Crack sensing sensor based on optical fiber sensing

Abstract

The utility model discloses a crack sensing sensor based on optical fiber sensing, and belongs to the technical field of civil structure health monitoring. The problems that the testing precision of an existing crack measuring device is extremely prone to being interfered by the surrounding environment, and the measuring precision is low are solved. The optical fiber grating sensor comprises a mounting shell, a cantilever beam and an optical fiber grating, the mounting shell is of a cavity structure with a fixed connecting end and a stretching movable end, and the fixed connecting end and the stretching movable end can slide relatively; the cantilever beam is of a long-strip-shaped structure with elastic deformation and resilience capacity, the cantilever beam is horizontally arranged in a cavity of the installation shell, the length direction of the cantilever beam is the same as the moving direction of the stretching movable end, the tip end of the cantilever beam is fixedly connected to the fixed connecting end, and the tail end of the cantilever beam abuts against the stretching movable end and is in a bent state. The fiber bragg grating is installed on the cantilever beam, and the length direction of the fiber bragg grating is consistent with the length direction of the cantilever beam. The device is mainly used for measuring cracks in the road surface and the roadbed.

Description

Technical Field

[0001] The utility model belongs to the technical field of civil structure health monitoring, and in particular relates to a crack sensing sensor based on optical fiber sensing. Background Art

[0002] During the service life of structures such as roads, bridges and tunnels, materials will deteriorate and structures will crack due to the combined effects of the environment and loads. Furthermore, if structural cracks are not discovered and handled in time, unbearable economic losses and casualties may occur. Therefore, it is very necessary to monitor the occurrence of structural cracks in real time and analyze the laws of crack expansion to avoid structural fractures.

[0003] With the development of fiber optic sensing technology, fiber optic sensors have been widely used in civil engineering, aerospace, petrochemical, electric power, medical, shipbuilding and other fields due to their advantages of anti-electromagnetic interference, corrosion resistance, high insulation, wide measurement range, and easy multiplexing into networks. The most common ones are fiber optic Bragg grating sensors and distributed fiber optic sensors. Taking fiber optic Bragg grating sensors as an example, when the external force on the fiber optic Bragg grating changes, the strain distribution at the grating changes accordingly, changing the grating pitch, thereby causing the change of the center wavelength of the fiber optic Bragg grating; through the fiber optic Bragg grating demodulation equipment, the change of the center wavelength can be converted into a change of optical power, and the detection of strain can be achieved by detecting the change of optical power.

[0004] However, civil engineering structures are complex, and it is difficult to accurately determine the size, expansion pattern, and location of cracks, making it even more difficult to assess the true performance status of the structure. However, most existing crack measurement devices are electrical tests, and the output results are current and voltage, etc. The test accuracy is easily affected by the surrounding environment. Therefore, developing a durable crack sensing sensor that can measure structural cracks for a long time is a problem that technicians in this field urgently need to solve. Utility Model Content

[0005] In order to solve the above technical problems, the utility model provides a crack sensing sensor based on optical fiber sensing. The equal-strength beam is deformed by changing the distance between the fixed connection end and the stretching active end of the installation shell. Through the coordinated deformation between the optical fiber grating and the equal-strength beam, the optical signal changes, thereby realizing the measurement of the crack.

[0006] The technical solution adopted by the utility model to solve the above technical problems is:

[0007] A crack sensing sensor based on optical fiber sensing comprises a mounting shell, a cantilever beam and an optical fiber Bragg grating; the mounting shell is a cavity structure having a fixed connection end and a stretchable movable end, and the fixed connection end and the stretchable movable end can slide relative to each other; the cantilever beam is a long strip structure with elastic deformation and rebound capabilities, the cantilever beam is horizontally arranged in the cavity of the mounting shell, and the length direction of the cantilever beam is the same as the moving direction of the stretchable movable end, the tip of the cantilever beam is fixedly connected to the fixed connection end, the tail end abuts against the stretchable movable end and is in a bent state, the optical fiber Bragg grating is mounted on the cantilever beam, and the length direction of the optical fiber Bragg grating is consistent with the length direction of the cantilever beam.

[0008] Preferably, the mounting shell comprises a "U"-shaped bracket, a fixed top plate, a movable bottom plate and movable side plates, the movable side plates are installed in the side opening of the "U"-shaped bracket and enclose a square frame body with the "U"-shaped bracket, and the movable side plates are slidingly connected to the inner side walls of the "U"-shaped bracket; the fixed top plate and the movable bottom plate are respectively arranged at the upper opening and the lower opening of the square frame body, the fixed top plate is buckled at the upper opening of the square frame body, and is fixedly mounted on the "U"-shaped bracket, and the fixed top plate and the "U"-shaped bracket form a fixed connection end of the mounting shell; the movable bottom plate is buckled at the lower opening of the square frame body, and is slidingly connected to the "U"-shaped bracket, the movable bottom plate is fixedly connected to the movable side plates, and forms a stretching movable end of the mounting shell; the tip of the cantilever beam is connected to the "U"-shaped bracket, and the tail end of the cantilever beam abuts against the movable side plate.

[0009] Preferably, each of the four top corners of the "U"-shaped bracket has a threaded hole, and each of the four top corners of the fixed top plate also has a threaded hole. The threaded holes on the fixed top plate are arranged one-to-one with the threaded holes on the "U"-shaped bracket and are fixedly connected by screws.

[0010] Preferably, a rubber pad is provided between the fixed top plate and the "U"-shaped bracket.

[0011] Preferably, the width of the movable side panel is equal to the distance between the two opposite side panels in the "U"-shaped bracket; the movable side panel is inserted between the two opposite side panels, and a movable distance is left with the port of the side opening of the "U"-shaped bracket, and this movable distance is greater than the width of the crack; sealant is applied between the movable side panel and the inner wall of the "U"-shaped bracket.

[0012] Preferably, the length of the movable bottom plate is greater than the length of the "U"-shaped bracket, one end of the movable bottom plate away from the movable side plate extends out of the side end surface of the "U"-shaped bracket, and the length of the extended part of the movable bottom plate is greater than the width of the crack; sealant is applied to the lower opening of the movable bottom plate and the "U"-shaped bracket.

[0013] Preferably, an adjustment block is also provided in the installation shell. The adjustment block is installed on the stretching movable end and is arranged opposite to the cantilever beam. The tail end of the cantilever beam is bent upward and abuts on the abutment surface of the adjustment block. The angle between the abutment surface and the horizontal plane is a, and the value range of a is 45° to 90°.

[0014] Preferably, the adjusting block is a right-angle trapezoidal block, the side wall of the right-angle side of the adjusting block is connected to the movable side plate, the bottom wall of the adjusting block is connected to the movable bottom plate, and the inclined side wall of the adjusting block faces one side of the cantilever beam to form an abutment surface.

[0015] Preferably, the cantilever beam is an iso-strength beam.

[0016] Preferably, two fiber gratings are arranged, and are respectively arranged on the upper surface and the lower surface of the cantilever beam.

[0017] Compared with the prior art, the utility model has the following beneficial effects:

[0018] 1. This application uses fiber Bragg grating as a sensing element, so that the crack sensing sensor has the advantages of anti-electromagnetic interference, high sensitivity, high test accuracy, and strong durability. The sensor can realize real-time dynamic monitoring. The real-time monitoring data can reflect the size of the structural cracks, the evolution law from scratch to the expansion process, and meet the needs of the civil engineering field for structural crack monitoring. In addition, the optical fiber transmission loss is small, and long-distance remote control monitoring can be realized. Furthermore, the fiber Bragg grating has good insulation performance, a wide range of applications, and is safe and reliable. The optical fiber itself is composed of electrolytes and does not require power drive.

[0019] 2. Since fiber Bragg gratings are sensitive to both temperature and force, the present application sets up temperature-compensated fiber Bragg gratings as needed, that is, fiber Bragg gratings are arranged on the upper and lower surfaces of the cantilever beam respectively. After the wavelength signals of the two fiber Bragg gratings are decoupled, the sensor measurement error caused by temperature during real-time measurement can be eliminated, thereby improving the measurement accuracy.

[0020] 3. The sensitivity and range of the sensor in this application are related to the angle a between the abutment surface and the horizontal plane. The larger the angle a, the greater the sensitivity of the sensor and the larger the range. Conversely, the smaller the sensitivity and the smaller the range. Therefore, when using this application, the adjustment blocks with different angles can be replaced as needed to meet the measurement requirements. In addition, according to the threshold requirements of the specified crack width, the abutment surface of the adjustment block can be made into a variable slope value. When the crack width exceeds a certain limit, the crack will accelerate the expansion, and the inflection point of the abutment surface can be set as a warning value point to achieve the purpose of warning.

[0021] 4. The cantilever beam of the present application is an iso-strength beam, so that the deformation of the key monitoring points of the fiber grating remains consistent, thereby avoiding the chirp phenomenon.

[0022] 5. The sensor of the present application can be used to measure cracks inside the pavement structure, and can also be pasted on the surface of a bridge / tunnel to measure the road surface, and has wide adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] As a part of this application, the accompanying drawings are used to provide a further understanding of the present invention.

[0024] Figure 1 Schematic diagram of the internal structure of the crack sensing sensor Figure 1 .

[0025] Figure 2 Schematic diagram of the internal structure of the crack sensing sensor Figure 2 .

[0026] Figure 3 This is a schematic diagram of the cooperation between the "U"-shaped bracket and the cantilever beam.

[0027] Figure 4 Schematic diagram of the structure of the fixed top plate.

[0028] Figure 5 This is a structural schematic diagram of the adjustment block being installed on the movable bottom plate and the movable side plate.

[0029] Explanation of the reference numerals: 1-installing housing; 1-1-U-shaped bracket; 1-2-fixed top plate; 1-3-movable bottom plate; 1-4-movable side plate; 1-5-adjusting block; 1-5-1-abutting surface; 1-6-fixing bolt hole; 2-cantilever beam; 3-fiber grating. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the utility model clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings in the embodiments of the utility model. The following embodiments are used to illustrate the utility model but are not used to limit the scope of the utility model.

[0031] Most existing crack measurement sensors are electrical tests, and the output results are current and voltage, etc. The test accuracy is easily affected by the surrounding environment. Therefore, this embodiment proposes a crack perception sensor based on optical fiber sensing; see Figure 1The crack sensing sensor includes a mounting shell 1, a cantilever beam 2 and a fiber Bragg grating 3; the mounting shell 1 is a cavity structure having a fixed connection end and a stretchable movable end, and the fixed connection end and the stretchable movable end can slide relative to each other; the cantilever beam 2 is a long strip structure with elastic deformation and rebound capabilities, the cantilever beam 2 is horizontally arranged in the cavity of the mounting shell 1, and the length direction of the cantilever beam 2 is the same as the moving direction of the stretchable movable end, the tip of the cantilever beam 2 is fixedly connected to the fixed connection end, the tail end abuts against the stretchable movable end and is in a bent state, the fiber Bragg grating 3 is mounted on the cantilever beam 2, and the length direction of the fiber Bragg grating 3 is consistent with the length direction of the cantilever beam 2.

[0032] In this embodiment, since the fiber Bragg grating 3 realizes the measurement function through deformation, the cantilever beam 2 used to support the fiber Bragg grating 3 needs to have the ability of elastic deformation under the action of external force, and the cantilever beam 2 is arranged in the installation shell 1, and its original state is in a bent state; the stretching active end of the installation shell 1 and the cantilever beam 2 are connected by abutment. After the stretching active end and the fixed connection end are displaced, the cantilever beam 2 is deformed under its own resilience, and then the fiber Bragg grating 3 arranged on the cantilever beam 2 is deformed to generate a fiber signal. In addition, this embodiment also includes a demodulator and a terminal processing device. The crack sensing sensor transmits the measured fiber signal to the demodulator for demodulation, and then transmits the demodulated data to the terminal processing device for resolution. It should be noted that this application only protects the sensor structure itself, and the resolution of the data is not the key point of protection in this application.

[0033] In the specific implementation of this embodiment, the crack sensor is integrally buried inside the pavement structure or pasted on the surface of a bridge / tunnel. When a crack occurs in the monitoring area, the fixed connection end and the tensile active end of the mounting shell 1 are driven by the structures on both sides of the crack to increase the distance between them. The cantilever beam 2 is deformed under its own resilience. Through the coordinated deformation between the fiber grating 3 and the cantilever beam 2, the grating pitch increases, and then the optical signal changes. The optical signal is transmitted to the demodulator and the terminal processing device, and the relationship between the change in the optical signal and the crack width is established through the indoor calibration test relationship, thereby monitoring the crack.

[0034] Furthermore, the mounting housing 1 comprises a U-shaped bracket 1-1, a fixed top plate 1-2, a movable bottom plate 1-3 and a movable side plate 1-4, the movable side plate 1-4 is mounted in the side opening of the U-shaped bracket 1-1, and is enclosed with the U-shaped bracket 1-1 to form a square frame, the movable side plate 1-4 is slidably connected to the inner side wall of the U-shaped bracket 1-1; the fixed top plate 1-2 and the movable bottom plate 1-3 are respectively arranged at the upper opening and the lower opening of the square frame, and the fixed top plate 1-2 is buckled It is fitted at the upper opening of the square frame and fixedly mounted on the "U"-shaped bracket 1-1, and the fixed top plate 1-2 and the "U"-shaped bracket 1-1 form a fixed connection end of the mounting shell 1; the movable bottom plate 1-3 is buckled at the lower opening of the square frame and is slidably connected to the "U"-shaped bracket 1-1, and the movable bottom plate 1-3 is fixedly connected to the movable side plate 1-4, and forms a tensile movable end of the mounting shell 1; the tip of the cantilever beam 2 is connected to the "U"-shaped bracket 1-1, and the tail end of the cantilever beam 2 abuts against the movable side plate 1-4.

[0035] Among them, the "U"-shaped bracket 1-1 is composed of three side panels. The two adjacent side panels can be made in one piece or connected by welding. In addition, since the cantilever beam 2 is pasted with a fiber grating 3, and the fiber grating 3 transmits signals through optical fibers, it is also necessary to open a hole on the side panel to facilitate the extraction of the optical fiber. It should be noted that in order to ensure the sealing of the installation shell 1, the opening should be sealed with rubber. In addition, in order to facilitate the connection between the fixed top plate 1-2 and the "U"-shaped bracket 1-1, a threaded hole is opened at each of the four top corners of the "U"-shaped bracket 1-1, and a threaded hole is also opened at each of the four top corners of the fixed top plate 1-2. The threaded holes on the fixed top plate 1-2 correspond to the threaded holes on the "U"-shaped bracket 1-1 one by one, and are fixedly connected by screws. Furthermore, in order to form a sealed cavity in the installation shell 1, a rubber pad is padded between the fixed top plate 1-2 and the "U"-shaped bracket 1-1 to play a sealing role.

[0036] Among them, the width of the movable side plate 1-4 is equal to the inner diameter of the "U"-shaped bracket 1-1 in the width direction, that is, equal to the distance between the two opposite side plates in the "U"-shaped bracket 1-1; after the movable side plate 1-4 is inserted between the two opposite side plates, a certain movable distance is left with the port of the side opening of the "U"-shaped bracket 1-1, and this movable distance is greater than the width of the crack, so as to ensure that the movable side plate 1-4 will not be separated from the "U"-shaped bracket 1-1 during the movement, thereby ensuring the sealing of the inner cavity of the installation shell 1. In addition, in order to further ensure the sealing of the inner cavity of the installation shell 1, a sealant is applied between the movable side plate 1-4 and the inner wall of the "U"-shaped bracket 1-1, and the sealant serves the purpose of waterproofing; it should be noted that this sealant is soft in texture and very low in strength, and will not affect the sliding between the movable side plate 1-4 and the "U"-shaped bracket 1-1, so it will not affect the accuracy of crack monitoring.

[0037] Among them, the length of the movable bottom plate 1-3 is greater than the length of the "U"-shaped bracket 1-1. When the movable bottom plate 1-3 is buckled at the lower opening of the "U"-shaped bracket 1-1, the end of the movable bottom plate 1-3 away from the movable side plate 1-4 extends out of the side end surface of the "U"-shaped bracket 1-1, and the length of the extended part of the movable bottom plate 1-3 is greater than the width of the crack, so as to ensure that the movable bottom plate 1-3 always blocks the lower opening of the "U"-shaped bracket 1-1 during the movement, thereby ensuring the sealing of the inner cavity of the installation shell 1. In addition, in order to further ensure the sealing of the inner cavity of the installation shell 1, the movable bottom plate 1-3 and the lower opening of the "U"-shaped bracket 1-1 are coated with sealant, and the sealant serves the purpose of waterproofing; it should be noted that this sealant is soft in texture and very low in strength, and will not affect the sliding between the movable bottom plate 1-3 and the "U"-shaped bracket 1-1, so it will not affect the accuracy of crack monitoring.

[0038] Among them, when cracks occur in the roadbed structure, in order to ensure that the structures at both ends of the cracks can generate tension on the fixed connection end and the stretching movable end of the installation shell 1 to realize the detection of the cracks, this embodiment installs a fixing bolt hole 1-6 on the outer plate surface of the movable side plate 1-4 and the outer plate surface of the "U"-shaped bracket 1-1 opposite to the movable side plate 1-4. The connection direction of the two fixing bolt holes 1-6 is consistent with the length direction of the cantilever beam 2 to ensure that when cracks occur in the roadbed structure and the sensor is stretched, the fixed connection end and the stretching movable end of the installation shell 1 are subjected to forces of the same dimension.

[0039] It should be noted that the height and thickness of the side panels used to make the "U"-shaped bracket 1-1 can be adjusted according to actual monitoring needs; when the sensor needs to be buried inside the structure, the side panels need to have higher strength and rigidity to prevent the installation shell 1 from being damaged and deformed when cracks occur, so the thickness of the side panels can be increased; when the sensor is attached to the surface of the structure and is not affected by other loads, the thickness of the side panels can be reduced. Similarly, the height of the side panels can also be adjusted according to the stress state during the monitoring process. The thickness of the movable bottom plate 1-3 and the thickness of the fixed top plate 1-2 can be adjusted according to the strength requirements. When the sensor needs to be monitored under load conditions and there is a vehicle load, the thickness of the fixed top plate 1-2 and the movable bottom plate 1-3 can be appropriately increased as required, otherwise the thickness can be appropriately reduced to avoid material waste.

[0040] Furthermore, in order to adjust the sensitivity and range of the sensor, an adjustment block 1-5 is also provided in the mounting shell 1 described in this embodiment. The adjustment block 1-5 is installed on the stretching active end and is arranged opposite to the cantilever beam 2. The tail end of the cantilever beam 2 is bent upward and abuts against the abutment surface 1-5-1 of the adjustment block 1-5. The angle between the abutment surface 1-5-1 and the horizontal plane is a, and the value range of a is 45° to 90°.

[0041] The sensitivity and range of the sensor in this embodiment are related to the angle a between the abutment surface and the horizontal plane. The larger the angle a is, the greater the sensitivity of the sensor is and the larger the range is. Conversely, the smaller the sensitivity is, the smaller the range is. Therefore, when using this embodiment, the adjustment blocks 1-5 with different angles can be replaced as needed to meet the measurement requirements. In addition, the abutment surface of the adjustment blocks 1-5 can be made into a variable slope value according to the threshold requirements of the specified crack width. When the crack width exceeds a certain limit, the crack will accelerate the expansion, and the inflection point of the abutment surface is set as a warning value point to achieve the purpose of warning.

[0042] The adjustment block 1-5 can be a semi-cone, a triangular prism, a trapezoidal block or a cylinder, etc., preferably a right-angled trapezoidal block; the side wall of the right-angle side of the adjustment block 1-5 is connected to the movable side plate 1-4, the bottom wall of the adjustment block 1-5 is connected to the movable bottom plate 1-3, and the inclined side wall of the adjustment block 1-5 faces one side of the cantilever beam 2 and forms a contact surface. In addition, the thickness of the adjustment block 1-5 is consistent with the width of the cantilever beam 2, and the centers of the two are aligned. The top height of the adjustment block 1-5 is slightly higher than the height of the cantilever beam 2. When the adjustment block 1-5 moves, the cantilever beam 2 is deformed under its own resilience.

[0043] In this embodiment, by setting the adjustment block 1-5, the distance between the abutment surface of the stretching movable end and the end surface of the fixed connection end is shortened, thereby shortening the length of the cantilever beam 2 and ensuring the accuracy of crack measurement. In the specific implementation process, when cracks occur in the monitoring area, the movable bottom plate 1-3 and the movable side plate 1-4 of the mounting housing 1 drive the adjustment block 1-5 to move away from the cantilever beam 2, and the tail end of the cantilever beam 2 gradually slides downward along the abutment surface 1-5-1 and always abuts against the abutment surface 1-5-1, and the cantilever beam 2 is deformed.

[0044] Furthermore, in order to keep the deformation of the key monitoring points of the fiber Bragg grating 3 consistent and thus avoid the chirping phenomenon, the cantilever beam 2 described in this embodiment is a beam of equal strength.

[0045] The thickness of the isostrength beam can be adjusted according to different use conditions. When the measured area is a non-stressed area and only small cracks occur, the thickness of the isostrength beam should be reduced to increase the actual sensitivity and resolution of the crack sensor, and vice versa. In addition, the material of the isostrength beam should usually be a material with good toughness. In this embodiment, spring steel is used. In the implementation process, other materials or other forms of structures can also be used as long as the deformation function can be achieved. The essence is no different from this example.

[0046] This embodiment changes the cross-sectional stiffness of the cantilever beam 2 to keep the deformation of the key monitoring points of the fiber Bragg Bragg grating 3 consistent, so that the relative drift of the Bragg reflection wavelength at different positions on the fiber Bragg grating is the same, and the half-width of the reflection spectrum is stable, thereby avoiding the chirp phenomenon (the fiber Bragg grating chirp effect refers to the fact that when light passes through the fiber Bragg grating, due to the existence of tiny periodic changes in the grating, the frequency of the light changes, which in turn causes the light frequency deviation, resulting in frequency shift or chirp. If the deformation is inconsistent, the widening of different grids of the grating will be different, and then the refractive index change will be different, the periodicity and frequency of the light will change, causing chirp), and the signal is stable.

[0047] Furthermore, in order to avoid the measurement error of the crack sensor caused by temperature, two fiber Bragg gratings 3 are arranged in this embodiment, and are arranged respectively on the upper surface and the lower surface of the cantilever beam 2, wherein the fiber Bragg grating 3 is mounted on the cantilever beam 2 by pasting. In addition, each fiber Bragg grating 3 is connected to an optical fiber for signal transmission.

[0048] In this embodiment, since the fiber Bragg grating 3 is sensitive to both temperature and force, it can be known from material mechanics that when the adjustment block 1-5 moves to one side, the force on the cantilever beam 2 decreases, and the cantilever beam 2 deforms under its own resilience (from a large angle bend to a small angle bend), the upper surface of the cantilever beam 2 still shows compression, and the lower surface of the cantilever beam 2 shows tension, and the tension and pressure are the same; in order to distinguish the two fiber Bragg gratings 3 on the upper and lower surfaces of the cantilever beam 2, in this embodiment, the fiber Bragg grating 3 on the upper surface of the cantilever beam 2 is called a compressed fiber Bragg grating, and the fiber Bragg grating 3 on the lower surface of the cantilever beam 2 is called a tensile fiber Bragg grating. Among them, the wavelength of the compressed fiber Bragg grating will increase after being compressed, and the observed wavelength signal actually reflects temperature-force (assuming that the temperature rises); the wavelength of the tensile fiber Bragg grating will decrease after being tensile, and the observed wavelength signal actually reflects temperature+force. Therefore, after the two wavelength signals are decoupled, the influence of temperature can be eliminated, avoiding the measurement error of the crack sensor caused by temperature (thermal expansion and contraction), and ensuring the measurement accuracy.

[0049] The following is a further description of the manufacturing, installation and working process of the utility model to further demonstrate the working principle and advantages of the utility model:

[0050] 1. Production and installation process of crack sensing sensor:

[0051] Step 1, manufacturing an installation shell 1 and an equal strength beam, wherein the installation shell 1 and the equal strength beam can be completed by welding, rolling or 3D printing technology, and the installation shell 1 has corrosion resistance and good anti-deformation characteristics; and the equal strength beam has the ability of elastic deformation and rebound, and preferably uses a spring steel plate with a thickness of 1 cm to meet the strength and rebound performance requirements in the actual test process. After the deformation disappears, it can be restored to the stage before deformation, ensuring that the equal strength beam is in the elastic stage during the entire deformation process without plastic deformation;

[0052] Step 2, the fiber Bragg grating 3 is pasted on the processed equal strength beam by using a special adhesive. When pasting, it is necessary to keep the thickness of the adhesive uniform to avoid causing too large a structural change to the original equal strength beam, and try to avoid bubbles in the packaging adhesive at the fiber Bragg grating, otherwise it is easy to cause a multi-peak phenomenon of the sensor;

[0053] Step 3, after the special adhesive is cured, fix one end of the equal strength beam on the "U"-shaped bracket 1-1, and pass the optical fiber connected to the fiber grating 3 through the lead-in hole on the "U"-shaped bracket 1-1; the lead-out optical fiber is protected by an armored wire, and the optical fiber connector is connected by an optical fiber fusion splicer to facilitate the connection between the sensor and the demodulator;

[0054] Step 4, splice the "U"-shaped bracket 1-1 of the mounting housing 1 with the movable bottom plate 1-3 and the movable side plate 1-4. At this time, the equal strength beam is squeezed by the adjustment block 1-5, and the tail end of the equal strength beam slides upward along the abutment surface 1-5-1 of the adjustment block 1-5 and is in a bent state; the friction between the equal strength beam and the abutment surface 1-5-1 keeps the components stable; and the connection between the "U"-shaped bracket 1-1 and the movable bottom plate 1-3 and the connection between the "U"-shaped bracket 1-1 and the movable side plate 1-4 are sealed with sealant respectively;

[0055] Step 5, install the fixed top plate 1-2 on the "U"-shaped bracket 1-1 by screws, add rubber pads at the connection and use sealant for sealing;

[0056] Step 6, depending on the monitoring object, if road monitoring is performed, a groove of the same size as the installation shell 1 can be cut on the road surface, the crack sensing sensor can be placed in it, and fixed with bolts through the fixing bolt holes 1-6. The remaining pore positions are filled with cold patch materials or fine-grained asphalt mixture. If bridge or tunnel monitoring is performed, surface fixed monitoring can be performed by implanting expansion bolts at both ends at the mid-span position of the bridge or the top position of the tunnel lining. It should be noted that before monitoring, an indoor calibration test should be carried out to quantify the relationship between the crack width and the optical fiber deformation (it can also be analyzed theoretically, and the optical fiber deformation size at different positions of the adjustment block 1-5 is calculated by the cantilever beam deformation calculation method).

[0057] 2. Working process of crack sensing sensor:

[0058] The crack sensor is embedded in the pavement structure or pasted on the surface of the bridge / tunnel. When cracks occur in the monitoring area, the "U"-shaped bracket 1-1 and the movable side plate 1-4 are fixedly connected to the structure to be measured, so the "U"-shaped bracket 1-1 and the movable side plate 1-4 are subjected to outward pulling force, and the distance between the "U"-shaped bracket 1-1 and the movable side plate 1-4 becomes larger. Driven by the movable side plate 1-4, the distance between the adjustment block 1-5 and the equal-strength beam also becomes smaller. At the same time, the extrusion pressure on the equal-strength beam becomes smaller, and the tail end of the equal-strength beam moves along the abutment surface of the adjustment block 1-5. 1-5-1 sliding, the bending degree of the equal-strength beam becomes smaller under its own resilience, and the deformation changes. Through the coordinated deformation between the fiber grating and the equal-strength beam, the grating pitch becomes larger, and then the optical signal changes. The relationship between the change in optical signal and the crack width is established through indoor calibration test relationship, so as to monitor the crack. By pasting two distributed optical fibers / fiber gratings on the upper and lower plates, the beam body produces different deformations when subjected to force. The difference in deformation can be used to calculate the influence of temperature on the deformation of the optical fiber, and then temperature compensation can be achieved, so that the size of the crack width can be accurately obtained.

[0059] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments, and other arrangements may be designed without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the features described in the various dependent claims and herein may be combined in a manner different from that described in the original claims. It may also be understood that the features described in conjunction with the individual embodiments may be used in other described embodiments.

Claims

1. A crack sensing sensor based on optical fiber sensing, characterized in that: The invention comprises a mounting shell (1), a cantilever beam (2) and an optical fiber Bragg grating (3); the mounting shell (1) is a cavity structure having a fixed connection end and a stretchable movable end, and the fixed connection end and the stretchable movable end are capable of sliding relative to each other; the cantilever beam (2) is a long strip structure having elastic deformation and rebound capabilities, the cantilever beam (2) is horizontally arranged in the cavity of the mounting shell (1), and the length direction of the cantilever beam (2) is the same as the moving direction of the stretchable movable end, the tip of the cantilever beam (2) is fixedly connected to the fixed connection end, and the tail end abuts against the stretchable movable end and is in a bent state, the optical fiber Bragg grating (3) is mounted on the cantilever beam (2), and the length direction of the optical fiber Bragg grating (3) is consistent with the length direction of the cantilever beam (2).

2. The crack sensing sensor based on optical fiber sensing according to claim 1, characterized in that: The mounting housing (1) comprises a "U"-shaped bracket (1-1), a fixed top plate (1-2), a movable bottom plate (1-3) and a movable side plate (1-4); the movable side plate (1-4) is mounted in a side opening of the "U"-shaped bracket (1-1) and encloses a square frame body with the "U"-shaped bracket (1-1); the movable side plate (1-4) and the inner side wall of the "U"-shaped bracket (1-1) are slidably connected; the fixed top plate (1-2) and the movable bottom plate (1-3) are respectively arranged at the upper opening and the lower opening of the square frame body; the fixed top plate (1-2) is buckled in The upper opening of the square frame is fixedly mounted on a "U"-shaped bracket (1-1); the fixed top plate (1-2) and the "U"-shaped bracket (1-1) form a fixed connection end of the mounting shell (1); the movable bottom plate (1-3) is buckled at the lower opening of the square frame and is slidably connected to the "U"-shaped bracket (1-1); the movable bottom plate (1-3) is fixedly connected to the movable side plate (1-4) and forms a tensile movable end of the mounting shell (1); the tip of the cantilever beam (2) is connected to the "U"-shaped bracket (1-1), and the tail end of the cantilever beam (2) abuts against the movable side plate (1-4).

3. The crack sensing sensor based on optical fiber sensing according to claim 2 is characterized in that: The four top corners of the "U"-shaped bracket (1-1) each have a threaded hole, and the four top corners of the fixed top plate (1-2) each have a threaded hole. The threaded holes on the fixed top plate (1-2) are arranged in one-to-one correspondence with the threaded holes on the "U"-shaped bracket (1-1) and are fixedly connected by screws.

4. The crack sensing sensor based on optical fiber sensing according to claim 3 is characterized in that: A rubber pad is provided between the fixed top plate (1-2) and the "U"-shaped bracket (1-1).

5. The crack sensing sensor based on optical fiber sensing according to claim 2 is characterized in that: The width of the movable side plate (1-4) is equal to the distance between two opposite side plates in the "U"-shaped bracket (1-1); the movable side plate (1-4) is inserted between the two opposite side plates and leaves a movable distance with the port of the side opening of the "U"-shaped bracket (1-1), and the movable distance is greater than the width of the crack; and sealant is applied between the movable side plate (1-4) and the inner wall of the "U"-shaped bracket (1-1).

6. The crack sensing sensor based on optical fiber sensing according to claim 2, characterized in that: The length of the movable bottom plate (1-3) is greater than the length of the "U"-shaped bracket (1-1); one end of the movable bottom plate (1-3) away from the movable side plate (1-4) extends out of the side end surface of the "U"-shaped bracket (1-1); and the length of the extended portion of the movable bottom plate (1-3) is greater than the width of the crack; and sealant is applied to the lower opening of the movable bottom plate (1-3) and the "U"-shaped bracket (1-1).

7. The crack sensing sensor based on optical fiber sensing according to claim 1, characterized in that: An adjustment block (1-5) is also provided in the installation housing (1). The adjustment block (1-5) is installed on the stretching movable end and is arranged opposite to the cantilever beam (2). The tail end of the cantilever beam (2) is bent upward and abuts against the abutment surface (1-5-1) of the adjustment block (1-5). The angle between the abutment surface (1-5-1) and the horizontal plane is a, and the value range of a is 45° to 90°.

8. The crack sensing sensor based on optical fiber sensing according to claim 7, characterized in that: The adjusting block (1-5) is a right-angled trapezoidal block, the side wall of the right-angle side of the adjusting block (1-5) is connected to the movable side plate (1-4), the bottom wall of the adjusting block (1-5) is connected to the movable bottom plate (1-3), and the inclined side wall of the adjusting block (1-5) faces one side of the cantilever beam (2) to form an abutting surface.

9. The crack sensing sensor based on optical fiber sensing according to claim 1, characterized in that: The cantilever beam (2) is a beam of equal strength.

10. The crack sensing sensor based on optical fiber sensing according to claim 1, characterized in that: Two optical fiber gratings (3) are arranged, and are respectively arranged on the upper surface and the lower surface of the cantilever beam (2).

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