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- X-ray refraction (3)
- Chaboche model (2)
- Computed tomography (2)
- GTN model (2)
- 3D printing (1)
- 3D printing Polyamide 12 (1)
- Additive Fertigung (AM) (1)
- Bending property (1)
- CFR-PEEK (1)
- CMAS (1)
Organisationseinheit der BAM
- 8.5 Röntgenbildgebung (9) (entfernen)
Die Integrität der Verstärkungsfasern in Komposit-Zahnstiften ist entscheidend für die Biegefestigkeit und die langfristige Haftung am Zement in den Wurzelkanälen. Es wurde vermutet, dass die Integrität von glasfaserverstärkten Zahnstiften durch das Beschleifen während der zahnmedizinischen Behandlung beeinträchtigt wird. Eine Beschädigung der Fasern führt zu einer erheblichen strukturellen Schwächung über den gesamten Stiftdurchmesser. Glasfragmente, die durch den Kontakt mit dem Zahnbohrer entstehen, können sich vom Stift lösen und die Haftfähigkeit erheblich verringern. Mit Hilfe hochauflösender Synchrotron-Röntgen-Refraktions-Radiographie (SXRR) konnte das Ausmaß der Schäden zuverlässig identifiziert und charakterisiert werden.
Dazu wurden die Glasfaserstifte sowohl im Herstellungszustand als auch nach der Bearbeitung mit einem Diamantbohrer untersucht. Die Datensätze wurden zur Visualisierung und Quantifizierung der morphologischen Charakteristika intakter und durch das Beschleifen beschädigter Regionen analysiert. Sie zeigen Schäden im bearbeiteten Bereich (z. B. Brüche, Splitter und Risse) sowie herstellungsbedingte Inhomogenitäten der Fasern mit einer signifikanten Zunahme der inneren Oberflächen in Probenregionen, die durch das Beschleifen beschädigt wurden.
Objectives. There is concern that the integrity of fiberglass dental posts may be affected by chairside trimming during treatment. We hypothesize that hard X-ray methods of phase contrast-enhanced micro-CT (PCE-CT) and synchrotron based X-ray refraction (SXRR) can reliably identify and help characterize the extent of damage.
Methods. Fiberglass posts were imaged both as manufactured and following trimming with a diamond bur. Each of the posts was imaged by SXRR and by PCE-CT. Datasets from PCE-CT were used to visualize and quantify 2D and 3D morphological characteristics of intact and of damage-affected regions caused by trimming. Results. The SXRR images revealed fiber inhomogeneities from manufacturing with a significant increase in internal surfaces in sample regions corresponding to damage from trimming. PCE-CT volumes unveiled the micromorphology of single fibers in the posts and some damage in the trimmed area (e.g. fractures, splinters and cracks). Area, perimeter, circularity, roundness, volume and thickness of the glass fibers in the trimmed area were statistically different from the control (p < 0.01).
Significance. The integrity of single fibers in the post is critical for bending resistance and for long-term adhesion to the cement in the root canals. Damage to the fibers causes substantial structural weakening across the post diameter. Glass fragments produced due to contact with the dental bur may separate from the post and may significantly reduce bond capacity. The above mentioned synchrotron-based imaging techniques can further facilitate assessment of the structural integrity and the appearance of defects in posts (e.g. after mechanical load).
Material extrusion of thermoplastic polymers enables the realization of complex specific designs with high performance composites. The present study aims at evaluating the mechanical properties of carbon fiberreinforced semi-crystalline thermoplastic polymer polyether ether ketone (CFR-PEEK) manufactured by material extrusion and correlating them with results obtained by micro-CT. Samples in the shape of small bars were provided by Kumovis (Munich, Germany). The determination of surface roughness and density was followed by three-point bending tests. To reveal the pore distribution as well as the fusion quality of CFR PEEK when applied with external forces, micro-CT scans were performed with an X-ray microscope before and after the mechanical test to localize the sites where the fracture is generated. The density of CFR-PEEK bars indicated that they had superior mechanical properties compared with our previous study on unfilled 3D printed PEEK (bending modulus: (5.4 ± 0.5) GPa vs. (1.05 ± 0.05) GPa to (1.48 ± 0.10) GPa; bending strength: (167 ± 11) MPa vs. (51 ± 15) to (193 ± 7) MPa). Micro-CT analyses revealed the local 3D-distribution of voids. Voids of 30 μm diameter are nearly spherical and make up the main part of the total porosity. The larger the voids, the more they deviate from a spherical shape. Significant lack-of-fusion voids are located between the deposited filaments. By growing and merging, they act as seeds for the forming fracture line in the region of the flexural specimens where the maximum local tensile stresses occurred under bending load. Our work provides a detailed analysis of printed PEEK with fiber additive and relates this with mechanical properties.
In order to characterise the material and damage behaviour of additively manufactured polyamide 12 (PA12) under quasi-static load and to implement it in a numerical model, experiments under quasi-static load as well as microstructural investigations were carried out. Selective laser sintering (SLS) was used as the manufacturing process. For the classification of the material behaviour, quasi-static cyclic tests with holding times as well as tensile tests were performed. X-ray refraction and computed tomography (CT) were used to investigate the damage behaviour. The Chaboche model, which has already been applied for metallic materials under thermomechanical loading, served as the basis for the selection of the numerical material model. The same procedure was used for the selection of the damage model, where the Gurson–Tvergaard–Needleman (GTN) model was chosen, which was already used for porous metallic materials. The Chaboche model shows very good agreement with experimental results. Furthermore, the coupling with the GTN model allows a very good modelling of the damage behaviour. Finally, it could be shown that the selected models are suitable to simulate the material and damage behaviour of 3D printed PA12.
The material and damage behaviour of additively manufactured polyamide 12 under cyclic loading was characterized by cyclic tests and microstructure analysis by using microscopy, X-ray refraction, and computed tomography. The results were used to determine parameters for the viscoplastic material model by Chaboche and a damage model by Gurson-Tvergaard-Needleman. The temperature was monitored during the experiments and the self-heating effect was observed. By including this effect, a higher accuracy could be achieved with the results of mechanical experiments.
Degradation of thermal barrier coatings (TBCs) in gas‐turbine engines due to calcium–magnesium–aluminosilicate (CMAS) glassy deposits from various sources has been a persistent issue since many years. In this study, state of the art electron microscopy was correlated with X‐ray refraction techniques to elucidate the intrusion of CMAS into the porous structure of atmospheric plasma sprayed (APS) TBCs and the formation and growth of cracks under thermal cycling in a burner rig. Results indicate that the sparse nature of the infiltration as well as kinetics in the burner rig are majorly influenced by the wetting behavior of the CMAS. Despite the obvious attack of CMAS on grain boundaries, the interaction of yttria‐stabilized zirconia (YSZ) with intruded CMAS has no immediate impact on structure and density of internal surfaces. At a later stage the formation of horizontal cracks is observed in a wider zone of the TBC layer.
Determination of short carbon fiber orientation in zirconium diboride ceramic matrix composites
(2024)
In fiber-reinforced components, the fiber alignment and orientation have paramount influence on the thermomechanical properties of the resulting composite, for both short and continuous fiber. Here we present the case of an ultra-refractory matrix intended for extreme environment applications, ZrB2, reinforced with 20 vol% and 50 vol% short carbon fibers. In both cases, fibers tend to align perpendicular to the uniaxial pressure applied during shaping and sintering of a pellet, although the fiber tilt across the pellet thickness is difficult to determine. Moreover, for high volume fractions of reinforcement, the spatial distribution of the fibers is heterogeneous and tends to have domains of preferential orientations. We compare the information on the fiber distribution as collected by scanning electron microscopy images, X-ray computed tomography and synchrotron X-ray refraction radiography (SXRR). The three techniques prove to be complementary. Importantly, we demonstrate that SXRR yields the most statistically significant information due to the largest field of view, yet with a sensitivity down to the nanometer, and that can be successfully applied also to heavy matrix materials, such as zirconium boride.
Die Degradation von Wärmedämmschichten(thermal barrier coatings - TBCs) in Gasturbinen durch glasartige Calcium-Magnesium-Aluminiumsilikat (CMAS)Ablagerungen aus verschiedenen Quellen istseit vielen Jahren ein anhaltendes Problem. In dieser Studie wurde mit Hilfe derSynchrotron-Röntgen-Refraktions-Radiographie (SXRR), und vergleichend mit der Elektronenmikroskopie, das Eindringen von CMAS in die poröse Struktur von atmosphärisch plasmagespritzten (APS)TBCs sowie die Bildung und das Wachstum von Rissen unter thermisch zyklischer Belastung untersucht. Die Ergebnisse deuten darauf hin, dass die Infiltration sowie deren Kinetik im Brenner-Teststand wesentlich vom Benetzungsverhalten des CMAS beeinflusst werden. Trotz desoffensichtlichen Angriffs von CMAS auf die Korngrenzen hat die Wechselwirkung von Yttriumdioxid-stabilisiertem Zirkoniumdioxid (YSZ) mit intrudiertem CMAS keinen unmittelbaren Einfluss auf die Struktur und Dichte der innen Oberflächen(Risse, Poren). In einem späteren Stadium wird die Bildung von Rissen senkrecht zur äußeren Oberfläche in einer breiteren Zone der TBC-Schicht beobachtet.
Um das Material- und Schädigungsverhalten von additiv gefertigtem Polyamid 12 (PA12) unter quasistatischer Belastung zu charakterisieren, wurden mechanische Tests und Röntgenverfahren zur Bestimmung der Mikrostruktur eingesetzt. Die Proben wurden nach dem Prinzip des Selektiven Lasersinterns (SLS) hergestellt. Unter quasistatischer Belastung mit Haltezeiten ergab sich ein viskoplastisches Materialverhalten. Im Zugversuch wurde eine maximale Zugfestigkeit von 40.6 MPa und eine Bruchdehnung von 7.4% beobachtet. Mittels Röntgenrefraktion wurde eine Erhöhung von inneren Oberflächen beobachtet, die senkrecht zur Zugrichtung orientiert sind. Die Analyse der Gesamtporosität aus Computertomographie-Messungen ergab keine Änderung infolge der Zugbelastung. Jedoch wurde eine bimodale Porengrößenverteilung und eine steigende Sphärizität festgestellt. Das Materialverhalten wurde mit dem Chaboche-Modell simuliert und ergab eine sehr gute Übereinstimmung mit den experimentellen Ergebnissen. Allerdings gestattet dieses Modell nicht, das Schädigungsverhalten abzubilden. Daher wurde zur Simulation des Schädigungsverhaltens das Modell gemäß dem Ansatz von Gurson, Tvergaard und Needleman unter Berücksichtigung der mikrostrukturellen Parameter erweitert. Der Schwerpunkt des Beitrags liegt auf den Röntgenverfahren zur experimentellen Bestimmung der Mikrostruktur.