Optical fiber self-monitoring FRP rod and fiber stripping method thereof

Abstract

The present invention proposes a fiber optic self-monitoring FRP rod and a fiber stripping method thereof, belonging to the field of intelligent structural materials. This invention solves the problem of existing self-monitoring FRP bars / rods that it is difficult to simultaneously ensure high fiber bonding performance and convenient fiber stripping. The fiber optic self-monitoring FRP rod comprises a bare optical fiber, a thermoplastic tight jacket layer, and a thermosetting FRP layer. The bare optical fiber is coated with a thermoplastic tight jacket layer, which is then coated with a thermosetting FRP layer. The thermosetting FRP layer comprises fibers and a thermosetting resin. The fibers are impregnated with the thermosetting resin, then wrapped around the thermoplastic tight jacket layer and subjected to a pultrusion process to form the thermosetting FRP layer. It is primarily used for structural health monitoring.

Description

Technical Field

[0001] The invention belongs to the field of intelligent structural materials, and in particular relates to an optical fiber self-monitoring FRP rod and a fiber stripping method thereof. Background Art

[0002] Fiber-reinforced plastic (FRP) rods / ribs are formed by pultruding fibers and resins, offering excellent properties such as lightness, high strength, corrosion resistance, and fatigue resistance. Common FRP materials include carbon fiber composites (CFRP), glass fiber composites (GFRP), basalt fiber composites (BFRP), and aramid fiber composites (AFRP).

[0003] In concrete and anchor structures, replacing steel with FRP bars effectively addresses the issue of steel corrosion. In bridge cable structures and long-span cable-stayed structures, replacing steel cables with FRP rods significantly reduces the deadweight of the structure, surpassing the span limits of steel-stayed bridges. The use of FRP rods and bars in civil engineering structures is crucial for lightweighting, improving durability and fatigue resistance in complex environments, and ultimately extending the lifespan of the structure.

[0004] Fiber optic sensing and monitoring technology offers advantages such as long sensing distance, high sensitivity, strong resistance to radiation interference, high stability, and the ability to deform synergistically with FRP materials. Fiber optic sensors can monitor the strain, temperature, and vibration of structures and have been widely used to address structural health monitoring issues. Currently, commonly used fiber optic monitoring technologies include fiber Bragg grating (FBG), weak grating technology, Brillouin scattering (BOTDA / R), Rayleigh time-domain reflectometry (OTDR), and Rayleigh frequency-domain reflectometry (OFDR). Measurement equipment developed based on OFDR technology can now achieve strain monitoring with a maximum spatial resolution of 1 mm and a maximum strain measurement accuracy of ±1.0 με. This requires close bonding of the optical fiber to the structure and synergistic deformation to ensure high measurement accuracy.

[0005] Fiber optic sensors, fibers, and resins can be fabricated through a pultrusion process into fiber-optic sensing FRP self-monitoring bars / rods. These bars / rods not only protect the fragile optical fibers within, but also provide both sensing and load-bearing capabilities. This allows for long-term monitoring of structures such as concrete, cables, and anchors, as well as the FRP bars / rods themselves. Ou Jinping and others at Harbin Institute of Technology were the first in China to embed fiber Bragg gratings (FBGs) within FRP bars. This technology has been applied in several bridge engineering monitoring projects, playing a significant role in safety assessments.

[0006] However, since the fiber-optic self-monitoring FRP rod requires the ends of the optical fibers to be welded to the fiber connectors during use for connection to monitoring equipment, the fiber inside the FRP self-monitoring rod must be able to be quickly removed to meet the long-term continuous production requirements of the pultrusion process and the ready-to-use of finished products of any length. At the same time, to meet the monitoring requirements of high spatial resolution and high-precision monitoring technologies such as OFDR, the optical fiber and the FRP layer must maintain coordinated deformation, that is, excellent interfacial bonding between the two. This creates the dilemma of requiring rapid stripping of the internal optical fiber of the self-monitoring FRP rod while also ensuring good bonding performance.

[0007] There are three existing methods for rapidly removing optical fibers from FRP self-monitoring ribs / rods. The first involves reserving a section of fiber for wiring after each FRP rod of the required length is produced during pultrusion. However, this method fails to achieve long-term continuous production or readily available fiber lengths, significantly reducing production efficiency and practicality. The second method involves wrapping the optical fiber with a Teflon sleeve to prevent direct adhesion to the FRP layer, allowing for rapid removal of the outer FRP layer. However, this prevents the internal optical fiber and FRP layer from deforming in concert, failing to meet the requirements of high spatial resolution and high-precision monitoring technologies like OFDR. The third method is to replace the thermosetting resin used to impregnate the fiber with a thermoplastic resin during the pultrusion process to produce a FRTP self-monitoring rod, and then heat the FRTP rod to soften the outer layer of FRTP to achieve optical fiber stripping. However, the current thermoplastic pultrusion production process is not mature, and this process will seriously reduce the tensile strength of the rod and increase production costs. At the same time, this method is difficult to implement in the actual optical fiber stripping process. Since the optical fiber diameter is only about 125 microns and the entire rod uses a matrix, the optical fiber has no additional tight-fitting layer to protect and distinguish it. Therefore, even if the outer layer of FRTP is softened, the optical fiber will still break together with the fiber during the stripping process, or the optical fiber cannot be found at all. Summary of the Invention

[0008] In view of this, the present invention aims to propose an optical fiber self-monitoring FRP rod and a fiber stripping method thereof, so as to solve the problem that the existing self-monitoring FRP ribs / rods are difficult to simultaneously ensure high optical fiber bonding performance and convenient optical fiber stripping.

[0009] To achieve the above-mentioned purpose, according to one aspect of the present invention, there is provided an optical fiber self-monitoring FRP rod, comprising a bare optical fiber, a thermoplastic tight jacket layer and a thermosetting FRP layer, wherein the outer layer of the bare optical fiber is coated with the thermoplastic tight jacket layer, and the outer layer of the thermoplastic tight jacket layer is coated with the thermosetting FRP layer; the thermosetting FRP layer comprises fibers and a thermosetting resin, and the fibers are impregnated with the thermosetting resin and then wrapped on the thermoplastic tight jacket layer, and then subjected to a pultrusion process to form a thermosetting FRP layer.

[0010] Furthermore, the bare optical fiber is a commercial uncoated optical fiber, an EA-coated optical fiber, a polyimide-coated optical fiber, a grating optical fiber or a weak-grating optical fiber.

[0011] Furthermore, the thermoplastic tight-fitting layer is Hytrel thermoplastic resin, PVC thermoplastic resin, ABS thermoplastic resin or PLA thermoplastic resin.

[0012] Furthermore, the fiber is carbon fiber, glass fiber, basalt fiber or aramid fiber.

[0013] According to another aspect of the present invention, a method for stripping an optical fiber self-monitoring FRP rod is provided, comprising the following steps:

[0014] S1. Rod cutting: Cut a certain length of the required self-monitoring FRP rod. The cut length is the sum of the required length and the length of the optical fiber lead.

[0015] S2, FRP ring cutting, using a ring cutting tool to perform ring cutting at a position a certain length away from the end of the self-monitoring FRP rod;

[0016] S3, FRP is broken, and the end of the self-monitoring FRP rod is bent at a certain angle to the main body of the self-monitoring FRP rod along the ring cutting mark, so that the thermosetting FRP layer is completely broken, while the bare optical fiber and the thermoplastic tight jacket layer remain connected;

[0017] S4. Heat stripping: Use a heating device to fully heat the broken self-monitoring FRP rod end to a temperature above the melting point of the thermoplastic tight jacket layer. After the thermoplastic tight jacket layer softens, the thermosetting FRP layer and the thermoplastic tight jacket layer at the end are completely stripped off to expose the bare optical fiber.

[0018] Furthermore, in step S2, the circumferential cutting tool is used to perform circumferential cutting at a position 300 mm away from the end of the self-monitoring FRP rod, so that the diameter of the rod body of the remaining self-monitoring FRP rod after circumferential cutting is 2 mm.

[0019] Furthermore, the circular cutting tool in step S2 is a pipe circular cutting knife or an angle grinder.

[0020] Furthermore, the lead length is the length from the ring cutting position to the end, and the lead length is greater than or equal to 200 mm.

[0021] Furthermore, in step S3, the end of the self-monitoring FRP rod is bent repeatedly in four directions: front, back, left, and right.

[0022] Furthermore, the heating device in step S4 is a high-temperature heating air gun.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The fiber self-monitoring FRP rod uses a thermoplastic tight jacket layer to wrap the bare optical fiber, ensuring a tight bond between the bare optical fiber and the thermoplastic tight jacket layer. The thermosetting FRP layer and the thermoplastic tight jacket layer are tightly bonded under the combined action of bonding force, friction force, and mechanical bite force. As a result, the inner and outer layers of the self-monitoring FRP rod can all deform synergistically, resulting in extremely high measurement accuracy for the bare optical fiber.

[0025] 2. The inner layer of optical fiber can be quickly stripped out, and rods of any length can be cut. By heating the end of the self-monitoring FRP rod, the internal thermoplastic tight layer is softened, and the inner layer of optical fiber can be quickly stripped out for welding jumper joints. As a result, the self-monitoring FRP rod can be cut, stripped, and connected to any length, greatly improving the practicality of the project.

[0026] 3. The setting of the middle thermoplastic tight jacket layer avoids the problem of traditional integrated rod arrangement that easily causes the fiber and optical fiber to break during fiber stripping;

[0027] 4. Low material cost, convenient production, and high tensile strength. The cost of the thermoplastic tight-jacketed optical fiber used is about 1 / 10 to 1 / 100 of the existing strippable Teflon optical fiber;

[0028] 5. By directly adding optical fibers to the existing mature thermosetting FRP rod pultrusion production line, production can be achieved, reducing the cost of line modification without reducing the strength of the self-monitoring FRP rod; BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0030] Figure 1 This is a structural schematic diagram of an optical fiber self-monitoring FRP rod according to the present invention;

[0031] Figure 2 This is a fiber stripping flow chart of an optical fiber self-monitoring FRP rod according to the present invention;

[0032] Figure 3 This is a physical picture of the optical fiber self-monitoring FRP rod after fiber stripping described in the present invention.

[0033] Bare optical fiber 101; thermoplastic tight jacket layer 102; thermosetting FRP layer 103; self-monitoring FRP finished rod 201; unheated integral rod 202; bare optical fiber 203 stripped after heating; FRP rod and tight jacket layer 204 stripped after heating. DETAILED DESCRIPTION

[0034] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely explain the technical solutions in the embodiments of the present invention. It should be noted that the embodiments of the present invention and the features therein can be combined with each other in the absence of conflict, and the embodiments described are only part of the embodiments of the present invention, not all of the embodiments.

[0035] Referring to the accompanying drawings, this embodiment is described. According to one aspect of the present invention, there is provided an optical fiber self-monitoring FRP rod, comprising a bare optical fiber 101, a thermoplastic tight sleeve layer 102 and a thermosetting FRP layer 103. The outer layer of the bare optical fiber 101 is coated with the thermoplastic tight sleeve layer 102, and the outer layer of the thermoplastic tight sleeve layer 102 is coated with the thermosetting FRP layer 103; the thermosetting FRP layer 103 comprises fibers and thermosetting resin, and the fibers are impregnated with thermosetting resin and then wrapped on the thermoplastic tight sleeve layer 102, and then subjected to a pultrusion process to form the thermosetting FRP layer 103. The thermoplastic tight sleeve layer 102 covering the bare optical fiber 101 is produced by an extrusion tight sleeve process, and the interface is tightly bonded, which can ensure the coordinated deformation of the bare optical fiber 101 and the thermoplastic tight sleeve layer 102. The pultrusion process ensures that the thermosetting FRP layer 103 and the thermoplastic tight sleeve layer 102 are tightly bonded under the combined action of bonding force, friction force and mechanical bite force, thereby ensuring that the optical fiber self-monitoring FRP rod of the entire three-layer structure can be cooperatively deformed, so that the bare optical fiber 101 has extremely high measurement accuracy.

[0036] In this embodiment, the bare optical fiber 101 is a commercial uncoated optical fiber, an EA-coated optical fiber, a polyimide-coated optical fiber, a grating optical fiber, or a weak-grating optical fiber.

[0037] In this embodiment, the thermoplastic tight-fitting layer 102 is made of Hytrel thermoplastic resin, PVC thermoplastic resin, ABS thermoplastic resin or PLA thermoplastic resin.

[0038] In this embodiment, the fiber is carbon fiber, glass fiber, basalt fiber or aramid fiber.

[0039] According to another aspect of the present invention, a method for stripping an optical fiber self-monitoring FRP rod is provided, comprising the following steps:

[0040] S1. Rod cutting: Cut a certain length of the required self-monitoring FRP rod. The cut length is the sum of the required length and the length of the optical fiber lead.

[0041] S2, FRP ring cutting, using a ring cutting tool to perform ring cutting at a position a certain length away from the end of the self-monitoring FRP rod;

[0042] S3, the FRP is broken, and the end of the self-monitoring FRP rod is bent at a certain angle to the main body of the self-monitoring FRP rod along the ring cutting mark, so that the thermosetting FRP layer 103 is completely broken, while the bare optical fiber 101 and the thermoplastic tight jacket layer 102 remain connected;

[0043] S4, heating and stripping, using a heating device to fully heat the broken end of the self-monitoring FRP rod to a temperature above the melting point of the thermoplastic tight jacket layer 102. After the thermoplastic tight jacket layer 102 softens, the thermosetting FRP layer 103 and the thermoplastic tight jacket layer 102 at the end are completely stripped off to expose the bare optical fiber 101.

[0044] In this embodiment, the circumferential cutting tool is used in step S2 to perform circumferential cutting at a position 300 mm away from the end of the self-monitoring FRP rod, so that the diameter of the remaining self-monitoring FRP rod after circumferential cutting is 2 mm.

[0045] In this embodiment, the circular cutting tool in step S2 is a pipe circular cutting knife or an angle grinder.

[0046] In this embodiment, the lead length is the length from the ring cutting position to the end portion, and the lead length is greater than or equal to 200 mm.

[0047] In this embodiment, the method of bending the end of the self-monitoring FRP rod in step S3 is to repeatedly bend it in four directions, front, back, left, and right.

[0048] In this embodiment, the heating device in step S4 is a high-temperature heating air gun.

[0049] The present invention discloses a fiber self-monitoring FRP rod, which adopts a three-layer structure of a bare optical fiber 101, a thermoplastic tight jacket layer 102 and a thermosetting FRP layer 103. It can ensure that the bare optical fiber 101, the thermoplastic tight jacket layer 102 and the thermosetting FRP layer 103 are deformed in a coordinated manner, thereby ensuring that the bare optical fiber 101 has extremely high measurement accuracy. At the same time, with this three-layer structure, the thermoplastic tight jacket layer 102 and the thermosetting FRP layer 103 can be quickly peeled off after ring cutting and heating, thereby improving the fiber stripping efficiency. Due to the provision of the intermediate thermoplastic tight jacket layer 102, the problem of the traditional rod being easily broken together when stripping is avoided due to the integrated provision of the rod. When stripping, the traditional rod not only has the problem of reduced strength due to pulling during the stripping process, but also has the phenomenon of not even being able to find the optical fiber during the stripping process. The structure of the fiber self-monitoring FRP rod disclosed by the present invention can well solve the above problems. At the same time, an existing processing method is to reserve a section of optical fiber for wiring after each FRP rod of the required length is produced during pultrusion production. The structure adopted in this application does not require reserving a section of optical fiber, so long-distance production can be achieved, the process is simplified, and production costs are reduced. It can achieve the effect of taking it for use at any time, and also improves the convenience of using the self-monitoring FRP rod.

[0050] The embodiments of the present invention disclosed above are intended only to illustrate the present invention. The embodiments do not describe all details in detail, nor do they limit the present invention to the specific embodiments described. Numerous modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention.

Claims

1. A fiber stripping method for an optical fiber self-monitoring FRP rod, characterized by: The optical fiber self-monitoring FRP rod comprises a bare optical fiber (101), a thermoplastic tight jacket layer (102) and a thermosetting FRP layer (103); the outer layer of the bare optical fiber (101) is coated with the thermoplastic tight jacket layer (102), and the outer layer of the thermoplastic tight jacket layer (102) is coated with the thermosetting FRP layer (103); the thermosetting FRP layer (103) comprises fibers and thermosetting resin; the fibers are impregnated with thermosetting resin and then wrapped on the thermoplastic tight jacket layer (102), and then subjected to a pultrusion process to form the thermosetting FRP layer (103); The fiber stripping method includes the following steps: S1. Rod cutting: Cut a certain length of the required self-monitoring FRP rod. The cut length is the sum of the required length and the length of the optical fiber lead. S2, FRP ring cutting, using a ring cutting tool to perform ring cutting at a position a certain length away from the end of the self-monitoring FRP rod; S3, the FRP is broken, and the end of the self-monitoring FRP rod is bent at a certain angle to the main body of the self-monitoring FRP rod along the ring cutting mark, so that the thermosetting FRP layer (103) is completely broken, while the bare optical fiber (101) and the thermoplastic tight jacket layer (102) remain connected; S4, heating and stripping, using a heating device to fully heat the broken end of the self-monitoring FRP rod to a temperature above the melting point of the thermoplastic tight jacket layer (102), and after the thermoplastic tight jacket layer (102) softens, the thermosetting FRP layer (103) and the thermoplastic tight jacket layer (102) at the end are completely stripped to expose the bare optical fiber (101).

2. The method for stripping an optical fiber self-monitoring FRP rod according to claim 1, characterized in that: The bare optical fiber (101) is a commercial uncoated optical fiber, an EA-coated optical fiber, a polyimide-coated optical fiber, a grating optical fiber or a weak-grating optical fiber.

3. The method for stripping an optical fiber self-monitoring FRP rod according to claim 1, characterized in that: The thermoplastic tight jacket layer (102) is Hytrel thermoplastic resin, PVC thermoplastic resin, ABS thermoplastic resin or PLA thermoplastic resin.

4. The method for stripping an optical fiber self-monitoring FRP rod according to claim 1, characterized in that: The fiber is carbon fiber, glass fiber, basalt fiber or aramid fiber.

5. The method for stripping an optical fiber self-monitoring FRP rod according to claim 1, characterized in that: In step S2, the ring cutting tool is used to perform ring cutting at a position 300 mm away from the end of the self-monitoring FRP rod, so that the diameter of the remaining self-monitoring FRP rod after the ring cutting is 2 mm.

6. A fiber stripping method for an optical fiber self-monitoring FRP rod according to claim 1 or 5, characterized in that: The circular cutting tool in step S2 is a pipe circular cutting knife or an angle grinder.

7. The method for stripping an optical fiber self-monitoring FRP rod according to claim 1, characterized in that: The lead length is the length from the ring cutting position to the end, and the lead length is greater than or equal to 200 mm.

8. The method for stripping an optical fiber self-monitoring FRP rod according to claim 1, characterized in that: In step S3, the end of the self-monitoring FRP rod is bent by repeatedly bending it in four directions, front, back, left, and right.

9. The method for stripping an optical fiber self-monitoring FRP rod according to claim 1, characterized in that: The heating device in step S4 is a high-temperature heating air gun.

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