8.6 Faseroptische Sensorik
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- Distributed acoustic sensing (29)
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Organisationseinheit der BAM
- 8 Zerstörungsfreie Prüfung (237)
- 8.6 Faseroptische Sensorik (237)
- 8.1 Sensorik, mess- und prüftechnische Verfahren (28)
- 3 Gefahrgutumschließungen; Energiespeicher (26)
- 8.4 Akustische und elektromagnetische Verfahren (20)
- 7 Bauwerkssicherheit (17)
- 2 Prozess- und Anlagensicherheit (16)
- 8.2 Zerstörungsfreie Prüfmethoden für das Bauwesen (16)
- 7.4 Baustofftechnologie (14)
- 1 Analytische Chemie; Referenzmaterialien (13)
The use of artificial neural networks (ANNs) is demonstrated for efficient real-time data processing in optical fiber sensing applications. Using ANN-based algorithms, two orders of magnitude improved computation time and improved measurement resolution is achieved for distributed strain sensing using the wavelength-scanning coherent optical time domain reflectometry technique.
The distributed measurement of relative humidity is a sought-after capability for a wide range of applications in civil engineering and structural health monitoring. We show that polymethyl methacrylate (PMMA) optical fi-bers can be employed as a sensor medium to conduct distributed humidity measurement by analyzing Rayleigh backscattering traces obtained by OTDR. We make use of the effect that water penetrates the fiber core and directly influences the local fiber attenuation and Rayleigh backscatter coefficient. We conducted distributed backscattering analysis for two different pulse wavelengths: 500 nm and 650 nm. The 650 nm results are susceptible to both, attenuation changes and backscatter changes, whereas backscatter results at 500 nm are not affected by humidity-induced attenuation and only exhibit a change of Rayleigh backscattered power as a function of humidity. The combined measurement and analysis of both parameters at these two wavelengths has the advantage that cross-sensitivities on backscatter change and attenuation, such as strain and tempera-ture changes, could be separated from the humidity response of the fiber. We present laboratory results for a humidity range between 30% and 90% for both pulse wavelengths: including step responses, humidity cycles and hysteresis analysis. In addition to the attenuation and backscatter coefficient dependence, we also analyze optical runtime changes as a function of humidity. POFs have the advantage that they can be directly embed-ded into materials such as concrete or soil to measure water content or localize water ingress. Standard step-index PMMA POFs can be used as a distributed relative humidity sensor up to 200 m distance.
We present our research on the development of a Brillouin optical frequency-domain analysis (BOFDA) using a perfluorinated graded-index polymer optical fiber (PFGI-POF) as a sensing fiber. The described works include investigations both on the selection of the setup components with respect to mode coupling effects and on the impact of the humidity cross-sensitivity. The suitability of the developed POF-based BOFDA is proved by a distributed measurement on an 86 m long PFGI-POF recorded with the spatial resolution of 6 m.
Humidity is one of principal environmental parameters that plays an important role in various application areas. Distributed humidity/water sensing is sought after in wide range of applications including concrete condition monitoring in civil engineering, SHM of large structures such as dykes or dams, soil moisture measurement in agriculture or leak detection in pipeline or sewage industry. Using humidity-induced strain of specialty hygroscopic coating materials, such as polyimide (PI) seems as the most promising approach so far. In this work, relative humidity and temperature response of different commercial PI-coated and tight-buffer fibers is investigated for the development of distributed humidity sensor.
Humidity is one of principal environmental parameters that plays an important role in various application areas. Using measurement of strain induced in an optical fiber by a water swellable coating represents a promising approach for realization of distributed humidity sensing (DHS). In this work, humidity and temperature response of four different commercial PI-coated fibers and four tight-buffered (TB) fibers is investigated with the aim of evaluating their potential for development of DHS in context of water ingress sensor for high-voltage power cable splices. PI-coated fibers exhibited close-to-linear humidity and temperature response. While the temperature response is relatively coating-independent, magnitude of humidity response was broadly correlated to the relative fiber-to-coating thickness ratio. In contrast, both humidity and temperature response of TB fibers is strongly influenced by buffer type, with Leoni TB900L fiber with Hytrel buffer exhibiting largest humidity and temperature sensitivity. While the response of tight-buffered fibers is generally nonlinear, roughly three-times higher humidity response can be achieved with TB900L compared to the most sensitive PI-coated fiber. Using the TB fiber can be, therefore, advantageous for simpler water detection applications, such as one targeted in this study, when larger sensitivity is more important than the linear response of the sensor.
In the present study, the impact of static traffic loading on the slight deflection effects in the concrete structure of an existing bridge has been investigated using distributed fiber optic sensors. In the face of increasing traffic density and severe traffic loading, the results of the load tests on the Amsterdam bridge 705 make an important contribution to the understanding of its structural behavior. The concept of the static loading was based on the use of two 36-ton trucks stopped on the bridge at multiple pre-determined locations. The load applied in this way led to location-dependent small deflection effects recorded as longitudinal strain of the sensing fiber embedded at the underside of the bridge. The measurements were performed with a commercially-available solution based on Tunable Wavelength Coherent Optical Time Domain Reflectometry with the measurement accuracy in the range of 0.5 µm/m.
Pipe integrity is a central concern regarding technical safety, availability, and environmental compliance of industrial plants and pipelines. A condition monitoring system that detects and localizes threats in pipes prior to occurrence of actual structural failure, e.g., leakages, especially needs to target transient events such as impacts on the pipe wall or pressure waves travelling through the medium. In the present work, it is shown that fiber-optic distributed acoustic sensing (DAS) in conjunction with a suitable application geometry of the optical fiber sensor allows to track propagating acoustic waves in the pipeline wall on a fast time-scale. Therefore, short impacts on the pipe may be localized with high fidelity. Moreover, different acoustic modes are identified, and their respective group velocities are in good agreement with theoretical predications. In another set of experiments modeling realistic damage scenarios, we demonstrate that pressure waves following explosions of different gas mixtures in pipes can be observed. Velocities are verified by local piezoelectric pressure transducers. Due to the fully distributed nature of the fiber-optic sensing system, it is possible to record accelerated motions in detail. Therefore, in addition to detection and localization of threatening events for infrastructure monitoring, DAS may provide a powerful tool to study the development of gas explosions in pipes, e.g., investigation of deflagration-to-detonation-transitions (DDT).
In the present study, the impact of static traffic loading on the slight deflection effects in the concrete structure of an existing bridge has been investigated using distributed fiber optic sensors. In the face of increasing traffic density and severe traffic loading, the results of the load tests on the Amsterdam bridge 705 make an important contribution to the understanding of its structural behavior. The concept of the static loading was based on the use of two 36-ton trucks stopped on the bridge at multiple pre-determined locations. The load applied in this way led to location-dependent small deflection effects recorded as longitudinal strain of the sensing fiber embedded at the underside of the bridge. The measurements were performed with a commercially-available solution based on Tunable Wavelength Coherent Optical Time Domain Reflectometry with the measurement accuracy in the range of 0.5 µm/m.
Wavelength-scanning distributed acoustic sensing for structural monitoring and seismic applications
(2019)
We introduce wavelength-scanning coherent optical time domain reflectometry (WS-COTDR) for dynamic vibration sensing along optical fibers. The method is based on spectral shift computation from Rayleigh backscatter spectra. Artificial neural networks (ANNs) are used for fast and high-resolution strain computation from raw measurement data. The applicability of the method is demonstrated for vibration monitoring of a reinforced concrete bridge. We demonstrate another application example for quasi-static and dynamic measurement of ground deformation and surface wave propagation along a dark fiber in a telecommunication cable.
Wavelength-scanning distributed acoustic sensing for structural monitoring and seismic applications
(2019)
We introduce wavelength-scanning coherent optical time domain reflectometry (WS-COTDR) for dynamic vibration sensing along optical fibers. The method is based on spectral shift computation from Rayleigh backscatter spectra. Artificial neural networks (ANNs) are used for fast and high-resolution strain computation from raw measurement data. The applicability of the method is demonstrated for vibration monitoring of a reinforced concrete bridge. We demonstrate another application example for quasi-static and dynamic measurement of ground deformation and surface wave propagation along a dark fiber in a telecommunication cable.
Auf der Grundlage der in DIN EN 61757-2-2:2017 beschriebenen Standardisierungsmethoden wurden in dieser Arbeit wichtige Leistungsparameter von vier kommerziellen Messsystemen zur ortsaufgelösten faseroptischen Erfassung der temperatur- und dehnungsabhängigen Brillouin-Frequenzverschiebung untersucht. Gemäß der oben genannten Norm konzentrierte sich hier die Ermittlungsprüfung auf messtechnische Aspekte reiner Temperaturmessungen. Dabei diente die Ermittlung von einem festgelegten Satz dreier Betriebsverhaltenskenngrößen in Form von quantitativen Angaben des Messfehlers, der Wiederholgenauigkeit sowie der räumlichen Unsicherheit einem Vergleich der getesteten Messsysteme.
Alle faseroptischen Messungen wurden mit einer Faserschleife ausgeführt, d. h. als Sensorkonfiguration der Messfaser wurde eine Schleifenanordnung gewählt. Die Messverfahren der getesteten Messysteme basierten somit auf der Brillouin-optischen Zeit- bzw. Frequenzbereichsanalyse. Die Betriebsverhaltenskenngrößen wurden ferner bei unterschiedlichen Werten zweier messtechnischer Parameter, des Frequenzschrittes und der Mittelungsrate, für Standardeinstellungen der Laserleistungswerte der in die Sensorfaser einzukoppelnden Laserlichtsignale ermittelt. Auf diesem Weg lassen sich relevante Aussagen zur Optimierung der Messgenauigkeiten in Bezug auf Messdauer treffen.
Auf der Grundlage der in DIN EN 61757-2-2:2017 beschriebenen Standardisierungsmethoden wurden in dieser Arbeit wichtige Leistungsparameter von vier kommerziellen Messsystemen zur ortsaufgelösten faseroptischen Erfassung der temperatur- und dehnungsabhängigen Brillouin-Frequenzverschiebung untersucht. Gemäß der oben genannten Norm konzentrierte sich hier die Ermittlungsprüfung auf messtechnische Aspekte reiner Temperaturmessungen. Dabei diente die Ermittlung von einem festgelegten Satz dreier Betriebsverhaltenskenngrößen in Form von quantitativen Angaben des Messfehlers, der Wiederholgenauigkeit sowie der räumlichen Unsicherheit einem Vergleich der getesteten Messsysteme.
Alle faseroptischen Messungen wurden mit einer Faserschleife ausgeführt, d. h. als Sensorkonfiguration der Messfaser wurde eine Schleifenanordnung gewählt. Die Messverfahren der getesteten Messysteme basierten somit auf der Brillouin-optischen Zeit- bzw. Frequenzbereichsanalyse. Die Betriebsverhaltenskenngrößen wurden ferner bei unterschiedlichen Werten zweier messtechnischer Parameter, des Frequenzschrittes und der Mittelungsrate, für Standardeinstellungen der Laserleistungswerte der in die Sensorfaser einzukoppelnden Laserlichtsignale ermittelt. Auf diesem Weg lassen sich relevante Aussagen zur Optimierung der Messgenauigkeiten in Bezug auf Messdauer treffen.
For the purpose of increasing payload and reduce freight cost, lightweight composite tank containers used for Transportation have been progressively developed during the last years. Compared to conventionally produced cylindrical steel tanks, the fiber-reinforced solutions allow greater flexibility in the tank design. Despite a number of further material-related benefits of fiber-reinforced composites as non-conductive and non-magnetic behavior as well as corrosion resistance and high strength, the optimization of their thermal degradation properties during combustion is still a challenge. To improve the fire performance of lightweight composite containers, special intumescent fire protection coatings can be applied onto the outside tank surface. This paper presents fire tests on glass-fiber-reinforced plastic transport tanks with complex geometries sheltered with different surface-applied fire protection systems. To evaluate the fire resistance of the tank structures, a fiber optic monitoring system was developed. This system is based on distributed temperature measurements using high-Resolution optical backscatter reflectometry and pointwise reference measurements using fiber Bragg gratings. Thereby, all the fiber optic sensors were directly integrated in the composite layer structure of the tanks. The focus of the presented work is on the demonstration of capability of fiber optic monitoring system in such high-temperature application. Moreover, the fiber optic measurements provide new insights into the efficiency of intumescent coating applied for fire protection of fiber-reinforced plastic transport tanks.
We demonstrate the use of a 3D printed radial collimator in X-ray powder diffraction and surface sensitive grazing incidence X-ray diffraction. We find a significant improvement in the overall Signal to background ratio of up to 100 and a suppression of more than a factor 3⋅10⁵ for undesirable Bragg reflections generated by the X-ray “transparent” windows of the sample environment.
The background reduction and the removal of the high intensity signals from the windows, which limit the detector’s dynamic range, enable significantly higher sensitivity in experiments within sample environments such as vacuum chambers and gas- or liquid-cells. Details of the additively manufactured steel collimator geometry, alignment strategies using X-ray fluorescence, and data analysis are also briefly discussed. The flexibility and affordability of 3D prints enable designs optimized for specific detectors and sample environments, without compromising the degrees of freedom of the diffractometer.
Smart geosynthetics with embedded optical fibers as distributed sensors provide solutions both for applications in geotechnical engineering and for cost-effective monitoring of critical infrastructures. The incorporation of glass or polymer optical fibers (GOFs or POFs) in geotextiles and geogrids allows early detection of mechanical deformations, temperature and humidity. This paper presents selected examples of smart geosynthetics based on Brillouin and Rayleigh scattering effects in incorporated fiber optic sensors for monitoring of large geotechnical structures like dikes, dams, railways, embankments or slopes. The focus of the presented work is on real field tests of measurement capability with respect to the chosen measurement principle and used fiber type.
Kurzfassung. Die meisten Faserverbundbehälter, die in Europa für den Transport gefährlicher Stoffe oder als Speicherbehälter für Wasserstoff oder Erdgas in Fahrzeugen Verwendung finden, werden für eine nicht begrenzte Lebensdauer ausgelegt. In regelmäßigen Abständen sind für diese Druckbehälter wiederkehrende Prüfungen vorgeschrieben, die in der Regel aus visuellen Inspektionen und hydraulischen Innendruckprüfungen bestehen [1]. Die wiederkehrenden Prüfungen sind jedoch weder geeignet, die sichere Betriebsdauer festzulegen noch den Alterungszustand der Druckbehälter zu beurteilen. Aufgrund des weiter steigenden Drucks zur Kosten- und Gewichtsreduktion von Faserverbundbehältern und der damit einhergehenden Ausnutzung der existierenden Sicherheitsmargen gewinnen Methoden zur Beurteilung des Alterungsverhaltens dieser Druckbehälter immer mehr an Bedeutung.
Vor diesem Hintergrund wurde in der BAM das orhaben „Alterungsverhalten von Composite-Druckgefäßen mit Carbonfaser-Compositen unter gekoppelten Beanspruchungen (COD-AGE)“ gestartet, um die Alterung von Faserverbundbehältern mittels verschiedener zerstörungsfreier Prüfverfahren zu untersuchen. Die hier vorgestellten Ergebnisse wurden an einem Typ 4 Hybridbehälter mit Kunststoffliner gewonnen, in den im Rahmen des Herstellungsprozesses optische Glasfasern in verschiedenen Schichten integriert wurden. Der Behälter wurde mittels hydraulischem Innendruck und erhöhter Umgebungstemperatur zyklisch bis zum Lebensende belastet. Zwischen den einzelnen Lastsequenzen erfolgte eine an die wiederkehrende Prüfung im Betrieb angelehnte hydraulische Druckbelastung.
Sowohl die hydraulische Alterung als auch die Druckrampen wurden mittels Schallemissionsprüfung (SEP) und verteilter faseroptischer Sensorik mit dem Ziel einer frühzeitigen Versagensvorhersage überwacht. Durch die Schallemissionsanalyse sollte untersucht werden, ob zum Lebensende hin ein signifikanter Anstieg der Schallemissionsaktivität und -intensität, unterteilt in verschiedene Lastbereiche, beobachtet werden kann. Zusätzlich zum kontinuierlichen Monitoring der Zyklierung sollten die Druckrampen separat untersucht werden, um hier Potenziale für die wiederkehrende Prüfung zu erkennen.
We present the results of distributed fibre optic strain sensing for condition monitoring of a hybrid type IV composite fully wrapped pressure vessel using multilayer integrated optical fibres. During load cycle tests material fatigue could be localised and monitored 17,000 load cycles before burst. Results have been validated by acoustic emission analysis.