Intelligent rib based on fiber bragg grating and preparation method thereof

Abstract

The invention relates to an intelligent rib based on a fiber bragg grating and a preparation method thereof, the intelligent rib comprises a fiber bragg grating sensor, a coating layer and a protection assembly, the coating layer is arranged on the external surface of the fiber bragg grating sensor, and the protection assembly is arranged at the tail part of the intelligent rib; the preparation method comprises the following steps: preparing the fiber bragg grating sensor, arranging the coating layer outside the fiber bragg grating sensor, and installing the protection assembly at the tail fiber connection part. The technical problems that in civil engineering structure health monitoring, the laying process of fiber grating sensors is complex, the sensors are prone to damage, and long-term high-precision monitoring cannot be achieved are solved.

Description

Technical Field

[0001] The present invention relates to an intelligent rib based on optical fiber grating and a preparation method thereof. Background Art

[0002] Civil engineering structures and infrastructure, such as concrete, geotechnical, cable-type structures, and steel cables, inevitably experience damage accumulation and resistance degradation during service due to the combined effects of environmental loads, fatigue, corrosion, and material aging, thus reducing their ability to withstand natural disasters. This was exemplified by the 2001 deck collapse of the Nanmen Bridge in Yibin, Sichuan. Therefore, effective and real-time health monitoring of civil engineering structures and infrastructure has become a pressing technical challenge that demands a solution.

[0003] The health monitoring projects of civil engineering structures mainly focus on strain and temperature. Traditional monitoring methods such as strain gauges and displacement gauges have disadvantages such as low accuracy, low stability, poor operability, susceptibility to interference, and inability to monitor in real time, making it difficult to achieve the purpose of long-term and effective monitoring.

[0004] The recently developed Fiber Bragg Grating (FBG) sensor is a high-performance sensitive element that senses minute changes in external stress through the shift in the Bragg reflection wavelength. This allows for high-precision, absolute measurement of structural strain. It boasts excellent electrical insulation, high stability, corrosion resistance, immunity to electromagnetic interference, and the integration of both transmission and sensing. Fiber Bragg Grating (FBG) sensing technology provides an excellent means for online, real-time monitoring of engineering structures, meeting the high-precision and long-term technical requirements for structural health monitoring. However, FBG sensors also have their limitations. They are relatively fragile and have poor shear resistance, requiring special protection during use. Their deployment is crucial.

[0005] CN105442758B (Large-scale FRP embedded steel wire composite optical fiber intelligent reinforcement and preparation method thereof) discloses an embedded steel wire FRP optical fiber intelligent composite reinforcement made of optical fiber sensors, steel strands and fiber-reinforced composite materials. However, it uses bare optical fiber wound on the steel strands. During the manufacturing process, the optical fiber becomes brittle and easily breaks. Summary of the Invention

[0006] The purpose of the present invention is to solve the above deficiencies in the prior art and to provide a fiber Bragg grating-based smart rib and a preparation method thereof.

[0007] A fiber grating (FBG)-based smart reinforcement includes a fiber grating (FBG) sensor, a cladding layer, and a protective component. The cladding layer is arranged on the outer surface of the fiber grating sensor, and the protective component is arranged at the tail of the smart reinforcement. The grating sensor is connected to the reinforcement material to detect the strain of the reinforcement material.

[0008] Furthermore, it also includes a composite reinforcement material, which is a hollow structure for accommodating a fiber optic Bragg grating sensor. The fiber optic Bragg grating sensor is arranged in the cavity of the composite reinforcement material, and the two are filled with a micro-expansion modified epoxy resin as a bonding material. The coating layer is arranged on the outer surface of the composite reinforcement material. The composite reinforcement material is a basalt fiber reinforced composite material and is composed of two hollow assembly modules nested by pultrusion through a mold.

[0009] Furthermore, the fiber grating sensor includes a fiber grating inner core, a polytetrafluoroethylene tube and a composite material sheath arranged in sequence from the inside to the outside; the coating layer is an epoxy resin-based composite fiber material with a single layer thickness of 1.5 mm to 3 mm, and the fiber material is selected from any one of basalt fiber, carbon fiber or glass fiber, preferably basalt fiber; the protective component includes a heat shrink tube, an optical cable protective cover and a spring protective cover.

[0010] A method for preparing a smart tendon based on fiber grating comprises the following steps:

[0011] S1: Prepare the fiber Bragg grating sensor and install it on the reinforcement to form an integral assembly;

[0012] S2: providing a coating layer on the outside of the overall component;

[0013] S3: Install the protective component on the pigtail connection part of the fiber optic Bragg grating sensor.

[0014] Furthermore, the step S1 includes:

[0015] S1.1: Prepare the reinforcement components of the hollow structure;

[0016] S1.2: Place the fiber Bragg grating sensor in the cavity of the reinforcement assembly and fix it with micro-expansion modified epoxy resin;

[0017] S1.3: Form the reinforcement components.

[0018] Furthermore, the reinforcement component is composed of two special-shaped hollow modules, which are produced by die pultrusion and assembled by nesting. The reinforcement forming is completed by assembly line traction and oven heating.

[0019] Furthermore, the preparation of the fiber Bragg grating sensor in step S1 includes: inserting the fiber Bragg grating core into a polytetrafluoroethylene tube, and then forming the fiber Bragg grating sensor through braiding, dipping and heating and curing processes.

[0020] Furthermore, the coating layer in step S2 is provided on the surface of the reinforcement material and is formed by compounding a woven fiber layer and an epoxy resin, and the fiber material is selected from basalt fiber, carbon fiber or glass fiber.

[0021] Furthermore, the protection assembly in step S3 includes a heat shrink tube for fusion splicing, an optical cable protection sleeve and a spring protection sleeve, which are sequentially installed in the pigtail connection area.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects:

[0023] Simplified packaging process and improved production efficiency

[0024] The smart reinforcement of this invention utilizes hollow basalt fiber composite reinforcement to encapsulate fiber Bragg grating sensors, eliminating the traditional grooving process and significantly improving the fabrication precision and production efficiency of the smart reinforcement. Furthermore, this structure enables the production of ultra-long, continuous smart reinforcements. The basalt fiber composite reinforcement exhibits moderate curvature, facilitating transport. Its modular design offers diverse forms, adapting to installation requirements on a variety of curved surfaces.

[0025] Enhanced sensor protection and deployment flexibility

[0026] The fiber Bragg grating (FBG) sensor in this invention is protected by a polytetrafluoroethylene (PTFE) tube and a basalt fiber-epoxy resin composite sheath, effectively preventing damage to the fiber during the repackaging process and significantly improving the sensor's survival rate. Multiple fiber Bragg grating sensors of the same type can be arranged in a continuous pattern to form a three-dimensional distributed sensing array, enabling real-time monitoring of multiple indicators within a structural area, including strain, settlement, displacement, tilt, and cracks.

[0027] Strong structural protection and long service life

[0028] The fiber braid not only effectively protects the sensor and its internal structure, but also offers excellent durability and overall waterproofing, ensuring the long-term stable operation of the smart reinforcement in harsh environments. Furthermore, the fiber pigtail armor design effectively protects the fiber and the pigtail splice from damage caused by external impact, extrusion, or bending, further extending the system's monitoring lifespan.

[0029] Excellent material performance and wide range of applications

[0030] The basalt fiber composite material used in the present invention has excellent mechanical properties such as high strength, light weight, creep resistance, and fatigue resistance. It can be used as a structural load-bearing component and is widely applicable to the performance monitoring needs of various complex engineering structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the smart muscle;

[0032] Figure 2 is the cross-sectional view of the smart reinforcement;

[0033] Figure 3 is a flow chart of the preparation method;

[0034] Figure 4 is a schematic diagram of a performance comparison table of the smart reinforcement in this embodiment and existing reinforcement materials;

[0035] In the figure, 1. Fiber Bragg grating sensor, 2. Reinforcement material, 3. Coating layer, 4. Protective component, 5. Inner core, 6. Polytetrafluoroethylene tube. DETAILED DESCRIPTION

[0036] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to embodiments and drawings. The embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0037] Example 1: Structure

[0038] A fiber Bragg grating (FBG)-based smart reinforcement includes a fiber Bragg grating (FBG) sensor 1, a cladding layer 3, and a protective component 4. The cladding layer 3 is arranged on the outer surface of the fiber Bragg grating (FBG) sensor 1, and the protective component 4 is arranged at the tail of the smart reinforcement. The FBG sensor is connected to the reinforcement material 2 and is used to detect the strain of the reinforcement material.

[0039] This embodiment integrates a fiber grating sensor 1 into the smart rib to achieve precise monitoring of physical quantities such as structural strain and temperature. The outside of the fiber grating sensor 1 is covered with a coating 3 to enhance its mechanical strength and environmental adaptability; the protective component 4 is arranged at the tail of the smart rib to fix and reinforce the connection of the optical fiber at the tail of the sensor to prevent damage to the connection. The fiber grating sensor 1 includes a fiber grating core 5, a polytetrafluoroethylene tube 6 and a composite material sheath structure from the inside to the outside, which can effectively resist external mechanical disturbances and improve the service life and signal stability of the sensor. The protective component 4 at the tail includes a heat shrink tube, an optical cable protective sleeve and a spring protective sleeve, which are respectively used to seal the fusion joint, provide flexible buffering and prevent the optical cable from bending due to external forces.

[0040] This structural design not only effectively encapsulates and protects the fiber grating sensor 1, enhancing its adaptability in complex environments, but also provides excellent mechanical properties and durability. The cladding layer 3 enhances the overall structural strength, effectively reducing damage to the sensor caused by environmental changes or during construction. The tail protection assembly 4 improves the reliability and fatigue resistance of the fiber connection, significantly increasing the stability and service life of the entire smart rib structure.

[0041] In one possible embodiment, the smart reinforcement further includes a composite reinforcement 2, which is a hollow structure for accommodating a fiber optic Bragg grating sensor 1. The fiber optic Bragg grating sensor 1 is disposed in the cavity of the composite reinforcement 2, and a micro-expansion modified epoxy resin is filled between the two as a bonding material. The coating layer 3 is disposed on the outer surface of the composite reinforcement 2. The composite reinforcement 2 is a basalt fiber reinforced composite material and is composed of two hollow assembly modules nested by pultrusion through a mold.

[0042] The implementation method configures a hollow composite reinforcement 2 inside the smart reinforcement to accommodate the fiber optic Bragg grating sensor 1, and fills the gap therein with a micro-expansion modified epoxy resin to play a role in strong bonding and strain transmission, ensuring that the fiber optic Bragg grating sensor 1 can accurately sense the stress state of the composite reinforcement. The composite reinforcement 2 is made of basalt fiber reinforced epoxy resin, which has excellent strength, corrosion resistance and temperature stability. Its structure is composed of two special-shaped hollow reinforcement assembly modules that are continuously pultruded by corresponding male and female molds and then nested and combined to form a stable and reliable hollow structure. The inner cavity size is not less than 2.5mm and the wall thickness is not less than 2mm to ensure structural strength and installation space. The coating layer 3 is arranged on the outside of the composite reinforcement 2 to further enhance the protection performance and wear resistance. The structure as a whole forms an integrated smart reinforcement component with good mechanical properties and signal acquisition capabilities.

[0043] By utilizing hollow basalt fiber-reinforced composite reinforcement, the smart reinforcement boasts both high strength and lightweight construction. The hollow structure effectively accommodates fiber Bragg grating sensors (FBGs), and, combined with micro-expansion modified epoxy resin for securement, enables efficient and stable strain transmission. The modular assembly of the reinforcement improves production efficiency and reduces manufacturing complexity, while also enabling continuous mass production, facilitating widespread application.

[0044] In one possible embodiment, the fiber grating sensor 1 includes a fiber grating core 5, a polytetrafluoroethylene tube 6 and a composite material sheath arranged in sequence from the inside to the outside; the coating layer 3 is an epoxy resin-based composite fiber material with a single layer thickness of 1.5 mm to 3 mm, and the fiber material is selected from any one of basalt fiber, carbon fiber or glass fiber, preferably basalt fiber; the protective component 4 includes a heat shrink tube, an optical cable protective cover and a spring protective cover.

[0045] This embodiment describes in detail the structural composition and protection mechanism of the fiber grating sensor 1. The fiber grating core 5 is the core of the sensing function, which can respond to structural strain or temperature changes and reflect them as changes in the reflected wavelength. In order to enhance its mechanical protection and insulation performance, it is wrapped with a polytetrafluoroethylene tube 6, and the outer layer is a basalt fiber reinforced epoxy composite sheath. The composite sheath not only provides mechanical protection, but also has excellent weather resistance and pressure resistance. The coating layer 3 adopts epoxy resin-based composite fiber material, and the thickness of the single layer is controlled between 1.5 and 3 mm to ensure the structural integrity of the sensor and its shielding effect against external forces. The fiber can be selected from basalt, carbon fiber or glass fiber to adapt to different environments. Basalt fiber is preferred to take into account both strength and cost. The protection component 4 includes a heat shrink tube, an optical cable protective sleeve and a spring protective sleeve arranged in the tail fusion zone. The three work together to achieve sealing, buffering and anti-fatigue protection of the optical fiber tail, thereby ensuring the long-term stable operation of the sensor.

[0046] Through layered protection and structural optimization, the stability and reliability of the fiber Bragg grating sensor 1 have been significantly improved. The selection of different materials provides greater flexibility for engineering applications of the smart reinforcement. This structure maintains excellent performance, particularly in high-stress, humid, or corrosive environments. Furthermore, the tail protection design effectively extends the sensor's service life and reduces maintenance frequency, demonstrating its excellent practicality and potential for engineering application.

[0047] Example 2: Preparation method

[0048] A method for preparing a fiber Bragg grating (FBG)-based smart tendon comprises the following steps:

[0049] Step S1, preparing the fiber Bragg grating sensor 1: slowly inserting the fiber Bragg grating core 5 into the polytetrafluoroethylene tube 6, starting the braiding machine and pulling equipment to braid the outer fiber layer, and simultaneously performing epoxy resin impregnation. The fiber Bragg grating sensor 1 is then cured by applying a load and heating to form a structurally stable fiber Bragg grating sensor 1. Multiple sensors can be arranged in series, and continuous transmission can be achieved through fiber fusion splicing.

[0050] During this process, pultrusion equipment is used to prepare two special-shaped hollow reinforcement 2 assembly modules. The modules are made of basalt fiber reinforced composite materials and are precisely cut to the required length.

[0051] Step S1 continues by embedding the prepared fiber Bragg grating sensor 1 into the cavity of one of the special-shaped hollow reinforcement 2 assembly modules, with the minimum size of the cavity being not less than 2.5 mm to accommodate the sensor structure; then filling it with micro-expansion modified epoxy resin to ensure that the sensor is fixed and stable, and finally covering the other assembly module to form a sealed structure to constitute a basalt fiber composite reinforcement.

[0052] After the assembly is completed, the structure is clamped and fixed by using a fixed chuck seat and a movable chuck seat, and is sent into the assembly line oven through a traction and guide rail device for rapid thermal curing to complete the integrated molding of the reinforcement 2.

[0053] Step S2: Applying a coating layer 3 to the outer surface of the formed composite reinforcement 2: The basalt fiber composite reinforcement is placed on a support and either end is passed through a braiding machine to weave the outer layer of yarn bundles. The yarn bundles can be made of carbon fiber, glass fiber, or basalt fiber, preferably the same material as the reinforcement, namely basalt fiber. During the coating and weaving process, epoxy resin is applied to ensure uniform fiber distribution and no dripping. After completion, the coating is cured by heating. To enhance protective performance, the braiding can be repeated to form a multi-layer structure.

[0054] Step S3, installing the protective component 4 on the pigtail connection part of the fiber optic Bragg grating sensor 1: after stripping the fiber sheath of the pigtail, put on the heat shrink tube and perform the fiber optic fusion splicing operation, then heat and shrink the heat shrink tube to ensure that it fits tightly; in order to further improve the resistance of the connection to mechanical damage, the optical cable protective cover and the spring protective cover are sequentially put on the heat shrink tube and the tail of the optical cable to form a layered protection structure.

[0055] This manufacturing method achieves intelligent reinforcement manufacturing with integrated structure and function through process integration. Precision fiber placement and embedding, module assembly, bonding and curing, and pultrusion achieve tight coupling between the sensor and the composite reinforcement. The outer fiber braiding and resin impregnation enhance structural strength and environmental adaptability. A tail protection system improves connection reliability, ensuring signal stability and resistance to external interference. The entire production process is suitable for continuous, automated control.

[0056] This method can produce ultra-long, continuous smart reinforcements with consistent length, stable structure, and reliable performance, effectively addressing the difficulties of deploying and short lifespan of traditional embedded sensors. The reinforcement, constructed from a basalt fiber and epoxy resin system, offers advantages such as high strength, lightweight, and corrosion resistance. The continuous deployment of fiber Bragg grating sensors and the tail protection structure further ensure continuous and stable signal acquisition, making it suitable for health monitoring of large-scale concrete structures, bridges, tunnels, and other infrastructure.

[0057] like Figure 4 As shown in the table, we can analyze the impact of different production processes on performance:

[0058] 1. Tensile strength (core performance indicator):

[0059] The strengths of experimental group 1 (950 MPa) and experimental group 2 (800 MPa) were significantly higher than those of ordinary steel bars (400-560 MPa), and slightly lower than those of the control group;

[0060] Although the tensile strength of control group 1 (1200 MPa) was higher, the fiber survival rate was low (40%), indicating poor structural integrity;

[0061] The bonding structure of the experimental group has both high tensile strength and good optical fiber protection effect.

[0062] 2. Fiber survival rate (fiber damage rate):

[0063] The experimental groups were ≥95%, much higher than control group 1 (40%) and control group 2 (45%), indicating that the nested bonding method can effectively protect the optical fiber structure and is suitable for intelligent monitoring scenarios;

[0064] This shows that the experimental group scheme has significant advantages in maintaining the stability of optical fiber signals.

[0065] 3. Product length limit:

[0066] The experimental group maintained at 500m, far exceeding the control group (20-30m), and had the ability to achieve continuous batch production;

[0067] This is particularly critical for large-scale applications required in actual engineering monitoring.

[0068] 4.Production efficiency (m / h):

[0069] The efficiency of the experimental group (1.4, 1.3, and 1.4 m / h) was significantly higher than that of the control group (1.0, 0.6, and 0.7 m / h);

[0070] This shows that the nested bonding structure not only has excellent performance, but is also suitable for automated assembly line processes.

[0071] The experimental data listed in Table 1 demonstrates that the nested-bonded intelligent rib structure of the present invention outperforms traditional surface-bonded or slotted-bonded structures in key performance aspects, including tensile strength, fiber survival rate, and production efficiency. In the experimental group, the nested ribs achieved a fiber survival rate of 95% while maintaining sensor performance, far exceeding the 40% to 45% achieved with traditional ribs, significantly improving sensor signal stability and acquisition reliability.

[0072] Furthermore, the control group used basalt composite reinforcement. Conventional steel bars exhibited strengths between 400 and 560 MPa, demonstrating the significant mechanical advantages of the intelligent reinforcement. The finished product reached a maximum length of 500 meters, with a continuous production rate of 1.31.4 m / h. This significantly surpasses the conventional process, which can only produce lengths of 20 to 30 meters. This demonstrates the feasibility and practicality of the intelligent reinforcement for large-scale engineering structures.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A smart tendon based on fiber Bragg grating, characterized in that: It includes a fiber grating sensor, a cladding layer and a protective component. The cladding layer is arranged on the outer surface of the fiber grating sensor, the protective component is arranged at the tail of the smart reinforcement, and the grating sensor is connected to the reinforcement material to detect the strain of the reinforcement material.

2. The smart reinforcement according to claim 1, characterized in that: It also includes a composite reinforcement material, which is a hollow structure for accommodating a fiber optic Bragg grating sensor. The fiber optic Bragg grating sensor is arranged in the cavity of the composite reinforcement material, and the two are filled with a micro-expansion modified epoxy resin as a bonding material. The coating layer is arranged on the outer surface of the composite reinforcement material. The composite reinforcement material is a basalt fiber reinforced composite material and is composed of two hollow assembly modules nested by pultrusion through a mold.

3. The smart reinforcement according to claim 1 or 2, characterized in that: The fiber grating sensor includes a fiber grating inner core, a polytetrafluoroethylene tube and a composite material sheath arranged in sequence from the inside to the outside; the coating layer is an epoxy resin-based composite fiber material with a single layer thickness of 1.5 mm to 3 mm, and the fiber material is selected from any one of basalt fiber, carbon fiber or glass fiber, preferably basalt fiber; the protective component includes a heat shrink tube, an optical cable protective cover and a spring protective cover.

4. A method for preparing a smart tendon based on fiber Bragg grating, characterized in that: The following steps are involved: S1: Prepare the fiber Bragg grating sensor and install it on the reinforcement to form an integral assembly; S2: providing a coating layer on the outside of the overall component; S3: Install the protective component on the pigtail connection part of the fiber optic Bragg grating sensor.

5. The preparation method according to claim 4, characterized in that The step S1 comprises: S1.1: Prepare the reinforcement components of the hollow structure; S1.2: Place the fiber Bragg grating sensor in the cavity of the reinforcement assembly and fix it with micro-expansion modified epoxy resin; S1.3: Form the reinforcement components.

6. The preparation method according to claim 5, characterized in that The reinforcement component is composed of two special-shaped hollow modules, which are produced by die pultrusion and assembled by nesting. The reinforcement forming is completed by assembly line traction and oven heating.

7. The preparation method according to claim 4 or 5, characterized in that The preparation of the fiber Bragg grating sensor in step S1 includes: inserting the fiber Bragg grating core into a polytetrafluoroethylene tube, and then forming the fiber Bragg grating sensor through braiding, dipping and heating and curing processes.

8. The preparation method according to any one of claims 4 to 6, characterized in that In step S2, the coating layer is provided on the surface of the reinforcement material and is formed by compounding a woven fiber layer and an epoxy resin. The fiber material is selected from basalt fiber, carbon fiber or glass fiber.

9. The preparation method according to claim 4, characterized in that The protection assembly in step S3 includes a heat shrink tube for fusion splicing, an optical cable protection sleeve, and a spring protection sleeve, which are sequentially installed in the pigtail connection area.

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