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- Tribology (3)
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Abstract Hydrogenated nitrile butadiene rubber (HNBR) elastomer was thermo-oxidatively aged at different temperatures up to 150 °C. Fourier transform infrared spectroscopy (FTIR), compression stress relaxation (CSR) and international rubber hardness degree (IRHD) microhardness were used to characterise the chemo-mechanical changes of HNBR O-rings during thermo-oxidative ageing. FTIR shows the development of carbonyl, methyl and ester groups but the nitrile content was not affected by ageing. The effect of sample geometry during CSR was investigated. CSR data were converted through integrated kinetic laws. The conversion has proven its sensibility to detect heterogeneous ageing. This was confirmed by the IRHD measure-ments across the section of O-rings. The influence of compression during ageing was assessed through IRHD measurements across the section of compressed and uncom-pressed aged O-rings. The DLO effect was more pronounced in compressed O-rings. By applying the model of Wise et al., theoretical IRHD and oxidation profiles were determined on the basis of IRHD experimental data of compressed O-rings. Good agreements between the experimental and the theoretical IRHD profiles in the core region were obtained. However, near the edge, the theoretical IRHD values were overestimated.
Packaging containers for dangerous goods that include aggressive liquids require that any packaging material that is based on high-density polyethylene has a high degree of stability and durability. This work is focused on testing the environmental stress cracking of the high-density polyethylenes used for such containers in contact with crop protection formulations, in particular, two model liquids established in Germany as standardized test media representatives for crop protection formulations containing the various admixtures typical for such products. One of the liquids is water-based and contains mostly surface-active ingredients, while the other is solvent-based and includes some emulsifiers. Originally established for pin impression tests, these model liquids and their individual components were here used for the first time as environmental media in the Full Notch Creep Test, which addresses the resistance against environmental stress cracking. The Full Notch Creep Test was carried out on five high-density polyethylene types with both model liquids, and also on one selected material with its components. The evaluation was focused on the fracture surface structures, which were visualized by a scanning electron microscope and by optical in situ imaging of the notch opening. While the water-based model liquid and its surface-active individual components induced environmental stress cracking with the characteristic pattern for a craze-crack mechanism and so-called brittle fracture on the surface, the solvent-based model liquid and its soluble ingredients exhibited rather ductile failure behavior, caused by the plasticizing effect on the polymer that reduced the yield stress of the high-density polyethylene.
For both cases, fracture surface analysis, together with side views of the crack opening, showed a clear relation between surface pattern, notch deformation (e.g., by blunting), or crack opening due to crack growth with time to failure and the solubility of the liquids in high-density polyethylene.
Unter Berücksichtigung praktischer und wissenschaftlich-technischer Erkenntnisse der letzten 15 Jahre - insbesondere auch auf der Basis verschiedener BAM-Forschungsergebnisse und Zulassungsverfahren - erfolgte eine Überarbeitung der Grundlagen, Bauprinzipien, Ausführungs- und Einbaukriterien sowie der Zulassungs- und Gütesicherungsmaßnahmen für insgesamt 4 Bauarten von Fugenfüllsystemen für hochbeanspruchte Verkehrsflächen. In diesem - für den Bundesfernstraßenbereich verbindlichen bautechnischen Regelwerk - finden insbesondere auch die Ergebnisse mehrerer wissenschaftlicher Vorhaben der BAM bezüglich labortechnischer Untersuchungen und Felduntersuchungen zum Funktionsverhalten und zur Dauerhaftigkeit erste baurechtliche Konsequenzen. Auf der Basis von Untersuchungen u.a. im Brückenbau wurden Regelungen für die Fugenausbildung in Asphalt und bei Befestigungskombinationen erarbeitet und umgesetzt. Damit konnten umfassende Regelungen für die maßgebenden Fahrbahnbeläge im Bundesfernstraßenbereich der Straßenbauverwaltung und ausführenden Industrieunternehmungen zur Verfügung gestellt werden. Die Neufassung dieser Regelungen dient darüber hinaus dem Ziel, den von der BAM vertretenen Wechsel hin zu einer performance-bezogenen Bewertungsmethodik, vorzubereiten.
Nach mehr als 15-jähriger Anwendung und mit der zwischenzeitlichen Einführung europäisch harmonisierter Normen für Fugenmaterialien war eine Anpassung Qualitäts- und Gütesicherungsanforderungen für Fugenfüllungen im Bundesfernstraßenbereich erforderlich. Hierbei ging es insbesondere darum, Maßnahmen und Verfahren zu entwickeln, um das nationale Qualitäts- und Gütesicherungsniveau weiter zu entwickeln und weiterhin sicher stellen zu können. Nach den Untersuchungserfahrungen im Labor und im Feld ging darum, neuartige Material- und Stoffkombinationen qualitätssicher dem Bauprozess zur Verfügung stellen zu können. Erforderliche Anforderungskriterien und zulässige Toleranzen der Lieferqualität wurden neu gefasst. Es wurde ein Verfahren entwickelt, europäische Bauprodukte qualitätsgesichert in den Bauprozess im Bundesfernstraßenbericht zu überführen.
This chapter offers observations and considerations concerning black writing inks encountered in writing supports transmitting documentary and literary texts of the late Antiquity and early Middle Ages. It discusses different types of inks, the Methods of their detection and their use in different times and geographical areas.
The program PowderCell is a crystallographic tool for visualization of Crystal structures. However, it offers also non-conventional features like the fulautomatical generation of subgroups or the consideration of non-standard settings of space-group types. On the one Hand the program is very useful for non-crystallographers who like to get an impression of the atomic arrangement within the unit cell. But also for crystallographers it is recommendable because it contains a lot of additional information which can be extracted and used like data given in the International Tables for Crystallography, Vol. A. However, the most important advantage of the program is the simultaneous calculation of the X-ray or neutron diffraction powder patterns for a mixture of up to 10 crystalline phases. Between more than 7 different characteristic radiations can be chosen and their influence on the resulting powder pattern can be studied. Furthermore, experimental diffractograms can be analysed using a refinement procedure. The implemented LeBail-algorithm allows the investigation of unknown phases. In combination with the refinement algorithm an interface to Shelx offers the possibility for a step by step ab initio structure analysis. Certainly, the user-friendly shell is one reason that especially users who are not so familar with space-group symmetry, crystal structure data or diffractometry use this powerful tool for the solution of scientific or analytical problems as well as in teaching.
X-ray stress analysis on crystalline materials is based on the determination of elastic lattice strains. The strains described by the shift of peak positions are converted to stresses by the means of theory of elasticity. The development of the sin2ψ-method of X-ray stress analysis introduced an enormous progress in X-ray stress analysis during the last decades. This report outlines some important elements of X-ray physics and fundamentals of theory of elasticity. The Standard measuring procedure are described and special experimental differences to the common powder diffractometry are outlined.
To better understanding the failure of adhesive joints tensile tests were carried out on miniature test specimens from Norway spruce in the synchrotron. Urea-formaldehyde resin was used as adhesive. e. For comparison purposes, tensile tests were carried out on solid wood and on bonded miniature tensile shear samples with acoustic emission. The acoustic emission signals of all the experiments occurred with classified pattern recognition. This resulted in two classes of signals for each two frequency peaks. One class consisted of the low-frequency and the other of the higher-frequency peak of higher intensity, but this was essentially independent from the structure (solid wood or plywood) and size scale of the test specimens. The influence of the adhesive layers was determined on wood test specimens on laboratory scale and on miniature test specimens with an adhesive layer and selected fiber orientations. This gave evidence that the sound emission signals from the failure of the adhesive layer presumably of the class with low frequency signals peak in the range of services can be assigned.
In the field of modelling hydrogen assisted cracking (HAC) phenomenon, hydrogen diffusivity is an important input parameter for numerical simulation. In terms of hydrogen diffusion coefficients, they have great impact on realistic assessment of the evolution of possible crack critical hydrogen concentrations. In addition, the chemical compositions of steels can have a strong effect on hydrogen diffusion. Unfortunately, literature provides a wide range of available hydrogen diffusion coefficients even for similar microstructures and equal temperatures. The scattering of the data can lead to significant deviations in the results of simulating the evolving hydrogen concentrations due to hydrogen uptake (by fabrication or service). Thus, the application of such data to crack-models or for component life tie predictions can be realized up to the present only by considering envelope curves of such value, corresponding to a work or bench case scenario, respectively. For improved reliability of numerical simulaitons, it is necessary to minimize the mentioned deviation of these data. Hence, this work focuses on the validation of hydrogen diffusion coefficients obtained from permeation experiments at room temperature. Two baintic steels with different alloying concepts were investigated, the creep-resistant 7CrMoVTiB10-10 and the reactor pressure vessel grade 20MnMoNi4-5. A numerical model is presented for simulation of the corresponding hydrogen diffusion during permeation experiments using the finite element software ANSYS. Three different diffusion coefficients (obtained from different common calculation methods) are considered and compared to numerical results. The vases of thes calculation methods are permeation transients which are a direct measure for hydrogen. The results of the simulated hydrogen diffusion coefficients show that only one procedure for calculation of diffusion coefficitnes is suitable in comparision to the experimental values. Thus, it is suggested to use this method for analysis of experimental results in case of hydrogen diffusion during permeation experiments. Furthermore, this work supplies validated values for the hydrogen diffusion coefficients of both steel grades.
The described investigation of carbon-fibre-reinforced plastics (CFRP) documents that damage evolution can be observed by means of X-ray refractography. Comparative investigations with synchrotron technique on CFRP and grey-scale analysis on glass fibre-reinforced-plastics (GFRP) confirm these results. Moreover it was found that the fracture mechanical properties of the matrix system influence damage nucleation and propagation in the laminate during static and fatigue loads. Single-step fatigue tests were carried out on Laminates with RIM135 and LY556 matrix systems made from non-crimped fabric (NCF) or twill weave in different fibre orientations. The damage to the LY556 laminates was characterized by laminate cracks growing rapidly over the whole specimen width, whereas the damage on the RIM135 laminates was characterized by an earlier onset of micro-cracking followed by laminate cracks. The specimens were fatigued up to 108 (very high cycle fatigue (VHCF) regime) load cycles. S-N-curves of damage initiation were drawn and boundaries were identified for endurance within the VHCF regime. A phenomenology based model focusing on matrix stress was applied to reproduce the first inter-fibre failure (IFF) under static and fatigue loads.