A desensitization type high-temperature-resistant fiber grating strain sensor

Abstract

The present application relates to the technical field of high-temperature strain measurement, and provides a desensitization type high-temperature resistant fiber grating strain sensor.The desensitization type high-temperature resistant fiber grating strain sensor comprises a fiber grating, a center fiber sleeve, a clamping strain transmission sleeve and an outer encapsulation protective sleeve.The center fiber sleeve constitutes a desensitization configuration, and the desensitization configuration requires that, under high temperature, the center fiber sleeve generates a heat expansion amount along the axial direction inward, which can partially offset the elongation amount generated by the axial thermal expansion of the whole desensitization type high-temperature resistant fiber grating strain sensor, thereby reducing the additional tensile strain transmitted to the fiber grating and achieving temperature compensation and desensitization.Through the multi-layer cooperative structure and the desensitization design, the present application realizes long-term high-precision stable measurement of the sensor under high-temperature environment.

Description

Technical Field

[0001] This invention relates to the field of high-temperature strain measurement technology, and specifically to a desensitized high-temperature resistant fiber optic strain sensor. Background Technology

[0002] In numerous industrial sectors such as energy, petrochemicals, aerospace, and metallurgy, there are many critical devices and structures that require long-term operation in high-temperature environments, such as high-temperature thermal storage containers, high-temperature reactors, high-temperature pipelines, engine hot-end components, and high-temperature furnaces. These devices and structures typically withstand harsh conditions including high temperatures and thermo-mechanical coupling loads, and their structural integrity, long-term safety, and reliability directly affect the operational safety and economy of related systems. Therefore, high-temperature strain monitoring of critical components of such high-temperature equipment or structures has become an indispensable technical means to prevent structural failure and assess their service life.

[0003] Currently, strain monitoring technologies suitable for high-temperature environments mainly face the following challenges: First, traditional electrical strain gauges (such as resistance strain gauges) suffer from large signal drift, poor durability, and susceptibility to electromagnetic interference at high temperatures, making it difficult to meet the requirements for long-term, stable monitoring. Second, although fiber Bragg grating sensors have advantages such as resistance to electromagnetic interference, corrosion resistance, and the ability to perform distributed measurements, their application in high-temperature structural monitoring still faces several technical bottlenecks: one is that ordinary fiber Bragg gratings cannot withstand long-term high-temperature environments; another is that if the thermal expansion coefficients between the sensor substrate material and the measured structure do not match, significant additional strain will occur during temperature changes, leading to measurement signal distortion; and the third is how to achieve reliable, low-stress fixation of the fiber Bragg grating under high-temperature conditions and effectively protect the fragile fiber leads. Existing technologies lack a high-temperature fiber Bragg grating strain sensor that can achieve thermal expansion matching with the high-temperature measurement object, possess a high-temperature durable packaging structure, and accurately transmit strain.

[0004] Therefore, developing a sensor specifically designed for high-temperature equipment that can achieve long-term stable, accurate, and reliable strain monitoring has significant engineering application value and is a practical necessity. Summary of the Invention

[0005] The purpose of this invention is to provide a desensitized high-temperature resistant fiber Bragg grating strain sensor to solve the technical problems of insufficient measurement stability and limited service life of existing fiber Bragg grating strain sensors in high-temperature environments.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A desensitized high-temperature resistant fiber Bragg grating strain sensor includes a fiber Bragg grating, a central fiber optic sleeve, a strain transfer clamping sleeve, and an outer protective encapsulation sleeve. The fiber Bragg grating is a high-temperature resistant fiber Bragg grating, and its grating region is located in the central strain sensing region of the desensitized high-temperature resistant fiber Bragg grating strain sensor. The central fiber optic sleeve consists of two sections, respectively fitted on the left and right sides of the grating region of the fiber Bragg grating, for transmitting axial strain to the fiber Bragg grating. The strain transfer clamping sleeve adopts a symmetrical short-segment design, consisting of two sections, respectively fitted outside the two central fiber optic sleeves, belonging to the middle layer of the desensitized high-temperature resistant fiber Bragg grating strain sensor, and providing support for the central fiber optic sleeve. The strain-transferring sleeve has an outer diameter that matches the clamping hole size of the mounting bracket. It is the only component directly clamped by the mounting bracket. External strain is transmitted to the internal fiber optic grating via the mounting bracket, the strain-transferring sleeve, and the central fiber optic sleeve. The outermost protective sleeve is an integral long sleeve that covers the main area of ​​the two sleeves: the inner central fiber optic sleeve and the strain-transferring sleeve. It serves as the main structure of the entire desensitized high-temperature fiber optic grating strain sensor, providing mechanical protection, environmental isolation, and enhancing the overall rigidity of the encapsulation structure. The desensitized high-temperature fiber optic grating strain sensor is fixed to the component being measured by the mounting bracket. The central fiber optic sleeve constitutes a desensitization configuration. The desensitization configuration requires that, at high temperatures, the central fiber optic sleeve generates an axial inward thermal expansion, which can partially offset the elongation generated by the overall axial thermal expansion of the desensitized high-temperature resistant fiber optic strain sensor, thereby reducing the additional tensile strain transmitted to the fiber optic grating and achieving temperature-compensated desensitization.

[0007] Furthermore, the design of the desensitized high-temperature resistant fiber Bragg grating strain sensor includes the following steps: Step 1: Set the basic parameters of the desensitized high-temperature resistant fiber Bragg grating strain sensor: The distance between the inner ends of the two clamping strain transfer sleeves is the measuring gauge length. The axial length of the single-sided central fiber optic sleeve is The grating length of the fiber Bragg grating is The coefficient of thermal expansion of the outer protective sleeve 4 is . The coefficient of thermal expansion of the materials of the central fiber optic sleeve and the clamping strain transfer sleeve is: Let the desensitization factor be... ;in and It is adjustable; Step 2: Establish the functional relationship between the basic parameters: Step 3: Under the following constraints, select the appropriate function based on the functional relationship from Step 2. and : The value ranges from 0.1 to 0.5; The length of a single segment of the central fiber optic sleeve is greater than the length of a single segment of the strain transfer clamping sleeve. The length of the outer encapsulation protective sleeve is greater than the sum of the lengths of the two clamping strain transfer sleeves and the length of the exposed central optical fiber sleeve. Step 4: Design the other dimensional parameters of the central fiber optic sleeve, the clamping strain transfer sleeve, and the outer encapsulation protective sleeve.

[0008] Furthermore, the outer packaging protective sleeve and mounting bracket of the desensitized high-temperature fiber Bragg grating strain sensor are made of the same material as the component being measured, so as to match the thermal expansion coefficient of the component being measured and reduce the measurement error caused by temperature changes.

[0009] Furthermore, the annular contact areas between the central fiber optic sleeve and both ends of the fiber optic grating, the annular contact area between the clamping strain transfer sleeve and the outer end of the central fiber optic sleeve, and the annular contact area between the outer encapsulation protective sleeve and the inner end of the clamping strain transfer sleeve are filled with high-temperature resistant ceramic adhesive for end-face sealing. The annular gap between the two ends of the outer encapsulation protective sleeve and the central fiber optic sleeve is sealed with high-temperature resistant ceramic adhesive. After end-face sealing, a sealed cavity is formed at the grating area of ​​the fiber optic grating.

[0010] Furthermore, before the high-temperature resistant ceramic adhesive is fully cured, a high-purity inert gas is introduced into the sealed cavity to isolate oxygen and water vapor, suppress the thermal oxidation degradation and hydrogen embrittlement effect of the fiber Bragg grating under high temperature conditions, and extend the long-term high-temperature service life and measurement stability of the desensitized high-temperature resistant fiber Bragg grating strain sensor.

[0011] Furthermore, the fiber grating is a quartz fiber grating or a sapphire fiber grating, or a fiber grating made of other high-temperature resistant optical fibers capable of forming fiber gratings; the fiber grating is a type II fiber grating and is prepared by methods including femtosecond laser etching; the surface of the optical fiber is coated with a polyimide coating, or coated with other high-temperature resistant organic coatings.

[0012] Furthermore, a three-layer protective structure is adopted for the optical fibers at both outer ends of the strain transfer sleeve. The three-layer protective structure, from the inside out, includes: a polyimide coating or other high-temperature resistant organic coating, a stainless steel capillary, and a glass fiber braided layer.

[0013] Furthermore, the mounting bracket has four cylindrical support columns at the bottom, which are used to weld and fix the desensitized high-temperature fiber Bragg grating strain sensor to the surface of the component being tested, and the support columns ensure that the desensitized high-temperature fiber Bragg grating strain sensor is stably attached to the surface of the component being tested, whether it is planar or curved.

[0014] Compared with the prior art, the significant advantages of the present invention are: (1) The desensitized high-temperature fiber optic strain sensor provided by the present invention, by designing the clamping function and the protection function in layers, has a short clamping strain transmission sleeve that undertakes the sole clamping and strain introduction, ensuring the preset measurement gauge length and clear strain transmission path. At the same time, the integrated outer encapsulation protective sleeve provides fully enclosed protection and structural rigidity, avoiding the interference of clamping force on the sensing element.

[0015] (2) The desensitization configuration of the central fiber optic sleeve utilizes the thermal expansion direction of the material itself to counteract thermal stretching, thereby achieving effective temperature compensation, significantly reducing high-temperature measurement errors and improving the stability of the desensitized high-temperature fiber optic strain sensor at high temperatures.

[0016] (3) The sealed cavity, combined with inert gas filling, significantly suppresses the performance degradation of fiber gratings at high temperatures and extends their service life.

[0017] (4) The use of stainless steel, high temperature type II grating and multi-layer composite protective fiber that are thermally matched with the component being measured enables the desensitized high temperature fiber optic strain sensor to work reliably for a long time on the surface of the flat or curved component being measured in a high temperature environment; the four-point support design of the mounting bracket ensures good fit and welding firmness of the desensitized high temperature fiber optic strain sensor on flat and curved surfaces. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the desensitized high-temperature resistant fiber optic strain sensor of the present invention; Figure 2 This is a schematic diagram of the installation structure of the desensitized high-temperature resistant fiber optic strain sensor of the present invention; Figure 3 This is a schematic diagram of the fiber optic protection structure; Figure 4 This is a flowchart of the design method for a desensitized, high-temperature resistant fiber Bragg grating strain sensor.

[0019] In the figure: 1 Fiber Bragg grating; 2 Central fiber optic sleeve; 3 Clamping strain transfer sleeve; 4 Outer encapsulation protective sleeve; 5 High-temperature resistant ceramic adhesive; 6 Sealed cavity; 7 Mounting bracket; 8 Support column; 9 Polyimide coating; 10 Stainless steel capillary; 11 Glass fiber braided layer. Detailed Implementation

[0020] The present invention will now be further described in conjunction with the accompanying drawings, providing a clear and complete description of the embodiments of the invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on the other component or there may be an intermediate component. When a component is considered to be "connected to" another component, it can be directly connected to the other component or there may be an intermediate component present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used in this specification are for illustrative purposes only and do not represent the only possible implementation.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0023] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] The present invention further provides a desensitized high-temperature resistant fiber Bragg grating strain sensor, which covers a design method for a desensitized high-temperature resistant fiber Bragg grating strain sensor, specifically including axial length design (desensitization configuration), radial diameter design, and wall thickness design (based on high-temperature strength and functional constraints), to guide the optimal size of the desensitized high-temperature resistant fiber Bragg grating strain sensor under different working conditions.

[0025] I. Axial length design; Let the distance between the inner ends of the two clamping strain transfer sleeves 3 be the measuring gauge length L. g The length can be selected according to measurement needs; a recommended length is 50–150 mm. The axial length of the single-sided center fiber optic sleeve 2 is L. c (From the end point of the grating region to the inner end face of the clamping strain transfer sleeve 3), the length of the grating region of the fiber optic grating 1 is L. t The outer protective sleeve 4 and the tested structure both have the coefficient of thermal expansion α. sThe coefficient of thermal expansion of the central fiber optic sleeve 2 material and the strain transfer sleeve 3 is α. c Under a temperature change ΔT, the actual strain transmitted to fiber grating 1 is: Define desensitizing factors: Desensitizing factors The sensitivity of the desensitized high-temperature fiber Bragg grating strain sensor to temperature strain was characterized. The smaller the value, the more the additional strain caused by temperature is offset (the stronger the desensitization effect). Complete compensation can be achieved in a timely manner; A negative value indicates overcompensation. Fiber Bragg grating 1 is subjected to compressive strain when heated, which may cause fiber Bragg grating 1 to fail.

[0026] Taking into account measurement sensitivity, long-term stability, and manufacturing tolerances, this invention recommends a desensitization factor. The range of values ​​for is: That is, the actual temperature strain is only 10% to 50% of the free thermal strain of the desensitized high-temperature fiber Bragg grating strain sensor. This range can effectively suppress thermally induced errors while retaining sufficient positive strain response, avoiding the risk of negative strain caused by overcompensation.

[0027] according to The range of values ​​can be used to derive the conditions that the design length should meet.

[0028] 1) When the outer protective sleeve and the central fiber optic sleeve are made of the same material, ,but: That is, the difference between the measuring gauge length and the axial length of twice the center fiber optic sleeve 2 should be controlled within 0.1 to 0.5 times the grating region length of fiber optic grating 1. For a typical grating region length... ,have: .

[0029] 2) When the outer protective sleeve and the central fiber optic sleeve are made of different materials, ,but: Selected based on the actual component being measured Then select desensitizing factors Then determine based on the selected materials. Finally, it is presumed Numerical value.

[0030] In this embodiment, the outer protective sleeve 4 and the component under test are made of 316L stainless steel, while the central fiber optic sleeve 2 and the strain transfer clamping sleeve 3 are made of HK40 cast austenitic stainless steel. The average linear expansion coefficients of the two materials at 20~600℃ are as follows: .

[0031] The measuring gauge length in this embodiment gate length Desensitizing factors Substituting the material coefficients and solving the inequalities, we get... .

[0032] At this temperature rise of 600℃, the actual thermal strain transferred to fiber grating 1 is only 35.3% of the free thermal strain of 316L.

[0033] II. Radial Diameter and Wall Thickness Design; Based on the initial selection of the pipe length, the range of radial diameter and wall thickness is further limited.

[0034] 1) The diameter and wall thickness range of the central fiber optic sleeve 2; The inner diameter of the central fiber optic sleeve 2 The coating must accommodate the outer diameter (155μm) of the fiber grating 1 coating plus the adhesive layer thickness (0.1mm~1.5mm on each side), and the inner diameter should not be too small to ensure uniform filling of the high-temperature resistant ceramic adhesive 5. Overall range: This embodiment takes .

[0035] Central fiber optic sleeve 2 wall thickness Primarily responsible for transmitting axial strain and providing thermal compensation, axial tensile strength constraints must be considered. In this example, the inner diameter... Wall thickness The cross-sectional area is: Maximum axial tensile force High temperature yield strength is Safety factor taken ,Require: in, The cross-sectional area of ​​the central fiber optic sleeve; Solving .

[0036] Considering the strength attenuation and stress concentration of the adhesive layer under long-term high-temperature creep, an empirical upper limit of 1.0 mm is adopted after taking a safety factor in engineering practice. Therefore, the wall thickness of the central fiber optic sleeve 2 is taken as follows: In this embodiment The outer diameter of the central fiber optic sleeve 2 .

[0037] 2. The range of diameter and wall thickness of the strain transfer sleeve; Clamping strain transfer sleeve 3 inner diameter Needs to accommodate the outer diameter of the central fiber optic sleeve 2 The thickness of the adhesive layer (0.1mm~1.5mm on one side) and the inner diameter should not be too small to ensure uniform filling of the high-temperature resistant ceramic adhesive 5. Overall range: This embodiment takes .

[0038] The clamping strain transfer sleeve 3 bears the circumferential compressive stress and axial thermal stress generated by the clamping force of the mounting bracket 7, and its wall thickness must meet the requirements for resistance to local buckling stability. The mounting bracket 7 has an outer diameter... With wall thickness Under the given proportional relationship, local buckling under radial clamping force should be avoided. According to the theory of elastic stability, the critical buckling pressure of a thin-walled cylinder under radial concentrated force is... It can be represented as: in The high-temperature elastic modulus of the material. The coefficients are related to the boundary conditions. Let be the average radius. To avoid buckling failure, the following is required: Under typical high-temperature engineering conditions (critical instability external pressure) ,temperature , , ), we can obtain .

[0039] Considering strain transfer efficiency, the shear strain concentration of the constrained adhesive layer is proportional to the wall thickness of the clamping strain transfer sleeve 3, based on the shear hysteresis model: To ensure that the adhesive layer does not experience creep failure, it is required that .

[0040] Therefore, the wall thickness of the strain transfer sleeve 3 is determined as follows: In this embodiment Then the outer diameter .

[0041] 3. The diameter and wall thickness range of the outer protective sleeve; Outer encapsulation protective sleeve 4 inner diameter It needs to accommodate a strain transfer sleeve with an outer diameter of 3. Add gap (0.1 on one side) ~1.0 This facilitates assembly and the formation of a sealed cavity. Overall scope: This embodiment takes .

[0042] The outermost protective sleeve 4 is the outermost layer and needs to provide overall protection and isolation from external mechanical loads. Its wall thickness is... Should meet: Consider the outer protective sleeve 4 as a simply supported beam, with a span of... Bearing lateral concentrated force Maximum bending moment Flexural section modulus: Bending stress ,Require Solving for the problem, we get... .

[0043] Excessive wall thickness increases heat capacity and reduces temperature response speed; therefore, it is recommended to... .

[0044] Therefore, the range of wall thickness values ​​for the outer protective sleeve is: In this embodiment Then the outer diameter .

[0045] Using the above system design method, the optimal basic parameters of the desensitized high-temperature resistant fiber optic strain sensor can be quickly obtained for different operating temperatures (room temperature to 600℃), different measured structural materials, and different accuracy requirements. Figure 4 As shown.

[0046] The following is combined Figures 1 to 3 Describing the desensitized high-temperature resistant fiber Bragg grating strain sensor of the present invention: refer to Figure 1 In one embodiment, the desensitized high-temperature fiber optic strain sensor includes a fiber optic grating 1, a central fiber optic sleeve 2, a strain transfer clamping sleeve 3, an outer encapsulation protective sleeve 4, a high-temperature resistant ceramic adhesive 5, and a sealed cavity 6.

[0047] Fiber Bragg grating 1 is a type II pure silica fiber Bragg grating etched by femtosecond laser, with a grating area length of 10 mm, located in the central strain sensing region of the desensitized high-temperature fiber Bragg grating strain sensor. The central fiber sleeve 2 is made of HK40 cast austenitic stainless steel, with two 40 mm long sections symmetrically distributed on the left and right sides of fiber Bragg grating 1. The inner end distance between the two central fiber sleeve sections 2 is 10 mm, forming the theoretical strain transfer reference for the desensitized high-temperature fiber Bragg grating strain sensor. The annular contact area between the central fiber sleeve 2 and the optical fiber is filled with high-temperature resistant ceramic adhesive 5 to ensure continuous and rigid transmission of axial strain.

[0048] The clamping strain transfer sleeve 3 is made of HK40 cast austenitic stainless steel, with a single section length of 20mm. Two sections are used, one on each side of the central fiber optic sleeve 2. The inner end distance between the two clamping strain transfer sleeves 3 is controlled at 92mm, forming the measuring gauge length of the desensitized high-temperature fiber optic strain sensor. This clamping strain transfer sleeve 3 is the only component directly clamped by the mounting bracket 7. Its short-segment, split design efficiently transfers external strain to the internal fiber optic grating 1 while significantly reducing additional measurement errors caused by thermal expansion of the overall structure. The annular contact area between the clamping strain transfer sleeve 3 and the central fiber optic sleeve 2 is filled with high-temperature resistant ceramic adhesive 5.

[0049] The outer protective sleeve 4 is made of stainless steel, with a length of 80mm. It is an integral long sleeve that coaxially covers the two clamping strain transfer sleeves 3 and the exposed central optical fiber sleeve 2. The outer protective sleeve 4 provides mechanical protection for the entire desensitized high-temperature fiber Bragg grating strain sensor, isolates it from the external environment, and enhances the overall rigidity of the encapsulation structure.

[0050] The gap between the clamping strain transfer sleeve 3 and the outer encapsulation protective sleeve 4 employs a differentiated segmented filling process: only the annular contact areas, each 5mm long, at both ends are filled with high-temperature resistant ceramic adhesive 5, while the middle area, approximately 54mm long, naturally forms a sealed cavity 6. The annular gaps between the two ends of the outer encapsulation protective sleeve 4 and the central fiber optic sleeve 2 are sealed at the end faces using high-temperature resistant ceramic adhesive 5, achieving complete isolation of the sealed cavity 6 from the external environment. Before the high-temperature resistant ceramic adhesive 5 is fully cured, high-purity nitrogen gas (99.999% purity) is injected into the sealed cavity 6 through a pre-reserved micro-inflation port, and then the inflation port is sealed. The nitrogen atmosphere effectively isolates oxygen and water vapor, suppressing the thermal oxidation degradation and hydrogen embrittlement effect of the fiber optic grating 1 under high-temperature conditions, extending the long-term service life and measurement stability of the desensitized high-temperature resistant fiber optic strain sensor.

[0051] refer to Figure 2The mounting bracket 7 for the desensitized high-temperature fiber Bragg grating strain sensor described in this invention is made of stainless steel. A semi-circular groove with a diameter of 4mm is formed at the center of the upper surface of the mounting bracket 7 to place and position the outer encapsulation protective sleeve 4 with an outer diameter of 4mm. A cylindrical support column 8, with a diameter of 4mm and a height of 5mm, is welded to each of the four corners of the mounting bracket 7. The bottom ends of the four support columns 8 are used for welding and fixing to the structure being measured. By adjusting the height of the support columns 8, the desensitized high-temperature fiber Bragg grating strain sensor can be stably fitted to curved surfaces or planes with different curvatures, avoiding the influence of installation stress on the measurement results.

[0052] refer to Figure 3 The optical fiber lead-out end of the present invention adopts a three-layer composite protection structure, which includes, from the inside out: Polyimide coating 9: Directly coated on the fiber surface, with a thickness of 15μm, providing basic high-temperature resistance and insulation protection; Stainless steel capillary 10: With an inner diameter of 0.8mm, it is fitted over the polyimide coating 9, providing mechanical strength protection to prevent fiber bending and breakage; Glass fiber braided layer 11: Covering the stainless steel capillary 10, it further enhances wear and impact resistance. This three-layer composite protection system can operate stably for a long time in a high-temperature environment of 600℃, effectively protecting the fiber optic lead from mechanical damage during installation, cabling, and use.

[0053] 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 desensitizing, high-temperature resistant fiber Bragg grating strain sensor, characterized in that, The system includes a fiber optic grating (1), a central fiber optic sleeve (2), a strain transfer sleeve (3), and an outer protective sleeve (4). The fiber optic grating (1) is a high-temperature resistant fiber optic grating, and its grating region is located in the central strain sensing region of the desensitized high-temperature resistant fiber optic grating strain sensor. The central fiber optic sleeve (2) consists of two sections, which are respectively fitted on the left and right sides of the grating region of the fiber optic grating (1) to transfer axial strain to the fiber optic grating (1). The strain transfer sleeve (3) adopts a symmetrical short-segment design, consisting of two sections, which are respectively fitted on the outside of the two central fiber optic sleeves (2). It belongs to the middle layer of the desensitized high-temperature resistant fiber optic grating strain sensor and plays a supporting role for the central fiber optic sleeve (2). The outer diameter of the tube (3) matches the size of the clamping hole of the mounting bracket (7), and is the only component directly clamped by the mounting bracket (7). External strain is transmitted to the internal fiber grating (1) through the mounting bracket (7), the clamping strain transmission sleeve (3), and the central fiber optic sleeve (2). The outer encapsulation protective sleeve (4) is located on the outermost layer. It is an integral long sleeve that covers the main area of ​​the two sleeves of the internal central fiber optic sleeve (2) and the clamping strain transmission sleeve (3). As the main structure of the entire desensitized high-temperature fiber optic strain sensor, it can provide mechanical protection, environmental isolation, and enhance the overall rigidity of the encapsulation structure. The desensitized high-temperature fiber optic strain sensor is fixed to the component under test by the mounting bracket (7). The central fiber optic sleeve (2) constitutes a desensitization configuration. The desensitization configuration requires that, at high temperatures, the central fiber optic sleeve (2) generates an axial inward thermal expansion that can partially offset the elongation generated by the overall axial thermal expansion of the desensitized high-temperature resistant fiber optic strain sensor. The design of a desensitized, high-temperature resistant fiber Bragg grating strain sensor includes the following steps: Step 1: Set the basic parameters of the desensitized high-temperature resistant fiber Bragg grating strain sensor: The distance between the inner ends of the two clamping strain transfer sleeves (3) is the measuring gauge length. The axial length of the single-sided central fiber optic sleeve (2) is The grating length of the fiber grating (1) is The coefficient of thermal expansion of the outer protective sleeve (4) is The coefficient of thermal expansion of the materials of the central fiber optic sleeve (2) and the clamping strain transfer sleeve (3) is: Let the desensitization factor be... ;in and It is adjustable; Step 2: Establish the functional relationship between the basic parameters: Step 3: Under the following constraints, select the appropriate function based on the functional relationship from Step 2. and : The value ranges from 0.1 to 0.5; The length of a single segment of the central fiber optic sleeve (2) is greater than the length of a single segment of the clamping strain transfer sleeve (3); The length of the outer encapsulation protective sleeve (4) is greater than the sum of the lengths of the two clamping strain transfer sleeves (3) and the length of the exposed central optical fiber sleeve (2); Step 4: Design other dimensional parameters for the central fiber optic sleeve (2), the clamping strain transfer sleeve (3), and the outer encapsulation protective sleeve (4).

2. The desensitizing high-temperature resistant fiber optic strain sensor according to claim 1, characterized in that, The outer packaging protective sleeve (4) and mounting bracket (7) of the desensitized high-temperature fiber optic strain sensor are made of the same material as the component being tested.

3. The desensitizing high-temperature resistant fiber optic strain sensor according to claim 1, characterized in that, The annular contact areas between the central fiber optic sleeve (2) and the fiber optic grating (1), the annular contact area between the clamping strain transfer sleeve (3) and the outer end of the central fiber optic sleeve (2), and the annular contact area between the outer encapsulation protective sleeve (4) and the inner end of the clamping strain transfer sleeve (3) are filled with high-temperature resistant ceramic adhesive (5) for end-face sealing. The annular gap between the two ends of the outer encapsulation protective sleeve (4) and the central fiber optic sleeve (2) is sealed with high-temperature resistant ceramic adhesive (5). After the end-face sealing, a sealed cavity (6) is formed at the grating area of ​​the fiber optic grating (1).

4. The desensitizing high-temperature resistant fiber optic strain sensor according to claim 3, characterized in that, Before the high-temperature resistant ceramic adhesive (5) is fully cured, high-purity inert gas is introduced into the sealed cavity (6).

5. The desensitizing high-temperature resistant fiber optic strain sensor according to claim 1, characterized in that, The fiber grating (1) is a quartz fiber grating or a sapphire fiber grating, or a fiber grating made of other high-temperature resistant optical fibers capable of forming fiber gratings; the fiber grating is a type II fiber grating and is prepared by means including femtosecond laser etching; the surface of the optical fiber is coated with a polyimide coating, or coated with other high-temperature resistant organic coatings.

6. The desensitized high-temperature resistant fiber optic strain sensor according to claim 1, characterized in that, The optical fibers at the outer ends of both sides of the clamping strain transfer sleeve (3) adopt a three-layer protection structure. The three-layer protection structure includes, from the inside out: polyimide coating (9) or other high-temperature resistant organic coating, stainless steel capillary (10), and glass fiber braided layer (11).

7. The desensitizing high-temperature resistant fiber optic strain sensor according to claim 1, characterized in that: The mounting bracket (7) has four cylindrical support columns (8) at the bottom, which are used to weld and fix the desensitized high temperature fiber optic strain sensor to the surface of the component being tested, and to make the desensitized high temperature fiber optic strain sensor stably fit with the surface of the component being tested, which is either planar or curved, through the support columns (8).

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