A test device for characterizing the shrinkage characteristics of hydraulic materials based on the DIC method

Abstract

The present invention provides a test device for characterizing the shrinkage characteristics of hydraulic materials based on the DIC method, which belongs to the field of civil engineering materials. It includes a sample table, a column, an upper crossbar, a lower crossbar, a camera fixing support, a support adjustment slider, a limit adjustment shaft, a support connecting rod, a flat chuck, an industrial camera, a hollow light source, a light source bracket, a light source adjustment slider, a self-shrinkage sample pool and a drying shrinkage sample pool. The freshly mixed hydraulic material is filled into the sample pool and a speckle with grayscale contrast is produced on the sample surface. The spatial position brightness of the industrial camera is adjusted so that the test sample pool is completely within the imaging field of view and has appropriate brightness, and then a real-time image of the test sample is captured according to the test requirements. The image data collected by the present invention can support the analysis of the shrinkage strain field. Compared with the traditional cement-based material shrinkage test device, the device of the present invention can collect the full strain field of the sample and provide technical support for the quantitative analysis of the shrinkage stress distribution.

Description

Technical Field

[0001] The present invention relates to the field of testing and characterization of inorganic non-metallic materials, and in particular to a testing device for characterizing the shrinkage characteristics of hydraulic materials based on a DIC method. Background Art

[0002] Hydraulic materials, represented by cementitious materials, are widely used in civil engineering. With the increasing demands of infrastructure construction and rapid urbanization, a growing number of fast-setting cementitious materials, such as geopolymers, alkali-activated cements, and magnesium phosphate cements, are demonstrating significant advantages in this field. While these fast-setting cementitious materials exhibit rapid mechanical property improvements after mixing, they also present significant challenges, such as significant shrinkage deformation within the matrix. This nonuniform shrinkage strain within the matrix often leads to premature cracking in the cementitious materials, resulting in reduced bearing capacity and durability in civil engineering structures, limiting the application and development of fast-setting cementitious materials. Therefore, in-depth analysis of the shrinkage strain evolution of fast-setting cementitious materials during and after the curing process is crucial to lay a theoretical foundation for regulating the shrinkage strain field and controlling shrinkage cracking. Currently, conventional methods for measuring shrinkage of cementitious materials include the comparator method, the resistance strain gauge method, and the strain gauge method. While these methods are simple to use, they also have certain limitations. The above-mentioned method can usually only reflect the shrinkage deformation of the sample by the average linear variation within a certain gauge range of the hardened sample. The effective data collected is relatively limited, and it is difficult to provide support for the quantitative analysis of the shrinkage strain field of heterogeneous materials. Compared with the traditional method of measuring the shrinkage of cement-based materials, the digital image correlation method (DIC) has the advantages of non-contact characteristics, full-field measurement and high measurement accuracy. It provides an effective method for measuring the shrinkage deformation development of hydraulic materials during the full curing process. At the same time, it can also provide comprehensive data support for the quantitative analysis of the shrinkage strain field of heterogeneous materials. Based on the above needs, it is necessary to design a test device based on the DIC method to characterize the shrinkage characteristics of hydraulic materials. Summary of the Invention

[0003] The object of the present invention is to provide a testing device for characterizing the shrinkage characteristics of hydraulic materials based on the DIC method to solve the problems raised in the above background technology.

[0004] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0005] A test device for characterizing the shrinkage characteristics of hydraulic materials based on the DIC method includes a sample table, a column, an upper crossbar, a lower crossbar, a camera fixing support, a support adjustment slider, a limit adjustment shaft, a support connecting rod, a flat plate chuck, an industrial camera, a hollow light source, a light source bracket, a light source adjustment slider, a self-shrinkage sample cell and a drying shrinkage sample cell; the self-shrinkage sample cell includes a removable sealing structure, including a removable sample chamber, a handle, a self-shrinkage sample chamber top surface, a self-shrinkage sample test mold and a self-shrinkage sample chamber bottom surface; the drying shrinkage sample cell includes an environmental sensor, a drying shrinkage sample test mold, a drying shrinkage sample chamber top surface, a drying shrinkage sample chamber bottom surface and a single-channel precision balance.

[0006] The sample stage is located at the bottom of the entire device, the column is located at the upper end of the sample stage and is vertically fixed to the sample stage, the upper cross bar and the lower cross bar are located in the plane of the column, vertically connected to the column and can move up and down along the direction of the column, the industrial camera is clamped and fixed by the flat plate chuck, the flat plate chuck is located at the end of the limit adjustment shaft, the limit adjustment shaft is equipped with a rigid spring along its axial direction to assist in clamping the industrial camera, the tail end of the limit adjustment shaft is connected to the camera fixed support, and the position of the limit adjustment shaft is locked by a fastening nut, and the camera fixed support is connected to the support connecting rod It is connected to the support adjustment slider, and the support adjustment slider can slide horizontally along the upper cross bar to adjust the relative position of the industrial camera. The hollow light source is horizontally placed on the light source bracket, and the light source bracket and the light source adjustment slider are rigidly connected. The light source adjustment slider can slide horizontally along the lower cross bar to adjust the relative position of the hollow light source. The self-shrinking sample pool and the drying shrinkage sample pool can be placed through the sample pool positioning groove a and the sample pool positioning groove b of the sample stage. There is no fixed match between the sample pool and the sample pool positioning groove. The self-shrinking sample pool and the drying shrinkage sample pool can be separated from the sample stage.

[0007] Furthermore, before the test begins, the self-shrinking sample pool is removed from the sample table, the removable sample chamber is pulled out of the self-shrinking sample pool by pulling the handle, the self-shrinking sample mold is taken out, the freshly mixed hydraulic material sample to be tested is filled into the self-shrinking sample mold, and speckles are made on the upper surface of the sample to be tested. Then, the self-shrinking sample mold is put back into the removable sample chamber, and the removable sample chamber is put back into the self-shrinking sample pool to ensure that the removable sample chamber is completely sealed in the self-shrinking sample pool.

[0008] Furthermore, the drying shrinkage sample pool is removed from the sample table, and the environmental sensor and the single-channel precision balance are started, the single-channel precision balance is reset, the drying shrinkage sample mold is taken out from the drying shrinkage sample pool, the drying shrinkage sample mold is filled with the freshly mixed hydraulic material sample to be tested, and speckles are made on the upper surface of the sample to be tested, and then the drying shrinkage sample mold is put back into the drying shrinkage sample pool. At this time, the single-channel precision balance begins to display the mass change of the corresponding sample to be tested.

[0009] Furthermore, the self-shrinkage sample pool and the drying shrinkage sample pool are put back on the sample stage, and the self-shrinkage sample pool and the drying shrinkage sample pool are placed in limited positions by the sample pool positioning groove a and the sample pool positioning groove b.

[0010] Furthermore, the industrial camera is placed vertically between the flat plate chucks, with the camera lens facing the plane where the self-shrinkage sample pool and the drying shrinkage sample pool are located. The industrial camera is connected to a computer so that the real-time field of view image of the industrial camera is presented at the output end of the computer. The upper cross bar, the limit adjustment shaft and the supporting connecting rod are moved to adjust the spatial orientation of the industrial camera so that the self-shrinkage sample pool and the drying shrinkage sample pool are completely within the field of view of the industrial camera, and then the fastening nuts of the upper cross bar, the limit adjustment shaft and the supporting connecting rod are locked.

[0011] Furthermore, the hollow light source is placed on the light source bracket and turned on, the hollow light source is moved to directly below the industrial camera, the real-time field of view image of the industrial camera is observed to determine the appropriate position of the hollow light source, the lower cross bar and the light source adjustment slider are moved to adjust the relative position of the hollow light source, so that the samples to be tested in the self-shrinking sample pool and the drying shrinkage sample pool can be clearly imaged in the real-time field of view of the industrial camera, and then the fastening nut of the lower cross bar is locked, and the brightness of the hollow light source is adjusted according to the clarity of the real-time field of view image of the industrial camera.

[0012] Furthermore, the test is started, the spatial positions of the various components of the entire device are kept moderate and fixed, the brightness of the hollow light source is kept stable, the shooting frequency of the industrial camera is set according to the test plan, and the real-time image of the test sample is captured until the test is completed. The standard calibration points on the top surface of the self-shrinkage sample chamber and the top surface of the drying shrinkage sample chamber are used for initial calibration in the analysis phase, the images of the test samples in the self-shrinkage sample mold and the drying shrinkage sample mold are used for quantitative analysis of the shrinkage strain field, the reading change of the single-channel precision balance is used to determine the moisture loss of the test sample, and the environmental sensor collects the changes in ambient temperature and humidity during the test to assist in determining the systematic error of the test data.

[0013] Compared with the existing technology, the present invention is a testing device for characterizing the shrinkage characteristics of hydraulic materials based on the DIC method. It combines the shrinkage development and evolution characteristics of hydraulic materials with the technical requirements of the digital speckle correlation method for testing strain fields, and specifically designs the sample pool and main components of the device. It fully utilizes the advantages of the digital speckle correlation method in strain field testing, and uses an industrial camera to effectively collect original image data of the shrinkage development process of hydraulic materials. This greatly improves the test accuracy of shrinkage deformation of cement-based materials and similar materials, and provides technical support for quantitative analysis of shrinkage strain distribution and shrinkage damage of hydraulic materials during the curing process and in the later stage of curing. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0015] Figure 1 This is a schematic diagram of the structure of a testing device for characterizing the shrinkage characteristics of hydraulic materials based on the DIC method according to an embodiment of the present invention;

[0016] Figure 2 A schematic structural diagram of a sample stage in a testing device for characterizing shrinkage characteristics of hydraulic materials based on a DIC method according to an embodiment of the present invention;

[0017] Figure 3 A schematic structural diagram of a self-shrinkage sample cell in a testing device for characterizing shrinkage characteristics of hydraulic materials based on a DIC method according to an embodiment of the present invention;

[0018] Figure 4 This is a schematic structural diagram of a drying shrinkage sample cell in a testing device for characterizing shrinkage characteristics of hydraulic materials based on a DIC method according to an embodiment of the present invention;

[0019] Description of reference numerals:

[0020] 1. Sample stage; 2. Column; 3. Upper crossbar; 4. Lower crossbar; 5. Camera fixing support; 6. Support adjustment slider; 7. Limit adjustment shaft; 8. Support connecting rod; 9. Flat plate chuck; 10. Industrial camera; 11. Hollow light source; 12. Light source bracket; 13. Light source adjustment slider; 14. Self-shrinking sample cell; 15. Drying and shrinking sample cell; 16. Sample cell positioning groove a; 17. Sample cell positioning groove b; 18. Removable sample chamber; 19. Handle; 20. Top surface of self-shrinking sample chamber; 21. Self-shrinking sample test mold; 22. Bottom surface of self-shrinking sample chamber; 23. Environmental sensor; 24. Drying and shrinking sample test mold; 25. Top surface of drying and shrinking sample chamber; 26. Bottom surface of drying and shrinking sample chamber; 27. Single-channel precision balance. DETAILED DESCRIPTION

[0021] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0022] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the present invention.

[0023] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "connection" and "connected" should be understood in a broad sense. For example, it can mean a fixed connection, a detachable connection, or an integral connection; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium, or it can mean internal communication between two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0024] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] See Figures 1-4As shown, the present invention provides a technical solution: a testing device for characterizing the shrinkage characteristics of hydraulic materials based on the DIC method, comprising a frame structure consisting of a sample platform 1, a column 2, an upper crossbar 3, and a lower crossbar 4. The sample platform 1 is a horizontal flat surface with a sample cell positioning groove a16 and a sample cell positioning groove b17 designed thereon. The self-shrinkage sample cell 14 and the drying shrinkage sample cell 15 are positioned by the sample cell positioning grooves a16 and b17. The column 2 is vertically connected to the upper end of the sample platform 1. The upper crossbar 3 is connected to the column 2 and can move up and down within the plane of the column 2. The lower crossbar 4 is located directly below the upper crossbar 3 and is connected to the column 2. The lower crossbar 4 can move up and down within the plane of the column 2.

[0026] The self-shrinking sample pool 14 is removed from the sample table 1, and the removable sample chamber 18 is pulled out using the handle 19. The self-shrinking sample mold 21 is removed from the bottom surface 22 of the self-shrinking sample chamber and placed on the test platform outside the device. The self-shrinking sample mold 21 is filled with freshly mixed hydraulic test samples, such as cement mortar, geopolymer mortar, magnesium phosphate cement, and fiber composite cement-based materials. The test samples in the self-shrinking sample mold 21 are vibrated and the surface is smoothed. Then, inert micropowder particles such as graphite powder and titanium dioxide are sprayed on the surface of the test samples to produce speckles. After completing the above operations, the self-shrinking sample mold 21 is returned to the bottom surface 22 of the self-shrinking sample chamber, and the removable sample chamber 18 is then replaced in the self-shrinking sample pool 14. The removable sample chamber 18 is pushed tightly using the handle 19 to ensure that the self-shrinking sample pool 14 is sealed.

[0027] At the same time, the drying shrinkage sample pool 15 is removed from the sample table 1 and placed on the test platform outside the device, the environmental sensor 23 is turned on to collect the ambient temperature and humidity parameters, the single-channel precision balance 27 is turned on and the tare and zero operation is performed, and then the drying shrinkage sample mold 24 is taken out and placed on the test platform outside the device, and the freshly mixed hydraulic test samples, such as cement mortar, geopolymer mortar, magnesium phosphate cement and fiber composite cement-based materials, are filled into the drying shrinkage sample mold 24, and the test samples in the drying shrinkage sample mold 24 are vibrated and the surface is smoothed, and then graphite powder, titanium dioxide and other inert micropowder particles are sprayed on the surface of the test samples to produce speckles. After completing the above operations, the drying shrinkage sample mold 24 is returned to the bottom surface 26 of the drying shrinkage sample chamber. At this time, the single-channel precision balance 27 displays the mass of the corresponding test sample and displays the real-time mass of the test sample during the test.

[0028] After completing the above operations, the self-shrinkage sample pool 14 and the drying shrinkage sample pool 15 are put back into the sample stage 1 and placed in a limited position by the sample pool positioning groove a16 and the sample pool positioning groove b17. After placement, the samples to be tested in the self-shrinkage sample pool 14 and the drying shrinkage sample pool 15 are basically located in the center of the sample stage 1.

[0029] After being connected to a computer, an industrial camera 10 is placed vertically above the sample stage 1 via a flatbed chuck 9. Real-time images captured by the industrial camera 10 are displayed via the computer output. The flatbed chuck 9 is connected to the camera support 5 via a limit adjustment shaft 7. The camera support 5 is connected to the support adjustment slider 6 via a support connecting rod 8. The support adjustment slider 6 is connected to the upper crossbar 3 and can move horizontally along the upper crossbar 3. Before the test starts, first move the upper cross bar 3 up and down to adjust the object distance of the industrial camera 10, and then lock the fastening nut of the upper cross bar 3 after the field of view of the industrial camera 10 meets the test requirements; then move the support adjustment slider 6 left and right, and move the support connecting rod 8 back and forth, so that the field of view center of the industrial camera 10 is basically located at the geometric center of the sample stage 1, and lock the fastening nut of the upper support connecting rod 8; finally, move the limit adjustment shaft 7 left and right to fine-tune the field of view of the industrial camera 10, so that the self-shrinkage sample pool 14 and the drying shrinkage sample pool 15 all enter the field of view of the industrial camera 10, lock the fastening nut of the limit adjustment shaft 7, and complete the spatial position adjustment of the industrial camera 10.

[0030] Turn on the hollow light source 11 and place it on the light source bracket 12. Move the hollow light source 11 forward and backward and the light source adjustment slider 13 left and right so that the hollow light source 11 is directly below the industrial camera 10. Move the lower crossbar 4 up and down so that the hollow light source 11 does not block the field of view of the industrial camera 10. Tighten the fastening nut of the lower crossbar 4 to complete the spatial position adjustment of the hollow light source 11. Adjust the brightness of the hollow light source 11 according to the image clarity requirements within the field of view of the industrial camera 10.

[0031] The test begins, strictly maintaining the entire apparatus in a vibration-free environment and keeping the positions of all components and the test sample fixed. The brightness of the hollow light source 11 remains constant, and the shooting frequency of the industrial camera 10 is set according to the actual test requirements. Real-time images of the test sample are captured until the test is completed. After image acquisition is completed, the first image captured at the start of the test is used as the reference image for shrinkage strain field analysis. The standard calibration points on the top surface 20 of the self-shrinkage sample chamber and the top surface 25 of the drying shrinkage sample chamber are used for initial calibration during the analysis phase. The images of the test samples in the self-shrinkage sample mold 21 and the drying shrinkage sample mold 24 are used for quantitative analysis of the shrinkage strain field. The reading changes of the single-channel precision balance 27 are used to determine the amount of water loss of the test sample during the drying shrinkage process. The environmental sensor 23 collects changes in ambient temperature and humidity during the test to assist in analyzing the systematic errors of the shrinkage strain field.

[0032] After the test is completed, the cured test samples in the autogenous shrinkage sample mold 21 and the drying shrinkage sample mold 24 are taken out and cleaned. The autogenous shrinkage sample mold 21 and the drying shrinkage sample mold 24 can be recycled and reused.

[0033] The embodiments of the present invention disclosed above are intended only to help illustrate the present invention. The embodiments do not describe all details in detail, nor do they limit the present invention to the specific embodiments described. Numerous modifications and variations are possible based on the contents of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention.

Claims

1. A test device for characterizing the shrinkage characteristics of hydraulic materials based on the DIC method, characterized by: The invention comprises a sample stage (1), wherein the sample stage (1) is provided with two vertical columns (2), the two columns (2) are located at the ends of the sample stage, an upper cross bar (3) and a lower cross bar (4) are arranged between the two columns (2), the upper cross bar (3) and the lower cross bar (4) are respectively connected to the two columns (2) vertically, the upper cross bar (3) and the lower cross bar (4) are parallel to each other, the upper cross bar (3) and the lower cross bar (4) can move up and down along the plane of the two columns (2), the upper cross bar (3) is connected to a support adjustment slider (6), the support adjustment slider (6) can slide horizontally along the upper cross bar (3), the support adjustment slider (6) is connected to a camera fixed support (5) through a support connecting rod (8), and the two side wings of the camera fixed support (5) are respectively connected to two limit The two limit adjustment shafts (7) are connected, and the ends of the two limit adjustment shafts (7) are respectively provided with flat plate clamps (9), and the two flat plate clamps (9) are used to clamp and fix the industrial camera (10), and the lens of the industrial camera (10) is located just above the hollow part of the hollow light source (11), and the hollow light source (11) is horizontally placed on the light source bracket (12), and the light source bracket (12) is connected to the light source adjustment slider (13), and the light source adjustment slider (13) is connected to the lower cross bar (4), and the light source adjustment slider (13) can move horizontally along the lower cross bar (4), and the sample stage (1) is equipped with a self-shrinkage sample pool (14) and a drying shrinkage sample pool (15), and the self-shrinkage sample pool (14) and the drying shrinkage sample pool (15) are respectively placed horizontally on the sample stage (1).

2. The testing device for characterizing shrinkage characteristics of hydraulic materials based on the DIC method according to claim 1, characterized in that: The sample table (1) is provided with a sample pool positioning groove a (16) and a sample pool positioning groove b (17) for placing a self-shrinking sample pool (14) and a drying shrinking sample pool (15); the self-shrinking sample pool (14) can be pulled out of a removable sample chamber (18) by a handle (19); the removable sample chamber (18) is equipped with three self-shrinking sample test molds (21) placed on the bottom surface (22) of the self-shrinking sample chamber; the self-shrinking sample test molds (21) are separable from the bottom surface (22) of the self-shrinking sample chamber; the upper surface of the self-shrinking sample pool (14) is the top surface (20) of the self-shrinking sample chamber; the top surface (20) of the self-shrinking sample chamber is sealed high-transmittance glass located directly above the self-shrinking sample test molds (21); and the top surface of the self-shrinking sample chamber other than the high-transmittance glass is sprayed with standard calibration points.

3. The testing device for characterizing shrinkage characteristics of hydraulic materials based on the DIC method according to claim 1, characterized in that: The drying shrinkage sample pool (15) is equipped with three drying shrinkage sample test molds (24) placed on the bottom surface (26) of the drying shrinkage sample chamber. The drying shrinkage sample test molds (24) are separable from the bottom surface (26) of the drying shrinkage sample chamber. The upper surface of the drying shrinkage sample pool (15) is the drying shrinkage sample chamber top surface (25). The drying shrinkage sample chamber top surface (25) is located directly above the drying shrinkage sample test molds (24) and is a hollow open space, so that the drying shrinkage sample test molds (24) are exposed to the test environment. The area of ​​the drying shrinkage sample chamber top surface (25) other than the hollow part is sprayed with standard calibration points. An environmental sensor (23) is provided at the upper end of the drying shrinkage sample chamber top surface (25) for monitoring the ambient temperature and humidity during the test process. Three independent single-channel precision balances (27) are provided at the lower end of the drying shrinkage sample chamber top surface (25) for displaying the mass change of the test samples located in the three drying shrinkage sample test molds (24) during the test process.

4. The testing device for characterizing shrinkage characteristics of hydraulic materials based on the DIC method according to claim 1, characterized in that: The position of the industrial camera (10) can be adjusted horizontally by the limit adjustment shaft (7), the limit adjustment shaft (7) is equipped with a rigid spring along the axial direction and is fixed to the camera fixed support (5) by a fastening nut, one end of the limit adjustment shaft (7) located inside the camera fixed support (5) is connected to a flat plate chuck (9), and the flat plate chuck (9) is used to clamp and fix the industrial camera (10), the support connecting rod (8) can be moved forward and backward to adjust the camera fixed support (5), and then adjust the position of the industrial camera (10) in a direction perpendicular to the plane of the column (2), and the support connecting rod (8) is fixedly connected to the support adjustment slider (6) by a fastening nut.

5. The testing device for characterizing shrinkage characteristics of hydraulic materials based on the DIC method according to claim 1, characterized in that: The hollow light source (11) is located directly below the industrial camera (10) to provide a stable light source for collecting sample images in the self-shrinkage sample pool (14) and the drying shrinkage sample pool (15); the light source adjustment slider (13) can be adjusted horizontally along the lower crossbar (4); the hollow light source (11) moves on the light source bracket (12) to provide lighting in coordination with the position of the industrial camera (10).

6. The testing device for characterizing shrinkage characteristics of hydraulic materials based on the DIC method according to claim 1, characterized in that: The industrial camera (10) supports computer software control triggering and external control switch triggering for image acquisition.

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