CN211235458U - Iron-carbon coated long-period fiber grating sensor for monitoring corrosion of steel bars - Google Patents
Iron-carbon coated long-period fiber grating sensor for monitoring corrosion of steel bars Download PDFInfo
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- CN211235458U CN211235458U CN201922135797.7U CN201922135797U CN211235458U CN 211235458 U CN211235458 U CN 211235458U CN 201922135797 U CN201922135797 U CN 201922135797U CN 211235458 U CN211235458 U CN 211235458U
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Abstract
The utility model provides an iron carbon coating film long period fiber grating sensor for monitoring of corrosion of steel bars belongs to structure health monitoring technical field. The iron-carbon coated long-period fiber grating sensor for monitoring the corrosion of the steel bars comprises a long-period grating, a fiber core, a cladding, a buffer coating layer, a conductive film and an iron-carbon film. The device realizes nondestructive, online real-time and quantitative monitoring of the corrosion condition of the concrete structure steel bar and accurately judges the durability of the concrete structure based on the high sensitivity of the long-period fiber grating to the refractive index of the external environment and the iron-carbon film with the same main component as carbon steel, thereby ensuring the safety of important structures. The utility model has the advantages of simple structure and reasonable design, the suitability is strong, and sensitivity is high, and the good reliability has wide application prospect and popularization market.
Description
Technical Field
The utility model relates to an iron carbon coating film long period fiber grating sensor for concrete structure steel bar corrosion monitoring belongs to structural health monitoring technical field, especially an iron carbon coating film long period fiber grating sensor for steel bar corrosion monitoring.
Background
The concrete structure is widely applied to civil engineering construction because the concrete structure fully exerts two mechanical properties of high tensile strength of the steel bar and high compressive strength of the concrete, and is the civil engineering material which is most applied in the world at present. However, for concrete structures in marine environments such as harbor works, docks, coastal highway bridges, sea-crossing bridges, and other coastal construction works, steel reinforcement corrosion is one of the important factors for durability failure of concrete structures. Therefore, the corrosion condition of the steel bars of the structure must be effectively monitored, the actual damage degree of the structure is grasped in real time, and important basis is provided for the durability evaluation of the structure, the residual life prediction and the reinforcement maintenance.
At present, the method for monitoring the corrosion of the steel bar can be roughly divided into an electrochemical method and a non-electrochemical method. Among them, the electrochemical methods include a half-cell potential method, a linear polarization method, an alternating current impedance method, an electrochemical noise method, and the like, and the non-electrochemical methods include an apparent inspection method, a weight loss method, an ultrasonic method, an eddy current method, an acoustic emission method, and the like. However, most of the above monitoring methods have the problems of inconvenient operation, complex monitoring process, long monitoring execution time, low monitoring accuracy and the like.
In recent years, due to the advantages of small and light optical fibers, electromagnetic interference resistance, networking capability and the like, some sensors based on the optical fiber sensing technology are also used for monitoring corrosion of reinforcing steel bars. Compared with the common optical fiber sensing technology, the long-period optical fiber grating has high sensitivity to the refractive index of the external environment, and is better suitable for monitoring the corrosion of the steel bars in the concrete.
Therefore, aiming at the monitoring of the corrosion condition of the steel bar, based on the high sensitivity of the long-period fiber grating to the refractive index of the external environment, it is necessary to provide an anti-interference, highly sensitive, accurate and reliable long-period fiber grating sensor to the corrosion state of the steel bar, thereby providing an important basis for the durability life prediction of the concrete structure.
SUMMERY OF THE UTILITY MODEL
The technical problem to be solved by the utility model is to provide an iron carbon coating film long period fiber grating sensor for monitoring of steel bar corrosion, its purpose is to realize the harmless, real-time, quantitative monitoring of online to concrete structure steel bar corrosion situation, accurately judges concrete structure durability to ensure the safety of great important engineering structure.
The technical scheme of the utility model:
a long-period fiber grating sensor of iron-carbon coating film for monitoring the corrosion of steel bars comprises a long-period grating 1, a fiber core 2, a cladding 3, a buffer coating layer 4, a conductive film 5 and an iron-carbon film 6;
the fiber core 2, the cladding 3, the buffer coating layer 4, the conductive film 5 and the iron-carbon film 6 are all cylindrical mediums;
the long period grating 1 is written into the middle local position of the fiber core 2;
the outer side of the fiber core 2 is a cladding 3, the outer sides of two ends of the cladding 3 are buffer coating layers 4, the outer side of the middle part of the cladding is a conductive film 5, and the outer side of the conductive film 5 is an iron-carbon film 6.
The long-period grating 1 is a one-dimensional grating with a one-dimensional periodic structure, and the period and the total length of the grating are adjusted according to the size of a detection object.
The refractive index of the core 2 is greater than that of the cladding 3.
The conductive film 5 is formed by depositing a conductive material, and the conductive material is graphene, silver or gold.
The thicknesses of the conductive film 5 and the iron-carbon film 6 are adjusted according to the sensitivity requirement of the sensor.
The utility model discloses the theory of operation:
long-period fiber gratings are distributed structures with periodic modulation of the refractive index of the core, which causes propagation in the fundamental mode of the coreThe impinging light couples with the co-propagating cladding modes, producing a series of attenuation bands in the transmission spectrum due to absorption and scattering. Resonance wavelength λ of attenuation bandresDepends on the grating period and the refractive indices of the core, cladding and surrounding medium and is given by:
in the formula, ncore(lambda) is the effective refractive index of the fundamental core mode at wavelength lambda,
the effective refractive index of the ith-order cladding mode, Λ is the grating period;
is the core refractive index n1Refractive index n of the cladding2And its surrounding medium refractive index n3As a function of (c).
Thus, the resonance wavelength λresRefractive index n of medium surrounding grating3Is changed.
An iron carbon film electroplated on the outside of the long period grating was used to simulate the composition of mild steel widely used in reinforced concrete structures. When the iron carbon film is corroded, the refractive index of the medium around the grating is n3Become n'3Resulting in a change in the transmission spectrum from λ, the resonance wavelength in the transmission spectrumresBecomes lambda'res。
The change amount of the resonance wavelength is
Namely, it is
Iron carbon film mass loss percentage η and resonance wavelength change caused by corrosion
Can be represented by the following formula:
wherein β is the change between the mass loss percentage η of the Fe-C film and the resonance wavelength
The linear relation coefficient of (a) is determined by experimental fitting.
Therefore, the iron-carbon coated long-period fiber grating sensor is arranged around the steel bar in the concrete structure, and the change amount of the resonance wavelength of the iron-carbon coated long-period fiber grating sensor is measured
And obtaining the mass loss percentage η of the iron-carbon film according to the relation (3), so that the quantitative monitoring of the corrosion state of the iron-carbon film can be realized, and the quantitative monitoring of the corrosion state of the measured steel bar can be realized because the iron-carbon film and the steel bar in the concrete structure have the same components.
The utility model has the advantages that:
(1) the utility model discloses a monitoring long period fiber grating transmission spectrum resonance wavelength's change realizes the quantitative monitoring to the reinforcing bar corrosion degree.
(2) The utility model discloses sensitivity is high, makes highly sensitive to the reinforcing bar corrosion state because of the high sensitivity to external environment refracting index.
(3) The utility model discloses it is convenient to lay, can realize the online real-time supervision to the steel bar corrosion state.
(4) The utility model discloses have high resolution ratio, can reach nanometer or sub-nanometer magnitude.
(5) The utility model discloses can realize the nondestructive monitoring, monitoring concrete structure's that can be harmless reinforcement corrosion situation to implement better management and maintenance to the engineering structure.
(6) The utility model discloses the monitoring is fast, and the precision is high, provides theoretical foundation and test data support for engineering structure durability life-span prediction.
(7) The utility model discloses environmental suitability is good, long service life.
(8) The utility model has the advantages of simple structure and reasonable design, the suitability is strong, has wide application prospect and popularization market.
Drawings
FIG. 1 is a schematic structural diagram of an iron-carbon coated long-period fiber grating sensor for monitoring corrosion of steel bars according to the present invention;
FIG. 2 is a sectional view of the cross section A-A of the long-period fiber grating sensor for monitoring corrosion of steel bars;
FIG. 3 is a cross-sectional view of the cross-section B-B of the long-period fiber grating sensor for monitoring corrosion of steel bars;
fig. 4 is a schematic layout diagram of the long-period fiber grating sensor for monitoring corrosion of steel bars, which is applied to monitoring of steel bars in an actual concrete structure, according to the present invention;
FIG. 5 is a schematic diagram of a sensing mechanism of a long-period fiber grating sensor coated with iron carbon before the iron carbon film is corroded;
FIG. 6 is a schematic diagram of a sensing mechanism of a long-period fiber grating sensor coated with iron-carbon film after the iron-carbon film is corroded.
In the figure: 1, long period grating; 2 a fiber core; 3, cladding; 4, buffering a coating layer; 5 a conductive film; 6 iron carbon film.
Detailed Description
In order to make the objects, features and advantages of the present invention more obvious and understandable, the drawings in the embodiments of the present invention are combined below to clearly and completely describe the technical solutions in the embodiments of the present invention, and obviously, the embodiments described below are only some embodiments of the present invention, but not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative efforts belong to the protection scope of the present invention.
As shown in fig. 1-3, the present invention provides an embodiment of an iron-carbon coated long-period fiber grating sensor for monitoring corrosion of steel bars, which includes a long-period grating 1, a fiber core 2, a cladding 3, a buffer coating layer 4, a conductive film 5, and an iron-carbon film 6;
the fiber core 2, the cladding 3, the buffer coating layer 4, the conductive film 5 and the iron-carbon film 6 are all cylindrical mediums;
the long-period grating 1 is written into the middle local position of the fiber core 2;
the outer side of the fiber core 2 is provided with a cladding 3, the outer sides of two ends of the cladding 3 are provided with buffer coating layers 4, the outer side of the middle part of the cladding 3 is provided with a conductive film 5, and the outer side of the conductive film 5 is provided with an iron-carbon film 6; the conductive film 5 is a silver film;
the period of the long-period grating 1 is 386.9 μm, and the total length is 40 mm;
the diameter of the fiber core 2 is 8.2 μm, the diameter of the cladding 3 is 125 μm, and the diameter of the buffer coating layer 4 is 245 μm;
the refractive index of the fiber core 2 is 1.469, and the refractive index of the cladding 3 is 1.463;
the thickness of the silver film is 800nm, the thickness of the iron-carbon film 6 is 20 microns, and the lengths of the silver film and the iron-carbon film 6 are both 10 cm;
in the embodiment of the present invention, a method for manufacturing an iron-carbon coated long-period fiber grating sensor for monitoring corrosion of steel bars, including any one of the above-mentioned iron-carbon coated long-period fiber grating sensor for monitoring corrosion of steel bars, includes the following steps:
step S1: doping a segment with GeO2The single mode optical fiber (Corning SMF-28e fiber) of (1) was stripped of a 10 cm-long buffer coating at a central part of the fiber by using a fiber stripper.
Step S2: the stripped fiber was placed on a moving platform (model number Newport PM500) with a resolution of 100 nm.
Step S3: by using CO2The laser beam emitted by the laser is focused by a cylindrical lens with the focal length of 50mm to formA narrow line segment perpendicular to the fiber axis, having a length of about 2mm and a width of about 100 μm, is moved by the motion stage under computer control to contact the CO2The laser moves coordinately, and long period grating is written into the position of the optical fiber stripped with 10cm long buffer coating point by point;
further, CO2The output power of the laser was about 7.8W, and a broadband light source (BBS, Agilent 83437) and an optical spectrum analyzer (OSA, Yokogawa AQ6319) were used together to ensure a transmitted spectral intensity loss of greater than 20dB during the long period grating fabrication process.
Step S4: the optical fiber after the long period grating was written was cleaned with a 20% NaOH solution for 10 minutes to remove contaminants attached to the surface thereof, then cleaned with distilled water for 3 minutes using an ultrasonic cleaner, and finally dried in an oven at 100 ℃ for 5 minutes.
Step S5: performing sputtering deposition coating on the cleaned long-period grating by using a radio frequency magnetron sputtering system (Denton Vacuum Discovery-18) and an Ag target (Kurt J.Lesker company) with the purity of 99.99%, the diameter of 76.2mm and the thickness of 6.35 mm;
further, the cleaned optical fiber was fixed on a copper frame to ensure that the optical fiber was kept straight during the deposition of the silver thin film, and the copper frame was placed on a stage rotating at a constant speed to ensure that the silver thin film was uniformly deposited;
further, the silver target is pretreated for 30 minutes before a shutter between the silver target and the long-period grating is opened; the silver film deposition is completed under the power of 100w, and the basic pressure of the deposition chamber before the sputtering of the system is about 10-4Pa, and the deposition chamber is filled with flowing high-purity argon gas of 40 cubic centimeters during sputtering, and the working pressure is about 1 Pa.
Step S6: immersing the long-period grating region into an electroplating solution at room temperature of 21 ℃, connecting the positive electrode of a power supply to a graphite rod inserted into the solution, connecting the negative electrode of an external power supply to a silver film by using an alligator clip and a conductive rubber ring, and electroplating for about 2 hours to generate an iron-carbon film with the thickness of 20 microns;
further, an electroplating solution was prepared by dissolving FeSO4.7H2O (40g/L), citric acid (1.2g/L) and L-ascorbic acid (3.0g/L) in distilled water, the composition of the electroplating solution being intended to produce an iron-carbon thin film having the same composition as the main component of the carbon steel; the conductive rubber ring is placed between the crocodile clip and the silver film to protect the silver film and have good electrical connection.
The above embodiments are only used to illustrate the technical solution of the present invention, and not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the present invention in its corresponding aspects.
Claims (8)
1. The long-period fiber grating sensor for monitoring the corrosion of the steel bars is characterized by comprising a long-period grating (1), a fiber core (2), a cladding (3), a buffer coating layer (4), a conductive film (5) and an iron-carbon film (6);
the fiber core (2), the cladding (3), the buffer coating layer (4), the conductive film (5) and the iron-carbon film (6) are all cylindrical mediums;
the long-period grating (1) is written into the middle local position of the fiber core (2);
the outer side of the fiber core (2) is provided with a cladding (3), the outer sides of two ends of the cladding (3) are provided with buffer coating layers (4), the outer side of the middle part of the cladding is provided with a conductive film (5), and the outer side of the conductive film (5) is provided with an iron-carbon film (6).
2. The iron-carbon coated long-period fiber grating sensor for monitoring the corrosion of the steel bars as claimed in claim 1, wherein the long-period grating (1) is a one-dimensional grating with a one-dimensional periodic structure, and the period and the total length of the one-dimensional grating are adjusted according to the size of a detection object.
3. The iron-carbon coated long period fiber grating sensor for monitoring corrosion of steel bars according to claim 1 or 2, characterized in that the refractive index of the fiber core (2) is larger than that of the cladding (3).
4. The long-period fiber grating sensor with iron-carbon coating for monitoring steel bar corrosion according to claim 1 or 2, wherein the conductive film (5) is deposited by conductive material, and the conductive material is graphene, silver or gold.
5. The long-period FBG sensor with the iron-carbon coating for monitoring the corrosion of the steel bar according to claim 3, wherein the conductive film (5) is formed by depositing a conductive material, and the conductive material is graphene, silver or gold.
6. The iron-carbon coated long-period fiber grating sensor for monitoring corrosion of steel bars as claimed in claim 1, 2 or 5, wherein the thicknesses of the conductive film (5) and the iron-carbon film (6) are adjusted according to the sensitivity requirement of the sensor.
7. The iron-carbon coated long-period fiber grating sensor for monitoring the corrosion of the steel bars as claimed in claim 3, wherein the thicknesses of the conductive film (5) and the iron-carbon film (6) are adjusted according to the sensitivity requirement of the sensor.
8. The iron-carbon coated long-period fiber grating sensor for monitoring the corrosion of the steel bars as claimed in claim 4, wherein the thicknesses of the conductive film (5) and the iron-carbon film (6) are adjusted according to the sensitivity requirement of the sensor.
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