A preparation method of a concrete DIC three-point notched beam fracture experiment test piece

Abstract

The application discloses a preparation method of a concrete DIC three-point notched beam fracture test specimen, and comprises the following steps: selecting a suitable mold according to the size of the test specimen required by the test, and performing pre-test treatment on the mold; pouring concrete into the mold to form the test specimen; cutting a prefabricated crack on the test specimen by using a cutting device after the test specimen reaches a specified curing test specimen; calculating the optimal speckle size of the test according to the DIC instrument parameters and the test specimen height parameters, randomly generating a speckle pattern by using software, and manufacturing a speckle transfer sticker; performing primer spraying by using a matte white self-spraying paint; and transferring the speckle pattern of the speckle transfer sticker to the surface of the test specimen. The preparation method simplifies the tedious process of filling the surface of the test specimen with gypsum and polishing; the prefabricated crack is obtained by cutting, so that the distribution of the aggregate and the admixture in the interior of the concrete during pouring is not affected, and the success rate is high; the DIC speckle is prefabricated on the test specimen by using the speckle transfer sticker, and the operation is simple and the precision is high.

Description

Technical Field

[0001] This invention relates to the field of concrete material testing technology, specifically to a method for preparing a concrete DIC three-point notch beam fracture test specimen. Background Technology

[0002] Concrete is an important building material with advantages such as high compressive strength, good plasticity, and low cost. It is widely used in housing construction, bridges, roads, hydraulic engineering, nuclear power plants, and military projects. However, concrete structures often suffer from cracking, which can lead to serious damage to the concrete material and affect the safety of the building. Therefore, studying concrete cracking is crucial for assessing the safety of buildings.

[0003] In the field of materials mechanics research, the DIC (Digital Image Correlation) three-point notched beam fracture test is a commonly used experimental method for evaluating the toughness and fracture properties of materials, and is widely applied in concrete evaluation. In this test, three-point bending loads are applied to the specimen, and the displacement and strain fields are measured and analyzed using DIC technology to study the mechanical properties and fracture behavior of the material during loading. The specimen preparation method is crucial to the accuracy and repeatability of the experimental results.

[0004] Currently, the preparation of traditional concrete DIC three-point notched beam fracture test specimens requires plaster filling and grinding of the specimen surface, which is cumbersome. During concrete pouring, cracks are pre-cast by inserting blades; however, drying shrinkage occurs during concrete setting, and the concrete strength is low when the blades are removed, potentially leading to crack extension at the crack ends and a low yield of pre-cast cracks. Furthermore, the blades can affect the internal structure of the specimen, resulting in uneven material distribution. Moreover, precasting DIC speckle requires extensive practice to achieve qualified speckle using spray painting, making the operation complex. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned problems and provide a method for preparing a concrete DIC three-point cut beam fracture test specimen. This method involves pre-treating the surface of the mold to facilitate specimen demolding and simplifies the tedious processes of plaster filling and polishing the specimen surface. Pre-fabricating cracks through cutting does not affect the distribution of aggregates and admixtures during concrete pouring, resulting in a high success rate. Furthermore, pre-fabricating DIC speckles on the specimen using speckle transfer stickers is simple to operate and highly accurate.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing a concrete DIC three-point notched beam fracture test specimen includes the following steps:

[0008] (1) Select a suitable mold according to the specimen size required for the experiment, and treat the mold before the experiment;

[0009] (2) Pour concrete into the mold to form a specimen;

[0010] (3) After the specimen reaches the specified curing specimen, use a cutting device to cut pre-made cracks in the specimen;

[0011] (4) Calculate the optimal speckle size based on the DIC instrument parameters and specimen height parameters, generate speckle patterns randomly using software, and make speckle transfer stickers.

[0012] (5) Apply a primer to the surface of the specimen using matte white spray paint;

[0013] (6) Use speckle transfer stickers to transfer the speckle pattern onto the surface of the specimen to complete the preparation of the concrete DIC three-point cut beam fracture test specimen.

[0014] In a preferred embodiment of the present invention, step (1), the pre-experiment treatment of the mold, specifically includes:

[0015] (1.1) Clean the inner surface of the mold with a scraper to ensure that there is no concrete residue on the inner surface, and then wipe the inner surface clean with a cloth.

[0016] (1.2) Seal the vent hole under the mold with insulating and waterproof tape;

[0017] (1.3) Use a brush to evenly brush the water-based release agent onto the inner surface of the mold, and then invert the mold to allow the excess water-based release agent inside the mold to flow out.

[0018] Preferably, the specific process of step (2) is as follows:

[0019] (2.1) Weigh the raw materials according to the mix proportion and start preparing concrete according to the corresponding method;

[0020] (2.2) Pour the prepared concrete into the treated mold, so that the concrete surface covers the mold;

[0021] (2.3) Use a vibrator to vibrate the concrete into the mold until no more air bubbles emerge from the concrete surface;

[0022] (2.4) Place the mold on a level surface and smooth the concrete on the upper surface of the mold with a trowel, and wait for the concrete inside the mold to set.

[0023] (2.5) After the concrete in the mold has initially set, use an air pump to inflate the vent hole of the mold to separate the concrete from the mold. Then place the demolded concrete under suitable curing conditions to form a specimen.

[0024] Preferably, the specific process of step (3) is as follows:

[0025] (3.1) Select the appropriate cutting disc according to the crack width and depth required in the experiment;

[0026] (3.2) Place the specimen with the required precast crack locations marked on a horizontal surface;

[0027] (3.3) Place the cutting device on a horizontal surface and adjust its position so that the sliding rod of the cutting device is above the specimen and the sliding base plate of the cutting device is behind the specimen.

[0028] (3.4) Adjust the height of the lifting bracket and the level of the level instrument by turning the knob to make the stainless steel base plate fit against the upper surface of the specimen;

[0029] (3.5) The cutting observation port on the stainless steel base plate is aligned with the line drawn at the location of the precast crack to determine the location of the crack cutting; after the cutting observation port is aligned with the line drawn at the location of the precast crack, the location of the precast crack (or the line drawn) is located on the plane of the cutting blade of the cutting machine, which ensures greater accuracy during the cutting process.

[0030] (3.6) Start the cutting machine and wait for its speed to stabilize. Then slowly push the cutting machine on the sliding base plate forward so that the cutting machine moves along the slide bar. The cutting blade of the cutting machine cuts the specimen to complete the prefabrication of the crack.

[0031] Preferably, the specific process of step (4) is as follows:

[0032] (4.1) Query the camera resolution used by the DIC system, where the resolution is A pixels × B pixels;

[0033] (4.2) The actual height of the specimen is h, and the actual height H corresponding to the camera acquisition area must be greater than h, and satisfy H=α×h, where α is the magnification factor;

[0034] (4.3) The actual length corresponding to each vertical pixel of the specimen is The speckle size is

[0035] (4.4) Input the speckle size into the software that generates random speckle patterns, and generate a speckle image containing the desired speckle pattern;

[0036] (4.5) Make speckle images into speckle transfer stickers. The size of the speckle images is the same as the actual size. That is, the speckle images cannot be scaled and printed into speckle transfer stickers. They are printed at a 1:1 ratio, and the size of the speckle transfer stickers is the same as the size of the speckle images.

[0037] Preferably, in step (5), the specific steps for applying a primer to the surface of the specimen using matte white spray paint are as follows: clean the surface of the specimen that needs to be treated with DIC, apply matte white spray paint evenly to the surface, and complete the primer application after the paint has dried.

[0038] Preferably, the specific steps in step (6) are as follows: apply the speckle transfer sticker to the surface of the specimen, wet the surface of the speckle transfer sticker with water, and press the wet speckle transfer sticker firmly onto the surface of the specimen with a wet towel. After waiting for several minutes, peel off the speckle transfer sticker. The speckle pattern of the speckle transfer sticker is transferred to the surface of the specimen. Use a wet towel to gently wipe the surface of the specimen to remove excess glue. At this time, the preparation of the concrete DIC three-point cut beam fracture test specimen is completed.

[0039] Preferably, the mold is a plastic mold. This is because it is lightweight and easy to demold.

[0040] Preferably, in step (3), the cutting device cuts the bottom surface of the specimen, which ensures that the surface used for DIC is smooth and improves the test accuracy.

[0041] Preferably, in step (4.3), the speckle size calculation needs to be based on the height corresponding to the assumed DIC camera acquisition area to arrange the camera position, so as to ensure the accuracy of the speckle.

[0042] Compared with the prior art, the present invention has the following advantages:

[0043] 1. The method for preparing concrete DIC three-point cut beam fracture test specimens in this invention simplifies the tedious process of plaster filling and polishing the surface of the specimens required in traditional specimen preparation.

[0044] 2. The method for preparing concrete DIC three-point cut beam fracture test specimens in this invention pre-fabricates cracks by cutting, which does not affect the distribution of aggregates and admixtures inside the concrete during pouring, reduces errors caused by the experiment itself, and has the advantages of high success rate, cost saving and convenient operation.

[0045] 3. The method for preparing concrete DIC three-point cut beam fracture test specimens in this invention uses speckle transfer stickers, which can reduce the difficulty of the experiment, improve the speckle quality, and improve the accuracy of the experiment. Attached Figure Description

[0046] Figure 1 This is a flowchart illustrating a method for preparing a concrete DIC three-point cut beam fracture test specimen according to the present invention.

[0047] Figure 2 This is a schematic diagram of the cutting device in this invention.

[0048] Figure 3 This is a schematic diagram of the sliding base plate structure in the cutting device of the present invention.

[0049] Figure 4 This is a side view of the cutting device in this invention.

[0050] Figure 5 This is a top view of the cutting device in this invention.

[0051] Figure 6 This is a schematic diagram illustrating the calculation of speckle size in this invention.

[0052] In the diagram: 1. Lifting bracket; 2. Sliding rod; 3. Sliding base plate; 4. Cutting machine; 5. Base; 6. Lifting bolt; 7. Scissor bar; 8. Knob; 9. Buckle; 10. Fixing bolt; 11. Guide hole; 12. Stainless steel base plate; 13. Cutting observation port; 14. Level; 15. Cutting port; 16. Specimen with incomplete crack cutting; 17. Marking the location of precast crack; 18. Specimen for fracture test of concrete DIC three-point cut beam; 19. Upper clamp for fracture test; 20. Lower clamp for fracture test; 21. Precast crack; 22. Camera acquisition area; 23. Precast crack depth a0. Detailed Implementation

[0053] To enable those skilled in the art to fully understand the technical solutions of the present invention, the present invention will be further described below in conjunction with embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0054] See Figures 1-6 This embodiment discloses a method for preparing a concrete DIC three-point notch beam fracture test specimen, including the following steps:

[0055] (1) Select a suitable mold according to the specimen size required for the experiment, and perform pre-experiment treatment on the mold, specifically including:

[0056] (1.1) Clean the inner surface of the mold with a scraper to ensure that there is no concrete residue on the inner surface, and then wipe the inner surface clean with a cloth.

[0057] (1.2) Seal the vent hole under the mold with insulating and waterproof tape. The insulating and waterproof tape should be as thin as possible. Preferably, the thickness of the insulating and waterproof tape is less than 0.2 mm.

[0058] (1.3) Use a brush to evenly brush the water-based release agent onto the inner surface of the mold, and then invert the mold to allow the excess water-based release agent inside the mold to flow out.

[0059] (2) Pouring concrete into the mold to form a specimen, specifically including:

[0060] (2.1) Weigh the raw materials according to the mix proportion and start preparing concrete according to the corresponding method;

[0061] (2.2) Pour the prepared concrete into the treated mold, so that the concrete surface covers the mold;

[0062] (2.3) Use a vibrator to vibrate the concrete into the mold until no more air bubbles emerge from the concrete surface;

[0063] (2.4) Place the mold on a level surface and smooth the concrete on the upper surface of the mold with a trowel, and wait for the concrete inside the mold to set.

[0064] (2.5) After the concrete in the mold has initially set, use an air pump to inflate the vent hole of the mold to separate the concrete from the mold. Then place the demolded concrete under suitable curing conditions to form a specimen.

[0065] (3) After the specimen reaches the specified curing stage, pre-fabricated cracks are cut into the specimen using a cutting device, specifically including:

[0066] (3.1) Select the appropriate cutting disc according to the crack width and depth required in the experiment;

[0067] (3.2) Place the specimen with the required precast crack locations marked on a horizontal surface;

[0068] (3.3) Place the cutting device on a horizontal surface and adjust its position so that the slide bar 2 of the cutting device is above the specimen and the sliding base plate 3 of the cutting device is behind the specimen.

[0069] (3.4) Adjust the height of the lifting bracket 1 and the level of the level instrument 14 by using the knob 8 to make the stainless steel base plate 12 fit against the upper surface of the specimen.

[0070] (3.5) The cutting observation port on the stainless steel base plate 12 is aligned with the line drawn at the location of the precast crack to determine the location of the crack cutting; after the cutting observation port 13 is aligned with the line drawn at the location of the precast crack, the location of the precast crack (or the line drawn) is located on the plane of the cutting blade of the cutting machine 4, which ensures greater accuracy during the cutting process.

[0071] (3.6) Start the cutting machine 4. After its speed stabilizes, slowly push the cutting machine 4 on the sliding base plate 3 forward so that the cutting machine 4 moves along the slide bar 2. The cutting blade of the cutting machine 4 cuts the specimen to complete the prefabrication of the crack.

[0072] (4) Calculate the optimal speckle size based on the DIC instrument parameters and specimen height parameters, randomly generate speckle patterns using software, and create speckle transfer stickers, specifically including:

[0073] (4.1) The DIC instrument parameter is the camera resolution used by the DIC. Query the camera resolution used by the DIC system. The resolution is A pixels × B pixels.

[0074] (4.2) The actual height of the specimen is h. Since the specimen will move up and down during the experiment, the actual height H corresponding to the camera acquisition area 23 must be greater than the specimen height h, and satisfy H=α×h, where α is the magnification factor. There is a certain distance between the camera and the specimen. The specimen will move during the loading process. Therefore, the actual height H corresponding to the camera acquisition area 23 must be greater than the specimen height h. α is generally taken as 1.5 in the experiment.

[0075] (4.3) The actual length corresponding to each vertical pixel of the specimen is According to the literature, the best effect is achieved when the speckle size is controlled between 3 and 7 pixels. Therefore, the speckle size is...

[0076] (4.4) Input the speckle size (i.e., speckle dimensions) into the software that generates speckle patterns randomly, and generate a speckle image containing the desired speckle pattern;

[0077] (4.5) Make speckle images into speckle transfer stickers. The size of the speckle images is the same as the actual size. Specifically, the speckle images can be sent to the merchant to customize speckle transfer stickers. That is, the speckle images cannot be scaled and printed into speckle transfer stickers. They should be printed at a 1:1 ratio, and the size of the speckle transfer stickers should be the same as the size of the speckle images.

[0078] (5) Apply a primer to the surface of the test piece using matte white spray paint. Specifically, clean the surface of the test piece that needs to be treated with DIC, apply the matte white spray paint evenly to the surface, and complete the primer application after the paint has dried.

[0079] (6) Use speckle transfer stickers to transfer the speckle pattern onto the surface of the specimen to complete the preparation of the concrete DIC three-point notch beam fracture test specimen. Specifically, this includes: applying the speckle transfer sticker to the surface of the specimen, wetting the surface of the speckle transfer sticker with water, and pressing the wet speckle transfer sticker firmly onto the surface of the specimen with a wet towel. After waiting for several minutes, remove the speckle transfer sticker. The speckle pattern of the speckle transfer sticker is transferred to the surface of the specimen. Use a wet towel to gently wipe the surface of the specimen to remove excess glue. At this point, the preparation of the concrete DIC three-point notch beam fracture test specimen is complete.

[0080] Specifically, the mold is a plastic mold. The purpose is to make it lightweight and easy to demold.

[0081] Specifically, in step (3), the cutting device cuts the bottom surface of the specimen, which ensures that the surface used for DIC is smooth and improves the test accuracy.

[0082] See Figure 6 In step (4.3), the speckle size calculation needs to be based on the height corresponding to the assumed DIC camera acquisition area 23 to arrange the camera position, so as to ensure the accuracy of the speckle.

[0083] See Figure 6 After the specimen is prepared, it needs to be fixed by a fixture to complete the experiment. The fixture includes an upper fixture 20 for fracture testing and a lower fixture 21 for fracture testing.

[0084] In step (3), wait 3 minutes and then peel off the spot transfer sticker.

[0085] The speckle pattern of the speckle transfer sticker is transferred onto the surface of the specimen in order to measure and analyze the DIC displacement and strain field.

[0086] See Figures 2-5 The cutting device in this embodiment includes a lifting mechanism, a slide bar 2, a sliding base plate 3, and a cutting machine 4. There are two slide bars 2, which are arranged parallel to each other. The sliding base plate 3 is slidably mounted on the two slide bars 2, and the cutting machine 4 is mounted on the sliding base plate 3. The lifting mechanism is a scissor mechanism, with a total of 4, of which 2 lifting mechanisms are supported at both ends of one of the slide bars 2, and the other 2 lifting mechanisms are supported at both ends of the other slide bar 2.

[0087] See Figures 2-5The lifting mechanism includes a base 5, a scissor bar 7, a buckle 9, and a lifting bracket 1. The scissor bar 7 is disposed between the base 5 and the lifting bracket 1. The buckle 9 is disposed on the lifting bracket 1 and is used to install a sliding rod 2. The buckle 9 is provided with a fixing bolt 10 for fixing the sliding rod 2 to the buckle 9. The sliding base plate 3 is provided with a guide hole 11, through which the sliding rod 2 passes and is slidably connected. The lifting bracket 1 is controlled to lift by a knob 8 in the middle. The scissor bar 7 is connected to the base 5 by a lifting bolt 6.

[0088] See Figures 2-6 The sliding base plate 3 is provided with a stainless steel base plate 12. The stainless steel base plate 12 is provided with a cutting opening 15 and a cutting observation opening 13. The cutting observation opening 13 facilitates alignment with the pre-drawn lines 18 on the specimen 19 to indicate the location of the pre-fabricated crack.

[0089] See Figures 2-5 Two mutually perpendicular levels 14 are provided on the stainless steel base plate 12 near the cutting observation port 13 to facilitate the adjustment of the lifting bracket 1 and keep it level.

[0090] See Figures 2-5 When the cutting machine 4 is fixed to the sliding base plate 3, the cutting blade of the cutting machine 4 should be on the extension line of the cutting observation port 13.

[0091] Two parallel cracks are cut in the middle of the specimen. When marking the specimen, a laser marking machine is used to ensure accuracy and consistency.

[0092] The above are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above content. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a concrete DIC three-point notch beam fracture test specimen, characterized in that, Includes the following steps: (1) Select a suitable mold according to the specimen size required for the experiment, and treat the mold before the experiment; (2) Pour concrete into the mold to form a specimen; (3) After the specimen has reached the specified curing time, use a cutting device to cut pre-made cracks into the specimen; (4) Calculate the optimal speckle size based on the DIC instrument parameters and specimen height parameters, generate speckle patterns randomly using software, and make speckle transfer stickers. (5) Apply a primer to the surface of the specimen using matte white spray paint; (6) Use speckle transfer stickers to transfer the speckle pattern onto the surface of the specimen to complete the preparation of the concrete DIC three-point cut beam fracture test specimen; The specific process of step (2) is as follows: (2.1) Weigh the raw materials according to the mix proportion and start preparing concrete according to the corresponding method; (2.2) Pour the prepared concrete into the treated mold so that the concrete surface covers the mold; (2.3) Use a vibrator to vibrate the concrete into the mold until no more air bubbles emerge from the concrete surface; (2.4) Place the mold on a level ground and smooth the concrete on the upper surface of the mold with a trowel, and wait for the concrete inside the mold to set. (2.5) After the concrete in the mold has initially set, use an air pump to inflate the vent hole of the mold to separate the concrete from the mold. Then place the demolded concrete under suitable curing conditions to form a specimen. The specific process of step (3) is as follows: (3.1) Select the appropriate cutting disc according to the crack width and depth required in the experiment; (3.2) Place the specimen with the required precast crack location marked on a horizontal surface; (3.3) Place the cutting device on a horizontal surface and adjust its position so that the sliding rod of the cutting device is above the specimen and the sliding base plate of the cutting device is behind the specimen; (3.4) Adjust the height of the lifting bracket and the level of the level instrument by turning the knob to make the stainless steel base plate fit against the upper surface of the specimen; (3.5) Align the cutting observation opening on the stainless steel base plate with the line drawn at the location of the precast crack to determine the location of the crack cutting; (3.6) Start the cutting machine and wait for its speed to stabilize. Then slowly push the cutting machine on the sliding base plate forward so that the cutting machine moves along the slide bar. The cutting blade of the cutting machine cuts the specimen to complete the prefabrication of the crack. The specific process of step (4) is as follows: (4.1) Query the camera resolution used by the DIC system, where the resolution is... ; (4.2) The actual height of the specimen is The actual height corresponding to the camera's acquisition area Must be greater than and satisfy ,in, This is the magnification factor; (4.3) The actual length corresponding to each vertical pixel of the specimen is The speckle size is ; (4.4) Input the speckle size into the software that generates speckle patterns randomly, and generate a speckle image containing the desired speckle pattern; (4.5) Make speckle images into speckle transfer stickers, with the speckle images being the same size as the actual images.

2. The method for preparing a concrete DIC three-point notch beam fracture test specimen according to claim 1, characterized in that, In step (1), the mold is processed before the experiment, specifically including: (1.1) Clean the inner surface of the mold with a scraper to ensure that there is no concrete residue on the inner surface, and then wipe the inner surface clean with a cloth; (1.2) Seal the vent hole under the mold with insulating and waterproof tape; (1.3) Use a brush to evenly brush the water-based release agent onto the inner surface of the mold, and then invert the mold to allow the excess water-based release agent inside the mold to flow out.

3. The method for preparing a concrete DIC three-point notch beam fracture test specimen according to claim 1, characterized in that, In step (5), the specific steps for applying a primer to the surface of the specimen using matte white spray paint are as follows: clean the surface of the specimen that needs to be treated with DIC, apply the matte white spray paint evenly to the surface, and complete the primer application after the paint has dried.

4. The method for preparing a concrete DIC three-point notch beam fracture test specimen according to claim 3, characterized in that, The specific steps in step (6) are as follows: Apply the speckle transfer sticker to the surface of the specimen, wet the surface of the speckle transfer sticker with water, and press the wet speckle transfer sticker firmly onto the surface of the specimen with a wet towel. After waiting for several minutes, peel off the speckle transfer sticker. The speckle pattern of the speckle transfer sticker has been transferred to the surface of the specimen. Gently wipe the surface of the specimen with a wet towel to remove excess adhesive. At this point, the preparation of the concrete DIC three-point notch beam fracture test specimen is complete.

5. The method for preparing a concrete DIC three-point notch beam fracture test specimen according to claim 1, characterized in that, The mold is a plastic mold.

6. The method for preparing a concrete DIC three-point notch beam fracture test specimen according to claim 1, characterized in that, In step (3), the cutting device cuts the bottom surface of the specimen.

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