Synchronous CT triaxial test method for lunar soil sample

Abstract

The invention belongs to the related technical field of lunar soil mechanical research, and discloses a synchronous CT triaxial test method for a lunar soil sample, which comprises the following steps: S1, preparing the lunar soil sample in a triaxial tester, and installing the triaxial tester after the lunar soil sample is prepared on a rotating table of a CT scanning system; s2, adopting CT scanning to confirm the loading effect of the lunar soil sample; s3, applying confining pressure to the lunar soil sample to preset pressure and maintaining for preset time; s4, acquiring an initial scanning image of the lunar soil sample before the axial pressure is applied by adopting CT (Computed Tomography) scanning; s5, axial pressure is applied to the lunar soil sample, a scanning image is obtained through CT scanning, and synchronous CT triaxial testing of the lunar soil sample is achieved. According to the method, the step of confirming the sample loading effect through CT scanning is adopted, the precision of a test result can be improved on the basis of ensuring the accuracy of trace real lunar soil sample loading, the authenticity and reliability of the test result are ensured, meanwhile, repeated sample loading caused by sample loading operation errors is avoided, and lunar soil loss can be reduced.

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 mainly include compressibility and shear strength, which are the basis for exploring lunar landing, lunar exploration, and lunar construction. Triaxial testing is an important means to study the three-dimensional deformation strength characteristics of soil and construct soil constitutive models, and is also used to study the stress-strain relationship of lunar soil. In addition, in order to explore the microscopic mechanisms behind the macroscopic mechanical properties of lunar soil, such as the movement of lunar soil particles, and to establish a macroscopic constitutive model based on microscopic mechanisms, X-ray micro-CT imaging technology is usually used to explore the microscopic mechanical behavior of lunar soil at the particle scale under triaxial shear.

[0003] In traditional triaxial tests on soil, due to the large size of the sample, the naked eye is often used to determine whether the sample meets the requirements. When using real lunar soil for triaxial tests, due to the scarcity and preciousness of real lunar soil, only a small amount of sample is used for the test, so the size of the prepared sample is often small, making it difficult to use traditional methods to determine whether the sample meets the test requirements, and thus it is difficult to ensure the accuracy of the test results. Summary of the invention

[0004] In response to the above 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-mentioned object, according to the present invention, a synchronous CT triaxial testing method for lunar soil samples is provided, which 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 table arranged between the radiation source and the detector. The synchronous CT triaxial testing method includes:

[0006] 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;

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

[0008] S3, applying confining pressure to the lunar soil sample confirmed to meet the requirements through a triaxial tester to a preset pressure and maintaining 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, applying axial pressure to the lunar soil sample through a triaxial tester, and using CT scanning to obtain scanning images of the lunar soil sample during the process of applying the axial pressure, 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 machine in S1 specifically includes:

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

[0013] Use tweezers to place the permeable stone on the support column of the triaxial tester base for placing the sample, cover the permeable stone with a layer of filter paper, put the latex film on the support column and the permeable stone and filter paper above, and put 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 force to the wall of the sample making mold to make the latex film close to the inner wall of the mold, and turn down the upper part of the latex film and put it on the upper end of the sample making mold;

[0016] The lunar soil samples are 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 in sequence, turn the latex film on the upper end of the sample preparation mold upside down and put it on the outside of the filter paper, permeable stone and pressure column, and put a rubber ring 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] According to 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 in the pressure chamber where the lunar soil sample is located is increased to 80-120 kPa through the confining pressure loading device of the triaxial tester and maintained 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 the axial pressure application process;

[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, and 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 a plurality of predetermined strain values ​​specifically includes:

[0030] Conduct triaxial tests on simulated lunar soil samples to obtain stress-strain curves of 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 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 the original position to 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 samples 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 the evolution information 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 synchronous CT triaxial testing method for lunar soil samples provided by the present invention is as follows:

[0042] 1. The triaxial test method is combined with X-ray micro-CT imaging technology to simultaneously explore the macroscopic and microscopic mechanical properties of lunar soil samples and realize non-destructive testing of samples. After the lunar soil samples are prepared, the step of using CT scanning to confirm the loading effect is added. This can improve the accuracy of the test results on the basis of ensuring the accuracy of the loading of trace real lunar soil, ensure the authenticity and reliability of the test results, and avoid repeated loading due to loading operation errors, which is conducive to reducing the loss of real lunar soil samples.

[0043] 2. Considering that the size of real lunar soil samples is small (mm level), the control of axial pressure loading also needs to meet higher requirements. During the experiment, displacement control is used for axial pressure loading, and multiple predetermined strain values ​​are designed to design the axial pressure loading process, and the maximum strain value is designed to control the end of axial pressure loading, which is conducive to protecting the real lunar soil samples to the greatest extent and reducing the loss of samples.

[0044] 3. The publicly 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; 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 It is a schematic diagram of the installation and sample loading results of the triaxial tester according to an embodiment of the present invention;

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

[0048] Figure 4 is a schematic diagram of the Mohr circle of 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 purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain 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 can 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 table arranged between the radiation source and the detector. The synchronous CT triaxial testing method includes:

[0053] 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;

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

[0055] S3, applying confining pressure to the lunar soil sample confirmed to meet the requirements through a triaxial tester to a preset pressure and maintaining 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, applying axial pressure to the lunar soil sample through a triaxial tester, and using CT scanning to obtain scanning images of the lunar soil sample during the process of applying the axial pressure, 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 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 arranged 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, and is used 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, and the moving end of the linear displacement mechanism is connected with 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, and the moving end of the linear displacement mechanism is also connected with 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 delivered to the pressure chamber 06 and thereby controlling the confining pressure in the pressure chamber 06; the data acquisition control system 01 includes various sensors and control elements, and also includes a data processing unit which may be a computer, and each sensor and control element is connected to the data processing unit through a connecting wire 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. The radiation light source is Figure 3 The wall of the pressure chamber 06 can be made of transparent materials such as glass to achieve 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, and 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] The sample-making mold is fixed on the periphery of the latex film; the sample-making 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] Apply suction force to the wall surface of the sample making mold, draw vacuum so that the latex film is closely attached to the inner wall of the mold, and turn down the upper part of the latex film to cover the upper end of the sample making mold; an opening is provided on the wall surface of the sample making mold, the opening is connected to the internal cylindrical hole, and a nozzle can be connected to the opening, and suction force is applied to the nozzle, and the suction force acts on the internal cylindrical hole to achieve the effect of drawing vacuum, ensuring that the latex film is closely attached to the inner wall of the mold, and then turn down the upper part of the latex film to cover the upper end of the sample making mold;

[0067] The lunar soil sample 05 is evenly loaded into the latex film in layers; the real lunar soil sample 05 prepared in advance is evenly loaded 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 in sequence, turn up the latex film on the upper end of the sample preparation mold and put it on the outside of filter paper 11, permeable stone 04 and pressure column 03, and 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 force 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 tester. That is, stop the suction force applied to the nozzle of the sample preparation mold, and remove the sample preparation mold.

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

[0071] Before preparing the lunar soil sample in the three-axis 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 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 fixed frame and the axial pressure loading device, to the top cover 12 of the pressure chamber 06 with bolts, and finally adjusting the loading rod 13 to just contact with the top surface of the pressurized 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 pressurized 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] According to the distribution of sample particles and the shape of the sample edge in the cross-sectional grayscale image, it is judged whether the lunar soil sample is evenly distributed, cylindrical, and vertically placed. If so, the lunar soil sample meets the requirements. According to the cross-sectional grayscale image obtained by CT scanning, the distribution of sample particles and the shape of the sample edge can be judged by naked eyes, and then whether the sample meets the requirements.

[0077] S3 specifically includes:

[0078] The confining pressure in the pressure chamber 06 where the lunar soil sample is located is increased to 80-120 kPa by 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 is applied, and the confining pressure is increased to the target pressure of 100 kPa by the control panel of the confining pressure loading device 08, and the real lunar soil sample is 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 0.08-0.12mm / min, that is, axial pressure is applied to the lunar soil sample through displacement control. Controlling the speed of axial pressure loading by displacement is beneficial to avoid damage to the lunar soil due to 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 the axial pressure application process;

[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, and 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 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 preset strain values ​​are 2%, 5% and 10%; the maximum strain value is 20%. According to the stress-strain curve of the triaxial test of simulated lunar soil sample 05, the preset value of the axial strain of the real lunar soil sample is determined, and the preset value needs to include the axial strain corresponding to the peak stress. In addition, the maximum axial strain during loading control should not exceed 20%, otherwise it will cause the destruction of the latex film and the damage of the real 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 the original position to wait for the next scan.

[0090] Furthermore, the synchronous CT triaxial testing method for the lunar soil sample 05 further includes: S6, recovering the 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, take the triaxial instrument off 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-pressurization 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 pressurization column 03, permeable stone 04, and filter paper 11 from the whole; open the glass bottle of real lunar soil sample 05, 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 a sealing film.

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

[0095] The test data of the triaxial tester were analyzed to obtain the stress-strain relationship and shear strength of lunar soil sample 05. The test data of the CT scanning system were analyzed to obtain the evolution information 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] Obtaining the shear strength of lunar soil sample 05 specifically includes: conducting multiple triaxial tests on the lunar soil sample, wherein the confining pressure of each triaxial test is different, obtaining multiple deviator stress-axial strain curves corresponding to the multiple tests; calculating the abscissa and radius of the center of the Mohr circle corresponding to different confining pressures according to the multiple deviator stress-axial strain curves; then drawing multiple Mohr circles corresponding to different confining pressures at the corresponding positions of the shear strength-stress graph, and drawing a common tangent line between every two Mohr circles. Finally, obtaining the slopes and intercepts of the multiple common tangent lines, taking the average of the slopes and intercepts, obtaining the internal friction angle and cohesion of the lunar soil sample, and then obtaining the relationship between shear strength and stress.

[0100] For example, three triaxial tests can be conducted, that is, the lunar soil samples are subjected to triaxial tests at three different confining pressures; based on the deviatoric stress-axial strain curves obtained in the three tests, the shear strength indicators of the real lunar soil samples can be further obtained: internal friction angle and cohesion. The confining pressure value of the real 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 three different confining pressures (σ 3 represents the confining pressure), the maximum deviatoric stress value (σ 1 -σ 3 ), σ 1 represents the maximum axial stress. Then calculate the abscissa and radius of the center of the Mohr circle corresponding to the 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] The present invention discloses a synchronous CT triaxial test method for a trace real lunar soil sample 05, which belongs to the technical field of the research on the mechanical properties of real lunar soil. Its purpose is to improve the accuracy of the test results on the basis of ensuring the accuracy of the sample loading of the trace real lunar soil, and at the same time minimize the loss of the real lunar soil sample 05. It includes: installing a triaxial test device, preparing a test sample, judging the sample loading effect according to the CT scan, fixing the triaxial test device to the rotating table in the CT scanning device, debugging the CT scanning device, increasing the confining pressure to the target pressure through the confining pressure loading device 08, performing an initial CT scan on the test sample, controlling the application of axial pressure, stopping the loading when the predetermined value is reached, scanning the test sample again, repeating the two steps of applying axial pressure-scanning the sample until the loading is completed, and recovering the test sample. The present invention can realize the accurate judgment of the sample preparation effect of the trace real lunar soil, improve the reliability of the test results; reduce the repeated loading caused by the operation error due to the small sample size, can minimize the loss of the real lunar soil sample 05, and provide technical support for the mechanical property testing of samples such as asteroids and Mars.

[0108] It will be easily understood by those skilled in the art that the above description is only 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 protection scope of the present invention.

Claims

1. A synchronous CT triaxial testing method for lunar soil samples, which is performed on a synchronous CT triaxial testing device, which includes a triaxial tester and a CT scanning system, and the CT scanning system includes a radiation source, a detector, and a rotating table arranged between the radiation source and the detector, characterized in that: The simultaneous CT triaxial testing method includes: 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 lunar soil samples; S3, applying confining pressure to the lunar soil sample confirmed to meet the requirements through a triaxial tester to a preset pressure and maintaining 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 pressure to the lunar soil sample through a triaxial tester, and using CT scanning to obtain scanning images of the lunar soil sample during the process of applying the axial pressure, to achieve synchronous CT triaxial testing of the lunar soil sample.

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 preset mass of lunar soil sample according to test requirements; Use tweezers to place the permeable stone on the support column of the triaxial tester base for placing the sample, cover the permeable stone with a layer of filter paper, put the latex film on the support column and the permeable stone and filter paper above, and put 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 force to the wall of the sample making mold to make the latex film close to the inner wall of the mold, and turn down the upper part of the latex film and put it on the upper end of the sample making mold; The lunar soil samples are 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 in sequence, turn the latex film on the upper end of the sample preparation mold upside down and put it on the outside of the filter paper, permeable stone and pressure column, and put a rubber ring 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: 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; According to 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.

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

5. 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.

6. The synchronous CT triaxial testing method for lunar soil samples according to claim 1, characterized in that: S5 specifically includes: Monitor and obtain the real-time axial stress and real-time axial strain of lunar soil samples during the axial pressure application process; 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, and 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.

7. The synchronous CT triaxial testing method for lunar soil samples according to claim 6, characterized in that: Setting multiple predetermined strain values ​​specifically includes: Conduct triaxial tests on simulated lunar soil samples to obtain stress-strain curves of 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.

8. 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 the original position to wait for the next scan.

9. 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.

10. 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 the evolution information of the internal structure of the lunar soil samples during the compression process; the shear strength of the lunar soil samples is specifically: Among them, τ f is the shear strength, c is the cohesion, σ is the stress, is the internal friction angle.

Images