Flexible microfiber pull-out test device and use method thereof

Abstract

The invention relates to a flexible microfiber pull-out test device and a using method thereof.The flexible microfiber pull-out test device comprises an upper connecting piece, a base, a displacement platform, a force sensor and a laser displacement sensor, the upper connecting piece and the base are oppositely arranged, and the displacement platform capable of being finely adjusted in the X-axis direction and the Y-axis direction of the horizontal plane is installed on the base; a concrete fixing device for fixing a concrete test piece is arranged on the displacement platform; wherein the force sensor and the specially-made fiber clamp are sequentially connected below the upper connecting piece, the specially-made fiber clamp comprises a U-shaped connecting piece and a pair of steel clamping plates, the pair of steel clamping plates and the U-shaped connecting piece form an adjustable clamping space through fastening screws, and the specially-made fiber clamp is of a steel clamping plate structure with staggered tooth-shaped teeth. And flexible fibers with different diameters and materials can be firmly and reliably clamped, so that slippage or fiber damage in a fiber drawing process is effectively prevented, and the stability of a test process and the accuracy of a measurement result are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete test equipment, and particularly to a pulling test device for flexible fibers in concrete and a using method thereof. Background Art

[0002] Fiber-reinforced concrete has excellent crack resistance and tensile properties and is widely used in engineering structures. Flexible fibers (such as polypropylene fibers, polyvinyl alcohol fibers, etc.), as a new type of reinforcing material, can significantly improve the crack resistance of concrete materials due to their softness, high toughness, and good deformation ability. However, the bonding performance between flexible fibers and the concrete matrix directly affects the overall mechanical properties of fiber-reinforced concrete. Therefore, it is crucial to accurately evaluate the bonding performance of the interface between flexible fibers and the concrete matrix.

[0003] Currently, the pulling test devices for the bonding performance of the interface between fibers and the concrete matrix generally have problems such as complex structures, cumbersome test preparations, and difficulties in clamping flexible fibers, making it difficult to meet the requirements of convenience and test accuracy for flexible fiber pulling tests. For example, Chinese Patent CN 222087497U discloses a bonding strength detection device for concrete fibers, which winds and calibrates the fibers through a fiber winding rod and a toothed bushing, and relies on mechanical rotation to straighten the fibers, which may cause shear stress damage to the flexible fibers; Chinese Patent CN 210427321U discloses a fiber-concrete bonding force test device based on an in-situ tensile table, but this device can only test specimens with one fiber embedment depth at a time and cannot conveniently study the influence of different fiber embedment depths on the bonding and slip performance of the fiber-matrix interface; Chinese Patent CN 117110057A discloses a pulling test device for steel fibers in concrete and a using method thereof, but when burying steel fibers between the concrete fixture and the specimen, there is a possibility of fiber slip in the concrete fixture, making it difficult to accurately measure the true bonding performance of the fiber-concrete interface; the structure of the steel fiber pulling device in concrete disclosed in Chinese Patent CN 107764738A is complex, and only one fiber can be pulled in one test, with poor versatility and low test efficiency. In addition, the displacement measurement methods adopted in most current patents have limited accuracy. Often, the displacement value of the actuator of the testing machine itself is directly used, resulting in insufficient measurement accuracy; or a linear variable differential transformer (LVDT) is used, but the LVDT is easy to damage and prone to non-linear drift during long-term use, affecting the test accuracy, and its range is limited and cannot meet the requirements of long fiber pulling tests.

[0004] Therefore, researching and developing a flexible fiber pulling test device with a simple structure, strong versatility, which can be directly installed on an existing universal testing machine and has high-precision displacement measurement ability is of great significance for improving the accuracy, convenience, and test efficiency of flexible fiber pulling tests. Summary of the Invention

[0005] The present invention aims to solve the problems existing in the above-mentioned prior art, and provides a device for pulling out flexible fibers in concrete and its usage method, which can solve the problems such as complex device structure, cumbersome test preparation process, difficult clamping of flexible fibers, and insufficient measurement accuracy in the prior art, and meet the actual needs of accurately testing the interfacial bonding performance between flexible fibers and concrete matrix.

[0006] The technical solution adopted by the present invention to solve its technical problems: This kind of flexible micro-fiber pulling test device includes an upper connecting piece, a base, a displacement platform, a force sensor and a laser displacement sensor. The upper connecting piece and the base are arranged opposite to each other. The base is equipped with a displacement platform that can be finely adjusted along the X-axis and Y-axis directions of the horizontal plane. The displacement platform is provided with a concrete fixing device for fixing concrete specimens. Among them, a force sensor and a special fiber clamp are sequentially connected below the upper connecting piece. The special fiber clamp includes: a U-shaped connecting piece and a pair of steel splints that form an adjustable clamping space with the U-shaped connecting piece through tightening screws. The top of the U-shaped connecting piece is screwed to the force sensor, and a mirror is installed on the side of the U-shaped connecting piece. A pair of the steel splints have tooth-shaped jaws that are staggered and engaged, and the tooth-shaped jaws are used for clamping the fibers in the concrete specimens. The laser displacement sensor is fixed on the displacement platform, and measures the fiber displacement by laser reflection through the mirror. And the laser light path direction emitted by the laser displacement sensor is parallel to the fiber pulling direction.

[0007] Preferably, the two sides of the U-shaped connecting piece are provided with first connection holes, and the steel splints are provided with second connection holes. A pair of the steel splints are located inside the U-shaped connecting piece, and the second connection holes on the steel splints are respectively connected and fixed to the first connection holes on the left and right sides of the U-shaped connecting piece through tightening screws. Among them, the tooth-shaped jaws at the lower parts of a pair of steel splints are evenly distributed, and the tooth-shaped jaws on a pair of steel splints are arranged in a staggered and engaged state.

[0008] Preferably, the tooth-shaped jaws of the steel splints are triangular sawteeth; or the tooth-shaped jaws of the steel splints are wavy sawteeth, and the clamping surfaces of the steel splints are covered with an elastic silica gel layer, and tooth-shaped grooves corresponding to the tooth-shaped jaws are arranged on the surface of the silica gel layer.

[0009] Preferably, the top of the upper connecting piece is provided with an upper ball head screw, and the upper connecting piece is connected to the upper chuck of a universal testing machine arranged outside through the upper ball head screw. The lower end of the base is provided with a lower ball head screw, and the base is connected to the lower chuck of the universal testing machine arranged outside through the lower ball head screw.

[0010] Preferably, a spherical head groove is provided at the top of the upper connecting member, and the upper spherical head screw has a first spherical head, and the first spherical head is arranged in the spherical head groove, and the first spherical head is in clearance fit with the inner wall of the first spherical head groove; A lower spherical head groove is provided at the bottom of the base, and the lower spherical head screw has a second spherical head, and the second spherical head is arranged in the lower spherical head groove, and the second spherical head is in clearance fit with the inner wall of the lower spherical head groove.

[0011] Preferably, the force sensor is a screw type tension and compression sensor. A first connecting portion is provided at the upper end of the force sensor, and a second connecting portion is provided at the lower end of the force sensor. A first threaded hole is provided at the bottom of the upper connecting member, and a second threaded hole is provided at the top of the U-shaped connecting member. The first threaded hole is arranged along the center position of the upper connecting member and the second threaded hole is arranged along the center position of the U-shaped connecting member. The first connecting portion is connected to the first threaded hole, and the second connecting portion is connected to the second threaded hole, and the axes of the first connecting portion, the second connecting portion and the upper spherical head screw are collinear.

[0012] Preferably, the concrete fixing device includes a pair of side plates and a cover plate. The side plates are fixed on the displacement platform by welding, and the cover plate is located above the pair of side plates. The cover plate is connected and fixed to the pair of side plates by fixing screws. Wherein, a V-shaped positioning groove for abutting against the concrete specimen is provided on the inner side of the side plate, and a rubber pressing strip is provided on the lower surface of the cover plate, and the rubber pressing strip covers the upper surface of the concrete specimen.

[0013] Preferably, the displacement platform includes an upper platform, a middle platform and a lower platform. The upper platform, the middle platform and the lower platform are stacked and connected in sequence from top to bottom. A fixing member is provided at the bottom of the lower platform, and the fixing member is fixed to the base by screws. An X-axis differential knob is provided on the right side of the lower platform. The middle platform is arranged on the lower platform, and the middle platform moves along the X-axis direction of the lower platform through the X-axis differential knob. A Y-axis differential knob is provided on the front side of the middle platform. The upper platform is arranged on the middle platform, and the upper platform moves along the Y-direction of the upper platform through the Y-axis differential knob.

[0014] Preferably, the mirror surface is a replaceable plane mirror. A magnetic adsorption layer is provided on the back surface of the mirror surface, which is attached to the surface of the U-shaped connecting member, and calibration scale lines are provided at the edge of the mirror surface for initial position calibration of the laser displacement sensor.

[0015] A usage method of a flexible microfiber drawing test device includes the following steps: S1. Install the upper connecting member to the upper chuck of the universal testing machine through the upper spherical head screw, and install the base to the lower chuck through the lower spherical head screw, ensure that the spherical head is in clearance fit with the groove, and fixedly connect the lower platform of the displacement platform to the base through the screws of the fixing member; S2. Place the precast concrete specimen in the concrete fixing device of the displacement platform, position it using the V-shaped positioning groove on the side plate, press the specimen tightly with the rubber pressing strip on the cover plate, and lock the cover plate with screws. S3. Adjust the X-axis differential knob and Y-axis differential knob of the displacement platform to move the middle platform and the upper platform, align the fiber to be tested with the clamping center of the special fiber fixture, and verify that the optical path of the laser displacement sensor is parallel to the fiber drawing direction through the calibration scale line on the edge of the mirror surface. S4. Loosen the fixing screw, place the fiber between the staggered tooth-shaped jaws of the steel splint, and tighten the screw to ensure that the elastic silicone layer evenly covers the surface of the fiber. S5. Connect the force sensor and the laser displacement sensor to the data acquisition system, and calibrate the zero point of the force sensor and the initial position of the laser displacement. S6. Start the universal testing machine, apply the drawing force and synchronously record the drawing force and displacement data until the fiber debonds or breaks. If the measurement is abnormal due to the mirror surface offset during this period, pause the test and replace the magnetically adsorbed mirror surface. S7. After the test is completed, reset the testing machine, quickly align the next fiber to be tested by rotating the Y-axis differential knob and the X-axis differential knob, and repeat the above steps until all fibers are tested.

[0016] The present invention has the following beneficial effects: 1. The special fiber fixture adopts a steel splint structure with staggered tooth-shaped jaws, which can firmly and reliably clamp flexible fibers of different diameters and materials, effectively prevent slippage or fiber damage during the fiber drawing process, and significantly improve the stability of the test process and the accuracy of the measurement results.

[0017] 2. The structure of this device is simple and compact, and it can be directly installed on a general universal testing machine without the need to purchase additional special testing equipment. The installation, disassembly, and operation process of the device are convenient and efficient, which can significantly reduce the test cost.

[0018] 3. The displacement measurement system uses a high-precision non-contact laser displacement sensor to measure the distance by reflecting laser through the mirror surface on the fiber fixture. It has high measurement accuracy and good repeatability, overcomes the defects of traditional linear variable differential transformers (LVDTs) such as being easily damaged, generating non-linear drift during long-term use, and insufficient range, and can realize precise drawing tests for long fibers.

[0019] 4. Adopting a precision two-dimensional manual displacement platform, it can move freely and precisely in the horizontal X and Y directions. Multiple fibers can be implanted in a single concrete specimen on the same straight line at the same time. By simply moving the displacement platform, continuous drawing tests for multiple fibers can be realized one by one without repeatedly disassembling and replacing the concrete specimen, which significantly improves the test efficiency, saves the test cost, and effectively avoids test errors caused by repeated installation.

[0020] 5. The concrete fixing device is structurally stable and reliable. The cover plate and the side plate are fixed by bolts. During the test, the concrete specimens are not easily loosened, avoiding the slippage or movement of the fibers in the non-test area, and ensuring the authenticity and accuracy of the bond performance data measured in the test.

[0021] 6. This device has strong versatility and is applicable to the pull-out tests of flexible fibers with different types and lengths. At the same time, it is also applicable to the pull-out tests of rigid fibers, with a wide range of applications and strong practical test application value. Brief Description of the Drawings

[0022] Figure 1 It is a schematic structural diagram of a flexible microfiber pull-out test device of the present invention; Figure 2 is Figure 1 an enlarged structural view of part A in Figure 3 a schematic structural diagram of a toothed mouth with a wavy serrated shape; Figure 4 a schematic structural diagram of a special fiber fixture; Figure 5 a schematic structural diagram of a displacement platform; Figure 6 a schematic structural diagram of a toothed mouth with an inclined triangular serrated shape; Figure 7 a schematic structural diagram of a toothed mouth with a flat mouth shape.

[0023] Description of the reference numerals: 1a, upper ball screw; 1b, lower ball screw; 2, upper connecting piece; 3, force sensor; 4, special fiber fixture; 5, mirror; 6, laser displacement sensor; 7, displacement platform; 8, base; 9, fiber; 10, concrete; 11, U-shaped connecting piece; 12, fastening screw; 13, steel splint; 14, toothed mouth; 15, cover plate; 16, screw; 17, side plate; 18, upper platform; 19, Y-axis differential knob; 20, middle platform; 21, X-axis differential knob; 22, lower platform; 23, fixing piece; 24, upper ball groove; 25, first ball; 26, lower ball groove; 27, second ball; 28, first connecting part; 29, second connecting part; 30, first threaded hole; 31, second threaded hole; 32, first connecting hole; 33, second connecting hole; 34, silica gel layer; 35, V-shaped positioning groove; 36, rubber pressing strip. Detailed Description of the Invention

[0024] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following describes in detail the specific implementation manner, structure, features and effects of the present invention in conjunction with the accompanying drawings and preferred embodiments.

[0025] AsFigures 1 to 5 As shown in the figure, a flexible microfiber drawing test device includes an upper connecting member 2, a base 8, a displacement platform 7, a force sensor 3, and a laser displacement sensor 6. The upper connecting member 2 and the base 8 are arranged opposite to each other. The base 8 is equipped with a displacement platform 7 that can be finely adjusted along the X-axis and Y-axis directions of the horizontal plane. The displacement platform 7 is provided with a concrete fixing device for fixing the concrete specimen 10. Among them, the force sensor 3 and a special fiber fixture 4 are sequentially connected below the upper connecting member 2. The special fiber fixture 4 includes a U-shaped connecting member 11 and a pair of steel clamping plates 13 that form an adjustable clamping space with the U-shaped connecting member 11 through tightening screws 12. The top of the U-shaped connecting member 11 is screwed to the force sensor 3, and a mirror 5 is installed on the side of the U-shaped connecting member 11. The pair of steel clamping plates 13 have tooth-shaped jaws 14 that are staggered and engaged. The tooth-shaped jaws 14 are used to clamp the fiber 9 in the concrete specimen 10. The laser displacement sensor 6 is fixed to the displacement platform 7, and the fiber displacement is measured by reflecting the laser through the mirror 5. Moreover, the laser light path direction emitted by the laser displacement sensor 6 is parallel to the fiber drawing direction.

[0026] The upper connecting member 2 and the base 8 are arranged opposite to each other. The base 8 is equipped with a displacement platform 7 that can be finely adjusted along the X-axis and Y-axis directions of the horizontal plane. The displacement platform 7 is provided with a concrete fixing device for fixing the concrete specimen 10. In this embodiment, the force sensor 3 and a special fiber fixture 4 are sequentially connected below the upper connecting member 2. The special fiber fixture 4 is composed of a U-shaped connecting member 11 and a pair of steel clamping plates 13 that form an adjustable clamping space with the U-shaped connecting member 11 through tightening screws 12. The top of the U-shaped connecting member 11 is screwed to the force sensor 3, and a mirror 5 is installed on its side. The pair of steel clamping plates 13 have tooth-shaped jaws 14 that are staggered and engaged. These tooth-shaped jaws 14 can firmly clamp the fiber 9 in the concrete specimen 10, effectively preventing the fiber from slipping or being damaged during the drawing process, ensuring the stability of the test process and the accuracy of the measurement results. In addition, the laser displacement sensor 6 is fixed to the displacement platform 7, and the fiber displacement is measured by reflecting the laser through the mirror 5. Moreover, the laser light path direction emitted by the laser displacement sensor 6 is parallel to the fiber drawing direction, realizing high-precision non-contact displacement measurement, overcoming the defects of the traditional linear displacement gauge being easily damaged, generating non-linear drift during long-term use, and having insufficient range, ensuring the accuracy and reliability of the measurement data. And the device has a simple and compact structure, can be directly installed on a general universal testing machine, without the need to purchase additional special testing equipment, significantly reducing the test cost. At the same time, the design of the precision two-dimensional manual displacement platform enables multiple fibers in a single concrete specimen to be quickly tested one by one, reducing the test error and greatly improving the test efficiency.

[0027] It is worth mentioning that the laser displacement sensor 6 has a repeatability accuracy of less than 0.01 mm, a sampling frequency of greater than 80 kHz, and a linear accuracy better than 0.02%F.S.

[0028] Preferably, as Figure 1 and Figure 2 shown, first connection holes 31 are provided on both sides of the U-shaped connector 11, and second connection holes 32 are provided on the steel splints 13. A pair of steel splints 13 are located inside the U-shaped connector 11, and the second connection holes 32 on the steel splints 13 are respectively connected and fixed to the first connection holes 31 on the left and right sides of the U-shaped connector 11 through fastening screws 12. Among them, the toothed jaws 14 at the lower part of the pair of steel splints 13 are evenly distributed, and the toothed jaws 14 on the pair of steel splints 13 are arranged in an interlocking manner.

[0029] First connection holes 31 are provided on both sides of the U-shaped connector 11, and second connection holes 32 are provided on the steel splints 13. A pair of steel splints 13 are located inside the U-shaped connector 11 and are respectively connected and fixed to the first connection holes 31 on the left and right sides of the U-shaped connector 11 through fastening screws 12, so that the steel splints 13 can be flexibly adjusted according to needs to adapt to the fiber clamping requirements of different diameters and materials. In this embodiment, the toothed jaws 14 at the lower part of the pair of steel splints 13 are evenly distributed and are arranged in an interlocking manner. This unique toothed design can significantly enhance the firmness of fiber clamping, effectively prevent the fibers from slipping or being damaged during the drawing process, ensure the stability of the test process and the accuracy of the measurement results. The interlocking toothed jaws 14 not only increase the clamping force but also can disperse the clamping stress, avoiding fiber breakage or damage caused by local stress concentration. Through this precise design, the special fiber fixture 4 can provide reliable clamping performance under various complex test conditions, thereby improving the practicality and test accuracy of the entire drawing test device.

[0030] Furthermore, as Figures 2 to 4 shown, the toothed jaws 14 of the steel splint 13 are triangular sawteeth; or the toothed jaws 14 of the steel splint 13 are wavy sawteeth, and the clamping surface of the steel splint 13 covers an elastic silica gel layer 34, and tooth-shaped grooves corresponding to the toothed jaws 14 are provided on the surface of the silica gel layer 34.

[0031] The steel splint 13 is designed with two different types of toothed jaws 14 to meet different fiber clamping requirements: one is a toothed jaw 14 with triangular serrations, and the other is a toothed jaw 14 with wavy serrations; both of these toothed designs can provide strong clamping force to ensure that the fiber does not slip or fall off during the drawing process. The triangular serrated design can provide higher friction and biting force during clamping, and is suitable for relatively hard or larger-diameter fibers; while the wavy serrated design can reduce damage to the fiber surface while ensuring the clamping force, and is particularly suitable for clamping soft or fine-diameter fibers. Moreover, the clamping surface of the steel splint 13 is covered with an elastic silicone layer 34, and the surface of the silicone layer 34 is provided with toothed grooves corresponding to the toothed jaws 14. This can not only provide buffering during clamping to prevent the fiber from being damaged due to excessive pressure, but also increase the friction coefficient of the clamping surface to ensure that the fiber is firmly clamped. Through this precise design, the steel splint 13 can provide reliable clamping performance under various complex test conditions, significantly improving the practicality and test accuracy of the entire drawing test device, making the fiber drawing test more stable and accurate.

[0032] It should be noted that, as Figure 6 and Figure 7 shown, the steel splint 13 of this embodiment can also adopt an inclined triangular serration, or the toothed jaw 14 inside the steel splint 13 can be replaced with a flat jaw parallel to the laser light path direction emitted by the laser displacement sensor 6 for surface-to-surface clamping.

[0033] Preferably, as Figure 1 shown, the top of the upper connecting member 2 is provided with an upper ball screw 1a, and the upper connecting member 2 is connected to the upper chuck of the universal testing machine provided outside through the upper ball screw 1a. The lower end of the base 8 is provided with a lower ball screw 1b, and the base 8 is connected to the lower chuck of the universal testing machine provided outside through the lower ball screw 1b.

[0034] The top of the upper connecting member 2 is provided with an upper ball screw 1a and is connected to the upper chuck of the universal testing machine provided outside through the upper ball screw 1a; at the same time, the lower end of the base 8 is provided with a lower ball screw 1b and is connected to the lower chuck of the universal testing machine provided outside through the lower ball screw 1b. The upper ball screw 1a and the lower ball screw 1b are respectively in clearance fit with the grooves on the upper connecting member 2 and the base 8 through their ball heads, thereby allowing a certain degree of free rotation and angle adjustment to meet the installation requirements under different test conditions. This not only simplifies the installation and disassembly process of the device, but also can reduce eccentric loading during the test, improve the axial application accuracy of the drawing force, and avoid measurement errors caused by improper installation.

[0035] Furthermore, as Figure 1As shown in the figure, the top of the upper connecting member 2 is provided with an upper ball head groove 24. The upper ball head screw 1a has a first ball head 25. The first ball head 25 is arranged in the upper ball head groove 24, and the first ball head 25 is in clearance fit with the inner wall of the upper ball head groove 24. The bottom of the base 8 is provided with a lower ball head groove 26. The lower ball head screw 1b has a second ball head 27. The second ball head 27 is arranged in the lower ball head groove 26, and the second ball head 27 is in clearance fit with the inner wall of the lower ball head groove 26.

[0036] The top of the upper connecting member 2 is provided with an upper ball head groove 24 and is used in cooperation with the first ball head 25 of the upper ball head screw 1a. The first ball head 25 is arranged in the upper ball head groove 24 and is in clearance fit with the inner wall of the groove, allowing the upper ball head screw 1a to freely rotate and adjust the angle within a certain range, so as to ensure that the upper connecting member 2 can be accurately connected to the upper chuck of the external universal testing machine flexibly. Similarly, the bottom of the base 8 is provided with a lower ball head groove 26 and is used in cooperation with the second ball head 27 of the lower ball head screw 1b. The second ball head 27 is arranged in the lower ball head groove 26 and is in clearance fit with the inner wall of the groove, enabling the base 8 to be stably connected to the lower chuck of the external universal testing machine. This design not only simplifies the installation and disassembly process of the device, but also can reduce eccentric loading during the test, improve the axial application accuracy of the pulling force, avoid measurement errors caused by improper installation, and the clearance fit design of the ball head screw enhances the stability of the whole device during the test, ensuring the accuracy and repeatability of the fiber pulling test.

[0037] Preferably, as Figure 1 shown in the figure, the upper end of the force sensor 3 is provided with a first connecting portion 28, the lower end of the force sensor 3 is provided with a second connecting portion 29. The bottom of the upper connecting member 2 is provided with a first threaded hole 30. The top of the U-shaped connecting member 11 is provided with a second threaded hole 31. The first threaded hole 30 is arranged along the central position of the upper connecting member 2 and the second threaded hole 31 is arranged along the central position of the U-shaped connecting member 11. The first connecting portion 28 is connected to the first threaded hole 30, the second connecting portion 29 is connected to the second threaded hole 31, and the axes of the first connecting portion 28, the second connecting portion 29 and the upper ball head screw 1a are collinear.

[0038] The upper end of the force sensor 3 is provided with a first connecting part 28, and the lower end is provided with a second connecting part 29. The bottom of the upper connecting piece 2 is provided with a first threaded hole 30, and the top of the U-shaped connecting piece 11 is provided with a second threaded hole 31. Both of these threaded holes are located at the center positions of their respective components to ensure the collinearity of the axes during installation. The first connecting part 28 is connected to the first threaded hole 30 at the bottom of the upper connecting piece 2 by screwing, while the second connecting part 29 is connected to the second threaded hole 31 at the top of the U-shaped connecting piece 11 by screwing. This not only ensures the precise centering of the force sensor 3 in the vertical direction but also ensures that its axis is collinear with the axis of the upper ball screw 1a, thereby reducing the influence of eccentric loading and improving the stability and measurement accuracy of the pull-out test.

[0039] It is worth mentioning that the force sensor 3 is a screw-type tension and compression force sensor with a rated range < 100 N and an accuracy ≤ 0.1% F.S. The setting of the force sensor 3 for load measurement can effectively achieve accurate measurement of the fiber pull-out force in the low-load range.

[0040] Preferably, as Figure 1 and Figure 3 shown, the concrete fixing device includes a pair of side plates 17 and a cover plate 15. The side plates 17 are fixed to the displacement platform 7 by welding, and the cover plate is located above the pair of side plates. The cover plate 15 is connected and fixed to the pair of side plates 17 by fixing screws 16. Among them, a V-shaped positioning groove 35 for abutting against the concrete specimen 10 is provided on the inner side of the side plate 17, and a rubber pressure strip 36 is provided on the lower surface of the cover plate 15, and the rubber pressure strip 36 covers the upper surface of the concrete specimen 10.

[0041] The concrete fixing device includes a pair of side plates 17 and a cover plate 15. The side plates 17 are fixed to the displacement platform 7 by welding, and the cover plate 15 is located above the pair of side plates and is connected and fixed to the side plates 17 by fixing screws 16. In this embodiment, a V-shaped positioning groove 35 is provided on the inner side of the side plate 17 for precisely fixing the position of the concrete specimen 10 to prevent it from moving or sliding during the test. In addition, a rubber pressure strip 36 is provided on the lower surface of the cover plate 15, and the rubber pressure strip 36 presses on the upper surface of the concrete specimen 10 to provide an additional clamping force and protect the surface of the specimen from being damaged, ensuring the stability of the concrete specimen fiber protruding from the space area opened in the cover plate during the pull-out test, effectively avoiding measurement errors caused by specimen loosening, and improving the accuracy and reliability of the test results. It is worth mentioning that a spring with a fine-tuning variable can be added at the tail of the V-shaped positioning groove 35. The spring is connected to the inner side of the side plate 17. The concrete specimen 10 is placed between the pair of side plates 17, so that the V-shaped positioning grooves 35 of the two side plates 17 are squeezed to realize the positioning of concrete specimens 10 of different sizes.

[0042] Preferably, as Figure 1 and Figure 3As shown, the displacement platform 7 includes an upper platform 18, a middle platform 20, and a lower platform 22. The upper platform 18, the middle platform 20, and the lower platform 22 are stacked and connected in sequence from top to bottom. A fixing member 23 is provided at the bottom of the lower platform 22, and the fixing member 23 is fixed to the base 8 by screws. An X-axis differential knob 21 is provided on the right side of the lower platform 22. The middle platform 20 is disposed on the lower platform 22 and moves along the X-axis direction of the lower platform 22 through the X-axis differential knob 21. A Y-axis differential knob 19 is provided on the front side of the middle platform 20. The upper platform 18 is disposed on the middle platform 20 and moves along the Y-direction of the upper platform 18 through the Y-axis differential knob 19.

[0043] The displacement platform 7 is composed of three parts: an upper platform 18, a middle platform 20, and a lower platform 22, which are stacked and connected in sequence. A fixing member 23 is provided at the bottom of the lower platform 22 and is fixedly connected to the base 8 by screws. An X-axis differential knob 21 is provided on the right side of the lower platform 22. The X-axis differential knob 21 drives the middle platform 20 to move precisely along the X-axis direction of the lower platform 22 through a lead screw mechanism. One end of the X-axis lead screw is connected to the X-axis differential knob 21, and the other end passes through the lower platform 22 and extends below the middle platform 20. There is a nut below the middle platform 20, and this nut cooperates with the X-axis lead screw and is fixed to the bottom of the middle platform 20. The middle platform 20 moves precisely along the X-axis direction of the lower platform 22 through the X-axis differential knob 21. A Y-axis differential knob 19 is provided on the front side of the middle platform 20. The Y-axis differential knob 19 drives the upper platform 18 to move precisely along the Y-axis direction through another set of lead screw mechanisms. The Y-axis differential knob 19 is connected to another lead screw, and this lead screw passes through the middle platform 20 and is fixed to the upper platform 18. The upper platform 18 moves precisely along the Y-axis direction through the Y-axis differential knob 19. The design of this two-dimensional manual displacement platform enables multiple fibers to be implanted into a single concrete specimen on the same straight line simultaneously, and continuous pulling tests of multiple fibers can be achieved through simple knob adjustment without repeatedly disassembling and replacing the concrete specimen, significantly improving the test efficiency, reducing the test error, and enhancing the overall test accuracy.

[0044] Preferably, as Figure 1 shown, the mirror surface 5 is a replaceable plane mirror. A magnetic adsorption layer is provided on the back of the mirror surface 5, which fits the surface of the U-shaped connecting member 11. Calibration scale lines are provided at the edge of the mirror surface 5 for initial position calibration of the laser displacement sensor 6.

[0045] The mirror surface 5 is a replaceable plane mirror, with a magnetic adsorption layer on the back, which can be firmly attached to the surface of the U-shaped connector 11. Calibration scale lines are provided at the edge of the mirror surface 5 for the initial position calibration of the laser displacement sensor 6. This not only facilitates the installation and replacement of the mirror surface, but also ensures that the laser light path emitted by the laser displacement sensor 6 is always parallel to the fiber drawing direction, thereby achieving high-precision non-contact displacement measurement. Through this precise design, the mirror surface can provide a reliable reflection effect under various complex test conditions, ensuring the measurement accuracy of the laser displacement sensor 6.

[0046] A method for using a flexible micro-fiber drawing test device, the steps of which include: S1. Install the upper connector 2 to the upper chuck of the universal testing machine through the upper ball head screw 1a, and install the base 8 to the lower chuck through the lower ball head screw 1b, ensuring clearance fit between the ball head and the groove, and fixedly connect the lower platform 22 of the displacement platform 7 to the base 8 through the screw of the fixing member 23; S2. Place the precast concrete specimen 10 in the concrete fixing device of the displacement platform 7, position it using the V-shaped positioning groove of the side plate 17, press the specimen tightly with the rubber strip of the cover plate 15, and lock the cover plate 15 with the screw 16; S3. Adjust the X-axis differential knob 21 and Y-axis differential knob 19 of the displacement platform 7 to move the middle platform 20 and the upper platform 18, so that the fiber 9 to be measured is aligned with the clamping center of the special fiber fixture 4, and verify that the light path of the laser displacement sensor 6 is parallel to the drawing direction of the fiber 9 through the calibration scale line at the edge of the mirror surface 5; S4. Loosen the fastening screw 12, place the fiber 9 between the staggered tooth-shaped jaws 14 of the steel splint 13, and tighten the screw 12 to ensure that the elastic silica gel layer evenly covers the surface of the fiber 9; S5. Connect the force sensor 3 and the laser displacement sensor 6 to the data acquisition system, and calibrate the zero point of the force sensor and the initial position of the laser; S6. Start the universal testing machine, apply the drawing force and synchronously record the drawing force and displacement data until the fiber 9 debonds or breaks. During this period, if the measurement is abnormal due to the deviation of the mirror surface 5, pause the test and replace the magnetically adsorbed mirror surface; S7. After the test is completed, reset the testing machine, quickly align the next fiber 9 to be measured by rotating the Y-axis differential knob 19 and the X-axis differential knob 21, and repeat the above steps until all the fibers 9 are tested.

[0047] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments with equivalent changes within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A flexible microfiber pulling test device, comprising an upper connecting member (2), a base (8), a displacement platform (7), a force sensor (3) and a laser displacement sensor (6), wherein: The upper connecting member (2) is arranged opposite to the base (8); a displacement platform (7) that can be finely adjusted along the X-axis and Y-axis directions of a horizontal plane is installed on the base (8); a concrete fixing device for fixing the concrete specimen (10) is provided on the displacement platform (7); The upper connecting member (2) is connected to a force sensor (3) and a special fiber clamp (4) in sequence below the upper connecting member (2), wherein the special fiber clamp (4) comprises: a U-shaped connecting member (11) and a pair of steel clamps (13) which are connected to the U-shaped connecting member (11) through a fixing screw (12) to form an adjustable clamping space, the top of the U-shaped connecting member (11) is screwed to the force sensor (3), a mirror (5) is installed on the side of the U-shaped connecting member (11), and the pair of steel clamps (13) have staggered tooth-shaped teeth (14), and the tooth-shaped teeth (14) are used to clamp the fibers (9) in the concrete specimen (10); The laser displacement sensor (6) is fixed to the displacement platform (7), and measures the fiber displacement by reflecting laser light through the mirror (5), and the direction of the laser light path emitted by the laser displacement sensor (6) is parallel to the fiber drawing direction.

2. The flexible microfiber pulling test device according to claim 1, characterized in that: The U-shaped connecting member (11) is provided with first connecting holes (31) on both sides, and the steel clamping plate (13) is provided with second connecting holes (32). A pair of the steel clamping plates (13) are located inside the U-shaped connecting member (11), and the second connecting holes (32) on the steel clamping plates (13) are respectively connected and fixed to the first connecting holes (31) on the left and right sides of the U-shaped connecting member (11) by means of fixing screws (12); The toothed teeth (14) at the lower part of the pair of steel clamps (13) are evenly distributed, and the toothed teeth (14) on the pair of steel clamps (13) are arranged in a staggered occlusal shape.

3. A flexible microfiber pulling test device according to claim 2, characterized in that: The toothed teeth (14) of the steel clamping plate (13) are triangular saw teeth; or the toothed teeth (14) of the steel clamping plate (13) are wavy saw teeth, and the clamping surface of the steel clamping plate (13) is covered with an elastic silicone layer (34), and the surface of the silicone layer (34) is provided with toothed grooves corresponding to the toothed teeth (14).

4. The flexible microfiber pulling test device according to claim 1, characterized in that: An upper ball screw (1a) is arranged at the top of the upper connecting member (2), and the upper connecting member (2) is connected to an upper chuck of an externally arranged universal testing machine via the upper ball screw (1a); a lower ball screw (1b) is arranged at the lower end of the base (8), and the base (8) is connected to a lower chuck of an externally arranged universal testing machine via the lower ball screw (1b).

5. A flexible microfiber pulling test device according to claim 4, characterized in that: An upper ball head groove (24) is provided at the top of the upper connecting member (2), and the upper ball head screw (1a) has a first ball head (25), the first ball head (25) is arranged in the upper ball head groove (24), and the first ball head (25) is clearance-matched with the inner wall of the groove of the first ball head (25); A lower ball head groove (26) is provided at the bottom of the base (8); the lower ball head screw (1b) has a second ball head (27); the second ball head (27) is arranged in the lower ball head groove (26); the second ball head (27) is clearance-matched with the inner wall of the lower ball head groove (26).

6. The flexible microfiber pulling test device according to claim 4, characterized in that: The force sensor (3) is a screw-type tension and pressure sensor, wherein a first connection portion (28) is provided at the upper end of the force sensor (3), and a second connection portion (29) is provided at the lower end of the force sensor (3); a first threaded hole (30) is provided at the bottom of the upper connection member (2), and a second threaded hole (31) is provided at the top of the U-shaped connection member (11); the first threaded hole (30) is provided along the upper connection member (2) and the second threaded hole (31) is provided along the center position of the U-shaped connection member (11); the first connection portion (28) is connected to the first threaded hole (30), and the second connection portion (29) is connected to the second threaded hole (31), so that the axes of the first connection portion (28), the second connection portion (29) and the upper ball screw (1a) are collinear.

7. The flexible microfiber pulling test device according to claim 2, characterized in that: The concrete fixing device comprises a pair of side plates (17) and a cover plate (15), wherein the side plates (17) are fixed to the displacement platform (7) by welding, and the cover plate is located above the pair of side plates, and the cover plate (15) is connected and fixed to the pair of side plates (17) by fixing screws (16). The inner side of the side plate (17) is provided with a V-shaped positioning groove (35) that abuts against the concrete specimen (10), and the lower surface of the cover plate (15) is provided with a rubber strip (36), which covers the upper surface of the concrete specimen (10).

8. The flexible microfiber pulling test device according to claim 1, characterized in that: The displacement platform (7) comprises an upper platform (18), a middle platform (20) and a lower platform (22), wherein the upper platform (18), the middle platform (20) and the lower platform (22) are stacked and connected in sequence from top to bottom, a fixing member (23) is arranged at the bottom of the lower platform (22), and the fixing member (23) is fixed to the base (8) by screws, an X-axis differential knob (21) is arranged on the right side of the lower platform (22), the middle platform (20) is arranged on the lower platform (22), the X-axis differential knob (21) drives the middle platform (20) to move along the X-axis direction of the lower platform (22) through a screw mechanism, and a Y-axis differential knob (19) is arranged on the front side of the middle platform (20), the upper platform (18) is arranged on the middle platform (20), and the Y-axis differential knob (19) drives the upper platform (18) to move along the Y-direction of the upper platform (18) through a screw mechanism.

9. The flexible microfiber pulling test device according to claim 1, characterized in that: The mirror surface (5) is a replaceable plane mirror, the back of the mirror surface is provided with a magnetic adsorption layer, which fits the surface of the U-shaped connecting piece (11), and the edge of the mirror surface (5) is provided with a calibration scale line for calibrating the initial position of the laser displacement sensor (6).

10. A method for using a flexible microfiber pulling test device, the steps comprising: S1. Install the upper connecting member (2) to the upper chuck of the universal testing machine through the upper ball screw (1a), install the base (8) to the lower chuck through the lower ball screw (1b), ensure that the ball head and the groove have clearance fit, and fix the lower platform (22) of the displacement platform (7) to the base (8) through the screws of the fixing member (23); S2, placing the precast concrete specimen (10) in the concrete fixture of the displacement platform (7), positioning it using the V-shaped positioning groove of the side plate (17), pressing the specimen with the rubber pressure strip of the cover plate (15), and locking the cover plate (15) with screws (16); S3, adjusting the X-axis differential knob (21) and the Y-axis differential knob (19) of the displacement platform (7) to move the middle platform (20) and the upper platform (18) so that the fiber to be tested (9) is aligned with the clamping center of the special fiber clamp (4), and verifying that the optical path of the laser displacement sensor (6) is parallel to the pulling direction of the fiber (9) through the calibration scale line on the edge of the mirror (5); S4, loosen the fixing screw (12), place the fiber (9) between the staggered toothed teeth (14) of the steel clamping plate (13), and tighten the screw (12) to ensure that the elastic silicone layer (34) evenly covers the surface of the fiber (9); S5, connecting the force sensor (3) and the laser displacement sensor (6) to the data acquisition system, and calibrating the zero point of the force sensor and the initial position of the laser displacement; S6, start the universal testing machine, apply a pulling force and simultaneously record the pulling force and displacement data until the fiber (9) is debonded or broken. During this period, if the mirror (5) is offset and causes measurement abnormality, suspend the test and replace the magnetic adsorption mirror; S7. After the test is completed, the test machine is reset, and the next fiber (9) to be tested is quickly centered by rotating the Y-axis differential knob (19) and the X-axis differential knob (21), and the above steps are repeated until all fibers (9) are tested.

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