JP6973324B2 - Anomaly detection method - Google Patents

Description

The present invention relates to an abnormality detection method for inspecting deterioration or abnormality of a non-metal layer provided on the surface of an object by using electromagnetic waves.

In recent years, research and development of terahertz wave imaging and radar have been carried out, and their application to non-destructive inspection and sensing is expected. Most of the terahertz waves are transmitted when irradiated with a non-metal material such as resin, while most of them are reflected when irradiated with a metal material. By utilizing such properties of terahertz waves, the unevenness of the surface of a substrate made of a metallic material (hereinafter referred to as a metal substrate) existing under a layer made of a non-metal material such as a resin (hereinafter referred to as a non-metal layer). Has been proposed (Non-Patent Document 1). A technique for detecting an abnormality between a non-metal layer such as a resin layer and a lower metal substrate by utilizing the property of this terahertz wave is being studied.

For example, in steel structures, in general, the surface is often coated with a non-metal layer (hereinafter collectively referred to as an anticorrosion layer) such as a paint or resin having excellent environmental resistance for corrosion protection. The anticorrosion layer exerts its predetermined function by reducing the degree of adhesion to the steel surface due to poor surface treatment before construction, inadequate temperature control during construction, and deterioration over time, and eventually peeling off. Will not be. Therefore, the work of peeling off the anticorrosion layer on the surface and then applying the anticorrosion layer again is executed at predetermined time intervals.

On that basis, the following six judgment methods are adopted as the judgment method regarding the deterioration of the anticorrosion layer. That is, first, visual inspection, second, image processing analysis, third, current interrupter measurement (measurement of resistance value of the metal surface under the anticorrosion layer), fourth, adhesion evaluation of the anticorrosion layer, and fifth, thickness of the anticorrosion layer. Measurement, sixth, chemical analysis of anticorrosion layer, etc.

Jun Yamaguchi, "Development of Terahertz Imaging System", PIONEER R & D (2014)

However, the first and second judgment methods are limited to qualitative evaluation, and there is a problem that quantitative evaluation cannot be performed. In addition, while the third to sixth judgment methods can be evaluated quantitatively, they need to be executed in close proximity to the object to be measured, so that inspections for large structures and structures at high places can be performed. At that time, it was necessary to erection a scaffolding.

The present invention has been made in view of the above, and an object thereof is to provide a structure in which a non-metal layer is provided in close contact with the surface of a metal substrate, the non-metal layer and the metal substrate at an arbitrary position. It is an object of the present invention to provide an abnormality detection method capable of detecting an abnormality such as peeling that occurs between them without removing the non-metal layer.

(1) In order to solve the above-mentioned problems and achieve the object, the abnormality detection method according to one aspect of the present invention is terahertz at a predetermined position on the surface of an object in which a non-metal layer is provided on an upper layer of a metal substrate. A terahertz wave transmitting means capable of irradiating waves and scanning the surface of the object, and a terahertz wave reflected at the predetermined position of the object can be detected, and the above-mentioned The polarization direction is on the terahertz wave detecting means capable of scanning the surface of an object, the transmitting side linear polarizing means provided on the emitting side of the terahertz wave in the terahertz wave transmitting means, and the detecting side of the terahertz wave detecting means. In an abnormality detection method using an abnormality detection device provided with a detection-side linear polarization means provided so as to be 90 ° different from the polarization direction of the transmission-side linear polarization means, the terahertz wave emitted from the terahertz wave transmission means is used. By irradiating the non-metal layer and detecting the portion where the intensity of the terahertz wave transmitted through the non-metal layer is minimized by the terahertz wave detecting means, the stress generated in the non-metal layer is isotropic. It is characterized in that a certain part is detected as an abnormal part.

(2) The abnormality detecting method according to one aspect of the present invention is the present invention, wherein the transmitting side linearly polarizing means and the detecting side linearly polarizing means are the polarization direction of the transmitting side linearly polarizing means and the detection. The terahertz wave detecting means is configured to be rotatable while maintaining a state in which the polarization direction of the side linearly polarized light means is different by 90 °, and when the transmitting side linearly polarized light means and the detection side linearly polarized light means are rotated. It is characterized in that the abnormal portion is detected by detecting the portion where the intensity of the terahertz wave detected by is maintained to the minimum.

(3) The abnormality detection method according to one aspect of the present invention is provided on the exit side of the terahertz wave transmitting means in the above invention (1), and the linearly polarized terahertz wave transmitted through the transmitting side linear polarizing means is transmitted. A transmission side phase conversion means that gives a phase difference so as to be circularly polarized, and a detection side phase conversion means that is provided on the incident side of the terahertz wave with respect to the detection side linear polarization means and gives a phase difference to the terahertz wave. , The abnormal portion is detected by detecting the portion where the intensity of the terahertz wave detected by the terahertz wave detecting means is extremely small.

According to the abnormality detection method according to the present invention, in a structure in which a non-metal layer is provided in close contact with the surface of a metal substrate, an abnormality such as peeling that occurs between the non-metal layer and the metal substrate at an arbitrary position is performed. Can be detected without removing the non-metal layer.

FIG. 1 is a diagram showing a configuration of a stress measuring device for executing the abnormality detection method according to the first embodiment of the present invention. FIG. 2 is a diagram showing a configuration of a stress measuring device for executing the abnormality detection method according to the second embodiment of the present invention. FIG. 3 is a diagram showing a schematic configuration of a photoelastic stress measuring device for explaining a stress measuring method by a conventional photoelastic method.

Hereinafter, the abnormality detection method and the abnormality detection device according to the embodiment of the present invention will be described with reference to the drawings. In all the drawings of the following embodiments, the same or corresponding parts are designated by the same reference numerals. Further, the present invention is not limited to the embodiments described below.

First, in explaining the abnormality detection method according to the present invention, the principle of the present invention will be described in order to facilitate the understanding of the present invention. Normally, the surface of a structure is coated with a paint or resin having excellent environmental resistance to protect the members. Typical examples of these are coating and coating as an anticorrosion layer made of a non-metal layer that protects a structure made of steel (steel structure) from corrosion (hereinafter collectively referred to as an anticorrosion layer). There is. The anticorrosion layer is usually in close contact with the surface of the member. However, when the anticorrosion layer deteriorates, the degree of adhesion of the anticorrosion layer to the steel surface of the steel material decreases.

Here, in order to evaluate the degree of adhesion of the anticorrosion layer, for example, a cross-cut test method (Japanese Industrial Standards, K5600-5-6) is also known for coating. The cross-cut test method is to make vertical and horizontal cuts on the surface of the coating with a razor blade at fine intervals, observe the peeling condition of the coating, and compare it with the standard judgment image to improve the adhesion of the coating in 5 stages. It is a method of evaluation. However, the cross-cut test method not only requires the inspector to approach the surface of the coating, but also is a method that only evaluates locally and damages the coating, so it is applicable to actual structures. Had a limit.

It is known that the above-mentioned anticorrosion layer shrinks in the process of drying and hardening, so that tensile residual stress is generated on the surface. That is, in the anticorrosion layer of a steel structure or the like, based on the construction process, an isotropic tensile residual stress is reached when the construction is completed. For example, in the case of painting, the coating film itself shrinks in the process of drying, while the contact portion with the steel material, which is a metal substrate, becomes a drag force, resulting in a state of tensile residual stress. Furthermore, in the drying process, the drying usually proceeds uniformly, so that the tensile residual stress becomes isotropic. In the case of coating, the coating is applied to the steel material in a state of being softened by heating. At this time, while heat shrinkage occurs in the process of cooling the coating cover, the contact portion with the steel material becomes a drag force as in the case of coating, resulting in a state of tensile residual stress. Since cooling proceeds uniformly in heat shrinkage, the tensile residual stress becomes isotropic.

From the above points, in the place where the anticorrosion layer is sound, that is, in the normal part where the anticorrosion layer is normally in close contact with the steel surface of the steel material, the stress state in the anticorrosion layer is isotropic tensile residual stress and structure. The stress due to the strain caused by the dead load of the object is superimposed. Since the strain due to dead load is generally not isotropic, the stress state of the anticorrosion layer at a healthy place is not isotropic and has anisotropy. On the other hand, in places where the anticorrosion layer is not sound, that is, in abnormal parts where the anticorrosion layer does not normally adhere to the steel surface of the steel material, the adhesion between the anticorrosion layer and the steel material is reduced or the lower part of the anticorrosion layer is corroded. It may be corroded. In this case, since the anticorrosion layer is in a floating state due to peeling or the like, the drag force of the adhesion portion to the anticorrosion layer disappears, and only the isotropic compressive residual stress remains. Therefore, the unhealthy part of the anticorrosion layer is in an isotropic stress state in the compression direction, which is opposite to the healthy part. Therefore, by detecting whether the stress of the anticorrosion layer on the surface of the steel structure is isotropic or anisotropic, the abnormal portion of the anticorrosion layer can be detected, and the soundness of the anticorrosion state by the anticorrosion layer is evaluated. can.

Therefore, a method for detecting anisotropy and isotropic of the stress generated in the anticorrosion layer will be described. Conventionally, as a method for evaluating the stress of a resin, a photoelastic stress measurement method (hereinafter referred to as a photoelastic method), which utilizes the fact that a birefringence phenomenon occurs when an external force is applied to a transparent material such as epoxy resin or glass, is known. Has been done. The photoelastic method is a method of obtaining a stress distribution by applying an external force to a model created of a material in which a birefringence phenomenon occurs and observing the birefringence phenomenon generated in the model. FIG. 3 is a diagram showing a schematic configuration of a photoelastic stress measuring device for explaining a stress measuring method by a conventional photoelastic method.

As shown in FIG. 3, the conventional photoelastic stress measuring apparatus 100 includes a visible light source 101, a first polarizing plate 102, a λ / 4 wave plate 103, 104, and a second polarizing plate 105, which are arranged linearly with each other. And a camera 106. If necessary, a lens or the like is further provided. Of these, the first polarizing plate 102 and the second polarizing plate 105 are provided so that the polarization directions differ from each other by 90 ° (π / 2). On the other hand, the λ / 4 wave plates 103 and 104 are provided so that their principal axis directions differ from each other by 90 °. On top of that, the polarization direction of the first polarizing plate 102 and the main axis direction of the λ / 4 wave plate 103 are provided so as to be different from each other by 45 ° (π / 4). Similarly, the main axis direction of the λ / 4 wave plate 104 and the polarization direction of the second polarizing plate 105 are provided so as to be different from each other by 45 °. The measurement object 110 to which the stress is measured is made of, for example, an epoxy resin that is transparent to visible light. The object to be measured 110 is arranged at a predetermined position between the λ / 4 wave plates 103 and 104.

When measuring the stress generated in the object to be measured 110 by the photoelastic stress measuring device 100, first, visible light is emitted from the visible light source 101. The visible light emitted from the visible light source 101 is linearly polarized by the first polarizing plate 102, and then circularly polarized by the λ / 4 wave plate 103. Visible light that has become circularly polarized light enters the measurement object 110 and causes a phase difference δ due to birefringence caused by the stress field of the measurement object 110, resulting in elliptically polarized light. The elliptically polarized light includes the case of circularly polarized light. Here, the phase difference δ generated by birefringence is proportional to _{the principal stress difference (σ 1} − σ ₂ ) of the object to be measured 110, as shown in the following equation (1).
δ = 2πCt (σ ₁ − σ ₂ ) / λ… (1)
Λ is the wavelength of the light used, C is the photoelastic modulus of the material of the object to be measured 110, and t is the thickness of the object to be measured 110.

The light transmitted through the object to be measured 110 is linearly polarized by the λ / 4 wave plate 104, and then the polarized light component that has passed through the second polarizing plate 105 is imaged by the camera 106. The light intensity I detected in this case depends on the phase difference δ generated by birefringence, as shown in the following equation (2).
I = A ² sin ² (δ / 2)… (2)
Note that A is the amplitude of the incident light.

That is, an image depending on the phase difference generated in the measurement object 110 can be captured by the camera 106, and the stress state of the measurement object 110 can be observed. The image captured by the camera 106 is obtained as an image of photoelastic fringes of a bright and dark pattern on the measurement object 110. The obtained light-dark pattern photoelastic stripes are called uniform color lines. _{By observing the imaged uniform color lines, the principal stress difference (σ 1} − σ ₂ ) as a photoelastic parameter can be derived from the thickness t of the object to be measured 110 and the photoelastic coefficient C.

On the other hand, in the photoelastic stress measuring device 100 shown in FIG. 3, the principal stress direction can be further measured by removing the λ / 4 wave plates 103 and 104. That is, in the photoelastic stress measuring device 100, the λ / 4 wave plates 103 and 104 are removed from the optical axis between the visible light source 101 and the camera 106. In this configuration, the visible light emitted from the visible light source 101 passes through the first polarizing plate 102, is polarized into linearly polarized light, and then is incident on the object to be measured 110. The light intensity I detected in this case depends on the phase difference δ generated by birefringence and the angle φ formed by the principal stress direction and the linearly polarized light direction, as shown in the following equation (3).
I = A ² sin ² 2φ ・ sin ² (δ / 2)… (3)

Specifically, when the polarization direction of the first polarizing plate 102, that is, the polarization direction of the linearly polarized light and the principal stress direction coincide with each other, the linearly polarized light passes through the object to be measured 110 without changing the polarization direction. .. In this case, the angle φ formed by the principal stress direction and the linearly polarized light direction is 0. Since the light transmitted through the object to be measured 110 is linearly polarized light parallel to the polarization direction of the first polarizing plate 102, it hardly transmits through the second polarizing plate 105. When the light transmitted through the second polarizing plate 105 is observed in this state, a dark line called an isobaric line appears in the measurement object 110. On the other hand, when the polarization direction and the principal stress direction of the first polarizing plate 102 do not match, the light transmitted through the measurement object 110 has a phase difference δ due to birefringence, so that the light passes through the measurement object 110. The resulting light becomes elliptically polarized light, is polarized by the second polarizing plate 105, and is transmitted. As shown in the equation (3), the intensity I of the transmitted light changes according to the angle φ formed by the polarization direction and the principal stress direction of the first polarizing plate 102. As a result, the first polarizing plate 102 and the second polarizing plate are rotated so that the angle of the polarization direction of the visible light incident on the measurement object 110 changes while maintaining the state in which the polarization directions differ from each other by 90 °. Then, light and darkness occurs in the light imaged by the camera 106, and the photoelastic fringes are imaged corresponding to the rotation angle of the first polarizing plate 102. Based on the image of the photoelastic fringes captured by the camera 106, the principal stress direction in the measurement object 110 can be detected.

As described above, the photoelastic stress measuring device 100 _{can detect the principal stress difference (σ 1} − σ ₂ ) and the principal stress direction as photoelastic parameters. Here, when the stress field to be evaluated is isotropic, the principal stress difference (σ ₁ − σ ₂ ) becomes 0 (σ ₁ − σ ₂ = 0), so the phase difference δ is also 0 from Eq. (1). Therefore, the detected light intensity I also becomes 0. Therefore, in the photoelastic method, when the light transmitted through the measurement object 110 is detected by using the photoelastic stress measuring device 100 shown in FIG. 3, the portion where the detected light intensity becomes 0 is the measurement object 110. It can be judged that the stress state is isotropic.

Further, in the photoelastic stress measuring device 100 shown in FIG. 3, when light is detected using the configuration in which the λ / 4 wave plates 103 and 104 are removed, the first polarizing plate 102 and the second polarizing plate 105 are rotated. It can be determined that the portion where the detected light is always 0 when the polarization direction is changed is in an isotropic stress state in the measurement object 110. Therefore, in the photoelastic method, even if the photoelastic stress measuring device 100 having the configuration in which the λ / 4 wave plates 103 and 104 are removed is used, the portion where the detected light is always 0 is isotropic in the measurement object 110. It can be judged that it is in a stress state.

However, in the stress measurement by the photoelastic method using the conventional photoelastic stress measuring device 100 described above, since the visible light emitted from the visible light source 101 is used, the visible light is used as the measurement object 110. It was limited to those made of permeable transparent materials. On the other hand, since the resin material constituting the coating or coating used for anticorrosion against actual structures is opaque to visible light, the photoelastic method using visible light is used. Was difficult to apply.

Therefore, the present inventor came up with the idea of using a terahertz wave, which is a kind of electromagnetic wave, instead of visible light, and studied an abnormality detection method by a photoelastic method using a terahertz wave. Most of the terahertz waves are transmitted when irradiated with a non-metal material such as resin, while most of them are reflected when irradiated with a metal material. The present inventor pays attention to the property of the terahertz wave, and by using it in combination with the principle of the photoelastic method in which the birefringence phenomenon of electromagnetic waves occurs, the principal stress is also applied to a resin which is a non-metal layer opaque to visible light. I came up with the idea that it is possible to measure the direction and detect whether the stress is isotropic or not. By measuring the main stress direction in the anticorrosion layer by the diligent study of the present inventor, it becomes possible to measure the abnormality at an arbitrary position of the anticorrosion layer in close contact with the surface of the structure in a non-contact manner. Furthermore, the present inventor has conceived that a photoelastic method using a terahertz wave (terahertz wave photoelastic method) is also possible because most of the terahertz wave is reflected when the metal material is irradiated. The present invention described below has been devised by the above diligent studies.

(First Embodiment)
(Abnormality detection device)
FIG. 1 is a diagram showing a configuration of an abnormality detection device according to the first embodiment of the present invention. As shown in FIG. 1, the abnormality detection device 1 according to the first embodiment includes an analysis control unit 10, a terahertz wave transmitter 11, and a terahertz wave detector 12. In the steel structure 15 to be measured in the first embodiment, an anticorrosion layer 15b made of a non-metal layer is provided on the surface of the steel material 15a as a metal substrate.

The anomaly detection device 1 is configured to be able to irradiate the surface of the steel structure 15 by polarized the _{terahertz wave L 1} and to be able to detect _{the terahertz wave L 2 reflected from the steel structure 15 after being polarized.} It consists of a reflected terahertz wave measuring device. That is, the abnormality detecting device 1 has both a terahertz wave transmitting means and a terahertz wave detecting means. Here, the terahertz wave is an electromagnetic wave belonging to the so-called terahertz region, which is a frequency region of about ^{1 terahertz (1 THz = 10 12} Hz), specifically, a frequency region on the order of 100 GHz to 10 THz (10 ¹¹ to 10 ^{13 Hz).} The terahertz region is a frequency region that has both straightness of light and transmission of radio waves. In the first embodiment, the frequency of the terahertz wave can be selected according to conditions such as the material and thickness of the anticorrosion layer 15b, and the attenuation (transmittance) of the terahertz wave in the anticorrosion layer 15b. May be selected by.

The terahertz wave transmitter 11 as a terahertz wave transmitting means has, for example, a terahertz wave generating element 11a equipped with a resonance tunneling diode (RTD) or the like, a hemispherical lens 11b, a collimating lens 11c, and an objective lens 11d. It is composed. A light conduction antenna (PCA: Photo Conductive Antenna) may be used instead of the resonance tunnel diode. On the transmitting side of the terahertz wave transmitter 11, a first polarizing plate 13a as a transmitting side linearly polarizing means and a λ / 4 wave plate 14a as a transmitting side phase conversion means are provided. The linearly polarized light means functions as a phase conversion means for performing phase conversion on an electromagnetic wave. The polarization direction of the first polarizing plate 13a and the main axis direction of the λ / 4 wave plate 14a are provided so as to be different from each other by 45 °. The terahertz wave transmitter 11, the first polarizing plate 13a, and the λ / 4 wave plate 14a constitute an optical system arranged linearly, but are not necessarily limited to the case where they are arranged linearly. and further includes a reflecting mirror for reflecting the terahertz wave L _1, it may be an optical system for bending the terahertz wave. Terahertz wave transmitter 11, outgoing optical system composed of the first polarizing plate 13a, and lambda / 4 wave plate 14a is a terahertz wave L _1p is linearly polarized light of the terahertz wave L _1, the plane of the steel structures 15 It is configured to be able to irradiate at a predetermined angle α.

The terahertz wave detector 12 as a terahertz wave detecting means includes, for example, a terahertz wave detecting element 12a made of an RTD, a hemispherical lens 12b, and a condenser lens 12c. The terahertz wave detector 12 is provided in the abnormality detecting device 1 in a state where the reflected waves of the terahertz wave (terahertz waves L ₂ , L _{2p) can be received by the terahertz wave detecting element 12a.} On the detection side of the terahertz wave detector 12, a second polarizing plate 13b as a detection-side linearly polarizing means and a λ / 4 wave plate 14b as a detection-side phase conversion means are provided. The main axis direction of the λ / 4 wave plate 14b and the polarization direction of the second polarizing plate 13b are provided so as to be different from each other by 45 °.

The first polarizing plate 13a and the second polarizing plate 13b are provided so that the polarization directions differ from each other by 90 °. Here, the fact that the first polarizing plate 13a and the second polarizing plate 13b are provided so that the polarization directions differ by 90 ° means that the λ / 4 wavelength plates 14a and 14b are not provided and the compound refraction phenomenon occurs. The terahertz wave reflected on a predetermined surface does not pass through the second polarizing plate 13b after being linearly polarized by the first polarizing plate 13a in a state where no member is provided. Is to become. Further, due to the relationship between the first polarizing plate 13a and the second polarizing plate 13b described above, the λ / 4 wave plates 14a and 14b differ from each other by 90 ° in the principal axis direction.

In the abnormality detection device 1 configured as described above, the terahertz composed of at least a terahertz wave transmitter 11, a terahertz wave detector 12, a first polarizing plate 13a, a second polarizing plate 13b, and a λ / 4 wave plate 14a, 14b. The wave optical system is integrally tradable relative to the steel structure 15. As a result, the abnormality detection device 1 is configured to be able to irradiate the _{terahertz wave L 1} and detect the reflected terahertz wave while scanning a predetermined range on the surface of the steel structure 15. As a scanning mechanism for scanning the terahertz wave optical system of the abnormality detection device 1 relative to the surface of the steel structure 15, various conventionally known scanning mechanisms can be adopted, and further, scanning is performed manually. It is also possible to make it.

The analysis control unit 10 as an analysis means and a control means includes a signal amplification unit 10a, a bias generation unit 10b, a lock-in detection unit 10c, and an analysis processing unit 10d. The analysis control unit 10 performs various controls on the terahertz wave transmitter 11. Further, the analysis control unit 10 performs various processes on the terahertz wave signal detected by the terahertz wave detector 12. The signal amplification unit 10a amplifies the signal detected by the terahertz wave detector 12 and outputs it to the lock-in detection unit 10c as terahertz wave reception data. The bias generation unit 10b generates a bias voltage to bias the terahertz wave generating element 11a and the terahertz wave detecting element 12a, thereby changing the transmitted terahertz wave or the detected terahertz wave according to the bias voltage. The terahertz wave transmitted or detected by the terahertz wave generating element 11a and the terahertz wave detecting element 12a may be weak. In this first embodiment, an example is shown in which the transmitted or detected terahertz wave is weak, and lock-in detection is used for the detection of the terahertz wave. At the time of lock-in detection, in the terahertz wave transmitter 11, the noise component of the terahertz wave detection signal is removed by using the reference signal modulated as the bias voltage of the terahertz wave generating element 11a. As a result, even if the transmitted or detected terahertz wave is weak, the detection can be performed with high accuracy. The analysis processing unit 10d as an analysis processing means includes a predetermined recording unit (not shown) for storing the detected terahertz wave reception data, and performs analysis processing on the terahertz wave reception data.

(Abnormality detection method)
Next, an abnormality detection method using the abnormality detection device 1 configured as described above will be described. As described above, the steel structure 15 is provided with the anticorrosion layer 15b on the steel surface 15as of the steel material 15a. The steel material 15a is a typical material generally used in structures such as bridges and pipes. The steel structure 15 includes, for example, a steel structure having a coating and covering, and a non-metal layer on the upper layer of the base, with a predetermined surface of a metal base such as aluminum (Al) or stainless steel (SUS) as a base. Can be various objects formed by.

The anticorrosion layer 15b functions as an anticorrosion layer on the steel surface 15as of the underlying steel material 15a, and also includes an adhesive and the like. The anticorrosion layer 15b is provided in close contact with the steel surface 15as of the steel material 15a. Therefore, when strain is generated in the steel material 15a to which the anticorrosion layer 15b is in close contact due to stress, most of the generated strain is propagated to the anticorrosion layer 15b, and strain similar to that of the steel material 15a is also generated in the anticorrosion layer 15b. In this case, in the normal portion where the anticorrosion layer 15b is normally in close contact with the steel surface 15as, the stress state in the anticorrosion layer 15b is due to the isotropic tensile residual stress and the strain caused by the dead load of the steel structure 15. It is in a state where stress is superimposed. On the other hand, in the abnormal portion 15d in which the anticorrosion layer 15b is not normally adhered to the steel surface 15as, the adhesion between the anticorrosion layer 15b and the steel material 15a is deteriorated or the lower part of the anticorrosion layer 15b is corroded. In this case, since there is no drag due to the adhesion of the anticorrosion layer 15b to the steel surface 15as, only isotropic compression residual stress remains.

In steel structures 15 anticorrosion layer 15b is provided on the steel surface 15As, it emits the terahertz wave L ₁ toward the surface 15bs of the anticorrosion layer 15b from the terahertz wave oscillator 11 of the abnormality detecting apparatus 1. Specifically, the terahertz wave generated in the terahertz wave generating element 11a is emitted as a _{terahertz wave L 1} via the hemispherical lens 11b, the collimating lens 11c, and the objective lens 11d. Here, the transmitted terahertz wave L ₁ is typically a continuously transmitted terahertz continuous wave, but may be an intermittently transmitted terahertz pulse wave or tone burst wave.

_{The terahertz wave L 1} transmitted from the terahertz wave transmitter 11 is linearly polarized by the first polarizing plate 13a. The linearly polarized terahertz wave that has passed through the first polarizing plate 13a passes through the λ / 4 wave plate 14a and becomes circularly polarized light. The circularly polarized terahertz wave L _1p is incident on the anticorrosion layer 15b of the steel structure 15 at an incident angle of a predetermined angle α. The terahertz wave L _1p incident on the anticorrosion layer 15b is completely reflected by the steel surface 15as while birefringence corresponding to the strain occurs in the anticorrosion layer 15b. _{The terahertz wave L 2} completely reflected on the steel surface 15 as is emitted from the surface 15 bs while birefringence corresponding to the strain occurs in the anticorrosion layer 15 b.

_{The terahertz wave L 2} emitted from the surface 15 bs causes a phase difference δ by birefringence and is polarized into elliptically polarized light or circularly polarized light. The terahertz wave L ₂ passes through the λ / 4 wave plate 14b to become linearly polarized light, and then the terahertz wave L _2p, which is a polarizing component that has passed through the second polarizing plate 13b, is detected by the terahertz wave detector 12. .. As a result, the intensity of the terahertz wave depending on the phase difference δ generated by the birefringence in the anticorrosion layer 15b is detected by the terahertz wave detector 12.

_{As described above, the intensity of the terahertz wave L 2p} detected by the terahertz wave detector 12 is a physical quantity proportional to the principal stress difference (σ ₁ − σ _{2) of the anticorrosion layer 15b.} Therefore, in the normal portion of the anticorrosion layer 15b, the principal stress difference (σ ₁ − σ ₂ ) does not become 0, and the terahertz wave L _2p is detected by the terahertz wave detector 12. On the other hand, in the abnormal portion of the anticorrosion layer 15b, the principal stress difference (σ ₁ − σ ₂ ) becomes 0, so that the detection intensity of the _{terahertz wave L 2p becomes extremely small.} Further, the above-mentioned scanning mechanism causes the above-mentioned terahertz wave optical system to scan a predetermined range along the surface of the steel structure 15. As a result, the terahertz wave intensity distribution according to the strain of the anticorrosion layer 15b is detected by the terahertz wave detector 12 in a predetermined range of the surface 15bs of the steel structure 15. The intensity distribution of the terahertz wave detected by the terahertz wave detector 12 is obtained as the distribution of the uniform color lines of the photoelastic stripes of the terahertz wave in the anticorrosion layer 15b. In addition, the portion where the detection intensity of the terahertz wave L _2p is minimized is detected as an abnormal portion in the anticorrosion layer 15b. The calculation for detecting these abnormal portions is executed by the analysis processing unit 10d of the analysis control unit 10 or the like.

According to the abnormality detection method according to the first embodiment described above, the terahertz wave is irradiated to the steel structure 15, and the principal stress of the anticorrosion layer 15b is based on the intensity of the terahertz wave reflected by the steel surface 15as of the steel material 15a. The difference (σ ₁ − σ ₂ ) can be derived. Therefore, by detecting the portion where the intensity of the reflected terahertz wave becomes the minimum and the principal stress difference (σ ₁ − σ ₂ ) becomes 0, the degree of adhesion of the anticorrosion layer 15b to the steel surface 15as is reduced. It becomes possible to detect the part.

(Second embodiment)
Next, the abnormality detection device and the abnormality detection method according to the second embodiment of the present invention will be described. FIG. 2 is a diagram showing a configuration of an abnormality detection device according to the second embodiment.

(Abnormality detection device)
As shown in FIG. 2, the abnormality detection device 2 has a configuration in which the λ / 4 wave plates 14a and 14b are not provided in the abnormality detection device 1. Further, the abnormality detecting device 2 is provided with a first polarizing plate 21a and a second polarizing plate 21b corresponding to the first polarizing plate 13a and the second polarizing plate 13b in the abnormality detecting device 1, respectively. The first polarizing plate 21a and the second polarizing plate 21b are each composed of disk-shaped polarizing plates having the same diameter, and have a disk gear shape in which external teeth having the same pitch are formed on the outer peripheral portion of the disk shape. Have.

In the abnormality detecting device 2, a polarizing plate synchronous rotation mechanism 22 is provided between the first polarizing plate 21a and the second polarizing plate 21b. The polarizing plate synchronous rotation mechanism 22 includes a turning head 22a, a gear box 22b, and a polarizing plate synchronous rotation gear 22c. The swivel head 22a is connected to the polarizing plate synchronous rotation gear 22c via a conventionally known gear box 22b. By rotating the swivel head 22a around the rotation shaft O, the polarizing plate synchronous rotation gear 22c is rotated via a plurality of gears in the gearbox 22b. External teeth that mesh with the external teeth of the outer peripheral portions of the first polarizing plate 21a and the second polarizing plate 21b are formed on the outer peripheral portion of the polarizing plate synchronous rotary gear 22c. By engaging the external teeth of the polarizing plate synchronous rotation gear 22c with the external teeth of the first polarizing plate 21a and the second polarizing plate 21b, the first polarizing plate 21a and the first polarizing plate 21a and the first polarizing plate 21a and the first polarizing plate 21a and the first 2 The polarizing plate 21b is configured to be rotatable in the same rotation direction. Here, the outer diameter of the first polarizing plate 21a and the outer diameter of the second polarizing plate 21b are the same as each other. Therefore, when the turning head 22a is rotated to rotate the polarizing plate synchronous rotation gear 22c, the first polarizing plate 21a and the second polarizing plate 21b differ in the polarization direction by a predetermined polarization direction, here, by an angle of 90 °. It rotates in the same direction of rotation while maintaining the state of rotation. Other configurations are the same as those of the abnormality detection device 1.

(Abnormality detection method)
Next, an abnormality detection method using the above-mentioned abnormality detection device 2 will be described. That is, as shown in FIG. 2, the terahertz wave L ₁ emitted from the terahertz wave oscillator 11, after being polarized into linearly polarized light passes through the first polarizer 21a, enters the anticorrosion layer 15b of steel structures 15 Will be done. _{The terahertz wave L 1p} incident on the anticorrosion layer 15b is completely reflected by the steel surface 15as of the steel material 15a and is emitted through the anticorrosion layer 15b. In this state, the polarizing plate synchronous rotation gear 22c is rotated to rotate the first polarizing plate 21a and the second polarizing plate 21b while maintaining a state in which the polarization directions differ from each other by 90 °.

As described above, the stress state of the anticorrosion layer 15b is not isotropic, that is, has anisotropy in the normal portion where the anticorrosion layer 15b is in close contact with the steel surface 15as. _{Therefore, as shown in Eq. (3), the intensity of the terahertz wave L 2P} transmitted through the second polarizing plate 21b with the rotation of the first polarizing plate 21a and the second polarizing plate 21b is light and dark, that is, maximum and minimum. It changes to repeat.

On the other hand, in the abnormal portion where the anticorrosion layer 15b is not in close contact with the steel surface 15as, the stress of the anticorrosion layer 15b is isotropic, so that δ = 0 in the equation (3). Therefore, even if the first polarizing plate 21a and the second polarizing plate 21b are rotated, the _{intensity of the terahertz wave L 2p} transmitted through the second polarizing plate 21b is maintained at the minimum state.

That is, unlike the case where the normal portion of the anticorrosion layer 15b described above is irradiated with the terahertz wave, the maximum and the minimum due to the rotation of the first polarizing plate 21a and the second polarizing plate 21b are detected without alternately appearing. The intensity of the terahertz wave L _2p is kept at a minimum. As a result, even if the first polarizing plate 21a and the second polarizing plate 21b are rotated _{, the portion where the intensity of the detected terahertz wave L 2p} is maintained at the minimum is detected as an abnormal portion in the anticorrosion layer 15b. can. The calculation for detecting these abnormal portions is executed by the analysis processing unit 10d of the analysis control unit 10 or the like.

Further, by the above-mentioned scanning mechanism (not shown), a second terahertz wave optical system in which at least a terahertz wave transmitter 11, a terahertz wave detector 12, a first polarizing plate 21a, and a second polarizing plate 21b are integrated is provided. A predetermined range is scanned along the surface of the steel structure 15. As a result, the terahertz wave detector 12 detects the intensity distribution of _{the terahertz wave L 2p} along the principal stress direction of the anticorrosion layer 15b in a predetermined range of the steel structure 15. _{The intensity distribution of the terahertz wave L 2p} detected by the terahertz wave detector 12 is obtained as an isobaric line of the terahertz wave in the anticorrosion layer 15b. When the anticorrosion layer 15b is in close contact with the steel material 15a, the obtained photoelastic stripes have the same inclination line in the steel material 15a.

(Modification example)
Next, a modified example of the abnormality detection method according to the second embodiment described above will be described. That is, in the abnormality detection device 2 shown in FIG. 2, the first polarizing plate 21a and the second polarizing plate 21b rotate in the same rotation direction while maintaining a state in which the polarization directions differ by 90 °. In this case, the detection intensity at a position in an arbitrary polarization direction and the position where the first polarizing plate 21a and the second polarizing plate 21b are rotated by 45 ° while maintaining a state in which the polarization directions differ by 90 ° from that position. detects the intensity of the terahertz wave L _2p, by adding the intensities of the two detected terahertz waves L _2p, it is also possible to determine the principal stress difference (σ ₁ -σ _2).

More specifically, the intensity I ₁ of the light detected in an arbitrary polarization direction is the angle φ between the phase difference δ caused by birefringence and the principal stress direction and the polarization direction, as shown in the following equation (4). Depends on.
I ₁ = A ² sin ² 2φ ・ sin ² (δ / 2)… (4)
Note that A is the amplitude of the incident light.

Further, from the position where the light intensity I ₁ is detected, the first polarizing plate 21a and the second polarizing plate 21b are detected at a position rotated by 45 ° while maintaining a state in which the polarization directions differ from each other by 90 °. _{The intensity I 2} of the light to be formed is as shown in Eq. (5).
I ₂ = A ² sin ² 2 (φ + π / 4) ・ sin ² (δ / 2)… (5)

When the light intensities I ₁ and I ₂ detected as described above are combined, the combined light intensity I is the angle φ between the principal stress direction and the polarization direction as shown in the following equation (6). Does not depend on.
I = I ₁ + I ₂ = A ² sin ² (δ / 2)… (6)
This means that in the photoelastic method, the same result as when circularly polarized light is used can be obtained. As a result, the abnormality detecting device 2 can derive both the principal stress direction and the principal stress difference (σ ₁ − σ _{2) of the anticorrosion layer 15b.} Other configurations are the same as those of the second embodiment described above.

According to the abnormality detection method according to the second embodiment described above, the terahertz wave is irradiated to the steel structure 15, and the isotropic layer of the anticorrosion layer 15b is based on the intensity of the terahertz wave reflected by the steel surface 15as of the steel material 15a. Can detect the specific part. Therefore, with a simple configuration, it is possible to detect an abnormal portion in which the degree of adhesion of the anticorrosion layer 15b to the steel material 15a is reduced from a predetermined range on the surface of the steel structure 15.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications based on the technical idea of the present invention are possible. For example, the configurations of the anomaly detection devices 1 and 2 described in the first embodiment described above are merely examples, and the principal stress difference and the principal stress direction of the non-metal layer in close contact with the surface of the structure using the terahertz wave. If necessary, a device having a different configuration may be used as long as the configuration is such that the above can be measured. Further, the present invention is not limited by the description and drawings which form a part of the disclosure of the present invention according to the above-described embodiment.

For example, in the above-described embodiment, the terahertz wave is spot-irradiated to the steel structure 15 and is spot-reflected by the steel surface 15as of the steel material 15a, but the steel structure 15 is not necessarily spot-irradiated and reflected. Not limited. For example, instead of the terahertz wave transmitter 11, a terahertz wave light source capable of emitting a terahertz wave in a planar manner is used, and instead of the terahertz wave detector 12, a terahertz wave L _2p can be detected as a planar distribution. It is also possible to use a wave detection array or the like.

For example, in the second embodiment described above, in the abnormality detection device 2, a mechanism for rotating the first polarizing plate 21a and the second polarizing plate 21b while maintaining the polarization directions different from each other by 90 °. However, the polarizing plate synchronous rotation mechanism 22 is used, but the mechanism is not necessarily limited to this mechanism. If it is possible to rotate the first polarizing plate 21a and the second polarizing plate 21b while maintaining the polarization directions different from each other by 90 °, it is possible to adopt various conventionally known rotation mechanisms. be.

For example, in the above-described embodiment, the anomaly detection devices 1 and 2 have an optical system for emitting a terahertz wave toward the steel structure 15 and an optical system for detecting the terahertz wave reflected by the steel surface 15as. The system is configured to be non-coaxial with different optical axes, but it is not necessarily limited to non-coaxial. Specifically, by using a half mirror or the like, it is possible to configure the optical system that emits the terahertz wave and the optical system that detects the reflected terahertz wave to be coaxial in which the optical axes overlap.

1, 2 Abnormality detection device 10 Analysis control unit 10a Signal amplification unit 10b Bias generation unit 10c Lock-in detection unit 10d Analysis processing unit 11 Terahertz wave transmitter 11a Terahertz wave generator 11b, 12b Hemispherical lens 11c Collimated lens 11d Objective lens 12 Terahertz Wave detector 12a Terahertz wave detection element 12c Condensing lens 13a, 21a First polarizing plate 13b, 21b Second polarizing plate 14a, 14b λ / 4 wave plate 15 Steel structure 15a Steel material 15as Steel surface 15b Anticorrosion layer 15bs Surface 15d Abnormality Part 22 Polarizing plate synchronous rotation mechanism 22a Swivel head 22b Gearbox 22c Polarizing plate synchronous rotation gear L ₁ , L _1p , L ₂ , L _2p Terahertz wave

Claims (4)

A terahertz wave transmitting means capable of irradiating a predetermined position on the surface of an object provided with a non-metal layer on a metal substrate and scanning the surface of the object, and the object. It is configured to be able to detect the terahertz wave reflected at the predetermined position, and is provided with a terahertz wave detecting means capable of scanning the surface of the object and a terahertz wave emitting side of the terahertz wave transmitting means. Abnormality provided with the transmitting side linear polarizing means and the detecting side linear polarizing means provided on the detection side of the terahertz wave detecting means so that the polarization direction differs from the polarization direction of the transmitting side linear polarizing means by 90 °. In the abnormality detection method by the detection device,
The transmitting side linearly polarizing means and the detecting side linearly polarizing means are configured to rotate while maintaining a state in which the polarization direction of the transmitting side linearly polarizing means and the polarization direction of the detecting side linearly polarizing means differ by 90 °. Being done
A portion where the intensity of the reflected terahertz wave detected by the terahertz wave detecting means is maintained at a minimum without increasing or decreasing with the rotation of the transmitting side linearly polarizing means and the detecting side linearly polarizing means is referred to as the metal substrate. An abnormality detection method comprising determining an abnormal portion having a reduced degree of adhesion to the non-metal layer. A terahertz wave transmitting means capable of irradiating a predetermined position on the surface of an object provided with a non-metal layer on a metal substrate and scanning the surface of the object, and the object. It is configured to be able to detect the terahertz wave reflected at the predetermined position, and is provided with a terahertz wave detecting means capable of scanning the surface of the object and a terahertz wave emitting side of the terahertz wave transmitting means. The detection side linear polarization means provided on the detection side of the transmission side linear polarization means and the terahertz wave detection means so that the polarization direction differs from the polarization direction of the transmission side linear polarization means by 90 °, and the terahertz wave transmission. The transmitting side phase conversion means provided on the emitting side of the means and giving a phase difference so that the linearly polarized terahertz wave transmitted through the transmitting side linear polarizing means becomes circularly polarized, and the detection side linear polarizing means are described above. In an abnormality detection method using an abnormality detection device provided on the incident side of a terahertz wave and provided with a detection side phase conversion means for giving a phase difference to the terahertz wave.
While scanning a predetermined range along the surface of the object, the terahertz wave emitted from the terahertz wave transmitting means irradiates the non-metal layer, and the reflected terahertz wave is detected by the terahertz wave detecting means. in the terahertz wave intensity distribution of which is the reflection obtained by detecting a portion where the detection intensity becomes minimum degree of adhesion between the non-metal layer and the metal substrate and judging the abnormal point with a reduced Abnormality detection method. The metal substrate is a steel material, and the non-metal layer is a resin layer opaque to visible light.
The abnormality detection method according to claim 1 or 2, wherein the abnormality is detected. The intensity of the terahertz wave detected by the terahertz wave detecting means is defined as the intensity based on a physical quantity proportional to the principal stress difference of the resin layer, and the portion where the physical quantity becomes 0 is determined to be an abnormal portion in the resin layer.
The abnormality detection method according to claim 3, wherein the abnormality is detected.

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