CN114322814B - Anti-scouring high-temperature strain sensor cast by sapphire fiber grating metal - Google Patents
Anti-scouring high-temperature strain sensor cast by sapphire fiber grating metal Download PDFInfo
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Abstract
The invention discloses a scouring-resistant high-temperature strain sensor cast by sapphire fiber bragg grating metal, which comprises a tail fiber, wherein a sleeve is sleeved outside the tail fiber; the sleeve is fixedly connected with two ends of the tail fiber through high-temperature glue; one end of the tail fiber is welded with one end of the sapphire fiber, and the other end of the sapphire fiber is ground into an oblique angle; a first grating and a second grating are inscribed in the sapphire optical fiber; the second grating is sleeved and fixedly connected with a protective sleeve; the sapphire optical fiber is sleeved and fixedly connected with casting metal. The invention has reasonable structure, can realize single-mode system transmission, effectively filter out high-order modes, reduce 3dB bandwidth and improve measurement accuracy; the problems of instability, low measurement precision and the like of a multimode system are avoided; meanwhile, the difficult problem of strain measurement in a high-temperature state can be solved, the anti-scouring capability of the sensor can be effectively improved by adopting a metal pouring technology, and the high-temperature strain measurement application of complex scouring force thermal environments such as the inside of an engine, rocket tail nozzles and the like can be satisfied.
Description
Technical Field
The invention relates to the technical field of optical fiber sensors, in particular to a scouring-resistant high-temperature strain sensor cast by sapphire optical fiber grating metal.
Background
The temperature strain sensor has wide application value in the fields of national defense industry, material chemical industry, building health monitoring, security maintenance and the like. With the development of the fields of aerospace technology, high new material smelting, national defense industry and the like, new requirements of higher temperature resistance, electromagnetic interference resistance, scouring resistance, corrosion resistance, high sensitivity, miniaturization, long service life and the like are provided for the temperature strain sensor. Most of the prior commercial temperature sensors are contact type electric sensors based on thermal electromotive force and thermal resistance and non-contact type sensors based on a thermal imaging principle, while most of the commercial strain sensors are electric strain sensors based on platinum sheet type, welding type and wire winding type, and the two types of sensors are more or less limited by problems of electromagnetic interference, limited material tolerance temperature, large volume, single variable measurement and the like, so that the temperature and strain double-parameter simultaneous measurement under a complex environment (such as an ultra-high temperature environment above 1600 ℃) is difficult to meet.
The optical fiber sensor has the advantages of small volume, low cost, high sensitivity, compact structure, convenient integration and multiplexing, realization of multi-parameter in-situ simultaneous measurement and the like, provides a new technical idea for the research of a novel high-temperature strain sensing system, and has achieved a plurality of achievements in the aspect. Currently, fiber temperature sensors mainly include Bragg fiber grating type, blackbody radiation type, fluorescence sensing type and Fabry-Perot type. The Bragg fiber Bragg grating type temperature sensor mainly influences the drift of a specific wavelength of a spectrum through the thermo-optical effect and the thermal expansion effect of the fiber Bragg grating, so that temperature measurement is realized. However, the existing Bragg fiber grating type temperature sensor is mainly limited by the tolerance temperature of the fiber material, and the temperature sensor manufactured by adopting the common fused quartz fiber grating can measure the high temperature of about 1200 ℃ at most, so that the measurement requirement of higher temperature is difficult to meet. The blackbody radiation type optical fiber temperature sensor mainly comprises an optical fiber and an opaque cavity attached to the tip of the optical fiber. It is known from planck's law that the spectral radiant flux detected at the end of the fiber is related to the temperature of the cavity, so that temperature information is obtained by measuring the spectral intensity or intensity distribution. Blackbody sensors can theoretically operate over a wide range of temperatures. However, since the radiation intensity is almost exponentially related to the temperature, the signal intensity in a lower temperature region is weak, and thus achieving a full range accurate measurement of the temperature is a great problem for a blackbody radiation temperature sensor. In contrast, fluorescent temperature sensors are only suitable for measuring low temperatures due to the limitations of the fluorescent material itself. Such sensors are temperature sensing based on temperature dependent decay times of fluorescence or fluorescence intensities of suitable materials. Because the fluorescence quenching effect has weaker fluorescence intensity at high temperature and the background noise of blackbody radiation at high temperature becomes stronger, the high-temperature sensing signal-to-noise ratio of the optical fiber sensor of the sensing principle is poorer, and the application of the optical fiber sensor in high-temperature measurement is limited.
The current methods and sensors for testing in-situ strain of a structure at high temperature are mainly divided into two types: electrical and optical fiber; the electrical strain sensor mainly comprises three strain sensors, namely a foil strain gauge, a welding strain gauge and a wire-wound strain gauge, and the wire-wound strain gauge can work at 1000 ℃ and the welding strain gauge can work at 600 ℃ at the highest, so that the foil-type working temperature is lower; the optical fiber type mainly comprises a quartz fiber strain sensor and a sapphire fiber strain sensor. Quartz fiber strain sensors can work at 1000 ℃ at most, but for application environments above 1000 ℃, strain sensing test technology based on sapphire fibers (melting point of 2050 ℃) can only be adopted. In addition, electrical strain gauges such as foil strain gauges and soldering strain gauges require an electrical signal output line when applied, which not only limits the temperature at which they are used, but also is subject to electromagnetic interference. And some electric strain sensors have large volume, even need to punch holes on an engine for measurement, and the structure of the measured object is easily influenced. The sapphire optical fiber strain sensor has the advantages of small volume, electromagnetic interference resistance, easiness in multiplexing and the like, meanwhile, the sapphire optical fiber strain sensor has the characteristics of high temperature resistance (the melting point is 2050 ℃), high hardness (Mohs 9) and the like of a sapphire material, and the sapphire optical fiber is a feasible scheme for being applied to the optical fiber high-temperature strain sensor. The existing sapphire fiber grating high-temperature strain sensor main measurement systems are all based on multimode fiber systems (such as China patent CN210774419U, the system composition does not mention multimode solutions, uncertainty exists in the measurement system), more high-order modes exist, signals are easy to be interfered by vibration, bending and the like of the optical fibers, larger instability exists, the line width of a reflection spectrum is larger (the existing systems are all between 1nm and 10 nm), the measurement precision is not high, the mode change is obvious in a high-temperature state, the reflection spectrum signal is unstable, and larger measurement errors exist; in addition, there are systems based on single-mode fiber fusion-spliced sapphire fibers (such as chinese patent CN110118614 a), but in principle, according to the mode selection effect of the single-mode fiber itself, and the existence of a single-mode field region in the sapphire fiber near the fusion point (10 mm), where a grating is written to realize few-mode or single-mode transmission, this method is difficult to apply in a wide range of high-temperature fields, and this method cannot realize strain measurement in the high-temperature fields. There is a need for a sapphire fiber grating metal cast, anti-scour, high temperature strain sensor that overcomes the above-mentioned shortcomings.
Disclosure of Invention
The invention aims to provide a scouring-resistant high-temperature strain sensor cast by sapphire fiber grating metal, which solves the problems in the prior art.
In order to achieve the above object, the present invention provides the following solutions: the invention provides a scouring-resistant high-temperature strain sensor cast by sapphire fiber grating metal, which comprises a tail fiber, wherein a sleeve is sleeved outside the tail fiber; the sleeve is fixedly connected with two ends of the tail fiber through high-temperature glue;
One end of the tail fiber is welded with one end of a sapphire optical fiber, and the other end of the sapphire optical fiber is ground into an oblique angle; a first grating and a second grating are inscribed in the sapphire optical fiber; the second grating is sleeved and fixedly connected with a protective sleeve; the sapphire optical fiber is sleeved and fixedly connected with casting metal.
Preferably, a stainless steel tube is sleeved and fixedly connected at the welding point of the tail fiber and the sapphire optical fiber, and the stainless steel tube is arranged in the sleeve; the sleeve is fixedly connected with the stainless steel tube through the high-temperature glue.
Preferably, the fusion point is in a conical structure, the length of a conical region of the fusion point is 145-155 mu m, and the minimum diameter of the conical region is equivalent to the diameter of the sapphire optical fiber; the maximum diameter of the cone area is equal to the diameter of the tail fiber
Preferably, the tail fiber is a common single mode fiber, the material of the tail fiber is SiO 2, the core diameter is 9-10 mu m, the cladding diameter is 125-130 mu m, and the length is 50-60 cm; the sapphire optical fiber is made of AL 2O3, has a hexagonal prism shape, has a diameter of 60-80 μm and a length of 15-20 cm.
Preferably, the length of the first grating region is 2.66mm-2.67mm, the first grating region is of a double-layer scribing structure, the scribing depth is 4 mu m-5 mu m, the upper layer and the lower layer are separated by 5 mu m-7 mu m, the Bragg wavelength of the grating is 1550nm-1600nm, and the scribing position is 13cm-16cm away from the front end welding point of the sapphire optical fiber.
Preferably, the length of the second grating region is 2.67mm-2.68mm, the second grating region is of a double-layer scribing structure, the scribing depth is 4 μm-5 μm, the upper layer and the lower layer are separated by 5 μm-7 μm, the Bragg wavelength of the grating is 1550nm-1600nm, and the scribing position is 0.5cm-1cm away from the tail end of the sapphire optical fiber.
Preferably, the material of the protective sleeve is Al 2O3, the length is 4mm-5mm, the inner diameter is 200 mu m-300 mu m, and the outer diameter is 500 mu m-600 mu m; and the protective sleeve is welded and fixed with the sapphire optical fiber at the second grating.
Preferably, the casting metal material is high-melting-point metal; the diameter of the cylinder of the casting metal is 8cm-10cm, the length of the cylinder is 14cm-15cm, and the length of the cone angle is 3cm-4cm.
Preferably, the casting mould for casting the metal comprises a filling groove and a casting groove which are communicated, the filling groove and the casting groove are both in a cylindrical and conical composite structure, and the bottom of the filling groove is communicated with the bottom of the casting groove through a channel; a filter screen is arranged below the filling groove; the sapphire optical fiber is placed in the casting groove.
The invention discloses the following technical effects: according to the anti-scouring type high-temperature strain sensor for casting the sapphire fiber grating metal, disclosed by the invention, the tail fiber and the sapphire fiber are welded through a welding machine welding tapering technology, a tapering region structure at a welding position can effectively filter out a high-order mode, low-order mode and even basic mode transmission is realized, a single-mode system effectively avoids interference of vibration and fiber bending, so that the system stability is improved, and stable signal transmission is realized; the 3dB bandwidth of the reflection spectrum is effectively reduced, the measurement precision is obviously improved, and the complex force and heat environment test requirement is met; meanwhile, due to the good mode filtering effect, the double gratings of the first grating and the second grating are inscribed on the sapphire optical fiber, so that the temperature and strain double-parameter cross sensitivity problem can be well reduced, and further the strain measurement in a high temperature state is realized; the temperature measurement range is from room temperature to 1800 ℃, and the strain range is from 0 to 1500 mu epsilon; the casting metal is fixedly arranged outside the sapphire optical fiber in a casting mode, so that the anti-scouring capability of the sapphire optical fiber grating sensor can be effectively improved, and the high-temperature strain measurement application of complex scouring force thermal environments such as the inside of an engine and rocket tail nozzle can be satisfied. The invention has reasonable structure, can realize single-mode system transmission, effectively filter out high-order modes, reduce 3dB bandwidth and improve measurement accuracy; the problems of instability, low measurement precision and the like of a multimode system are avoided; meanwhile, the difficult problem of strain measurement in a high-temperature state can be solved, the anti-scouring capability of the sensor can be effectively improved by adopting a metal pouring technology, and the high-temperature strain measurement application of complex scouring force thermal environments such as the inside of an engine, rocket tail nozzles and the like can be satisfied.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a metal cast anti-scouring high temperature strain sensor with a sapphire fiber grating;
FIG. 2 is an enlarged view of a portion of FIG. 1A;
FIG. 3 is a schematic diagram of a method for casting a metal cast anti-scouring type high temperature strain sensor with a sapphire fiber grating and a monitoring system according to the present invention;
FIG. 4 is a schematic view of a casting mold according to the present invention;
Wherein, 1, tail fiber; 2. a sleeve; 3. high-temperature glue; 4. a sapphire optical fiber; 5. a first grating; 6. a second grating; 7. a protective sleeve; 8. casting metal; 9. stainless steel tube; 10. casting a mold; 11. filling into a tank; 12. a casting tank; 13. a channel; 14. a filter screen; 15. a broadband light source; 16. an optical circulator; 17. a grating demodulator; 18. a sapphire fiber grating sensor; 19. a computer; 20. a fixing frame; 21. and (5) welding points.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
Referring to fig. 1-4, the invention provides a sapphire fiber grating metal cast anti-scouring high temperature strain sensor, which comprises a tail fiber 1, wherein a sleeve 2 is sleeved outside the tail fiber 1; the sleeve 2 is fixedly connected with two ends of the tail fiber 1 through high-temperature glue 3;
One end of the tail fiber 1 is welded with one end of a sapphire optical fiber 4, and the other end of the sapphire optical fiber 4 is ground into an oblique angle; a first grating 5 and a second grating 6 are inscribed in the sapphire optical fiber 4; the second grating 6 is sleeved and fixedly connected with a protective sleeve 7; the sapphire optical fiber 4 is sleeved and fixedly connected with casting metal 8.
According to the anti-scouring type high-temperature strain sensor based on cascaded sapphire optical fiber 4 grating metal pouring, the tail fiber 1 and the sapphire optical fiber 4 are welded through the welding and tapering technical piece of the welding machine, the cone area structure of the welding point 21 can effectively filter out high-order modes, low-order mode and even fundamental mode transmission is realized, the interference of vibration and optical fiber bending is effectively avoided by a single-mode system, and the stability of the system is improved, so that stable signal transmission is realized; the 3dB bandwidth of the reflection spectrum is effectively reduced, the measurement precision is obviously improved, and the complex force and heat environment test requirement is met; meanwhile, due to the good mode filtering effect, the double-grating structure of the first grating 5 and the second grating 6 inscribed on the sapphire optical fiber 4 can better reduce the temperature and strain double-parameter cross sensitivity problem, thereby realizing strain measurement in a high temperature state; the temperature measurement range is from room temperature to 1800 ℃, and the strain range is from 0 to 1500 mu epsilon; the casting metal 8 is fixedly arranged outside the sapphire optical fiber 4 in a casting mode, so that the anti-scouring capability of the sapphire optical fiber grating sensor 18 can be effectively improved, and the high-temperature strain measurement application of complex scouring force thermal environments such as the inside of an engine and rocket tail nozzle can be satisfied.
In a further optimized scheme, a stainless steel tube 9 is fixedly sleeved outside the welding point 21 of the tail fiber 1 and the sapphire optical fiber 4, and the stainless steel tube 9 is arranged in the sleeve 2; the sleeve 2 is fixedly connected with the stainless steel tube 9 through the high-temperature glue 3; the fusion point 21 is in a conical structure, the length of a conical region of the fusion point 21 is 145-155 mu m, and the minimum diameter of the conical region is equivalent to the diameter of the sapphire optical fiber 4; the maximum diameter of the cone region is equivalent to the diameter of the tail fiber 1. The tail fiber 1 and the sapphire optical fiber 4 are fused by a fusion splicer; the junction 21 of the pigtail 1 and the sapphire fiber 4 is tapered. The mode field matching of the sapphire optical fiber 4 and the tail optical fiber 1 is realized, the higher-order mode is filtered, the 3dB bandwidth of the reflection spectrum is effectively reduced, a single-mode sapphire optical fiber 4 sensor system is realized, the single-mode system effectively avoids the interference of vibration and optical fiber bending, the system stability is improved, the measuring precision and the stability of the sensing system are improved, and the complex force thermal environment test requirement is further met.
Furthermore, the main components of the high-temperature glue 3 are inorganic ceramic materials and modified curing agents, and the tolerance temperature can reach 1730 ℃.
Further, the sleeve 2 is a Kevlar metal pipe, is made of an aramid composite material, has the length of 50cm, the inner diameter of 300 mu m and the outer diameter of 500 mu m, protects the tail fiber 1 and the conical welding point 21 embedded with the stainless steel pipe 9 through the sleeve 2, and adopts high-temperature glue 3 to fix the tail fiber 1 and the protective sleeve 7 in a water-fixing way; protecting the pigtail 1 and the fusion point 21.
According to a further optimization scheme, the tail fiber 1 is a common single-mode fiber, the material of the tail fiber 1 is SiO 2, the core diameter is 9-10 mu m, the cladding diameter is 125-130 mu m, and the length is 50-60 cm; the sapphire optical fiber 4 is made of AL 2O3, has a hexagonal prism shape, has a diameter of 60-80 μm and a length of 15-20 cm. The surface of the tail fiber 1 is provided with a gold coating layer, the gold coating layer at one end is removed, and the tail fiber is cut and flattened by a common optical fiber cutting knife and welded with the sapphire optical fiber 4; in addition, the whole optical fiber is nested into the sleeve 2 for protection, and the two are fixed by using the high-temperature glue 3; the sapphire optical fiber 4 is a special optical fiber with the diameter of 75 mu m, a first grating 5 and a second grating 6 are inscribed in the sapphire optical fiber 4 through a femtosecond laser direct writing technology, the first grating and the second grating are both in a double-layer grating structure, and a protective sleeve 7 is nested at the sapphire optical fiber 4 where the second grating 6 is positioned in a laser welding mode.
Furthermore, the tail fiber 1 adopts a single mode fiber with the model number of CorningSMF-28e, and is welded and fixed with the flat end opening of the sapphire optical fiber 4 through a welding machine welding tapering technology to form a welding point 21.
Further, the end face of the sapphire optical fiber 4 welded with the tail optical fiber 1 is ground into a flat end face by an optical fiber grinding technology, and the roughness of the end face reaches the nanometer level; the other port is ground into an inclined angle of 8 degrees by adopting an optical fiber grinding technology, and the end surface smoothness also reaches the nanometer level.
According to a further optimization scheme, the length of the grating area of the first grating 5 is 2.66mm-2.67mm, the grating is of a double-layer scribing structure, the scribing depth is 4 mu m-5 mu m, the distance between the upper layer and the lower layer is 5 mu m-7 mu m, the Bragg wavelength of the grating is 1550nm-1600nm, and the scribing position is 13cm-16cm away from the welding point 21 at the front end of the sapphire optical fiber 4. The first grating 5 is inscribed by a femtosecond laser direct writing technology, the Bragg wavelength of the first grating 5 is 1550nm, the length is 2.66mm, the line structure is a double-layer structure, the reflectivity is 10%, and the position is 13cm away from the front end fusion point 21 of the sapphire optical fiber 4.
According to a further optimization scheme, the length of the grating area of the second grating 6 is 2.67mm-2.68mm, the grating is of a double-layer grating structure, the grating depth is 4 mu m-5 mu m, the upper layer and the lower layer are 5 mu m-7 mu m apart, the Bragg wavelength of the grating is 1550nm-1600nm, and the writing position is 0.5cm-1cm away from the tail end of the sapphire optical fiber 4. The second grating 6 is inscribed by a femtosecond laser direct writing technology, the Bragg wavelength of the second grating 6 is 1555nm, the length is 2.67mm, and the inscription position is 0.5cm away from the inclined port at the tail end of the sapphire optical fiber.
According to a further optimization scheme, the protective sleeve 7 is made of Al 2O3, has a length of 4mm-5mm, an inner diameter of 200 mu m-300 mu m and an outer diameter of 500 mu m-600 mu m; the protective sleeve 7 is welded and fixed with the sapphire optical fiber 4 at the second grating 6. The protective sleeve 7 is nested outside the second grating 6, and the protective sleeve 7 and the sapphire optical fiber 4 are welded together by adopting a laser welding technology; the sensor is used for enabling the second grating 6 to respond to temperature only, comparing the temperature and the strain of the unprotected first grating 5, realizing the double-parameter synchronous measurement of the temperature and the strain, and the temperature range of the sensor is from room temperature to 1800 ℃ and the strain range is 0-1500 mu epsilon.
According to a further optimization scheme, the casting metal 8 is made of high-melting-point metal; the diameter of the cylinder of the casting metal 8 is 8cm-10cm, the length of the cylinder is 14cm-15cm, and the length of the cone angle is 3cm-4cm. The casting metal 8 is made of high-melting-point materials including but not limited to aluminum, copper, steel and the like, the sapphire optical fiber 4 is cast in the metal through the casting die 10, and the sensor is buried in the metal, so that the application capacity of the sensor in a complex scouring force environment can be effectively improved, the anti-scouring capacity of the sensor is effectively realized, and the high-temperature strain measurement application of the complex scouring force thermal environments such as the inside of an engine, rocket tail nozzles and the like is satisfied.
In a further optimized scheme, the casting die 10 for casting the metal 8 comprises a filling groove 11 and a casting groove 12 which are communicated, the filling groove 11 and the casting groove 12 are of a composite structure of a cylinder and a cone, and the bottoms of the filling groove 11 and the casting groove 12 are communicated through a channel 13; a filter screen 14 is arranged below the filling groove 11; the sapphire optical fiber 4 is placed in the casting groove 12. Placing the sapphire optical fiber 4 into a casting groove 12, vertically fixing the sapphire optical fiber 4 at the central position of the casting groove 12, melting the casting metal 8, pouring the melted casting metal 8 into a pouring groove 11, entering the casting groove 12 through a channel 13, and casting the melted casting metal 8 into the casting metal 8 through the sapphire optical fiber 4; the filter screen 14 can effectively filter out impurities in the molten cast metal 8.
Further, the pouring tank 11 and the casting tank 12 are made of high-temperature ceramic materials, and are prevented from being melted by the molten casting metal 8 in the casting process.
The manufacturing method comprises the following steps:
First, the sapphire optical fiber 4 is polished
Firstly, cleaning the surface of a sapphire optical fiber 4 with a specification diameter of 75 mu m and a length of 20cm by dipping a proper amount of dust-free paper, and cleaning an optical fiber clamp (with a size of 85mm, 5mm and 40 fiber inserting ports); secondly, fixing one end of the sapphire optical fiber 4 in an optical fiber inserting port of an optical fiber clamp, and adjusting the exposed length of the sapphire optical fiber 4 to be 0.2mm by adopting an altimeter; then, the jig carrying the sapphire optical fiber 4 was fixed on a special grinder (specification: HCX-36EPolisher, grinding paper specification: 0.5 μm) and subjected to flat end face grinding in a four-corner pressurizing mode, and corresponding parameters were set: the grinding speed is 1200r/min, and the grinding time is 8 minutes. And finally, adopting the steps, grinding the inclined end face by adopting a unilateral double-angle pressurizing mode, wherein the grinding parameters are the same, and grinding the inclined end face to obtain the inclined end face.
Secondly, the tail fiber 1 is welded with the sapphire optical fiber 4;
Firstly, adopting a single-mode fiber with the specification of CorningSMF-28e as a tail fiber 1, removing a coating layer at one end of the single-mode fiber, and adopting a general cutting knife (the specification is ancient river S326) to cut and flatten; then, wiping the single-mode fiber and the sapphire fiber 4 by adopting dust-free paper dipped with a proper amount of alcohol, so as to ensure the end surface to be clean; secondly, respectively placing the two in an optical fiber fixing groove of a fusion splicer (specification: guhe S176A); finally, manually aligning the centers of the two, and setting corresponding parameters to weld (discharge amount: 15, discharge time: 1200ms, propulsion distance: 100 μm); in the welding process, a proper butt joint position is required to be selected according to the discharge condition of a welding machine, so that damage to the sapphire optical fiber 4 caused by overlarge discharge is avoided; in addition, the size and uniformity of the cone region can be effectively controlled by the proper butt joint position; finally, the stainless steel tube 9 is arranged at the position of the welding point 21 to protect the welding point 21, and the stainless steel tube 9 and the welding point 21 are fixed through the high-temperature glue 3.
Third, writing the grating of the sapphire optical fiber 4;
firstly, cleaning the surface of a sapphire optical fiber 4 (specification: 75 μm in diameter and 15cm in length) and an optical fiber clamp (specification: 90 mm. Times.30 mm. Times.10 mm, glass) by adopting dust-free paper dipped with a proper amount of alcohol; secondly, fixing the wiped sapphire optical fiber 4 in an optical fiber clamp, enabling the proper end face of the sapphire optical fiber 4 to face upwards, and placing the clamp carrying the sapphire optical fiber 4 on a stage of a femtosecond laser writing platform (specification: repetition frequency 200KHz, laser energy 7 mW); then, a proper amount of glycerin (with a refractive index of 1.51) is dripped on the optical fiber position to be inscribed, and a 63X oil immersion objective lens of a femtosecond laser inscribing platform is adopted to inscribe a first grating 5 and a second grating 6 according to corresponding parameters; wherein, the first grating 5 parameter: the period is 1.332 mu m, the period is 2000, the length is 2.66mm, and the writing speed is 0.2mm/s; second grating 6 parameters: cycle 1.336, cycle 2000, length 2.67mm.
Fourth, packaging:
Firstly, a sleeve 2 (the specification: the material is Al 2O3, the length is 50cm, the inner diameter is 250 mu m, the outer diameter is 500 mu m) is nested at the positions of a tail fiber 1 and a welding point 21, so that the welding point 21 and the tail fiber 1 are ensured to be sleeved in the sleeve 2; then, nesting the sapphire optical fiber 4 at the second grating 6 by adopting a protective sleeve 7 (specification: al 2O3, length 4mm, inner diameter 200 mu m and outer diameter 500 mu m) to ensure that the second grating 6 is partially and completely in the protective sleeve 7, and then sucking high-temperature glue 3 by adopting a medical needle tube (the pinhole specification is 0.5 mm) to spray the gap between the protective sleeve 7 and the sapphire optical fiber 4, and standing for curing; finally, the protective sleeve 7 is welded with the sapphire optical fiber 4 by adopting a laser welding technology.
The schematic diagram of the pouring method and the monitoring system of the anti-scouring type high-temperature strain sensor based on cascaded sapphire fiber 4 grating metal pouring is shown in fig. 3, and the whole system comprises a broadband light source 15, an optical circulator 16, a sapphire fiber grating sensor 18, a casting mold 10, a grating demodulator 17 and a computer 19; the output end of the broadband light source 15 is connected with the input port of the optical circulator, the transmission output end of the optical circulator 16 is connected with the input end of the sapphire fiber grating sensor 18, the reflection output end of the optical circulator is connected with the input port of the grating demodulator 17, and the output port of the grating demodulator 17 is connected with the input port of the computer 19 for data processing.
The pouring method of the anti-scouring type high-temperature strain sensor based on the cascade type sapphire fiber 4 grating metal pouring is shown in fig. 2, the sapphire fiber grating sensor 18 is fixed through the fixing frame 20, and the sapphire fiber grating sensor 18 is kept in the center of the pouring groove 12; then pouring the molten casting metal 8 into the casting mold through the pouring slot 11; the molten casting metal 8 then passes through a filter screen 14 below the pouring trough 11 to remove impurities from the metal; clean molten metal enters the casting groove 12 through the channel 13, high temperature and solidification strain of the molten casting metal 8 act on the sensing position of the sapphire optical fiber 4 grating, so that Bragg wavelengths of the first grating 5 and the second grating 6 drift, data collection is carried out through the grating demodulator 17, and finally data processing is carried out through the computer 19, so that temperature and strain monitoring is realized.
The working principle of the grating is as follows:
The femtosecond laser direct writing fiber grating technology mainly modulates the refractive index of a fiber core periodically through laser, so that the FBG is equivalent to a narrow-band filter and can reflect the characteristic light wave, wherein the basic formula of grating design is as follows:
λBragg＝2neffΛ
Where lambda Bragg is the Bragg wavelength, n eff is the effective refractive index of the fiber core, and lambda is the grating period. When temperature and strain act on the grating, the temperature affects the effective refractive index and the grating period respectively mainly through the thermo-optic effect and the thermal expansion effect, so that the Bragg wavelength is changed; the strain affects the effective refractive index and the grating period of the optical fiber respectively mainly through the elasto-optical effect and the axial stretching deformation of the optical fiber material, thereby achieving the effect of changing the Bragg wavelength, and the main formula is as follows:
ΔλBrogg＝2ΛΔneff+2neffΔΛ
the refractive index and temperature, and strain are as follows:
wherein mu is Poisson's ratio; p 1i is the photoelastic tensor pockels piezoelectric coefficient; p is the effective elasto-optical coefficient; ζ is a thermo-optic coefficient; epsilon is the axial strain; delta T is the amount of temperature change.
The relationship between cycle and temperature, strain is as follows:
Wherein α is the coefficient of thermal expansion.
The Bragg wavelength is related to temperature and strain as follows:
When the optical fiber at one grating in the double grating structure is protected by the corundum tube, the grating at the position is isolated from the interference of strain and is only sensitive to temperature; the unprotected gratings are sensitive to temperature and strain at the same time, and because the two gratings are different in corresponding Bragg wavelength, the strain information in the measurement of the other grating can be further demodulated by the temperature compensation of the protected gratings in the measurement process, so that the double-parameter measurement of temperature and strain is realized.
The invention has reasonable structure, can realize single-mode system transmission, effectively filter out high-order modes, reduce 3dB bandwidth and improve measurement accuracy; the problems of instability, low measurement precision and the like of a multimode system are avoided; meanwhile, the difficult problem of strain measurement in a high-temperature state can be realized.
In the description of the present invention, it should be understood that the terms "longitudinal," "transverse," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate or are based on the orientation or positional relationship shown in the drawings, merely to facilitate description of the present invention, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present invention.
The foregoing embodiments are merely illustrative of the preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, but various modifications and improvements made by those skilled in the art to which the present invention pertains are made without departing from the spirit of the present invention, and all changes and modifications and improvements fall within the scope of the present invention as defined in the appended claims.
Claims (3)
1. A kind of sapphire fiber grating metal casts the anti-scouring type high temperature strain sensor, characterized by that: the fiber comprises a tail fiber (1), wherein a sleeve (2) is sleeved outside the tail fiber (1); the sleeve (2) is fixedly connected with the two ends of the tail fiber (1) through high-temperature glue (3);
The sleeve (2) is a Kevlar metal pipe, the material of the sleeve comprises an aramid composite material, the length of the sleeve is 50cm, the inner diameter of the sleeve is 300 mu m, and the outer diameter of the sleeve is 500 mu m;
one end of the tail fiber (1) is welded with one end of the sapphire optical fiber (4), and the other end of the sapphire optical fiber (4) is ground into an oblique angle; a first grating (5) and a second grating (6) are inscribed in the sapphire optical fiber (4); the second grating (6) is sleeved and fixedly connected with a protective sleeve (7); the sapphire optical fiber (4) is sleeved and fixedly connected with casting metal (8);
A stainless steel tube (9) is sleeved and fixedly connected at the welding point (21) of the tail fiber (1) and the sapphire optical fiber (4), and the stainless steel tube (9) is arranged in the sleeve (2); the sleeve (2) is fixedly connected with the stainless steel tube (9) through the high-temperature glue (3);
The main components of the high-temperature glue (3) comprise inorganic ceramic materials and modified curing agents, and the tolerance temperature can reach 1730 ℃;
the fusion point (21) is of a conical structure, the length of a conical region of the fusion point (21) is 145-155 mu m, and the minimum diameter of the conical region is equal to the diameter of the sapphire optical fiber (4); the maximum diameter of the cone area is equal to the diameter of the tail fiber (1);
The tail fiber (1) is a common single mode fiber, the material of the tail fiber is SiO 2, the core diameter is 9-10 mu m, the cladding diameter is 125-130 mu m, and the length is 50-60 cm; the sapphire optical fiber (4) is made of AL 2O3, has a hexagonal prism shape, has a diameter of 60-80 μm and a length of 15-20 cm;
The length of the grating area of the first grating (5) is 2.66mm-2.67mm, the grating is of a double-layer scribing structure, the scribing depth is 4 mu m-5 mu m, the upper layer and the lower layer are separated by 5 mu m-7 mu m, the Bragg wavelength of the grating is 1550nm-1600nm, and the scribing position is 13cm-16cm away from the front end welding point (21) of the sapphire optical fiber (4);
the casting metal (8) is made of high-melting-point metal; the diameter of a cylinder of the casting metal (8) is 8cm-10cm, the length of the cylinder is 14cm-15cm, and the length of a cone angle is 3cm-4cm;
The casting die (10) for casting the metal (8) comprises a filling groove (11) and a casting groove (12) which are communicated, wherein the filling groove (11) and the casting groove (12) are of a cylindrical and conical composite structure, and the bottoms of the filling groove (11) and the casting groove (12) are communicated through a channel (13); a filter screen (14) is arranged below the filling groove (11); the sapphire optical fiber (4) is placed in the casting groove (12).
2. The sapphire fiber grating metal cast, anti-scour, high temperature strain sensor of claim 1, wherein: the length of the grating area of the second grating (6) is 2.67mm-2.68mm, the grating is of a double-layer scribing structure, the scribing depth is 4 mu m-5 mu m, the upper layer and the lower layer are separated by 5 mu m-7 mu m, the Bragg wavelength of the grating is 1550nm-1600nm, and the scribing position is 0.5cm-1cm away from the tail end of the sapphire optical fiber (4).
3. The sapphire fiber grating metal cast, anti-scour, high temperature strain sensor of claim 1, wherein: the material of the protective sleeve (7) is Al 2O3, the length is 4mm-5mm, the inner diameter is 200 mu m-300 mu m, and the outer diameter is 500 mu m-600 mu m; and the protective sleeve (7) is welded and fixed with the sapphire optical fiber (4) at the second grating (6).
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