Concrete test crack observation method based on fluorescence tracing technology

Abstract

The invention discloses a concrete test crack observation method based on a fluorescence tracing technology, and relates to the technical field of civil engineering research, and the concrete test crack observation method comprises the following specific steps: S100, building a concrete crack tracking detection device, S200, coating the surface of a concrete test piece with a fluorescence tracer agent, S300, collecting a fluorescence image, and S400, calculating a quantitative parameter. S500, establishing dynamic correlation between crack evolution and mechanical parameter variation, the crack development condition in the concrete uniaxial and splitting test process is directly observed by using a fluorescent agent and an ultraviolet lamp in the concrete uniaxial and splitting test process, a stress-strain curve in the concrete is recorded in real time through a computer in the mechanical loading test process, and the dynamic correlation between the crack evolution and the mechanical parameter variation is established. A high-speed camera is adopted to capture a high-definition fluorescence image of concrete surface crack propagation in real time, and the fluorescence image recorded in real time is quantified to obtain the development condition of concrete surface cracks, so that the relation between macroscopic strength such as uniaxial compression and microscopic cracks is established.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of civil engineering research, in particular to a concrete test crack observation method based on fluorescence tracing technology. BACKGROUND

[0002] The occurrence of cracks in concrete structures is an external manifestation of changes in the internal stress state of the structure. By observing the development of cracks, potential safety hazards in the structure can be detected in a timely manner. For example, when the width and length of cracks continue to increase, the carrying capacity of the structure will decrease, and the risk of damage will increase. In terms of durability analysis, the presence of cracks will damage the protective layer of concrete, exposing the steel bars to the external environment. Water, oxygen and harmful substances from the external environment can more easily penetrate into the interior of the concrete, accelerating the corrosion of the steel bars and affecting the durability of the concrete structure. Therefore, observing the development of cracks can help understand the degree and speed of erosion of the concrete structure, so that effective protective measures can be taken.

[0003] Currently, the existing methods for observing microcracks in concrete have limitations. Traditional methods are difficult to achieve real-time tracking of the entire process from crack initiation to propagation, especially in the early detection of microcracks. The measurement accuracy of key parameters such as crack width, length and propagation rate is low, which cannot meet the needs of fine evaluation. Moreover, existing technologies usually separate crack observation from mechanical property testing, making it difficult to establish a direct correlation between crack development and stress-strain relationship, limiting the understanding of the damage mechanism of concrete and ignoring the dynamic development process of cracks and their warning effect on the change of macroscopic mechanical properties.

[0004] Therefore, there is an urgent need to develop an efficient concrete crack observation method that can simultaneously correlate with mechanical properties. The present application introduces fluorescence tracing technology and combines real-time image data from a high-speed camera to achieve dynamic visualization monitoring of concrete cracks and simultaneous analysis of mechanical properties, providing a new technical solution to solve the above problems. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art and provide a concrete test crack observation method based on fluorescence tracing technology. By applying a fluorescent agent to the surface of the concrete specimen, the fluorescent agent can penetrate into the cracks when the specimen is stressed, allowing the use of a violet light lamp to observe the position changes of the fluorescent agent. A high-speed camera can record the entire process of crack propagation and evolution, and the real-time stress-strain curve characteristics can be combined to establish a relationship between macroscopic mechanical parameters and crack propagation during the stress process of concrete.

[0006] To solve the above technical problems, the present application provides the following technical solution: a concrete test crack observation method based on fluorescence tracing technology, the specific steps of which are as follows:

[0007] S100, build a concrete crack tracking detection device integrating fluorescence excitation-ultraviolet development;

[0008] S200, coat the surface of the concrete specimen with a fluorescent tracer, and use a plastic film to separate the surface in contact with the test instrument to prevent the fluorescent tracer from sticking to the instrument when compressed, and also coat the fluorescent agent on the front surface of the specimen;

[0009] S300, carry out mechanical loading test, and record the stress-strain curve of the concrete in real time through the computer during the test, and simultaneously use a high-speed camera to capture high-definition fluorescent images of the crack propagation on the surface of the concrete under the irradiation of the ultraviolet lamp;

[0010] S400, quantitatively process the real-time recorded fluorescent images using Image-ProPlus software, calculate the quantitative parameters of the surface cracks of the concrete, and determine the development of the cracks;

[0011] S500, analyze the corresponding relationship between the stress-strain curve and the crack development parameters, and establish the correlation between the dynamic evolution of the concrete cracks and the dynamic changes of the macroscopic mechanical parameters.

[0012] Further, the additional device of the concrete crack tracking detection device in S100 can be installed on the mechanical instrument of the universal testing machine, the uniaxial compression test device, and the Brazilian split test device.

[0013] Further, the instrument used in the concrete crack tracking detection device in S100 comprises a mechanical test device, a fluorescent tracer, an ultraviolet lamp, a computer, and a high-speed camera.

[0014] The mechanical test device comprises a uniaxial compression device, a Brazilian split test device, a universal testing machine, and each component thereof.

[0015] The fluorescent tracer is sodium fluorescein;

[0016] The ultraviolet lamp displays the distribution of the fluorescent agent on the surface of the concrete by irradiation;

[0017] The computer is used to collect the stress-strain curve characteristics of the concrete during loading;

[0018] The high-speed camera records the dynamic development and expansion of the cracks of the concrete during loading.

[0019] Further, the specific process of S300 is as follows:

[0020] After the concrete specimen coated with the fluorescent agent is installed on the mechanical test device, a load is applied, and the force value signal is transmitted to the computer in real time to generate a continuous stress-strain curve;

[0021] During the loading process, the ultraviolet light is turned on to irradiate the surface of the test piece. When the crack occurs, the fluorescent agent penetrates into the crack and develops under the excitation of ultraviolet light. At the same time, the high-speed camera is started to capture the high-definition fluorescent image sequence of the dynamic expansion of the crack at a fixed angle to the front and upper surface of the test piece;

[0022] The high-speed camera and the computer data acquisition system are activated to ensure that the stress-strain curve and the time stamp of the fluorescent image are synchronized;

[0023] The stress-strain curve data recorded by the computer is stored in real time, and key nodes including the micro-crack origin point, the stress peak value, and the failure point are labeled. The fluorescent image sequence captured by the high-speed camera is recorded, and the crack position, direction, and branch morphology are marked in the developed area.

[0024] Further, the specific process of S400 is:

[0025] The fluorescent image sequence captured by the high-speed camera is imported into the Image-ProPlus software in chronological order, and the image is preprocessed, including removing image noise, correcting fluorescent brightness unevenness, and cropping invalid shooting areas to focus on the crack development area of the test piece surface;

[0026] Each frame of the preprocessed image is subjected to crack identification, the crack boundary is located through the fluorescent brightness difference and morphological characteristics, the crack area and non-crack area are distinguished, and quantitative parameter calculation is performed based on the identification result;

[0027] The obtained quantitative parameters are sorted in chronological order to generate a data set of crack development parameters changing with time, which is input into the computer and labeled corresponding to the key nodes recorded in S300, so as to clearly show the crack development characteristics in different test stages, thereby completely presenting the dynamic development of the concrete surface crack.

[0028] Further, the quantitative parameters include the length, width, area, number, and expansion rate of the concrete surface crack, wherein:

[0029] Crack length: the straight-line distance from the starting point to the ending point along the crack direction;

[0030] Crack width: at least three measurement points are selected at different positions of the crack, and the average value is taken as the width of the crack in the frame image;

[0031] Crack area: the pixel area of the crack area, which is converted into the actual area according to the image scale;

[0032] Crack number: the number of independent cracks in each frame of image is counted, and the main crack and branch crack are distinguished, and the number change is recorded respectively;

[0033] Crack propagation rate: according to the time interval of adjacent two frames of images and the change amount of corresponding crack length, the crack length growth value in unit time is calculated to obtain the propagation rate at different time.

[0034] Further, the specific process of S500 is:

[0035] The stress-strain curve data recorded in S300 and the crack development quantification parameter data set generated in S400 are time axis aligned, taking the initial loading time of the stress-strain curve as zero point, matching the quantification parameters at the same time point, to form a complete space-time correspondence;

[0036] Key nodes are extracted from the stress-strain curve and associated with the dynamic changes of crack quantification parameters, including:

[0037] Microcrack origin point: when the stress reaches 10%-20% of the peak strength, the corresponding crack length first increases, and the crack initiation position is marked;

[0038] Stress peak point: the maximum stress value, corresponding to the maximum crack propagation rate and the rapid increase of crack number;

[0039] Failure point: when the stress decreases to 80% of the peak value, the total crack area reaches 5%-10% of the specimen surface area, and the crack branch morphology is recorded;

[0040] Thus, the whole process characteristic analysis of stress-strain-crack development of concrete in the failure process is obtained.

[0041] Further, the whole process characteristic analysis results are input into the computer, and a dynamic correlation report of the whole process of concrete failure is generated, which includes:

[0042] Characteristic curve: draw the stress-crack propagation rate time series superimposed curve and mark the key nodes;

[0043] Parameter correlation table: summarize the correlation coefficients of crack parameters and mechanical parameters;

[0044] Failure stage division: based on the characteristic analysis results, the failure process is divided into three stages, including microcrack initiation period, stable expansion period and accelerated failure period, wherein the stress is less than 50% of the peak value for the microcrack initiation period, the stress is between 50% and 80% of the peak value for the stable expansion period, and the stress is greater than 80% of the peak value for the accelerated failure period.

[0045] Compared with the prior art, the concrete test crack observation method based on fluorescence tracing technology has the following beneficial effects:

[0046] The present application can directly observe the crack development of the test piece in the process of uniaxial and splitting test of concrete by using fluorescent agent and purple light lamp, and can record the stress-strain curve of the concrete in real time by computer during the process of mechanical loading test, capture the high-definition fluorescent image of the crack expansion on the surface of the concrete in real time by high-speed camera, further quantitatively process the real-time recorded fluorescent image by Image-ProPlus software, obtain the development of the crack on the surface of the concrete, and establish the connection between uniaxial compression and micro-crack, thereby providing guidance and basis for effectively taking protective measures in engineering.

[0047] Other advantages, objects, and features of the application will be set forth in part in the following specification taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art from a consideration of the following specification and drawings, or can be learned from the practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0049] Figure 1 It is a kind of concrete test crack observation method based on fluorescent tracer technology operation flow chart;

[0050] Figure 2 It is the overall structure schematic diagram of the test device in embodiment one;

[0051] Figure 3 It is the fluorescent display effect diagram of fluorescent agent in concrete.

[0052] In the figure: 1, universal testing machine;2, fluorescent agent;3, purple light lamp;4, computer;5, high-speed camera. DETAILED DESCRIPTION

[0053] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the specific embodiments, structures, features and effects according to the present application will be described in detail below in combination with the drawings and preferred embodiments.

[0054] Embodiment one

[0055] The working principle of a concrete test crack observation method based on a fluorescent tracer technology is provided in the embodiment. The method builds a concrete crack tracking detection device integrating fluorescent excitation-ultraviolet development. A fluorescent tracer is coated on the surface of a concrete test piece. The high-definition fluorescent image of crack expansion is captured by using a high-speed camera in combination with a mechanical loading test. Quantitative processing is performed by using an Image-ProPlus software. Finally, the correlation between the dynamic evolution of the concrete crack and the dynamic change of the macro mechanical parameters is established. The accurate observation and analysis of the whole process of the concrete crack from initiation to expansion are realized. A strong basis is provided for in-depth understanding of the concrete failure mechanism and engineering protection.

[0056] Firstly, the test device building stage (S100) is entered. The test system for synchronous fluorescent tracing and mechanical loading is assembled. The instrument and equipment for fluorescent excitation, crack observation and mechanical property test are organically integrated. The concrete crack tracking detection device integrating fluorescent excitation-ultraviolet development is built. It is ensured that the fluorescence can be excited and the crack change and mechanical parameters can be recorded in real time during the stress process of the concrete test piece. The additional device of the concrete crack tracking detection device can be installed on the mechanical instrument of the universal testing machine, uniaxial compression test device or Brazilian splitting test device. A suitable mechanical test device is selected. The universal testing machine 1 is selected as the mechanical loading equipment in the embodiment. Because the universal testing machine can provide stable and various forms of load, the test requirements of the concrete test piece under different stress states are met. The composition of the instrument used in the concrete crack tracking detection device includes the universal testing machine 1, the fluorescent tracer 2, the violet lamp 3, the computer 4 and the high-speed camera 5. The specific process in this stage is as follows. The fluorescent tracer 2 is prepared. Sodium fluorescein is used as the fluorescent tracer 2. This is because sodium fluorescein has good water solubility and fluorescent characteristics. It can emit strong fluorescence under ultraviolet light irradiation. It is easy to penetrate into the concrete crack. It is convenient for subsequent observation. The violet lamp 3 is installed. The violet lamp 3 can uniformly irradiate the surface of the concrete test piece. The violet lamp 3 emits ultraviolet rays. The sodium fluorescein emits fluorescence under the excitation of the ultraviolet rays. Therefore, the distribution of the fluorescent agent on the surface of the concrete can be clearly displayed. This provides the light source basis for subsequent crack observation. The high-speed camera 5 is placed. The high-speed camera 5 is fixed on a tripod. The angle is adjusted. The high-speed camera 5 can be aligned with the front and upper surface of the test piece at a fixed angle. The high-speed camera 5 continuously shoots the image of the concrete test piece in the stress process. Therefore, each detail of the dynamic development and expansion of the crack is recorded. The computer 4 is connected with the universal testing machine 1 and the high-speed camera 5. The computer 4 collects the stress-strain curve characteristics of the concrete in the stress process. The image data transmitted by the high-speed camera 5 is received. The devices are connected through the data line. The stability and real-time performance of the data transmission are ensured. This lays a foundation for subsequent synchronous analysis.

[0057] Then, enter the specimen processing phase (S200), this phase by coating the surface of the concrete specimen fluorescent tracer 2, for subsequent crack when the fluorescent agent penetration and development ready, at the same time, the surface in contact with the test instrument processing, to avoid the fluorescent tracer in the test process adhesion to the instrument affect the test results, the surface of the concrete specimen for cleaning, remove the surface dust, debris and other impurities, to ensure that the specimen surface clean and smooth, so that the fluorescent tracer can be evenly attached to the specimen surface, improve the accuracy of subsequent observation, configure the appropriate amount of fluorescein sodium solution as a fluorescent tracer 2, with a brush evenly coated in the concrete specimen front, coating process to ensure uniform thickness, covering the entire specimen front area, so that the specimen front any position crack can have fluorescent agent penetration, for the specimen surface in contact with the universal testing machine, first coated with a layer of fluorescent tracer 2, then immediately separated by plastic film, to prevent in the test loading process, the specimen and test machine contact surface pressure will fluorescent tracer 2 adhesion to the test machine, thereby contaminating the instrument, resulting in the specimen surface fluorescent tracer 2 reduction, affect the crack observation effect.

[0058] Next, enter the mechanical loading and data acquisition phase (S300), to apply load to the concrete specimen, so that the specimen produces stress and strain, at the same time, under the excitation of ultraviolet light 3, let the fluorescent agent 2 into the crack development, through the high-speed camera 5 and computer 4 synchronous recording crack propagation image and stress-strain curve, so as to obtain real-time data of crack development and mechanical parameters, the specific operation process is: the treated concrete specimen installed in the specified position of the universal testing machine 1, ensure that the specimen is installed firmly, centered, to avoid uneven load distribution due to improper installation, affect the accuracy of the test results, start the universal testing 1, begin to apply load to the specimen, the load application method is determined according to the test purpose, this embodiment uses a hierarchical loading method, gradually increasing the load, in the loading process, the universal testing 1 real-time force value signal transmission to the computer 4, the computer 4 according to the force value and the cross-sectional area of the specimen to calculate the stress, at the same time, according to the deformation of the specimen to calculate the strain, and then generate a continuous stress-strain curve, at the same time, turn on the purple light 3, so that the ultraviolet light 3 continuously irradiate the specimen surface, when the specimen under load produces cracks, due to the negative pressure or capillary action inside the crack, the fluorescent tracer 2 coated on the specimen surface will quickly penetrate into the crack, and the fluorescein sodium will emit fluorescence under the excitation of ultraviolet light, so that the crack is clearly developed under the ultraviolet light, which is convenient for the high-speed camera 5 to capture, to ensure that every moment of crack propagation can be captured, its fluorescent agent display effect is as follows: Figure 3As shown, the high-speed camera 5 is aligned with the front and upper surface of the test piece at a fixed angle, and starts to continuously shoot high-definition fluorescent image sequences of the dynamic crack propagation. The synchronization function of the high-speed camera 5 and the computer 4 data acquisition system is activated, and the time stamp synchronization technology is used to ensure that the stress-strain curve and the fluorescent image are consistent in time. After time synchronization, the crack development parameters and the mechanical parameters can be effectively analyzed. For example, when the stress-strain curve appears a key node, the corresponding fluorescent image can be accurately found, the crack state at this time can be observed, the computer 4 stores the stress-strain curve data in real time, and marks the key nodes on the curve, including the microcrack origin point, the stress peak value, and the failure point. The microcrack origin point refers to the moment when the test piece starts to appear a small crack, at which time the stress usually reaches 10%-20% of the peak strength. The stress peak value refers to the moment when the stress reaches the maximum value, at which time the load-carrying capacity of the test piece reaches the limit. The failure point refers to the moment when the stress drops to 80% of the peak value, at which time the test piece has been seriously damaged. At the same time, the fluorescent image sequences shot by the high-speed camera 5 are also stored in the computer 4 in real time. For the developed area in the image, the position, direction and branching form of the crack are marked, providing original data for subsequent quantitative processing.

[0059] Secondly, enter the image quantitative processing stage (S400), this stage uses Image-ProPlus software to process and analyze the fluorescent image shot by the high-speed camera 5, removes interference factors through preprocessing, identifies the crack and calculates its quantitative parameters, so as to convert the image information into quantifiable data analysis results. The software can process a batch of images to improve the processing efficiency. The imported image is preprocessed, first, remove image noise. Due to the influence of shooting environment, equipment itself and other factors, there may be noise in the image. These noises will interfere with the identification of cracks and correct the uneven phenomenon of fluorescent brightness. Adjust the brightness of the image to make the fluorescent brightness of the specimen surface tend to be uniform. Crop the invalid shooting area. The part of the image that does not belong to the crack development area of the specimen surface is cropped. Focus on the crack area of the specimen surface to reduce the interference of irrelevant information and improve the efficiency and accuracy of subsequent processing. Identify the crack of each frame of preprocessed image. Locate the crack boundary by analyzing the fluorescent brightness difference and morphological characteristics. The crack area has fluorescent agent penetrating, so the fluorescent brightness is usually higher than that of the non-crack area. At the same time, the crack has certain linear or branching morphological characteristics. According to these characteristics, the crack area and the non-crack area can be distinguished. Based on the identification results, the quantitative parameter calculation is carried out, including crack length, width, area, number and expansion rate. The crack length is the straight-line distance from the starting point to the ending point along the crack direction. The starting point and the ending point of the crack are identified, and the straight-line distance is calculated as the crack length. The crack width is the average value of the width of at least three measurement points selected at different positions of the crack. The software measures the width of each point and takes the average value as the width of the crack in the image. Selecting multiple measurement points to take the average value can reduce measurement error and improve the accuracy of width calculation. The crack area is the pixel area of the crack area. The number of pixels in the crack area is counted, and the pixel area is converted into the actual area according to the scale of the image (i.e. the actual length represented by each pixel). The crack number is the number of independent cracks in each frame of image. The main crack and the branch crack are distinguished, and the number change is recorded respectively. The main crack refers to the crack that appears first and has the largest expansion degree. The branch crack is a smaller crack extending from the main crack. Distinguishing between the two helps to analyze the development law of the crack.The crack propagation rate: according to the time interval of two adjacent images and the change of the corresponding crack length, the crack length growth value in unit time is calculated, the time interval is obtained by acquiring the time stamp of two adjacent images, and the length change of the same crack in two images is calculated, and the crack propagation rate in this time period is obtained by dividing the two, and then the propagation rate at different time is obtained, and the obtained quantitative parameters are arranged in time sequence, and a data set of crack development parameters changing with time is generated, which is input into the computer 4, and is marked corresponding to the key nodes recorded in S300, and the crack development characteristics in different test stages are clear, so that the dynamic development of the concrete surface crack is completely presented.

[0060] Finally, enter the data analysis and correlation stage (S500), align the stress-strain curve data and the crack development quantitative parameter data set on the time axis, analyze the corresponding relationship between the two, establish the correlation between the dynamic evolution of concrete cracks and the dynamic change of macro mechanical parameters, and then generate a dynamic correlation report to reveal the failure mechanism of concrete. The stress-strain curve data recorded in S300 and the crack development quantitative parameter data set generated in S400 are imported into the computer 4, with the starting loading time of the stress-strain curve as the zero point, and the stress, strain data and crack quantitative parameters at the same time point are matched through the time stamp to form a complete space-time corresponding relationship data set. Key nodes are extracted from the stress-strain curve and correlated with the dynamic change of crack quantitative parameters:

[0061] Microcrack origin point: when the stress reaches 10%-20% of the peak strength, the crack length first increases, which is marked as the crack initiation position. Through analysis, it is found that in this stage, micro cracks begin to appear in the concrete. Although these cracks are small, they have already begun to affect the stress performance of the concrete. Small changes in stress will lead to the first significant increase in crack length.

[0062] Stress peak point: at the moment when the stress reaches the maximum value, the crack propagation rate reaches the maximum value and the number of cracks increases rapidly. This is because when the stress reaches the peak value, the bearing capacity of the concrete specimen reaches the limit, and the internal cracks begin to expand rapidly, resulting in the maximum crack propagation rate and the rapid increase in the number of cracks.

[0063] Failure point: when the stress drops to 80% of the peak value, the total crack area reaches 5%-10% of the surface area of the specimen, and the crack branching morphology is recorded at this time. In this stage, the concrete specimen has been severely damaged, and the cracks have expanded and interconnected to form a complex crack network. The total crack area reaches a certain proportion, and the mechanical properties of the specimen decrease significantly.

[0064] According to the correlation analysis results, a dynamic correlation report of the whole process of concrete failure is generated, including:

[0065] Characteristic curve diagram: draw the stress-crack propagation rate time series superimposed curve, mark the microcrack origin point, stress peak point, failure point and other key event nodes on the curve, through the curve diagram, the change relationship of stress and crack propagation rate in time can be directly observed, and the mutual influence of the two in different stages can be clearly understood.

[0066] Parameter correlation table: summarize the correlation coefficients of crack parameters (such as length, width, area, number, propagation rate) and mechanical parameters (such as stress, strain), the correlation coefficient can quantitatively represent the correlation between the two, a positive correlation coefficient indicates that the change trends of the two are consistent, a negative correlation coefficient indicates that the change trends of the two are opposite, and the closer the absolute value of the correlation coefficient is to 1, the stronger the correlation is.

[0067] Failure stage division: based on the characteristic analysis results, the failure process is divided into three stages, including microcrack initiation period, stable expansion period and accelerated failure period, wherein the stress is less than 50% of the peak value in the microcrack initiation period, in this stage, a small amount of cracks begin to initiate and expand slowly; the stress is in the range of 50%-80% of the peak value in the stable expansion period, the cracks expand at a relatively stable speed and the number gradually increases; the stress is greater than 80% of the peak value in the accelerated failure period, the crack expansion speed increases rapidly and the number increases rapidly until the specimen fails.

[0068] In summary, by building an integrated test device, the concrete specimen is reasonably processed, the stress-strain data and crack fluorescence image are synchronously collected during the mechanical loading process, and through quantitative processing and correlation analysis, the precise observation of the whole process of concrete crack from initiation to expansion is realized, and the close correlation between crack dynamic evolution and macro mechanical parameters is established. This method not only can clearly capture the subtle changes of cracks and improve the accuracy and timeliness of crack observation, but also can deeply reveal the failure mechanism of concrete, providing important test basis and technical support for the design, construction and maintenance of concrete structure.

[0069] Embodiment Two

[0070] As shown in the Figure 1 , the embodiment provides a concrete test crack observation method based on fluorescence tracing technology, and the working process of the concrete test crack observation method is as follows:

[0071] (1) Build a test device

[0072] Prepare a mechanical test device (such as a universal testing machine, a uniaxial compression device, etc.), a fluorescence tracer (fluorescein sodium), a purple light lamp, a computer and a high-speed camera.

[0073] Install the additional device of the crack tracking detection device to the selected mechanical instrument.

[0074] Connect the computer with the mechanical testing device and the high-speed camera to ensure normal communication between the devices.

[0075] (2) Processing of concrete specimens

[0076] Apply sodium fluorescein to the surface of the concrete specimen, both the front and the top surface.

[0077] For the specimen surface in contact with the testing instrument, use plastic film to separate it.

[0078] (3) Conducting mechanical loading tests

[0079] Install the specimen coated with fluorescent agent to the mechanical testing device.

[0080] Turn on the computer data acquisition system and set the parameters to record the stress-strain curve.

[0081] Apply load to the specimen and transmit the force value signal to the computer in real time to generate a continuous stress-strain curve.

[0082] Turn on the ultraviolet light and shine it on the surface of the specimen coated with fluorescent agent.

[0083] Start the high-speed camera and aim it at the front and top surface of the specimen at a fixed angle.

[0084] Synchronize the high-speed camera and the computer data acquisition system to ensure that the timestamps of the stress-strain curve and the fluorescent image are consistent.

[0085] Store the stress-strain curve data in real time and mark the key nodes such as the origin of microcracks, stress peak, and failure point.

[0086] Store the fluorescent image sequence taken by the high-speed camera in real time and mark the crack location, direction, and branching morphology.

[0087] (4) Processing of fluorescent images and calculation of parameters

[0088] Import the fluorescent image sequence into the Image-ProPlus software in chronological order.

[0089] Preprocess the images, including removing noise, correcting uneven fluorescent brightness, and cropping invalid areas.

[0090] Identify cracks in each preprocessed image based on the difference in fluorescent brightness and morphological features to locate the crack boundaries.

[0091] Calculate quantitative parameters (length, width, area, number, and expansion rate) based on the identification results.

[0092] The quantitative parameters are arranged in chronological order to generate a time-varying data set, which is input into a computer.

[0093] The data set is marked with key nodes of the stress-strain curve to determine the crack development characteristics in different stages.

[0094] (5) Analysis of correlation

[0095] The stress-strain curve data and the crack development parameter data set are aligned on the time axis to match the parameters at the same time point.

[0096] The key nodes of the stress-strain curve are extracted and correlated with the dynamic changes of the crack parameters (such as the micro-crack origin point corresponding to the first sudden increase point of crack length).

[0097] A dynamic correlation report is generated, including characteristic curve graphs, parameter correlation tables, and damage stage division (micro-crack initiation period, stable expansion period, and accelerated damage period).

[0098] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with a preferred embodiment, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the present application, and any equivalent embodiments with equivalent changes are also within the scope of the present application. Any modification, change, or modification of the above embodiments, which does not depart from the technical essence of the present application, is still within the scope of the present application.

Claims

1. A method for observing a test crack of concrete based on a fluorescent tracer technique, characterized by, The specific steps of the method are: S100, build an integrated fluorescence excitation-ultraviolet development concrete crack tracking detection device; S200, coat the surface of the concrete specimen with a fluorescent tracer, and use a plastic film to separate the surface in contact with the testing instrument to prevent the fluorescent tracer from sticking to the instrument during compression. Also coat the front surface of the specimen with a fluorescent agent; S300, conduct a mechanical loading test. During the test, record the stress-strain curve of the concrete in real time through the computer, and use a high-speed camera to capture high-definition fluorescent images of the crack propagation on the surface of the concrete under ultraviolet light irradiation in real time; S400, use Image-ProPlus software to quantitatively process the real-time recorded fluorescent images to calculate the quantitative parameters of the surface cracks of the concrete and determine the development of the cracks; S500, analyze the corresponding relationship between the stress-strain curve and the crack development parameters to establish the correlation between the dynamic evolution of the concrete cracks and the dynamic changes of the macroscopic mechanical parameters.

2. The method according to claim 1, wherein The additional device of the concrete crack tracking detection device in S100 can be installed on a universal testing machine, a uniaxial compression testing device, or a Brazilian split testing device.

3. The method according to claim 1, wherein the method is characterized by, The instrument used in the concrete crack tracking detection device in S100 consists of a mechanical testing device, a fluorescent tracer, an ultraviolet light, a computer, and a high-speed camera. The mechanical testing device includes a uniaxial compression device, a Brazilian split testing device, a universal testing machine, and their respective components. The fluorescent tracer is sodium fluorescein. The ultraviolet light displays the distribution of the fluorescent agent on the surface of the concrete through irradiation. The computer is used to collect the stress-strain curve characteristics of the concrete during loading. The high-speed camera records the dynamic development and expansion of the cracks in the concrete during loading.

4. The method of claim 1, wherein the method is based on a fluorescent tracer technique. The specific process of S300 is: After the fluorescent agent-coated concrete specimen is installed on the mechanical testing device, apply a load and transmit the force value signal to the computer in real time to generate a continuous stress-strain curve; During the loading process, turn on the ultraviolet light to irradiate the specimen surface. When cracks occur, the fluorescent agent penetrates into the cracks and develops under ultraviolet excitation. At the same time, start the high-speed camera to capture high-definition fluorescent image sequences of the dynamic expansion of the cracks at a fixed angle on the front and upper surfaces of the specimen; Activate the high-speed camera and the computer data acquisition system to ensure that the timestamps of the stress-strain curve and the fluorescent images are synchronized; Store the stress-strain curve data recorded by the computer in real time, label the key nodes, which include the microcrack origin point, the stress peak value, and the failure point, and record the fluorescent image sequences captured by the high-speed camera. The development area marks the crack position, direction, and branch morphology.

5. The method of claim 1, wherein the method is based on a fluorescent tracer technique. The specific process of S400 is: Import the fluorescent image sequences captured by the high-speed camera into the Image-ProPlus software in chronological order, and preprocess the images, including removing image noise, correcting the uneven fluorescence brightness, and cropping the invalid shooting area to focus on the crack development area on the surface of the specimen; S500. Quantitative analysis of crack development S400. Quantitative analysis of crack development 6. The method according to claim 5, wherein the method is characterized by, The quantitative parameters include the length, width, area, number and expansion rate of the cracks on the concrete surface, wherein: Crack length: the straight-line distance from the starting point to the ending point along the crack direction; Crack width: at least three measurement points are selected at different positions of the crack, and the average value is taken as the width of the crack in the frame image; Crack area: the pixel area of the crack region, which is converted into the actual area according to the image scale; Crack number: the number of independent cracks in each frame image is counted, and the main cracks and branch cracks are distinguished, and the number changes are recorded respectively; Crack expansion rate: according to the time interval of adjacent two frames of images and the change amount of the corresponding crack length, the crack length growth value per unit time is calculated, and the expansion rate at different times is obtained.

7. The method of claim 1, wherein the method is based on a fluorescent tracer technique. The specific process of S500 is as follows: The stress-strain curve data recorded in S300 and the crack development quantitative parameter data set generated in S400 are time axis aligned, taking the starting loading time of the stress-strain curve as the zero point, matching the quantitative parameters at the same time point, forming a complete space-time correspondence; The key nodes are extracted from the stress-strain curve and associated with the dynamic changes of the crack quantitative parameters, including: Micro-crack origin point: when the stress reaches 10%-20% of the peak strength, the first point of crack length sudden increase is marked as the crack initiation position; Stress peak point: the maximum stress point, corresponding to the maximum crack expansion rate and the stage of rapid increase of crack number; Failure point: when the stress decreases to 80% of the peak value, the total crack area reaches 5%-10% of the surface area of the specimen, and the crack branch morphology is recorded. Thus, the whole process characteristic analysis of stress-strain-crack development of concrete in the failure process is obtained.

8. The method according to claim 7, wherein the method is characterized by, The whole process characteristic analysis result is input into the computer, and a dynamic correlation report of the whole process of concrete failure is generated, which includes: Characteristic curve diagram: draw the stress-crack expansion rate time series superimposed curve and mark the key nodes; Parameter correlation table: summarize the correlation coefficients of crack parameters and mechanical parameters; Damage stage division: based on the characteristic analysis result, the failure process is divided into three stages, including micro-crack initiation period, stable expansion period and accelerated failure period, wherein stress < 50% peak value is micro-crack initiation period, stress is 50%-80% of peak value is stable expansion period, and stress > 80% of peak value is accelerated failure period.

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