A test system for tensile properties of aeolian sand modified soil

Abstract

A test system for tensile properties of aeolian sand modified soil is specially suitable for convenient and accurate testing of direct tensile strength of aeolian sand modified materials. It is characterized in that the left pull block and the right pull block are interlocked to form an integral pull block, and a fixing buckle is arranged in the contact area of ​​the outer wall of the left pull block and the right pull block, and the fixing buckles are interlocked with each other to limit the horizontal lateral movement and dislocation of the integral pull block during sample preparation, one end of the extensometer is connected to the end of the left pull block, and the other end is connected to the end of the right pull block, the upper part of the integral pull block is connected to the left guard arm and the right guard arm, and the two guard arms are connected to the integral pull block through the protruding limit platforms in the middle of the two ends of the integral pull block, the lower pressure plate directly acts on the sample, and three transmission columns for transmitting pressure are fixed at equal intervals in the upper part of the lower pressure plate, and the upper part of the transmission column is fixed with the upper pressure plate; it is suitable for accurately, conveniently and efficiently testing the tensile strength of aeolian sand modified soil using a conventional press under laboratory conditions.

Description

Technical Field

[0001] The invention relates to a tensile property testing system for aeolian sand modified soil, which is specially suitable for convenient and accurate testing of the direct tensile strength of aeolian sand modified materials. Background Art

[0002] Aeolian sand is a Quaternary aeolian deposit formed by wind and sand flow in alluvial plains. It is widely distributed in nine provinces and regions in my country, including Xinjiang, Inner Mongolia, Qinghai, Gansu, Shaanxi and Ningxia. However, aeolian sand has the characteristics of large pores, strong permeability, no plasticity and low shear strength. It is difficult to build an embankment that meets the requirements of high-grade line projects (high-speed railways, highways) with aeolian sand alone. It is urgent to add cement and other bonding materials to modify it, so that it can not only reduce the cost of the project, but also meet the requirements of line projects for deformation and stability. Therefore, it is particularly important to test and analyze the mechanical indicators of aeolian sand modified soil in different states. As a brittle material, among many strength indicators, the tensile strength test of aeolian sand-modified soil is particularly difficult and critical. Among the existing test methods, both direct tensile method and indirect tensile method have certain defects. For example, when the Brazilian splitting method is used to test the tensile strength, the aeolian sand-modified soil sample is not only "broken" when it is destroyed, but also affected by the compressive stress, which leads to errors in the test data; for example, the Brazilian disc splitting method is used in patent CN105043866A. When the tensile strength of the sample is too small than the compressive strength, the error of the tensile strength value is large; for example, the pulling method used in patent CN206832593U is manually loaded, and the speed of manual loading will directly affect the accuracy and convenience of the test data; for example, patent CN205175835U uses a weight plate for loading. Although the consistency of the loading speed is improved, it is impossible to achieve fine control of the measurement rate. At the same time, a dial indicator is used for displacement measurement, and the test data is not accurate enough. The present invention provides a tensile strength testing system for aeolian sand modified soil integrating sample preparation and testing, which not only realizes the integration of sample preparation for aeolian sand modified soil, but also can use a material testing machine commonly used in laboratories to perform tensile strength tests on samples, thereby solving the current problems of inconvenient tensile strength tests for aeolian sand modified soil and inaccurate test accuracy, and providing an effective laboratory testing method for the research and application of aeolian sand modified materials in desert areas. Summary of the invention

[0003] In view of the material property that the tensile strength of aeolian sand modified materials is much smaller than the compressive strength, a tensile strength testing system is provided, which is convenient for sample preparation and accurate testing in laboratory conditions. It is suitable for accurately, conveniently and efficiently testing the tensile strength of aeolian sand modified soil using a conventional press under laboratory conditions.

[0004] The technical solution adopted by the present invention to solve its technical problem is:

[0005] A test system for tensile properties of aeolian sand modified soil, characterized in that the parts are connected in the following order from bottom to top: a left pull block (6) and a right pull block (7) are engaged and connected to form an integral pull block; a fixing buckle (10) is arranged in the contact area of ​​the outer walls of the left pull block (6) and the right pull block (7); the fixing buckles (10) are engaged with each other to limit the horizontal lateral movement and dislocation of the integral pull block during sample preparation; an extensometer (11) is connected to the end of the left pull block (6) at one end and to the end of the right pull block (7) at the other end; a left guard arm (15) and a right guard arm (16) are connected to the upper part of the integral pull block; the two guard arms are connected to the integral pull block through a protruding limit platform in the middle of the two ends of the integral pull block; a lower pressure plate (21) directly acts on the sample; three transmission columns (20) for transmitting pressure are longitudinally equidistantly fixed on the upper part of the lower pressure plate (21); an upper pressure plate (17) is fixed on the upper part of the transmission column (20);

[0006] The rectangular base frame (1) is rigidly connected to the left pull plate (3), and the base frame (1) is arranged with a slide rail. The upper part of the right movable integral pull block is connected to the left guard arm (15) and the right guard arm (16). The two guard arms are connected to the integral pull block through the protruding limit platforms in the middle of the two ends of the integral pull block. The lower pressure plate (21) directly acts on the sample. Three transmission columns (20) for transmitting pressure are longitudinally equidistantly fixed on the upper part of the lower pressure plate (21), and the upper pressure plate (17) is fixed on the upper part of the transmission column (20);

[0007] The rectangular base frame (1) is rigidly connected to the left pull plate (3), the base frame (1) is arranged with a slide rail, the right movable pull plate (4) is connected to the slide rail to form a movable end, a plurality of fixed corner columns (2) are fixed at each end of the base frame (1), the top of the fixed corner column (2) is connected to the top fixed cover (13), the body of the hydraulic conversion tube (9) passes through the central reserved hole of the top fixed cover (13), the lower pipe mouth piston (8) of the hydraulic conversion tube (9) corresponds to the stress gauge (12) rigidly connected to the center of the right movable pull plate (4), and the upper pipe mouth piston of the hydraulic conversion tube (9) is connected to the pressure acting end (22).

[0008] Furthermore, the left pull block (6) and the right pull block (7) are provided with a sawtooth bite (18) at the junction, and the sawtooth bite (18) is provided with a step limiting portion (19).

[0009] Furthermore, the top fixing cover (13) in the tensile strength test mold adopts a hollow design to reduce the pressure on the fixed corner column (2).

[0010] The sample (14) is placed in the integral pull block, the right movable pull plate (4) slides on the slide rail (5), and the piston (8) of the hydraulic conversion tube (9) and the right movable pull plate (4) move in the same direction on the slide rail (5); the protruding limit platforms at the ends of the left pull block (6) and the right pull block (7) are aligned with the central grooves of the left pull plate (3) and the right movable pull plate (4) of the tensile strength test mold and pushed in, the fixing buckle (10) is unlocked, and the position of the piston (8) is adjusted to make it closely contact the stress gauge (12), the extensometer (11) and the stress gauge (12) collect data and transmit the data to the data acquisition terminal (23);

[0011] The hydraulic conversion tube (9) converts the longitudinal pressure of the conventional press into a transverse pulling force; on the one hand, the longitudinal pressure of the press is converted to the right movable pull plate (4) at a constant speed level, and on the other hand, the pressure applied to the right movable pull plate (4) is measured;

[0012] A fixing buckle (10) that engages with each other is provided at the middle part where the outer walls of the left pull block (6) and the right pull block (7) contact each other. The fixing buckle (10) is locked during sample preparation to ensure that the sample will not move or be misplaced in the horizontal direction during sample preparation. The fixing buckle (10) is unlocked during testing to release the horizontal constraint on the sample.

[0013] A hydraulic conversion device is used to convert the longitudinal pressure of a traditional press into a lateral tension; the upper end of the hydraulic conversion device is in direct contact with the loading end of the press, and the lower end corresponds to a pressure sensor, which is rigidly connected to the right movable pull plate. On the one hand, the longitudinal pressure of the press is converted to the right movable pull plate at a constant speed, and on the other hand, the pressure applied to the tension plate can be accurately measured and recorded as P. The tensile force F applied to both ends of the aeolian sand modified soil sample is obtained by using the dynamic friction coefficient μ of the slide rail tested before the test, that is, F=PG·μ, where G is the sum of the weights of the pressure sensor and the right end tension plate; during the test, the pull block containing the aeolian sand modified soil sample is pushed horizontally into the left and right pressure plates, ensuring that the pull block and the pull plate are buckled and there is no gap, and then placed on the press platform, the pull block fixing buckle is unfastened, the press loading rate is set, the pressure sensor acquisition device and the displacement meter acquisition device are turned on, the data acquisition terminal is connected to the computer, the press is started, and the tensile strength test of the aeolian sand modified soil can be carried out.

[0014] A system for testing the tensile properties of aeolian sand modified soil has an overall structure of two parts: a sample mold for aeolian sand modified soil and a tensile strength test mold for aeolian sand modified soil.

[0015] The mold for preparing the sample of aeolian sand modified soil mainly consists of the following parts: a pull block, a guard arm and a pressure plate. The pull block is designed as an "I-shaped" shape, which can provide constraints for the forming of aeolian sand modified soil and a tensile force surface for testing the tensile strength. In order to avoid affecting the stress concentration effect of the test, a circular arc design is adopted at the connection part. The pull block is symmetrically divided into two parts, left and right, from the middle. The internal structure of the two parts is consistent to ensure that the tensile strength of the sample does not deviate due to the change in shape. The joint is connected by a serrated bite to limit the horizontal displacement of the sample during sample preparation or testing. The sides of the left and right parts of the pull block are respectively arranged with cross-interlocking fixed locks to ensure that the two parts are combined into one when preparing the sample, and when testing the tensile strength of the sample, the fixed locks must be opened so that the left and right parts can be pulled apart without obstacles. An extensometer is installed at the end of the pull block, and the extensometers face each other to measure the deformation of the sample during the tensile failure process. The guard arm and pressure plate participate in the sample preparation operation simultaneously. The guard arm is nested above the pulling block to provide compression space for the pressure plate to fully compress the original loose sample and prevent the sample of specified weight from partially escaping to the outside of the pulling block after being compressed. The pressure plate compacts the aeolian sand modified soil to ensure that the concentrated force acts evenly on each stress surface of the aeolian sand modified soil.

[0016] Aeolian sand modified soil tensile mold In view of the fact that the existing conventional material testing machines in the laboratory cannot accurately test the tensile strength of aeolian sand modified soil, a hydraulic conversion device is used to convert the longitudinal pressure of the traditional press into a transverse tension. The upper end of the hydraulic conversion device is in direct contact with the loading end of the press, and the lower end corresponds to the pressure sensor. The pressure sensor is rigidly connected to the right movable pull plate. On the one hand, the longitudinal pressure of the press is converted to the right movable pull plate at a constant speed, and on the other hand, the pressure applied to the tension plate (denoted as P) can be accurately measured. Using the dynamic friction coefficient (μ) of the slide rail, the tensile force (F) applied to both ends of the aeolian sand modified soil sample can be obtained, that is, F = PG·μ, where G is the sum of the weight of the pressure sensor and the right end tension plate. During the test, push the pulling block containing the aeolian sand modified soil sample horizontally into the left and right pressure plates, ensure that the pulling block and the pulling plates are buckled together without any gap, and then place it on the press platform. Unfasten the fixing buckle of the pulling block, set the loading rate of the press, turn on the pressure sensor acquisition device and the displacement meter acquisition device, connect the data acquisition terminal to the computer, start the press, and then the tensile strength test of the aeolian sand modified soil can be carried out.

[0017] Beneficial Effects of the Invention

[0018] The sample preparation mold for modified aeolian sand is used in conjunction with the tensile strength test mold for modified aeolian sand. The sample preparation mold is specially designed for the tensile strength test mold and has a high degree of fit. After the sample preparation is completed, the sample is not taken out. The sample is placed in the mold and built into the test system to prevent the sample from being damaged due to external disturbances caused by the fragility of the sample strength after it is taken out. This system can complete the two operations of sample preparation and tensile strength testing at one time, greatly reducing the test cost and instability caused by time. The sample preparation and tensile strength testing processes are both automatically controlled to reduce the errors caused by human factors and effectively ensure the accuracy of the test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention is further described below in conjunction with the accompanying drawings and embodiments:

[0020] Figure 1 This is the overall structure diagram of the tensile strength test system

[0021] Figure 2 This is a schematic diagram of the sample making mold structure

[0022] Figure 3 This is the front view of the tensile test mold

[0023] Figure 4 Right view of the tensile test mold

[0024] Figure 5 It is a left and right pull block assembly diagram

[0025] Figure 6 Schematic diagram of hydraulic conversion tube

[0026] In the figure: 1. Base frame; 2. Fixed corner column; 3. Left pull plate; 4. Right movable pull plate; 5. Slide rail; 6. Left pull block; 7. Right pull block; 8. Piston; 9. Hydraulic conversion tube; 10. Fixing buckle; 11. Extensometer; 12. Strain gauge; 13. Top fixed cover; 14. Specimen; 15. Left guard arm; 16. Right guard arm; 17. Upper pressure plate; 18. Sawtooth bite contact part; 19. Step limit part; 20. Transfer column; 21. Lower pressure plate; 22. Pressure application end; 23. Data acquisition terminal DETAILED DESCRIPTION

[0027] The implementation method of the present invention is mainly divided into two parts: preparing samples and testing the tensile strength of the samples.

[0028] The connection order of each part from bottom to top is as follows: a sample preparation mold, a left pull block (6) and a right pull block (7) are connected to form an integral pull block through a sawtooth bite (18) that limits the horizontal longitudinal deformation and displacement of the sample when it is compressed and deformed, a step limiter (19) is arranged below the sawtooth bite (18) to prevent the sample from being vertically displaced during sample preparation, a fixing buckle (10) is arranged in the contact area of ​​the outer wall of the left pull block (6) and the right pull block (7), and the fixing buckles (10) are mutually engaged to limit the horizontal lateral displacement and displacement of the integral pull block during sample preparation. An extensometer (11) is connected to the ends of the left pull block (6) and the right pull block (7), and the upper part of the integral pull block is connected to a left guard arm (15) and a right guard arm (16), and the two guard arms are connected to the integral pull block through a limiter protruding in the middle of the two ends of the integral pull block to avoid a gap between the guard arms and the integral pull block. The lower pressure plate (21) acts directly on the sample and evenly distributes the concentrated force to the sample. Three transmission columns (20) for transmitting pressure are fixed longitudinally and equidistantly on the upper part of the lower pressure plate (21). The upper pressure plate (17) is fixed on the upper part of the transmission columns (20). The upper pressure plate (17) is the area where pressure directly acts.

[0029] A tensile strength test mold, a rectangular base frame (1) is rigidly connected to a left pull plate (3), a short distance slide rail is arranged at the right middle of the base frame (1), and a right movable pull plate (4) is connected to the slide rail to form a movable end, and a reinforcing rib design is adopted to ensure the uniformity of displacement. Four fixed corner columns (2) are fixed at each end of the base frame (1), the top of the fixed corner column (2) is connected to a top fixed cover (13), the body of the hydraulic conversion tube (9) passes through a hole reserved in the center of the top fixed cover (13), the lower pipe mouth piston (8) of the hydraulic conversion tube (9) corresponds to a stress gauge (12) rigidly connected to the center of the right movable pull plate (4), and the upper pipe mouth piston of the hydraulic conversion tube (9) is connected to a pressure acting end (22).

[0030] To test the tensile strength of the sample, place the sample (14) in the integral pull block, adjust the right movable pull plate (4) to an appropriate position on the slide rail (5), align the protruding stoppers at the ends of the left pull block (6) and the right pull block (7) with the central grooves of the left pull plate (3) and the right movable pull plate (4) of the tensile strength test mold and push them in, buckle the fixing buckle (10), and adjust the position of the piston (8) so that it is in close contact with the stress gauge (12). The extensometer (11) and the stress gauge (12) collect data and transmit the data to the data acquisition terminal (23).

[0031] Working process

[0032] Combine the left and right pull blocks, lock the fixing buckles to form a whole, and place the guard arm on top to lock it. Prepare the required aeolian sand modification materials, compact them in layers with pressing plates, and maintain them in the pull block.

[0033] The cured specimen is pushed into the tensile test mold together with the pull block and fastened to the cardboard. The tensile test mold is placed under the press, and the piston connected to the right end of the hydraulic conversion tube is adjusted to make it closely contact the center of the stress gauge. The initial loading rate of the press is set, and the pressure is slowly increased until the pressure gauge is debugged to adjust the extensometer and the use of the pressure gauge. During the test, the monitoring data of the stress gauge and extensometer reflect the stress-strain characteristics and tensile strength characteristics of the specimen, providing a data basis for the study of the tensile strength of aeolian sand modified soil.

[0034] Data Correction

[0035] Inevitable factors during the test cause errors in the test data. The friction between the base of the right movable pull plate and the slide rail causes the strain gauge reading to be too large, and the friction coefficient will change in different test environments, so the data obtained from the test needs to be corrected. First, the friction coefficient must be measured. The environment in which the friction coefficient is measured should be as close as possible to the environment in which the tensile strength of the specimen is measured to reduce interference from external factors and eliminate the measurement error of the strain gauge. The friction coefficient μ is measured before sample preparation. Push the empty pull groove with the locked fixing buckle into the tensile test mold, start the press and slowly and evenly load at the sample loading rate until the right movable pull plate begins to move evenly and then stop, read the stress gauge reading σ1 (MPa), S is the piston area connected to the hydraulic conversion tube (contact area with the stress gauge sensor) (mm 2 ). At this time, the friction

[0036] F f =σ1·S, the exact value of μ can be calculated

[0037]

[0038] Wherein, σ1 is the reading of the uniform motion of the right movable pull plate (MPa); M1 is the mass of the right pull block (kg); M2 is the mass of the right movable pull plate (kg).

[0039] The friction force F between the right movable pull plate and the slide rail f Calculate according to the following formula

[0040]

[0041] Where μ is the friction coefficient between the bottom of the right movable pull plate and the slide rail, M1 is the mass of the right pull block (kg), M2 is the mass of the right movable pull plate (kg), M3 is the mass of the sample (kg), and g is 9.8 N / kg.

[0042] After the test, the tensile strength R of the sample m (MPa), calculated as follows

[0043] R m =(σh ·sF f ) / s A

[0044] In the formula, σ h is the reading on the stress gauge when the sample is broken (MPa); s is the area of ​​the piston connected to the hydraulic conversion tube (mm 2 );F f is the friction force between the right movable pull plate and the slide rail when the sample is broken (N); s A is the original cross-sectional area of ​​the specimen (mm 2 ).

[0045] By analyzing the data measured in the test, the tensile stress and strain of the sample are calculated using auxiliary formulas, and finally the tensile strength of the sample is obtained. Using the above data, we can have a deep understanding of the stress-strain characteristics and tensile strength characteristics of aeolian sand modified soil under different loading conditions, thus providing experimental references for the modification and engineering application of aeolian sand.

Claims

1. A tensile strength test system for aeolian sand modified soil, characterized in that: The connection order of the parts from bottom to top is as follows: the left pull block (6) and the right pull block (7) are interlocked to form an integral pull block; a fixing buckle (10) is arranged in the contact area of ​​the outer wall of the left pull block (6) and the right pull block (7); the fixing buckles (10) are interlocked with each other to limit the horizontal lateral movement and dislocation of the integral pull block during sample preparation; one end of the extensometer (11) is connected to the end of the left pull block (6) and the other end is connected to the end of the right pull block (7); the upper part of the integral pull block is connected to the left guard arm (15) and the right guard arm (16); the two guard arms are connected to the integral pull block through the protruding limit platforms in the middle of the two ends of the integral pull block; the lower pressure plate (21) directly acts on the sample; three transmission columns (20) for transmitting pressure are longitudinally equidistantly fixed on the upper part of the lower pressure plate (21); the upper part of the transmission column (20) is fixed to the upper part of the upper pressure plate (17); The rectangular base frame (1) is rigidly connected to the left pull plate (3), the base frame (1) is arranged with a slide rail, the right movable pull plate (4) is connected to the slide rail to form a movable end, a plurality of fixed corner columns (2) are fixed at each end of the base frame (1), the top of the fixed corner column (2) is connected to the top fixed cover (13), the body of the hydraulic conversion tube (9) passes through the central reserved hole of the top fixed cover (13), the lower pipe mouth piston (8) of the hydraulic conversion tube (9) corresponds to the stress gauge (12) rigidly connected to the center of the right movable pull plate (4), and the upper pipe mouth piston of the hydraulic conversion tube (9) is connected to the pressure acting end (22); The left pull block (6) and the right pull block (7) in the sample making mold are provided with a sawtooth bite (18) at the intersection, and the sawtooth bite (18) is provided with a step limit portion (19).

2. According to the tensile strength testing system for aeolian sand modified soil as described in claim 1, the top fixing cover (13) in the tensile strength testing mold adopts a hollow design to reduce the pressure on the fixed corner column (2).

3. The method of using the aeolian sand modified soil tensile strength testing system as claimed in claim 1 is characterized in that: The sample (14) is placed in the integral pull block, the right movable pull plate (4) slides on the slide rail (5), and the piston (8) of the hydraulic conversion tube (9) moves in the same direction as the right movable pull plate (4) on the slide rail (5); the protruding limit platforms at the ends of the left pull block (6) and the right pull block (7) are aligned with the central grooves of the left pull plate (3) and the right movable pull plate (4) of the tensile strength test mold and pushed in, the fixing buckle (10) is unlocked, and the position of the piston (8) is adjusted to make it closely contact the stress gauge (12), and the extensometer (11) and the stress gauge (12) collect data and transmit the data to the data collection terminal (23); The hydraulic conversion tube (9) converts the longitudinal pressure of the conventional press into a transverse tension; on the one hand, the longitudinal pressure of the press is converted to the right movable pull plate (4) at a constant speed, and on the other hand, the pressure applied to the right movable pull plate (4) is measured; A fixing buckle (10) that engages with each other is provided at the middle portion where the outer walls of the left pull block (6) and the right pull block (7) contact each other. The fixing buckle (10) is locked during sample preparation to ensure that the sample will not move or be misaligned in the horizontal direction during sample preparation. The fixing buckle (10) is unlocked during testing to release the horizontal constraint on the sample.

4. The method according to claim 3, characterized in that: A hydraulic conversion device is used to convert the longitudinal pressure of a conventional press into a transverse tension; the upper end of the hydraulic conversion device is in direct contact with the loading end of the press, and the lower end corresponds to a strain gauge (12), and the strain gauge (12) is rigidly connected to the right movable pull plate. On the one hand, the longitudinal pressure of the press is converted to the right movable pull plate at a constant speed, and on the other hand, the pressure applied to the tension plate can be accurately measured and recorded as P , using the dynamic friction coefficient m of the slide rail, the tensile force applied to both ends of the aeolian sand modified soil sample is obtained F ,Right now F = P -G×m, where G is the sum of the weights of the stress gauge (12) and the right end tension plate; during the test, the pull block containing the aeolian sand modified soil sample is pushed horizontally into the left and right pressure plates, ensuring that the pull block and the tension plate are interlocked and there is no gap, and then placed on the press platform, the pull block fixing buckle is unlocked, the press loading rate is set, the stress gauge (12) acquisition device and the extensometer (11) are turned on, the data acquisition terminal is connected to the computer, and the press is started to carry out the tensile strength test of the aeolian sand modified soil.

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