Fiber Bragg grating built-in prestressed composite material and processing method thereof

Abstract

The present invention provides a fiber Bragg grating built-in prestressed composite material and a processing method thereof, wherein the processing method comprises applying a first tension force to the prestressed composite material to be processed, and keeping the tension state unchanged; wherein the coating layer of the fiber Bragg grating peripheral device is transformed from a glass state to a highly elastic state within a first preset temperature range; the grating area of ​​the fiber Bragg grating in the prestressed composite material, the preset area of ​​the head fiber segment, and the tail fiber segment are heated until the temperature of the coating layer reaches the first preset temperature, and the wavelength of the fiber Bragg grating is continuously monitored; when it is monitored that the wavelength of the fiber Bragg grating remains unchanged, the heating of the prestressed composite material is stopped; when the temperature of the prestressed composite material drops to room temperature, the first tension force on the prestressed composite material is removed to obtain a prestressed composite material with a built-in pre-compressed fiber Bragg grating. The method provided by the present invention can reduce the strain of the fiber Bragg grating in the working state, increase the fatigue life of the fiber Bragg grating, and thus increase the service life.

Description

Technical Field

[0001] The invention relates to the technical field of composite materials, and in particular to a fiber grating built-in prestressed composite material and a processing method thereof. Background Art

[0002] Prestressed fiber composite materials have the advantages of light weight, high strength, good corrosion resistance, good tensile strength, etc. They have great advantages in the field of building reinforcement, especially in bridge reinforcement, and have been widely used.

[0003] In order to monitor the stress changes of the stressed structure in the prestressed reinforcement system, strain sensors are often used to measure the deformation of the stressed structure, and then calculate the actual stress value of the prestressed system. At present, there are two main measurement methods. One is to directly attach a strain sensor to the intended measurement location, such as a strain gauge, substrate-type or packaged fiber Bragg grating strain sensor to measure the deformation of the stressed structure. The other is to directly bury the fiber Bragg grating in the prestressed fiber composite material to measure the stress of the stressed structure in the prestressed reinforcement system.

[0004] However, although the direct external strain sensor is simple, its durability and long-term stability of data are poor due to long-term exposure to outdoor environments. Although the stress of the reinforcement system can be truly measured by directly embedding the fiber Bragg grating in the prestressed fiber composite material, the prestressed fiber composite material is often subjected to greater stress in actual working conditions. When the fiber Bragg grating sensor is embedded in the prestressed fiber composite material, the fiber Bragg grating is in a state of high stress and strain for a long time, especially when the reinforced part is subjected to fatigue stress, the service life of the fiber Bragg grating sensor will be greatly reduced, making it impossible to monitor the prestressed fiber composite material for a long time. Summary of the invention

[0005] The embodiment of the present invention provides a fiber Bragg grating embedded prestressed composite material and a processing method thereof, so as to solve the problem of reduced service life of the current fiber Bragg grating sensor when embedded in the prestressed fiber composite material.

[0006] In a first aspect, an embodiment of the present invention provides a method for processing a fiber Bragg grating internal prestressed composite material, comprising:

[0007] Applying a first tension force to the prestressed composite material to be processed, and keeping the tension state unchanged; wherein a coating layer is provided on the periphery of the fiber grating, and the coating layer is transformed from a glass state to a highly elastic state within a first preset temperature range;

[0008] The grating area of ​​the fiber Bragg grating in the prestressed composite material, the preset area of ​​the head fiber segment and the tail fiber segment are heated until the temperature of the coating layer reaches a first preset temperature, and the wavelength of the fiber Bragg grating is continuously monitored;

[0009] When it is monitored that the wavelength of the fiber grating remains unchanged, the heating of the prestressed composite material is stopped;

[0010] When the temperature of the prestressed composite material drops to room temperature, the first tension on the prestressed composite material is removed to obtain a prestressed composite material with built-in pre-compressed optical fiber Bragg gratings.

[0011] In a possible implementation, the processing method further includes:

[0012] When it is detected that the signal peak shape transmitted through the prestressed composite material is distorted, the fiber grating built-in prestressed composite material is tensioned multiple times until the signal peak shape returns to normal.

[0013] In a possible implementation, the head fiber segment is the optical fiber from the grating area of ​​the fiber Bragg grating to the optical fiber interface of the prestressed composite material, the tail fiber segment is the optical fiber from the grating area of ​​the fiber Bragg grating to the tail of the fiber Bragg grating completely buried in the prestressed composite material, and the length of the tail fiber segment is 0.5 meters to 2 meters; the sum of the lengths of the head fiber segment and the tail fiber segment is less than the length of the prestressed composite material;

[0014] The preset area of ​​the head fiber segment is an area of ​​the head fiber segment close to the grating area of ​​the fiber grating, and the length of the preset area is greater than or equal to 10 cm.

[0015] In a possible implementation, the first preset temperature is greater than a temperature at which the prestressed composite material is normally used, and is less than a temperature at which the prestressed composite material is damaged by heat.

[0016] In a possible implementation, the first tension force is selected in a range of 60% to 140% of the stress of the fiber Bragg grating built-in composite material during actual installation.

[0017] In a possible implementation, the first tension force is selected in a range of 100%-105% of the stress of the fiber Bragg grating built-in composite material during actual installation.

[0018] In a second aspect, an embodiment of the present invention provides a prestressed composite material with an optical fiber Bragg grating built in, wherein the optical fiber Bragg grating built in the prestressed composite material is a pre-compressed optical fiber Bragg grating formed by a pre-compression process, wherein a coating layer is provided on the periphery of the pre-compressed optical fiber Bragg grating, and the coating layer is transformed from a glass state to a highly elastic state within a first preset temperature range;

[0019] The method for pre-compression treatment of pre-compressed fiber Bragg grating is: under the state of applying a first tensile force to the prestressed composite material, the grating area of ​​the fiber Bragg grating, the preset area of ​​the head fiber segment and the tail fiber segment in the prestressed composite material are heated until the coating layer is transformed from a glass state to a highly elastic state, and the heating is stopped after the wavelength of the fiber Bragg grating is stabilized. When the temperature of the prestressed composite material drops to room temperature, the first tensile force on the prestressed composite material is removed.

[0020] In a possible implementation, the head fiber segment is the optical fiber from the grating area of ​​the fiber Bragg grating to the optical fiber interface of the prestressed composite material, the tail fiber segment is the optical fiber from the grating area of ​​the fiber Bragg grating to the tail of the fiber Bragg grating completely buried in the prestressed composite material, and the length of the tail fiber segment is 0.5 meters to 2 meters; the sum of the lengths of the head fiber segment and the tail fiber segment is less than the length of the prestressed composite material;

[0021] The preset area of ​​the head fiber segment is an area of ​​the head fiber segment close to the grating area of ​​the fiber grating, and the length of the preset area is greater than or equal to 10 cm.

[0022] In a possible implementation, the length of the pigtail segment is 0.5 m-1 m, and the length of the preset area of ​​the head fiber segment is greater than or equal to 20 cm and less than or equal to 50 cm.

[0023] In a possible implementation, the coating layer is made of an acrylic material, and the first preset temperature is greater than or equal to 100° C. and less than or equal to 120° C.

[0024] The embodiment of the present invention provides a fiber Bragg grating built-in prestressed composite material and a processing method thereof. First, a first tension is applied to the prestressed composite material to be processed, and the tension state is kept unchanged. Next, the grating area of ​​the fiber Bragg grating in the prestressed composite material, the preset area of ​​the head fiber segment, and the tail fiber segment are heated until the temperature of the coating layer reaches the first preset temperature, and the wavelength of the fiber Bragg grating is continuously monitored. Then, when it is monitored that the wavelength of the fiber Bragg grating remains unchanged, the heating of the prestressed composite material is stopped. Finally, when the temperature of the prestressed composite material drops to room temperature, the first tension on the prestressed composite material is removed, and a prestressed composite material with a built-in pre-compressed fiber Bragg grating can be obtained. By pre-compressing a partial area of ​​the fiber Bragg grating embedded in the prestressed composite material by heating, on the one hand, the maximum range of the fiber Bragg grating sensor can be increased, and on the other hand, the strain of the fiber Bragg grating in the working state can be reduced, thereby increasing the fatigue life of the fiber Bragg grating and increasing the service life of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0026] Figure 1 It is a flow chart of a method for processing a fiber Bragg grating built-in prestressed composite material provided by an embodiment of the present invention;

[0027] Figure 2 It is a schematic diagram of the structure of the fiber Bragg grating provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0028] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below in conjunction with the accompanying drawings.

[0030] Bridges, tunnels, dams and other buildings will have their bearing capacity reduced as time goes by, materials age, environmental corrosion and natural disasters affect them, and in severe cases, they will cause immeasurable damage. Therefore, prestressed fiber composite materials, especially prestressed carbon fiber plates or carbon fiber tendons, are widely used in the field of building reinforcement, especially bridge reinforcement.

[0031] In order to monitor the change of prestress in the stressed structure of the prestressed reinforcement system, strain sensors are often used to measure the deformation of the stressed structure. As described in the background technology, a relatively simple method is to directly attach a strain sensor to the part to be measured, such as a strain gauge, substrate-type or packaged fiber grating strain sensor. However, in practical applications, on the one hand, since prestressed reinforcement materials are often exposed to outdoor environments for a long time, the harsh environment will seriously challenge the durability of external sensors and the long-term stability of data. On the other hand, although the weather resistance of the packaged sensor is improved to a certain extent, the barrier of the packaging material will also affect the sensitivity and hysteresis of the external strain sensor.

[0032] Therefore, in recent years, the monitoring method of directly embedding fiber Bragg gratings in prestressed composite materials has attracted attention. On the one hand, directly embedding fiber Bragg gratings in prestressed composite materials can more realistically measure the actual stress of the material. At the same time, the fiber Bragg gratings will be protected by the composite material itself and have better weather resistance. However, prestressed composite materials are often subject to greater stress in actual working conditions. Therefore, when using fiber Bragg gratings to monitor prestressed composite materials, the fiber Bragg gratings themselves will be in a state of large stress or large strain for a long time. For example, the elongation of prestressed carbon fiber plates under normal working conditions is often higher than 0.6%, corresponding to a micro strain of 6000 for fiber Bragg gratings, while the range of fiber Bragg gratings commonly used in the market is about 10,000 micro strains. When fiber Bragg gratings are in a state of large strain for a long time, especially when the reinforced components are subjected to fatigue stress, their fatigue life decreases exponentially, which seriously affects the application of fiber Bragg grating sensors in the field of long-term monitoring of prestressed composite materials.

[0033] In order to solve the problems in the prior art, an embodiment of the present invention provides a fiber Bragg grating built-in prestressed composite material and a processing method thereof. Firstly, the processing method of the fiber Bragg grating built-in prestressed composite material provided by the embodiment of the present invention is introduced below.

[0034] like Figure 1 As shown, the implementation flow chart of the processing method of the fiber Bragg grating built-in prestressed composite material provided by the embodiment of the present invention is described in detail as follows:

[0035] Step S110: applying a first tensioning force to the prestressed composite material to be processed, and keeping the tensioning state unchanged.

[0036] The outer periphery of the fiber Bragg grating is provided with a coating layer, and the coating layer is transformed from a glass state to a highly elastic state within a first preset temperature range. The coating layer here can be provided on the outer periphery of the entire optical fiber, or only on the part that needs to be processed, which is not limited here, and the coating range of the coating layer is determined according to the actual use scenario.

[0037] In this embodiment, the fiber Bragg grating is an embedded sensor, that is, during the pultrusion process of the prestressed composite material, the fiber Bragg grating is directly embedded in the prestressed composite material to form an integral body. Among them, the fiber Bragg grating can be a strain grating sensor.

[0038] In some embodiments, the optical fiber outside the grating area of ​​the fiber Bragg grating can be divided into a head fiber and a pigtail fiber. The head fiber segment is the optical fiber from the grating area of ​​the fiber Bragg grating to the optical fiber interface of the prestressed composite material, which is the end drawn out of the prestressed composite material. The pigtail fiber segment is the optical fiber from the grating area of ​​the fiber Bragg grating to the tail of the fiber Bragg grating completely buried in the prestressed composite material.

[0039] In this embodiment, in order not to affect the subsequent processing of the fiber grating, the length of the head fiber segment can be adjusted according to the specific design requirements, but it must be satisfied that the sum of the lengths of the head fiber segment and the tail fiber segment is less than the length of the prestressed composite material. Since a too short tail fiber segment will affect the anchoring effect of the fiber grating inside the prestressed composite material, a too long tail fiber segment will make the heating area during the pre-compression process too large and increase the resistance to fiber retraction, affecting the final processing effect. Therefore, the length of the tail fiber segment can be set to within the range of 0.5 meters to 2 meters. In order to maximize the fatigue life of the fiber grating, the length of the tail fiber segment can be set to 0.5 meters to 1 meter.

[0040] In some embodiments, in order to accurately measure the wavelength of the fiber Bragg grating using a fiber Bragg grating demodulator, a fiber Bragg grating processed by toe-cutting technology can be selected, which has a higher side mode suppression ratio ≥15dB and a sharper signal peak shape, which is conducive to the fiber Bragg grating demodulator to accurately measure the wavelength of the fiber Bragg grating.

[0041] In some embodiments, if the tension value is too small, the pre-compression degree of the fiber Bragg grating will be low, and the fatigue life of the fiber Bragg grating cannot be effectively improved. If the tension value is too large, it may cause damage or destruction to the prestressed composite material, affecting the yield rate of the production product and the stability of the product quality during actual construction. Therefore, the selection range of the first tension force can be 60%-140% of the stress of the fiber Bragg grating built-in composite material when it is actually installed. Specifically, the selection range of the first tension force is 100%-105% of the stress of the fiber Bragg grating built-in composite material when it is actually installed.

[0042] Step S120, heating the grating area of ​​the fiber Bragg grating in the prestressed composite material, the preset area of ​​the head fiber segment and the tail fiber segment until the temperature of the coating layer reaches a first preset temperature, and continuously monitoring the wavelength of the fiber Bragg grating.

[0043] Since the fiber Bragg grating is provided with a coating layer, the coating layer is transformed from a glassy state to a highly elastic state within the first preset temperature range. Such materials are transformed from a glassy state to a highly elastic state within the first preset temperature range, and will solidify again after the temperature drops. When the bonding force between the fiber core of the fiber Bragg grating and the coating layer fails, the fiber core of the fiber Bragg grating will gradually rebound from the tensioned state to a state with lower deformation.

[0044] In some embodiments, Figure 2 As shown, in order to prevent the distortion of the fiber Bragg grating signal peak shape caused by uneven stress in the grating area after pre-compression, which affects the collection of measurement data, the preset area of ​​the head fiber segment is the area of ​​the head fiber segment close to the grating area of ​​the fiber Bragg grating, and the length of the preset area is greater than or equal to 10 cm.

[0045] Specifically, the length of the preset area of ​​the head fiber segment may be greater than or equal to 20 cm and less than or equal to 50 cm.

[0046] In some embodiments, if the heating temperature is too low, the resistance of the fiber Bragg grating will increase when it rebounds, affecting the effect of pre-compression, and if the temperature is too high, it will affect or even damage the composite material itself. In order not to affect the effect of pre-compression, the first preset temperature can be greater than the temperature of the prestressed composite material during normal use and less than the temperature at which the prestressed composite material is damaged by heat.

[0047] When the coating material of the fiber grating is an acrylic material, it will be transformed from a glass state to a highly elastic state when the temperature is higher than 70°C-100°C, so the first preset temperature can be set to 80°C-120°C. Specifically, the first preset temperature can be set to 100°C-120°C.

[0048] In some embodiments, a temperature-controlled electric heating plate can be used to directly heat the area of ​​the prestressed composite material that needs to be heated. A temperature-controlled oil bath can also be used, and an oil pipe can be wrapped around the area that needs to be heated. The heated silicone oil can be pressurized using an oil pump to circulate the hot silicone oil in the pipe and the oil bath pot to achieve a heating effect. In addition, in order to prevent large-scale heating from having an adverse effect on the prestressed composite material or the prestressed composite material body is too large to be heated from the outside, the heating resistor wire can also be buried together with the fiber grating when the optical fiber is buried, so that the heating resistor wire is close to the part of the fiber grating that needs to be heated or distributed 1-5mm near it. When heating is required, the resistor wire is energized to heat the fiber grating locally.

[0049] In some embodiments, before heating, a fiber optic jumper can be used to connect the fiber grating in the prestressed composite material to a fiber grating demodulator through an interface, and the wavelength data of the fiber grating can be monitored by the demodulator.

[0050] Step S130: When it is monitored that the wavelength of the fiber grating remains unchanged, the heating of the prestressed composite material 5 is stopped.

[0051] At the beginning of heating, due to the increase in temperature, the wavelength of the fiber Bragg grating will increase to a certain extent. When the internal temperature of the prestressed composite material rises to the first preset temperature range of the coating layer, the bonding force between the fiber Bragg grating core and the coating layer fails, causing the fiber Bragg grating core to gradually rebound from the tensioned state.

[0052] To a state with lower deformation, the wavelength data of the corresponding fiber Bragg grating will be significantly reduced. However, since the coating layer still has a certain viscosity after the high elastic state, the fiber Bragg grating will still be subjected to a certain tensile stress, so its wavelength data will not be reduced to the initial wavelength. It should be noted that when the fiber Bragg grating is not heated and tension is applied, the wavelength data of the fiber Bragg grating monitored by the demodulator is the initial wavelength.

[0053] Step S140: When the temperature of the prestressed composite material drops to room temperature, the first tension on the prestressed composite material is removed to obtain a prestressed composite material with a built-in pre-compressed optical fiber Bragg grating.

[0054] 5 When the temperature of the prestressed composite material drops to room temperature, the coating layer solidifies again and forms an anchoring effect between the fiber core and the prestressed composite material. Then the first tension is removed from the prestressed composite material, and as the elastic deformation of the composite material recovers, the fiber Bragg grating inside it will be pre-compressed.

[0055] After the fiber Bragg grating is pre-compressed, the monitored wavelength value will be smaller than the initial wavelength. Thereafter, after the prestressed composite material is tensioned during installation and construction, the fiber Bragg grating will eventually be in a lower strain state.

[0056] 0 After pre-compression of the fiber Bragg grating, the maximum range of tensile strain of the fiber Bragg grating sensor can be increased.

[0057] The maximum range is the initial range of the fiber Bragg grating plus the pre-compression strain value.

[0058] In addition, when using the pultrusion process to prepare the prestressed composite material with embedded fiber Bragg grating, the fiber Bragg grating will be subjected to a large extrusion force in the mold, which is easy to cause residual stress in the grating area during the molding process.

[0059] In the present invention, when the fiber Bragg grating is pre-compressed, the fiber Bragg grating 5 undergoes a relaxation process, and under appropriate process parameters, the residual stress in the grating area can be effectively eliminated, the signal peak shape is restored to normal, and the signal stability of the fiber Bragg grating sensor is improved.

[0060] In some embodiments, when it is detected that the signal peak shape of the prepared fiber Bragg grating built-in prestressed composite material is distorted, the fiber Bragg grating built-in prestressed composite material is repeatedly tensioned to eliminate residual stress and correct the peak shape of the fiber Bragg grating until the signal peak shape returns to normal.

[0061] The processing method provided by the embodiment of the present invention first applies a first tensioning force to the prestressed composite material to be processed, and keeps the tensioning state unchanged. Next, the grating area of ​​the fiber grating in the prestressed composite material, the preset area of ​​the head fiber segment, and the tail fiber segment are heated until the temperature of the coating reaches the first preset temperature, and the wavelength of the fiber grating is continuously monitored. Then, when it is monitored that the wavelength of the fiber grating remains unchanged, the heating of the prestressed composite material is stopped. Finally, when the temperature of the prestressed composite material drops to room temperature, the first tension on the prestressed composite material is removed to obtain a prestressed composite material with a built-in pre-compressed fiber grating. By pre-compressing a partial area of ​​the fiber grating embedded in the prestressed composite material by heating, on the one hand, the maximum range of the fiber grating sensor can be increased, and on the other hand, the strain of the fiber grating in the working state can be reduced, thereby increasing the fatigue life of the fiber grating and increasing the service life of the sensor.

[0062] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0063] Based on the processing method of the fiber Bragg grating built-in prestressed composite material provided in the above embodiment, the present invention also provides a specific implementation of the fiber Bragg grating built-in prestressed composite material obtained by processing the processing method of the fiber Bragg grating built-in prestressed composite material. Please refer to the following embodiments.

[0064] A fiber grating built-in prestressed composite material, wherein the fiber grating built into the prestressed composite material is a pre-compressed fiber grating formed by pre-compression treatment, wherein a coating layer is provided on the periphery of the pre-compressed fiber grating, and the coating layer is transformed from a glass state to a highly elastic state within a first preset temperature range.

[0065] Specifically, the method for pre-compression treatment of pre-compressed fiber Bragg gratings is as follows: while applying a first tensile force to the prestressed composite material, the grating area of ​​the fiber Bragg grating, the preset area of ​​the head fiber segment, and the tail fiber segment in the prestressed composite material are heated until the coating layer is transformed from a glassy state to a highly elastic state, and the heating is maintained until the wavelength of the fiber Bragg grating is stable, and the first tensile force on the prestressed composite material is removed when the temperature of the prestressed composite material drops to room temperature.

[0066] The fiber Bragg grating is an embedded sensor, that is, during the pultrusion process of the prestressed composite material, the fiber Bragg grating is directly embedded in the prestressed composite material to form an integral body. The fiber Bragg grating can be a strain grating sensor.

[0067] In some embodiments, the optical fiber outside the grating area of ​​the fiber Bragg grating can be divided into a head fiber and a pigtail fiber. The head fiber segment is the optical fiber from the grating area of ​​the fiber Bragg grating to the optical fiber interface of the prestressed composite material, which is the end drawn out of the prestressed composite material. The pigtail fiber segment is the optical fiber from the grating area of ​​the fiber Bragg grating to the tail of the fiber Bragg grating completely buried in the prestressed composite material.

[0068] In this embodiment, in order not to affect the subsequent processing of the fiber grating, the length of the head fiber segment can be adjusted according to the specific design requirements, but it must be satisfied that the sum of the lengths of the head fiber segment and the tail fiber segment is less than the length of the prestressed composite material. Since a too short tail fiber segment will affect the anchoring effect of the fiber grating inside the prestressed composite material, a too long tail fiber segment will make the heating area during the pre-compression process too large and increase the resistance to fiber retraction, affecting the final processing effect. Therefore, the length of the tail fiber segment can be set to within the range of 0.5 meters to 2 meters. In order to maximize the fatigue life of the fiber grating, the length of the tail fiber segment can be set to 0.5 meters to 1 meter.

[0069] Specifically, Figure 2 As shown, in order to prevent the distortion of the fiber Bragg grating signal peak shape caused by uneven stress in the grating area after pre-compression, which affects the acquisition of measurement data, the preset area of ​​the head fiber segment is the area of ​​the head fiber segment close to the grating area of ​​the fiber Bragg grating, and the length of the preset area is greater than or equal to 10 cm. Exemplarily, the length of the preset area of ​​the head fiber segment can be greater than or equal to 20 cm and less than or equal to 50 cm.

[0070] In some embodiments, in order to accurately measure the wavelength of the fiber Bragg grating using a fiber Bragg grating demodulator, a fiber Bragg grating processed by toe-cutting technology can be selected, which has a higher side mode suppression ratio ≥15dB and a sharper signal peak shape, which is conducive to the fiber Bragg grating demodulator to accurately measure the wavelength of the fiber Bragg grating.

[0071] In some embodiments, if the tension value is too small, the pre-compression degree of the fiber Bragg grating will be low, and the fatigue life of the fiber Bragg grating cannot be effectively improved. If the tension value is too large, it may cause damage or destruction to the prestressed composite material, affecting the yield rate of the production product and the stability of the product quality during actual construction. Therefore, the selection range of the first tension force can be 60%-140% of the stress of the fiber Bragg grating built-in composite material when it is actually installed. Specifically, the selection range of the first tension force is 100%-105% of the stress of the fiber Bragg grating built-in composite material when it is actually installed.

[0072] In some embodiments, if the heating temperature is too low, the resistance of the fiber Bragg grating will increase when it rebounds, affecting the effect of pre-compression, and if the temperature is too high, it will affect or even damage the composite material itself. In order not to affect the effect of pre-compression, the first preset temperature can be greater than the temperature of the prestressed composite material during normal use and less than the temperature at which the prestressed composite material is damaged by heat.

[0073] When the coating material of the fiber grating is an acrylic material, it will be transformed from a glass state to a highly elastic state when the temperature is higher than 70°C-100°C, so the first preset temperature can be set to 80°C-120°C. Specifically, the first preset temperature can be set to 100°C-120°C.

[0074] By pre-compressing the fiber Bragg grating in the composite material, on the one hand, the strain of the fiber Bragg grating in the working state can be reduced, thereby increasing the fatigue life of the fiber Bragg grating and improving the service life of the sensor. On the other hand, by pre-compressing the fiber Bragg grating, the maximum range of the tensile strain of the sensor can be increased, and the maximum range is changed to the sum of the original range of the fiber Bragg grating and the pre-compression strain value. In addition, when the fiber Bragg grating embedded prestressed composite material is prepared by using the pultrusion molding process, the fiber Bragg grating will be subjected to a large extrusion force in the mold, and it is easy to cause residual stress in the grating area during the molding process, resulting in distortion of the fiber Bragg grating signal peak shape. In the present invention, when the fiber Bragg grating is pre-compressed, the fiber Bragg grating undergoes a relaxation process again. Under the appropriate process parameter conditions, the residual stress in the grating area can be effectively eliminated, the signal peak shape is restored to normal, and the signal stability of the fiber Bragg grating sensor is improved. In addition, when it is detected that the signal peak shape of the prepared fiber Bragg grating embedded prestressed composite material is distorted, the fiber Bragg grating embedded prestressed composite material can be repeatedly stretched to eliminate the residual stress and correct the peak shape of the fiber Bragg grating until the signal peak shape is restored to normal.

[0075] The performance of the fiber Bragg grating built-in prestressed composite material provided by the present invention is described in detail below through some experimental data.

[0076] Data before and after treatment of prestressed composite material A:

[0077] First, when the fiber Bragg grating in the prestressed composite material A is not processed and no tension is applied, the initial wavelength of the fiber Bragg grating monitored by the demodulator is 1547.144 nm, and the micro strain με collected by the fiber Bragg grating sensor is 0.

[0078] Then, a tension force of 1000 MPa was applied to the prestressed composite material A, and its tension state was kept unchanged. At this time, the wavelength of the tested fiber Bragg grating increased to 1554.945 nm, and the microstrain collected by the fiber Bragg grating sensor was 6250.

[0079] Next, when the prestressed composite material A is treated by the treatment method provided by the present invention and the prestressed composite material is completely free from tensile stress, the wavelength of the pre-compressed fiber grating tested at this time is reduced to 1541.073 nm.

[0080] Finally, a tensile force of 1000 MPa was applied to the treated prestressed composite material A again, and its tensile state was kept unchanged. At this time, the wavelength of the tested fiber Bragg grating increased to 1548.881 nm, and the microstrain collected by the fiber Bragg grating sensor was 1392.

[0081] Data before and after treatment of prestressed composite material B:

[0082] First, when the fiber Bragg grating in the prestressed composite material B is not processed and no tension is applied, the initial wavelength of the fiber Bragg grating monitored by the demodulator is 1549.963 nm, and the micro strain με collected by the fiber Bragg grating sensor is 0.

[0083] Then, a tension force of 1000 MPa was applied to the prestressed composite material B, and its tension state was kept unchanged. At this time, the wavelength of the tested fiber Bragg grating increased to 1559.291 nm, and the microstrain collected by the fiber Bragg grating sensor was 6250.

[0084] Next, when the prestressed composite material B is treated by the treatment method provided by the present invention, the wavelength of the pre-compressed fiber grating measured at this time is reduced to 1544.373 nm.

[0085] Finally, a tensile force of 1000 MPa was applied to the treated prestressed composite material B again, and its tensile state was kept unchanged. At this time, the wavelength of the tested fiber Bragg grating increased to 1553.479 nm, and the microstrain collected by the fiber Bragg grating sensor was 2356.

[0086] In addition, the original maximum range of the fiber Bragg gratings in the selected prestressed composite materials A and B is 10,000 microstrain, and the pre-compression of the fiber Bragg gratings in the two prestressed composite materials A and B is about 4,000 microstrain. Therefore, the measurement range of the fiber Bragg grating built-in prestressed composite material after pre-compression treatment becomes approximately 14,000 microstrain.

[0087] The life of the treated fiber Bragg grating in the prestressed composite material can be compared through the following data:

[0088] For bare fiber Bragg grating without coating, when the maximum micro strain of fatigue test is reduced from 6000 to 3000, its fatigue life is increased from 10 3 Increase to 10 6times. For a fiber grating sensor encapsulated with simple glass fiber, when the maximum micro-strain of its fatigue test is reduced from 8000 to 6000, its fatigue life is increased from about 300,000 times to about 3.5 million times, and the fatigue life is increased by more than 10 times. In the prestressed carbon fiber plates or carbon fiber tendons that are most widely used in prestressed composite materials, the more typical tensile stress is 1200MPa. According to the elastic modulus of the carbon fiber composite material, the micro-strain of the fiber grating is about 7500 at this time. After being treated with the method provided by the present invention, that is, after pre-compression of the fiber grating, the maximum micro-strain that the fiber grating can withstand under the working state can be reduced by at least 4000, that is, the fiber grating is monitored for a long time under a micro-strain state of about 3500. Therefore, it can be seen that the fatigue life of the fiber grating treated with the method provided by the present invention under the actual working state can be significantly improved.

[0089] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for processing a fiber Bragg grating built-in prestressed composite material, characterized in that: include: Applying a first tensioning force to the prestressed composite material to be processed, and keeping the tensioning state unchanged; wherein the outer periphery of the fiber grating is provided with a coating layer, and the coating layer is transformed from a glass state to a highly elastic state within a first preset temperature range; The grating area of ​​the fiber Bragg grating in the prestressed composite material, the preset area of ​​the head fiber segment and the tail fiber segment are heated until the temperature of the coating layer reaches a first preset temperature, and the wavelength of the fiber Bragg grating is continuously monitored; When it is monitored that the wavelength of the fiber grating remains unchanged, stopping heating the prestressed composite material; When the temperature of the prestressed composite material drops to room temperature, the first tension on the prestressed composite material is removed to obtain a prestressed composite material with built-in pre-compressed optical fiber Bragg gratings.

2. The processing method according to claim 1, characterized in that The processing method also includes: When it is detected that the signal peak shape transmitted through the prestressed composite material is distorted, the fiber grating built-in prestressed composite material is tensioned multiple times until the signal peak shape returns to normal.

3. The processing method according to claim 1, characterized in that: The head fiber segment is the optical fiber from the grating area of ​​the fiber Bragg grating to the optical fiber interface of the prestressed composite material, and the pigtail fiber segment is the optical fiber from the grating area of ​​the fiber Bragg grating to the tail of the fiber Bragg grating completely buried in the prestressed composite material, and the length of the pigtail fiber segment is 0.5 meters to 2 meters; the sum of the lengths of the head fiber segment and the pigtail fiber segment is less than the length of the prestressed composite material; The preset area of ​​the head fiber segment is an area of ​​the head fiber segment close to the grating area of ​​the fiber grating, and the length of the preset area is greater than or equal to 10 cm.

4. The processing method according to claim 3, characterized in that: The first preset temperature is greater than a temperature at which the prestressed composite material is normally used, and is less than a temperature at which the prestressed composite material is damaged by heat.

5. The processing method according to claim 1, characterized in that: The first tension force is selected in a range of 60% to 140% of the stress of the fiber grating built-in composite material during actual installation.

6. The processing method according to claim 5, characterized in that: The first tension force is selected in a range of 100%-105% of the stress of the fiber grating built-in composite material during actual installation.

7. A fiber Bragg grating built-in prestressed composite material, characterized in that: The fiber grating embedded in the prestressed composite material is a pre-compressed fiber grating formed by pre-compression treatment, wherein the periphery of the pre-compressed fiber grating is provided with a coating layer, and the coating layer is transformed from a glass state to a highly elastic state within a first preset temperature range; The method for pre-compression treatment of the pre-compressed fiber Bragg grating is as follows: while applying a first tensile force to the prestressed composite material, heating the grating area of ​​the fiber Bragg grating, the preset area of ​​the head fiber segment and the tail fiber segment in the prestressed composite material until the coating layer is transformed from a glassy state to a highly elastic state, and maintaining the state until the wavelength of the fiber Bragg grating is stable, then stopping the heating, and removing the first tensile force on the prestressed composite material when the temperature of the prestressed composite material drops to room temperature.

8. The fiber Bragg grating internal prestressed composite material according to claim 7, characterized in that: The head fiber segment is the optical fiber from the grating area of ​​the fiber Bragg grating to the optical fiber interface of the prestressed composite material, and the pigtail fiber segment is the optical fiber from the grating area of ​​the fiber Bragg grating to the tail of the fiber Bragg grating completely buried in the prestressed composite material, and the length of the pigtail fiber segment is 0.5 meters to 2 meters; the sum of the lengths of the head fiber segment and the pigtail fiber segment is less than the length of the prestressed composite material; The preset area of ​​the head fiber segment is an area of ​​the head fiber segment close to the grating area of ​​the fiber grating, and the length of the preset area is greater than or equal to 10 cm.

9. The fiber Bragg grating internal prestressed composite material according to claim 8, characterized in that: The length of the pigtail fiber segment is 0.5 m-1 m, and the length of the preset area of ​​the head fiber segment is greater than or equal to 20 cm and less than or equal to 50 cm.

10. The fiber Bragg grating internal prestressed composite material according to claim 7, characterized in that: The coating layer is made of an acrylic material, and the first preset temperature is greater than or equal to 100° C. and less than or equal to 120° C.

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