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A high-performance fiber Bragg grating-based (FBG) sensor device has been developed for the detection of small magnetic fields. Based on a smart multilayer jacket around the fibre over the physical length of the FBG, magnetic fields generated by rotating machine parts, power generators or power cable can be easily detected, analysed and evaluated. Consequently, this innovative, on-line and non-contact inspection method results in an increase in quality and reliability of high-performing machine parts, devices and cables. The basic physical principle is based on a magnetostrictive multilayer system that strains the high-resolution FBG element in presence of magnetic fields. Subsequently, a fixed relationship between induced magnetic field and wavelength change of the FBG element describes the characteristic sensitivity curve. Intensive tests regarding characterisation of this magnetic field FBG sensor have been carried out and its performance has been evaluated.
Sensors integrated into devices and structures provide essential data to control, optimize or manage machines and structural components. In the last years, processes, applications and machine parts became more and more intelligent. Consequently, the need for sensor validation increased significantly in order to rely on sensor data and measurement results.
Structure-integrated fibre optic strain sensors, such as fiber Bragg gratings (FBG), are of special interest in the composite manufacturing industry. This type of sensor makes it possible to gain information and to collect measurement data about entire production processes and whole life-time cycles of composite-made machine parts and structures. However, validation concepts and approaches for this type of sensors are barely reported in literature. Furthermore, all the reported activities have the drawback that the sensor diagnosis strategy is implemented as limited mathematical models and/or complex time-consuming spectral analysis tools which are applied in data post-processing loops. However, to automate sensor validation and to apply real-time and in-field sensor fault detection, it is necessary to acquire measurement data and information about the measurement reliability at the same time.
An auto-validation tool for the reliability quantification of materials integrated fiber Bragg grating (FBG) strain sensors have been developed and tested. The FBG strain sensor was jacketed with a magnetostrictive layer based on iron-nickel which, when excited by a specific magnetic field, adds an artificial strain to the sensor. The fixed relationship between magnetic induction and wavelength shift of the FBG strain sensor characterizes the bond strength and adhesion between the sensor and the surrounding structure. Due to an easily applicable magnetic field, it is possible to validate the sensor performance in a non-contact, fast way without disturbing the data-acquisition process.
A new concept for the self-diagnosis of embedded fiber Bragg grating (FBG) strain sensors was developed, simulated and experimentally tested. This concept is based on a magnetostrictive metallic layer directly coated on the fibre cladding over the grating segment of the FBG sensor, so that an on-demand external magnetic field in a millitesla scale can produce a controllable artificial strain as an indication signal for the remote optical interrogator. The relationship between the pre-defined magnetic field and its induced Bragg wavelength shift characterizes this validation concept. Any deviation of the local bonding state of the interfaces from the initial or/and any change of shear strain transferring mechanism from composite matrix to the optical fibre core will result in alterations in this sensitive relationship, and thus triggers an immediate alert for a further inspection. The finite element method is used to simulate the strain of this configuration as result of different values of the magnetic field in order to optimize the geometrical sensor parameters. The simulations are verified by experiments results. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
A highly resolving fibre optic sensor based on the Fabry-Perot technology has been developed for
integration into concrete piles with the purpose of static and dynamic pile testing as well as monitoring. The
paper presents the design of the sensitive element and first results of large-scale model pile tests.
Static and dynamic pile tests are carried out to determine the load bearing capacity and the quality of reinforced concrete piles. As part of a round robin test to evaluate dynamic load tests, structure integrated fibre optic strain sensors were used to receive more detailed information about the strains along the pile length compared to conventional measurements at the pile head. This paper shows the instrumentation of the pile with extrinsic Fabry-Perot interferometers sensors and fibre Bragg gratings sensors together with the results of the conducted static load test as well as the dynamic load Tests and pile integrity tests.
Reinforced concrete piles are used in case of structures that are constructed on soft ground to transfer the loads into deeper strata with sufficient bearing capacity. In order to determine the pile’s behavior and possible damage, static and dynamic pile tests are carried out. Dynamic measurements taken from the pile head can show the bearing behavior and structural integrity by using the theory of wave propagation. In order to receive more precise information about the pile features, now, a string of sensors is embedded at different levels of the pile. A fiber optic strain wave sensor, based on the extrinsic Fabry-Perot interferometer (EFPI), has already been developed and tested in full-scale field tests by Schallert (2010). It was possible to detect the introduced deformation caused by the static load and the dilatational wave during dynamic loading. Although the full-scale tests were successful, the engineering design of the sensor body left room - from the economical point of view - to be optimized. After laboratory tests with the optimized sensor, a cast-in-situ bored pile has been built at the BAM Test Site Technical Safety in Horstwalde, South of Berlin. Additionally to the EFPI sensors, fiber Bragg grating (FBG) sensors, temperature sensors and resistance strain gauge (RSG) sensors are embedded in order to compare the signals with each other. In this paper, the modified sensor and the Setup of the cast-in-situ bored pile along with results of dynamic tests are shown.
Zur Gründung von Bauwerken auf weichen, gering tragfähigen Böden werden unter anderem Betonpfähle, einzeln oder in Pfahlgruppen, eingesetzt. Deren Bewertung bzgl. Tragverhalten bzw. Integrität ist bei bestimmten Baugrundverhältnissen und Pfahlgeometrien schwierig. Hierfür werden statische und dynamische Pfahlprüfungen durchgeführt. Aus Messwerten vom Pfahlkopf bzw. vom oberen Pfahlbereich werden üblicherweise die notwendigen Aussagen abgeleitet. Eine genauere Bewertung ist möglich, wenn präzise Messwerte über die gesamte Pfahllänge vorliegen. Deshalb wurden hochauflösende betoneinbettbare Messwertaufnehmer auf Basis von Faser-Fabry-Perot-Sensoren entwickelt, die in Modell- und in realen Rammpfählen getestet wurden. Der Beitrag beschreibt den Sensor, die Installation und exemplarisch einige Testergebnisse zur Erfassung der Wellenausbreitung im Modellpfahl. Feldtests wurden zurzeit der Erstellung des Manuskripts erfolgreich begonnen.
Reinforced concrete piles are often used for structures on non-sufficiently bearing soil areas. Assessment of bearing capacity and bearing behaviour of large concrete piles remains a difficult task under specific soil conditions and pile geometries. Usually static and dynamic pile tests are carried out for quality assurance. From dynamic measurements taken only from the pile head, the bearing behaviour and structural integrity can be derived using the one-dimensional theory of wave propagation. More precise information about the pile features can be achieved by highly resolving fibre-optic sensors based on Fabry-Perot technology, distributed over several locations along the pile length. Small scale piles and real driven piles have been tested. This paper describes the sensor, the sensor installation, and experimental results of tests in laboratory as well as test results for recording the wave propagation in the small scale piles.