Filtern
Erscheinungsjahr
Dokumenttyp
- Beitrag zu einem Tagungsband (39)
- Zeitschriftenartikel (36)
- Beitrag zu einem Sammelband (32)
- Vortrag (21)
- Sonstiges (8)
- Posterpräsentation (8)
- Forschungsbericht (2)
- Buchkapitel (1)
Sprache
- Englisch (86)
- Deutsch (60)
- Mehrsprachig (1)
Schlagworte
- X-ray tomography (9)
- Computed tomography (8)
- Computertomographie (7)
- X-ray refraction (7)
- Self-corrosion (6)
- Concrete parameters (5)
- Dimensionelles Messen (4)
- Synchrotron radiation (4)
- Bragg magnification (3)
- Computed Tomography (3)
Eingeladener Vortrag
- nein (21)
Rock porosity determination by combination of X-ray computerized tomography with mercury porosimetry
(1997)
Abstract First results are described of coupling of mercury porosimetry with X-ray computerized tomography (CT) as a new combination technique for rock porosity studies. This technique is suitable for rock samples with a pronounced mercury intrusion-extrusion hysteresis and includes CT measurements before and after mercury intrusion. The entrapped portion of mercury, when the pressure after the intrusion into the rock sample is reduced to 0.1 MPa, serves as a contrast agent in the porous network to localize spatial distribution of rock porosity by CT. The results obtained show that the mercury intrusion and therefore the porosity were quite different for the separate mineral phases. Therefore the combination of mercury porosimetry and computer tomography can give 3-D data on mineral-specific porosity distributions with additional pore size information. In contrast to mercury porosimetry as a single method, results of the combination technique with CT represent a direct visualization of porosity variation and do not depend on any special pore network model.
A new method for the physical characterization of rock matrices for use in site investigations of nuclear waste repositories has been developed. The method can provide information needed in the assessment of the performance of the geosphere working as a natural barrier retarding the migration of radionuclides by diffusion into the rock matrix. Most conventional methods for the physical characterization of rocks give only bulk information. The combination of mercury porosimetry and computer tomography can give 3-D data on mineral-specific porosity distributions with additional pore size information. Additionally, limits for mineral-specific internal surface areas can be estimated, which is essential for the assessment of water-rock interaction and reactive interaction with radionuclides (sorption). Results of measurements on granitic rock (granodiorite) from the Baltic shield are discussed and integrated with results by complementary methods.
The application of two sets of methods for the characterization of rock pore systems is reported. Both are discussed in the context of other techniques described in the literature. (i) Impregnation with labelled polymethylmethacrylate (PMMA) and autoradiography or direct measurement of the tracer activity allows the investigation of the pattern of the spatial porosity distribution and quantitative measurement of mineral-specific, local porosities, porosity gradients as well as an assessment of hydraulic and diffusive transport properties. (ii) Quantitative information on surface areas within certain pore size ranges can be achieved by combination of mercury intrusion porosimetry with X-ray absorption computertomography. As examples of applications of these techniques, the effects of weathering, alteration, mechanical stress and large diameter coring on the pore network of rocks have been studied.
Die sehr gute Reproduzierbarkeit von tomographischen Messungen zusammen mit den digital vorliegenden Ergebnissen ermöglicht die zerstörungsfreie dreidimensionale quantitative Analyse der untersuchten Bauteile und Proben mit Methoden der Bildverarbeitung. Vorwiegend für den Nachweis von Poren eingesetzt, lassen sich mit CT auch unterschiedliche Materialbestandteile analysieren, wobei die einzige Voraussetzung ein hinreichender Unterschied (es genügen wenige Prozent) in den Röntgenabsorptionseigenschaften der zu unterscheidenden Bestandteile ist.
Mit den in der Bundesanstalt für Materialforschung und -prüfung entwickelten Computertomographieanlagen kann der Anteil von Hohlräumen und Materialbestandteilen einer Probe bestimmt werden, wobei die Größe der nachzuweisenden Bestandteile sich über mehrere Größenordnungen erstreckt.
An ausgewählten Beispielen aus den Bereichen Keramik, Bodenproben und Fahr-bahnübergangssystemen aus Asphalt werden die quantitativen Ergebnisse dargestellt und die in der Bestandteilanalyse erreichbare Genauigkeit diskutiert.
Drucksondierungen, teufengenaue Probenahme und Präparation MKW-kontaminierter Lockersedimente
(2000)
The fabric of mineral liner materials that had been exposed to organic compounds over a 12-year period was investigated as part of a wider research project. Macromorphological and micromorphological changes in the fabric were identified using computed tomography and polarisation microscopy.
Special care was taken to ensure artefact free sampling and sample preparation, in particular, the drying method used, has a substantial influence on the quality of the thin sections.
Fabric changes due to contaminant permeation over several years are, by and large, relatively small and their intensity is material specific. Silty clay CML1, in particular, contains a somewhat greater number of fissures and voids in comparison with the original material. The superposition of various processes in both test procedures and sample preparation may lead to fabric changes which can impede interpretation of the results.
Herakles - Untersuchung der Bronzestatue mittels Radiographie und Röntgen-Computertomographie 2001
(2003)
A novel 3D-CT scanner was set up at BAM to extend the applicability of the X-ray transmission microtomography (µ-CT) to specimens up to 30 cm in diameter. The scanner consists of a bipolar 320 kV micro focus tube and a flat panel detector of amorphous silicon. Minimisation of scattered radiation, control of room and system temperature, and corrective preprocessing on the projection data are necessary to achieve expectable CT images. Statistical evaluations to show the limits and results of CT investigations are reported.
Summary
Beside several favourable properties, like high specific strength and damping capacity, most magnesium alloys also exhibit an excellent castability and are therefore usually fabricated by high pressure die casting. Due to the high casting speed, the melt flow is non-laminar and air can be entrapped during the casting process causing porosity when the melt solidifies. The volume fraction of porosity can be up to 4%. Porosity highly influences the mechanical properties, reducing significantly the values of elongation, tensile strength and especially fatigue strength [1-5]. Additionally, no heat treatment is possible to reach the optimum mechanical properties of the material. An alternative casting technology to reduce porosity is the Thixomolding process where the material is cast in the semi-solid state.
Different methods of non-destructive testing are possible to detect and remove affected components to ensure using components with a low content of porosity. One alternative of evaluating the porosity is the computerized tomography (CT). The CT enables a 3-dimensional view of the cast component.
For the first time Metal Matrix Composites (MMC) have been investigated by 3D Computed Tomography combined with enhanced interface contrast due to X-ray refraction. X-ray refraction is a relatively new approach for the characterization of advanced materials. The related techniques of Refraction Topography and Refraction Computed Tomography have been developed and applied at our laboratory during the last decade to meet the actual demand for improved nondestructive characterization of high performance composites, ceramics and other low density materials and components. X-ray refraction occurs, when X-rays crosses interfaces of spherical or cylindrical shape (e.g. pores or fibres) in the same way as visible light is refracted by lenses. These X-ray optical effects can be observed at small scattering angles of few minutes of arc as the refractive index n of X-rays is nearly unity (n = 1 10-6). Due to the short X-ray wavelength of about 0.1 nm the technique determines the amount of inner surfaces and interfaces of nanometer dimensions. The technique is expected to solve many problems in understanding the meaning of micro and sub micro structures in materials science. With the results of the CT investigation, some questions could be clarified for a better understanding of fatigue failure mechanisms under cyclic loading conditions. The specimens for the test programme have been provided by MTU Aero Engines. They consist of a titanium matrix (Ti6242) reinforced by SiC fibres (SCS6). The investigations have been performed at the materials research station of BAM (BAMline) at the Synchrotron Facility BESSY in Berlin, Germany.
Use of 3D Micro Tomography for the Investigation of the Mechanical Properties of Cellular Metals
(2003)
Kurzfassung
Röntgen-Computertomographie (CT) ist eine industriell eingeführte Technik zur zerstörungsfreien Fehlererkennung. Seit einiger Zeit werden industrielle CT-Anlagen auch zur Geometriebestimmung, d.h. für dimensionelle Messungen eingesetzt. Bei diesen Messungen treten Messabweichungen auf, die wegen komplexer Einflussgrößen derzeit nur schlecht quantifiziert werden können. Die Größe der beobachteten Messabweichungen erschwert zum Teil noch die weitere Anwendung der CT als Messtechnik. Das momentan mit CT messbare Teilespektrum wird bei dickwandigen Bauteilen durch die fehlende Verfügbarkeit von Röntgendetektoren für hohe Energien (speziell Flächendetektoren) beschränkt. Im folgenden wird ein Forschungsprojekt zwischen 10 deutschen Industrieunternehmen und Instituten und zwei deutschen Bundesanstalten (Physikalisch-Technische Bundesanstalt (PTB) und Bundesanstalt für Materialforschung und -prüfung) vorgestellt, dass die Weiterentwicklung der CT als dimensionelle Messtechnik zur Aufgabe hat. Das Projekt hat eine Laufzeit von drei Jahren (Start 01.Okt. 2003). Es werden hier die Projektziele und erste Ergebnisse vorgestellt.
Micro-computed tomography (µCT) provides quantitative three-dimensional information of bone around titanium implants similar to classical histology. The study, based on an animal model, using cuboid-shaped biofunctionalised Ti6Al4V implants with surrounding bone after 4 weeks, is performed using 3 µCT-systems with X-ray tubes, one synchrotron-radiation-based µCT-system (SRµCT), and classical histology. Although the spatial resolution of the µCTsystems is comparable, only the results of SRµCT agree with results of classical histology. The X-ray tube sources give rise to huge artefacts in the tomograms (interface scattering, beam hardening), which impaired the quantitative analysis of bone up to about 200 µm from the implant surface. Due to the non-destructive character of µCT the specimens can be subsequently examined by classical histology
without restriction. The quantitative comparison of bone formation uncovers the strong dependence of the detected amount of newly formed bone from the selected slice. This
implies the necessity of 3D analysis. SRµCT and classical histology prove that surface modifications of the titanium implant significantly influence the bone formation. Using SRµCT, the preparation artefacts due to cutting and polishing are excluded.
Erstmals wurden MMCs mit Hilfe der Interface-Kontrast verstärkenden Röntgen-Refraktions-Technik in Kombination mit der 3D-CT-Technik untersucht. Die Methode der Röntgen-Refraktions-Topography sowie der Röntgen-Refraktions-Tomography wurden in den letzten Jahren speziell für die zerstörungsfreie Charakterisierung von Leichtbau-Hochleistungs-Werkstoffen wie Verbund-Werkstoffen und Keramiken entwickelt. Die Technik basiert auf der Refraktion von Röntgenlicht an Grenzflächen zwischen Bereichen unterschiedlicher Elektronendichte wie z.B. Faser- und Matrix-Werkstoff. Auf Grund der kurzen Röntgen-Wellenlänge hat der Brechungsindex einen Wert dicht bei eins, sodass der Streuwinkel nur wenige Bogenminuten beträgt. Der Vorteil der kurzen Wellenlänge besteht jedoch darin, dass Poren und Risse detektiert werden können, deren Größe im Nanometerbereich liegen. Damit kann die Refraktions-Technik zum besseren Verständnis von Mikro- und Submikro-Strukturen in der Materialwissenschaft eingesetzt werden. Mit der hier vorgestellten Refraktions-CT wurden Ermüdungsmechanismen an MMCs, bestehend aus SiC-Faser verstärktem Titan (Ti6242) untersucht. Die Messungen wurden am Röntgen-Messplatz der BAM (BAMline) am Synchrotron-Speicherring-BESSY in Berlin Adlershof durchgeführt.
Throughout human history, wood has been used for various purposes: for
building shelters, houses and bridges, for manufacturing furniture and
household or agricultural appliances (from ploughs to spoons), as burning
material or simply as walking sticks. Contemporarily, vast amounts of wood
are going into paper production. As a consequence, different qualities of
wood are selected appropriately for the various applications. Beams incorporated
into buildings and constructions have to be sturdy and durable;
boards for furniture are supposed to be free of knots or are expected to have
certain ornamental structures. As long as wood is not simply destined for
burning it should be free of undesired knots or internal damages such as rot
or worm holes. Particularly in cases of infestation with wood destroying
fungi that definitely impairs mechanical strength and even may generate
hollows such damages are frequently invisible from the outside. Radiographic
methods are capable to detect internal damages as well as hidden
knots without the need of drilling holes or cutting a specimen to pieces.
The most thoroughly method to visualise the interior of a wooden specimen
is tomography which shows annual growth rings in their complete circumference
and all the knots or damages that might be included. However, some
of them as well as patterns of annual rings suitable for dendrological investigations
are recognisable with a less laborious method that might be applicable
even in the field, i.e. contemporary digital radiography combined with
image processing. Samples of lumber shall be presented showing the typical
annual ring structures and some infested areas.
In this paper the characterisation of functionally graded materials is elucidated by several different methods. These methods described here are used for the quantitative analysis of materials with a local dependence of microstructure parameters. Using X-ray microscopy (computed tomography) for 3D-measurements and optical microscopy on polished sections for 1D and 2D measurements on the same sample, a ceramic filter consisting of sintered spherical particles, various mathematical evaluation methods are described and compared.
Analysis of morphology and composition with computed tomography exemplified at porous asphalt
(2007)
The in vivo effects of coating titanium implants with organic extracellular matrix molecules were examined in the sheep tibia. Titanium screws (5.0 mm) were coated with type I collagen (Ti/Coll) or type I collagen and chondroitin sulfate (Ti/Coll/CS) by biomimetic fibrillogenesis. Uncoated screws (Ti) and screws coated with hydroxyapatite (Ti/HA) served as control. Six adult female sheep received one screw of each type to stabilize a midshaft tibial fracture with external fixation. Four cylindrical implants of 4-mm outer diameter and 3.3-mm inner diameter with the same coatings were inserted into the tibial head. No pin track infections were seen at the time of implant retrieval 6 weeks after implantation. Extraction torque was greater for Ti/HA (1181 Nmm) and Ti/Coll/CS (1088 Nmm) compared to Ti/Coll (900 Nmm) and Ti (904 Nmm) [N.S.]. Newly formed bone was noted around all coated screws within the medullary cavity. Macrophage and osteoclast activity was significantly reduced around Ti/Coll/CS in both types of implants compared to uncoated controls (p < 0.05). Osteoblast activity was significantly increased around loaded Ti/Coll and Ti/Coll/CS screws compared to uncoated Ti screws (p < 0.05). Microtomographic evaluation (SRµCT) revealed no significant differences in new bone formation around the unloaded tibial head implants.Coating of external fixation devices with of type I collagen and chondroitin sulfate appears to have similar effects with respect to stability and bone healing as HA but with less osteoclast activity. These findings were more pronounced under loaded than unloaded conditions in the sheeptibia.
Carrying out dimensional measurements by CT means assessing coordinates in space. CT must therefore be treated as a coordinate measuring technique similar to optical or tactile Coordinate Measuring Machines (CMMs). The well-established standards and guidelines for the acceptance- and verificationtesting of CMMs require the use of calibrated reference standards to achieve measurement machine characteristics.
Hence, transferring these concepts from coordinate metrology to CT, a dedicated CT-specific reference standard was designed, manufactured and calibrated using a tactile CMM. For comparison purposes, a CAD model was created by reverse engineering using the calibration data. The calibrated model was fed into a virtual CT and the measurement process was simulated. The reference standard was measured by micro-CT.
By comparing the characteristics of the measurement output of CT and the output gained from simulation, the influences of measurement artefacts can be judged, for the first time, in analogy to existing Guidelines of coordinate metrology.
Die Struktur eines Materials bestimmt wesentlich dessen Gebrauchsverhalten. Diese einfache Weisheit ist Motivation für die ständige Weiterentwicklung des Untersuchungsinstrumentariums zur Gefügekennzeichnung von Baustoffen. Nachdem die Gefügeaufklärung insbesondere bei mineralischen Baustoffen bereits integrierter Bestandteil der Baustoffcharakterisierung ist, erhöht insbesondere die zunehmende Spezialisierung und Weiterentwicklung der Asphaltbaustoffe zusammen mit der Forderung nach gebrauchsgerechtem Leistungsnachweis den Bedarf an methodischer Entwicklung bei der Strukturkennzeichnung. Besondere Möglichkeiten zur tiefenaufgelösten und zerstörungsfreien räumlichen Visualisierung des Gefüges, der Ableitung strukturbeschreibender Kennwerte aber auch für eine anschließende Diskretisierung der inneren Struktur mittels finiter Elemente bietet das Verfahren der Computertomographie mit Röntgenstrahlen. Mit Hilfe verschiedener Anwendungen soll auf die Möglichkeiten dieser Methodik aufmerksam gemacht werden.
Charakterisierung typischer Defektstrukturen in modernen Werkstoffen mittels Computertomographie
(2008)
The high-resolution synchrotron-based imaging stations at the BAMline (BESSY) and TopoTomo (ANKA)
(2008)
The BAMline at the BESSY light source in Berlin and the TopoTomo beamline at the ANKA synchrotron facility in Karlsruhe (both Germany) operate in the hard X-ray regime (above 6 keV) with similiar photon flux density. For typical imaging applications, a double multilayer monochromator or a filtered white beam is used. In order to optimise the field of view and the resolution of the available indirect pixel detectors, different optical systems have been installed, adapted, respectively, to a large field of view (macroscope) and to high spatial resolution (microscope). They can be combined with different camera systems, ranging from 16-bit dynamic range slow-scan CCDs to fast CMOS cameras. The spatial resolution can be brought substantially beyond the micrometer limit by using a Bragg magnifier. The moderate flux of both beamlines compared to other 3rd generation light sources is compensated by a dedicated scintillator concept. For selected applications, X-ray beam collimation has proven to be a reliable approach to increase the available photon flux density. Absorption contrast, phase contrast, holotomography and refraction-enhanced imaging are used depending on the application. Additionally, at the TopoTomo beamline digital white beam synchrotron topography is performed, using the digital X-ray pixel detectors installed.
The use of high brilliance and partial coherent synchrotron light for radiography and computed tomography (CT) allows to image micro-structured, multi-component specimens with different contrast modes and resolutions up to submicrometer range. This is of high interest for materials research, life science and non-destructive evaluation applications. An imaging setup for microtomography and radiography installed at BESSY II (a third generation synchrotron light source located in Berlin, Germany) as part of its first hard X-ray beamline (BAMline) can now be used for absorption, refraction as well as phase contrast dedicated to inhouse research and applications by external users. Monochromatic synchrotron light between 6 keV and 80 keV is attained via a fully automated double multilayer monochromator. For imaging applications the synchrotron beam transmitted by the sample is converted with a scintillator into visible light. By use of microscope optics this luminescence image is then projected onto, e.g., a CCD chip. Several scintillating materials are used in order to optimise the performance of the detector system. Different optical systems are available for imaging ranging from a larger field of view and moderate resolutions (macroscope up to 14 mm x 14 mm field of view) to high resolution (microscope down to 0.35 μm pixel size), offering magnifications from 1.8× to 40×. Additionally asymmetric cut Bragg crystals in front of the scintillator can be used for a further magnification in one dimension by a factor of about 20. Slow and fast cameras are available, with up to 16 bit dynamic range. We show the suitability of the setup for numerous applications from materials research and life science.
X-ray refraction topography techniques are based on ultra-small angle scattering by micro-structural elements causing phase-related effects such as refraction and total reflection at a few minutes of arc as the refractive index of X-rays is nearly unity. The refraction contrast is several times higher than true absorption and results in images of cracks, pores and fibre debonding separations below the spatial resolution of the detector. In most cases the investigated inner surface and interface structures correlate to mechanical properties. For the exploration of micro structured materials the refraction technique has been improved by a 3D Synchrotron Refraction Computed Tomography test station. The specimen is placed in an X-ray beam between two single crystals, which suppresses all sample scattering. In addition, an asymmetric cut second crystal can magnify the image up to 50 times revealing nano meter resolution. The technique is an alternative to other attempts on raising the spatial resolution of CT machines.
Corrosion of steel reinforcement in concrete exposed to chloride containing
environments is a serious problem in civil engineering practice. Electrochemical
methods, e.g. potential mapping, provide information whether the steel reinforcement
is still passive or depassivation has been initiated. By applying such techniques no
information on the type of corrosion, its extent and distribution of corrosion products
is available. Particular the corrosion progress is a significant problem. Especially in
the case of element corrosion in reinforced concrete structures, the development at
the anode can not be separated into corrosion damage causing by element corrosion
or self-corrosion. Until now also in laboratory tests it is impossible to collect such
information without destroying specimens after electrochemical testing was
performed place. To overcome this problem it was tried to study the steel surface
within the mortar specimens by X-ray tomography (CT). Within the scope of these
investigations it could be shown, that X-ray tomography is suitable to make corrosion
pits visible which are embedded in a mortar with a cover thickness of about 35 mm.
In this publication the corrosion damage of reinforced steel is documented timedependent
by X-ray tomography.