A pre-shrunk fiber bragg grating sensor and its use in prestressed composites

Abstract

The present application relates to the technical fields of fiber grating and building material, and particularly relates to a pre-shrunk fiber grating sensor and application thereof in prestressed composite material. The pre-shrunk fiber grating sensor provided by the present application is applied in the prestressed composite material, and specifically, a resin system coating layer is arranged outside the fiber grating sensor; wherein the resin system of the coating layer is the same as the system of the prestressed composite material to be applied, and the solidification shrinkage of the coating layer is adapted to the strain value corresponding to the prestress applied by the prestressed composite material. The preparation method of the pre-shrunk fiber grating sensor provided by the present application is simple in steps and easy to realize batch production. The pre-shrunk fiber grating sensor is applied in the prestressed composite material, so that the pre-shrinkage value of the fiber grating sensor can be accurately controlled, the service life of the fiber grating sensor is improved, and there is no interface layer between the pre-shrunk fiber grating sensor and the prestressed composite material, so that the hidden danger of interface failure is eliminated.

Description

Technical Field

[0001] This invention relates to the field of fiber optic gratings and building materials technology, specifically to a pre-shrink fiber optic grating sensor and its application in prestressed composite materials. Background Technology

[0002] A fiber Bragg grating strain sensor is a sensor that uses a Bragg FBG fiber grating as the sensing element, combined with a fiber grating demodulator, and is fixed to or embedded within the surface of the object being measured to measure, detect, and monitor strain. In recent years, the application of fiber grating strain sensors in conjunction with prestressed composite materials in the external prestressing tensioning reinforcement of buildings or highway bridges has become increasingly common. However, the tensile strain of prestressed composite materials during external tensioning is generally about 0.5% to 0.8%, while the maximum strain of current fiber grating strain sensors encapsulated in polymer materials is mostly 10000 με (micro-strain), i.e., a strain of about 1%. It is evident that the tensile strain of prestressed composite materials approaches the maximum strain of the fiber grating strain sensor. Moreover, due to the long-term dynamic loads on buildings or highway bridges, the fiber grating strain sensors, already under high strain conditions, are constantly subjected to strain changes, making them highly susceptible to fatigue failure and ultimately rendering them ineffective.

[0003] To address the above issues, the applicant currently has a method for pre-compressing fiber optic grating sensors embedded in prestressed composite materials to reduce their strain values ​​during subsequent use, as described in patent application number 202211669061.8. Specifically, the method involves: first, embedding the fiber optic grating sensor in the prestressed composite material using a coating bonding method; then, tensioning the prestressed composite material to the required stress value, at which point the fiber optic grating within the prestressed composite material is also elongated; second, heating the grating portion of the prestressed composite material softens the coating on the fiber optic surface, causing the bonding between the fiber optic grating and the prestressed composite material to fail, thus allowing the fiber optic grating to retract to a naturally relaxed state; gradually reducing the heating temperature of the grating portion of the prestressed composite material, at which point the coating on the fiber optic surface gradually hardens, allowing the fiber optic grating to re-bond with the prestressed composite material through the coating layer; finally, releasing the tensile stress of the prestressed composite material, causing it to retract to its original state, thus completing the pre-compression of the fiber optic grating embedded within the prestressed composite material.

[0004] However, the above method still has shortcomings: First, tensioning each strand of the prestressed composite material with embedded fiber Bragg grating sensors requires high manpower and time costs, resulting in low production efficiency and preventing mass production in advance; Second, the coating used in this method is a polymer material, but polymers do not have precise melting points, making it impossible to accurately control the heating temperature, which may lead to incomplete fiber Bragg grating retraction or damage to the prestressed composite material; Third, this method uses a coating layer between the fiber Bragg grating sensor and the prestressed composite material, separating them and causing differences in their sensitivity to stress and temperature. Under the long-term influence of temperature changes and dynamic load changes during subsequent use, the interface coating layer is likely to fail. Therefore, the current method for pre-compressing fiber Bragg gratings in prestressed composite materials is inefficient, the pre-compression range is not precise enough, and there is a risk of interface failure. Summary of the Invention

[0005] In view of this, the present invention provides a pre-shrink fiber Bragg grating sensor and its application in prestressed composite materials. The method can mass-produce pre-shrink fiber Bragg grating sensors with a preset curing shrinkage rate. Applying them to prestressed composite materials can improve the service life of fiber Bragg grating sensors and can also achieve precise control of the pre-shrinkage value of fiber Bragg grating sensors. Moreover, there is no interface layer between the pre-shrink fiber Bragg grating sensor obtained by this method and the prestressed composite material, eliminating the hidden danger of interface failure.

[0006] To solve the above technical problems, the present invention provides a pre-shrink fiber Bragg grating sensor applied to prestressed composite materials, specifically by providing a resin system coating layer on the outside of the fiber Bragg grating sensor;

[0007] The resin system of the coating layer is the same as that of the prestressed composite material to be applied, and the curing shrinkage rate of the coating layer is compatible with the strain value corresponding to the prestress applied to the prestressed composite material.

[0008] This invention provides a pre-shrinkable fiber Bragg grating sensor for use in prestressed composite materials. A resin-based coating layer is applied to the outside of the fiber Bragg grating sensor to achieve coordinated shrinkage of both the sensor and the resin system. The resin system of the coating layer is identical to that of the prestressed composite material to be used, allowing for better integration between the resin system of the pre-shrinkable fiber Bragg grating sensor and the prestressed composite material system. This enables more sensitive monitoring of the load condition of the prestressed composite material. Furthermore, the curing shrinkage rate of the coating layer is matched to the strain value corresponding to the applied prestress in the prestressed composite material, ensuring that the pre-shrinkable fiber Bragg grating sensor is in a fully relaxed state when the prestressed composite material is tensioned to a preset strain.

[0009] In conjunction with the first aspect, the method for testing the curing shrinkage rate of the resin system coating layer includes the following steps:

[0010] A sample with the same resin system for preparing the coating layer as the resin system of the pre-shrinked fiber Bragg grating sensor to be tested is prepared. The sample includes at least two fiber Bragg grating sensors, wherein at least one fiber Bragg grating sensor is encapsulated with a capillary tube and at least one fiber Bragg grating sensor is not encapsulated. The initial wavelength of each fiber Bragg grating sensor is measured, and then the fiber Bragg grating sensors are vertically immersed in the resin system at equal depth and cured.

[0011] The wavelengths of each of the cured fiber optic grating sensors were measured separately;

[0012] Calculate the wavelength difference A1 of the fiber optic grating sensor before and after curing of the unencapsulated sample;

[0013] Calculate the wavelength difference A2 of the fiber optic grating sensor sample before and after curing using a capillary encapsulation. Subtract A2 from A1 to eliminate the effect of temperature on the wavelength of the fiber optic grating sensor.

[0014] The wavelength difference between A1 and A2 is converted into a strain value, which gives the curing shrinkage rate of the resin system coating layer.

[0015] By following the above test method for the curing shrinkage rate of the resin system coating layer, the curing shrinkage rate of any resin system can be obtained, thereby obtaining a coating layer resin system that is compatible with a prestressed composite material with any strain value.

[0016] In conjunction with the first aspect, the resin system is contained in a vertically placed flexible tube, which is then placed in a curing device for curing. During the curing process, the flexible tube and the resin system can simultaneously contract or expand; using a flexible tube to contain the resin system prevents the resin from detaching from the tube wall surface during curing.

[0017] In conjunction with the first aspect, the thickness of the resin system coating layer is 0.25 to 0.5 mm. This thickness of resin system coating layer does not affect the application of fiber Bragg grating sensors in prestressed composite materials, and can also provide a certain degree of protection for fiber Bragg grating sensors.

[0018] A second aspect of the present invention provides a method for fabricating a pre-shrink fiber Bragg grating sensor, comprising the following steps:

[0019] Select a resin system with a preset curing shrinkage rate;

[0020] Insert the fiber Bragg grating sensor into a tube with a closed bottom, and inject the resin system with the preset curing shrinkage rate into the tube;

[0021] When the fiber Bragg grating sensor is completely immersed in the resin system, the open end of the hose is sealed and it is placed vertically in the curing equipment for curing;

[0022] After curing, the pre-shrink fiber Bragg grating sensor is demolded from the tubing.

[0023] The method for fabricating the pre-shrink fiber Bragg grating sensor provided by this invention only requires a bottom-sealed tubing and a curing device, without the need for other complex molds or equipment. The operation steps are simple and it is easy to achieve mass production.

[0024] In conjunction with the second aspect, the resin system is the same as the system of the prestressed composite material to be applied. A resin system with a preset curing shrinkage rate is selected by blending the resins in the compound resin system. Different resins have different curing shrinkage rates, and precise control of the curing shrinkage rate of the resin system can be achieved through blending multiple resins.

[0025] In conjunction with the second aspect, resin systems with a preset curing shrinkage rate are screened according to the above-mentioned test method for curing shrinkage rate.

[0026] Preferably, the curing equipment is a microwave curing equipment; wherein the curing procedure is as follows: setting the microwave power to 180-220W, curing for 1-2 hours; setting the microwave power to 380-420W, curing for 1-2 hours; setting the microwave power to 780-820W, curing for 0.4-0.6 hours.

[0027] In the early stage of curing, a lower microwave power is set to gradually increase the viscosity of the resin system, ensuring good adhesion between the resin system and the fiber Bragg grating sensor. In the middle stage of curing, a moderate microwave power is set to promote further curing of the resin system, but the microwave power should not be too high to prevent the resin system from shrinking drastically and damaging the structure of the fiber Bragg grating sensor.

[0028] A third aspect of the present invention provides an application of a pre-shrinkable fiber Bragg grating sensor, wherein the aforementioned pre-shrinkable fiber Bragg grating sensor or a pre-shrinkable fiber Bragg grating sensor prepared according to the aforementioned method is applied to a prestressed composite material to monitor the stress condition of the prestressed composite material. Specific application methods include embedding, pasting, or other fixing methods that can combine the pre-shrinkable fiber Bragg grating sensor with the prestressed composite material to be applied. For the method of embedding the pre-shrinkable fiber Bragg grating sensor in the prestressed composite material to be applied, please refer to the applicant's granted patent application number 202210102810.2.

[0029] In conjunction with the third aspect, the pre-shrink fiber Bragg grating sensor is applied to a prestressed composite material in which the preset strain and the curing shrinkage rate of the resin system coating layer of the pre-shrink fiber Bragg grating sensor are compatible. When the prestressed composite material is tensioned to the preset strain, the pre-shrink fiber Bragg grating sensor is in a relaxed state. The fiber Bragg grating sensor will not fail due to frequent dynamic loading of the prestressed composite material under high load conditions, thereby improving the service life of the fiber Bragg grating sensor.

[0030] The beneficial effects of this invention are as follows: The pre-shrinkable fiber Bragg grating sensor provided by this invention achieves synergistic shrinkage of the fiber Bragg grating sensor and the resin system by setting a resin system coating layer outside the fiber Bragg grating sensor. Its preparation method is simple and easy to achieve mass production. Applying this pre-shrinkable fiber Bragg grating sensor to prestressed composite materials can improve the service life of the fiber Bragg grating sensor. Furthermore, the pre-shrinkage value of the fiber Bragg grating sensor can be precisely controlled by precisely controlling the curing shrinkage rate of the resin system coating layer. Moreover, there is no interface layer between the pre-shrinkable fiber Bragg grating sensor and the prestressed composite material, eliminating the risk of interface failure. Attached Figure Description

[0031] Figure 1 This is a schematic diagram illustrating the fabrication of the pre-shrink fiber Bragg grating sensor according to the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0033] Example 1

[0034] This embodiment provides a pre-shrinkable fiber Bragg grating sensor, which is applied to a prestressed composite material. Specifically, a resin system coating layer is provided outside the fiber Bragg grating sensor; the resin system of the coating layer is the same as that of the prestressed composite material to be applied, and the curing shrinkage rate of the coating layer is compatible with the strain value corresponding to the prestress applied to the prestressed composite material.

[0035] Example 2

[0036] This embodiment provides a method for testing the curing shrinkage rate of a resin system coating layer, specifically including the following steps:

[0037] A sample with the same resin system for preparing the coating layer as the resin system of the pre-shrinked fiber Bragg grating sensor to be tested is prepared. The sample includes at least two fiber Bragg grating sensors, of which at least one fiber Bragg grating sensor is encapsulated with a capillary tube and at least one fiber Bragg grating sensor is not encapsulated. The initial wavelength of each fiber Bragg grating sensor is measured, and then the fiber Bragg grating sensors are vertically immersed in the resin system at equal depth and cured.

[0038] The wavelengths of each of the cured fiber optic grating sensors were measured separately;

[0039] Calculate the wavelength difference A1 of the fiber optic grating sensor before and after curing of the unencapsulated sample;

[0040] Calculate the wavelength difference A2 of the fiber optic grating sensor sample before and after curing using a capillary encapsulation. Subtract A2 from A1 to eliminate the effect of temperature on the wavelength of the fiber optic grating sensor.

[0041] The wavelength difference between A1 and A2 is converted into a strain value, which gives the curing shrinkage rate of the resin system coating layer.

[0042] Example 3

[0043] This embodiment provides a method for fabricating a pre-shrink fiber Bragg grating sensor, including the following steps:

[0044] Select a resin system with a preset curing shrinkage rate;

[0045] Insert the fiber Bragg grating sensor into a tube with a closed bottom, and inject the resin system with the preset curing shrinkage rate into the tube;

[0046] When the fiber Bragg grating sensor is completely immersed in the resin system, the open end of the hose is sealed and it is placed vertically in the curing equipment for curing;

[0047] After curing, the pre-shrink fiber Bragg grating sensor is demolded from the tubing.

[0048] Example 4

[0049] This embodiment provides an application of a pre-shrinkable fiber Bragg grating sensor, which applies the pre-shrinkable fiber Bragg grating sensor provided in Embodiment 1 or the pre-shrinkable fiber Bragg grating sensor prepared according to the preparation method in Embodiment 3 to a prestressed composite material.

[0050] Example 5

[0051] This embodiment provides an application of a pre-shrinkable fiber Bragg grating sensor, which is applied to a carbon fiber plate with a preset strain value of 3‰. The specific method includes:

[0052] Following the testing method for the curing shrinkage rate of the resin system coating layer in Example 2, the curing shrinkage rate of the resin system obtained by compounding bisphenol A diglycidyl ether and bisphenol A tetraglycidyl diaminodiphenylmethane in a molar ratio of 1:9 was measured to be 3‰. A pre-shrinked fiber Bragg grating sensor was prepared using this resin system as the coating layer, and the specific preparation method is as follows:

[0053] Insert the fiber Bragg grating sensor into a tube with a sealed bottom, and inject the resin system into the tube into which the curing shrinkage rate has been measured.

[0054] When the fiber Bragg grating sensor is completely immersed in the resin system, the open end of the sealed tubing is sealed and the device is placed vertically in a microwave device for curing. The curing procedure is as follows: microwave power 200W, curing for 1.5h; microwave power 400W, curing for 1.5h; microwave power 800W, curing for 0.5h. The curing agent used in this resin system is methyltetrahydrophthalic anhydride, and the curing agent is added at a ratio of 1:1 between the active hydrogen equivalent and the epoxy equivalent of the above-mentioned compound resin system.

[0055] After curing, the pre-shrink fiber Bragg grating sensor is obtained by demolding from the tubing, wherein the thickness of the resin system coating layer is 0.35 mm.

[0056] When mass-producing pre-shrink fiber Bragg grating sensors, sensors that are not immediately used can be stored in a constant temperature and humidity chamber.

[0057] The pre-shrink fiber Bragg grating sensor was embedded in a carbon fiber plate of bisphenol A epoxy resin system, and the fatigue life of the pre-shrink fiber Bragg grating sensor under different dynamic load frequencies was tested. The results are shown in Table 1.

[0058] Example 6

[0059] This embodiment provides an application of a pre-shrink fiber Bragg grating sensor. The pre-shrink fiber Bragg grating sensor is applied to a carbon fiber plate with a preset strain value of 5‰. The specific method is similar to that in Embodiment 5, except that the molar ratio of bisphenol A diglycidyl ether and bisphenol A tetraglycidyl diaminodiphenylmethane in the resin system is 1:8.5, the curing shrinkage rate of the resin system is 5‰, and the curing agent used in the resin system is methyltetrahydrophthalic anhydride. The curing agent is added at a ratio of active hydrogen equivalent to epoxy equivalent of the above-mentioned compound resin system at 1:1. The remaining method steps are the same as in Embodiment 5.

[0060] Example 7

[0061] This embodiment provides an application of a pre-shrinkable fiber Bragg grating sensor. The pre-shrinkable fiber Bragg grating sensor is applied to a carbon fiber plate with a preset strain value of 7‰. The specific method is similar to that of Embodiment 5, except that the molar ratio of bisphenol A diglycidyl ether and bisphenol A tetraglycidyl diaminodiphenylmethane in the resin system is 1:8, the curing shrinkage rate of the resin system is 7‰, and the curing agent used in the resin system is methyltetrahydrophthalic anhydride, added at a ratio of active hydrogen equivalent to the epoxy equivalent of the above-mentioned composite resin system at 1:1. All other method steps are the same as in Embodiment 5.

[0062] Example 8

[0063] This embodiment provides an application of a pre-shrinkable fiber Bragg grating sensor, which is applied to a carbon fiber plate with a preset strain value of 3‰. The specific method includes:

[0064] Following the test method for the curing shrinkage rate of the resin system coating layer in Example 2, the curing shrinkage rate of the resin system obtained by compounding bisphenol A diglycidyl ether and bisphenol F diglycidyl ether in a molar ratio of 1:7 was measured to be 3‰. A pre-shrinked fiber Bragg grating sensor was prepared using this resin system as the coating layer, and the specific preparation method is as follows:

[0065] Insert the fiber Bragg grating sensor into a tube with a sealed bottom, and inject the resin system into the tube into which the curing shrinkage rate has been measured.

[0066] When the fiber optic grating sensor is completely immersed in the resin system, the open end of the sealed tubing is sealed and the device is placed vertically in a microwave device for curing. The curing procedure is as follows: microwave power 180W, curing for 2 hours; microwave power 380W, curing for 2 hours; microwave power 780W, curing for 0.6 hours. The curing agent used in this resin system is methyltetrahydrophthalic anhydride, and the curing agent is added at a ratio of 1:1 between the active hydrogen equivalent and the epoxy equivalent of the above-mentioned compound resin system.

[0067] After curing, the pre-shrink fiber Bragg grating sensor is obtained by demolding from the tubing, wherein the thickness of the resin system coating layer is 0.25 mm.

[0068] When mass-producing pre-shrink fiber Bragg grating sensors, sensors that are not immediately used can be stored in a constant temperature and humidity chamber.

[0069] The pre-shrink fiber Bragg grating sensor was embedded in a carbon fiber plate of bisphenol A + bisphenol F epoxy resin system, and the fatigue life of the pre-shrink fiber Bragg grating sensor under different dynamic load frequencies was tested. The results are shown in Table 1.

[0070] Example 9

[0071] This embodiment provides an application of a pre-shrinkable fiber Bragg grating sensor. The pre-shrinkable fiber Bragg grating sensor is applied to a carbon fiber plate with a preset strain value of 5‰. The specific method is similar to that of Embodiment 8, except that in the resin system used, bisphenol A diglycidyl ether and bisphenol F diglycidyl ether are used in a molar ratio of 1:5, the curing shrinkage rate of the resin system is 5‰, and the curing agent used in the resin system is methyltetrahydrophthalic anhydride, added in a 1:1 ratio of active hydrogen equivalent to the epoxy equivalent of the above-mentioned composite resin system. All other method steps are the same as in Embodiment 8.

[0072] Example 10

[0073] This embodiment provides an application of a pre-shrinkable fiber Bragg grating sensor. The pre-shrinkable fiber Bragg grating sensor is applied to a carbon fiber plate with a preset strain value of 7‰. The specific method is similar to that of Embodiment 8, except that in the resin system used, bisphenol A diglycidyl ether and bisphenol F diglycidyl ether are used in a molar ratio of 1:4, the curing shrinkage rate of the resin system is 7‰, and the curing agent used in the resin system is methyltetrahydrophthalic anhydride, added in a 1:1 ratio of active hydrogen equivalent to the epoxy equivalent of the above-mentioned composite resin system. All other method steps are the same as in Embodiment 8.

[0074] Example 11

[0075] This embodiment provides an application of a pre-shrinkable fiber Bragg grating sensor, which is applied to a carbon fiber plate with a preset strain value of 3‰. The specific method includes:

[0076] Following the testing method for the curing shrinkage rate of the resin system coating layer in Example 2, the curing shrinkage rate of the resin system obtained by compounding bisphenol A diglycidyl ether and aliphatic cyclohexanediethanol diglycidyl ether in a molar ratio of 1:2 was measured to be 3‰. A pre-shrinked fiber Bragg grating sensor was prepared using this resin system as the coating layer, and the specific preparation method is as follows:

[0077] Insert the fiber Bragg grating sensor into a tube with a sealed bottom, and inject the resin system into the tube into which the curing shrinkage rate has been measured.

[0078] When the fiber optic grating sensor is completely immersed in the resin system, the open end of the sealed tubing is sealed and the device is placed vertically in a microwave device for curing. The curing procedure is as follows: microwave power 220W, curing for 1.5h; microwave power 420W, curing for 1.5h; microwave power 820W, curing for 0.4h. The curing agent used in this resin system is methyltetrahydrophthalic anhydride, and the curing agent is added at a ratio of 1:1 between the active hydrogen equivalent and the epoxy equivalent of the above-mentioned compound resin system.

[0079] After curing, the pre-shrink fiber Bragg grating sensor is obtained by demolding from the tubing, wherein the thickness of the resin system coating layer is 0.5 mm.

[0080] When mass-producing pre-shrink fiber Bragg grating sensors, sensors that are not immediately used can be stored in a constant temperature and humidity chamber.

[0081] The pre-shrink fiber Bragg grating sensor was embedded in a carbon fiber plate of bisphenol A + aliphatic glycidyl ether epoxy resin system, and the fatigue life of the pre-shrink fiber Bragg grating sensor under different dynamic load frequencies was tested. The results are shown in Table 1.

[0082] Example 12

[0083] This embodiment provides an application of a pre-shrink fiber Bragg grating sensor. The pre-shrink fiber Bragg grating sensor is applied to a carbon fiber plate with a preset strain value of 5‰. The specific method is similar to that of Embodiment 11, except that in the resin system used, bisphenol A diglycidyl ether and aliphatic cyclohexanediethanol diglycidyl ether are used in a molar ratio of 1:1.7, the curing shrinkage rate of the resin system is 5‰, and the curing agent used in the resin system is methyltetrahydrophthalic anhydride, added in a 1:1 ratio of active hydrogen equivalent to the epoxy equivalent of the above-mentioned composite resin system. All other method steps are the same as in Embodiment 11.

[0084] Example 13

[0085] This embodiment provides an application of a pre-shrinkable fiber Bragg grating sensor. The pre-shrinkable fiber Bragg grating sensor is applied to a carbon fiber plate with a preset strain value of 7‰. The specific method is similar to that of Embodiment 11, except that in the resin system used, bisphenol A diglycidyl ether and aliphatic cyclohexanediethanol diglycidyl ether are used in a molar ratio of 1:1.4, the curing shrinkage rate of the resin system is 7‰, and the curing agent used in the resin system is methyltetrahydrophthalic anhydride, added in a 1:1 ratio of active hydrogen equivalent to the epoxy equivalent of the above-mentioned composite resin system. All other method steps are the same as in Embodiment 11.

[0086] Table 1. Fatigue life test results of the pre-shrinked fiber Bragg grating sensors obtained in Examples 5-13 in carbon fiber plates.

[0087] (Unit: 10,000 times)

[0088]

[0089]

[0090] In Table 1, glass fiber encapsulation is the conventional glass encapsulation; the fiber grating sensor corresponding to the heat pre-shrinking treatment method is prepared according to the method in the patent application document with application number 202211669061.8.

[0091] As shown in Table 1, compared with the fiber grating sensor obtained by simple glass fiber encapsulation and the fiber grating sensor obtained by heating pre-shrinking treatment under different tensile strains of carbon fiber plates and different dynamic load frequencies applied under the same tensile strain, the fatigue life of the pre-shrinking fiber grating sensor provided by this invention is significantly improved. Even under the conditions of a strain value of 7‰ generated by the carbon fiber plate and a dynamic load frequency of 15Hz, it can still be used 2 million times, which is much higher than the 300,000 times of the fiber grating sensor obtained by heating pre-shrinking treatment under the same test conditions, and even 1,000 times the number of cycles of the fiber grating sensor that is encapsulated by glass fiber and not pre-shrinked.

[0092] It should be noted that the prestressed composite material in this invention includes, but is not limited to, carbon fiber plates. Applying the pre-shrink fiber grating sensor provided by this invention to any prestressed composite material is within the protection scope of this invention.

[0093] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A pre-shrink fiber Bragg grating sensor, applied to prestressed composite materials, characterized in that, A resin-based coating layer is applied to the outside of the fiber Bragg grating sensor; The resin system of the coating layer is the same as that of the prestressed composite material to be applied, and the curing shrinkage rate of the coating layer is compatible with the strain value corresponding to the prestress applied to the prestressed composite material, so as to ensure that the pre-shrink fiber Bragg grating sensor can effectively prevent damage when the prestressed composite material is tensioned to the preset strain. It is in a completely relaxed state.

2. The pre-shrink fiber Bragg grating sensor as described in claim 1, characterized in that, The method for testing the curing shrinkage rate of the resin system coating layer includes the following steps: A sample with the same resin system for preparing the coating layer as the resin system of the pre-shrinked fiber Bragg grating sensor to be tested is prepared. The sample includes at least two fiber Bragg grating sensors, wherein at least one fiber Bragg grating sensor is encapsulated with a capillary tube and at least one fiber Bragg grating sensor is not encapsulated. The initial wavelength of each fiber Bragg grating sensor is measured, and then the fiber Bragg grating sensors are vertically immersed in the resin system at equal depth and cured. The wavelengths of each of the cured fiber optic grating sensors were measured separately; Calculate the wavelength difference A1 of the fiber optic grating sensor before and after curing of the unencapsulated sample; Calculate the wavelength difference A2 of the fiber optic grating sensor sample before and after curing using a capillary encapsulation. Subtract A2 from A1 to eliminate the effect of temperature on the wavelength of the fiber optic grating sensor. The wavelength difference between A1 and A2 is converted into a strain value, which gives the curing shrinkage rate of the resin system coating layer.

3. The pre-shrink fiber Bragg grating sensor as described in claim 2, characterized in that, The resin system is contained in a vertically placed hose, which is then placed in a curing device for curing.

4. The pre-shrink fiber Bragg grating sensor as described in claim 1, characterized in that, The thickness of the resin system coating layer is 0.25~0.5mm.

5. A method for fabricating a pre-shrink fiber Bragg grating sensor, characterized in that, Includes the following steps: A resin system with a preset curing shrinkage rate is selected. The resin system is the same as the system of the prestressed composite material to be applied, and the curing shrinkage rate of the resin system is compatible with the strain value corresponding to the prestress applied to the prestressed composite material, so as to ensure that the pre-shrink fiber grating sensor is in a fully relaxed state when the prestressed composite material is tensioned to the preset strain. Insert the fiber Bragg grating sensor into a tube with a closed bottom, and inject the resin system with the preset curing shrinkage rate into the tube; When the fiber Bragg grating sensor is completely immersed in the resin system, the open end of the hose is sealed and it is placed vertically in the curing equipment for curing; After curing, the pre-shrink fiber Bragg grating sensor is demolded from the tubing.

6. The method for fabricating a pre-shrink fiber Bragg grating sensor as described in claim 5, characterized in that, Resin systems with a preset curing shrinkage rate are selected by comparing the resin ratios in the compound resin system.

7. The method for fabricating a pre-shrink fiber Bragg grating sensor as described in claim 6, characterized in that, The method for screening resin systems with a preset curing shrinkage rate is performed according to the curing shrinkage rate test method described in claim 2.

8. The method for fabricating a pre-shrink fiber Bragg grating sensor as described in claim 5, characterized in that, The curing equipment is a microwave curing equipment; the curing procedure is as follows: set the microwave power to 180~220W and cure for 1~2 hours; set the microwave power to 380~420W and cure for 1~2 hours; set the microwave power to 780~820W and cure for 0.4~0.6 hours.

9. An application of a pre-shrink fiber Bragg grating sensor, characterized in that, The pre-shrink fiber Bragg grating sensor according to any one of claims 1 to 4 or the pre-shrink fiber Bragg grating sensor prepared according to any one of claims 5 to 8 is applied to prestressed composite materials.

10. The application of the pre-shrink fiber Bragg grating sensor as described in claim 9, characterized in that, By applying pre-shrink fiber Bragg grating sensors to prestressed composite materials where the preset strain is compatible with the curing shrinkage rate of the resin system coating layer of the pre-shrink fiber Bragg grating sensor, the pre-shrink fiber Bragg grating sensor is in a relaxed state when the prestressed composite material is tensioned to the preset strain. This prevents the fiber Bragg grating sensor from failing due to frequent dynamic loading of the prestressed composite material under high load conditions, thereby improving the service life of the fiber Bragg grating sensor.

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