TY - JOUR A1 - Liehr, Sascha A1 - Münzenberger, Sven A1 - Krebber, Katerina T1 - Wavelength-scanning coherent OTDR for dynamic high strain resolution sensing N2 - Distributed vibration sensing in optical fibers opened entirely new opportunities and penetrated various sectors from security to seismic monitoring. Here, we demonstrate a most simple and robust approach for dynamic strain measurement using wavelength-scanning coherent optical time domain reflectometry (C-OTDR). Our method is based on laser current modulation and Rayleigh backscatter shift correlation. As opposed to common single-wavelength phase demodulation techniques, also the algebraic sign of the strain change is retrieved. This is crucial for the intended applications in structural health monitoring and modal analysis. A linear strain response down to 47.5 pε and strain noise of 100 pε/√Hz is demonstrated for repetition rates in the kHz range. A field application of a vibrating bridge is presented. Our approach provides a cost-effective high-resolution method for structural vibration analysis and geophysical applications. KW - Fiber optics sensors KW - Optical time domain reflectometry KW - Rayleigh Scattering KW - Distributed acoustic sensing KW - Distributed strain sensing PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-448069 DO - https://doi.org/10.1364/OE.26.010573 SN - 1094-4087 VL - 26 IS - 8 SP - 10573 EP - 10588 PB - Optical Society of America AN - OPUS4-44806 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Strangfeld, Christoph A1 - Kruschwitz, Sabine T1 - Monitoring of the absolute water content in porous materials based on embedded humidity sensors N2 - Moisture transport monitoring may indicate the onset of deterioration in porous building materials Prior to damage occurring. Most moisture measurement systems provide only qualitative values, require extensive calibration, or are destructive. Thus, non-destructive and calibration-free monitoring Systems are required. Our approach of moisture monitoring is to embed sensors that measure the relative humidity. In our experiment, screed samples are monitored during the Hydration and evaporation process. Every test sample is equipped with 10 embedded sensors which measure the relative humidity across the sample thickness. Based on Hillerborg’s approach, the relative humidity is converted into the corresponding pore saturation. In our study, the free water is computed without knowledge of the Sorption isotherm. The free water in the pore system is predicted and validated. The predicted weight decrease corresponds conclusively to gravimetrically measured weights. The embedded sensors yield the absolute liquid water content and enable an experimental, non-destructive monitoring of liquid water in porous materials. KW - Moisture measurements KW - Porous materials KW - Embedded sensors KW - Partial pore saturation KW - Sorption isotherm PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-453476 DO - https://doi.org/10.1016/j.conbuildmat.2018.05.044 SN - 0950-0618 VL - 177 SP - 511 EP - 521 PB - Elsevier AN - OPUS4-45347 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Illerhaus, Bernhard A1 - Kunisch, E. A1 - Kinne, R. W. T1 - Serial in situ compression of spongiosa cylinder observed by μCT, compared to simulated stress, strain, and movement N2 - Minimally invasive injection of calcium phosphate cement into bone defects in aged sheep vertebrae has been used as a model for the treatment of osteoporotic vertebral fractures. One of the therapeutic criteria is a compression test of non-treated or treated vertebral bodies. In the present study, an in situ compression test with a stepwise load increase was performed with small spongiosa cylinders from the vertebrae under continuous monitoring by μCT. This allows localization of bone cracks and the visualization of correct placement and form of the bone cylinder. In addition, the effects of an uneven load distribution on the sample due to an irregular shape and a subsequent underperformance of the test sample can be excluded by controlling its shape under increasing load. There was a good agreement between the measured data and those obtained by simulated load-dependent transformation on the basis of a digital volume correlation between consecutive compression tests on the bone surface under the assumption of homogeneous bone material. Mechanic simulation was executed by directly using structural voxel data, resulting in maps of Von Mise stresses and predicted displacements. T2 - 12th ECNDT CY - Gothenburg, Sweden DA - 11.6.2018 KW - Computed tomography KW - In-situ compression KW - Simulation PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-453317 SN - 978-91-639-6217-2 SP - 0162, 1 EP - 7 AN - OPUS4-45331 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gaal, Mate A1 - Schadow, Florian A1 - Nielow, Dustin A1 - Trappe, Volker T1 - Prüfung von Rotorblattschalen mit Luftultraschall N2 - Um den sicheren Betrieb von Windkraftanlagen zu gewährleisten, werden Rotorblätter nach der Fertigung und nach Reparatur mit verschiedenen zerstörungsfreien Verfahren auf Schaden untersucht. Bei der Fertigung von Blattschalen, die in einer Sandwich-Schalenbauweise gefertigt werden, entstehen Imperfektionen, die unter Belastung zu großen Rissen führen können. Zur Prüfung von Blattschalen wird unter anderem Ultraschallprüfung in Kontakttechnik eingesetzt. Um den Wartungsaufwand von Ultraschallanlagen zu reduzieren und um manche Kompositstrukturen vor Koppelmittel zu schützen, wird die Anwendung von Luftultraschall erforscht. Insbesondere große Fortschritte gibt es im Bereich der Entwicklung neuer Wandler. In diesem Beitrag berichten wir über die Luftultraschallprüfung von Schalen für Rotorblätter. Es wurden typische Sandwichschalenstrukturen hergestellt und mit einem eigenentwickelten Schalenprüfstand unter simulierter Betriebsbeanspruchung belastet. Die in den Schalenprüfkörpern entstandenen Schäden wurden außerhalb des Prüfstandes mit Luftultraschall in Durchschallung untersucht. Es wurden fokussierende Wandler auf Basis von Ferroelektreten entwickelt und für diese Prüfungen eingesetzt. Mit zusätzlicher elektrischer Vorspannung konnte die Empfindlichkeit der Empfänger deutlich erhöht werden. Die nach dem Lastwechsel entstandenen Schäden in den Rotorblattschalen waren eindeutig zu detektieren. T2 - DGZfP-Jahrestagung CY - Leipzig, Germany DA - 07.05.2018 KW - Wandler KW - Rotorblattschalen KW - Luftultraschall KW - Ferroelektret PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-453066 SP - 7 PB - Deutsche Gesellschaft für zerstörungsfreie Prüfung e.V. (DGZfP) AN - OPUS4-45306 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lugovtsova, Yevgeniya A1 - Prager, Jens T1 - Analysis of Guided Wave Propagation in an Aluminium-CFRP Plate N2 - Guided waves cover comparably long distances and thus allow for online structural health monitoring of safety relevant components, e.g. lightweight composite overwrapped pressure vessels (COPV) as used for the transportation of pressurised gases. Reliable non-destructive assessment of COPVs’ condition is not available yet due to their complex composite structure comprising a thin metal liner and a fibre reinforced plastics (FRP) overwrap. The conventional overload hydrostatic pressure testing used for the metal vessels is not suitable for the composite vessels, because it may damage the FRP overwrap reducing the service life of the COPV. Therefore, ISO and CEN defined a maximum service life of composite pressure vessels as of 15 to 20 years. To extend the COPVs’ service life and to ensure a safer usage a structural health monitoring system based on guided ultrasonic waves is to be developed. In this contribution first results of guided waves propagation in a flat composite plate consisting of an aluminium layer firmly bonded to a carbon fibre reinforced plastic laminate are presented. Based on experimental results material properties of FRP are reconstructed by means of the Scaled Boundary Finite Element Method (SBFEM). T2 - ECNDT 2018 CY - Gothenburg, Sweden DA - 11.06.2018 KW - Structural Health Monitoring KW - Pressure tanks KW - Hydrogen storage KW - Natural gas KW - Composites PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-452084 SP - 1 EP - 6 AN - OPUS4-45208 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gaal, Mate A1 - Kotschate, Daniel T1 - New technologies for air-coupled ultrasonic transducers N2 - Air-coupled ultrasonic testing (ACUT) has experienced rapid growth within the last years. It is especially well suited to inspection of lightweight structures consisting of composite materials and adhesive joints. Uniform coupling and easy maintenance are its advantages compared to contact technique. However, the impedance mismatch between the transducer and air poses a major challenge to the development of ACUT transducers. Commercially available air-coupled transducers consist of a piezocomposite material and matching layers. Their fabrication is difficult in handling and their signal-to-noise ratio sometimes not sufficient for various testing requirements. However, there are several innovative approaches using other materials and other physical principles to transmit and receive an ultrasonic pulse. We present a review of the latest advances in research on air-coupled transducers for non-destructive testing, including previously unpublished results. We recognize two major directions as most promising: ferroelectrets and thermoacoustic transducers. Ferroelectrets are charged cellular polymers exhibiting piezoelectric properties. Their small acoustic impedance is matched to air better than matching layers applied in conventional air-coupled transducers. Applying bias voltage to a ferroelectret receiver is the latest development in this field, which increased the received signal by 12 to 15 dB. Thermoacoustic transducers use heat to initiate an ultrasonic wave, acting as transmitters. The working principle is known from nature as thunder and lightning: thermal energy of an electrically heated material, which can also be air, is converted into acoustic energy. Some thermoacoustic transmitters consist of a conductive layer with a thickness in the nanometer range deposited on a solid substrate. Another possibility is to use an electric spark. For the first time, measurements of the sound field of an electric spark up to 500 kHz were performed. Thermoacoustic transducers enable excitation of extremely broadband pulses while producing high pressure levels, which opens new possibilities for advanced signal processing. T2 - 12th European conference on Non-Destructive Testing CY - Gothenburg, Sweden DA - 11.06.2018 KW - Air-coupled ultrasonic testing KW - Atmospheric pressure plasma KW - Cellular polypropylene KW - Ferroelectret KW - Transducer PY - 2018 SP - ECNDT-0608-2018, 1 EP - 9 AN - OPUS4-45209 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Grager, J.-C. A1 - Kotschate, Daniel A1 - Gamper, J. A1 - Gaal, Mate A1 - Pinkert, K. A1 - Mooshofer, H. A1 - Goldammer, M. A1 - Grosse, C. U. T1 - Advances in air-coupled ultrasonic testing combining an optical microphone with novel transmitter concepts N2 - Air-coupled ultrasound (ACU) is increasingly used for automated and contactless inspection of large-scale composite structures as well as for non-destructive testing (NDT) of water-sensitive or porous materials. The major challenge to overcome using ACU in NDT is the enormous loss of ultrasonic energy at each solid-air interface caused by the high acoustic impedance mismatch. Resonant low-frequency piezoceramic transducers are specially designed to achieve high sound pressure levels. For an expanded use of this technique, however, the spatial resolution needs to be increased. Recent studies of our collaborative research group demonstrated the successful application of a resonance-free, highly sensitive receiver that uses a Fabry-Pérot etalon instead of piezoceramic materials or membranes. However, to reach the full potential of this broadband small-aperture optical microphone, novel transmitter concepts have to be developed and evaluated for advanced NDT applications. Different types of transmitter were tested in combination with the optical microphone acting as receiver and they were compared to conventional piezoceramic transducers in through-transmission mode. Monolithic carbon fiber-reinforced plastics (CFRP) and CFRP sandwich structures containing different defect types were inspected. Presented results are processed as C-scan images and further evaluated for spatial resolution, signal-to-noise ratio and sensitivity of each measurement setup. Novel transmitter concepts, such as ferroelectret and thermoacoustic emitters, show promising findings with a considerably improved time and spatial resolution for ACU-NDT. T2 - 12th European conference on Non-Destructive Testing CY - Gothenburg, Sweden DA - 11.06.2018 KW - Air-coupled ultrasonic testing KW - Optical microphone KW - Thermoacoustic KW - Cellular polypropylene KW - Ferroelectret KW - Transducer PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-452114 SP - ECNDT-0166-2018, 1 EP - 10 AN - OPUS4-45211 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kapa, Thomas A1 - Schreier, Andy A1 - Krebber, Katerina T1 - 63 km BOFDA for temperature and strain monitoring N2 - We demonstrate (and are the first to do so) 63 km Brillouin Optical Frequency-Domain Analysis (BOFDA) for temperature and strain monitoring using a 100 km fiber loop. The use of BOFDA for long-range applications can be considered a novel approach, as previous investigations focused on the utilization of Brillouin Optical Time-Domain Reflectometry and Analysis (BOTDR and BOTDA, respectively). At 51.7 km, a 100 m hotspot (37 °C) was detected without using distributed Raman amplification or image processing. KW - Distributed sensing KW - Stimulated Brillouin scattering KW - Fiber optics sensors PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-449679 DO - https://doi.org/10.3390/s18051600 SN - 1424-8220 VL - 18 IS - 5 SP - 1600, 1 EP - 9 PB - MDPI CY - Basel, Switzerland AN - OPUS4-44967 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Lugovtsova, Yevgeniya A1 - Bulling, Jannis A1 - Krome, Fabian A1 - Prager, Jens T1 - Effiziente Modellierung von geführten Wellen mit der Scaled Boundary Finite Elemente Methode und deren Anwendung für Composite-Druckbehälter N2 - Die Scaled Boundary Finite Elemente Methode (SBFEM) ist eine semi-analytische Methode, die speziell für Modellierung von geführten Wellen weiterentwickelt und optimiert wurde. Da nur den Rand der Rechendomäne diskretisiert wird, hat die SBFEM einen geringen Rechenaufwand. In diesem Beitrag wird die SBFEM benutzt, um die Ausbreitung geführter Wellen in einer Metall-Faserverbund-Werkstoffstruktur zu analysieren. Mittels der SBFEM ist es möglich, verschiede Fehlertypen, z.B. Ermüdungsrisse, Poren, Delaminationen, Korrosion, in das numerische Modell zu integrieren und damit Defekt-Mode-Wechselwirkung zu analysieren. Die Ergebnisse wurden für die Entwicklung einer Methode zur Zustandsüberwachung von Composite-Druckbehältern verwendet. T2 - DGZfP-Jahrestagung 2018 CY - Leipzig, Germany DA - 07.05.2018 KW - Wasserstoffspeicher KW - Automobilindustrie KW - Kohlenstofffaserverstärkter Kunststoff KW - Hybrid Materialien PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-449797 SP - 1 EP - 4 AN - OPUS4-44979 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wilrich, Cordula A1 - Brandes, E. A1 - Michael-Schulz, Heike A1 - Schröder, Volkmar A1 - Schwarz, Silke T1 - Classification of chemicals according to UN-GHS and EU-CLP: A review of physical hazard classes and their intricate interfaces to transport and former EU legislation N2 - The Globally Harmonized System of Classification and Labelling of Chemicals (UN-GHS) is being implemented in more and more countries all over the world; the EU has done so with the CLP-Regulation (EU-CLP). Compared to the undeniably important questions on health and environmental hazards, the classification of physical hazards of chemicals often has not been in the focus, although their implementation can be challenging and there are traps and pitfalls to be avoided. The following overview of the classification systematics for physical hazards aims at a principle understanding without detailing all criteria or test methods. Similarities and differences between the classification systems of the UN-GHS and EU-CLP, the transport of dangerous goods and the former EU system are reviewed with regard to the physical hazard classes. Available physical hazard classifications for the transport of dangerous goods and according to the former EU system can be used as available information when classifying according to the GHS. However, the interfaces of these classification systems and their limitations have to be understood well when concluding on GHS/CLP classifications. This applies not only to industry when applying CLP but especially to legislators when adapting legislation that in one way or another refers to the classification of chemicals. KW - Chemicals classification KW - Globally harmonized system of classification and labelling of chemicals KW - Hazardous chemicals KW - Physical hazards KW - UN-GHS KW - EU-CLP KW - CLP-regulation PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-450012 UR - https://osjournal.org/ojs/index.php/OSJ/article/view/1389 DO - https://doi.org/10.23954/osj.v3i2.1389 SN - 2466-4308 VL - 3 IS - 2 SP - 1 EP - 24 PB - NVO Start CY - Temerin AN - OPUS4-45001 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -