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Fiber optic sensors have gained increasing importance in recent years and are well established in many areas of industrial applications. In this paper, we introduce a concept of a self-diagnostic fiber optic sensor. The presented sensor is to resolve the problems of embedded fiber optic sensors in complex structures and to enable the validation under operational conditions. For this purpose, different magnetostrictive coated fiber optic sensors were developed and various experiments were performed to verify their mode of Operation and to determine the respective reproducibility. The measuring principle is illustrated by obtained experimental results, which showed a change in wavelength from 1 pm at a magnetic field strength change of 0.25 mT.
In addition, the temperature characteristics of the implemented magnetostrictive sensor were analyzed and an experimental factor of 1.5 compared to a reference fiber optic sensor was determined.
Measurement and data recording systems are important parts of a holistic Structural Health Monitoring (SHM) system.
New sensor technologies such as fiber-optic sensors are often used; however, standards (or at least guidelines) are not yet available or internationally approved. This lack in standardization makes the acceptance of FOS technologies in complex SHM systems substantially difficult. A standard family for different FOS technologies is therefore being developed that should help to design SHM systems in an optimal way. International standardization activities take place in several standardization bodies such as IEC and ASTM, and within SHM societies such as ISHMII.
The paper reports on activities in standardization of fiber-optic sensors, on results already achieved, and on newly started projects. Combined activities of fiber sensor experts and SHM experts from Civil Engineering are presented. These contributions should help owners of structures as well as developers of sensors and monitoring systems to select effective and validated sensing technologies. Using these standards, both parties find recommendations how to proceed in development of SHM systems to evaluate the structural behavior based on e.g. standardized fiber optic sensors, and to derive necessary measures, e.g. the optimal maintenance strategy.
The stress vs. strain curve of materials is affected the rate of imposed straining. Among the methods for dynamic testing the technique known as 'split Hopkinson pressure bar' (SHPB) has evolved into the most widely used one to exert high-speed straining. The theory behind it comprises simple equations to compute stress and strain. The reliability of the strain analysis can be assessed by digital image correlation (DIC). The present results indicate that the visually observed strain is smaller than predicted by theory.
Innovative structural damage detection of bridges by least squares adjustment with constraints
(2016)
Long-term monitoring of bridges requires the early detection of spreading damage because very often the damage is not really visible. For many decades engineers and scientists relayed on dynamic methods especially modal ones. However, after fundamental tests by the U.S. FHWA in 1993, it became evident that more successful methods should be developed, but no innovation really happened. A substantial innovative detection method started four years ago from Lagrange Multiplier Testing which eventually resulted in experimental verification based on measurement of deflection and curvature of the bridge beam and together the methodological combination of both.
Innovative structural damage detection of bridges by least squares adjustment with constraints
(2015)
Fiber optic sensors have gained increasing importance in recent years and are well established in many areas of industrial applications. In this paper, we introduce a concept of a self-diagnostic fiber optic sensor. The presented sensor is to resolve the problems of embedded fiber optic sensors in complex structures and to enable the validation under operational conditions. For this purpose, different magnetostrictive coated fiber optic sensors were developed and various experiments were performed to verify their mode of operation and to determine the respective reproducibility. The measuring principle is illustrated by obtained experimental results, which showed a change in wavelength from 1 pm at a magnetic field strength change of 0.25 mT. In addition, the temperature characteristics of the implemented magnetostrictive sensor were analyzed and an experimental factor of 1.5 compared to a reference fiber optic sensor was determined.
Detecting spreading damage in bridges is a demanding task for engineers today when the ageing infrastracture of industriaiized countries is degradating more and more. To successfully deal with tbis problem, a really advanced method has been elaborated basing on Langrange Multiplier (LM) tests and following the principle of simplicity by Hilbert and extending comments by Helmholtz refering to a combination of measurement and analytical treatment. Finally, an easy mathematical fonnation has been created.
The Split Hopkinson Pressure Bar (SHPB) is a materials testing apparatus primarily designed for the analysis of viscoplastic material behavior at very high strain rates.
Because of its complexity it is common practice to simplify the underlying exact mechanical theory by making strong assumptions. On the one hand this has to be done to achieve any results at all on the other hand one commits systematic errors. Therefore we utilize different numerical and Simulation methods to analyze and minimize these errors.
The Split Hopkinson Pressure Bar (SHPB) is a method for material characterization which works at strain rates from 102 - 104 1/s. This method can be used for example in the field of military engineering, in the field of deformation technology, automobile indurstry, aerospace industry or in other industrial fields. Controlled tests with the SHPB device enable Information about the dynamic material deformaion behaviour in the named strain rate area. The setup of the SHPB is not standarized and the measurement principle is dependent on simplifications. Due to this amongst others the problem with the dispersion of the measurement signal occurs. Furthermore it is possible that measurement uncertainties appear caused by the misalignment of the SHPB setup. In this work the influence of the alignment and a dispersion correction by pulse shaping is presented. On the one side for the alignment calibration tests are done. And on the other side for the dispersion influence correction with pulse shaping tests are done with TiA16V4. This material was choosen due to the fact that it can be compared with existing literature data.