Test piece, mold and test method for fiber-cement oblique pull-out performance test

Abstract

The invention discloses a test piece, a mold and a test method for testing the oblique pull-out performance of fiber-cement. The appearance of the test piece is a prismoid, a single fiber is pre-buried and fixed in the middle of the test piece, the fiber is fixed in the geometric center of the test piece, and the pre-buried angle is variable. The mold comprises a switch type magnetic base, a bottom plate, a pair of side fasteners, a bolt short rod and a pair of middle fasteners. Through free rotation and fixation of the middle fastening piece, the intersection angle between the pouring base body and the fibers can be changed. By using the mold provided by the invention, the normalized manufacturing of the single fiber test pieces with different embedding angles can be realized, the quality stability of the test pieces is improved and the manufacturing cost of the test pieces is reduced through the repeated utilization of the template, and the oblique pulling of the single fibers is convenient to realize. By adopting the test piece, the mold and the test method provided by the invention, the expected effect is relatively good, single crack cracking of the ECC material in a tension-shear mixed fracture mode can be realized, and a fiber bridging stress-crack opening relation curve under the action of a tension-shear combined load can be accurately measured.

Description

Technical Field

[0001] The invention belongs to the field of mechanical property testing of high-ductility fiber-reinforced cement-based composite materials, and specifically relates to a test piece, a mold and a testing method for fiber-cement oblique pull-out performance testing. Background Art

[0002] In the field of civil engineering, fiber-reinforced composite materials are widely used in various structures due to their superior crack resistance and durability. In particular, the introduction of fibers into cement matrix can not only effectively improve the tensile strength of the material, but also inhibit the expansion of cracks. The interfacial bonding performance between the fiber and the matrix plays a key role in the overall mechanical properties of fiber-reinforced materials. Therefore, the study of single fiber pull-out performance is very necessary.

[0003] Most of the existing single fiber pull-out performance test methods focus on the situation where the fiber is subjected to vertical force relative to the matrix. However, in actual engineering, the fiber is often subjected to oblique pull-out force. However, most of the existing test devices and specimen designs cannot accurately simulate the situation where the fiber is subjected to oblique force in the cement matrix. The existing mold designs are also mostly used for fixed-angle fiber pull-out tests, and cannot flexibly adjust the fiber embedding angle, thus failing to adapt to the testing requirements of various oblique forces. Summary of the invention

[0004] To solve the above problems, the present invention discloses a test specimen, a mold and a test method for testing the oblique pull-out performance of fiber-cement, which can realize the oblique pull-out of a single fiber and accurately measure the oblique pull-out curve of the specimen, thereby reflecting the shear transfer mechanism of the ECC crack surface under the action of fiber bridging, and providing a scientific basis for the material design and engineering application of high-ductility fiber-reinforced composite materials.

[0005] To achieve the above objectives, the present invention proposes four design solutions, which are as follows: (1) Design a test specimen suitable for testing the fiber-cement oblique pull-out properties of high-ductility, multi-crack fiber-reinforced cementitious composites; (2) Design a mold for preparing the test specimens; (3) Design a method for preparing the test specimens for the above test; (4) Design a test method for the oblique pull-out performance of fiber-cement specimens made using the above-mentioned mold.

[0006] The specific technical solutions are as follows: A fiber-cement oblique pull-out performance test specimen has a prism-like appearance, a single fiber is embedded and fixed in the middle, the fiber is fixed at the geometric center of the specimen, and the angle of the embedded fiber can be adjusted as needed.

[0007] The second aspect of the present invention provides a mold for making a fiber-cement oblique pull-out performance test piece, including a switch-type magnetic base, a bottom plate, a pair of side fasteners, a bolt short rod and a pair of middle fasteners.

[0008] The switch type magnetic base has dimensions of 116 mm in length, 50 mm in width and 55 mm in height, and is used to fix the relative position of the intermediate fastener.

[0009] The bottom plate is made of acrylic material, which can fully transmit magnetic force and thus fix the middle fastener.

[0010] The pair of side fasteners have the same size and thickness as the lower middle fasteners. The side fasteners are fixed to the bottom plate by bolt short rods.

[0011] The intermediate fastener is a pair of hollow square iron blocks stacked up and down, fixed to the bottom plate through a switch-type magnetic base, which can adjust different angles between the fiber and the cement matrix to adapt to oblique pull-out tests at different angles.

[0012] The third aspect of the present invention provides a loading device for testing a specimen prepared by a fiber-cement oblique pull-out performance test specimen method, comprising a support, a pair of brackets, a pair of fixed pulleys, and an upper fixture. The fourth aspect of the present invention provides a method for preparing a test piece by using the mold of the fiber-cement oblique pull-out performance test piece, comprising the following steps: Step 1: Place the switchable magnetic base under the base plate, place the side fasteners relatively parallel to the base plate, and fix them with bolt short rods. Then, place an intermediate fastener and adjust its angle, open the magnetic base, fix the position of the intermediate fastener, wrap the two ends of the fiber around the fasteners on both sides, stack another intermediate fastener and fix it through the magnetic base.

[0013] Step 2: After evenly applying the isolation agent on the inner wall of the middle fastener, pour the cement-based material into the mold and vibrate it fully. After molding, cover it with plastic film, keep the surface moist, and let it stand for 1 to 2 days.

[0014] Step 3: Remove the mold, clean and dry each component, and place the prepared specimen in a standard curing room with a temperature of 20℃±2℃ and a relative humidity of ≥95% for 28 days to obtain the final test specimen.

[0015] The fifth aspect of the present invention provides a method for testing a test piece prepared by the method for preparing a test piece for testing the oblique pull-out performance of fiber-cement, comprising the following steps: Step 1: Cut the prepared specimen to the required embedding depth and use 502 glue to fix an acrylic plate of the same size as the upper fixture at the free end of the fiber.

[0016] Step 2: Use structural adhesive to bond the specimen to the rigid loading end below, and apply a preload of 5% of the ultimate load through the rigid loading end until the structural adhesive is completely cured.

[0017] Step 3: Pass the fiber around the fixed pulley; fix the acrylic plate in the groove of the upper fixture.

[0018] Step 4: Perform tensile loading at a speed of 0.02 mm / min through displacement-controlled loading and draw the oblique pull-out curve of the specimen.

[0019] The beneficial effects of the present invention are: The test piece form proposed in the present invention can realize the oblique pullout of single fibers of high-ductility fiber-reinforced cement-based composite materials.

[0020] The mold and preparation method proposed in the present invention realize variable pre-embedded inclination angle of a single fiber of a test piece through free rotation and fixation of a cement-based material forming template.

[0021] The specimen preparation method proposed in the present invention can realize one-time casting and molding of the fiber-cement oblique pull-out performance test specimen, is easy to operate, and can improve the specimen quality stability and reduce the specimen production cost through repeated use of the mold.

[0022] The testing method proposed in the present invention can realize the oblique pull-out of a single fiber and accurately measure the oblique pull-out curve of the specimen, thereby reflecting the shear transfer mechanism of the ECC crack surface under the action of fiber bridging, and providing a scientific basis for the material design and engineering application of high-ductility fiber-reinforced composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 : A three-dimensional schematic diagram of a fiber-cement oblique pull-out performance test specimen Figure 2 : A schematic diagram of the weakened surface of a fiber-cement oblique pull-out performance test specimen; Figure 3 : Schematic diagram of the overall structure of a fiber-cement oblique pull-out performance test specimen mold; Figure 4 : A schematic diagram of the disassembled structure of a fiber-cement oblique pull-out performance test specimen mold; Figure 5 : Schematic diagram of a loading device for testing the oblique pull-out performance of high fiber-cement.

[0024] List of Figure Symbols: 1. Switchable magnetic base; 2. Bottom plate; 3. Side fasteners; 4. Bolt short rods; 5. Intermediate fasteners; 11. Support; 12. Bracket; 13. Fixed pulley; 14. Upper clamp; 15. Acrylic plate. DETAILED DESCRIPTION

[0025] The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0026] In a first aspect, the present embodiment provides a fiber-cement oblique pull-out performance test specimen, such as Figure 1 As shown, its appearance is a prism, with a single fiber embedded and fixed in the middle. The fiber is fixed at the geometric center of the specimen, and the angle of the embedded fiber can be adjusted as needed.

[0027] The second aspect of the present invention provides a processing device for preparing a fiber-cement oblique pull-out performance test specimen, such as Figure 3 As shown, it includes a switch-type magnetic base 1, a base plate 2, a pair of side fasteners 3, a bolt short rod 4 and a pair of middle fasteners 5, wherein the base plate 2 is made of acrylic material, the switch-type magnetic base 1 is arranged on the back of the base plate 2, a pair of side fasteners 3 are fixed to both sides of the front of the base plate 2 by bolt short rods 4, the number of the middle fasteners 5 is two, which are overlapped up and down and arranged between the pair of side fasteners 3, and the two bolt short rods 4 connect the two ends of the fiber.

[0028] Specifically, the switchable magnetic base 1 has dimensions of 116 mm in length, 50 mm in width, and 55 mm in height, and is used to fix the relative position of the intermediate fastener 5 .

[0029] Specifically, the bottom plate 2 is made of acrylic material, which can fully transmit magnetic force and thus fix the middle fastener 5.

[0030] Specifically, the pair of side fasteners 3 have the same size and thickness as the lower middle fastener. The side fasteners 3 are fixed to the bottom plate by bolt short rods 4.

[0031] Specifically, the intermediate fastener 5 is a pair of hollow square iron blocks stacked up and down, which are fixed on the base plate 2 through a switch-type magnetic base 1. Through the free rotation and fixation of the intermediate fastener 5, different angles between the fiber and the cement matrix can be adjusted to adapt to oblique pull-out tests at different angles.

[0032] The third aspect of the present invention provides a method for preparing a test piece by using the mold for testing the oblique pull-out performance of fiber-cement, comprising the following steps: Preparation step 1: Place the switchable magnetic base under the base plate, place the side fasteners relatively parallel to the base plate, and fix them with bolt short rods. Then, place an intermediate fastener and adjust its angle, open the magnetic base, fix the position of the intermediate fastener, wrap the two ends of the fiber around the fasteners on both sides, stack another intermediate fastener and fix it with the magnetic base.

[0033] Preparation step 2: After evenly applying the isolation agent on the inner wall of the middle fastener, pour the cement-based material into the mold and vibrate it thoroughly. After molding, cover it with plastic film, keep the surface moist, and let it stand for 1 to 2 days.

[0034] Preparation step 3: Remove the mold, clean and dry each component, and place the prepared specimen in a standard curing room with a temperature of 20℃±2℃ and a relative humidity of ≥95% for 28 days to obtain the final test specimen.

[0035] A fourth aspect of the present invention provides a loading device for testing a specimen prepared by a fiber-cement oblique pull-out performance test specimen method, comprising a support 11, a pair of brackets 12, a pair of fixed pulleys 13, and an upper clamp 14. The pair of brackets 12 are vertically arranged on the support 11 (at different heights), the fixed pulley 13 is arranged on the side of the bracket 12, and the upper clamp 14 is arranged above the support 11, and a groove is provided on the upper clamp 14.

[0036] A fifth aspect of the present invention provides a method for testing a test piece prepared by the method for preparing a test piece for testing the oblique pull-out performance of fiber-cement, comprising the following steps: Test step 1: Cut the prepared test piece to the required embedding depth, and use 502 glue to fix the acrylic plate 15 with the same size as the groove of the upper fixture 14 at the free end of the fiber; Test step 2: Use structural adhesive to bond the specimen to the rigid loading end below, and apply a preload of 5% of the ultimate load through the rigid loading end until the structural adhesive is completely cured; Test step 3: Pass the fiber around the fixed pulley 13; fix the acrylic plate 15 in the groove of the upper fixture 14; Test step 4: Perform tensile loading at a speed of 0.02 mm / min through displacement-controlled loading and draw the oblique pull-out curve of the specimen.

[0037] It should be noted that the above content merely illustrates the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications all fall within the protection scope of the claims of the present invention.

Claims

1. Fiber-cement oblique pull-out performance test specimen, characterized by: The appearance is a prism, with a single fiber embedded in the middle. The fiber is fixed at the geometric center of the specimen, and the angle of the embedded fiber can be adjusted as needed.

2. A mold for making the fiber-cement oblique pull-out performance test specimen according to claim 1, characterized in that: The invention comprises a switchable magnetic base (1), a base plate (2), a pair of side fasteners (3), a bolt short rod (4) and a pair of middle fasteners (5), wherein the base plate (2) is made of acrylic material, the switchable magnetic base 1 is arranged on the back of the base plate (2), the pair of side fasteners (3) are fixed to both sides of the front of the base plate (2) through the bolt short rod (4), the number of the middle fasteners (5) is two, they are stacked up and down, and are arranged between the pair of side fasteners (3), and the two bolt short rods (4) connect the two ends of the fiber.

3. The mold for the fiber-cement oblique pull-out performance test specimen according to claim 2, characterized in that: The switchable magnetic base (1) has dimensions of 116 mm in length, 50 mm in width and 55 mm in height, and is used to fix the relative position of the intermediate fastener (5).

4. The mold for the fiber-cement oblique pull-out performance test specimen according to claim 2, characterized in that: The pair of side fasteners (3) have the same size and thickness as the lower layer middle fastener.

5. The mold for the fiber-cement oblique pull-out performance test specimen according to claim 2, characterized in that: The intermediate fastener (5) is a pair of hollow square iron blocks stacked one above the other and fixed to the bottom plate (2) via a switchable magnetic base (1), and is capable of adjusting different angles between the fiber and the cement matrix to accommodate oblique pull-out tests at different angles.

6. A loading device for testing a test piece prepared by the method for preparing a test piece for testing the oblique pull-out performance of fiber-cement according to claim 1, characterized in that: The invention comprises a support (11), a pair of brackets (12), a pair of fixed pulleys (13), and an upper clamp (14), wherein the pair of brackets (12) of different heights are vertically arranged on the support (11), the fixed pulleys (13) are arranged on the sides of the brackets (12), the upper clamp (14) is arranged above the support (11), and a groove is provided on the upper clamp (14).

7. A method for preparing a test piece by using the mold for testing the oblique pull-out performance of fiber-cement according to claim 2, characterized in that: The following steps are involved: Step 1: Place the switchable magnetic base (1) under the base plate, place the side fasteners (3) relatively parallel to the base plate (2), and fix them with bolt short rods (4); then, place the lower middle fasteners and adjust their angles, open the switchable magnetic base (1), fix the position of the middle fasteners, wrap the two ends of the fiber around the fasteners on both sides, stack another middle fastener and fix it with the magnetic base; Step 2: After evenly applying the isolation agent on the inner wall of the middle fastener, pour the cement-based material into the mold and fully vibrate it; after molding, cover it with plastic film, keep the surface moist, and let it stand for 1 to 2 days; Step 3: Remove the mold, clean and dry each component, and place the prepared specimen in a standard curing room with a temperature of 20℃±2℃ and a relative humidity of ≥95% for 28 days to obtain the final test specimen.

8. A method for testing a prepared specimen using the loading device according to claim 6, characterized in that: The following steps are involved: Step 1: Cut the prepared specimen to the required embedding depth, and use 502 glue to fix an acrylic plate (15) of the same size as the upper fixture (14) at the free end of the fiber; Step 2: Use structural adhesive to bond the specimen to the rigid loading end below, and apply a preload of 5% of the ultimate load through the rigid loading end until the structural adhesive is completely cured; Step 3: Pass the fiber around the fixed pulley; fix the acrylic plate (15) in the groove of the upper fixture (14); Step 4: Perform tensile loading at a speed of 0.02 mm / min through displacement-controlled loading and draw the oblique pull-out curve of the specimen.

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