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- Laminography (3)
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The research and development (R&D) in the field of safety and security of sea-freight Containers has gained more importance after the U.S. house resolution 1 (H.R.1). According to this law, all the freight Containers which are transported from non-U.S. port of origin to U.S. ports should be inspected 100% against explosive and contraband materials using non-intrusive imaging equipment and radiation detectors. As the port of Hamburg and Bremerhaven are the leading Container ports in Europe, it is essential to develop reliable and high-resolution detection technologies for the non-destructive inspection of large sea-freight Containers.
Grouting defects, e.g. in post-tensioned structures or piped anchors may be identified by ultrasonic imaging. Since several years experiences are carried out with false color displayed phase values, which enable distinct localization of ungrouted regions.
In this contribution we report on progress in localizing grouting defects in tendon ducts, when they are only partly grouted and the unfilled part is not orientated into the direction of the measuring surface. This is frequently the case e.g. for box girder structures.
Düring the project specimens containing different types of grouting faults are investigated in Order to optimize measuring and evaluation techniques. A handheld linear array System (commercially available) is applied for fast 2D-measurement and subsequent phase sensitive 3D-imaging (new Software development).
In a large concrete wall specimen tendon ducts and real prestressing Systems containing grouting defects were built in. The ducts are partly covered by non prestressed reinforcement bars in order to investigate its disturbing influence. These included objects were investigated afterwards with the described methods. We report on large area measuring results, which were partly verified by y-radiography. In the frame of practical application results of measuring the position and extend of a blockade within a posttensioned structure are presen ted.
Zur Durchstrahlung großer, dichter Objekte reichen die Energien, die mit normalen Röntgenröhren erzielt werden können, ab gewissen Schichtdicken nicht mehr aus. Als hochenergetische Strahlenquellen stehen Kobalt-60 und Elektronenbeschleuniger zur Verfügung. Als Einschränkung der Hochenergieradiografie ist der geringere Kontrast besonders beim Vorhandensein leichterer Objekte umgeben von Körpern bestehend aus schweren Elementen anzusehen. Es ist daher zu erwarten, dass Objekte aus organischen Substanzen hinter dicken Schwermetallwänden oder in Bohrungen von Metallblöcken schwer zu erkennen sind. Im Unterschied zu einem Gammastrahler wie Kobalt-60 mit den beiden Spektrallinien um 1,3 MeV besitzt die Bremsstrahlung aus einem Beschleuniger einen wesentlichen Anteil an niederenergetischer Strahlung, der fließend zu höheren Energien übergeht. Es wird hier untersucht, welche Signaturen von leichten Materialien in einer Umgebung aus Schwermetall bis zu welcher Dicke und bis zu welchem Komplexitätsgrad erkennbar sind. Mit einem Betatron (JME X-ray Betatron 7,5 MeV) und einem Matrixdetektor (Perkin Elmer XRD 1621) wurden Aufnahmen von unterschiedlichen leichten Objekten angefertigt, die zunehmend in eine Umgebung aus Schwermetallen gestellt wurden. Mit unterschiedlichen Energieeinstellungen wurde untersucht, inwieweit eine Materialerkennung hinter welcher Abschirmung möglich ist. Die experimentellen Ergebnisse werden mit Simulationen verglichen, die mit einer Software zur Modellierung von Durchstrahlungsverfahren (aRTist) erzeugt wurden. Dabei wird dem Problem der Aufhärtung bei Anwendung von Bremsstrahlung Rechnung getragen. Die Ergebnisse können sowohl zur Erkennung von Fremdkörpern in Maschinen oder Pumpen als auch zur Überprüfung von Frachtladungen im Bereich der öffentlichen Sicherheit und bei Zollkontrollen dienen.
Digital detectors such as phosphor imaging plates (IP) and digital detector arrays (DDA) enable radiographic inspection with higher efficiency and improved image quality in comparison to the classic film technique. The mobile mechanised tomographic system TomoCAR (tomographic computer aided radiology) was developed first for inspection of circumferential welded seams of pipes. It consists of the manipulator based position control of an X-ray tube in front of the region to inspect and a digital detector array behind it. The high contrast sensitivity technique was combined with planar tomography. The tomographic reconstruction allows the three-dimensional (3D) representation of the material structure and included defects, equivalent to a metallographic cross sectioning. The hardware design is based on a specially developed flat X-ray tube and a direct converting CMOS detector array on CdTe basis. TomoCAR is applied for sizing of volumetric and planar defects. It allows the reliable detection of planar defects with openings larger than 25µm by subpixel resolution due to the achieved high signal-to-noise ratio. TomoCAR was successfully qualified as the result of a German pilot study on the basis of the European Network of Inspection and Qualification (ENIQ) guidelines for application in the nuclear power industry. Application examples are presented. The TomoCAR design was modified for in situ inspection of large aircraft components under production conditions. A gantry gate based planar tomograph was constructed and tested for inspection of the integrity of large flat CFRP panel components of up to 3 m × 9 m size. The integrity of imbedded stringers has been successfully observed. Different trials were performed to prove the finding rate of cracks in embedded stringers, which will be presented and discussed.
Hot crack assessment during production and processing of metallic materials is an essential prerequisite for the safety of welded structures. The hot cracking investigations presented here were carried out as part of a study aimed at the development of Cr/Ni low transformation temperature filler materials. Low transformation temperature alloys open up the possibility for welding high strength steels. The externally loaded Modified Varestraint Transvarestraint hot cracking test was employed in the experiments described. The hot cracking resistance was evaluated with the help of light microscopy applied at the specimen surface. The proportionality between hot cracking susceptibility and Cr/Ni alloy content was explained by the altered solidification kinetics and by the enlarged solidification interval. The internal crack paths and the three-dimensional structure of the crack net in the material volume were examined using X-ray computer tomography. The total crack lengths for different material depths and circumjacent rectangular volumes, respectively, were be determined. An increasing hot cracking susceptibility with increasing Cr/Ni alloy content was also be established for the specimen volume.
Zur Planung und Durchführung umfangreicher Sanierungs- und Umbaumaßnahmen im Pergamon-Museum Berlin bestand die Erfordernis einer Bauzustandsanalyse an antiken Baudenkmälern. Bestandsunterlagen waren unvollständig vorhanden bzw. fehlten. Hieraus ergab sich die Notwendigkeit des kombinierten Einsatzes zerstörungsfreier
Prüftechnik.