JP4551744B2 - Fiber type Bragg grating element and fixing method thereof - Google Patents

Description

The present invention relates to a fiber type Bragg grating element and a fixing method thereof , and more particularly to a fiber type Bragg grating element having heat resistance and a fixing method thereof .

  In recent years, the application range of optical fibers has been expanded mainly in the communication field, and the reliability thereof tends to improve and the manufacturing cost tends to decrease. For this reason, the development of application products and the provision of new services using the advantages of optical fibers as information transmission media have been actively carried out.

  On the other hand, fiber-type Bragg grating elements using optical fibers have been attracting attention as sensors capable of detecting strain, temperature, etc. For example, Patent Documents 1 and 2 disclose strains using fiber-type Bragg grating elements. Techniques relating to sensors and temperature sensors are disclosed.

  In addition, since the fiber type Bragg grating element is not easily affected by electrical noise and is very sensitive, application as a sensor for detecting minute environmental changes such as magnetism and vibration is also being studied. 3 discloses a technique of using a fiber Bragg grating element as a magnetic sensor. Patent Document 4 discloses a technology that uses a fiber-type Bragg grating element as a vibration sensor.

  The fiber-type Bragg grating element is formed by writing a Bragg grating (Bragg grating) having periodic streaks into, for example, an excimer laser in a partial region of an optical fiber core.

  When a light wave having a predetermined band is incident from one end of the fiber type Bragg grating element, only a light wave having a specific wavelength corresponding to the streak interval of the Bragg grating (Bragg grating) is reflected backward. That is, the wavelength (or frequency) of the reflected light corresponds to the streak interval of the Bragg grating (Bragg grating).

  In addition, the transmitted light transmitted through the fiber Bragg grating element is attenuated only by a light wave having a specific wavelength (or frequency) corresponding to the streak interval of the Bragg grating (Bragg grating), and other wavelength (or frequency) light waves are It passes through without attenuation.

  On the other hand, the streak interval of the Bragg grating (Bragg grating) changes depending on the external environment such as strain and temperature, and the wavelength of reflected light and the attenuation wavelength of transmitted light change along with this change.

  Accordingly, a light wave having a predetermined band is incident on the fiber type Bragg grating element, and the change in the wavelength of the reflected light from the Bragg grating (Bragg grating) or the attenuation wavelength of the transmitted light is monitored. It is possible to detect changes in the external environment such as the distortion and temperature around.

By the way, in general, an optical fiber (a part formed from a core part and a clad part) is made of SiO ₂ as a raw material and is fragile and easily broken. For this reason, handling is also inconvenient. Therefore, the surface of the optical fiber is generally coated with a UV curable transparent resin and reinforced (see Patent Document 5). However, the UV curable transparent resin is not necessarily a material excellent in heat resistance.

  Further, in the fiber type Bragg grating element, it is necessary to consider not only the improvement of brittleness and heat resistance but also the Young's modulus (elastic coefficient) as a material for coating the Bragg grating (Bragg grating) portion. When a fiber type Bragg grating element is used as a strain sensor or a vibration sensor, it often takes a form in which an object to be measured for measuring strain or vibration is closely bonded to the surface of a coating material. If a material with a low Young's modulus is used as the coating material, the distortion or vibration generated in the object to be measured is absorbed by the coating material, and the Bragg grating (Bragg grating) inside the coating material is strained or vibrated. Will not be transmitted accurately. Therefore, a material having a high Young's modulus is required as a material for coating the portion of the Bragg grating (Bragg grating). The property of accurately transmitting signals such as distortion and vibration generated in the object to be measured to the Bragg grating (Bragg grating) is hereinafter referred to as signal transmission.

  Therefore, in recent years, the Bragg grating (Bragg grating) part is made of polyimide resin or fluororesin that has excellent heat resistance and high Young's modulus so that excellent signal transmission can be ensured even in high temperature environments. A fiber-type Bragg grating element coated with sapphire has also been developed.

  In addition to the method of coating the Bragg grating (Bragg grating) part circumferentially, a film type in which a heat-resistant film is sandwiched and fixed with an adhesive so as to face the Bragg grating (Bragg grating) part. A technique related to a fiber type Bragg grating element is also disclosed (see Patent Document 6).

  On the other hand, in devices and plants that are operated in a high-temperature environment, such as aircraft, nuclear power plants, thermal power plants, steel plants, chemical plants, etc., the deterioration of the materials of the components constituting these devices and plants is caused by the life of the devices and plants. And greatly affects reliability.

  Therefore, a damage evaluation method for materials of components constituting these apparatuses and plants becomes very important. For example, regarding damage assessment of steam turbine members, methods such as defect detection by ultrasonic flaw detection tests, structure observation by replicas, hardness measurement, etc. are taken, but all are performed with the plant stopped periodically Is common.

On the other hand, in recent years, there has been an attempt to evaluate erosion damage due to foreign object collisions with the steam turbine blade while driving the steam turbine using an AE (Acoustic Emission) sensor (Patent Document 7).
JP-A-10-141922 Japanese Patent Laid-Open No. 11-51783 JP 2003-130934 A JP 2004-12280 A JP 2003-295209 A JP 2003-279760 A JP 2003-98162 A

As described above, the fiber-type Bragg grating element is coated to protect the optical fiber and improve the handleability. The optical fiber itself is made of SiO ₂ as a raw material, and does not melt even when used at a high temperature of about 1000 ° C. Therefore, the heat resistance of the coating material covering the optical fiber determines the heat resistance of the entire fiber type Bragg grating element.

  However, even in polyimide resins and fluororesins excellent in heat resistance disclosed in Patent Document 5 and the like, the heat-resistant temperature is limited to 250 ° C. at most. This heat resistant temperature is lower than the operating temperature of equipment operating at high temperatures such as aircraft, nuclear power plant, thermal power plant, steel plant, chemical plant and the like.

  Therefore, a conventional fiber type Bragg grating element with a coating material of polyimide resin or fluororesin is used for a long time to monitor deterioration or damage of high temperature members used in aircraft, nuclear power plant, thermal power plant, steel plant, chemical plant, etc. It is not possible.

  For this reason, development of a fiber type Bragg grating element having a higher heat-resistant temperature is demanded.

  In the development of fiber type Bragg grating elements, not only from the viewpoint of heat resistance temperature, but also from the viewpoint of sensitively transmitting changes in the signal such as distortion and vibration of the measured object to the Bragg grating (Bragg grating) part, It is also necessary to consider the viewpoint of transmission.

  Furthermore, not only the fiber type Bragg grating element itself but also the method for fixing the fiber type Bragg grating element to the object to be measured, there is a demand for the development of a fixing method that ensures high signal resistance and high heat resistance. .

  On the other hand, for equipment that operates at high temperatures, such as nuclear power plants, for the sake of efficient operation, while continuing operation from the conventional method of stopping operation and inspecting and diagnosing equipment deterioration and damage, The company is turning to methods for inspecting and diagnosing device deterioration and damage. Although the AE sensor disclosed in Patent Document 7 enables inspection and diagnosis during driving, it is necessary to guarantee the heat resistance and vibration resistance of the AE sensor itself. Further, the AE sensor itself has a certain volume, and may not be installed depending on the type of the object to be measured and the type of measurement signal.

  In this respect, the sensor based on the fiber type Bragg grating element has an extremely thin shape, and restrictions on the installation location of the sensor are smaller than those of the AE sensor.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a fiber type Bragg grating element that is excellent in heat resistance and can detect a change in the external environment with high sensitivity, and a fixing method thereof.

In order to solve the above problems, a fiber-type Bragg grating element according to the present invention writes a Bragg grating having a predetermined length in a core portion of an optical fiber composed of a core portion and a cladding portion. The fiber type Bragg grating element is provided with a metal coating having a melting point of 300 ° C. or higher and a Young's modulus of 100 GPa or more, which covers the outer periphery of the optical fiber densely in the range of the predetermined length or more including the Bragg grating. the coating forms a multilayer structure composed of different kinds of the metal, the metal forming the innermost layer of the multilayer structure are active metals contained Ti, Zr, and at least one or more Hf is the to form a reaction layer which is heat-treated between the surface and the coating of the inner surface of the metal fiber, the outer layer of the multilayer structure, the outermost Melting point than the inner layer and selecting a high Young's modulus metals higher, characterized in that.

According to the fiber type Bragg grating element and the fixing method thereof according to the present invention, it is excellent in heat resistance and can detect a change in the external environment with high sensitivity.

DESCRIPTION OF EMBODIMENTS Embodiments of a fiber type Bragg grating element and a fixing method thereof according to the present invention will be described with reference to the accompanying drawings.

(1) Fiber Bragg Grating Element and Manufacturing Method Thereof FIG. 1 shows a structure according to a first embodiment of a fiber Bragg grating element 1 (hereinafter abbreviated as an FBG (Fiber Bragg Grating) element 1) according to the present invention. FIG.

  The FBG element 1 includes a Bragg grating 5 in a region of a predetermined length d1 of the core part 2 in the optical fiber 4 including the core part 2 and the cladding part 3, and the FBG element 1 is longer than the predetermined length d1 including the Bragg grating 5. It is formed with a metal coating 6 on the surface of the optical fiber 4 in a long range (d2 in FIG. 1).

  The Bragg grating 5 is formed in the core portion 2 of the optical fiber 4 by writing a large number of striped gratings in the radial direction of the core portion 2 using, for example, an excimer laser. The axial length d1 of the Bragg grating 5 is not particularly limited, but is formed to a length of about 10 mm, for example.

  A relation of λ = 2nΛ is established between the interval Λ of the striped gratings constituting the Bragg grating 5 and the wavelength λ of the reflected light, where n is the refractive index of the core 2. When the grating interval Λ changes, the wavelength λ of the reflected light also changes.

The coating 7 is used for protecting a normal optical fiber, and protects the optical fiber 4 with, for example, a polyimide resin. The optical fiber 4 itself is made of SiO ₂ as a component and is brittle and easily broken. For this reason, coating with polyimide resin protects the optical fiber 4 and facilitates handling.

  In most conventional fiber type Bragg grating elements, the entire region of the optical fiber 4 in the axial direction is coated with a resin-based material such as polyimide resin. For this reason, there was a problem in heat resistance. For example, the heat resistance of polyimide resin is about 250 ° C., and it becomes difficult to use in a high temperature environment exceeding this.

  Therefore, in the FBG element 1 according to the present invention, the heat resistance is improved by replacing part of the film 7 made of polyimide resin with the metal film 6.

  When the FBG element 1 is used as a strain sensor or a vibration sensor, the metal film 6 closest to the Bragg grating 5 is used by being closely bonded to the object to be measured. This is because distortion and vibration generated in the object to be measured are easily transmitted to the Bragg grating 5 through the metal film 6.

  For this reason, in order to measure a high-temperature object to be measured, the metal film 6 needs to cover at least the region including the Bragg grating 5.

  The length d2 of the metal coating 6 is not particularly limited. The length may correspond to the region where the FBG element 1 is exposed to high temperature. When the object to be measured is such that the temperature is high over a wide range around the measurement point, the length d2 of the metal coating 6 is increased to ensure heat resistance over a wide range. It is necessary to keep.

One of the purposes of the metal coating 6 is to improve heat resistance in addition to protecting the optical fiber 4. The optical fiber 4 itself is mainly composed of SiO ₂ and has a melting point of about 1000 ° C. or higher. Therefore, in order to improve the heat resistance of the FBG element 1, it is necessary to form the coating 6 with a metal having a high melting point.

  Another object of the metal film 6 is to transmit a signal (distortion, vibration, etc.) of a measurement object bonded or fixed to the film 6 to the Bragg grating 5 with high sensitivity, that is, to ensure high signal transmission.

  When a metal having elasticity, that is, a low Young's modulus is used as the material of the film 6, the signal of the object to be measured, for example, vibration is attenuated while propagating from the surface Sa of the film 6 to the inner surface Sb of the film 6, and Bragg grating 5 is not transmitted with high sensitivity. For this reason, the film 6 needs to be formed of a metal having a high Young's modulus.

  According to the first embodiment of the FBG element 1 according to the present invention, the metal coating 6 having a melting point of 300 ° C. or higher and a Young's modulus of 100 GPa or higher, which covers the periphery of the optical fiber 4 including the Bragg grating 5 closely. By providing, it is excellent in heat resistance and can detect a change in the external environment with high sensitivity. In the conventional film, since the melting point of the polyimide resin was about 250 ° C., there was a problem in heat resistance. However, according to the FBG element 1 according to the present invention, the heat resistance is improved.

  In addition, when applying an FBG element as a magnetic sensor, since it is necessary to flow an electric current through a film | membrane on the principle of operation, a film must be comprised with an electrically conductive metal (for example, patent document 3). The metal coating for the purpose of electric conduction is different from the present invention in the problem to be solved, and is different from the present invention. For example, the metal coating exemplified in Patent Document 3 is made of gold (Au) having high electrical conductivity, and the Young's modulus is less than 100 GPa.

  More specifically, metals having a melting point of 300 ° C. or higher and a Young's modulus of 100 GPa or higher are Ag (silver), Be (beryllium), Co (cobalt), Cr (chromium), Cu (copper), and Fe (iron). , Hf (hafnium), Mn (manganese), Mo (molybdenum), Nb (niobium), Ni (nickel), Ta (tantalum), Ti (titanium), W (tungsten), and Zn (zinc) Metal.

  Metals having a melting point of 300 ° C. or higher and Young's modulus of 100 GPa or higher are Ag (silver), Be (beryllium), Co (cobalt), Cr (chromium), Cu (copper), Fe (iron), and Hf (hafnium). ), Mn (manganese), Mo (molybdenum), Nb (niobium), Ni (nickel), Ta (tantalum), Ti (titanium), W (tungsten), and alloys based on Zn (zinc) are also suitable. It is.

  In the embodiment in which the metal of the coating 6 is Ag (silver), the Young's modulus of Ag (silver) is 101 GPa and the melting point is 961 ° C. (according to “Metal Data Book” edited by the Japan Institute of Metals). High FBG element 1 can be realized.

  In FIG. 1, the thickness of the metal coating 6 is preferably 1 μm or more and 50 μm or less. If the thickness is too thin, the protection function of the optical fiber 4 cannot be secured.

  The metal film 6 can be formed on the optical fiber 4 by using at least one of known methods such as plating, physical vapor deposition, and chemical vapor deposition.

  FIG. 2A is a diagram showing a method of manufacturing the FBG element 1 having the Ag (silver) coating 6 by electroless plating.

  The plating bath 14 contains a plating solution 15 containing Ag ions and phosphoric acid. The optical fiber 4 (before the metal coating 6 is formed) is supplied to the plating bath 14 from the left side in FIG. The optical fiber 4 is connected to a winder (not shown) provided on the right side of FIG. 2A. After being immersed in the plating bath 14 for a certain period of time, the optical fiber 4 is wound outside the plating bath 14. Taken.

  FIG. 2 (b) shows a cross section of the optical fiber 4 before being supplied to the plating bath 14 and a cross section after being pulled up from the plating bath 14. A silver film 6 is formed on the one pulled up from the plating bath 14.

  The FBG element 1 can be manufactured by plating the optical fiber 4 in which the Bragg grating 5 is written in advance by the plating method shown in FIG.

  According to the plating method shown in FIG. 2, the FBG element 1 having the relatively long metal film 6 can also be manufactured.

  It is also possible to adjust the thickness of the metal coating 6 by adjusting the time of immersion in the plating bath 14.

  In addition, the metal coating 6 may be formed by a metal vapor heated to a high temperature or a physical vapor deposition method (PVD (Physical Vapor Deposition) method) using a liquid metal. This physical vapor deposition includes, for example, a thermal spraying method in which a gas containing silver is sprayed.

  Further, the metal film 6 may be formed by a chemical vapor deposition method (CVD (Chemical Vapor Deposition) method) using a chemical reaction.

  By the way, in order to transmit signals such as distortion and vibration of the object to be measured to the Bragg grating 5 of the FBG element 1 with high sensitivity, in addition to forming the film 6 using a metal having a high Young's modulus, It is necessary that the inner surface Sb (see FIG. 1) and the surface Sc of the optical fiber 4 in contact with the inner surface Sb are closely bonded. This is because when a deviation or slip occurs between the inner surface Sb of the coating 6 and the surface Sc of the optical fiber 4, signals such as distortion and vibration of the object to be measured are not accurately transmitted to the Bragg grating 5.

  The second embodiment of the FBG device 1 according to the present invention is a metal having a melting point of 300 ° C. or higher and a Young's modulus of 100 GPa, for example, Ag, at least one of Ti (titanium), Zr (zirconium), and Hf (hafnium). It is set as the form which forms the film 6 with the active metal containing the above. When the FBG element 1 having the coating 6 formed of such an active metal is heat-treated at a temperature in the range of, for example, 500 ° C. to 900 ° C., a reaction layer is formed between the inner surface Sb of the metal coating 6 and the surface Sc of the optical fiber 4. Thus, the adhesion between the inner surface Sb of the metal coating 6 and the surface Sc of the optical fiber 4 is enhanced.

  As a result, signals such as distortion and vibration of the object to be measured are transmitted to the Bragg grating 5 of the FBG element 1 with high sensitivity. That is, signal transmission is improved.

According to the FBG element 1 according to the second embodiment, in addition to the FBG element 1 according to the first embodiment, signal transmission can be further improved, and signals such as distortion and vibration of the measurement object can be detected. It can be measured well.

  FIG. 3 is a diagram showing a third embodiment of the FBG element 1 according to the present invention.

  The FBG element 1 according to the third embodiment has a metal film 6 having a multilayer structure. The innermost layer of the multilayer structure is formed of an active metal containing at least one of Ti (titanium), Zr (zirconium), and Hf (hafnium) as in the second embodiment. is there. By forming the innermost layer with an active metal, the adhesion between the inner surface Sb of the metal coating 6 and the surface Sc of the optical fiber 4 is increased.

  On the other hand, a metal having a higher melting point and a higher Young's modulus can be selected for the layer outside the multilayer structure, independently of the adhesion requirement.

  In the example shown in FIG. 3, the metal coating 6a has a two-layer structure, the inner layer 10 is formed of an active metal containing Ti in Ag (silver), and the outer layer 11 has a higher melting point than Ag and a Young It is made of Ni (nickel) with a high rate. By heat-treating such an FBG element 1 as in the second embodiment, the adhesion between the inner surface Sb of the metal coating 6a and the surface Sc of the optical fiber 4 can be enhanced.

  FIG. 4 is a view showing a fourth embodiment of the FBG element 1 according to the present invention.

  The FBG element 1 according to the fourth embodiment changes the composition ratio of the metal forming the coating 6b continuously or stepwise, and further, among Ti (titanium), Zr (zirconium), and Hf (hafnium). It includes at least one or more.

  In the example shown in FIG. 4, the coating 6 b is formed of a metal made of Ag (silver) and Ni (nickel), and the inner portion in contact with the surface Sc of the optical fiber 4 is mainly composed of Ag (silver). A gradient composition structure is obtained in which the composition ratio of Ni (nickel) is continuously increased toward the outside. Ti (titanium) is further contained in such a metal whose composition ratio continuously changes.

  As a result, an active metal composed of Ag (silver) and Ti (titanium) is formed inside the coating 6b, and Ni (nickel) having a high melting point and a high Young's modulus is the main component outside the coating 6b. A layer is formed, and heat treatment of the FBG element 1 improves the adhesion between the metal coating 6b and the optical fiber 4.

  According to the FBG element 1 according to the third and fourth embodiments, the signal transmission can be improved by improving the adhesion between the metal coating 6b and the optical fiber 4 as in the second embodiment. At the same time, it is possible to form a layer (high melting point / high Young's modulus) having more excellent environmental resistance on the outside of the metal coating 6.

  FIGS. 5 and 6 show another embodiment for improving the adhesion between the metal coating 6 and the optical fiber 4.

  FIG. 5 is a diagram showing a fifth embodiment of the FBG element 1 according to the present invention. In the FBG device 1 according to the fifth embodiment, the diameter of the optical fiber 4 inscribed in the metal coating 6 is made different between the area where the Bragg grating 5 is written and the area where the Bragg grating 5 is not written. In this structure, a step is formed by providing the protrusion 8 in the region.

  Due to the level difference of the convex portion 8, there is no displacement or slippage between the inner surface Sb of the metal coating 6 and the surface Sc of the optical fiber 4, and the adhesion between the two is increased and the signal transmission is improved.

The convex portion 8 of the optical fiber 4 can be formed, for example, by melting a part of the optical fiber 4 using hydrofluoric acid. Any solution capable of melting SiO ₂ which is the main component of the optical fiber 4 may be used, and the solution is not limited to hydrofluoric acid.

  FIG. 6 is a diagram showing a sixth embodiment of the FBG element 1 according to the present invention. Similar to the FBG element 1 according to the fifth embodiment, the diameter of the optical fiber 4 inscribed in the metal coating 6 is made different between a region where the Bragg grating 5 is written and a region where the Bragg grating 5 is not written.

  The FBG element 1 according to the sixth embodiment has a structure in which convex portions 9 are formed in two regions outside the Bragg grating 5. As in the fifth embodiment, the FBG element 1 according to the sixth embodiment also increases the adhesion between the inner surface Sb of the metal coating 6 and the surface Sc of the optical fiber 4 and improves the signal transmission.

(2) Fixing method of FBG element 1 When measuring distortion or vibration of an object to be measured using the FBG element 1, the FBG element 1 is connected to the FBG element 1 so that the distortion, vibration or the like is reliably transmitted to the FBG element 1. It is necessary to tightly fix the object to be measured. The device under test is not particularly limited as long as it is a structural member having a certain rigidity.

  The FBG element 1 according to the present invention can be used in a high temperature environment, and in the following description, a steam turbine nozzle 20 which is a component of a steam turbine premised on use in a high temperature environment. Is taken as an example of a structural member.

  FIG. 7 is a diagram for explaining the first embodiment of the fixing method of the FBG element 1 according to the present invention.

  FIG. 7A is a perspective view showing the steam turbine nozzle 20 and the FBG element 1 fixed to the surface of the steam turbine nozzle 20. FIG. 7B is a cross-sectional view taken along the line A-A ′ of FIG.

  The steam turbine nozzle 20 is made of, for example, an Fe—Cr metal material from the viewpoint of strength and environmental resistance. By measuring and analyzing distortion generated in the steam turbine nozzle 20, vibration generated from the steam turbine nozzle 20, and the like, for example, erosion of the steam turbine nozzle 20 can be estimated.

  The FBG element 1 is fixed to the surface of the steam turbine nozzle 20 as shown in FIG. The FBG element 1 has a coating 6 made of, for example, Ag (silver) and having a thickness of about 10 μm. The FBG element 1 includes a core part 2 in which a Bragg grating 5 is formed.

  The method of fixing the FBG element 1 to the steam turbine nozzle 20 is fixed via the metal layer 21 as shown in FIG. The metal layer 21 is formed so as to cover the FBG element 1 installed on the surface of the steam turbine nozzle 20, and tightly fixes the FBG element 1 and the surface of the steam turbine nozzle 20.

  The metal layer 21 is preferably formed of an Fe—Cr-based metal material that is the same as or similar to the material of the steam turbine nozzle 20. Since the generation of thermal stress can be reduced by making the material of the steam turbine nozzle 20 and the material of the metal layer 21 the same or similar, the metal layer 21 is not cracked or cracked.

  FIG. 8 shows a plasma spraying method as an example of a method for forming the metal layer 21. The plasma spraying method is a method in which a metal is melted with high-temperature plasma and sprayed onto a substrate surface at a high speed.

  First, the masking 25 is installed in a portion other than the region where the metal layer 21 is formed on the surface of the steam turbine nozzle 20. Next, a surface roughening process is performed by spraying alumina particles or the like on the surface of the steam turbine nozzle 20. Thereafter, the FBG element 1 is temporarily fixed to the surface subjected to the roughening treatment with an appropriate adhesive member, for example, an adhesive tape.

  Next, the molten Fe—Cr-based material 24 is sprayed from the plasma spray gun 23 to the temporarily secured FBG element 1 at a high speed. The sprayed molten Fe—Cr material 24 is solidified to form a metal layer 21 that covers the FBG element 1, and the FBG element 1 is fixed to the surface of the steam turbine nozzle 20.

  The method for fixing the FBG element 1 to the steam turbine nozzle 20 is not limited to physical vapor deposition such as plasma spraying. For example, after temporarily fixing the FBG element 1 to the steam turbine nozzle 20, the FBG element 1 and the steam turbine nozzle 20 are formed by immersing the FBG element 1 and the steam turbine nozzle 20 in the plating bath 14 to form a plating film. It may be fixed.

  In addition, the FBG element 1 and the steam turbine nozzle 20 may be fixed using a chemical vapor deposition method in which the metal layer 21 is formed using a chemical reaction.

  Further, the structural member to which the FBG element 1 is fixed is not limited to metal, and may be a structural member made of ceramic, for example. At this time, it is preferable to fix the ceramic structural member and the FBG element 1 through a ceramic layer from the viewpoint of reducing thermal stress.

  FIG. 9 is a diagram for explaining a second embodiment of the fixing method of the FBG element 1 according to the present invention.

  Similarly to the first embodiment, in the second embodiment, a steam turbine nozzle 20 will be described as an example of a structural member that is an object to be measured.

  In the fixing method of the FBG element 1 according to the second embodiment, the insertion hole 30 is provided in the steam turbine nozzle 20, and the FBG element 1 is inserted and fixed in the insertion hole 30. At this time, the FBG element 1 is inserted so that the Bragg grating 5 is located at a point to be measured of the steam turbine nozzle 20.

  There are various methods for fixing the inserted FBG element 1 in the insertion hole 30.

  FIG. 10A shows a method of fixing the FBG element 1 and the steam turbine nozzle 20 using a shrink fitting method. When the steam turbine nozzle 20 is heated, the insertion hole 30 expands. When the FBG element 1 is inserted into the expanded insertion hole 30 and then left to return to room temperature, the diameter of the insertion hole 30 contracts, and the FBG element 1 and the steam turbine nozzle 20 are fixed tightly.

  FIG. 10B shows a method of fixing the FBG element 1 and the steam turbine nozzle 20 using a cold fitting method. The insertion site of the FBG element 1 is cooled in, for example, liquid nitrogen. The diameter of the FBG element 1 contracts due to cooling. When the contracted FBG element 1 is inserted into the insertion hole 30 and left to return to room temperature, the diameter of the FBG element 1 expands to the original state, and the FBG element 1 and the steam turbine nozzle 20 are tightly fixed. The

  FIG. 11 shows a third embodiment of a method for fixing the FBG element 1 to the steam turbine nozzle 20.

  The difference between the third embodiment and the second embodiment is that an intermediate layer 40 is provided between the insertion hole 30 and the FBG element 1.

  The intermediate layer 40 is formed of a brazing material having a lower melting point than the metal coating 6 of the steam turbine nozzle 20 (structural member) and the FBG element 1. For example, the intermediate layer 40 may be formed by injecting a molten brazing material into the insertion hole 30 in which the FBG element 1 is inserted. Alternatively, a brazing material ring may be previously formed on the metal film 6 of the FBG element 1 and inserted into the insertion hole 30 and then heated to melt and adhere the brazing material.

  According to the fixing method of the FBG element 1 according to the third embodiment, the adhesion between the insertion hole 30 and the FBG element 1 is improved by the intermediate layer 40 made of the brazing material.

  Note that the third embodiment and the second embodiment may be combined. For example, an Ag intermediate ring (intermediate layer 40) is further fitted in advance from above the metal film 6 of the FBG element 1, and the Ag intermediate ring and the FBG element 1 are integrally cooled and then inserted into the insertion hole 30. It is good also as a form. According to such a form, the amount of cooling shrinkage is increased by the Ag intermediate ring, so that the adhesion is further improved when the temperature is returned to room temperature.

  The second and third embodiments are both fixing methods in which the FBG element 1 is inserted into the insertion hole 30 of the steam turbine nozzle 20 (structural member) and the both are closely fixed. Even in such a case, it is necessary to maintain adhesion.

  For this reason, it is necessary to make the amount that the diameter of the insertion hole 30 of the steam turbine nozzle 20 (structural member) expands due to thermal expansion smaller than the amount that the diameter of the FBG element 1 expands due to thermal expansion. There is.

  This relationship will be described with reference to FIG.

  The linear expansion coefficient of the steam turbine nozzle 20 (structural member) is L1. The thickness of the metal coating 6 of the FBG element 1 is t2, and the linear expansion coefficient is L2. Further, the radius of the optical fiber 4 of the FBG element 1 is t3, and the linear expansion coefficient is L3. At this time, by selecting the physical quantity so that the relationship of L1 <(L2 × t2 + L3 × t3) / (t2 + t3) is established among these physical quantities, L1, t2, L2, t3, and L3, the thermal expansion causes The amount of expansion of the diameter of the insertion hole 30 can be made smaller than the amount of expansion of the diameter of the FBG element 1. The right side of the inequality can be regarded as an average linear expansion coefficient between the coating 6 of the FBG element 1 and the optical fiber 4. That is, the inequality means that the linear expansion coefficient L1 of the steam turbine nozzle 20 (structural member) is configured to be lower than the average linear expansion coefficient of the FBG element 1 to be inserted.

  With such a configuration, even if the steam turbine nozzle 20 (structural member) and the FBG element 1 are thermally expanded in a high temperature environment, the adhesion between them is maintained.

  In addition, when applying the said inequality to 3rd Embodiment which has the intermediate | middle layer 40, let the total value of the thickness of the intermediate | middle layer 40 and the film 6 be t2, and let the average linear expansion coefficient of the intermediate | middle layer 40 and the film 6 be L2. And it is sufficient.

  It is possible to fix FBG element 1 and steam turbine nozzle 20 (structural member) also with forms other than the fixing method mentioned above.

  For example, a screw hole is provided in advance in the insertion hole 30 of the steam turbine nozzle 20. On the other hand, a thread is also cut in the insertion portion of the FBG element 1 in advance, and both are fixed by screwing the FBG element 1 into the insertion hole 30. According to such a fixing method, even when any one of the steam turbine nozzle 20 and the FBG element 1 is damaged, it is possible to replace the damaged one without damaging the other.

  In addition, in each region on both sides of the FBG element 1 across the Bragg grating 5, one or more detachable locking structures are provided, and the FBG element 1 is locked and fixed to these locking structures by insertion. It is good also as a form.

  In the description of each embodiment of the fixing method described above, the steam turbine nozzle 20 (structural member) is described as being mainly formed of a metal material, but the material of the structural member is not limited to metal. For example, a structural member made of ceramic may be used.

  FIG. 13A shows the result of measuring the distortion of the structural member using the FBG element 1 according to the present invention.

  In this measurement, the FBG element 1 having the coating 6 formed of Ag (silver) is fixed to the surface of the structural member using a thermal spraying method, and an external force is applied to the structural member to measure mechanical strain. For comparison, the same measurement was performed on an FBG element having a conventional polyimide resin coating.

  In the measuring method, the mechanical strain is gradually increased at a strain rate of 0.001% / min, and the increase is stopped when the mechanical strain becomes 0.1%, and the mechanical strain at that time is reduced to the FBG device 1 according to the present invention. And a conventional type FBG element. This measurement was performed at room temperature, 250 ° C., 500 ° C., and 750 ° C.

  In the graph shown in FIG. 13A, the horizontal axis indicates the temperature, and the vertical axis indicates the measured mechanical strain. As can be seen from the graph of FIG. 13 (a), the measurement results obtained with the FBG device 1 according to the present invention show that the measured mechanical strain is maintained at approximately 0.1% over the entire range from room temperature to 750 ° C. It was.

  On the other hand, the FBG element coated with the conventional type polyimide resin resulted in a sharp deterioration in measurement accuracy when the temperature exceeded 250 ° C. This is because the melting point of the polyimide resin is 250 ° C.

  FIG. 13 (b) summarizes the measurement results. The heat resistance temperature of the conventional FBG element is about 250 ° C., whereas the film 6 is formed (coated) with Ag (silver). The heat resistance temperature of the FBG device 1 according to the present invention was confirmed to be a significant improvement of 750 ° C.

  Note that the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, the constituent elements over different embodiments may be appropriately combined.

The figure which shows the structure of 1st Embodiment of the fiber type Bragg grating element which concerns on this invention. The figure which shows an example of the manufacturing method of 1st Embodiment of the fiber type Bragg grating element concerning this invention. The figure which shows the structure of 3rd Embodiment of the fiber type Bragg grating element which concerns on this invention. The figure which shows the structure of 4th Embodiment of the fiber type Bragg grating element which concerns on this invention. The figure which shows the structure of 5th Embodiment of the fiber type Bragg grating element which concerns on this invention. The figure which shows the structure of 6th Embodiment of the fiber type Bragg grating element which concerns on this invention. The 1st figure explaining 1st Embodiment of the fixing method of the fiber type Bragg grating element concerning the present invention. The 2nd figure explaining 1st Embodiment of the fixing method of the fiber type Bragg grating element concerning the present invention. The figure explaining 2nd Embodiment of the fixing method of the fiber type Bragg grating element concerning this invention. In 2nd Embodiment of the fixing method of the fiber type Bragg grating element which concerns on this invention, (a) is a figure explaining a shrink fitting method, (b) is a figure explaining a cold fitting method. The figure explaining 3rd Embodiment of the fixing method of the fiber type Bragg grating element concerning this invention. The figure explaining the relationship between linear expansion coefficient L1, L2, and L3, and thickness t2, t3. (A) is a figure which shows the result of having tested the heat resistance of the fiber type Bragg grating element which concerns on this invention, and the conventional fiber type Bragg grating element, (b) is a figure which shows the summary of a test result.

Explanation of symbols

1 Fiber type Bragg grating element (FBG element)
2 Core part 3 Cladding part 4 Optical fiber 5 Bragg grating 6, 6a, 6b Metal coating 8 Convex part (fifth embodiment)
9 Protrusions (sixth embodiment) and grains 10 Inner layer 11 Outer layer 20 Steam turbine nozzle (structural member)
21 Metal layer, ceramic layer 30 Insertion hole 31 Intermediate layer L1 Linear expansion coefficient L2 of structural member or linear expansion coefficient of metal coating or average linear expansion coefficient of metal coating and intermediate layer L3 Linear expansion coefficient t2 of optical fiber Metal coating Or total thickness of metal coating and intermediate layer t3 Radius of optical fiber

Claims (10)

In a fiber type Bragg grating element in which a Bragg grating of a predetermined length is written in the core part of an optical fiber composed of a core part and a clad part,
A metal film having a melting point of 300 ° C. or higher and a Young's modulus of 100 GPa or higher, which densely covers the outer periphery of the optical fiber in the range of the predetermined length or more including the Bragg grating;
The coating has a multilayer structure composed of the different types of metals,
The metal forming the innermost layer of the multilayer structure is an active metal containing at least one of Ti, Zr, and Hf, and heat treatment is performed between the surface of the optical fiber and the inner surface of the coating of the metal. Formed reaction layer ,
For the outer layer of the multilayer structure, a metal having a higher melting point and a higher Young's modulus than the innermost layer is selected.
A fiber-type Bragg grating element. The metal constituting the multilayer structure is a metal selected from Ag, Be, Co, Cr, Cu, Fe, Hf, Mn, Mo, Nb, Ni, Ta, Ti, W, and Zn, or those 2. The fiber type Bragg grating element according to claim 1, wherein the fiber type Bragg grating element is an alloy having a main component. The coating is formed so that the composition ratio of the different types of metals changes continuously or stepwise.
2. The fiber-type Bragg according to claim 1, wherein the metal formed so that the composition ratio changes continuously or stepwise is a metal containing at least one of Ti, Zr, and Hf. Grating element. 2. The fiber type Bragg grating element according to claim 1, wherein a diameter inscribed in the metal film is different between a region where the Bragg grating is written and a region where the Bragg grating is not written. In the fixing method of the fiber type Bragg grating element according to claim 1,
A fiber-type Bragg grating element, wherein the fiber-type Bragg grating element is fixed to the surface of a structural member which is a metal object to be measured used in a high-temperature environment through a metal layer having a melting point of 300 ° C. or higher. How to fix the element. The fiber-type Bragg grating element is temporarily fixed to the surface of the structural member with an appropriate adhesive member, and then the metal layer is formed by at least one of plating, physical vapor deposition, and chemical vapor deposition. 6. The method for fixing a fiber type Bragg grating element according to claim 5, wherein the fiber type Bragg grating element is fixed to the fiber type Bragg grating element. In the fixing method of the fiber type Bragg grating element according to claim 1,
An insertion hole is provided in a structural member, which is a metal object to be used in a high temperature environment,
Inserting the fiber Bragg grating element into the insertion hole;
A method for fixing a fiber type Bragg grating element, comprising fixing the fiber type Bragg grating element to the structural member. Forming a screw hole in the insertion hole;
Forming a screw at the insertion site of the fiber type Bragg grating element,
The method for fixing a fiber type Bragg grating element according to claim 7, wherein the fiber type Bragg grating element is fixed to the structural member by screw connection. 8. The method of fixing a fiber type Bragg grating element according to claim 7, wherein the fiber type Bragg grating element is detachably fixed at one or more points in each region sandwiching the Bragg grating of the fiber type Bragg grating element. An intermediate layer formed of a brazing material having a melting point lower than that of the metal film of the structural member and the fiber type Bragg grating element is provided between the inner surface of the insertion hole and the fiber type Bragg grating element. The fixing method of the fiber type Bragg grating element according to claim 7.

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