading is complete, and recovering the test sample. This method accurately determines the preparation effect of trace amounts of authentic lunar soil, improving the reliability of test results. It also reduces repeated loading caused by operational errors due to undersized specimens, minimizing the loss of authentic lunar soil sample 05, and providing technical support for mechanical property testing of samples from asteroids, Mars, and other sources.

[0108] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A synchronous CT triaxial testing method for lunar soil samples, performed on a synchronous CT triaxial testing device, comprising a triaxial tester and a CT scanning system, wherein the CT scanning system comprises a radiation source, a detector, and a rotating stage disposed between the radiation source and the detector, characterized in that: The simultaneous CT triaxial testing method includes: S1, prepare lunar soil samples in a triaxial tester, and install the triaxial tester after preparing the lunar soil samples on the rotating table of the CT scanning system; S2, using CT scanning to confirm the loading effect of lunar soil samples; S3: Apply confining pressure to the lunar soil sample that has been confirmed to meet the requirements through a triaxial tester to a preset pressure and maintain it for a preset time; S4, using CT scanning to obtain the initial scanning image of the lunar soil sample before axial compression; S5, applying axial compression to the lunar soil sample using a triaxial tester, and using CT scanning to obtain scanned images of the lunar soil sample during the axial compression process, thereby achieving synchronous CT triaxial testing of the lunar soil sample; S2 specifically includes: Perform a CT scan on the lunar soil sample in the triaxial tester to obtain a cross-sectional grayscale image of the lunar soil sample; Based on the distribution of sample particles and the shape of the sample edge in the cross-sectional grayscale image, determine whether the lunar soil sample is evenly distributed, cylindrical, and vertically placed. If all of these are true, the lunar soil sample meets the requirements. S5 specifically includes: Monitor and obtain the real-time axial stress and real-time axial strain of lunar soil samples during axial compression; Set multiple predetermined strain values ​​and a maximum strain value. When the real-time axial strain of the lunar soil sample reaches the predetermined strain value, stop the axial compressive loading. Use CT scanning to obtain a process scan image. Then continue the axial compressive loading until the maximum strain value is reached. Then use CT scanning to obtain a terminal scan image to end the test. The maximum strain value should not be exceeded during axial compression loading, otherwise it will cause damage to the real lunar soil.

2. The synchronous CT triaxial testing method for lunar soil samples according to claim 1, characterized in that: The preparation of lunar soil samples in the triaxial tester in S1 specifically includes: Weigh a lunar soil sample of a preset mass according to test requirements; Use tweezers to place the permeable stone on the support column of the triaxial tester base for placing specimens. Cover the permeable stone with a layer of filter paper. Place the latex film on the support column, the permeable stone above, and the filter paper. Finally, place a rubber ring on the outside of the latex film corresponding to the support column. Fix the sample preparation mold on the periphery of the latex film; Apply suction to the wall of the sample making mold so that the latex film is close to the inner wall of the mold, and turn the upper part of the latex film down and put it on the upper end of the sample making mold; The lunar soil samples were evenly packed into the latex film in layers; After placing filter paper, permeable stone, and pressure column on the upper surface of the lunar soil sample, the latex film on the upper end of the sample preparation mold is turned up and put on the outside of the filter paper, permeable stone, and pressure column, and a rubber ring is put on the outside of the latex film corresponding to the pressure column; Stop the suction applied to the wall of the sample preparation mold, remove the sample preparation mold, and complete the preparation of the lunar soil sample in the triaxial testing instrument.

3. The synchronous CT triaxial testing method for lunar soil samples according to claim 1, characterized in that: S3 specifically includes: The confining pressure loading device of the triaxial tester is used to increase the confining pressure in the pressure chamber where the lunar soil sample is located to 80-120 kPa, and maintain it for 20-40 minutes to allow the lunar soil sample to consolidate.

4. The synchronous CT triaxial testing method for lunar soil samples according to claim 1, characterized in that: In S5, the axial pressure applied to the lunar soil sample by the triaxial tester specifically includes: The axial pressure loading device in the triaxial tester was controlled to press down the lunar soil sample at a speed of 0.08-0.12 mm / min, that is, axial pressure was applied to the lunar soil sample through displacement control.

5. The synchronous CT triaxial testing method for lunar soil samples according to claim 1, characterized in that: Setting multiple predetermined strain values ​​specifically includes: Conduct triaxial tests on simulated lunar soil samples to obtain stress-strain curves of the simulated lunar soil samples; A reference strain value corresponding to the peak stress in the stress-strain curve, a strain value less than the reference strain value, and a strain value between the reference strain value and the maximum strain value are selected as predetermined strain values.

6. The synchronous CT triaxial testing method for lunar soil samples according to claim 1, characterized in that: The CT scanning of lunar soil samples in S2, S4 and S5 specifically includes: During the scanning process, the rotating stage is controlled to rotate 180° counterclockwise at a constant speed. After each scan is completed, the rotating stage is controlled to rotate clockwise back to its original position and wait for the next scan.

7. The synchronous CT triaxial testing method for lunar soil samples according to claim 2, characterized in that: Also includes: S6, recover lunar soil samples; Specifically, Remove the confining pressure and take out the lunar soil sample from the triaxial tester; Open the storage container of the lunar soil sample, transfer the lunar soil sample into the storage container, pour the lunar soil sample wrapped in latex film into the storage container, and use a sample brush to brush the lunar soil sample on the inner wall of the latex film into the storage container, and then close the storage container.

8. The synchronous CT triaxial testing method for lunar soil samples according to claim 1, characterized in that: The synchronous CT triaxial testing of lunar soil samples in S5 specifically includes: Analyze the test data of the triaxial tester to obtain the stress-strain relationship and shear strength of the lunar soil samples; analyze the test data of the CT scanning system to obtain information on the evolution of the internal structure of the lunar soil samples during the compression process; the shear strength of the lunar soil samples is specifically: ； in, is the shear strength, For cohesion, is stress, is the internal friction angle.

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