JP6029962B2 - Strain / stress measurement method of structure and strain / stress sensor - Google Patents

Description

  The present invention relates to a non-contact strain / stress measurement technique capable of measuring and detecting strain or stress generated in a structure using light. Specifically, the present invention relates to a strain / stress measurement technique using a fluorescent material made of an oxide ceramic whose emission wavelength fluctuates when irradiated with excitation light according to the magnitude of given strain / stress.

  Understanding the physical quantities acting on the structure is important for the safe use of the structure, and a variety of monitoring techniques have been developed. As sensors for measuring physical quantities acting on the structure, sensors for various physical quantities such as displacement, strain, force, acceleration, or torque are used. As a principle of these sensors, there are many cases where the above-mentioned various physical quantities are converted into strain and measured by the strain sensor. That is, a strain sensor that can measure strain and stress fields can be a basic device that can be applied to monitoring various physical quantities.

  As a strain sensor for measuring a strain / stress field, a sensor employing an electrical method such as a strain gauge or a piezoelectric film, and an optical fiber sensor as an optical method have been developed. However, as a problem common to these conventional strain sensors, an electrical / optical signal line (cable or conductor) is required between the strain sensor and the measurer, so-called contact type (wired) measurement. Is the premise. This not only costs the arrangement of the signal lines, but also restricts the measurement location and measurement target. Therefore, there are Patent Documents 1 to 3 as so-called non-contact (wireless) strain sensors using a stress-stimulated luminescent material that emits light when a dynamic stress is applied. In Patent Document 1 to Patent Document 3, a stress light-emitting material utilizes the characteristic that the “intensity” of light emission increases in proportion to the magnitude of stress. Specifically, it is possible to measure the generation, size, distribution, etc. of strain / stress by applying a stress luminescent material to a structure, etc., and measuring the luminescence intensity from the stress luminescent material. Yes. Stress-stimulated luminescent materials emit light using the dynamic change of stress as an energy source, and change the emission intensity in response to dynamic strain / stress, so that no external electrical or optical energy supply is required. Can be cited as an advantage.

On the other hand, the present applicant has also proposed Patent Document 4 as a non-contact type strain / stress sensor that measures displacement of a structure by measuring light emission “wavelength” instead of light emission “intensity”. In the strain / stress sensor of Patent Document 4, the emission wavelength when irradiated with excitation light varies depending on the magnitude of strain / stress, and the variation direction of the emission wavelength varies depending on the direction of strain / stress, It is made of oxide ceramics in which 0.1 to 3.0 at% Eu is added as a luminescent center ion to MAl ₂ O ₄ (M = Sr, Ca, or Ba).

Patent Document 5 ^discloses a stress measurement method for measuring stress generated in a measurement object made of a composite material in which alumina crystal particles containing Cr ³⁺ ions are dispersed as one of its compositions. Preparing a reference sample comprising the object to be measured or a reference sample having the same composition as the composite material, applying a stress to the reference sample, and applying a predetermined wavelength to a portion where a known stress is applied. Of the fluorescence emitted from the Cr ³⁺ ions contained in the reference sample by irradiation with laser light, the absolute wave value of the fluorescence peak located near the absolute wave value of 14400 cm ⁻¹ is measured, or for a predetermined absolute wave value A relative measurement step of measuring a relative wave value of the fluorescence peak to obtain a relationship between each stress value and an absolute wave value of the fluorescence peak or the relative wave value; and It is irradiated with a laser beam of long, absolute wave numerical value of the peak of the fluorescence which the Cr ³⁺ ions emitted contained in the composite material were measured or the measured measuring the relative wave value of the fluorescence peak, the actual From the absolute wave value or relative wave value of the fluorescence peak measured in step, the measured object is measured based on the relationship between the stress value obtained in the relationship measurement step and the absolute wave value or relative wave value of the fluorescence peak. A stress measurement method is disclosed that includes a stress value acquisition step for obtaining a stress value that has occurred.

Non-Patent Document 1 discloses a fluorescent material made of an oxide ceramic in which the wavelength of light emission (photoluminescence) when irradiated with excitation light according to the magnitude of applied stress is varied. . In the oxide ceramics here, Cr ³⁺ is added as a luminescent center ion in Al ₂ O ₃ . There is Non-Patent Document 2 as an analysis technique of stress distribution using this phenomenon. Non-Patent Document 2 proposes a method for detecting stress based on a change in emission wavelength of Cr ³⁺ added Al ₂ O ₃ generated at the interface between the thermal barrier coating and the metal substrate.

Non-Patent Document 3 discloses a fluorescent material made of an oxide-based ceramic whose emission wavelength fluctuates when irradiated with excitation light in accordance with a given hydrostatic pressure (isotropic compressive stress). Has been. In the oxide-based ceramics here, 1% of Eu ²⁺ is added as a luminescent center ion in SrAl ₂ O ₄ or CaAl ₂ O ₄ .

JP 2004-85483 A Japanese Patent Laid-Open No. 2005-307998 Table 2006-85424 JP 2011-127992 A JP 2005-147837 A

J. He, and D. R. Clarke, "Determination of the Piezospectroscopic Coefficients for Chromium-Doped Sapphire", J. Am, Ceram, Soc., 78 (5), 1347-1353 (1995) Kawasaki Heavy Industries, Ltd., "Leading research on damage measurement technology by fluorescence spectroscopy in aircraft engine maintenance" New Energy and Industrial Technology Development Organization, 2006 results report C. E. Tyner and H. G. Drickamer, "Studies of Luminescence Efficiency of Eu2 + Activated Phosphors as a function of Temperature and High Pressure", J. Chem, Phys., 67 (9), 4116-4122 (1977)

  Patent Documents 1 to 3 are strain sensors using a stress light-emitting material that enables non-contact monitoring of strain / stress fields that do not require a signal line. However, in Patent Documents 1 to 3, since the dynamic strain / stress distribution and the like are measured by measuring the light emission intensity of the stress light-emitting material, there are the following problems. In other words, the light emission intensity in the stress luminescent material not only simply depends on the magnitude of the stress or strain, but also greatly depends on the rate at which the stress or strain changes. Therefore, even if a stress-stimulated luminescent material is applied to a certain structure and a distribution of luminescence intensity is obtained, it is information that reflects the magnitude of strain and stress, or the rate of change thereof. It is difficult to determine what the object is being diagnosed. In addition, some stress-stimulated luminescent materials have a light emission intensity that is reduced by repeated stress, and it is difficult to obtain stable characteristics. Furthermore, when the stress or strain does not change, the light emission phenomenon stops, so static strain / stress sensing is impossible as it is. In order to diagnose these static strains / stresses, it is necessary to continuously monitor data from the initial no-stress state and continuously accumulate data on the changes. Have a problem.

  On the other hand, Patent Document 4 does not have the above-described problem because the displacement of the structure is measured by irradiating the excitation light to emit light and measuring the change in the emission wavelength. However, such strain / stress sensors are also required to have higher strain sensitivity.

Since the techniques of Patent Document 5, Non-Patent Document 1, and Non-Patent Document 2 also utilize the fact that the emission wavelength of the fluorescent material itself changes according to the stress, there is no such problem as described above. That is, it is possible to detect changes in the emission wavelength not only for dynamic strain / stress but also for static strain / stress, and since the entire fluorescent material surface emits light, it can be measured from the surface of the structure being measured. What is necessary is just to catch luminescence. However, the wavelength shift amount in the Cr ³⁺ added Al ₂ O ₃ is a change from 14429Cm ^-3 (wavelength 693.19Nm) against compressive stress of 1GPa 14426cm ^-3 to (wavelength 693.05Nm), stress Sensitivity (amount of wavelength shift per unit stress of 1 GPa) is 0.14 nm / GPa. When the Young's modulus of Al ₂ O ₃ is 335 GPa, the compressive strain for 1 GPa is 0.3%, and when the amount of wavelength shift per unit strain (1%) is defined as strain sensitivity, the strain in Cr ³⁺ added Al ₂ O ₃ is The sensitivity is 0.47 nm /%. As described above, the Cr ^{3 +} -added Al ₂ O ₃ described in Non-Patent Document 1 and Non-Patent Document 2 can detect not only dynamic strain / stress but also a change in emission wavelength with respect to static strain / stress. However, the strain sensitivity and stress sensitivity are low. If these strain sensitivity and stress sensitivity can be further improved, various advantages such as improved detection accuracy, shorter measurement time, and lower cost can be expected.

The technique of Non-Patent Document 3 also uses the fact that the emission wavelength of the fluorescent material itself changes according to the hydrostatic pressure (isotropic stress), and thus does not have the above problems. That is, it is possible to detect a change in the emission wavelength with respect to static stress. However, this document only describes the response of the emission wavelength to isotropic compressive stress under hydrostatic pressure. In the deformation of general structures, such a stress field is rarely expected, and deformation in one or two dimensions is almost all, and responsiveness not only in the compression direction but also in the tensile direction is essential. It is. Therefore, it is judged that the material system described in this document (Eu ²⁺ added as a luminescent center ion in SrAl ₂ O ₄ or CaAl ₂ O ₄ ) can be practically used as a strain / stress sensor for structures. Can not.

  Therefore, the present invention solves the above-mentioned problem, and can measure not only dynamic but also static strain or stress and its directionality (tensile direction or compression direction) with higher sensitivity at any timing. It is an object of the present invention to provide a contact-type strain / stress measurement method and a strain / stress sensor used therefor.

As a means for that purpose, the present invention changes the emission wavelength when the excitation light is irradiated according to the magnitude of strain / stress applied to the structure, and the direction of strain / stress (tensile strain / stress Fluorescent material whose emission wavelength varies depending on compression strain / stress), specifically, Cr is added to Sr _1-X Al ₂ O ₄ (X = 0.02 to 0.20 ) with 0.1 to 3 Cr. A strain / stress sensor including an oxide-based ceramic added with 0.0 at% (preferably 0.5 to 1.5 at%) as an effective material is installed, and the strain / stress sensor is irradiated with excitation light at an arbitrary timing. Fluorescence is emitted, the emission wavelength at this time is measured by the wavelength measuring means, and the emission wavelength change amount with respect to the reference emission wavelength and the direction of the change in a state where no strain or stress is applied to the structure measured in advance (Change to short wavelength side or change to long wavelength side )) To measure static and dynamic strain or stress generated in the structure and determine its directionality (tensile direction or compression direction). Can be proposed. Note that there is no direct relationship between the amount of Cr added and the amount of missing Sr (value of X).

In oxide-based ceramics (fluorescent material) made of Cr-added Sr _1-X Al ₂ O ₄ , the light emission phenomenon occurs when electrons excited between the electron orbits of Cr, which is the emission center ion, or in the defect level transition. cause. In this light emission phenomenon, when strain / stress acts on the crystal structure of Cr-added Sr _1-X Al ₂ O ₄ , the energy state between electron orbital or defect level changes due to the change of the ligand field. Applying the principle that the light emission characteristics change depending on. Then, in a state where strain or stress in the tensile or compressive direction is applied to the fluorescent material, fluorescence is emitted as a light emission phenomenon in the excitation-recombination process of electrons by photoluminescence (excitation light irradiation). The concept is that a light emission wavelength corresponding to the strain / stress distribution can be obtained even in a static strain / stress field.

  The strain / stress sensor may be bonded to the surface of the structure as a bulk body obtained by sintering the oxide ceramic, or may be formed on the surface of the structure as a thin film containing the oxide ceramic particles. it can. The bulk body is a three-dimensional shape having a certain thickness such as a plate shape (flaky shape) or a lump shape, and the specific shape is not particularly limited. The stress acting on the structure can be measured based on the Young's modulus of the structure that is the object to be measured from the amount of strain obtained by the strain / stress sensor.

Also, a strain / stress sensor that is installed in a structure and measures strain or stress generated in the structure, and the emission wavelength varies when excitation light is irradiated according to the magnitude of the strain / stress. In addition, Sr _1-X Al ₂ O ₄ (X = 0.02 to 0.20 ) has a Cr content of 0.1 to 3.0 at%, and the direction of fluctuation of the emission wavelength varies depending on the direction of strain and stress. A strain / stress sensor including an added oxide ceramic (preferably 0.5 to 1.5 at%) can also be proposed. The strain / stress sensor can also be adhered to the structure as a bulk body obtained by sintering the oxide ceramic, or can be formed on the surface of the structure as a thin film containing the oxide ceramic particles. .

The strain / stress sensor of the present invention includes an oxide-based ceramic that is a fluorescent material made of Cr-added Sr _1-X Al ₂ O _4, and an emission wavelength with respect to a reference emission wavelength according to the magnitude of the applied strain / stress. More than the conventional Cr ³⁺ added Al ₂ O ₃ and the strain / stress sensor using a fluorescent material in which Eu is added to MAl ₂ O ₄ (M = Sr, Ca or Ba) of Patent Document 4 Is also big. Therefore, according to the strain / stress sensor using this fluorescent material, the strain sensitivity and the stress sensitivity are higher than those of the conventional strain / stress sensor, and the strain or stress in the structure can be measured with high accuracy. It is also advantageous for shortening the measurement time and reducing the cost. Further, in the strain / stress sensor of the present invention, the direction of the emission wavelength shift is changed depending on the strain / stress application direction of tension / compression, and one-dimensional or two-dimensional strain / It has been found for the first time that it exhibits responsiveness to a stress field, and enables deformation diagnosis in an actual structure. That is, it is possible to reliably measure static and dynamic strains or stresses in the compression direction as well as the tensile direction generated in the structure. Moreover, it is possible to determine the directionality, that is, whether the strain / stress in the tensile direction or the strain / stress in the compression direction.

  Since the strain / stress measurement method of the structure of the present invention is a non-contact type measurement method using the light emission phenomenon of the fluorescent material, such as multi-point measurement in a large structure having a wide range of diagnosis targets, such as high places and access control areas, etc. High-precision measurement is possible even for diagnostic objects that are difficult or impossible with contact-type sensors, such as measurement in hazardous locations, measurement in a vacuum, and measurement in a high-speed rotating body. In addition, due to the nature of light that can be condensed and diverged, it is possible to select an arbitrary sensing area from the micro area of the measurement point, and to improve the accuracy of strain and stress distribution diagnosis in the plane by two-dimensional scanning. It is also effective for speeding up.

  In addition, since strain or stress is measured by the amount of change (shift) in the fluorescence emission wavelength when irradiated with excitation light, not only dynamic strain and stress fields as in the prior art, but also static strain and stress fields. Strain or stress can be measured. That is, the strain or stress can be measured not only at the moment when the stress is applied but also after the stress is applied. Since the wavelength change due to the strain / stress in the static strain / stress field is measured, there is no influence of the strain / stress change rate unlike the dynamic strain / stress field, and the strain or stress can be accurately measured. In addition, since it emits light whenever it is irradiated with excitation light, there is no need to constantly observe it like dynamic strain / stress, and strain or stress can be measured at any timing. In addition, since the present invention detects a change in emission wavelength based on a change in the structure of the fluorescent material, the spatial resolution can be narrowed by condensing light compared to the case of using a grating, and the detection direction of emission is also limited. I do not receive it.

  If the strain / stress sensor of the present invention is a bulk body obtained by sintering an oxide-based ceramic, the sensitivity to strain / stress is better than when a thin film is used. However, in this case, it is necessary to consider the heat resistance of the adhesive. On the other hand, if the strain / stress sensor is a thin film formed on the surface of the structure, an adhesive is not necessary, and it is not necessary to consider the heat resistance of the adhesive.

It is a schematic diagram which shows the mechanism of the strain / stress measurement method. It is a PL emission spectrum obtained by irradiating a strain / stress sensor with excitation light. It is a graph which shows the change of PL emitted light intensity according to Cr addition amount. It is a graph which shows the change of PL emitted light intensity according to Sr defect | deletion amount. It is a schematic diagram which shows the mechanism in which a tensile strain acts. It is a graph which shows the relationship between the magnitude | size of the tensile strain in the strain and stress sensor which consists of a bulk body, and the wavelength shift amount accompanying this. It is a graph which shows the relationship between the magnitude | size of the tensile strain in the strain and stress sensor which consists of a thin film, and the wavelength shift amount accompanying this.

  In the present invention, the emission wavelength varies when the excitation light is irradiated according to the applied strain / stress, and the emission wavelength varies according to the direction of the strain / stress (tensile direction or compression direction). A fluorescent material made of oxide ceramics with different directions is used as a strain / stress sensor to measure dynamic or static strain or stress when stress acts on a structure. In the following description, fluorescence emission due to excitation light irradiation may be referred to as PL emission.

The fluorescent material used in the strain / stress sensor of the present invention is an oxide-based ceramic made of Cr-added Sr _1-X Al ₂ O ₄ . Here, when the value of X (a missing amount of Sr) is 0.00 and there is no defect, the emission intensity is extremely low. By introducing an Sr defect with an X value of 0.02 to 0.20, The emission intensity can be increased. A preferable amount of Sr deficiency for obtaining higher emission intensity is in the range of 0.02 to 0.08, and more preferably 0.02 to 0.06. On the other hand, the addition ratio of Cr is added in the range of 0.1 to 3.0 at%. Outside this range, good emission intensity and strain sensitivity cannot be obtained. A preferable Cr addition ratio for obtaining higher light emission intensity is 0.5 to 1.5 at%, and more preferably 0.8 to 1.0 at%.

The PL light emission in the fluorescent material exhibits a light emission phenomenon due to an excitation-recombination process between electron orbits in a luminescent center ion or in a defect level. The fluorescent material of the present invention emits PL in red when irradiated with excitation light. When such a fluorescent material is used as a strain / stress sensor, light emission occurs due to a change in the ligand field caused by strain acting on the crystal structure of Sr _1-X Al ₂ O _{4 in} the above light emission phenomenon. The principle that the energy state of the central ion or defect level changes and the emission characteristics, that is, the PL emission wavelength fluctuate (shift) by this is applied.

  As one form of the strain / stress sensor using such oxide ceramics, a sintered body (bulk body) obtained by firing a ceramic raw material (starting raw material) can be used. Typically, it can be produced by a known solid phase reaction method in which ceramic raw material powders are mixed and fired. Specifically, various starting materials may be mixed and fired at a temperature lower than the melting point of each starting material to obtain a sintered body. At this time, if necessary, the starting materials are mixed and calcined at a temperature lower than the firing (fired) temperature, and the sintered body after the calcination is pulverized and molded, followed by firing (fired). ) Is preferable. This is because the composition can be made uniform and dense.

At this time, the amount of oxygen deficiency in the base material (Sr _1-X Al ₂ O ₄ ) and the oxidation state of the added Cr affect not only the shift amount of the PL emission wavelength but also the emission intensity. There is a tendency for strength to become weaker. Therefore, the firing process is performed in an oxygen-free atmosphere to prevent oxidation. The oxygen-free atmosphere may be an inert gas such as Ar gas or a nitrogen gas atmosphere.

  The shape of the strain / stress sensor made of a bulk body of oxide ceramics is not particularly limited as long as it is a shape that can be installed on a structure, but is preferably in the form of a flake (for example, about 0.1 to 5 mm in thickness). If it is flake-like, the followability to the strain generated in the structure is good and the workability is also good. Or it can also be set as the solid | 3D shape which has fixed thickness. The flaky strain / stress sensor can be directly sintered into a flaky shape, or a bulk material having a certain thickness can be formed into a flaky shape by post-processing such as cutting, cutting, or grinding. A strain / stress sensor made of a bulk body can be installed by adhering to the surface of the structure. At this time, a dent can be provided at an arbitrary part of the structure so as to embed the strain / stress sensor, or it can be installed so as to be sandwiched between two points in the structure. When installed so as to be sandwiched between structures, it is suitable for measurement of compressive stress.

  As another form of the strain / stress sensor, a thin film can be formed on the surface of the structure. Specifically, the oxide ceramics are prepared by applying, spraying, or printing a frit in which powders made of the above oxide ceramics are mixed and dispersed on the surface of the structure, and baking the frit to melt the frit on the surface of the structure. It can be installed by depositing a thin film containing As the frit here, a glass frit can be used. The baking temperature is a temperature not lower than the melting point of the frit and lower than the melting point of the oxide ceramic particles. Specifically, it may be performed at about 400 to 800 ° C.

A method for measuring strain or stress generated in the structure using the strain / stress sensor thus installed will be described. As shown in FIG. 1, when the strain / stress sensor 10 installed in the structure 1 is irradiated with excitation light 11, the strain / stress sensor 10 emits fluorescence. Measure by measuring means. As the excitation light 11 to be irradiated, light having a higher energy (short wavelength) than the emission wavelength is used. In the case of Cr-added Sr _1-X Al ₂ O ₄ , excitation light having a wavelength of about 250 to 600 nm can be mentioned. The wavelength measuring means is not particularly limited as long as it can measure the wavelength of light, and a known device can be used. A typical example is a spectroscope.

  On the premise of this, first, the reference emission wavelength in a state where the structure 1 is not distorted is measured in advance. The reference emission wavelength may be measured immediately after the strain / stress sensor 10 is installed on the structure 1 or before the strain / stress sensor 10 is installed on the structure 1. Then, after the strain / stress sensor 10 is installed on the structure 1, when the wavelength of the fluorescence emission 12 is measured at an arbitrary timing (after an arbitrary time has elapsed), if the structure 1 is distorted, the fluorescence emission The wavelength of 12 is different from the reference emission wavelength. Therefore, by measuring the emission wavelength change (shift amount) with respect to the reference emission wavelength, the strain generated in the structure 1 can be measured. At this time, depending on the direction of strain, that is, tensile strain or compression strain, the direction of emission wavelength change is reversed (shift to short wavelength side or shift to long wavelength side). Whether the strain is in the tensile direction or the strain in the compression direction can also be determined based on the directionality. Of course, if the structure 1 is not distorted, there is no change in the emission wavelength. Further, since the strain and the stress are in a proportional relationship with the Young's modulus as a proportional constant, the stress can be obtained from the measured strain value. At the same time, it can be determined whether it is tensile stress or compressive stress. It is efficient that the reference emission wavelength is stored in an information processing apparatus connected to the wavelength measuring means, and the reference emission wavelength and the emission wavelength are also compared by the information processing apparatus.

  The measurement object is not particularly limited as long as it is a structure on which stress can act, and includes various structures from large structures to small structure parts. In particular, since the strain / stress measurement method of the present invention is a non-contact measurement method, multipoint measurement in large structures with a wide diagnostic range such as dams and tunnels, steel towers such as radio towers and power transmission towers, high-rise buildings, power generation Suitable for measurements that are difficult or impossible with contact-type sensors, such as measurements in hazardous places such as high places and access control areas, measurements in high-speed rotating bodies such as turbines and motors, and measurements in sealed spaces such as in vacuum. It is.

(Bulk body test 1)
First, the performance according to Cr addition amount was evaluated about the strain / stress sensor which consists of a bulk body. There are four types of strain / stress sensor samples, Sr _1-X Al ₂ O ₄ with X = 0.02 and Cr addition ratios of 0.1, 0.5, 1.0, 5.0 at%. Was synthesized.

The synthesis process of Cr added _{Sr 1-X Al 2 O 4} . As starting materials, SrCO ₃ (99.9%, high purity chemical), α-Al ₂ O ₃ (99.99%>, high purity chemical), Cr ₂ O ₃ (99.9%>, high Each powder with a purity chemical) was weighed to match the respective stoichiometric composition, and mixed with ZrO ₂ balls in a PET container for 1 hour using ethanol as a dispersion medium. The mixed slurry was extracted from the mixed slurry by dispersing ethanol in an atmosphere at 130 ° C., and sized with a sieve having a mesh size of 250 μm while being pulverized in a mortar. Thereafter, uniaxial press molding was performed at a pressure of 350 kgf / mm ² into a shape of diameter 30 mmφ × thickness 5 mmt. The molded body was heated to 900 ° C. at a temperature rising rate of 200 ° C./h, held for 1 hour, calcined, and cooled at a furnace cooling rate. The sintered body after calcination was again pulverized in a mortar and sized with a sieve having a mesh size of 250 μm, and then pulverized for 24 hours with a ZrO ₂ ball and ZrO ₂ pot mill using ethanol as a dispersion medium. The ground slurry was similarly sprinkled with ethanol in a 130 ° C. atmosphere to extract a mixed powder, and sized with a sieve having a mesh size of 250 μm while being ground in a mortar. Thereafter, uniaxial press molding was performed at a pressure of 500 kgf / mm ² to a diameter of 20 mmφ and a thickness of ² mmt. Firing (main firing) of the molded body was a process of heating to 1400 ° C. at a temperature rising rate of 200 ° C./h, holding the temperature for 12 hours, and then lowering the temperature at the furnace cooling rate. The firing atmosphere was an Ar inert atmosphere. Finally, the obtained sintered body was processed into a thin piece having a thickness of 0.5 mm to obtain a strain / stress sensor composed of a bulk body obtained by sintering an oxide ceramic. These strain / stress sensors were bonded to a stainless steel plate (length 150 mmL × width 25 mmW × thickness 2 mmt) as a simulated structure.

About each obtained strain / stress sensor, PL emission spectrum was observed with the fluorescence characteristic evaluation system (Horiba, Fluorolog). Excitation light was changed as a wavelength range of 250 to 620 nm, and PL emission obtained by each excitation light was observed in a wavelength range of 650 to 850 nm. As a typical PL emission spectrum, an emission spectrum of Sr _0.98 Al ₂ O ₄ to which 1.0 at% Cr is added is shown in FIG. From these results, the emission intensity at an excitation wavelength of 350 nm and an emission wavelength of 770 nm is graphed in FIG. From the results shown in FIG. 3, the emission intensity in Sr _1-X Al ₂ O ₄ containing 1.0 at% Cr was the highest.

(Bulk body test 2)
Next, the Cr addition ratio is fixed at 1.0 at%, and the amount of Sr deficiency (value of X) in Cr-added Sr _1-X Al ₂ O ₄ is set to X = 0.02, 0.05, 0.2. With respect to three types of strain / stress sensors synthesized in the same manner as in bulk body test 1, PL emission spectra were observed respectively. In order to compare the emission intensities, the emission intensities at an excitation wavelength of 350 nm and an emission wavelength of 770 nm are shown in a graph in FIG. From the result of FIG. 4, the emission intensity was the strongest in Cr-added Sr _1-X Al ₂ O ₄ with X = 0.05.

Furthermore, in order to give tensile deformation to each of the Cr-added Sr _1-X Al ₂ O _{4 in which the} amount of Sr deficiency is changed, a tensile force is applied to the hydraulic cylinder that moves up and down of the hydraulic material strength test apparatus (manufactured by MTS, 858). Grip attachments were attached, and each test piece was set between them to give tensile deformation as shown in FIG. Reference numeral 1 denotes a stainless steel plate as a simulated structure, reference numeral 10 denotes a strain / stress sensor, and reference numeral 100 denotes a test piece. The hydraulic cylinder can be moved up and down in steps of 0.01 mm to give a quantitative tensile strain to each test piece.

  As the spectrometer for measuring the emission wavelength, a spectrometer (C10027-1, manufactured by Hamamatsu Photonics) capable of spectrally detecting a wavelength of 200 to 950 nm at a time using a CCD linear image sensor was adopted. As an excitation light source for irradiating each test piece, a UV-LED light source (manufactured by Hamamatsu Photonics, L9610) having an emission wavelength at 365 nm was used.

Further, as Comparative Example 1, a strain / stress sensor made of an oxide ceramic made of 1.0 at% Eu-added SrAl ₂ O ₄ was also tested in the same manner. In this synthesis process of Eu-added Sr _1-X Al ₂ O ₄ , SrCO ₃ (99.9%, manufactured by High Purity Chemical) and α-Al ₂ O ₃ (99.99%>, High Purity Chemical) are used as starting materials. And Eu ₂ O ₃ (99.95%>, manufactured by Kanto Chemical Co., Ltd.) are weighed to match the stoichiometric composition, and thereafter Cr-added Sr _1-X Al ₂ O Manufactured by the same process as ₄ . However, firing (main firing) of the Eu-added SrAl ₂ O ₄ shaped body was performed up to 1300 ° C. at a rate of temperature increase of 200 ° C./h, and the firing atmosphere was 4% H ₂ + Ar reducing atmosphere.

  The wavelength of the PL emission spectrum corresponding to the tensile strain thus obtained was converted into energy and fitting assuming a Gaussian distribution was performed, and the wavelength at the peak position was identified as the central wavelength of the Gaussian distribution. FIG. 6 shows the result of summarizing the relationship between the shift amount of the peak wavelength (vertical axis) and the magnitude of the tensile strain (horizontal axis).

From the slope of the result of FIG. 6, the wavelength change (strain sensitivity) per unit strain (1% strain) at the Sr deficit amount x = 0.02 is 9.07 nm /% (18.8 meV /%), and x = 0. In case of 05, 7.89 nm /% (16.4 meV /%), in case of x = 0.20, 2.85 nm /% (6.0 meV /%), and in the case of Eu addition Sr _1-X Al ₂ O ₄ as Comparative Example 1, It can be estimated as −2.29 nm /% (−10.6 meV /%), and it was confirmed that Cr-added Sr _1-X Al ₂ O ₄ has higher strain sensitivity than Comparative Example 1. There is no history such as hysteresis in the change in PL emission spectrum accompanying the increase in tensile strain, and it is also possible to evaluate the response to dynamic strain by continuously measuring the time change of this PL emission spectrum. .

(Thin film test)
Next, the strain / stress sensor in a form installed on the structure by film formation was also evaluated. The composition here was 1.0 at% Cr-added Sr _0.95 Al ₂ O ₄ with reference to the result of the bulk test 2. On the other hand, as Comparative Example 2, as in Comparative Example 1, 1.0 at% Eu-added SrAl ₂ O ₄ was used.

As a film forming method, a powder obtained by pulverizing a bulk body in bulk body test 2 was mixed with glass frit, and the mixed powder was applied to the surface of the structure and baked. First, a powder obtained by pulverizing a sintered body of Cr-added Sr _0.95 Al ₂ O ₄ or Eu-added SrAl ₂ O ₄ was prepared, and a glass frit (JYM0005M manufactured by Nippon Frit Co., Ltd .: recommended firing temperature of 650 to 900 ° C.) was prepared. The mixture was mixed at a weight ratio of 7: 3. Furthermore, this mixed powder is dispersed in a vehicle (added 7 wt% of PVB with respect to terpineol), and kneaded for about 20 minutes in an automatic mortar to obtain a printing paste. SUS430 (100 × 20 × 0.5 mm) base material The screen was printed as a circle with a diameter of 9 mm in the center. The ratio of the vehicle was 200 wt% (twice) with respect to the glass frit. The printed film was dried at 120 ° C. For the Cr-added Sr _0.95 Al ₂ O ₄ printed film, the atmosphere was Ar, and for the Eu-added SrAl ₂ O ₄ printed film as Comparative Example 2, the atmosphere was Ar + 4% H ₂ , respectively, at 900 ° C. It was baked for 2 hours at 350 ° C./h, and the temperature was lowered in the furnace.

The obtained Cr-added Sr _0.95 Al ₂ O ₄ printed film and the strain / stress sensor of Comparative Example 2 were subjected to tensile deformation in the same manner as in bulk test 2, and the peak wavelength shift obtained in the same manner as in bulk test 2 was obtained. The result of summarizing the relationship between the amount (vertical axis) and the magnitude of the tensile strain (horizontal axis) is shown in FIG. From the slope of the results in FIG. 7, the wavelength change (strain sensitivity) per unit strain (1% strain) in the Cr-added Sr _0.95 Al ₂ O ₄ printed film is 2.11 nm /% (4.4 meV /%), Comparative Example 2 can be estimated to be −0.82 nm /% (−3.8 meV /%), and it was confirmed that the Cr-added Sr _0.95 Al ₂ O ₄ printed film has higher strain sensitivity than Comparative Example 2. It was.

DESCRIPTION OF SYMBOLS 1 Structure 10 Strain / stress sensor 11 Excitation light 12 Fluorescence emission 100 Test piece

Claims (8)

Sr _1-X Al ₂ in which the emission wavelength varies when the structure is irradiated with excitation light according to the magnitude of strain / stress, and the variation direction of the emission wavelength varies depending on the direction of strain / stress. A strain / stress sensor including an oxide ceramic in which Cr is added to 0.1 to 3.0 at% in O ₄ (X = 0.02 to 0.20 ),
The strain / stress sensor is irradiated with excitation light to emit fluorescence, the emission wavelength is measured by a wavelength measuring means, and the emission wavelength change amount with respect to a reference emission wavelength in a state in which no strain / stress acts on the structure; A structure strain / stress measurement method for measuring static and dynamic strain or stress generated in a structure and determining its direction by measuring the direction of the change.   The strain / stress measurement method according to claim 1, wherein the added amount of Cr is 0.5 to 1.5 at%.   3. The strain / stress measurement method for a structure according to claim 1, wherein the strain / stress sensor is formed of a bulk body obtained by sintering the oxide ceramics, which is bonded to the structure.   3. The strain / stress measurement method for a structure according to claim 1, wherein the strain / stress sensor is a thin film including the oxide ceramic particles formed on a surface of the structure. A strain / stress sensor for measuring strain or stress in the tensile and compression directions generated in the structure when installed in the structure,
Sr _1-X Al ₂ O ₄ (X) in which the emission wavelength varies when the excitation light is irradiated according to the magnitude of strain / stress, and the variation direction of the emission wavelength varies depending on the direction of strain / stress. = including oxide-based ceramics and Cr added 0.1～3.0At% to .02-.20), strain and stress sensors.   The strain / stress sensor according to claim 5, wherein the amount of Cr added is 0.5 to 1.5 at%.   The strain / stress sensor for a structure according to claim 5 or 6, comprising a bulk body obtained by sintering the oxide ceramic.   The strain / stress sensor for a structure according to claim 5 or 6, comprising a thin film containing the oxide-based ceramic particles formed on the surface of the structure.