TY - CONF A1 - Brekow, Gerhard A1 - Kreutzbruck, Marc A1 - Boehm, Rainer A1 - Kitze, Jessica A1 - Eggers, H. A1 - Böwe, M. T1 - Using UT-SAFT for analysis of stress corrosion cracking N2 - Stress corrosion cracking is a transcrystalline or intercrystalline crack formation in materials which occurs under the influence of static tensile stress or residual stress and a specific aggressive medium such as chloride containing substances. This special sort of crack formation is involved in complex crack configurations, which may only insufficiently be captured by conventional ultrasonic probes with fixed angles of incidence. Only a number of different beam angles produce sufficient reflection to reconstruct the complete defect shape from measured ultrasonic data. The SAFT algorithm, which was recently successfully used in many industrial NDT-applications, is a promising tool for the reconstruction process. In addition, the combination of phased array technique and SAFT was developed in several projects by BAM, Berlin. Investigations using phased array equipment were performed to look into crack configurations in test blocks with different surface curvatures. UT-SAFT has been used for the analysis of spark-eroded notches simulating stress corrosion cracks at the thermo sleeve weld of a nozzle. For comparison, UT-SAFT has also been applied for the analysis of real reflectors at the same position in a nozzle used in a power plant, which was repaired later on. SAFT-scans received from reconstructed ultrasonic measurement data confirm the practical usefulness of the SAFTalgorithm developed by BAM. T2 - 8th International conference on NDE in relation to structural integrity for nuclear and pressurised components CY - Berlin, Germany DA - 2010-09-29 KW - Stress corrosion cracking KW - Real and simulated cracks KW - D-nozzle KW - Phased array technique KW - SAFT reconstruction PY - 2010 SN - 978-3-940283-30-6 IS - DGZfP-BB 125 (Th.2.B.1) SP - 1 EP - 10 CY - Berlin AN - OPUS4-23594 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gaal, Mate A1 - Bartusch, Jürgen A1 - Dohse, Elmar A1 - Kreutzbruck, Marc A1 - Amos, J. M. ED - Chimenti, D.E. ED - Bond, L.J. ED - Thompson, D.O. T1 - Air-coupled ultrasonic testing of metal adhesively bonded joints using cellular polypropylene transducers N2 - Adhesively bonded aluminum components have been widely used in the aerospace industry for weight-efficient and damage-tolerant structures. Automated squirter jet immersion ultrasonic testing is a common inspection technique to assure the bond integrity of large, contoured assemblies. However, squirter jet inspection presents several limitations in scanning speed, related to water splash noise over protruding stiffeners and splash interference crosstalk in multi-channel inspection systems. Air-coupled ultrasonic testing has been evaluated as an alternative, possibly offering the benefits of increased throughput by enabling higher speeds, and eliminating the contamination concerns and maintenance issues of water couplant systems. Adhesive joints of multi-layer aluminum plates with artificial disbonds were inspected with novel air-coupled ultrasonic probes based on cellular polypropylene. Disbonds of various sizes were engineered in several multi-layer configurations and at various depths. Results were compared with squirter jet immersion and conventional piezoelectric transducer designs in terms of scan contrast, resolution and inspection time. T2 - 40th Annual review of progress in quantitative nondestructive evaluation CY - Baltimore, Maryland, USA DA - 21.07.2013 KW - Air-coupled KW - Ultrasonic KW - Metal bond KW - Ferroelectret PY - 2014 SN - 978-0-7354-1212-5 SN - 978-0-7354-1211-8 U6 - https://doi.org/10.1063/1.4864857 SN - 0094-243X N1 - Serientitel: AIP conference proceedings – Series title: AIP conference proceedings VL - 1581 33A SP - 471 EP - 478 PB - AIP Publishing AN - OPUS4-31362 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gaal, Mate A1 - Bartusch, Jürgen A1 - Schadow, Florian A1 - Beck, Uwe A1 - Daschewski, M. A1 - Kreutzbruck, M. T1 - Airborne ultrasonic systems for one-sided inspection using thermoacoustic transmitters N2 - Airborne ultrasonic inspection is performed in through transmission, where the test piece (e.g. adhesive joint or polymer-based composite plate) is placed between the transmitter and the receiver. However, many structures with difficult shapes allow only one-sided inspection. The strong reflection of the signal from the surface overshadows the signals from the inside, so that broadband pulses are required. Thermoacoustic transmission, where the thermal energy of an electrically heated electrode is transformed into the acoustic energy of an ultrasonic wave, opens the possibility to excite broadband pulses and thus to inspect objects with one-sided access. We present various thermoacoustic transducers consisting of an electrically conductive film on a solid substrate. The first type of transducer is a transmitter with an indium-tin-oxide electrode on a glass substrate combined with a laser Doppler vibrometer as a receiver. The second type of transducer combines thermoacoustic transmission and piezoelectric reception, having a titanium electrode as a transmitter deposited onto charged cellular polypropylene serving as a piezoelectric receiver. Using a focusing thermoacoustic transmitter and a separate cellular polypropylene receiver, a through-transmission inspection of a 4 mm thick CFRP test piece with inserts as small as 1 mm was performed. The same emitter and a laser vibrometer as a receiver were used for a one-sided inspection of a Plexiglas block with a cross hole at 15 mm depth. A twin probe consisting of a thermoacoustic transmitter on a cellular polypropylene receiver was applied to a profile measurement on a step wedge with flat bottom holes. The smallest detected diameter of a flat bottom hole was 1 mm. Sound pressure level above 140dB was achieved with each of these transmitters. Thermoacoustic transmitters enable a step towards one-sided air-coupled ultrasonic inspection. T2 - IEEE International Ultrasonics Symposium CY - Tours, France DA - 18.09.2016 KW - Airborne KW - Air-coupled KW - Ultrasonic transducer KW - Thermoacoustic KW - Ferroelectret PY - 2016 SN - 978-1-4673-9897-8 SN - 1948-5719 SP - (online publication) 1 EP - 4 AN - OPUS4-37620 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gaal, Mate A1 - Dohse, Elmar A1 - Bartusch, Jürgen A1 - Köppe, Enrico A1 - Kreutzbruck, Marc A1 - Hillger, W. A1 - Amos, J. M. T1 - Ultrasonic testing of adhesively bonded joints using air-coupled cellular polypropylene transducers N2 - In air-coupled ultrasonic testing, the impedance mismatch between the transducer and the air is commonly being solved by adding matching layers to composite transducers. To avoid the difficult technological procedure regarding matching layers, some new piezoelectric materials have been proposed. Most promising are ferroelectrets, which are charged cellular polymers, having ferroelectric and consequently piezoelectric properties. In particular, the extreme softness of cellular polypropylene (cPP) leads to a high piezoelectric constant and to a good impedance match with the air, making matching layers redundant. Its elasticity modulus below 1 MPa causes an additional effect not observed with common piezoelectric materials: that is the electrostrictive effect, here defined as the thickness change due to the attractive force between the transducer electrodes. This effect exceeds the piezoelectric effect at excitation voltages over 1 kV. The extreme softness of cPP leads also to high flexibility, enabling easy focusing by bending the transducer. We have developed air-coupled ultrasonic transducers based on cPP. This includes the electrical matching networks for the transmitter and for the receiver. The transmitter is excited with voltages up to 2.5 kV, so that the electrostrictive effect dominates, leading to sound pressure around 145dB at the transducer surface. These transducers have been applied for testing carbon-fiber-reinforced polymer plates, adhesive joints and other composite structures. Here we report about ultrasonic transmission of two types of adhesive joints. The first one is multi-layer aluminium components with some artificial disbonds, which are common in aerospace industry, and the second one is an aluminium-steel joint with polyurethane adhesive, which is used in automotive industry. T2 - ECNDT 2014 - 11th European conference on non-destructive testing CY - Prague, Czech Republic DA - 06.10.2014 KW - Air-coupled KW - Ultrasonic testing KW - Ferroelectret KW - Cellular polypropylene KW - Transducer KW - Adhesive joint PY - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-317204 SN - 978-80-214-5018-9 SP - 1 EP - 8 PB - Brno University of Technology AN - OPUS4-31720 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Myrach, Philipp A1 - Maierhofer, Christiane A1 - Rahammer, M. A1 - Kreutzbruck, Marc T1 - Parameters in lock-in thermography of CFRP laminates N2 - Active thermography with lock-in excitation is a non-destructive testing method that is also feasible for testing of carbon fiber reinforced polymers (CFRP). For validating the method extensive investigations were done during a research project in order to advance a standardization process. The most important parameters of optical and ultrasonic excitation thermography were investigated. For example, the appropriate selection of spectral sensitivity of the used infrared camera systems is important for recording undisturbed thermal signals. Regarding excitation, influences of excitation power and ultrasonic frequency were studied. Furthermore, material parameters such as CFRP layup are known for strongly affecting the results of measurement. KW - Standardisierung KW - Lock-in thermography KW - Lock-in Thermografie KW - CFRP KW - CFK KW - optical excitation KW - ultrasonic excitation KW - Ultraschall KW - standardization PY - 2016 U6 - https://doi.org/10.3139/120.110814 SN - 0025-5300 VL - 58 IS - 1 SP - 31 EP - 35 PB - Carl Hanser Verlag CY - München AN - OPUS4-35479 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pohl, Rainer A1 - Commandeur, C. A1 - Erthner, Thomas A1 - Kreutzbruck, M. A1 - Pelkner, Matthias T1 - GMR-Streufluss-Prüfsystem zur Detektion verdeckter Fehler in Feinblechen N2 - BAM und TATA Steel untersuchen gemeinsam, ob sich die Prüfung von ferritischen Feinblechen mit einer Stärke von etwa 0,2 mm während der Fertigung durch den Einsatz von GMR-Sensorik verbessern lässt. Hierzu wurde eine Vorstudie an Feinblechen mit eingebrachten Mikronuten durchgeführt. Diese Nuten variieren in ihrer Tiefe zwischen 5 μm und 60 μm und wurden verdeckt mit ZfP-angepassten GMR-Sensorarrays geprüft. Die Ergebnisse der Vorstudie zeigten, dass bei verdeckter Prüfung schon kleinste Defekte mit einer Tiefe von 10 μm - gleichbedeutend mit einer Restwanddicke von 90 % – mit einem SNR > 6 dB detektiert werden konnten, wobei der Abstand der Prüfsonde zur Oberfläche bis zu 500 μm betrug. Zudem wurden in der Vorstudie Untersuchungen zur Prüfgeschwindigkeit und Praxistauglichkeit durchgeführt. Basierend auf den hier gewonnenen Ergebnissen wird ein erster Demonstrator für eine zuverlässige Prüfung eines Teilbereiches von 50 mm des Feinbleches innerhalb einer Produktionslinie aufgebaut. Zum Einsatz kommen Prüfsonden mit jeweils 24 GMR-Sensorelementen. Hierbei wird das Ziel einer umfassenden Prüfung des Feinblechs über die gesamte Breite von 1200 mm angestrebt. Eine besondere Herausforderung stellt dabei die hohe Anzahl von mehr als 1000 Sensorelementen dar. Das hierfür entwickelte Prüfkonzept umfasst neben einer angepassten Erzeugung des Magnetfeldes die Entwicklung einer geeigneten schnellen und sicheren Elektronik für die neuen Mehrkanalprüfköpfe. Neben der Vorstellung des Prüfkonzeptes und seiner Eigenschaften vergleichen wir die erzielten Prüfergebnisse an verschiedenen Vergleichsfehlern mit denen der Vorstudie. T2 - DACH-Jahrestagung 2015 CY - Salzburg, Austria DA - 11.05.2015 KW - Streuflussprüfung KW - GMR PY - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-343354 SN - 978-3-940283-68-9 IS - DGZfP BB 152 SP - Mi.2.B.3, 1 EP - 9 AN - OPUS4-34335 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rahammer, M. A1 - Myrach, Philipp A1 - Maierhofer, Christiane A1 - Busse, G. A1 - Kreutzbruck, M. T1 - Auflösungsgrenzen der Lockin-Thermografie zur Prüfung von Faserkunststoffverbunden N2 - Aktive Thermografie mit Lockin-Anregung ist ein zerstörungsfreies Prüfverfahren, das insbesondere auch die Prüfung von kohlenstofffaserverstärkten Kunststoffen ermöglicht. Um eine Standardisierung dieses Verfahrens voranzubringen, wurden im Rahmen eines Forschungsprojektes umfangreiche Untersuchungen zur Validierung des Verfahrens durchgeführt. Für die Anregungsmethoden optisch und Ultraschall wurden die wichtigsten Parameter systematisch untersucht. Auf der Auswertungsseite ist dies z.B. der Einfluss der spektralen Empfindlichkeit verschiedener Kamerasysteme. Für die Anregungen sind unter anderem die Einflüsse von Anregungsenergie und Ultraschallfrequenz untersucht worden. Auch Materialparameter, wie der Lagenaufbau bei CFK-Probekörpern, beeinflussen die Ergebnisse stark. T2 - 24. Stuttgarter Kunststoffkolloquium CY - Stuttgart, Germany DA - 25.02.2015 KW - Zerstörungsfreie Prüfung KW - Lockin-Thermografie KW - Faserkunststoffverbunde KW - Non-destructive testing KW - Lockin-Thermography KW - Fibre-reinforced plastics PY - 2015 SP - 1 EP - 7 AN - OPUS4-32876 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Richter, Regina A1 - Maierhofer, Christiane A1 - Kreutzbruck, Marc A1 - Schilling, M. T1 - Numerical method of active thermography for the reconstruction of back wall geometry N2 - The paper presents numerical methods to detect and classify defects and inhomogeneities by means of active thermography. The objective is to determine the wall thickness of structure elements with an inaccessible back wall, for example, of pipes or Containers. As test specimens we used approximately 2 cm thick PVC samples with spatial variations in the back wall geometry. Flash lamps provided the heating. To know the thickness of the wall, we used two inversion methods and compared the results achieved. One is an iterative echo defect shape method and already tested on Steel test specimens with good reconstruction results. The second one is the Levenberg-Marquardt method, applied here to thermographic data for non-destructive testing. Since data capturing using active thermography and the presented numerical methods can easily be automated, the combination of these two procedures is a promising approach providing a broad area of application. T2 - 6th Workshop 'NDT in progress' CY - Prague, Czech Republic DA - 10.10.2011 KW - Impulse-thermography KW - Inversion KW - Levenberg-Marquardt method KW - Echo defect shape KW - Defect shape reconstruction PY - 2011 SN - 978-80-214-4339-6 IS - Chapter 8 SP - 245 EP - 252 AN - OPUS4-25144 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schenk, Gottfried A1 - Brackrock, Daniel A1 - Boehm, Rainer A1 - Kreutzbruck, Marc A1 - Deutsch, W.A.K. A1 - Joswig, M. A1 - Maxam, K. A1 - Schuster, V. T1 - Untersuchungen zum Einfluss von Geometrie- und Temperaturabweichungen bei der Stangenprüfung mit Ultraschall-Gruppenstrahlertechnik N2 - Bei der automatisierten Prüfung von Stangen mit Ultraschall- Gruppenstrahlertechnik besteht grundsätzlich die Möglichkeit, Prüfkopfparameter wie Einschallwinkel, Fokustiefe und Schallbündelbreite programmgesteuert an sich verändernde Prüfbedingungen anzupassen. Zu diesen zählt die Temperatur des Koppelmediums (Wasser), die in einem Bereich von 10°C bis 50°C liegen kann, was zu unterschiedlichen Schallgeschwindigkeiten führt und den Einschallwinkel verändert. Mit der Folge, dass unter Umständen die geforderte 100%-Abdeckung des Prüfvolumens nicht mehr gewährleistet ist. Auch geometrische Abweichungen, wie sie durch die fertigungsbedingte Streuung des Prüflings gegeben sind, können Einfluss auf das Prüfergebnis nehmen. So führen Abweichungen vom idealen Geradheitszustand zu Fehlpositionierungen des Prüfkopfs, was wiederum Einfluss auf die Lage und Beschaffenheit des Schallbündels in der Stange hat. Ähnliches gilt für nicht vollkommen kreisförmig ausgebildete Stangendurchmesser, die unterschiedliche Schalleintrittsbedingungen bewirken und Abweichungen von den theoretisch ermittelten Werten zur Folge haben. Im Rahmen eines vom BMWi geförderten Forschungsvorhabens wurde der Einfluss dieser Parameter untersucht und ihre Auswirkungen für den Betrieb einer automatisierten Prüfanlage unter realen Betriebsbedingungen ermittelt. Dies betrifft vor allem den maximal möglichen Schallbündelversatz innerhalb des Arrays, der die Anzahl der erforderlichen Prüftakte bestimmt und damit die maximale Vorschubgeschwindigkeit des Prüflings. Des Weiteren werden Möglichkeiten zur programmgesteuerten Kompensation der untersuchten Temperatur- und Geometrieabweichungen durch eine flexible Anpassung der Gruppenstrahler- Prüfkopfparameter aufgezeigt. T2 - DGZfP-Jahrestagung 2010 CY - Erfurt, Deutschland DA - 2010-05-10 PY - 2010 SN - 978-3-940283-26-9 IS - DGZfP-BB 122 (Mi.4.A.1) SP - 1 EP - 8 CY - Berlin AN - OPUS4-21878 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schenk, Gottfried A1 - Brackrock, Daniel A1 - Brekow, Gerhard A1 - Kreutzbruck, Marc A1 - Deutsch, W.A.K. A1 - Joswig, M. A1 - Maxam, K. A1 - Schuster, V. ED - Thompson, D.O. ED - Chimenti, D.E. T1 - Ultrasonic inspection system for automated round-bar-testing based on phased array technique N2 - Within a know-how transfer project funded by the government conventional ultrasonic technique was replaced by phased array technique for automated round-bar testing. Instead of applying a great number of conventional probes to achieve acceptable volume coverage we used curved linear arrays. The benefits of phased array technique such as programmable skew angles, beamforming and beam positions, led not only to a significant decrease in inspection time, but also the number of probes could be substantially reduced . Finally, the testing parameters for a large range of bar-diameters could be adapted by software control instead of time-consuming mechanical replacement. The probe-design was carried out by a proprietary modelling program. Both the theoretical calculations as well as the latter experimental verifications revealed significant advantages of curved arrays versus the planar types. A radial oriented probe offers perfect adaption to the cylindrical shape of the specimen allowing wide variations of the sound field. Thus beam direction, beam size and beam position could be optimized with respect to a minimum of inspection cycles, as inspections have to be executed in-line during the production. A number of laboratory tests were carried out on special test components. In order to achieve an optimal performance of the reference rod we implemented three different types of reference reflectors: (i) flat-bottom-holes with diameters of 0.8 mm and 1.2 mm, (ii) side-drilled-holes with a diameter of 0.7 mm for the detection of volumetric flaws, and (iii) notches with a depth of 0.2 mm and 0.5 mm for the detection of surfaceoriented defects. All laboratory tests were carried out with the COMPAS-XXL inspection system, a proprietary development of BAM. T2 - 36th Annual Review of Progress in Quantitative Nondestructive Evaluation CY - Kingston, RI, USA DA - 2009-07-26 KW - Ultrasonic testing KW - Phased array KW - Round bar testing PY - 2010 SN - 978-0-7354-0748-0 SN - 0743-0760 SN - 0094-243X N1 - Serientitel: AIP conference proceedings – Series title: AIP conference proceedings VL - 29 SP - 1 EP - 7 CY - Melville, NY AN - OPUS4-21817 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -