An optical fiber sensor for monitoring the aging and shedding of coatings on steel structures

Abstract

The present invention provides an optical fiber sensor for monitoring the aging and shedding of steel structure coatings, belonging to the technical field of structural health monitoring. The sensor includes a flexible film; a single-mode optical fiber: a core, a cladding, and a coating layer; and an iron film. Based on the high sensitivity of the side-polished optical fiber to the refractive index of the external environment and the iron film having a main component similar to that of carbon steel, the device realizes non-destructive, online real-time, and quantitative monitoring of the aging and shedding state of the steel structure coating, and more accurately determines whether the steel structure is corroded and the degree of corrosion, thereby ensuring the safety of major and important structures. The present invention has a simple structure, reasonable design, strong applicability, high sensitivity, and strong reliability, and has broad application prospects and promotion markets.

Description

Technical Field

[0001] The invention relates to an optical fiber sensor for monitoring aging and shedding of steel structure coatings, belonging to the technical field of structural health monitoring. Background Art

[0002] Steel is widely used in the field of civil engineering due to its advantages such as good plasticity and toughness, high strength, good seismic performance and convenient manufacturing. It is one of the most widely used civil engineering materials in the world today. Anti-corrosion and fire prevention of steel structures are key links in the design and construction of steel structures, and steel structure coating is an effective way to extend the service life of steel structures. Therefore, it is necessary to monitor the aging and shedding of steel structure coatings and grasp the status of steel structure coatings, which provides an important basis for the assessment of the degree of corrosion, durability assessment and remaining life prediction of steel structures.

[0003] At present, there are several methods for monitoring coating shedding, such as visual method, interdigital electrode method, resistance probe method, electrochemical impedance spectroscopy method, etc. However, the above monitoring methods have some problems to a greater or lesser extent: the visual method is labor-intensive and cannot monitor in real time; the interdigital electrode sensor is mainly used for monitoring the status of metal coatings, but is insufficient for monitoring organic coatings; the resistance sensor cannot monitor the early stage of coating degradation and is affected by temperature fluctuations; and the electrochemical impedance spectroscopy method is mainly limited to laboratory use.

[0004] In recent years, due to the advantages of optical fiber, such as small size, light weight, anti-electromagnetic interference, and networking, some sensors based on optical fiber sensing technology have also been applied in the field of corrosion monitoring. Compared with ordinary optical fiber sensing technology, side-polished optical fiber sensors are highly sensitive to the refractive index of the external environment, and are better suited for monitoring the shedding of coatings on steel structures, and are applicable to both metal coatings and organic coatings.

[0005] Therefore, for the monitoring of the coating shedding condition of steel structures, it is very necessary to provide a side-polished optical fiber sensor that is highly sensitive, accurate and reliable to the coating shedding state based on the high sensitivity of the side-polished optical fiber to the refractive index of the external environment, thereby providing an important basis for evaluating the performance of steel structure coatings. Summary of the invention

[0006] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a fiber optic sensor for aging and shedding of steel structure coatings, with the purpose of realizing non-destructive, online real-time and quantitative monitoring of the aging and shedding status of steel structure coatings, accurately indicating the time to repair the coating, thereby reducing the occurrence of steel structure corrosion caused by aging and shedding of steel structure coatings, and ensuring the safety of major and important engineering structures.

[0007] The present invention adopts the following technical solution:

[0008] An optical fiber sensor for monitoring aging and shedding of steel structure coatings comprises a flexible sheet 1, a single-mode optical fiber 2 and an iron film 3; wherein the single-mode optical fiber 2 comprises a core 4, a cladding 5 and a coating 6;

[0009] A rectangular groove is polished in the middle of the flexible sheet 1 along the width direction;

[0010] The single-mode optical fiber 2 is completely wrapped by the flexible sheet 1 within its length;

[0011] A part of the cladding 5 of the single-mode optical fiber 2 is polished off on one side of the groove position of the flexible sheet 1 . This area is the polished area. The polished area is covered by the iron film 3 , and the non-polished area is wrapped by the flexible sheet 1 .

[0012] The size of the flexible sheet 1 is adjusted according to the requirements of the monitored object and service life;

[0013] The length of the single-mode optical fiber 2 is adjusted according to the requirements of the monitored object and the sensitivity of the sensor;

[0014] The polishing degree of the single-mode optical fiber 2 is adjusted according to the requirements of the monitored object and the sensitivity of the sensor;

[0015] The thickness of the iron film 3 in the polished area of ​​the single-mode optical fiber 2 is adjusted according to the sensor sensitivity requirements.

[0016] Working principle of the present invention:

[0017] The principle of the side-polished fiber sensor is shown in Figure 5. In a conventional single-mode fiber, the amplitude of the evanescent wave decays exponentially, and the interacting light and acoustic fields are almost completely confined within the fiber material, so the Brillouin frequency shift (BFS) is not affected by the ambient refractive index. However, after removing the cladding, the evanescent wave increases, and the light field can interact with the external medium through its evanescent field. In this case, the refractive index of the external medium affects the effective refractive index n eff , thus affecting the Brillouin frequency shift through equation (1).

[0018]

[0019] Where BFS is the Brillouin frequency shift, n eff V is the effective refractive index. a is the speed of sound in glass and λ is the wavelength.

[0020] Because the main component of steel is iron, the polished area of ​​the side-polished optical fiber is plated with an iron film. When the coating on the surface of the iron film ages and falls off, the iron film rusts when exposed to air, and the refractive index of the medium around the side-polished optical fiber changes, and the effective refractive index of the optical fiber n effTherefore, a change occurs, causing the Brillouin frequency shift to change from BFS to BFS′. The change in Brillouin frequency shift is ΔBFS, that is,

[0021] ΔBFS=BFS-BFS'(2)

[0022] The relationship between the coating mass loss percentage η caused by coating aging and shedding and the Brillouin frequency shift change ΔBFS can be expressed by the following formula:

[0023] ΔBFS=β(η)(3)

[0024] Where β is the functional relationship between the coating mass loss percentage η and the Brillouin frequency shift change ΔBFS, which is determined by experimental fitting.

[0025] Therefore, the steel structure coating aging and shedding monitoring sensor is arranged on the surface of the steel structure. By measuring the change in Brillouin frequency shift ΔBFS, and then obtaining the coating mass loss percentage according to formula (3), the quantitative monitoring of the coating aging and shedding state can be achieved. Because the properties of the iron film and the steel structure are similar, the bonding performance of the coating and the steel structure is similar to the bonding performance of the iron film and the coating. By measuring the mass loss rate of the coating on the iron film, the quantitative monitoring of the aging and shedding state of the tested steel structure coating is also achieved.

[0026] Beneficial effects of the present invention:

[0027] (1) The present invention realizes quantitative monitoring of the coating shedding state by monitoring the change in the Brillouin frequency shift of the side-polished optical fiber;

[0028] (2) The present invention has high sensitivity and uses side-polished optical fiber to enhance the sensitivity of the Brillouin frequency shift to the refractive index of the surrounding medium;

[0029] (3) The present invention is easy to deploy and can realize online real-time monitoring of the coating aging and shedding state;

[0030] (4) The present invention can realize non-destructive monitoring, can non-destructively monitor the aging and shedding state of the steel structure coating, and repair the coating in time, thereby avoiding corrosion damage to the steel structure caused by coating shedding;

[0031] (5) The present invention has good environmental adaptability and long service life;

[0032] (6) The present invention has strong applicability and is applicable to both metal coatings and organic coatings.

[0033] (7) The present invention can monitor many parameters. After fitting the relationship between the change in Brillouin frequency shift and the percentage of mass loss of the iron film due to corrosion through experiments, the corrosion state of the steel structure can be monitored while monitoring the aging and shedding state of the steel structure coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the structure of the optical fiber sensor for aging and shedding of coating on steel structure according to the present invention;

[0035] Figure 2 It is a top view of the optical fiber sensor for aging and shedding of coating on steel structure according to the present invention;

[0036] Figure 3 It is a cross-sectional view of the AA section of the optical fiber sensor for aging and shedding of coating on steel structure according to the present invention;

[0037] Figure 4 It is a cross-sectional view of a side-polished optical fiber used for an optical fiber sensor for aging and shedding of coating on a steel structure according to the present invention;

[0038] FIG5 is a schematic diagram of the optical fiber sensor for sensing aging and shedding of coating on steel structures according to the present invention; (a) is before the coating shedding, and (b) is after the coating shedding;

[0039] Figure 6 It is a schematic diagram of the arrangement of the optical fiber sensor for aging and shedding of coating on steel structure according to the present invention;

[0040] In the figure: 1 flexible sheet; 2 single-mode optical fiber; 3 iron film; 4 fiber core; 5 cladding; 6 coating layer. DETAILED DESCRIPTION

[0041] In order to make the purpose, features and advantages of the present invention more intuitive and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] like Figures 1 to 4 As shown, an example of a sensor for monitoring the aging and shedding of coatings on steel structures provided by the present invention includes an epoxy resin flexible sheet 1, a single-mode optical fiber 2, an iron film 3, a core 4, a cladding 5, and a coating layer 6.

[0043] A rectangular groove is polished in the middle of the flexible sheet 1 along the width direction;

[0044] The single-mode optical fiber 2 is completely wrapped by the flexible sheet 1 within its length;

[0045] A part of the cladding 6 of the single-mode optical fiber 2 is polished off on one side of the groove position of the flexible sheet 1 . This area is the polished area. The polished area is covered by the iron film 3 , and the non-polished area is wrapped by the flexible sheet 1 .

[0046] Furthermore, the material of the flexible sheet 1 is selected as epoxy resin;

[0047] Furthermore, the size of the flexible sheet 1 is 10 cm×8 cm×1 cm;

[0048] Further, the refractive index of the single-mode optical fiber 2 is 1.468;

[0049] Further, the length of the polishing area is 3 cm;

[0050] Furthermore, the diameter of the core 4 is 9 μm, the diameter of the cladding 5 is 125 μm, and the diameter of the coating layer 6 is 255 μm;

[0051] Furthermore, the iron film 3 has a thickness of 0.3 μm and covers the entire surface of the groove.

[0052] When monitoring is performed, the sensor is first bonded to the surface of the steel structure by epoxy resin glue or adhesive, and then the steel structure and the sensor are coated as a whole.

[0053] When the steel structure in the actual project has been coated, firstly, the same coating as the steel structure is applied to the iron film 3 of the sensor, and then the sensor is bonded to the surface of the steel structure by double-sided tape, glue, etc.

[0054] In an embodiment of the present invention, a method for preparing an optical fiber sensor for monitoring aging and shedding of a steel structure coating comprises the optical fiber sensor for monitoring aging and shedding of a steel structure coating as described in any one of the above, and comprises the following steps:

[0055] Step S1: Perform preparatory work such as cleaning, drying, and applying a release agent to the mold;

[0056] Step S2: Place the single-mode optical fiber flatly into the mold, fix it with a clamp, and straighten it;

[0057] Step S3: Mix the epoxy resin and the curing agent, pour them into the mold, and wait for them to cure;

[0058] Step S4: grinding a groove of appropriate size in the center of the epoxy resin sheet along the width direction using a grinding and polishing machine;

[0059] Step S5: Clean the surface of the groove by washing with distilled water using an ultrasonic cleaner for 3 minutes and drying in an oven at 70° C. for 5 minutes;

[0060] Step S6: using a radio frequency magnetron sputtering system (Denton Vacuum Discovery-18), a Fe target (produced by Kurt J. Lesker) with a purity of 99.99%, a diameter of 76.2 mm, and a thickness of 6.35 mm is used to perform sputtering deposition coating on the cleaned groove, and the surface of the non-groove part is covered with a plastic film during coating;

[0061] Furthermore, the iron target was pretreated for 30 minutes before the shutter between the iron target and the object to be coated was opened; the iron film deposition was completed at a power of 100 W, and the basic pressure of the deposition chamber before sputtering of the system was about 10 -4 Pa, while during sputtering the deposition chamber is filled with 40 cubic centimeters of flowing high-purity argon gas, and the working pressure is about 1Pa.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An optical fiber sensor for monitoring aging and shedding of steel structure coating, characterized in that: The optical fiber sensor comprises a flexible thin sheet (1), a single-mode optical fiber (2) and an iron film (3); wherein the single-mode optical fiber (2) comprises a core (4), a cladding (5) and a coating layer (6); A rectangular groove is ground into a middle portion of the flexible sheet (1) along the width direction; The single-mode optical fiber (2) is completely wrapped by the flexible sheet (1) within its length; A portion of the cladding (5) of the single-mode optical fiber (2) is polished off on one side of the groove position of the flexible sheet (1), and the area is a polished area. The polished area is covered by the iron film (3), and the non-polished area is wrapped by the flexible sheet (1); The length of the single-mode optical fiber (2) is adjusted according to the requirements of the monitored object and the sensitivity of the sensor; the polishing degree of the single-mode optical fiber (2) is adjusted according to the requirements of the monitored object and the sensitivity of the sensor; the thickness of the iron film (3) in the polishing area of ​​the single-mode optical fiber (2) is adjusted according to the sensitivity of the sensor; The refractive index of the external medium affects the effective refractive index n eff , thus affecting the Brillouin frequency shift through equation (1); Where BFS is the Brillouin frequency shift, n eff V is the effective refractive index. a is the speed of sound in glass, λ is the wavelength; The Brillouin frequency shift caused by the corrosion of the iron film changes from BFS to BFS′, and the change in the Brillouin frequency shift is ΔBFS, that is, ΔBFS=BFS-BFS'(2) The relationship between the coating mass loss percentage η caused by coating aging and shedding on the surface of the iron film and the Brillouin frequency shift change ΔBFS is expressed by the following formula: ΔBFS=β(η)(3) Where β is the functional relationship between the coating mass loss percentage η and the Brillouin frequency shift change ΔBFS, which is determined by experimental fitting.

2. The optical fiber sensor for monitoring aging and shedding of steel structure coating according to claim 1 is characterized in that: The size of the flexible sheet (1) is adjusted according to the requirements of the monitored object and service life.

Images