Optical fiber sensor and production method and production device thereof

Abstract

The invention is suitable for the technical field of optical fiber sensors, and provides an optical fiber sensor and a production method and device thereof, and the device comprises a creel which is used for unwinding an optical fiber and a plurality of glass fiber yarns; the gum dipping tank is used for containing a gum solution; the first guide assembly is used for guiding a first optical fiber and a glass fiber yarn into the glue dipping tank to be soaked in a glue solution; the second guide assembly is used for guiding the second optical fiber, so that the second optical fiber does not enter the gum dipping tank; and the pultrusion die is used for pultrusion, solidification and integration of the glass fiber yarn and the first optical fiber infiltrated with the glue solution and the second optical fiber not infiltrated with the glue solution into one bundle. The packaging structure is simple, the optical fiber sensor obtained after packaging is a circular cable, a specific length can be cut out according to the number of points needing to be measured, and the requirement for multiple measuring points in actual application is met. In addition, strain and temperature can be measured through the first optical fiber and the second optical fiber respectively.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber optic sensors, and particularly relates to a fiber optic sensor, a production method thereof, and a production device thereof. Background Art

[0002] Fiber Bragg grating sensors can be used to measure the strain and vibration changes during the force application process of materials, and are widely used in the monitoring of working environments and operation processes such as wind power generation, oil drilling platforms, mines, and underground pipe galleries. The fiber Bragg grating sensor itself is a bare optical fiber. Due to its low shear strength and susceptibility to damage by environmental factors such as humidity and vibration, it cannot be directly applied and needs to be encapsulated.

[0003] Existing encapsulation technologies usually encapsulate a small section of optical fiber, usually an optical fiber ranging from 0.1 to 1 meter, using metal, plastic and other shells through gluing, welding and other methods. The encapsulation structure is complex and the measurement points are limited. When multiple measurement points are required, two fiber optic sensors need to be fused together by the hot melting method. The fusion point is fragile and cannot guarantee the construction reliability and the long-term survival of the sensor. Summary of the Invention

[0004] The purpose of the embodiment of the present application is to provide a production device for a fiber optic sensor, aiming to solve the problems of complex existing fiber optic encapsulation structure and limited measurement points.

[0005] The embodiment of the present application is implemented as follows. A production device for a fiber optic sensor, the production device includes:

[0006] A yarn stand for unwinding an optical fiber and several glass fiber yarns, wherein the optical fiber includes a first optical fiber and a second optical fiber;

[0007] An impregnation tank for containing sizing;

[0008] A first guiding assembly for guiding the first optical fiber and the glass fiber yarn into the impregnation tank to soak in the sizing;

[0009] A second guiding assembly for guiding the second optical fiber so that the second optical fiber does not enter the impregnation tank;

[0010] A pultrusion die for pultruding and curing and integrating the glass fiber yarn soaked in the sizing, the first optical fiber, and the second optical fiber not soaked in the sizing into one bundle.

[0011] Another purpose of the embodiment of the present application is to provide a production method for a fiber optic sensor, the production method including:

[0012] Soaking the glass fiber yarn and the first optical fiber with sizing;

[0013] Pre-integrate the impregnated glass fiber yarn and the first optical fiber into a bundle. The glass fiber yarn and the sizing agent form a protective layer and wrap around the outer surface of the first optical fiber to obtain a semi-finished wire harness.

[0014] Pull the second optical fiber not impregnated with sizing agent, several third optical fibers, and the semi-finished wire harness into a bundle and heat-cure them into a cable-shaped fiber optic sensor.

[0015] Another object of the embodiments of the present application is to provide a fiber optic sensor, including a first optical fiber located in the inner layer. The first optical fiber is wrapped by glass fiber yarn and adhered to the glass fiber yarn through epoxy resin. The second optical fiber is arranged outside the glass fiber yarn, and the epoxy resin wraps the second optical fiber, the first optical fiber, and the glass fiber yarn together to form a bundle.

[0016] A production device for a fiber optic sensor provided by the embodiments of the present application. The glass fiber yarn, the first optical fiber, and the second optical fiber on the yarn rack are pulled by a traction device to move. The glass fiber yarn and the first optical fiber are immersed in a sizing tank through a first guiding component to impregnate the sizing agent. Then, the impregnated glass fiber yarn and the first optical fiber and the second optical fiber not impregnated with sizing agent are passed into a pultrusion die together for curing and forming, realizing the encapsulation of the optical fiber. The encapsulation structure is simple, and the obtained fiber optic sensor after encapsulation is a circular cable, which can intercept a specific length according to the number of measurement points required, meeting the needs of multiple measurement points in practical applications. Moreover, the first optical fiber and the second optical fiber are encapsulated simultaneously. After the first optical fiber is impregnated, it adheres to the glass fiber yarn and deforms together with the glass fiber yarn, making it sensitive to strain and improving the effect of measuring strain of the first optical fiber. The second optical fiber is not impregnated and is used to measure temperature. In this way, strain and temperature can be measured separately. Description of the Drawings

[0017] Figure 1 It is a schematic structural diagram of a production device for a fiber optic sensor provided by the embodiments of the present application;

[0018] Figure 2 It is a flowchart of a production method for a fiber optic sensor provided by the embodiments of the present application.

[0019] Wherein:

[0020] 10. First optical fiber; 20. Second optical fiber; 30. Glass fiber yarn; 40. Third optical fiber;

[0021] 100. Yarn rack; 110. Fiber Bragg grating sensing and measuring instrument; 200. Carding plate; 300. Tension control component; 400. Sizing tank; 510. First guiding component; 520. Second guiding component; 610. First bundling plate; 620. Bundling component; 700. Pultrusion die; 800. Traction device; 900. Finished product rack. Detailed Embodiments

[0022] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] The following describes the specific implementation of the present application in detail with reference to specific embodiments.

[0024] As Figure 1 shown, it is a schematic structural diagram of a production device for an optical fiber sensor provided by an embodiment of the present application. The production device includes: a yarn rack 100, an impregnation tank 400, a first guiding assembly 510, a second guiding assembly 520, and a pultrusion die 700.

[0025] The yarn rack 100 is used to unwind the optical fiber and several glass fiber yarns 30. Among them, the optical fiber includes a first optical fiber 10 and a second optical fiber 20. In some embodiments of the present application, the first optical fiber 10 and the second optical fiber 20 form a periodic grating structure in the fiber core, endowing it with wavelength selectivity and high-sensitivity sensing ability, and can be used as a sensor to detect external environmental parameters.

[0026] The impregnation tank 400 is used to hold the glue solution. In some embodiments, the glue solution is epoxy resin.

[0027] The first guiding assembly 510 is used to guide the first optical fiber 10 and the glass fiber yarn 30 into the impregnation tank 400 to soak the glue solution. Specifically, in some embodiments, the first guiding assembly 510 includes a plurality of rollers arranged in a row, and each roller guides a first optical fiber 10 or a glass fiber yarn 30. So that the first optical fiber 10 and the glass fiber yarn 30 are neatly arranged without being mixed. The plurality of rollers of the first guiding assembly 510 are arranged in the impregnation tank 400 to guide the first optical fiber 10 and the glass fiber yarn 30 into the impregnation tank 400 to soak the glue solution.

[0028] The second guiding assembly 520 is used to guide the second optical fiber 20 so that the second optical fiber 20 does not enter the impregnation tank 400. In some embodiments, the second guiding assembly 520 is a roller, and the roller of the second guiding assembly is arranged outside the impregnation tank 400 so that the second optical fiber 20 does not enter the impregnation tank 400.

[0029] The pultrusion die 700 is used to pultrude and cure the glass fiber yarn 30 and the first optical fiber 10 soaked with the glue solution and the second optical fiber 20 not soaked with the glue solution. In some embodiments, the pultrusion die 700 has a circular die hole with a diameter of 1 mm. The glass fiber yarn 30, the first optical fiber 10, and the second optical fiber 20 pass through the die hole together. The pultrusion die 700 heats up to cure the glue solution to obtain a finished optical fiber sensor, and the shape of the finished optical fiber sensor is a circular cable with a diameter of 1 mm.

[0030] In this embodiment, the glass fiber yarn 30, the first optical fiber 10, and the second optical fiber 20 on the yarn frame 100 are pulled by the traction device 800. The glass fiber yarn 30 and the first optical fiber 10 are immersed in the impregnating bath 400 through the first guiding assembly 510 to soak the sizing agent. Then, the glass fiber yarn 30 and the first optical fiber 10 soaked with the sizing agent and the second optical fiber 20 not soaked with the sizing agent are fed into the pultrusion die 700 together for curing and forming, realizing the encapsulation of the optical fiber. The encapsulation structure is simple. The obtained fiber optic sensor after encapsulation is a circular cable, and a specific length can be intercepted according to the number of measurement points required, meeting the needs of multiple measurement points in practical applications. Moreover, the first optical fiber 10 and the second optical fiber 20 are encapsulated simultaneously. After the first optical fiber 10 is soaked, it adheres to the glass fiber yarn 30 and deforms together with the glass fiber yarn 30, making it sensitive to strain, and reducing the strain loss caused by shear lag of the epoxy resin, enhancing strain transfer, and further improving the effect of the first optical fiber 10 in measuring strain. While the second optical fiber 20 is not soaked and is not sensitive to strain and is used to measure temperature. In this way, strain and temperature can be measured separately.

[0031] In some embodiments of the present application, the first optical fiber 10 is located in the innermost layer. The first optical fiber 10 is wrapped by the glass fiber yarn 30 and adhered to the glass fiber yarn 30 through epoxy resin. The second optical fiber 20 is arranged outside the glass fiber yarn 30. The epoxy resin outside the glass fiber yarn 30 wraps the second optical fiber 20 to form a bundle, obtaining a cable-shaped fiber optic sensor. In this way, the second optical fiber 20 is located in the outer layer and can better sense temperature. The first optical fiber 10 is located in the inner layer to reduce the interference caused by temperature changes and improve the measurement accuracy.

[0032] In some embodiments of the present application, the second optical fiber 20 can be made to have no chemical bonding with the epoxy resin through a coating or physical isolation, so that the stress generated by an external mechanical load cannot be transmitted to the second optical fiber 20, reducing interference.

[0033] In an example of the present application, the production device further includes a tension control assembly 300. The tension control assembly 300 is used to control the tensions of the glass fiber yarn 30, the first optical fiber 10, and the second optical fiber 20. In this embodiment, a pre-tension is applied to the optical fiber to offset the compressive stress caused by the shrinkage of the sizing agent during curing, reducing the zero drift of the fiber optic sensor caused by the curing of the sizing agent. Specifically, as Figure 1 shown, the tension control assembly 300 is arranged between the yarn frame 100 and the impregnating bath 400. The tension control assembly 300 includes a plurality of rollers. The optical fiber and the glass fiber yarn 30 are placed on the rollers. Pressure is applied to the rollers. By detecting the roller pressure, the tensions of the glass fiber yarn 30 and the optical fiber can be obtained, and the data is fed back to the yarn frame 100 and the traction device 800 to control the pulling forces at both ends of the optical fiber and the glass fiber yarn 30, and further control the tensions of the optical fiber and the glass fiber yarn 30 within a preset range. Specifically, in some embodiments, the range of the tension is 0N - 1N.

[0034] As Figure 1 shown, in some embodiments of the present application, a bundling assembly 620 is provided between the pultrusion die 700 and the sizing bath 400. The bundling assembly 620 is configured to pre-integrate the glass fiber yarn 30 and the first optical fiber 10 into a bundle, so that the glass fiber yarn 30 wraps the first optical fiber 10 to obtain a semi-finished wire harness. In this embodiment, the glass fiber yarn 30 and the first optical fiber 10 are pre-integrated into a bundle, such that the glass fiber yarn 30 wraps the first optical fiber 10, ensuring stable adhesion between the glass fiber yarn 30 and the first optical fiber 10. In the finished optical fiber sensor, the first optical fiber 10 deforms together with the glass fiber yarn 30, making the first optical fiber 10 sensitive to strain and improving the effect of measuring strain by the first optical fiber 10. The bundling assembly 620 includes a second bundling plate and a third bundling plate. A plurality of bundling holes for the glass fiber yarn 30 or the optical fiber to pass through are respectively provided on the second bundling plate and the third bundling plate. The first optical fiber 10 and the glass fiber yarns 30 on both sides of the first optical fiber 10 respectively pass through a bundling hole on the second bundling plate and converge into the same bundling hole on the third bundling plate to achieve bundling.

[0035] In some embodiments of the present application, as Figure 1 shown, a carding plate 200 is further provided between the yarn rack 100 and the tension control assembly 300. The carding plate 200 is used to arrange the glass fiber yarn 30 and the optical fiber neatly, preventing them from winding around each other.

[0036] In some embodiments of the present application, as Figure 1 shown, a traction device 800 is further provided at the discharge end of the pultrusion die 700. The traction device 800 is used to pull the finished optical fiber sensor out of the pultrusion die 700 and realize the traction of the first optical fiber 10, the second optical fiber 20, and the glass fiber yarn 30. In some embodiments, a finished product rack 900 for collecting the finished optical fiber sensor is further provided at the discharge end of the traction device 800.

[0037] In some embodiments of the present application, as Figure 1 shown, the yarn rack 100 is further connected to an optical fiber grating sensing and measuring instrument 110 to monitor the real-time states of the first optical fiber 10 and the second optical fiber 20 during the pultrusion process.

[0038] As Figure 1 shown, in some embodiments, a first bundling plate 610 is further provided between the sizing bath 400 and the bundling assembly 620. The first bundling plate 610 respectively pre-integrates the glass fiber yarns 30 on both sides of the first optical fiber 10 into bundles, facilitating better wrapping of the first optical fiber 10 subsequently.

[0039] In some embodiments of the present application, the cluster assembly 620 is also used to introduce a plurality of third optical fibers 40, and introduce the semi-finished wire harness, the plurality of third optical fibers 40, and the second optical fiber 20 together into the pultrusion die 700 for pultrusion and solidification into a bundle. In this embodiment, the semi-finished wire harness is located in the middle, and the plurality of third optical fibers 40 and the second optical fiber 20 are arranged around the semi-finished wire harness. When pultrusion is performed in the pultrusion die 700, the epoxy resin on the semi-finished wire harness will overflow, wrapping the second optical fiber 20 and the plurality of third optical fibers 40, and forming a cable-shaped optical fiber sensor after solidification.

[0040] like Figure 1 and Figure 2 As shown, the embodiment of the present application also provides a method for producing an optical fiber sensor, the production method comprising:

[0041] Step S100: Wetting the glass fiber yarn 30 and the first optical fiber 10 with glue.

[0042] In this embodiment, the glass fiber yarn 30 and the first optical fiber 10 are placed on the yarn rack 100, and the glass fiber yarn 30 and the first optical fiber 10 are pulled by the traction device 800 to make them move. The first guide assembly 510 guides the first optical fiber 10 and the glass fiber yarn 30 into the dipping tank 400 to be impregnated with glue.

[0043] In some embodiments, the glue is epoxy resin, the epoxy resin feed viscosity is 200-300mPa·s, the glass fiber yarn 30 and the epoxy resin constitute a glass fiber reinforced epoxy resin composite material, wherein the volume fraction of the glass fiber sand is 70%. In this way, it can be ensured that the first optical fiber 10 and the glass fiber yarn 30 can be infiltrated and will not flow out from the edge of the pultrusion die 700. In some embodiments of the present application, the temperature of the dipping tank 400 is set to 80-120°C, so as to better achieve the infiltration of the glue glass fiber yarn 30 and the first optical fiber 10.

[0044] Step S200: pre-integrate the soaked glass fiber yarn 30 and the first optical fiber 10 into a bundle, wherein the glass fiber yarn 30 and the adhesive form a protective layer and wrap the first optical fiber 10 to obtain a semi-finished wire harness.

[0045] In this embodiment, the glass fiber yarn 30 soaked in glue and the first optical fiber 10 are passed into the bundling assembly 620, and the bundling assembly 620 includes a second bundling plate and a third bundling plate. The second bundling plate and the third bundling plate are respectively provided with a plurality of bundling holes for the glass fiber yarn 30 or the optical fiber to pass through. The first optical fiber 10 and the glass fiber yarn 30 on both sides of the first optical fiber 10 respectively pass through a bundling hole on the second bundling plate and converge in the same bundling hole on the third bundling plate. The glass fiber yarn 30 and the glue form a protective layer and wrap around the surface of the first optical fiber 10 to obtain a semi-finished wire harness.

[0046] Step S300: Bundle the second optical fiber 20 not infiltrated with the sizing agent, several third optical fibers 40, and the semi-finished wire harness, and heat and cure them into a cable-shaped fiber optic sensor.

[0047] In this embodiment, unwinding devices are provided on both sides of the bundling assembly 620, and the unwinding devices introduce several third optical fibers 40 into the bundling assembly 620. After the second optical fiber 20, several third optical fibers 40, and the semi-finished wire harness pass through the bundling assembly 620, they converge and enter the pultrusion die 700, where they are bundled by pultrusion and heat-cured into a cable-shaped fiber optic sensor. In some embodiments, there are two third optical fibers 40, and the two optical fibers are arranged on the outermost sides. Refer to Figure 1 As shown, the two third optical fibers 40 are respectively arranged above and below the bundling assembly 620.

[0048] In this embodiment, by immersing the glass fiber yarn 30 and the first optical fiber 10 in the sizing tank 400 to infiltrate the sizing agent, and then performing pultrusion molding and heat curing on the glass fiber yarn 30 and the first optical fiber 10 infiltrated with the sizing agent together with the second optical fiber 20 not infiltrated with the sizing agent, the encapsulation of the optical fiber is realized. The encapsulation structure is simple, and the obtained fiber optic sensor after encapsulation is a circular cable, which can be cut to a specific length according to the number of measurement points required, meeting the requirements of multiple measurement points in practical applications. Moreover, by encapsulating the first optical fiber 10 and the second optical fiber 20 simultaneously, the first optical fiber 10 adheres to the glass fiber yarn 30 after infiltration and deforms together with the glass fiber yarn 30, making it sensitive to strain and improving the effect of the first optical fiber 10 in measuring strain, while the second optical fiber 20 is not infiltrated and is not sensitive to strain and is used to measure temperature. In this way, strain and temperature can be measured separately.

[0049] In some embodiments of the present application, the outer coating of the first optical fiber 10 is polyimide, and the polyimide coating can infiltrate epoxy resin. In some embodiments, the outer coating of the second optical fiber 20 is an acrylate coating, and the optical fiber with the acrylate coating cannot be infiltrated by epoxy resin.

[0050] In some embodiments of the present application, the tension of the glass fiber yarn 30, the first optical fiber 10, and the second optical fiber 20 is controlled at 0N - 1N, the temperature of the heat curing is 120°C - 200°C, and the traction speed of the pultrusion molding is 1 - 50 mm / min. Under the process parameters defined in this embodiment, the obtained fiber optic sensor can achieve better strength. Refer to Table 1 shown below for testing the breaking force and fracture force results of the finished fiber optic sensor.

[0051] Table 1:

[0052]

[0053] As can be seen from Table 1 above, when the parameters are within the defined ranges, better tensile strength and breaking strength can be obtained. In particular, when the tension is 0.2 N, the resin viscosity is 200 mPa·s, the dipping temperature is 120 °C, and the pultrusion die heating temperature is 200 °C, the finished fiber optic sensor can obtain better tensile strength and breaking strength, and the finished fiber optic sensor has higher strength.

[0054] In the embodiment of the present application, a fiber optic sensor is also provided, including a first optical fiber 10 located in the inner layer. The first optical fiber 10 is wrapped by a glass fiber yarn 30 and adhered to the glass fiber yarn 30 through epoxy resin. A second optical fiber 20 is arranged outside the glass fiber yarn 30, and the epoxy resin wraps the second optical fiber 20, the first optical fiber 10, and the glass fiber yarn 30 together to form a bundle.

[0055] In this embodiment, through the encapsulation of the optical fiber by the glass fiber reinforced epoxy resin composite material composed of the glass fiber yarn 30 and the epoxy resin, the encapsulation structure is simple. The obtained fiber optic sensor after encapsulation is a circular cable, and a specific length can be intercepted according to the number of measurement points required, meeting the requirements of multiple measurement points in practical applications. Moreover, the first optical fiber 10 and the second optical fiber 20 are encapsulated simultaneously. After the first optical fiber 10 is infiltrated, it adheres to the glass fiber yarn 30 and deforms together with the glass fiber yarn 30, making it sensitive to strain and improving the effect of the first optical fiber 10 in measuring strain. The second optical fiber 20 is not infiltrated and is located on the outer layer for measuring temperature. In this way, strain and temperature can be measured separately.

[0056] In some embodiments of the present application, the fiber optic sensor further includes a plurality of third optical fibers 40. The plurality of third optical fibers 40 are located outside the glass fiber yarn 30, and the third optical fibers 40 are wrapped by the epoxy resin. In this embodiment, the third optical fibers 40 are also used for measuring temperature, but no tension is applied to the third optical fibers 40. It can be understood that when the epoxy resin cures and shrinks, it will apply compressive stress to the optical fiber, resulting in an initial wavelength shift (zero drift) of the optical fiber. Through the differential tension design, it is convenient to actively perform stress compensation in the later stage, offset the residual stress of the encapsulation, and improve the measurement accuracy.

[0057] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A production device for an optical fiber sensor, characterized in that: The production device comprises: A creel, used for unwinding an optical fiber and a plurality of glass fiber yarns, wherein the optical fiber includes a first optical fiber and a second optical fiber; Glue dipping tank, used for holding glue liquid; A first guide assembly is used to guide the first optical fiber and the glass fiber yarn into the dipping tank to be soaked in glue; A second guiding assembly is used to guide the second optical fiber so that the second optical fiber does not enter the dipping tank; The pultrusion die is used for pultruding and solidifying the glass fiber yarn soaked in glue and the first optical fiber and the second optical fiber not soaked in glue into a bundle.

2. The production device of an optical fiber sensor according to claim 1, characterized in that: The production device also includes a tension control component, which is used to control the tension of the glass fiber yarn, the first optical fiber and the second optical fiber.

3. The production device of an optical fiber sensor according to claim 1, characterized in that: A bundling assembly is provided between the pultrusion die and the dipping tank, and the bundling assembly is used to pre-integrate the glass fiber yarn and the first optical fiber into a bundle, so that the glass fiber yarn wraps the first optical fiber to obtain a semi-finished wire harness.

4. The production device of an optical fiber sensor according to claim 3, characterized in that: The cluster assembly is also used to introduce a plurality of third optical fibers, and introduce the semi-finished wire bundle, the plurality of third optical fibers and the second optical fiber into the pultrusion die for pultrusion and solidification into a bundle.

5. A method for producing an optical fiber sensor, characterized in that: The production method comprises: The glass fiber yarn and the first optical fiber are impregnated with glue; The soaked glass fiber yarn and the first optical fiber are pre-integrated into a bundle, wherein the glass fiber yarn and the adhesive form a protective layer and wrap the first optical fiber to obtain a semi-finished wire bundle; The second optical fiber not soaked in glue, a plurality of third optical fibers and the semi-finished wire bundle are pulled and extruded into a bundle and heated and solidified into a cable-shaped optical fiber sensor.

6. The method for producing an optical fiber sensor according to claim 5, characterized in that: The outer coating of the first optical fiber is polyimide, the glue is epoxy resin, and the protective layer is a glass fiber reinforced epoxy resin composite material.

7. The method for producing an optical fiber sensor according to claim 5, characterized in that: The tension of the glass fiber yarn, the first optical fiber and the second optical fiber is controlled at 0N-1N, the temperature of the heating and curing is 120°C-200°C, and the pulling speed of the pultrusion is 1-50mm / min.

8. The method for producing an optical fiber sensor according to claim 6, characterized in that: The epoxy resin feed viscosity is 200-300 mPa·s, and the volume fraction of glass fiber sand in the glass fiber reinforced epoxy resin composite material is 70%.

9. An optical fiber sensor, characterized in that: It includes a first optical fiber located in the inner layer, the first optical fiber is wrapped by glass fiber yarn and adhered to the glass fiber yarn through epoxy resin, the second optical fiber is arranged on the outside of the glass fiber yarn, and the epoxy resin wraps the second optical fiber, the first optical fiber and the glass fiber yarn together to form a bundle.

10. The optical fiber sensor according to claim 9, characterized in that: It also includes a plurality of third optical fibers, which are located outside the glass fiber yarn and are wrapped by the epoxy resin.

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