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Für die Berechnung des Crashverhaltens von Fahrzeugstrukturen muss zusätzlich zur Dehnratenabhängigkeit des plastischen Verformungsverhaltens des Grundwerkstoffs auch das Verhalten von Fügestellen bei hoher Beanspruchungsgeschwindigkeit bestimmt werden. Ziel der VDEh-Arbeitsgruppe 'Hochgeschwindigkeitszugversuche an gefügten Stählen' war die Erstellung eines Stahl-Eisen-Prüfblattes (SEP) zur Ermittlung crashrelevanter Kennwerte für gefügte Stahl-Feinbleche unter vereinheitlichten Prüfbedingungen. Zur Erarbeitung der in dieser Richtlinie zu formulierenden Empfehlungen wurden Scherzugversuche bei hoher Geschwindigkeit an punktgeschweißten und lasergeschweißten Proben von elf Prüflaboratorien durchgeführt. Der Beitrag beschreibt die Ergebnisse dieses Ringversuchs und seine Auswirkungen auf das SEP.
Ultrasonic phased array NDE has been applied to ensure the integrity of canisters for encapsulation of spent nuclear fuel. The performance of the NDE system is evaluated by the POD analysis. The POD analysis using a common method, â versus a, has been modified for the phased array ultrasonic inspections by two approaches: to take more influencing parameters into a, and to use a more sophisticated quantity as â. The POD with new a allows more detailed interpretation of POD for each parameter, and the new â gives more realistic POD. The methods are discussed and demonstrated with experimental data. In addition, an investigation of human factors is being planned and the plan is discussed.
Zukünftig soll durch die Installation von Windparks in der ausschließlichen Wirtschaftszone und deren Betrieb ein wesentlicher Anteil des Strombedarfs in Deutschland gedeckt werden. Für die zugehörige Realisierung der Windenergieanlagen hat die zuständige Behörde, das Bundesamt für Seeschifffahrt und Hydrographie, Standards veröffentlicht, über deren Inhalte im Hinblick auf die zu errichtenden Stahlkonstruktionen von Windenergieanlagen berichtet wird. Über die zu absolvierenden Freigabephasen und deren Bestandteile sowie über die Anforderungen, die die Genehmigungsbehörde an die Art und den Umfang der zu erbringenden Nachweise für die Tragstrukturen stellt, wird im Rahmen des Aufsatzes berichtet. Bei der zuständigen Genehmigungsbehörde durchlaufen derzeit die ersten Anträge das Genehmigungsverfahren. Über die hierbei gesammelten Erfahrungen wird aus Sicht der zuständigen Behörde und deren Fachgutachtern berichtet. Speziell hierbei auftretende Diskussionspunkte werden benannt und Hinweise gegeben.
Polyolefin surfaces (polyethylene and polypropylene) were exposed to haloform (CHX3) plasmas for introduction of monosort halogen groups. Bromoform and chloroform plasmas produced selectively C-Br (100 Br/100 C) and C-Cl (200 Cl/100 C) groups in high yields. The bromoform plasma showed 1-3 and the chloroform plasma 2-7 post-plasma introduced O-functionalities per 100 C. The polyolefin C-Br groups were grafted wet-chemically or by exposure to the vapour of amines, diols and glycols. Thus, spacer molecules could be covalently bonded to maximal 15 spacer molecules per 100 C for the smallest grafted molecules and 1.2 molecules/100 C for larger molecules as octaaminophenylene-POSS. After metal evaporation the end groups of these polymer-bonded spacer molecules formed also covalent bonds to the metal. Thus, flexible, hydrophobic and barrier elements were introduced into the polymer-metal interfaces for high-impact, high-durable and water-resistant metal-polymer composites as measured by means of peel strengths.
Branch junctions are mechanically particularly
interesting areas of trees, because they have to withstand a
combination of static and dynamic loads, from the stem as
well as from the branch. In the present work, the local
adaptation of material properties at branch junctions was
assessed by mapping microfibril angle and tissue density.
Images of the density distribution were obtained by computer
tomography (CT). Wide angle X-ray scattering
(WAXS) was used to determine the microfibril angle distribution
with high-resolution around the junctions. The
stem tissue around the junctions showed increased density
and microfibril angle, which points towards an optimisation
for fracture toughness. The tissue at the branch bases
showed low density combined with high MFA, which
provides deformability and flexibility and might act as
protection of the stem against load transmission from the
branch.
Among new types of plasma processes, the underwater plasma is one of the most attractive methods for functionalization of polymer surfaces. The interesting features of plasma solution system are that the material surfaces to be modified remain in contact with the plasma-moderated solution. The role of plasma-moderated liquids, allows the reach of the reactive species through solution onto the geometrically hindered sites. The UV radiation produced in plasma formation helps in generating additional excited, ionized, and dissociated molecules and species in the reaction solution. An interesting feature of the technique is its flexibility to use a wide variety of additives as or in solution system. This allows us to create a selective or monotype functionalization of material surfaces. Such system was studied for the selective hydroxyl functionalization of polypropylene surface. The oxidation of polymer surfaces and the introduction of O-containing functional groups by underwater plasma was found to exceed concentrations typically achieved in oxygen low-pressure gas discharge plasmas up-to two-folds (maximal 56 O/100 C). The fraction of OH groups among all O-containing moieties amounts from 25 to 40% in comparison to that in the gas plasma of about 10% OH groups. Addition of hydrogen peroxide into this same system increases the fraction of C—O bonds up to 75% (27-OH/100 O). A study was focused to optimize the role of hydrogen peroxide on the efficiency of oxidation and selectivity with chemical derivatization with respect to the formation of mono-sort hydroxyl functionalities, calculated using a chemical derivatization technique.
Force–distance curves have been acquired with an Atomic Force Microscope on polymethyl methacrylate with embedded glass spheres. The glass spheres provide a stiff substrate with an irregular and complex topography hidden underneath a compliant and even polymer film. This situation is a special case of a mechanical double-layer, which we examined in detail in previous experiments. Up to now uniform and non-uniform polymer films on an even substrate were examined. The film thickness on each point of the sample surface was known and force–distance curves could be averaged in groups according to the film thickness. In this way we were able to develop a semi empirical approach which allows describing the shape of averaged force–distance curves depending on the Youngs moduli of the involved materials and on the film thickness. In this experiment we reconstruct a hidden topography, i.e., we determine the polymer thickness on each point of the sample by analyzing single force–distance curves with our semi empirical equation. The accuracy reached by this approach permits to obtain a reconstruction of the shape and position of the embedded particles limited by a maximum detection depth. Single curves are also analyzed qualitatively in order to locate areas where the adhesion at the polymer/glass interface is weak or the two phases are detached.
The class Dothideomycetes (along with Eurotiomycetes) includes numerous rock-inhabiting fungi (RIF), a group of ascomycetes that tolerates surprisingly well harsh conditions prevailing on rock surfaces. Despite their convergent morphology and physiology, RIF are phylogenetically highly diverse in Dothideomycetes. However, the positions of main groups of RIF in this class remain unclear due to the lack of a strong phylogenetic framework. Moreover, connections between rock-dwelling habit and other lifestyles found in Dothideomycetes such as plant pathogens, saprobes and lichen-forming fungi are still unexplored. Based on multigene phylogenetic analyses, we report that RIF belong to Capnodiales (particularly to the family Teratosphaeriaceae s.l.), Dothideales, Pleosporales, and Myriangiales, as well as some uncharacterised groups with affinities to Dothideomycetes. Moreover, one lineage consisting exclusively of RIF proved to be closely related to Arthoniomycetes, the sister class of Dothideomycetes. The broad phylogenetic amplitude of RIF in Dothideomycetes suggests that total species richness in this class remains underestimated. Composition of some RIF-rich lineages suggests that rock surfaces are reservoirs for plant-associated fungi or saprobes, although other data also agree with rocks as a primary substrate for ancient fungal lineages. According to the current sampling, long distance dispersal seems to be common for RIF. Dothideomycetes lineages comprising lichens also include RIF, suggesting a possible link between rock-dwelling habit and lichenisation.
The breakage of a fiber and its effect on the strain energy is studied in a model composite, this is, a single fiber embedded in a dogbone specimen. The fracture process is recorded by an acoustic emission device, the crack patterns are monitored under a microscope. A finite element analysis is performed in order to estimate the energy released by different failure scenarios. The abilities and limitations of the acoustic emission analysis in characterizing different failure types in fiber reinforced composites are evaluated.