Multi-core ultra-weak fiber bragg grating carbon fiber reinforcing rib and fiber bragg grating sensing system

Abstract

The utility model discloses a multi-core ultra-weak fiber bragg grating carbon fiber reinforcing rib and a fiber bragg grating sensing system, the reinforcing rib comprises a plurality of temperature-resistant optical fibers inscribed with ultra-weak fiber bragg grating sensing units, and the plurality of temperature-resistant optical fibers are axially distributed at equal intervals around the central axis of the reinforcing rib; the plurality of temperature-resistant optical fibers are wrapped and formed by carbon fiber bodies; the end part of the temperature-resistant optical fiber is provided with a sleeve which is partially led out, one part of the sleeve is led out together with the temperature-resistant optical fiber, and the other part of the sleeve is embedded in the reinforcing rib and is cured and formed. And the plurality of temperature-resistant optical fibers and the plurality of bundles of carbon fibers pre-impregnated with the phenolic resin are molded through hot pultrusion. The ultra-weak fiber bragg grating sensing system comprises ultra-weak fiber bragg grating carbon fiber reinforcing ribs implanted into a measured object, and the ultra-weak fiber bragg grating sensing system is connected with an ultra-weak fiber bragg grating analyzer and used for monitoring temperature, strain or spatial form. The reinforcing rib integrates the excellent performance of the carbon fiber and has the advantages of being high in strength, good in repeatability, easy to fuse with a large structure and the like.

Description

Technical Field

[0001] The utility model relates to the technical field of sensing optical fibers, in particular to a multi-core ultra-weak optical fiber grating carbon fiber reinforcement rib and a sensing system. Background Art

[0002] Ultra-weak fiber Bragg grating is a general term for gratings with a reflectivity of less than 0.1%. As a new type of fiber Bragg grating sensor in the field of optical fiber sensing, it not only inherits the characteristics of traditional fiber Bragg grating sensors, but also has the advantages of low loss during optical signal transmission, high mechanical strength, and strong multiplexing ability. It has become one of the hot research directions in the field of sensing. However, the packaging of ultra-weak fiber Bragg grating directly affects the accuracy of the sensor. Selecting good packaging materials and processes is an important part of the research on ultra-weak fiber Bragg grating sensors.

[0003] Fiber-reinforced composite packaging is to bury the ultra-weak fiber Bragg grating strain sensor directly into the composite material, which greatly improves the life and reliability of the sensor and becomes a very promising form of fiber optic sensor packaging. Carbon fiber composite materials have the advantages of light weight, high strength, corrosion resistance, fatigue resistance, extremely small thermal expansion coefficient, and good shock absorption performance. The use of carbon fiber and optical fiber composites can further improve the strength of the optical fiber and reduce the influence of temperature on the ultra-weak fiber Bragg grating sensing performance. In addition, optical fiber and carbon fiber have similar properties and can be smoothly compounded during hot pultrusion, which has obvious advantages in the production of long-distance linear sensors.

[0004] Carbon fiber composite packaging not only has good mechanical and temperature properties, but also has excellent elastic deformation recovery ability. After multiple ultra-weak fiber grating arrays are packaged with carbon fiber, it is expected to achieve good application results in the field of deformation sensing.

[0005] Traditional fiber Bragg grating sensors (FBG) have been applied in the field of shape sensing. For example, the Chinese patent "A fiber collimation coupled three-core fiber heavy metal ion sensor probe" (application number: 202210565326.3). At present, the fiber optic shape sensor mainly adopts a multi-sensor combination type, which uses multiple one-dimensional curvature sensors to combine at different orientations at the same position to form a measurement point of curvature size and bending direction. More often, three curvature sensors are arranged in an equilateral triangle at 120° to each other. The sensor can measure the bending direction while measuring the curvature. However, there are high process difficulties in bonding the fiber curvature sensor to the sensitization structure, the fiber survival rate is low, and the artificially combined and pasted sensor is large in size and the structure is severely affected by the environment. The accuracy of shape inversion is not good. Ultra-weak gratings have the characteristics of large capacity and long-distance operation. The introduction of new packaging technology, the multi-core ultra-weak fiber Bragg grating array and carbon fiber are double-checked to construct a shape sensing sensor with good elasticity, which is applied to engineering strain and shape perception, which is of great significance. Summary of the invention

[0006] Aiming at the problems of complex packaging process, cross-effect of temperature and strain, and poor deformation sensing function of existing ultra-weak fiber grating array, the utility model provides a multi-core ultra-weak fiber grating carbon fiber reinforcement rib. The intelligent carbon fiber reinforcement rib of the utility model is manufactured through special fiber structure design and high-temperature pultrusion molding, which can effectively sense the strain field distribution and spatial deformation of large structures and complex environments. It is cost-effective to construct a strain and deformation sensing system in combination with an ultra-weak fiber grating demodulator. The reinforcement rib integrates the excellent performance of carbon fiber, has the advantages of high strength, good repeatability, and easy integration with large structures, and has broad application prospects in the field of strain and deformation sensing.

[0007] The technical solution adopted by the utility model is:

[0008] A multi-core ultra-weak fiber Bragg grating carbon fiber reinforcement rib, comprising: a plurality of heat-resistant optical fibers engraved with ultra-weak fiber Bragg grating sensing units, the plurality of heat-resistant optical fibers being axially and evenly spaced around the central axis of the reinforcement rib; the plurality of heat-resistant optical fibers being wrapped and formed by a carbon fiber body; a partially led-out sleeve being provided at the end of the heat-resistant optical fiber, a portion of the sleeve being led out together with the heat-resistant optical fiber, and the other portion of the sleeve being buried inside the reinforcement rib and solidified. The heat-resistant optical fiber is provided with a high-temperature resistant outer coating layer.

[0009] A plurality of heat-resistant optical fibers and a plurality of bundles of carbon fibers pre-impregnated with phenolic resin are formed by hot pultrusion.

[0010] A partially led-out sleeve is provided at the end of the heat-resistant optical fiber, a part of the sleeve is led out together with the heat-resistant optical fiber, and the other part of the sleeve is buried inside the reinforcing rib and solidified into shape.

[0011] The temperature-resistant optical fiber comprises a fiber core, and the fiber core is sequentially wrapped with a cladding, an inner coating layer, and a high-temperature-resistant outer coating layer from the inside to the outside.

[0012] The high temperature resistant outer coating layer is a coating formed by secondary ultraviolet coating of modified acrylate, or an organic ceramic coating, or a coating formed by thermal curing of polyimide.

[0013] The reflectivity of the ultra-weak fiber grating sensing unit is lower than 0.1%, and it is prepared by online writing using a drawing tower process.

[0014] The temperature-resistant optical fiber is drawn from a G.657 optical fiber preform.

[0015] Multiple heat-resistant optical fibers are laid out in a space at 120° along the axis of the mold, and then heated and cooled to cure the prepreg impregnated with carbon fiber and phenolic resin.

[0016] The sleeve is made of flattened stainless steel wire, with the surface wrapped with a high-temperature resistant film, with a diameter greater than 1 mm, and is prefabricated 0.1 m at the head and tail ends of the required length of the reinforcement rib, with more than 0.5 m exposed.

[0017] There are three heat-resistant optical fibers, and from the cut surface of the three optical fibers, the three fiber cores are distributed on the same circumference at an angle of 120°, forming a three-core ultra-weak fiber Bragg grating carbon fiber reinforcement.

[0018] An ultra-weak fiber grating sensing system comprises an ultra-weak fiber grating carbon fiber reinforcement rib implanted in a measured object and connected to an ultra-weak fiber grating analyzer for monitoring temperature, strain, or spatial form.

[0019] The utility model discloses a multi-core ultra-weak fiber grating carbon fiber reinforcement rib, which has the following beneficial effects:

[0020] 1) Strain sensors have high strength, high monitoring accuracy and good stability:

[0021] Carbon fiber reinforcement has high tensile and compressive strength, with a strength of 3000MPa. The packaged sensor has high strength and is not easy to damage. Since the thermal expansion coefficient of carbon fiber composite is close to zero, the ultra-weak fiber Bragg grating is not affected by thermal expansion, and the strain monitoring accuracy is high. In addition, the optical fiber material is similar to the carbon fiber reinforcement, which can eliminate the creep phenomenon of traditional optical fiber, and has high strain transmission efficiency and good repeatability.

[0022] 2) Good elasticity, can be used for spatial shape inversion:

[0023] The density of ultra-weak fiber Bragg grating is high, and the strain on the reinforcement can be obtained at a resolution below 0.1m. The dense strain measurement points can reconstruct the bending deformation of the reinforcement and can be used to monitor the stress or shape of the structure.

[0024] By implanting multi-core ultra-weak fiber Bragg gratings and using ultra-weak fiber Bragg grating strain measurement equipment to measure the strain of the three fiber cores, the curvature and bending direction of the three-core optical fiber can be obtained through shape reconstruction algorithm calculation, and then the shape of the carbon fiber structure can be reconstructed.

[0025] 3) Simple structure, easy for mass production and convenient transportation:

[0026] The manufacturing method of multi-core ultra-weak fiber Bragg grating carbon fiber reinforcement is similar to that of single-core ultra-weak fiber Bragg grating carbon fiber reinforcement. Special optical fiber and carbon fiber are mixed and directly hot-pultruded. It can be customized according to the application requirements of complex shapes, overcoming the chirp problem in the composite process of ultra-weak fiber Bragg grating. Intelligent reinforcement has a small diameter and light weight. It can be transported in a reel and directly anchored on site. There is no need to strip the optical fiber from the reinforcement, and no prestressing is required. It is easy to install and construct.

[0027] 4) Resistance to environmental impact and low maintenance requirements:

[0028] Carbon fiber has excellent properties such as fatigue resistance, creep resistance, high temperature resistance, corrosion resistance, and wear resistance, and can be used for full life cycle monitoring of engineering structures in harsh environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the carbon fiber reinforcement structure of the multi-core ultra-weak fiber Bragg grating of the utility model.

[0030] Figure 2 This is a schematic diagram of the cross-sectional structure of a single heat-resistant optical fiber of the present utility model.

[0031] Figure 3 Schematic diagram of the carbon fiber reinforcement structure of three-core ultra-weak fiber Bragg grating.

[0032] Among them: 1: ultra-weak fiber Bragg grating sensing unit, 2: temperature-resistant optical fiber, 3: casing, 4: carbon fiber;

[0033] 2-1: core, 2-2: cladding, 2-3: inner coating, 2-4: high temperature resistant outer coating. DETAILED DESCRIPTION

[0034] like Figure 1 , Figure 2 As shown, a multi-core ultra-weak fiber Bragg grating carbon fiber reinforcement rib includes multiple heat-resistant optical fibers 2 engraved with ultra-weak fiber Bragg grating sensing units 1, and multiple heat-resistant optical fibers 2 are axially evenly spaced around the central axis of the reinforcement rib; multiple heat-resistant optical fibers 2 are wrapped and formed by a carbon fiber body, specifically, multiple heat-resistant optical fibers 2 and multiple bundles of carbon fibers 4 pre-impregnated with phenolic resin are formed by hot pultrusion through a mold. A partially led-out sleeve 3 is provided at the end of the heat-resistant optical fiber 2, and a part of the sleeve 3 is led out together with the heat-resistant optical fiber 2, and the other part of the sleeve 3 is buried in the reinforcement rib and cured. The heat-resistant optical fiber 2 is provided with a high-temperature resistant outer coating layer 2-4.

[0035] like Figure 2 As shown, the temperature-resistant optical fiber 2 includes a core 2-1, and the core 2-1 is sequentially wrapped with a cladding 2-2, an inner coating layer 2-3, and a high-temperature-resistant outer coating layer 2-4 from the inside to the outside.

[0036] The high temperature resistant outer coating layer 2-4 is a coating formed by secondary UV coating of modified acrylate, or an organic ceramic coating, or a coating formed by thermal curing of polyimide. The modified acrylate is formed by UV coating, has a diameter greater than 0.25 mm, and is heat resistant above 200°C.

[0037] The reflectivity of the ultra-weak fiber Bragg grating sensing unit 1 is 0.01%. It is formed by time division or wavelength division multiplexing to form a dense ultra-weak grating array, and is prepared by online writing using a drawing tower process. For example, in order to facilitate demodulation, gratings with wavelengths of 1530nm, 1542nm, and 1554nm can be repeatedly written within the wavelength range of 1528nm to 1568nm, and the grating interval is greater than 0.1 meters to facilitate resolution in the time domain.

[0038] The heat-resistant optical fiber 2 is drawn from a G.657 type optical fiber preform. Drawing from a G.657 type optical fiber preform can reduce the microbending loss caused by secondary coating. For example, the grating array made of the traditional G.652 optical fiber preform has an attenuation greater than 50dB / km. After using G.657 optical fiber, the loss is greatly reduced, and kilometer-level ultra-weak fiber grating sensing optical fiber can be produced.

[0039] like Figure 3 As shown, there are three heat-resistant optical fibers 2. From the cut surface of the three optical fibers, the three fiber cores are distributed on the same circumferential surface at an angle of 120°, forming a three-core ultra-weak fiber Bragg grating carbon fiber reinforcement. The three fiber cores are 0.5 mm away from the center O of the circumferential surface.

[0040] The multiple heat-resistant optical fibers 2 are laid out in a space of 120° along the axis of the mold, and are impregnated with the carbon fibers 4 and the prepreg of phenolic resin, and then heated and cooled to solidify into a mold with a diameter of 5mm and a tensile strength of more than 3000MPa.

[0041] The sleeve 3 is made of flattened stainless steel wire, with its surface wrapped in a high temperature resistant film, and has a diameter greater than 1 mm. 0.1 m is prefabricated at the head and tail ends of the required length of the reinforcement rib, with more than 0.5 m exposed.

[0042] The multi-core ultra-weak fiber Bragg grating carbon fiber reinforcement is embedded in the measured object, such as a large structure, landslide, mining tunnel, tunnel, etc., and connected to the ultra-weak fiber Bragg grating analyzer to form an ultra-weak fiber Bragg grating sensing system. The ultra-weak fiber Bragg grating strain measurement device is used to measure the strain of the three cores. The curvature and bending direction of the three-core optical fiber can be obtained through shape reconstruction calculation, which is used for spatial morphological deformation monitoring. The strain sensing accuracy of the system can reach 1με, and the temperature accuracy is 0.5℃.

[0043] The utility model provides a multi-core ultra-weak fiber Bragg grating carbon fiber reinforcement rib, which simplifies the packaging process of linear fiber optic sensors, reduces the cross-influence of temperature strain, can monitor the strain and spatial deformation of large structures and complex environments, avoids the use of expensive multi-core optical fibers and special couplers, and is combined with an ultra-weak fiber Bragg grating demodulator to construct a deformation sensing system with high cost performance and convenient installation. The reinforcement rib integrates the excellent performance of carbon fiber, has the advantages of high strength, large strain range, good repeatability, and easy integration with large structures, and has broad application prospects in the field of strain and deformation sensing.

Claims

1. A multi-core ultra-weak fiber Bragg grating carbon fiber reinforcement, characterized in that The invention comprises: a plurality of heat-resistant optical fibers (2) inscribed with ultra-weak fiber grating sensing units (1), the plurality of heat-resistant optical fibers (2) being axially evenly spaced around the central axis of the reinforcing rib; the plurality of heat-resistant optical fibers (2) being wrapped and formed by a carbon fiber body; a partially led-out sleeve (3) being provided at the end of the heat-resistant optical fiber (2), a portion of the sleeve (3) and the heat-resistant optical fiber (2) being led out together, and another portion of the sleeve (3) being buried inside the reinforcing rib and solidified and formed; and the heat-resistant optical fiber (2) being provided with a high-temperature resistant outer coating layer (2-4).

2. According to claim 1, a multi-core ultra-weak fiber Bragg grating carbon fiber reinforcement rib, characterized in that: A plurality of heat-resistant optical fibers (2) and a plurality of bundles of carbon fibers (4) pre-impregnated with phenolic resin are formed by hot pultrusion.

3. According to claim 1, a multi-core ultra-weak fiber Bragg grating carbon fiber reinforcement rib, characterized in that: The temperature-resistant optical fiber (2) comprises a fiber core (2-1), wherein the fiber core (2-1) is sequentially wrapped with a cladding (2-2), an inner coating layer (2-3), and a high-temperature-resistant outer coating layer (2-4) from the inside to the outside.

4. The multi-core ultra-weak fiber Bragg grating carbon fiber reinforcement according to claim 1, characterized in that: The high temperature resistant outer coating layer (2-4) is a coating formed by secondary ultraviolet coating of modified acrylate, or an organic ceramic coating, or a coating formed by thermal curing of polyimide.

5. The multi-core ultra-weak fiber Bragg grating carbon fiber reinforcement according to claim 1, characterized in that: The reflectivity of the ultra-weak fiber grating sensing unit (1) is lower than 0.1%.

6. The multi-core ultra-weak fiber Bragg grating carbon fiber reinforcement according to claim 1, characterized in that: The temperature-resistant optical fiber (2) is drawn from a G.657 type optical fiber preform.

7. The multi-core ultra-weak fiber Bragg grating carbon fiber reinforcement according to claim 1, characterized in that: A plurality of heat-resistant optical fibers (2) are laid out in a space at 120 degrees along the axis of the mold, and are impregnated with carbon fibers (4) and prepreg impregnated with phenolic resin, and then heated and cooled to cure and form.

8. The multi-core ultra-weak fiber Bragg grating carbon fiber reinforcement according to claim 1, characterized in that: The sleeve (3) is made of flattened stainless steel wire, with its surface wrapped with a high temperature resistant film, and its diameter is greater than 1 mm. 0.1 m is prefabricated at the head and tail ends of the required length of the reinforcement rib, with more than 0.5 m exposed.

9. The multi-core ultra-weak fiber Bragg grating carbon fiber reinforcement according to claim 1, characterized in that: There are three heat-resistant optical fibers (2). When viewed from the cross-section of the three optical fibers, the three fiber cores are distributed on the same circumferential surface at an angle of 120°, forming a three-core ultra-weak fiber Bragg grating carbon fiber reinforcement rib.

10. An ultra-weak fiber Bragg grating sensing system, characterized in that: It comprises an ultra-weak fiber Bragg grating carbon fiber reinforcement as claimed in any one of claims 1 to 9 implanted into the object to be measured, the reinforcement is connected to an ultra-weak fiber Bragg grating analyzer for temperature, strain, or spatial morphology monitoring.

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