The electronic structure of Pt overlayers on Co(0001) was investigated by spin-resolved and spin-... more The electronic structure of Pt overlayers on Co(0001) was investigated by spin-resolved and spin-integrated photoemission spectroscopy. The Pt/Co interface exhibits electronic interface states of mainly Pt-5d character. One of these interface states shows a peak separation of its spin components of about 170 meV indicating magnetic polarization of the Pt layer in intimate contact with Co.
Engineered barriers are a key element to enable safe nuclear waste disposal. One method currently... more Engineered barriers are a key element to enable safe nuclear waste disposal. One method currently under research for their construction is magnesia concrete applied in a shotcrete procedure. In this study, the ultrasonic echo method is evaluated as a means for quality assurance. Imaging of internal structures (backwall, boreholes) and defects, such as delamination, has successfully been achieved in the shotcrete. Additionally, detailed information about the potential cause of selected reflectors are obtained by phase analysis. In several test blocks of various sizes, no consistent concrete section boundaries have been found by ultrasonic imaging, which was verified by subsequent drilling and complementary tests. An experiment with artificial defects imitating cracks, air-filled voids, and material with lower density has been challenging and shows the limitations of the current methods. Although significant defects, such as a large delamination, are reliably identified, several small...
Quality assurance and condition assessment of concrete structures is an important topic world-wid... more Quality assurance and condition assessment of concrete structures is an important topic world-wide due to the ageing infrastructure and increasing traffic demands. Common topics include, but are not limited to, localisation of rebar or tendon ducts, geometrical irregularities, cracks, voids, honeycombing or other flaws. Non-destructive techniques such as ultrasound or radar have found regular, successful practical application but sometimes suffer from limited resolution and accuracy, imaging artefacts or restrictions in detecting certain features. Until the 1980s X-ray transmission was used in case of special demands and showed a resolution much higher than other NDT techniques. However, due to safety concerns and cost issues, this method is almost never used anymore. Muon tomography has received much attention recently. Novel detectors for cosmic muons and tomographic imaging algorithms have opened up new fields of application, such as the investigation of freight containers for co...
Ultrasonic echo technique with shear waves in the frequency rang of 50 kHz is one of the promisin... more Ultrasonic echo technique with shear waves in the frequency rang of 50 kHz is one of the promising methods for assessment of structural timber and is already frequently applied for this purpose. The article summarizes the state of the art of applying echo measurement via linear measurements as well as the development and first results for an imaging method for this purpose. The highly anisotropic properties of the ultrasonic velocity have to be considered. 3 D ultrasonic imaging results are described for the example of a pedestrian bridge made from Siberian larch.
Ultrasonic methods are used in concrete investigations since decades. While being limited to tran... more Ultrasonic methods are used in concrete investigations since decades. While being limited to transmission testing in the laboratory for a while, in-situ echo measurements for structural investigations and condition assessment have made their way into practical application in the past 20 years. However, several challenges remain. On one side, there are technical issues as limitations in depth of penetration, resolution and imaging capabilities. On the other side there are still gaps in validation, standardization and certification, which are limiting the applicability in condition/load capacity assessment. This review reports a couple of developments which will help to overcome these issues. This includes technical developments as new devices which are easier to handle on site or giving a much deeper penetration depth (e.g. the LAUS device at BAM) as well as improvements in imaging by hardware update (e. g. air coupled ultrasound or coded signals) or new software (e. g. RTM imaging)....
For the closure of radioactive waste disposal facilities engineered barriers- so called “drift se... more For the closure of radioactive waste disposal facilities engineered barriers- so called “drift seals” are used. The purpose of these barriers is to constrain the possible infiltration of brine and to prevent the migration of radionuclides into the biosphere. In a rock salt mine a large scale in-situ experiment of a sealing construction made of salt concrete was set up to prove the technical feasibility and operability of such barriers. In order to investigate the integrity of this structure, non-destructive ultrasonic measurements were carried out. Therefore two different methods were applied at the front side of the test-barrier: 1 Reflection measurements from boreholes 2 Ultrasonic imaging by means of scanning ultrasonic echo methods This extended abstract is a short version of an article to be published in a special edition of ASCE Journal that will briefly describe the sealing construction, the application of the non-destructive ultrasonic measurement methods and their adaptatio...
Kurzfassung. Aktuell wird die Ultraschallechotechnik für Holzbauteile genutzt, indem aus der Absc... more Kurzfassung. Aktuell wird die Ultraschallechotechnik für Holzbauteile genutzt, indem aus der Abschattung eines ansonsten stabilen Rückwandechos auf Auffälligkeiten im Holzbauteil geschlossen wird. Dabei werden Transversalwellen (Mittenfrequenz 50 kHz) mit der Polarisationsrichtung in Faserrichtung (L) angewendet. In einem 2012 abgeschlossenen Forschungsvorhaben wurde nun die direkte Abbildung von Streuern durch anisotrope SAFT-Rekonstruktion entwickelt. Dazu werden flächig aufgenommene Ultraschallmessdaten mit automatisiert scannenden Druckund Scherwellenköpfen erzeugt und auf Basis anisotroper Geschwindigkeitsverteilungen rekonstruiert. Benutzt werden die auch häufig für Beton eingesetzten trocken ankoppelnden Punktkontakt-Prüfköpfe. Da damit auch intensive Wellen an der Oberfläche erzeugt werden, entstehen im Material zusätzliche Kopfwellen, die ebenfalls bei der Rekonstruktion berücksichtigt werden. Da die Wellengeschwindigkeiten in Holz individuell stark schwanken, wird eine int...
Construction methods, environmental stressors, and aging factors are the main causes for defects ... more Construction methods, environmental stressors, and aging factors are the main causes for defects of reinforced concrete in nuclear power plants (NPP). These defects are typically occurred as corrosion of reinforcement steel, delamination, cracks, malfunction of post-tensioning or steel composite systems etc. Some of the challenges for assessing the performance of these structures by nondestructive testing methods (NDT) are that the assessment could be performed only during the annual overhauls when testing is time-limited and uncertainty of the accuracy and reliability of the available NDT testing devices combined with the lack of the international uniformity of the methods used for NDT tests. To overcome these challenges, a mock-up wall representing a section of the concrete containment of the NPP was built. The mock-up wall included simulated defects, which mimic the most common types of defects in NPP concrete structures such as dimensional errors, honeycombing, delamination, def...
Im Jahr 2011 hat der Bundestag in Deutschland den Ausstieg aus der Kernenergie beschlossen. Der a... more Im Jahr 2011 hat der Bundestag in Deutschland den Ausstieg aus der Kernenergie beschlossen. Der angefallene Abfall wird mehr als hunderttausend Jahre eine derartig hohe Aktivität besitzen, dass er eine erhebliche Gefahr für nachfolgende Generationen darstellen kann. Dieser radioaktive Abfall soll in tiefen geologischen Formationen (z. B. Salz, Ton oder Kristallin) sicher endgelagert werden. Die Endlager werden mittels sogenannter geotechnischer Abdichtbauwerke (Schacht‐ bzw. Streckenverschlüsse) verschlossen, wofür u. a. Zement‐ oder Sorel‐basierte Baustoffe (Betone) in Frage kommen. Die Beschreibung des Dichtvermögens dieser Bauwerke ist unabdingbar. In der Forschungsphase werden verschiedene Werkstoffe untersucht und Methoden für die zerstörungsfreie Untersuchung der Bauwerke als Mittel der Qualitätsprüfung entwickelt. Hierbei ist der Nachweis der Rissfreiheit bzw. die Detektion möglicher Risse ein vorrangiges Thema. In den letzten Jahren konnten bereits umfangreiche Erfahrungen mit der Untersuchung von in‐situ‐Versuchsobjekten in Realmaßstab gesammelt werden. Die Messungen wurden im Endlager für radioaktive Abfälle Morsleben am in‐situ‐Versuch “Abdichtbauwerk im Steinsalz” und in der Grube Teutschenthal am Großversuch GV2 durchgeführt. Es ist gelungen mit einem neu entwickelten Ultraschall‐Messsystem Eindringtiefen bis ca. 9,0 m zu realisieren. Die Messungen mit dem Large Aperture Ultrasonic System in Kombination mit der Rekonstruktion‐Methode Synthetic Aperture Focusing Technique zeigen, dass die zerstörungsfreie Prüfung von Abdichtbauwerken möglich und die Nutzung des Messsystems zur Qualitätssicherung bei der Erstellung der Verschlussbauwerke vielversprechend ist.
Quality assurance and condition assessment of concrete structures is an important topic world-wid... more Quality assurance and condition assessment of concrete structures is an important topic world-wide due to the aging infrastructure and increasing traffic demands. Common topics include, but are not limited to, localisation of rebar or tendon ducts, geometrical irregularities, cracks, voids, honeycombing or other flaws. Non-destructive techniques such as ultrasound or radar have found regular, successful practical application but sometimes suffer from limited resolution and accuracy, imaging artefacts or restrictions in detecting certain features. Until the 1980s X-ray transmission was used in case of special demands and showed a much better resolution than other NDT techniques. However, due to safety concerns and cost issues, this method is almost never used anymore. Muon tomography has received much attention recently. Novel detectors for cosmic muons and tomographic imaging algorithms have opened up new fields of application, such as the investigation of freight containers. Muon i...
Nondestructive Testing of Materials and Structures, 2011
The present paper describes the development and first application of ultrasonic imaging of timber... more The present paper describes the development and first application of ultrasonic imaging of timber (wood) by means of reconstruction calculation (3D-SAFT; Synthetic Aperture Focusing Technique). It considers the highly anisotropic ultrasonic velocity on wood. In order to validate such techniques we report on experiments carried out on test specimens made from pine and beech. Those specimens differ for the orientations of the annual rings. For the reconstruction calculation the slowness curves of the material are considered applying the elastic constants known from the literature. The anisotropic SAFT reconstruction is calculated from measured datasets and from synthetic data resulting from EFIT modelling (EFIT: Elastodynamic Finite Integration Technique).
There is a great demand for non-destructive testing methods for quality assurance and to assess t... more There is a great demand for non-destructive testing methods for quality assurance and to assess the safety and durability of wooden structures. Ultrasonic echo technique with shear waves in the frequency range of 50 kHz is one of those promising methods and is already frequently applied for usual and glued laminated timber. The article describes the development and first results for an imaging method for this purpose. The highly anisotropic properties of the ultrasonic velocity have to be considered. A 3D-SAFT (Synthetic Aperture Focusing Technique) imaging scheme is developed initially for synthetic data resulting from modelling the elastic wave propagation. The main part of the paper describes the experimental validation of this evaluation technique by experimental studies applying automated ultrasonic scanning techniques. 3D ultrasonic imaging results are described for test specimens made from pine and spruce wood. Another object of investigation was a pedestrian bridge made from...
The electronic structure of Pt overlayers on Co(0001) was investigated by spin-resolved and spin-... more The electronic structure of Pt overlayers on Co(0001) was investigated by spin-resolved and spin-integrated photoemission spectroscopy. The Pt/Co interface exhibits electronic interface states of mainly Pt-5d character. One of these interface states shows a peak separation of its spin components of about 170 meV indicating magnetic polarization of the Pt layer in intimate contact with Co.
Engineered barriers are a key element to enable safe nuclear waste disposal. One method currently... more Engineered barriers are a key element to enable safe nuclear waste disposal. One method currently under research for their construction is magnesia concrete applied in a shotcrete procedure. In this study, the ultrasonic echo method is evaluated as a means for quality assurance. Imaging of internal structures (backwall, boreholes) and defects, such as delamination, has successfully been achieved in the shotcrete. Additionally, detailed information about the potential cause of selected reflectors are obtained by phase analysis. In several test blocks of various sizes, no consistent concrete section boundaries have been found by ultrasonic imaging, which was verified by subsequent drilling and complementary tests. An experiment with artificial defects imitating cracks, air-filled voids, and material with lower density has been challenging and shows the limitations of the current methods. Although significant defects, such as a large delamination, are reliably identified, several small...
Quality assurance and condition assessment of concrete structures is an important topic world-wid... more Quality assurance and condition assessment of concrete structures is an important topic world-wide due to the ageing infrastructure and increasing traffic demands. Common topics include, but are not limited to, localisation of rebar or tendon ducts, geometrical irregularities, cracks, voids, honeycombing or other flaws. Non-destructive techniques such as ultrasound or radar have found regular, successful practical application but sometimes suffer from limited resolution and accuracy, imaging artefacts or restrictions in detecting certain features. Until the 1980s X-ray transmission was used in case of special demands and showed a resolution much higher than other NDT techniques. However, due to safety concerns and cost issues, this method is almost never used anymore. Muon tomography has received much attention recently. Novel detectors for cosmic muons and tomographic imaging algorithms have opened up new fields of application, such as the investigation of freight containers for co...
Ultrasonic echo technique with shear waves in the frequency rang of 50 kHz is one of the promisin... more Ultrasonic echo technique with shear waves in the frequency rang of 50 kHz is one of the promising methods for assessment of structural timber and is already frequently applied for this purpose. The article summarizes the state of the art of applying echo measurement via linear measurements as well as the development and first results for an imaging method for this purpose. The highly anisotropic properties of the ultrasonic velocity have to be considered. 3 D ultrasonic imaging results are described for the example of a pedestrian bridge made from Siberian larch.
Ultrasonic methods are used in concrete investigations since decades. While being limited to tran... more Ultrasonic methods are used in concrete investigations since decades. While being limited to transmission testing in the laboratory for a while, in-situ echo measurements for structural investigations and condition assessment have made their way into practical application in the past 20 years. However, several challenges remain. On one side, there are technical issues as limitations in depth of penetration, resolution and imaging capabilities. On the other side there are still gaps in validation, standardization and certification, which are limiting the applicability in condition/load capacity assessment. This review reports a couple of developments which will help to overcome these issues. This includes technical developments as new devices which are easier to handle on site or giving a much deeper penetration depth (e.g. the LAUS device at BAM) as well as improvements in imaging by hardware update (e. g. air coupled ultrasound or coded signals) or new software (e. g. RTM imaging)....
For the closure of radioactive waste disposal facilities engineered barriers- so called “drift se... more For the closure of radioactive waste disposal facilities engineered barriers- so called “drift seals” are used. The purpose of these barriers is to constrain the possible infiltration of brine and to prevent the migration of radionuclides into the biosphere. In a rock salt mine a large scale in-situ experiment of a sealing construction made of salt concrete was set up to prove the technical feasibility and operability of such barriers. In order to investigate the integrity of this structure, non-destructive ultrasonic measurements were carried out. Therefore two different methods were applied at the front side of the test-barrier: 1 Reflection measurements from boreholes 2 Ultrasonic imaging by means of scanning ultrasonic echo methods This extended abstract is a short version of an article to be published in a special edition of ASCE Journal that will briefly describe the sealing construction, the application of the non-destructive ultrasonic measurement methods and their adaptatio...
Kurzfassung. Aktuell wird die Ultraschallechotechnik für Holzbauteile genutzt, indem aus der Absc... more Kurzfassung. Aktuell wird die Ultraschallechotechnik für Holzbauteile genutzt, indem aus der Abschattung eines ansonsten stabilen Rückwandechos auf Auffälligkeiten im Holzbauteil geschlossen wird. Dabei werden Transversalwellen (Mittenfrequenz 50 kHz) mit der Polarisationsrichtung in Faserrichtung (L) angewendet. In einem 2012 abgeschlossenen Forschungsvorhaben wurde nun die direkte Abbildung von Streuern durch anisotrope SAFT-Rekonstruktion entwickelt. Dazu werden flächig aufgenommene Ultraschallmessdaten mit automatisiert scannenden Druckund Scherwellenköpfen erzeugt und auf Basis anisotroper Geschwindigkeitsverteilungen rekonstruiert. Benutzt werden die auch häufig für Beton eingesetzten trocken ankoppelnden Punktkontakt-Prüfköpfe. Da damit auch intensive Wellen an der Oberfläche erzeugt werden, entstehen im Material zusätzliche Kopfwellen, die ebenfalls bei der Rekonstruktion berücksichtigt werden. Da die Wellengeschwindigkeiten in Holz individuell stark schwanken, wird eine int...
Construction methods, environmental stressors, and aging factors are the main causes for defects ... more Construction methods, environmental stressors, and aging factors are the main causes for defects of reinforced concrete in nuclear power plants (NPP). These defects are typically occurred as corrosion of reinforcement steel, delamination, cracks, malfunction of post-tensioning or steel composite systems etc. Some of the challenges for assessing the performance of these structures by nondestructive testing methods (NDT) are that the assessment could be performed only during the annual overhauls when testing is time-limited and uncertainty of the accuracy and reliability of the available NDT testing devices combined with the lack of the international uniformity of the methods used for NDT tests. To overcome these challenges, a mock-up wall representing a section of the concrete containment of the NPP was built. The mock-up wall included simulated defects, which mimic the most common types of defects in NPP concrete structures such as dimensional errors, honeycombing, delamination, def...
Im Jahr 2011 hat der Bundestag in Deutschland den Ausstieg aus der Kernenergie beschlossen. Der a... more Im Jahr 2011 hat der Bundestag in Deutschland den Ausstieg aus der Kernenergie beschlossen. Der angefallene Abfall wird mehr als hunderttausend Jahre eine derartig hohe Aktivität besitzen, dass er eine erhebliche Gefahr für nachfolgende Generationen darstellen kann. Dieser radioaktive Abfall soll in tiefen geologischen Formationen (z. B. Salz, Ton oder Kristallin) sicher endgelagert werden. Die Endlager werden mittels sogenannter geotechnischer Abdichtbauwerke (Schacht‐ bzw. Streckenverschlüsse) verschlossen, wofür u. a. Zement‐ oder Sorel‐basierte Baustoffe (Betone) in Frage kommen. Die Beschreibung des Dichtvermögens dieser Bauwerke ist unabdingbar. In der Forschungsphase werden verschiedene Werkstoffe untersucht und Methoden für die zerstörungsfreie Untersuchung der Bauwerke als Mittel der Qualitätsprüfung entwickelt. Hierbei ist der Nachweis der Rissfreiheit bzw. die Detektion möglicher Risse ein vorrangiges Thema. In den letzten Jahren konnten bereits umfangreiche Erfahrungen mit der Untersuchung von in‐situ‐Versuchsobjekten in Realmaßstab gesammelt werden. Die Messungen wurden im Endlager für radioaktive Abfälle Morsleben am in‐situ‐Versuch “Abdichtbauwerk im Steinsalz” und in der Grube Teutschenthal am Großversuch GV2 durchgeführt. Es ist gelungen mit einem neu entwickelten Ultraschall‐Messsystem Eindringtiefen bis ca. 9,0 m zu realisieren. Die Messungen mit dem Large Aperture Ultrasonic System in Kombination mit der Rekonstruktion‐Methode Synthetic Aperture Focusing Technique zeigen, dass die zerstörungsfreie Prüfung von Abdichtbauwerken möglich und die Nutzung des Messsystems zur Qualitätssicherung bei der Erstellung der Verschlussbauwerke vielversprechend ist.
Quality assurance and condition assessment of concrete structures is an important topic world-wid... more Quality assurance and condition assessment of concrete structures is an important topic world-wide due to the aging infrastructure and increasing traffic demands. Common topics include, but are not limited to, localisation of rebar or tendon ducts, geometrical irregularities, cracks, voids, honeycombing or other flaws. Non-destructive techniques such as ultrasound or radar have found regular, successful practical application but sometimes suffer from limited resolution and accuracy, imaging artefacts or restrictions in detecting certain features. Until the 1980s X-ray transmission was used in case of special demands and showed a much better resolution than other NDT techniques. However, due to safety concerns and cost issues, this method is almost never used anymore. Muon tomography has received much attention recently. Novel detectors for cosmic muons and tomographic imaging algorithms have opened up new fields of application, such as the investigation of freight containers. Muon i...
Nondestructive Testing of Materials and Structures, 2011
The present paper describes the development and first application of ultrasonic imaging of timber... more The present paper describes the development and first application of ultrasonic imaging of timber (wood) by means of reconstruction calculation (3D-SAFT; Synthetic Aperture Focusing Technique). It considers the highly anisotropic ultrasonic velocity on wood. In order to validate such techniques we report on experiments carried out on test specimens made from pine and beech. Those specimens differ for the orientations of the annual rings. For the reconstruction calculation the slowness curves of the material are considered applying the elastic constants known from the literature. The anisotropic SAFT reconstruction is calculated from measured datasets and from synthetic data resulting from EFIT modelling (EFIT: Elastodynamic Finite Integration Technique).
There is a great demand for non-destructive testing methods for quality assurance and to assess t... more There is a great demand for non-destructive testing methods for quality assurance and to assess the safety and durability of wooden structures. Ultrasonic echo technique with shear waves in the frequency range of 50 kHz is one of those promising methods and is already frequently applied for usual and glued laminated timber. The article describes the development and first results for an imaging method for this purpose. The highly anisotropic properties of the ultrasonic velocity have to be considered. A 3D-SAFT (Synthetic Aperture Focusing Technique) imaging scheme is developed initially for synthetic data resulting from modelling the elastic wave propagation. The main part of the paper describes the experimental validation of this evaluation technique by experimental studies applying automated ultrasonic scanning techniques. 3D ultrasonic imaging results are described for test specimens made from pine and spruce wood. Another object of investigation was a pedestrian bridge made from...
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