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- X-ray absorption tomography (2)
- X-ray computer tomography (2)
- Accelerator magnet coils (1)
- Additive manufacturing (1)
- Adsorption (1)
- Biomedical engineering (1)
- Bronzeguss (1)
- Coil winding (1)
- Cracks (1)
- Dentistry (1)
Organisationseinheit der BAM
During Rutherford cable production the wires are plastically deformed and their initially round shape is distorted. Using X-ray absorption tomography we have determined the 3D shape of an unreacted Nb3Sn 11 T dipole Rutherford cable, and of a reacted and impregnated Nb3Sn cable double stack. State-of-theart image processing was applied to correct for tomographic artefacts caused by the large cable aspect ratio, for the segmentation of the individual wires and subelement bundles inside the wires, and for the calculation of the wire cross sectional area and shape variations. The 11 T dipole cable cross section oscillates by 2% with a frequency of 1.24 mm (1/80 of the transposition pitch length of the 40 wire cable). A comparatively stronger cross sectional area variation is observed in the individual wires at the thin edge of the keystoned cable where the wire aspect ratio is largest.
In the framework of the development of high field magnets made of Nb3Sn superconductor for projects like HL-LHC and FCC studies, it is needed to refine the understanding of the coil winding process and its impact on the overall mechanical behavior of the conductor. For this purpose, a new cable winding setup has been developed in order to compare the windability of different Nb3Sn Rutherford cables. In addition, various geometrical cable inspection methods were tested and compared. First experimental results obtained with the new set-up for winding tests are summarized.
Powdered activated carbon (PAC) for organic micro-pollutant (OMP) removal can be applied effectively on wastewater treatment plant (WWTP) effluents by using re-circulation schemes, accumulating the PAC in the system. This technique is complex because several factors are unknown: (i) the PAC concentration in the system, (ii) specific and average contact times of PAC particles, and (iii) PAC particle loadings with target compounds/competing water constituents. Thus, performance projections (e.g. in the lab) are very challenging. We sampled large-scale PAC plants with PAC sludge re-circulation on eight different WWTPs. The PAC plant-induced OMP removals were notably different, even when considering PAC concentrations in proportion to background organic sum parameters. The variability is likely caused by differing PAC products, varying water composition, differently effective plant/re-circulation operation, and variable biodegradation. Plant PAC samples and parts of the PAC plant influent samples were used in laboratory tests, applying multiples (0.5, 1, 2, 4) of the respective large-scale “fresh” PAC doses, and several fixed contact times (0.5, 1, 2, 4, 48 h). The aimwas to empirically identify suitable combinations of lab PAC dose (as multiples of the plant PAC dose) and contact time, which represent the PAC plant
performances in removing OMPs (for specific OMPs at single locations, and for averages of different OMPs at all locations). E.g., for five well adsorbing, little biodegradable OMPs, plant performances can be projected by using a lab PAC dose of twice the respective full-scale PAC dose and 4 h lab contact time (standard deviation of 13 %-points).
The impact of fracture geometry and aperture distribution on fluid movement and on non-reactive solute transport was investigated experimentally and numerically in single fractures. For this purpose a hydrothermally altered and an unaltered granite drill core with axial fractures were investigated. Using three injection and three extraction locations at top and bottom of the fractured cores, different dipole flow fields were examined. The conservative tracer (Amino-G) breakthrough curves were measured using fluorescence spectroscopy. Based on 3-D digital data obtained by micro-computed tomography 2.5-D numerical models were generated for both fractures by mapping the measured aperture distributions to the 2-D fracture geometries (x-y plane). Fluid flow and tracer transport were simulated using COMSOL Multiphysics®.
By means of numerical simulations and tomographic imaging experimentally observed breakthrough curves can be understood and qualitatively reproduced. The experiments and simulations suggest that fluid flow in the altered fracture is governed by the 2-D fracture geometry in the x-y plane, while fluid flow in the unaltered fracture seems to be controlled by the aperture distribution. Moreover, we demonstrate that in our case simplified parallel-plate models fail to describe the experimental findings and that pronounced tailings can be attributed to complex internal heterogeneities. The results presented, implicate the necessity to incorporate complex domain geometries governing fluid flow and mass transport into transport modeling.
The osseointegration in/around additively manufactured (AM) lattice structures of a new titanium alloy, Ti–19Nb–14Zr, was evaluated. Different lattices with increasingly high sidewalls gradually closing them were manufactured and implanted in sheep. After removal, the bone–interface implant (BII) and bone–implant contact (BIC) were studied from 3D X-ray computed tomography images. Measured BII of less than 10 µm and BIC of 95% are evidence of excellent osseointegration.
Since AMnaturally leads to a high-roughness surface finish, the wettability of the implant is increased.
The new alloy possesses an increased affinity to the bone. The lattice provides crevices in which the biological tissue can jump in and cling. The combination of these factors is pushing ossification beyond its natural limits. Therefore, the quality and speed of the ossification and osseointegration in/around these Ti–19Nb–14Zr laterally closed lattice implants open the possibility of bone spline key of prostheses. This enables the stabilization of the implant into the bone while keeping the possibility of punctual hooks allowing the implant to be removed more easily if required. Thus, this new titanium alloy and such laterally closed lattice structures are appropriate candidates to be implemented in a new generation of implants.
Im Frühjahr 1969 wurde bei Ausgrabungen der Universität Bonn unter Leitung von Elmar Edel auf der Qubbet el-Hawa ein außergewöhnliches Depot mit Materialien einer antiken Gusswerkstatt gefunden. Im Zuge der Fundteilung gelangten die meisten Stücke des Konvolutes in das Ägyptische Museum der Universität Bonn und werden dort aufbewahrt.
Die Deponierung des für die Forschung zur antiken Metallurgie bisher einzigartigen Konvoluts geschah im Zuge der Nachnutzung von Grabanlagen aus dem Alten Reich (um 2100 v. u. Z.) in der ägyptischen Spätzeit (um 550 – 400 v. u. Z.). Das Depot enthält Objekte, die alle Fertigungsstufen von Metallgegenständen im Wachsausschmelzverfahren dokumentieren. Es wurden Stücke von Rohwachs sowie Wachsmodelle und die zu deren Herstellung genutzten Negativformen gefunden. Weiterhin enthielt es vollständige Gussformen, die in einem aufwendigen Mehrschalenverfahren hergestellt wurden und teilweise bereits für den Guss ausgebrannt worden sind. Schließlich zählen einige Metallfiguren sowie weitere figürliche Objekte zum Konvolut, die alle in den Bereich einer kunsthandwerklichen Werkstatt deuten. Eine Besonderheit stellen zudem Gussformen dar, in denen Fragmente von Metallfiguren zur Reparatur im Überfangguss vorbereitet waren.
Das Depot wurde in der Gesamtpublikation der Bonner Grabungen bisher nur summarisch vorgestellt. 2014/15 initiierten die Abteilung Ägyptologie der Universität Bonn und das LVR-LandesMuseum Bonn unter Ludwig D. Morenz und Michael Schmauder ein gemeinsames und von der Fritz-Thyssen-Stiftung gefördertes Forschungsprojekt, das von Martin Fitzenreiter, Johannes Auenmüller und Frank Willer geleitet wurde. In Kooperation mit Dietmar Meinel (Bundesanstalt für Materialforschung und -prüfung Berlin / BAM, Fachbereich 8.5 Mikro-ZfP), Roland Schwab (Curt-Engelhorn-Zentrum Archäometrie gGmbH, Mannheim), Gerwulf Schneider (FU Berlin, Exzellenzcluster TOPOI), Ursula Baumer und Patrick Dietemann (beide Doerner-Institut / München), Thorsten Geisler-Wierwille (Steinmann Institut für Geologie, Mineralogie und Paläontologie der Universität Bonn) sowie Ursula Tegtmeier (Labor für Archäobotanik der Universität Köln) wurden die Objekte des Konvolutes eingehend und mit zeitgemäßen Verfahren untersucht. Die Ergebnisse dieses Forschungsprojekts werden in dieser Publikation vorgelegt.
Relation between crack opening and extent of the damage induced at the steel/mortar interface
(2018)
Cracks are inevitable in reinforced concrete structures and promote the diffusion of aggressive agents towards the reinforcement. In Eurocodes, for some exposure conditions, a threshold not to be exceeded for crack width near the rebar is recommended in order to limit risks of corrosion development and ensure structure durability. On the other hand, several studies show that the steel/mortar interface quality at the intersection with a crack strongly influences corrosion development. The aim of this study was therefore to test whether a relation exists between the extent of mechanical damage at the interface and the corresponding residual crack opening. To this end, specimens were cracked using three point bending test apparatus and the evolution of crack opening was determined on the outer surface and deep within the specimen. It was observed that the crack opening measured on the outer surface of the specimen was very close to that measured at various depths within the specimen at the same height level. In addition, the length of the mechanically damaged interface was determined for each residual crack opening.
It was deduced that cracks induced significant steel/mortar Interface damage independently of the size of their openings. The length of the mechanically damaged interface increased proportionally to the residual crack opening without showing marked variation after a certain crack opening value.
Based on the observed results, it is deduced that defining thresholds on crack openings is logical for esthetic reasons but is not articularly relevant for corrosion risk assessment.
Several cylindrical specimens and dental implants, presenting diagonal lattice structures with different cell sizes (600, 900 and 1200 µm) were additively manufactured by selective laser melting process. Then they were implanted for two months in a sheep. After removal, they were studied by Archimedes’ method as well as X-ray computed tomography in order to assess the penetration of bone into the lattice. We observed that the additive manufactured parts were geometrically conform to the theoretical specifications. However, several particles were left adhering to the surface of the lattice, thereby partly or entirely obstructing the cells. Nevertheless, bone penetration was clearly visible. We conclude that the 900 µm lattice cell size is more favourable to bone penetration than the 1200 µm lattice cell size, as the bone penetration is 84 % for 900 µm against 54 % for 1200 µm cell structures. The lower bone penetration value for the 1200 µm lattice cell could possibly be attributed to the short residence time in the sheep. Our results lead to the conclusion that lattice implants additively manufactured by selective laser melting enable better bone integration.