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Paper des Monats
- ja (32)
Pole figures are often used to present crystal orientation data. The huge number of single orientation measurements acquired by electron backscatter diffraction (EBSD) poses a challenge for pole figure representation due to the large number of calculations required. This significantly reduces the speed at which the data may be rotated and affects the ability to switch between different projection types. In the present work, it will be shown that satisfactory representation of orientation data in different projection types can generally be achieved by an imaging of a spherical projection. With this approach, explicit calculation of the projections is no longer required, allowing for both real-time dataset rotation and real-time switching between all projection types relevant to materials science. The technique can be applied to any other directional property distribution, for example, not only for EBSD orientation presentation.
A concept based on the application of a cube as a general polyhedron is presented for the visualization of point group symmetry. The cube is used to represent both the highest and lowest crystal symmetries, with differences observable as patterns characteristic to each point group. Patterns are generated using direction-specific color keys, which enable the recognition of point group-specific distribution of vectors in an external reference frame. For the visualization of the incoherent hexagonal crystal classes, two twinned cubes are applied in order to generate symmetry operators that would otherwise be missing. The resulting hexagonal dipyramid is described in the frame of a cube, reducing the number of used symmetry operators from 72 to 60. The complete set of 32 polyhedra are suitable, for example, as a visual aid for understanding the crystal symmetry and/or sub- and supergroup relationships.
Since the BSE signal depends on many factors, like the chemistry of the phase and the acceleration voltage, the size and position of the detector array is (slightly) different from phase to phase so that an (iterative) post-processing of the stored patterns is highly recommended. The derived BSE signal can be used for phase assignment in high resolution and high speed maps when EBSD fails and/or EDS (energy dispersive spectroscopy) needs too much time for a suitable and parallel signal acquisition.
The lecture includes the following topics:
- Computed Radiography with Phosphor Imaging Plates is gaining more and more importance for mobile inspection and Film Replacement.
- New High Definition CR (HD CR) systems allow the CR application for Weld and Casting inspection with low energy X-rays.
- New calibration methods enable the High Contrast Sensitivity Technology (HCS RT) for radiographic inspection. The contrast sensitivity can be enhanced by a factor of 10 in comparison to film.
- New Digital Detector Arrays (DDA) are now available for stationary and mobile testing. They are also applied for automated defect recognition (ADR), CT, Back Scatter and Dual Energy Applications.
- Back Scatter Techniques are increasingly applied for Security and NDT
- Numeric Radiographic Modelling is applied for Experiment Planning, Film replacement, POD-calculations and training
- Mobile and portable CT devices are suitable for non-destructive cross sectioning in nuclear power industry and aircraft applications.
- Neutron radiography at research reactors was enhanced for visualisation of motions.
Automated electron backscatter diffraction (EBSD) is generally unable to distinguish between multiple cubic phases in a specimen without additional information, such as that obtained by simultaneous energy dispersive X-ray spectroscopy (EDS). Small particles of phases with relatively similar compositions push the limits of phase identification using simultaneous EBSD and EDS, and a mismatch exists between the spatial resolutions of these two techniques due to them having different electron interaction volumes. In a recent paper, the present authors explored using backscatter detectors mounted on top of the EBSD detector to obtain atomic number (Z) contrast images that could be used for phase segmentation in cases where the results from the EBSD and EDS signals remain ambiguous. In the present work, we show that similar information can be obtained from the raw EBSD patterns themselves at higher spatial resolution than was obtained from the backscatter detectors, with the additional advantage of having no spatial mismatch between the data collection grids.
Copper is one of the most important components in brake pads and its amount can reach up to 14%. In spite of a number of positive features copper usage in brake pad formulations has recently become the subject of considerable discussions, primarily due to concerns about potential risks related to environmental impacts of copper particles. So, for developing new pad formulations with possible replacements of copper content, it is very important to understand the functionality of copper additions to brake friction materials. In the paper theoretical investigation of the role of copper as a pad ingredient was carried out on the basis of modelling by the method of movable cellular automata (MCA). Our previous studies show that copper as a constituent of the tribofilm formed during braking provides smooth sliding by forming a granular layer of mechanically mixed materials from the friction layers. In the present study the concentration of copper particles in a Fe3O4-matrix was varied systematically in the range 5.5-28 vol. % and compared to mixtures with the same amount of graphite nanoparticles. The sliding simulations were performed while assuming material properties at 500°C in order to assess the beneficial role of copper during severe braking conditions corresponding to fading cycles during dynamometer testing.
Mechanism of porosity growth during homogenisation in single crystal nickel-based superalloys
(2013)
Several mechanisms for porosity growth in single crystal nickel-based superalloys during homogenisation heat treatment have been proposed in the literature. They were carefully checked using different experimental methods, namely quantitative light microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and density measurements. It is shown that the main mechanism is the Kirkendall–Frenkel effect, i.e. generation of voids due to uncompensated efflux of Al atoms from dissolving γ/γ′-eutectic areas. The Al diffusion is supported by the afflux of vacancies from surrounding γ-matrix which results in porosity growth. This conclusion is confirmed by the estimation of the vacancy afflux towards the dissolving eutectic.
Biological systems exhibit a very high complexity, because they consist of various cell populations showing heterogenic characteristics. Therefore the individual analysis of single cells is important to understand cellular processes as well as their function in a cell system. Especially investigation in the question about what is biological variability and what is a substantial difference between two cells of the same type (which might lead to dysfunction or disease) is of high interest.
Today improved spatial and temporal resolution enable the use of laser ablation inductively coupled mass spectrometry (LA-ICP-MS) for element microscopy of single cells. Next to the characterization of natural trace elements the introduction of artificial metal labels into cells is of high interest. Element labeling of cell compartments and/or proteins allows its simultaneous analysis and localization within a cell via element microscopy. Two fast and simple metal staining procedures of adherent cells for identification of single cells via LA-ICP-MS at sub micrometer resolution are presented.
Two labeling reagents were selected which were already described in literature for applications around protein and cell analysis. An Iridium-intercalator is utilized to stain the cell nuclei whereas the whole cell is stained by maleimido-mono-amide-DOTA-complexes (mDOTA) loaded with lanthanide(III) isotope ions.
The metal staining procedures allow the visualization of single cells by element microscopy independent of a superposition of analyte’s 2D element intensity profile with a prior taken bright field image of the sample. The applicability was shown on an actual question in nano-toxicology (the cellular uptake of nanoparticles).
Explosion regions of propane, isopropanol, acetone, and methyl acetate/inert gas/air mixtures
(2016)
The explosion regions for propane, isopropanol, acetone, and methyl acetate with air in the presence of nitrogen, argon, helium, and carbon dioxide were determined experimentally according to EN 14756/EN1839, method T. Except for propane, all the measurements were executed at 323 K and 1 bar. Propane experiments were carried out at 293 K and 1 bar. The results show that for the same type of inert gas, propane, isopropanol, and acetone have great closeness concerning the concentration of the inert gas at the apex of the explosion envelope in a ternary diagram with air as oxidizer. This leads to consistency in the limiting oxygen concentration (LOC) and minimum required amount of inert gas (MAI) values. Concerning methyl acetate, the apex was always reached at higher percentages of inert gases compared with the other fuels. This can be attributed to the presence of two oxygen atoms inside the chemical structure. Calculation of the explosion regions was carried out based on calculated adiabatic flame temperature (CAFT) method. The flame temperatures for the experimentally determined fuel/air/N2 mixtures were calculated. Then, these temperatures were used to predict the explosion limits of similar mixtures with other inert gases than nitrogen. The modeling results show reasonable agreement with the experimental results.
Among the borates in the Middle European Zechstein Salt Succession boracite Mg3[B7O13Cl] is the most common mineral in quantity and local distribution. An exceptional enrichment is observed in Stassfurt Serie Z2) in the Stassfurth seam K2H. Boracite is to be found in two varieties: individual crystals in cubic, tetrahedral or dodecahedral habit on the one hand and fibrous crystals so-called “stassfurtite” on the other hand. The formation conditions such widely spread borates in the salt succession are ambiguous in two respects. First of all the synthetic formation of boracites is to be made by hydrothermal or melt conditions. Both processes can be suspended for the salt succession. Furthermore the cubic modification is stable above 265°C for the Mg-boracite. The cubic, tetrahedral or dodecahedral habit could be used as a geothermometer, but such conditions can be exclude by the paragenetic minerals, esp. carnallite (MgKCl3 x 6H2O). The chemical composition of orthorhombic, pseudo-cubic boracite depends on the location. Pure Mg-boracite in hexahedral habit and in fibrous habit, so-called “stassfurtite”, occurs in the North Harz region, whereas the Fe-, Mn-, Mg-boracite appears in the South Harz region. Until now the source of boron, the time of formation of crystals, but also the reasons for the differences in habit of the single hexahedral crystals are still unclear. The formation during a diagenetic/metamorphic process is evident. However, the preferred formation in Stassfurt seam could be an indication for the boron enrichment in an early diagenetic process. Furthermore permit the determination of the thermal stability and the volatile content of crystals conclusions to the chemical composition of the fluid. The observed variation suggests that the condition of crystal growth as well as the chemical composition of fluid repeatedly changed over the time. Randomly occuring xenomorpheous anhydrite and magnesite inclusions within single boracite crystals have been interpreted as an indication to factors of chemical milieu during the formation of crystals. The reversible phase transition temperature of the boracite is a linearly function of the iron and manganese content and varies from 265°C for Mg-boracite to 330°C for Fe(Mn)-boracite. The thermal decomposition of boracite is determined by two processes. The decomposition started with a boron-chlorine release (BOCl?), having a maximum rate at 1050°C. Additionally to this release one observes a simultaneous emission of H2O, HCl, HF, CO2 , N2 , SO2 , H2 , and hydro carbons. The results give evidence for the aged approach of a secondary formation of boracite within the complete Stassfurt seam, possibly in connection with the formation of salt diapirs in the Jura and Cretaceous period. The wider environmental distribution of borates is an indication of chemical transport processes within the salt succession. This should be a more important issue in the discussion about the utilisation of salt diapirs for the storage of nuclear waste.
The macro- and microstructure of iron meteorites provide valuable insights into both the inner structure of our planet and the history of our solar system. High speed collision events in the asteroid belt send the meteorites careening toward Earth. The collisions produce unique deformation microstructures. With cooling rates on the scale of a few degrees per million years, iron meteorites can consist of crystal sizes on the order of meters prior to the collision events. These extremely slow cooling rates result in phase transformations occurring at conditions near thermodynamic equilibrium. Preserving meteorite fragments is important for future studies of phase transformations, material behavior at high strain rates, and the origin of the universe.
Experimental characterization of the thermodynamic behavior of multicomponent gas mixtures of accurately known composition with traceability to National Standard is of great importance for testing the current reference equation of state (EoS) for natural gases and related mixtures, GERG-2008. Natural gas composition may change considerably due to the diversity of origins, or the possibility to incorporate hydrogen, biomethane or other non-conventional energy gases.
In this work, density measurements for three synthetic mixtures, representing two biomethane mixtures and a typical natural gas composition, are presented. Results are compared to the current reference EoS for natural gases and related mixtures, i.e., GERG-2008 and AGA8-DC92.
Optical and scanning electron microscopy, as well as electron microprobe analysis and electron backscatter diffraction, have been used to study diffusion processes that occur in a diffusion pair that consistsof a single-crystal CMSX-10 nickel-base superalloy and polycrystalline nickel, at temperatures of 1050–1250°C. It has been found that, in this system, the distributions of γ-stabilizing elements (Cr, Co, W, and Re) are described by the Boltzmann solution for diffusion between two semiinfinite plates of a binary alloy. The processing of these distributions has shown that the diffusion coefficients of Cr, Co, W, and Re in the multicomponent system are close to those in binary alloys of these elements with Ni. The diffusion redistribution of the elements leads to the dissolution of the γ′ phase in the nickel-base superalloy, growth of nickel grains toward the superalloy constituent of the diffusion pair, and the formation of porosity on both sides of the migrating interface, which is determined from a crystal misorientation of the alloy single crystal and nickel grains.
Messungen bei Fern- und Hochgeschwindigkeitsbahnen aus verschiedenen Ländern (Portugal, Spanien, Belgien, Großbritannien, Deutschland, Schweiz, China, Japan u.a.) sollen die besondere Wichtigkeit eines mittelfrequenten Erschütterungsanteils zeigen. Relativ einheitlich werden dabei drei zusammenhängende Terzen mit angehobenen Amplituden beobachtet. Dieser Erschütterungsanteil dominiert mit zunehmender Entfernung vom Gleis das Frequenzspektrum der Erschütterungen. Die hochfrequenteren Anteile nehmen aufgrund der Materialdämpfung des Bodens stärker ab, die tieffrequenteren Anteile aus der sogenannten Quasistatik, der Vorbeifahrt der statischen Achslasten, verschwinden innerhalb der ersten zehn Meter vom Gleis fast vollständig. Die Frequenzcharakteristik des mittelfrequenten Erschütterungsanteils wird durch die Achsfolge des Zuges bestimmt. Im Terzmaßstab ist die Achsfolge im Drehgestell maßgeblich für die Ausprägung von zwei Amplitudenminima, die den Frequenzbereich eingrenzen. Diese Achsfolgespektren sind auch bei Brückenschwingungen von Bedeutung. Sie können die schwächere oder stärkere Anregung einzelner Brückeneigenschwingungen regeln. Die Ursachen der Boden- oder Brückenschwingungen sind mit den Achsfolgespektren noch nicht geklärt. Bei der Brücke und beim Boden können kurzwelligere Gleislagefehler (auch Radunrundheiten 1. Ordnung) Fahrzeugbeschleunigungen und damit dynamische Kräfte auf das Gleis erzeugen. Bei der Brücke ist die diskontinuierliche Auf- und Abfahrt der Achsen ebenfalls eine relevante Anregung, während die Kraftimpulse auf das Gleis, die durch die Achsüberfahrten entstehen, für die Wellenausbreitung im Boden von Bedeutung sind. Heterogene Böden oder Gleise ergeben einen Zerstreuanteil der Achsüberfahrtimpulse. Fallbeispiele mit verschiedenen Böden und verschiedenen Fahrgeschwindigkeiten werden ausgewertet, um die Ursachen und Gesetzmäßigkeiten des mittelfrequenten Erschütterungsanteils zu erkennen.
Exploring the influence of counterpart materials on tribological behaviors of epoxy composites
(2016)
The dependence of the friction and wear of epoxy (EP) composites materials on counterpart materials, such as standard bearing steel, medium carbon steel and chrome-plating (Cr), was investigated. The conventional composite filled with short carbon fiber (SCF) and graphite shows the highest tribological performance when rubbing against Cr, whereas, the hybrid nanocomposite (EP filled with SCF, graphite and silica nanoparticles) exhibits the lowest friction and wear when sliding against the standard bearing steel. The role of nanoparticles in the tribological performance is distinctly different when sliding against with various counterpart materials. It is demonstrated that counterpart materials exert an important influence on material transfer, tribo-oxidation and mechanical mixing of wear products, resulting in the different formation mechanisms of transfer film.
This article presents the latest results of an ongoing national research project on improved models for the prediction of welding residual stresses of thick-plated welded I-girders. The experimental program is presented and the importance of different influencing factors on the residual stresses is discussed in detail. All results are compared for mild (S355J2+N) and high strength (S690QL) steel. Finally, conclusions for further works are drawn.
Microbiological biofilms on rocks are ubiquitous in nature and their influence on soil formation through rock weathering has been shown (Gorbushina 2007). However, most previous studies on rock weathering are limited to understanding the physical and chemical aspects overlooking the impact of biota. Due to the enormous amounts of variables that come with a biological process, the quantification of its influence is only possible by using well-controlled and simplified laboratory models. Thereby gaining more insight on the impact of rock inhabiting biofilms on mineral weathering. This presentation will show the impact of biotic weathering in terms of olivine dissolution rates
Natural forsterite was incubated in batch reactor flasks with and without a model consortium consisting of the phototrophic cyanobacterium Nostoc punctiforme and the rock-inhabiting ascomycete Knufia petricola, and submerged in a growth solution (pH 6). The flasks were incubated for 30 days under 25°C, 90 µmol photons/m2s and were shaken at 150 rpm. qPCR was performed to quantify the cell number of both organisms, BET to gather the specific surface of the used olivine and ICP-OES to follow up the change of concentration of the leached out metals.
Our results show that our model consortium, especially K. petricola does increase the dissolution rate of olivine. The pH increased from the initial 6 to around 7.2 for all setups. Initially Mg was preferentially released over Si (Mg/Si of 3.5), until after two days the ratio starts equilibrating around stoichiometric dissolution. During this timeframe the dissolution rate drops by nearly two orders of magnitude, just as observed by Daval et al., (2011). The difference in dissolution rates between the different setups is initially non-existent, but increases over time. After 30 days the setup with K. petricola gives a dissolution rate of 1.08 10-13 moles/cm2s, compared to 9.23 10-14 moles/cm2s for the abiotic setup.
We expect this study to cause awareness on the impact of microbiology on mineral weathering. Additionally it is a starting point for other, more complicated experiments using for instance flow through or drip flow reactors or other minerals.
Internal damage of an AlSi12CuMgNi alloy reinforced with planar randomshort fibres has been investigated after compression. This damage strongly influences the load partition between matrix and reinforcement. For fibres perpendicular to the applied load, breakage and interconnected cracks appear in significantly higher volume fraction than with fibres parallel to load.
The effect of porosity and microcracking on the mechanical properties (strength, fracture toughness,Young’s modulus, and fracture energy) and thermal expansion of diesel particulate filter (DPF) gradecordierite materials has been investigated. A method to deconvolute the effect of porosity and microc-racking on Young’s modulus is proposed. In addition, the microcrack density and the pore morphologyfactor are calculated by applying a micromechanical differential scheme. The values of the investigatedmechanical properties are shown to decrease with an increase in porosity, but the thermal expansionvalues are insensitive to porosity. The variation in mechanical properties as a function of porosity leadsto distinct porosity dependence of thermal shock resistance for crack initiation and crack propagationfor DPF grade synthetic cordierite.
Microcolonial fungi (MCF) are the most stress-resistant eukaryotes known to date. Black fungi are an interesting object to study mechanisms of stress resistance and to perform applied research to prevent material colonization and biodeterioration. Pigments, like melanin and carotenoids, have been proven to contribute to the unique robustness of MFCs. We study how these pigments ameliorate oxidative stress responses - one of the most significant environmental challenges encountered by MCF - using the model rock fungus Knufia petricola (Chaetothyriales) strain A95.
Genetic manipulation of protective pigments in a rock-inhabiting model fungus Knufia petricola A95
(2016)
Black ascomycetous microcolonial fungi are persistent inhabitants of rock surfaces, but are especially conspicuous in hostile environments like cold and hot deserts. The unique robustness of MFCs is supported by protective pigments, like melanin and carotenoids. We study the role of these pigments in the stress resistance of the model rock fungus Knufia petricola (Chaetothyriales) strain A95.
Microcolonial fungi (MCF) are able to survive extreme environmental conditions. This study is focusing on responses to oxidative stress - using the rock fungus Knufia petricola strain A95. Comparative gene expression analyses of a wild type and a PKS mutant are used to identify genes which are especially regulated under oxidative stress conditions to help elucidate mechanisms of cell wall maturation and oxidative stress defence strategies.
Die VDI Richtlinie 3783 mit Berechnungsmethoden zur Abschätzung der Ausbreitung störfallbedingter Freisetzungen im Rahmen von Sicherheitsberichten erschien in den Jahren 1987 (Blatt 1) und 1990 (Blatt 2). Während sich die VDI Richtlinie 3783 Blatt 1 auf dichteneutrale und leichte Gase bezieht, beschreibt die VDI Richtlinie 3783 Blatt 2 eine Berechnungsmethode für schwere Gase.
In der Kommission Reinhaltung der Luft im VDI und DIN wurde 2009 die Arbeitsgruppe „Ausbreitung von störfallbedingten Freisetzungen – Sicherheitsanalyse“ mit der Zielsetzung gegründet, die VDI-Richtlinie 3783 zu überarbeiten. Die Weiterentwicklung von Blatt 1 soll auf der Grundlage eines Lagrange´schen Partikelmodells (AUSTAL2000, VDI-Richtlinie 3945, Blatt 3) erfolgen, das auch zur Umsetzung der TA-Luft verwendet wird. Der Leistungsumfang der bisherigen Richtlinie muss erhalten bleiben.
Kritikpunkte an der VDI 3783 Blatt 1 sind:
- Keine Berücksichtigung der Bebauung.
- Die Ergebnisse im Nahbereich sind ungenau.
- Die Festlegung der Inversionshöhe ist problematisch.
- Die Vorgabe einer Mindestwärmeleistung für die Berücksichtigung einer Überhöhung ist nicht sinnvoll.
Mit dem Einsatz eines Lagrange´schen Partikelmodells können diese Kritikpunkte im Wesentlichen behoben werden. Problematisch ist die Kopplung zwischen dem Schwergasmodell und dem Lagrange´schen Partikelmodell. Das bisherige Vorgehen lässt sich bei Berücksichtigung der Bebauung nicht ohne weiteres übertragen. Eine Überarbeitung von Blatt 2 ist zurzeit nicht geplant. Um die in der Praxis auftretenden Probleme bei der Anwendung der Richtlinie zu verringern, müssten weitere experimentelle Untersuchungen durchgeführt werden.
Despite the massive literature and the efforts devoted to understand the creep behavior of aluminum alloys, a full description of this phenomenon on the basis of microstructural parameters and experimental conditions is, at present, still missing. The analysis of creep is typically carried out in terms of the so-called steady or secondary creep regime. The present work offers an alternative view of the creep behavior based on the Orowan dislocation dynamics. Our approach considers primary and secondary creep together as solid state isothermal transformations, similar to recrystallization or precipitation phenomena. In this frame, it is shown that the Johnson-Mehl-Avrami-Kolmogorov equation, typically used to analyze these transformations, can also be employed to explain creep deformation. The description is fully compatible with present (empirical) models of steady state creep. We used creep curves of commercially pure Al and ingot AA6061 alloy at different temperatures and stresses to validate the proposed model.
Organometallic oligoamides built from three to four ferrocene amino acid units (H-Fca-OH,1-amino-1'-ferrocene carboxylic acid) fold into hydrogen bonded secondary structures featuring eight-membered rings by cooperative hydrogen bonds. NMR studies and DFT calculations (CAM-B3LYP, LANL2DZ, IEFPCM (THF) reveal that the organometallic zigzag foldamer structures are highly resistant toward denaturation by hydrogen bond acceptors such as dimethyl sulfoxide and 2,4-lutidine. Replacing one ferrocene amino acid unit by the organic alpha-amino acid glycine at the C-terminal end (Fca goes to Gly) significantly destabilizes the secondary zigzag structure facilitating denaturation by DMSO. Highly stabilized ordered poly(Fca) architectures are very attractive for future applications of switchable hydrogen-bonded redox-active materials.
Based on a large set of 2D finite element analyses, parametric equations for weld toe stress concentration factors and through-thickness stress profiles are provided for butt-welded plates. These cover Single-Vand Double-V joints subject to tensile and bending loading. Compared to the most widespread solutions in the literature, which have also been tested against the finite element data in this work, the application range is extended particularly with respect to the weld toe radius(0.1≤ρ≤4 mm)andangle(10 °≤α≤60 °). Furthermore, two values of excess weld metal are considered (h=0.75;2.5mm). The analyses are performed for a plate thickness of 10 mm. Besides the extended validity range, the proposed equations show also an improved accuracy compared to the existing solutions.
Active thermography has been developed into a well-established non-destructive testing method and is used to detect cracks, voids, or material properties. The spatial-temporal structure of the external heating: spatially: planar (e.g., halogen lamp) or local (e.g., focused laser), and temporally: pulsed (e.g., flash lamp) or periodical (e.g., halogen lamp), has led to different testing modalities, as for instance flash and lock-in thermography. In this work, we combine a high-power laser with a spatial light modulator (SLM) allowing us to merge all degrees of freedom into a spatially and temporally controlled heat source. This approach allows us to launch a set of individually controlled and fully coherent high-energy thermal waves into the sample volume. As one possible application, we demonstrate the interference of two phase shifted thermal wave patterns in order to detect the position and depth of hidden defects, which is still a challenging task in thermographic and photothermal techniques. The patterns are positioned with a certain distance and a phase shift of pi to each other, creating an amplitude depletion zone that is centered between them. Now, when a defect is brought into the depletion zone, the destructive interference is disturbed and the defect can be recognized. This approach means that we intentionally exploit the vertical and lateral propagation directions of the thermal waves. In a more general view, controlling simultaneously control of phase and amplitude of a set of thermal waves enables us to have a defined propagation of the thermal wave field within the sample, which means that thermal waves can be controlled almost like acoustical or optical waves. However, in contrast to optical or acoustical waves, thermal waves are highly damped due to the diffusive character of the thermal heat flow and therefore limited in penetration depth in relation to the achievable spatial resolution. Nevertheless, the coherence length of thermal waves can be chosen in the mm-range for modulation frequencies below 10 Hz which is perfectly met by present SLM technology. Eventually, this offers the opportunity to transfer known technologies from wave shaping techniques to thermography methods and to exploit the possibilities of coherent thermal wave shaping.
IBESS steht für „Integrale Bruchmechanische Ermittlung der Schwingfestigkeit von Schweißverbindungen“ und ist das Ergebnis eines DFG-AiF-Clusters, an dem acht Partner beteiligt waren. Kernstück ist eine analytische Methode zur bruchmechanischen Beschreibung der Rissausbreitung unter Schwingbelastung, die im IBESS-Teilprojekt A3 entwickelt wurde. Da man es im Bereich der Schwingfes-tigkeit mit kurzen Rissen zu tun hat, auf die die etablierten Methoden der Langrissbruchmechanik nicht anwendbar sind, wurden Lösungen entwickelt, die es erlauben, sowohl die rissnahen Plastizitätsverhältnisse als auch die mit wachsendem Riss graduell zunehmenden Rissschließeffekte quantitativ zu beschreiben. Unter Einbeziehung der sogenannten „zyklischen R-Kurve“, deren experimentelle Methodik ebenfalls im Rahmen des Projekts weiterentwickelt wurde, ist es zudem möglich, Ausgangsrissgrößen vorherzusagen, die auf Dauerfestigkeitsniveau gerade so noch arretieren würden. Dies erlaubt umgekehrt eine Abschätzung der Dauerfestigkeit an den Schweißverbindungen sowie die statistisch basierte, analytische Vorhersagen des Zeitfestigkeitsastes der Wöhlerkurve. In diesem Aufsatz wird die Methodik vorgestellt und ihre Validierung an einem ausgewählten Beispiel diskutiert.
Within the field of optically excited thermography, full-field thermal imaging is used to characterize materials, to determine thicknesses of layers or to find inhomogeneities such as voids or cracks. Classical light sources, such as flash lamps (impulse heating) or halogen lamps (modulated heating), are hereby specifically used. This has led to the different testing methods lock-in and flash thermography. The VCSEL array promises to merge these excitation methods.
Vertical Cavity Surface Emitting Lasers (VCSELs) are laser diodes emitting light perpendicular to their surface. Due to the vertical structure they can be arranged in large arrays of many thousand individual lasers and still be controlled like ordinary diode lasers. Recently a high-power albeit very compact version of such a VCSEL-array became available which offers both the fast timing behavior of lasers and large illumination areas. Moreover, it allows a spatial and temporal control of the heating because individual parts of the VCSEL-array can be controlled arbitrarily in frequency, amplitude, and phase.
Although the VCSEL-array has a high potential for a new range of applications, it is too early to proclaim them. As one out of very few labs, we already adopted to this new VCSEL technology and show a thorough characterization and first results obtained with a 2.4 kW device. Specifically, we will discuss
- the linearity between control voltage and optical output
- the minimal pulse duration
- the maximal applicable modulation frequency
- optical projection and its influence on the optical output
- spatial control of the illumination and thermal wave shaping
Our results indicate that a VCSEL-array can be used for conventional impulse (aka flash) thermography whereas pulse duration and power are instantaneously accessible compared to flash lamp excitation. In case of lock-in thermography, we can apply frequencies in excess of 200 Hz without a loss in amplitude or an after glowing of the source, making it attractive for photo thermal applications. Consequently, this means that the VCSEL-array is able to merge the two main excitation methods lock-in and impulse thermography.
The presentation will discuss the difference between EU and US standards for the determination of explosion (flammability) limits and limiting oxygen concentration. Small differences observed in measured values can be traced back to the different test apparatuses and criteria. The discrepancies can be much greater in the case of limiting oxygen concentration because of the high amount of inert gases and the corresponding low laminar burning velocities. The paper describes some examples and the influence of the chosen criteria on the results. The European and US standards use the criteria of flame propagation in open test vessels and of pressure rise in closed ones. The examples discussed show that flame propagation is still possible at very small pressure rise values, as observed much below the pressure rise criterion of usual standards. However, flame propagation in a process plant can cause an accident or explosion and must be avoided. Therefore, the flame propagation criterion is recommended to be used in chemical safety engineering. The European safety database CHEMSAFE contains expert-evaluated safety data for cases where the determination method and criteria are known. Flammability characteristics based on the pressure rise criterion may suffice in certain cases, e.g. for explosion protection in closed vessels without any connecting pipes.
We have studied the mechanism of hydrogen storage in the aluminium based metal–organic framework CAU-1 or [Al4(OH)2 OCH3)4(O2C-C6H3NH2-CO2)3] using a complementary multidisciplinary approach of volumetric gas sorption analysis, in situ neutron diffraction and spectroscopy and ab initio calculations. The structure of CAU-1 forms two different types of microporous cages: (i) an octahedral cage with a diameter of about 10 Å and (ii) a tetrahedral cage with a diameter of about 5 Å. Though all metal sites of CAU-1 are fully coordinated, the material exhibits relatively high storage capacities, reaching 4 wt% at a temperature of 70 K. Our results reveal that hydrogen sorption is dominantly driven by cooperative guest–guest interactions and interactions between guest hydrogen molecules and organic linkers. The adsorption of hydrogen on the organic linkers leads to the contraction of the host framework structure and as a result to changes in the electronic potential surface inside the pores. This, in turn, leads to cooperative rearrangement of the molecules inside the pores and to the formation of additionally occupied positions, increasing hydrogen uptake. At the final stage we observe the formation of solid amorphous hydrogen inside the pores.
Die Bedeutung von Eisenbahn-Achsüberfahrten für die Bodenerschütterungen und Brückenschwingungen
(2016)
Messungen bei Fern- und Hochgeschwindigkeitsbahnen aus verschiedenen Ländern (Portugal, Spanien, Belgien, Großbritannien, Deutschland, Schweiz, China, Japan u.a.) sollen die besondere Wichtigkeit eines mittelfrequenten Erschütterungsanteils zeigen. Relativ einheitlich werden dabei drei zusammenhängende Terzen mit angehobenen Amplituden beobachtet. Dieser Erschütterungsanteil dominiert mit zunehmender Entfernung vom Gleis das Frequenzspektrum der Erschütterungen. Die hochfrequenteren Anteile nehmen aufgrund der Materialdämpfung des Bodens stärker ab, die tieffrequenteren Anteile aus der sogenannten Quasistatik, der Vorbeifahrt der statischen Achslasten, verschwinden innerhalb der ersten zehn Meter vom Gleis fast vollständig. Die Frequenzcharakteristik des mittelfrequenten Erschütterungsanteils wird durch die Achsfolge des Zuges bestimmt. Im Terzmaßstab ist die Achsfolge im Drehgestell maßgeblich für die Ausprägung von zwei Amplitudenminima, die den Frequenzbereich eingrenzen. Diese Achsfolgespektren sind auch bei Brückenschwingungen von Bedeutung. Sie können die schwächere oder stärkere Anregung einzelner Brückeneigenschwingungen regeln. Die Ursachen der Boden- oder Brückenschwingungen sind mit den Achsfolgespektren noch nicht geklärt. Bei der Brücke und beim Boden können kurzwelligere Gleislagefehler (auch Radunrundheiten 1. Ordnung) Fahrzeugbeschleunigungen und damit dynamische Kräfte auf das Gleis erzeugen. Bei der Brücke ist die diskontinuierliche Auf- und Abfahrt der Achsen ebenfalls eine relevante Anregung, während die Kraftimpulse auf das Gleis, die durch die Achsüberfahrten entstehen, für die Wellenausbreitung im Boden von Bedeutung sind. Heterogene Böden oder Gleise ergeben einen Zerstreuanteil der Achsüberfahrtimpulse. Fallbeispiele mit verschiedenen Böden und verschiedenen Fahrgeschwindigkeiten werden ausgewertet, um die Ursachen und Gesetzmäßigkeiten des mittelfrequenten Erschütterungsanteils zu erkennen.
The topographic effect of steel counterface, finished by mechanical grinding with Ra ranging from 0.01 to 0.95 µm, on the structure and functionality of the tribofilm of a hybrid nanocomposite, i.e. epoxy matrix filled with monodisperse silica nanoparticles, carbon fibers and graphite, was systematically investigated. The nanostructure of the tribofilm was comprehensively characterized by using combined focused ion beam and transmission electron microscope analyses. It was identified that oxidation of the steel surface, release, compaction and tribosintering of silica nanoparticles and deposition of an epoxy-like degradation product as well as fragmentation of carbon fibers are main mechanisms determining the structure and functionality of the tribofilm. The size of roughness grooves determines the type and size class of wear particles to be trapped at the surface. An optimum groove size leading to a maximum of surface coverage with a nanostructured tribofilm formed mainly from released silica nanoparticles was identified.
We present special applications of electron backscatter diffraction (EBSD) which aim to overcome some of the limitations of this technique as it is currently applied in the scanning electron microscope. We stress that the raw EBSD signal carries additional information which is useful beyond the conventional orientation determination. The background signal underlying the backscattered Kikuchi diffraction (BKD) patterns reflects the chemical composition and surface topography but also contains channeling-in information which is used for qualitative real-time orientation imaging using various backscattered electron signals. A significantly improved orientation precision can be achieved when dynamically simulated pattern are matched to the experimental BKD patterns. The breaking of Friedel’s rule makes it possible to obtain orientation mappings with respect to the point-group symmetries. Finally, we discuss the
determination of lattice parameters from individual BKD
patterns. Subgrain structure in a single quartz grain. The increased noise level in the left map reflects the lower precision of a standard orientation determination using band detection by the Hough transform. The right map results from the same experimental raw data after orientation refinement using a pattern matching approach. The colors correspond an adapted inverse pole figure color key with a maximum angular deviation of about 2° from the mean orientation.
The paper addresses the “Conventional Single-Sample vs. Multiple-Sample Hardness Testing: Hardness Testing Machine vs. Centrifuge” and the follow points are discussed in more detail: Principle of the centrifuge test, components of the centrifuge test, indenter geometries, microscopic measurement of Brinell and Vickers indents, and hardness testing: conventional vs. centrifuge.
This overview article provides insight into how to apply Raman spectroscopy in combination with a confocal, optical microscope setup on polycrystalline material systems, in order to obtain quantitative information on phase distribution, grain sizes, crystal orientations and microstrain. Although the present work uses Cu(In,Ga)(S,Se)₂ absorber layers in corresponding thin-film solar cells as a model system to demonstrate the capabilities of Raman microspectroscopy, the approaches discussed may be applied to any organic or inorganic, polycrystalline materials system.
Results of rolling contact fatigue (RCF) tests by balls-on-rod (BOR) method and two-roller methods have been compared to those by the balls-on-flat (BOF) method by using three different silicon nitride grades. The results suggest that the two-roller method could differentiate the bearing grade materials in terms of wear behavior.
A test campaign was launched to determine the mechanical properties of the HL-LHC 11 T Nb₃Sn magnet components in order to accurately model the mechanical properties in Finite Element simulations that predict the stress and strain distribution in these magnets. Static and dynamic test methods have been applied for determining elastic materials behavior, and highly accurate Young’s moduli are obtained with the dynamic methods resonance and impulse excitation. These non-destructive methods also enable temperature dependent modulus measurements during in situ heat cycles.
Bond monitoring in temperature dependent applications using Brillouin optical time domain analyser
(2016)
Adhesive bond has to be evaluated for its integrity over a range of temperature. Adhesive is being used to bond the sensors with structures. There is no validated technique to test its performance. In this paper, we propose a Brillouin Optical Time Domain Analyzer (BOTDA) based methodology to detect temperature-induced adhesive bond failure below room temperature using distributed fiber optic sensor. The differential coefficient of thermal expansion of the structure and fiber sensor can lead to bond failure at low temperature. Optical fiber impregnated in the structure will experience differential temperature/strain due to debond of the adhesive. This leads to the frequency and amplitude decomposition of the Brillouin spectra. This is a good indication for real-time monitoring of the integrity of a bond.
Determination of deflagration venting requirements in chemical/process plants is usually carried out using well established standards employing an empirically based formula. However, this formula is shown to have severe shortcomings, especially in the range of low KG-values, where either negative or inconceivably large venting areas can be predicted. Due to these shortcomings a method has been developed using the efflux function for gases as a basis to predict the mass flow through a vent opening in a vessel during an internal explosion. The simulated rise in pressure due to the internal explosion is quantitatively determined from the KG-value, with the mass flow through the vent opening in the vessel resulting from the pressure difference between the vessel and its surroundings. This enables the maximum overpressure as a function of the pressure relief surface area to be predicted. The method takes into account the temperature of the efflux gases and turbulence enhancement brought about by the venting process. In the following paper explosion pressure relief experiments are described and the results from these experiments are compared to predictions from the efflux method. It is shown that by adjusting the assumed turbulence which evolves during the venting process, the reduced explosion pressure can be reasonably well reproduced.
Tetrafluorethen wird von der Polymerindustrie seit Jahrzenten als monomeres Ausgangsmaterial sowohl für die Herstellung von Polymeren (PTFE) als auch für Kopolymere (PCTFE) eingesetzt.
Aufgrund seiner Eigenschaft als chemisch instabiles Gas kann TFE auch ohne Luftsauerstoff oder einen anderen Oxydator explosionsartig zerfallen. Nach der Initiierung des Zerfalls kann dieser unter bestimmten Bedingungen aufgrund des exothermen Reaktionsverhaltens sich selbstständig in Apparaten und Rohrleitungen ausbreiten. Dies geht aufgrund der freigesetzten Reaktionsenthalpie mit einem schlagartigen Anstieg von Druck und Temperatur einher, was zu erheblichen Belastungen der Materialien bis hin zum Versagen und Bruch und möglichen Folgeschäden einschließlich Personenschäden führen kann und in der Vergangenheit bereits mehrfach geführt hat.
Besonders nach Wartungsarbeiten besteht die Gefahr, dass Teilabschnitte im Rohrleitungssystem mit TFE, Stickstoff oder Luft gefüllt sind mit Drücken in einem Bereich zwischen technischem Vakuum und atmosphärischem Druck wohingegen angrenzende Rohrabschnitte oder Behälter immer noch TFE bei Betriebsdrücken bis 32 bar enthalten können. Dabei sind die Abschnitte in der Praxis häufig durch Kugelhähne voneinander getrennt, die aufgrund ihrer Öffnungscharakteristik bereits bei geringen Betätigungswinkeln eine große Querschnittsfreigabe für die Strömung im Rohr ermöglichen. Dadurch können schlagartige Kompressionsvorgänge des Gases im Niederdruckbereich ermöglicht werden, die allein aufgrund der thermodynamischen Zustandsänderung zu einer erheblichen Temperaturerhöhung führen und im schlimmsten Fall zur Initiierung der Zerfallsreaktion führen können.
Es wird erstmalig ein Versuchsaufbau im Industriemaßstab, der einer explosionsartigen Zerfallsreaktion von TFE standhalten kann. Zahlreiche Sicherheitskonzepte einschließlich diverser Berstscheibenkonfigurationen als auch zeitgesteuerte Schnellschlussventile wurden eingehend untersucht und bewertet, um die optimale Versuchskonfiguration für bestmögliche Reproduzierbarkeit festzulegen. Es fand eine systematische Untersuchung der schlagartigen Kompression der Systeme Luft/Luft, TFE/Luft, TFE/TFE und TFE/N2 statt.
In der Hochdrucksektion wurden Drücke bis 30 bar realisiert und im Niederdrucksektor konnten Anfangsdrücke im Bereich weniger Millibar bis hin zu Atmosphärendruck eingestellt werden.
Als Hauptergebnis wurde ein „Hazard diagram“ erstellt, mit dessen Hilfe die Zündwahrscheinlichkeit in Abhängigkeit vom Hochdruck und Niederdruck abgeschätzt werden kann. Gefährliche Bedingungen in Rohrleitungen können dadurch auf einfachem Weg identifiziert werden.
Als Referenzsystem zur Beurteilung der maximal erreichbaren nicht reaktiven Kompressions-temperaturen wurde Luft/Luft verwendet. Die damit ermittelten Daten dienten zur Bewertung von zusätzlichen exothermen Effekten, wie sie etwa bei Vorreaktion des TFE im Falle einer Dimerisierung auftreten können.
Entgegen der ursprünglichen Annahme konnten die Systeme TFE/Stickstoff und TFE/TFE im verwendeten Aufbau nicht durch Kompressionsvorgänge gezündet werden.
The polymeric industry handles Tetrafluoroethylene (TFE) as basic material for polymer (PTFE) and co-polymer (PCTFE) production. As a chemically unstable gas, it can react in an explosive way, without the presence of any other gases. Once initiated such an exothermic reaction can propagate through the pipe system of a plant and might lead to massive damages and/or fatalities. Especially after maintenance parts of the pipe systems can be filled with TFE, nitrogen or air at pressures up to atmospheric conditions whereas connected parts of pipes might still contain TFE at operating pressure state. Many of the regarding pipes are separated by ball valves, which allow a fast opening procedure. Thereby fast compression of the gas can occur and lead to a massive temperature increase which might induce unwanted reactions. Former tests in laboratory scale described by Meyer (2009) allowed an ignition of a TFE/air system by rapid compression only for a set of sharp defined boundary conditions. First tests in the lower industrial scale were done by Ferrero et al. (2013), where an ignition at typical industrial operating conditions was initiated. The results of the tests indicated that the critical achievable compression temperatures strongly depend on the setup and therefore on the pipe diameter as well. Therefore the necessity of further tests has been pointed out. The original setup presented by Ferrero (2013), which represents the smallest typical industrial size with an inner diameter of 1.125”, was modified to withstand an explosive decomposition reaction and to avoid a deflagration to detonation transition. Different safety concepts as burst discs and time controlled cut-off valves had been tested and evaluated to optimize the experimental setup for reproducible test conditions. This allowed the systematic investigation of the rapid compression of TFE–systems for the first time in the described scale without serious damages after an ignition. In the donor pipe always TFE at high pressure and in the receiving pipe TFE, nitrogen or air were present at an absolute pressure ranging from 500 Pa to atmospheric pressure.
The scope was to generate a “hazard diagram” in which the ignition probability in dependence of donor (high) pressure and the receiving (low) pressure is shown. Hazardous conditions can easily be determined. A reference method for the maximum achievable temperatures of non-reacting gas systems was created using an air/air-system. Thus reactive TFE-systems could be evaluated regarding additional exothermic effects. The final hazard diagram demonstrates that there is no sharp limit between a “safe” state and an “ignition” for a TFE/air-system. Rather a transition range exists, which decreases with rising donor pressure. An increased temperature in this range, sometimes combined with small pressure peaks in the profile, indicates first partial restricted reactions near the end flange. The more it gets closer to the “ignition” transition the more traces like soot or undefined solid fractions were found. A TFE/nitrogen- and a TFE/TFE-system could not be ignited at all. A description of the experimental tests as well as a detailed explanation of the hazard diagram will be presented.
In North America certain hazardous materials are transported in rail tank cars that must be able to survive an engulfing liquid hydrocarbon pool fire for 100 minutes without rupture. To meet this requirement these tanks are normally equipped with pressure relief valves (PRV) and some form of thermal insulation or thermal protection (TP).
These tanks sometimes have non-accident releases (NAR) due to unwanted activation of, or leakage from the pressure relief valves (PRV). These NARs are a nuisance for Industry and for this reason, the industry now wants to remove the PRVs from certain tanks. This is known as total containment and is common practice in Europe. However, Europe does not have a 100 minute fire survival requirement. This paper is about a series of fire tests of 1/3 rd linear scale US DOT 111 Tanks cars. The 2.4 m3 vessels were subjected to fully engulfing fires generated by liquid propane fueled burners.
A new technique for optical fiber defect detection using Brillouin distributed fiber optic sensor (DFOS) has been proposed and experimentally demonstrated in this paper. This technique is based on stimulated Brillouin scattering (SBS), which offers three wave interaction in single mode optical fiber (SMF -10 μm/125 μm acrylic coated fiber). The nonlinear effect of SBS is manipulated to locate the defect in optical fiber using distributed sensing technology. Various kind of defects may be present in optical fibers. This paper details a case study on observation of a defect, which manifests its presence in certain temperature values. The detail of defect detection through distributed fiber sensor using the SBS has been brought out. SBS is sensitive to temperature and strain. In order to study the effect of defect in distributed fiber sensor as function of temperature and strain, the distributed pre-strained and unstrained optical fiber is subjected to temperature variation and corresponding measurements are obtained with Brillouin optical time domain analyser (BOTDA). This technique enables the utilization of Brillouin parameters, such as decreased amplitude, frequency and increased linewidth in the defect region of the fiber length. The fiber defect location can be determined with spatial resolution accuracy of less than 50 cm of using BOTDA technique.
Four classes of unsaturated copolyesters of L-lactide were prepared either from isosorbide or bis(hydroxymethyl)tricyclodecane in combination with fumaric acid or from 1,4-butenediol or 1,4- butynediol with terephthalic acid. All syntheses were performed in such a way that lactide was oligomerized with a diol as the initiator and the resulting oligomers were polycondensed with a dicarboxylic acid dichloride either in a one-pot synthesis or in a two-step procedure. For most copolyesters the SEC measurements gave weight average molecular weights in the range of 30–60 kg mol⁻1 and dispersities in the range of 4.2–6.2. The MALDI-TOF mass spectra displayed a high content of cycles and indicated an irreversible kinetic course of all polycondensations. Glass-transition temperatures (Tg) above 90 °C were only found for two copolyesters of isosorbide. Addition of bromine to copolyesters of 1,4-butenediol yielded flame retarding biodegradable polymers.
Smart sensors and smart reference materials – an approach to the industrial internet of things
(2016)
The BAM targets within Bonares I4S are adaption of two online sensors being optimised for mobile applications: A LIBS spectrometer (Laser Induced Breakdown Spectroscopy) as well an a XRF spectrometer (X-Ray Fluorescence
Spectroscopy). Beyond , the certification of soil reference materials is scope of I4S at BAM. Therefore, a managable relational database structure is needed, based on a modular Architecture, which is dedicated to spectroscopy. The requirements to such a database are discussed.
The possibility to excite surface plasmon polaritons (SPPs) at the interface between two media depends on the optical properties of both media and geometrical aspects. Specific conditions allowing the coupling of light with a plasmon-active interface must be satisfied. Plasmonic effects are well described in noble metals where the imaginary part of the dielectric permittivity is often neglected ('perfect medium approximation (PMA)'). However, some systems exist for which such approximation cannot be applied, hence requiring a refinement of the common SPP theory. In this context, several properties of SPPs such as excitation conditions, period of the electromagnetic field modulation and SPP lifetime then may strongly deviate from that of the PMA. In this paper, calculations taking into account the imaginary part of the dielectric permittivities are presented. The model identifies analytical terms which should not be neglected in the mathematical description of SPPs on lossy materials. These calculations are applied to numerous material combinations resulting in a prediction of the corresponding SPP features. A list of plasmon-active interfaces is provided along with a quantification of the above mentioned SPP properties in the regime where the PMA is not applicable.
Various aldehyde-containing photoswitches have been developed whose reactivity toward amines can be controlled externally. A thermally stable bifunctional diarylethene, which in its ring-closed form exhibits imine formation accelerated by one order of magnitude, was used as a photoswitchable crosslinker and mixed with a commercially available amino-functionalized polysiloxane to yield a rubbery material with viscoelastic and self-healing properties that can be reversibly tuned by irradiation.
Polymers are favorable materials for gas separation membranes. In general, gas transport experiments are performed with films in the range of 100 µm thickness. However, in large-scale processes very thin selective polymer layers in the range of 100 nm to 1 µm are used. Moreover, it was shown that thin films behave different compared to thick films with respect to gas transport properties and physical aging as well. Thus, for fundamental research it is important to realize gas transport experiments with thin films. The Quartz Crystal Microbalance (QCM) is a very sensitive method to detect mass changes in the range of nanograms. Therefore, this method enables sorption experiments with thin films or layers attached to the QCM crystal (100 nm up to 1 µm). Here, we present the experimental set-up for using the QCM technique for characterizing the gas sorption behavior of thin polymer films in a temperature controlled pressurized environment (up to 50 bar) - also quartz crystals and crystal holders were optimized. The study aims for the characterization of long-term behavior and physical aging of high-performance polymers for gas separation membranes - such as polyimides and polymers of intrinsic microporosity (PIMs) and respective nanocomposites. Especially the differences of the behavior of thin films compared to films with thicknesses up to 100 µm as well as nanofiller induced-effects are adressed.
Computational Advances
(2014)
The presentation will discuss the difference between EU and US standards for the determination of explosion (flammability) limits and limiting oxygen concentration. Small differences observed in measured values can be traced back to the different test apparatuses and criteria. The discrepancies can be much greater in the case of limiting oxygen concentration because of the high amount of inert gases and the corresponding low laminar burning velocities. The paper describes some examples and the influence of the chosen criteria on the results. The European and US standards use the criteria of flame propagation in open test vessels and of pressure rise in closed ones. The examples discussed show that flame propagation is still possible at very small pressure rise values, as observed much below the pressure rise criterion of usual standards. However, flame propagation in a process plant can cause an accident or explosion and must be avoided. Therefore, the flame propagation criterion is recommended to be used in chemical safety engineering. The European safety database CHEMSAFE contains expert-evaluated safety data for cases where the determination method and criteria are known. Flammability characteristics based on the pressure rise criterion may suffice in certain cases, e.g. for explosion protection in closed vessels without any connecting pipes.
Bei der Power-to-Gas-Technologie wird überschüssiger Strom aus erneuerbaren Energien durch Elektrolyse von Wasser in Wasserstoff umgewandelt. Dieser Wasserstoff kann als „chemischer Energiespeicher“ dienen und rückverstromt werden oder aber in das Erdgasnetz eingespeist werden. Die Präsentation befasst sich mit den Auswirkungen von Wasserstoffzusätzen zum Erdgas im Hinblick auf den Explosionsschutz.
Von besonderem Interesse waren diejenigen Kenngrößen, die für reines Methan (Erdgas) und Wasserstoff deutliche Unterschiede aufweisen. Anders als bei vielen Literaturquellen, sollten im Rahmen dieser Untersuchungen ausschließlich die im Bereich der ATEX geltenden, harmonisierten Normen zur Bestimmung der Kenngrößen angewendet werden.
Die Untersuchungen ergaben, dass bei einem Zusatz von bis zu 10 Mol-% Wasserstoff keine der untersuchten Kenngrößen relevant beeinflusst wird. Die Gemische haben nur geringfügig erweiterte Explosionsbereiche und bleiben, wie die reinen Erdgase, in der Explosionsgruppe IIA. Auch die maximalen Explosionsdrücke und die zeitlichen Druckanstiege bei Gasexplosionen werden nur wenig beeinflusst.
Da die Zusammensetzung der Prozessgase bei Wasserstoffeinspeisung in das Netz schwanken kann, ist auf Basis experimenteller Daten ein Modell entwickelt worden, mit dem Explosionsgrenzen von reinem Brenngas und von Brenngas-Inertgas-Gemischen berechnet werden können.
Vergleichende Berechnungen zur Festlegung von explosionsgefährdeten Bereichen (Ex-Zonen) auf Basis von Gasausbreitungsberechnungen ergaben ebenfalls nur geringfüge Unterschiede zum reinen Erdgas.
Der Einsatz von Gaswarngeräten, die für Erdgas kalibriert wurden, ist für Erdgas-Wasserstoff-Gemische grundsätzlich möglich, erfordert aber eine gesonderte Sicherheitsbewertung und ggf. eine Nachjustierung.
The advent of simultaneous energy dispersive X-ray spectroscopy (EDS) data collection has vastly improved the phase separation capabilities for electron backscatter diffraction (EBSD) mapping. A major problem remains, however, in distinguishing between multiple cubic phases in a specimen, especially when the compositions of the phases are similar or their particle sizes are small because the EDS interaction volume is much larger than that of EBSD, and the EDS spectra collected during spatial mapping are generally noisy due to time limitations and the need to minimize sample drift. The backscatter electron (BSE) signal is very sensitive to the local composition due to its atomic number (Z) dependence. BSE imaging is investigated as a complimentary tool to EDS to assist phase segmentation and identification in EBSD through examination of specimens of meteorite, Cu dross, and steel oxidation layers. The results demonstrate that the simultaneous acquisition of EBSD patterns, EDS spectra, and the BSE signal can provide new potential for advancing multiphase material characterization in the scanning electron microscope.
Symmetry and Euler angles
(2014)
Modifying the level of mostly detrimental welding residual stresses already during the welding process would be highly attractive as time- and cost-consuming post processing may be prevented. The nature of stress buildup during welding-associated cooling is highly affected by phase transformations. Up to now, it is not clear in which way this is applicable to real component welding exhibiting high shrinkage restraint and complex heat input. In this study, two different low transformation temperature (LTT) alloys have been investigated concerning the stress development in restrained multi-run butt welding in order to evaluate the potential of stress reduction. Pulsed gas metal arc welding (P-GMAW) welding was executed on a testing facility designed to simulate real lifelike restraint conditions of component weldments. The effect of reducedMS-temperatures and the heat control on the globally acting stresses was monitored by in-situ measurement of the reaction forces during welding fabrication. Additional local residual stress measurements allowed analyzing global as well as local loading of the welded construction. Although phase transformation has a significant influence on unloading the joint during each weld pass, the reaction stress upon cooling to room temperature seems to be determined mainly by the heat input. On the surface, low longitudinal residual stresses were observed in case of LTT whereas transverse residual stresses are less affected.
Airborne ultrasonic inspection is performed in through transmission, where the test piece (e.g. adhesive joint or polymer-based composite plate) is placed between the transmitter and the receiver. However, many structures with difficult shapes allow only one-sided inspection. The strong reflection of the signal from the surface overshadows the signals from the inside, so that broadband pulses are required. Thermoacoustic transmission, where the thermal energy of an electrically heated electrode is transformed into the acoustic energy of an ultrasonic wave, opens the possibility to excite broadband pulses and thus to inspect objects with one-sided access.
We present various thermoacoustic transducers consisting of an electrically conductive film on a solid substrate. The first type of transducer is a transmitter with an indium-tin-oxide electrode on a glass substrate combined with a laser Doppler vibrometer as a receiver. The second type of transducer combines thermoacoustic transmission and piezoelectric reception, having a titanium electrode as a transmitter deposited onto charged cellular polypropylene serving as a piezoelectric receiver.
Using a focusing thermoacoustic transmitter and a separate cellular polypropylene receiver, a through-transmission inspection of a 4 mm thick CFRP test piece with inserts as small as 1 mm was performed. The same emitter and a laser vibrometer as a receiver were used for a one-sided inspection of a Plexiglas block with a cross hole at 15 mm depth. A twin probe consisting of a thermoacoustic transmitter on a cellular polypropylene receiver was applied to a profile measurement on a step wedge with flat bottom holes. The smallest detected diameter of a flat bottom hole was 1 mm. Sound pressure level above 140dB was achieved with each of these transmitters. Thermoacoustic transmitters enable a step towards one-sided air-coupled ultrasonic inspection.
We present a demodulation method that partially compensates for the nonlinear and random transfer function of fiber-optic direct detection coherent Rayleigh optical time-domain reflectometry (C-OTDR). Specifically, the proposed method is shown to improve the detection of small amplitude, high frequency dynamic optical fiber strain as it occurs in acoustic emission sensing. The method is applicable provided that the dynamic fiber strain to be sensed is known to affect a longer section of sensing fiber in a spatially homogeneous way. It is shown that this knowledge can be used to extract more quantitative information from the measured C-OTDR signal by averaging signal components from the affected fiber section in a suitable and efficient way. The theoretical basis of the method is developed and supporting experimental results are presented.
This article addresses the imperfections caused by the weld assembly in I-shape sections made of two structural steel grades. Load influencing imperfections are assumed as deviations from the ideal shape (e.g. bending distortion) and longitudinal residual stresses. The quality of a numerically aided design of components exposed to either compression and/or bending is significantly affected, depending on these parameters. The Eurocode (EC3) provides robust simplified models. As a result, the Ultimate Limit State (ULS) is approached on a conservative basis. The following investigations are aimed at providing further guidance on these values in component-like specimens. The long term goal is an improved understanding of the load-bearing capacity of such sections. As a first step in this process, the experimental and corresponding numerical studies are presented.
The industrial sector of incinerator bottom ash (IBA) treatment from municipal solid waste (MSW) is currently changing. Since established techniques are not yet suitable for fine grain sizes, pollutants are enriched and the effort for the treatment increases exponentially it is nowadays generally landfilled. Innovative treatment trains for the recovery of minerals and metals from the fine fraction will be presented and discussed. In fresh IBA this fraction < 2 mm amounts to around 25 % and contains different precious elemental and chemically bonded metals, especially copper. All copper species have higher densities compared to the bulk minerals. Investigations for the enrichment of copper carried out with a centrifugal classifier will be introduced.
Reaktive Flammschutzbeschichtungen bilden im Brandfall einen wärmeisolierenden Schaum, der die Stahlträger schützt. Diese Beschichtungen erhalten eine komplexe Mischung aus verschiedenen Chemikalien wie Additiven, Füllstoffen und Lösungsmitteln, die bei Kontakt mit Wasser freigesetzt werden können. Für eine Beurteilung der Auswirkung der auswaschbaren Substanzen auf die Umwelt sollte die gesamte Mischung und nicht nur Einzelkomponenten herangezogen werden. Ziel der vorgestellten Untersuchung war es die Frage zu klären, ob Elutionsverfahren in Kombination mit ökotoxikologischer Testung verwendet werden können, um eine Gefährdung der Umwelt auszuschließen.
Das Freisetzungspotential aus den drei Beschichtungen wurde mit Hilfe von zwei verschiedenen Elutionsverfahren nach DIN/TS 16637-2 (Probe ist permanent in Wasser getaucht) und DIN EN 16105 mehrere (Immersions- und Trocknungszyklen) untersucht. Neben chemischen Parametern (pH-Wert, Leitfähigkeit, Gesamtkohlenstoff, Kationen- und Anionenkonzentration und ein Screening auf organische Substanzen), wurde auch die Wirkung auf verschiedene Organismen (Algen, Daphnien, Fischembryonen und Leuchtbakterien) und die Gentoxizität (AMES) untersucht.
Insgesamt zeigen die Eluate keine bis moderate Toxizität, wobei ein Produkt eine deutlich höhere Toxizität als die anderen beiden Produkte aufweist. Die Eluate zeigen insgesamt eine geringe Leitfähigkeit von 20 bis 150 µS/cm und eine geringe Freisetzung von Kationen und Anionen, die oft unter oder in der Nähe der Bestimmungsgrenze liegen. Lediglich Zink, Barium und Phosphat konnten in nahezu allen Fraktionen des Tests nach DIN/TS 16637-2 nachgewiesen werden. Im Gegensatz dazu lag Phosphat in den Fraktionen des intermittierenden Tests unter der Nachweisgrenze. Dies ist wahrscheinlich auf die kürzere Kontaktzeit zurückzuführen. Die Barium und Zinkkonzentrationen sind ebenfalls geringer im Vergleich zum DIN/TS 16637-2. Das Konzentrationsprofil der DOC-Konzentration ist für die beiden Tests ebenfalls unterschiedlich: im intermittierenden Test sinkt die Konzentration mit den Immersionszyklen, während bei dem Test mit ständigen Tauchen die Konzentration in den letzten Fraktionen steigt. Ein Vergleich der Ökotoxizität der ersten Fraktionen und der Fraktion 7 zeigt, dass diese ebenfalls ansteigt.
Die Kombination der beiden Tests ermöglicht es, nach Produkten mit einem größeren und kleineren Risiko für die Umwelt zu unterscheiden. Allerdings müssen die Fraktionen, die für diese Testung ausgewählt werden je nach Elutionstest, Verwendungsszenario und Konzentrationsprofil der Analyten sorgfältig ausgewählt werden.
How much information do we need? A reflection of the correct use of real defects in POD-evaluations
(2016)
To evaluate the capability of a non destructive testing system the “truth” of the used defects is essential. But what exactly is the truth of a real defect? And how much information is usable for the study? This presentation gives an overview about an advanced use of multiple metallographic cuts for the POD evaluation. In the presentation an approach is shown where information of metallographic studies are reconstructed and weighted to gain the essential information about real defects and which information are important for the detection with radiographic testing equipment. Furthermore, different connection points are discussed were additional knowledge from simulation and artificial defects can be used to gain additional certainty for the result of the evaluation. The methodology is used for the evaluation for the digital radiographic testing system for the testing of electron-beam welds, which is one possible choice to seal the Finnish copper canisters for the final deposit of spent nuclear fuel.
Neues aus der Lagerung
(2016)
Self-ignition of coal dust deposits poses a higher risk of fires in oxygen-enriched oxy-fuel combustion systems. In this work, we develop a numerical method, using the commercial software COMSOL Multiphysics, to investigate self-ignition behaviour of coal dust accumulations with a main emphasis on the roles of oxygen, diluent gas and dust volume. A one-step 2nd-order reaction kinetic model considering both coal density and oxygen density is used to estimate reaction rate using the kinetic parameters from previously conducted hot-oven tests. This model is validated to predict the transient temperature and concentration profiles of South African coal dusts until ignition. The computed self-ignition temperatures of dust volumes show a good agreement with experimental results. In addition, it is found that the inhibiting effect of carbon dioxide is comparatively small and oxygen consumption increases dramatically after ignition. Parameter analysis shows that the heating value and kinetic parameters have a comparatively pronounced effect on self-ignition temperature. The model provides a satisfactory explanation for the dependence of self-ignition behaviour on gas atmospheres, thus helping to further understand the fire risk of self-ignition in oxy-fuel combustion systems.
The self-ignition of coal dust deposits and its subsequent smoldering combustion pose a high fire hazard to oxy-fuel power systems which burn fuels using pure oxygen for the sake of carbon capture and storage. The increasing risk of explosion in the gas-phase and self-ignition in the solid-phase for an oxygen enhanced combustion environment has not been well studied yet. In this work, the heterogeneous reactions of a bituminous coal dust are investigated by using a novel hot-basket apparatus with an emphasis on the roles of O2 and diluent gas in chemisorption and smoldering. Experiments show that increasing O2 mole fraction accelerates both self-ignition and the following smoldering combustion. On the other hand, the presence of CO2 increases the ignition temperature and reduces the maximum smoldering temperature. However, the promotion in the fire and explosion risk by elevating O2 mole fraction is substantially stronger than the retardation effected by presence of CO2. The emission-gas measurements show that the CO to CO2 ratio increases significantly after self-ignition, and CH4 counts for 1 % to 8 % of the total carbon emission. This research may help improve the understanding of heterogeneous coal combustion and the fire safety in oxy-fuel power systems.
Heat transfer to bodies engulfed in di-tert-butyl peroxide pool fires - Numerical simulations
(2016)
The thermal response of bodies engulfed in di-tert-butyl peroxide (DTBP) pool fires is studied numerically. High heat release rates, high velocities and high emissive powers portray the combustion of DTBP. This makes exceptionally hazard for bodies engulfed in DTBP fire accidents. The concept of adiabatic surface temperature (AST) is applied for DTBP pool fires to circumvent the difficulty of defining the fire exposure boundary condition at the solid surface. Adiabatic surface temperatures (AST) are computed for pool diameters 1.13 m and 3.4 m using the fire dynamics simulator. The thermal response of cask in a 1.13 m DTBP pool fire is studied to verify the concept of AST. It is found that a cask encounters twofold the heat fluxes in DTBP fires than in diesel pool fires. More than 30% of the net heat flux to the cask is a direct result of the convective heat exchange between the fire and the cask. This implies that the regular safety guidelines formulated for hydrocarbon pool fires are not adequate for the safety of the bodies engulfed in DTBP pool fires.
Am 12. August 2015 kam es in einem Containerlager im Hafen von Tianjin (China) zu einer Serie von Explosionen wobei 173 Menschen getötet und 797 verletzt wurden (Feuerwehrleute und andere Personen). Die ersten beiden Explosionen ereigneten sich innerhalb von 30 Sekunden. Die zweite Explosion war wesentlich heftiger und beruhte u. a. auf der detonativen Umsetzung von ca. 800 Tonnen Ammoniumnitrat. Nach einem Untersuchungsbericht der chinesischen Behörden (Februar 2016) war die Ursache eine Überhitzung eines Containers mit Nitrocellulose-Produkten.
Zusammen mit Kollegen von der Nanjing University of Science and Technology arbeiteten Kollegen der Abteilung 2 an der Analyse der Gründe für die Explosionen und deren Verlauf basierend auf den Kenntnissen und Erfahrungen bezüglich der Eigenschaften der involvierten Stoffe, insbesondere Ammoniumnitrat und Nitrocellulose, sowie der potentiellen Mechanismen für die Auslösung und Weiterleitung.
Beschrieben werden die in Deutschland gültigen Vorschriften für den Umgang, insbesondere die Lagerung, von Ammoniumnitrat und Nitrocellulose-Produkten.
Das Abbrandverhalten und die thermische Strahlung von Poolfeuern organischer Peroxide (OP) wurden bereits in der Vergangenheit ausführlich untersucht. Dabei ergaben sich zum Teil erhebliche Unterschiede hinsichtlich der Abbrandraten, Temperaturen, Strahlungsintensitäten und Flammenlängen im Vergleich zu flüssigen Kohlenwasserstoffen. Das größere Gefahrenpotenzial von OP führt zu strikteren Sicherheitsbestimmungen für Lagerung und Transport. Da das Gefahrenpotenzial maßgeblich von den tatsächlich auftretenden Szenarien abhängt, ist eine Bewertung solcher Ereignisse unumgänglich um nachhaltig die Gesundheit von Mensch und Umgebung zu sichern. Ein Metallfass, gefüllt mit 200 Litern DTBP (Di-tertiär-butylperoxid), wurde auf dem Testgelände Technische Sicherheit der BAM einem Außenfeuer ausgesetzt. Durch den starken Wärmeeintrag erhöht sich die Massenabbrandrate des Peroxids um ein Vielfaches und das Fass entleert sich schließlich unter Ausbildung mehrerer Feuerbälle. Die Flammengröße, Flammentemperatur und damit die thermische Strahlung überschreiten die der gewöhnlichen OP-Poolfeuer. Die resultierenden höheren Sicherheitsabstände sind abschließend berechnet.
Die thermische Zersetzung von AIBN wurde in einem Projekt mit mehreren Teilnehmern untersucht. Hierbei wurde die selbstbeschleunigende Zersetzungstemperatur SADT) sowohl experimentell als auf Grundlage von Simulationsrechnungen bestimmt. Die Besonderheit bei dem Feststoff AIBN ist, dass die Zersetzung sowohl in der festen, als auch in der flüssigen Phase nach dem Schmelzen stattfindet, was bei den durchgeführten Simulationsrechnungen berücksichtigt werden musste. Die berechneten SADT Werte stimmen mit den experimentell bestimmten sehr gut überein.
Azodicarbonamid (ADCA) ist ein bekanntermaßen deflagrationsfähiger Stoff, der in der Kunststoffindustrie als Treib- und Blähmittel eingesetzt wird. In diesem Beitrag wird die Deflagration von ADCA unter verschiedenen Bedingungen betrachtet. Es werden Ergebnisse von Experimenten in offenen und geschlossenen Systemen präsentiert. In geschlossenen Systemen wurde die Zusammensetzung der umgebenden Atmosphäre von Luft mit Umgebungsdruck über Luft mit Unter- und Überdruck hin zu Stickstoff mit Umgebungsdruck variiert. Um das Deflagrationsrisiko zu reduzieren wird eine Verarbeitung von ADCA im Vakuum vorgeschlagen.
The thermal decomposition of dicumyl peroxide dissolved in ethylbenzene has been studied in our laboratories using differential scanning calorimetry (DSC), calvet calorimetry (C80), adiabatic calorimetry, reaction calorimetry and micro calorimetry.
Based on the DSC and C80 experiments a formal kinetics model has been derived, which was compared to the other applied techniques. Finally we used our model to predict the thermal response of 216.5 L steel drums to exposure to constant elevated temperatures, both using the stationary Semenov approach as well as time-resolved CFD simulations. The prediction was compared to one-to-one testing using the UN-Test H.1. The observed level of consistency between model and experiments is remarkably good. The comparison with the 216.5 L testing clearly demonstrates that reliable and conservative predictions for technically relevant scales are possible as long as a validated model is used.
Die BAM erforscht mit Partnern an der TUM und DTU Methoden und Modelle für ein optimiertes Tragwerksmanagement von Infrastrukturbauwerken. Im Rahmen des vom BMVI und der BASt aufgelegten Projektclusters „Intelligente Brücke“ wurde ein Software-Prototyps zur zuverlässigkeitsbasierten Bewertung eines konkreten Spannbetonüberbaus unter Berücksichtigung von Inspektionen und Überwachungssystemen entwickelt. Der entwickelte Software-Prototyp ermöglicht Benutzern ohne vertiefte Kenntnisse der Zuverlässigkeitstheorie eine Berechnung des Einflusses von Bauwerksinformationen auf den Systemschädigungszustand und die Tragsicherheit. Auf dieser Grundlage können effiziente Inspektions- und Überwachungsmaßnahmen identifiziert und das Erhaltungsmanagement optimiert werden.
During the processing of superconducting Nb3Sn wire, several intermediate intermetallic phases including a previously encountered Cu-Nb-Sn phase show up. The yet unknown crystal structure of this phase is now identified by a combination of different experimental techniques and database search to be of the hexagonal NiMg2 type with a proposed composition of about (Nb0.75Cu0.25)Sn2. The structure determination started from an evaluation of the lattice parameters from EBSD Kikuchi patterns from quenched material suggesting hexagonal or orthorhombic symmetry. A database search then led to the hexagonal NiMg2 type structure, the presence of which was confirmed by a Rietveld analysis on the basis of high energy synchrotron X-ray powder diffraction data. Assuming a partial substitution of Nb in orthorhombic NbSn2 by Cu, the change of the valence electron concentration provokes a structural transformation from the CuMg2 type for NbSn2 to the NiMg2 type for (Nb0.75Cu0.25)Sn2. In the previous literature the (Nb0.75Cu0.25)Sn2 phase described here has occasionally been referred to as Nausite.
Fraunhofer Life Science Day
(2015)
Their high affinity, selectivity and specificity make monoclonal antibodies (mAbs) very important tools in research, diagnostics and therapy. The production of mAbs is routinely performed by hybridoma technique. Hybridomas are generated by fusing antibody-producing B cells with indefinitely proliferating myeloma cells. Both, cell fusion and the indispensable identification and isolation of the desired antibody-producing hybridoma clone is still far from being trivial.
We describe a novel method that should help to optimize the cell fusion, and the screening for antibody-secreting hapten-specific hybridoma cells by using fluorescence activated cell sorting and single-cell fusion. Hybridoma cells specific for a hapten were incubated with a hapten-peroxidase conjugate (hapten-HRP), which was subsequently incubated with a fluorophore-labeled polyclonal anti-peroxidase antibody (anti-HRP-Alexa Fluor® 488). To characterize the expression of membrane-bound immunoglobulin G (IgG) a fluorophore-labeled anti-mouse IgG antibody (anti-IgG-Alexa Fluor® 647) was used. Successful staining was verified by confocal laser scanning microscopy (CLSM). We show that it is possible to specifically label hapten-specific hybridoma cells. It should also be possible to use this labelling approach for the isolation of hapten-specific B cells from the spleen and use these cells for single-cell fusion. Parallelized cell fusion chips were developed to increase fusion efficiencies.
Niobium carbide (NbC) is an alternative cutting material. The Federal Institute for Materials Research and Testing (BAM) and the Institute for Machine Tools and Factory Management (IWF) of the TU Berlin assessed the cutting suitability of NbC with cobalt (Co)-binder compared to WC with Co-binder in the machining of a wide range of materials.
Ziel dieser Untersuchungen war die Bewertung der Beständigkeit häufig eingesetzter Dichtungswerkstoffe, wie FKM, FVMQ, VMQ, EPDM, CR, CSM, IIR, PA, NBR und PUR in Kraftstoffen und Heizöl mit und ohne biogene Zusätze bei 20 °C, 40 °C und 70 °C. E10, E85, Dieselkraftstoff mit max. 5 % Biodiesel, ungealtertes und 2 Jahre gealtertes B10 (Heizöl mit 10 % Biodiesel), reiner Dieselkraftstoff, Heizöl und Kraftstoff Super plus zählten zu den Testsubstanzen. Masse, Zugfestigkeit und Bruchdehnung wurden von den Prüfkörpern vor und nach der 84-tägigen Auslagerung in den Kraftstoffen und Heizöl bestimmt. Die visuelle Begutachtung einiger Elastomerprüfkörper zeigte eindeutig die hohe Quellung bis zur partiellen Auflösung. Die Shore-Härte A und D (für PA) der Prüfkörper wurden vor und nach der 42-tägigen Auslagerung in den Kraftstoffen bestimmt. In den internationalen Normen wird zur Bewertung der Beständigkeit von Elastomeren kein Grenzwert der Reduzierung der Zugeigenschaften und der Shore-Härte definiert. Deshalb wurde für die Beständigkeitsbewertung ein Grenzwert von 15 % festgelegt. Zusammenfassend kann die Aussage getroffen werden, dass die Beständigkeit der Fluorpolymere FKM und FVMQ in den Kraftstoffen und Heizöl mit und ohne biogene Zusätze die beste ist.
Young's modulus and Poisson's ratio changes due to machining in porous microcracked cordierite
(2016)
Microstructural changes in porous cordierite caused by machining were characterized using microtensile testing, X-ray computed tomography, and scanning electron microscopy. Young's moduli and Poisson's ratios were determined on similar to 215- to 380-mu m-thick machined samples by combining digital image correlation and microtensile loading. The results provide evidence for an increase in microcrack density and decrease of Young's modulus due to machining of the thin samples extracted from diesel particulate filter honeycombs. This result is in contrast to the known effect of machining on the strength distribution of bulk, monolithic ceramics.
We present a concept for assessing the system reliability of monitored jacket support struc-tures of offshore wind turbines subjected to fatigue. The concept assumes that a structural health monitoring system periodically records accelerations of the jacket structure caused by ambient excitations. The recorded data is processed by a stochastic subspace-based damage detection algorithm to provide information on the global damage state of the jacket structure. This information is generally uncertain. To determine the effect of such uncertain global monitoring information on the structural reliability, the deterioration state of the jacket structure is described by a probabilistic fatigue deterioration model of all structural elements, which considers stochastic dependence among element fatigue behavior. The system deterioration model is coupled with a probabilistic structural model to compute the system failure probability. Global damage detection information is included in the reliability assessment through Bayesian updating of the system failure probability.
For decades, the low-strain impact integrity testing using a hammer blow is well established as a method of quality assurance for various pile types. However, this method has its limitations. Our research and development focuses on improving the excitation signal using a shaker system in contrast to the standard hammer method. Another approach is to increase the amount of sensors used during testing. The purpose is to identify the direction of wave propagation which gives advantages under difficult conditions, such as piles below structures.
Pile integrity testing (PIT) using a shaker system was performed on two 11 m long piles of 90 cm in diameter. While one pile was intact, the other one showed a flaw at approx. 3.5 m below pile top, which was confirmed by standard PIT in 2012. A logarithmic sweep between 500 Hz and 1 KHz of 0.1 s was used as the input signal, being vertically injected into the pile. Prior to that, simulations on similar pile geometries showed that the depth of the pile toe as well as flaws within the pile can be extracted by applying regularized deconvolution. The result is the impulse response in the time domain.
The application of deconvolution on the measured signals shows that it is possible to identify the pile length but it is more difficult to clearly extract the flaw’s position in the pile. Additional digital signal processing techniques and the improvement of the regularized deconvolution method as well as the experimental setup need to be investigated.
Another way to improve the PIT method is to use a multichannel sensor arrangement. By arranging several accelerometers vertically along the accessible part of the pile shaft, it is possible to distinguish between downward and upward traveling waves. Furthermore, it is possible to estimate the unknown wave speed, which gives the possibility of more accurate pile length calculations. The method was evaluated successfully during a measurement campaign of a slab foundation with subjacent piles. In 20 of 28 cases the pile length could be detected accurately.
In diesem Aufsatz wird eine analytische Prozedur zur bruchmechanischen Beschreibung des Schwingverhaltens von Schweißverbindungen beschrieben, die im Rahmen des DFG-AiF-Clusters IBESS entwickelt wurde. Es wurden drei Verbindungen untersucht (Stumpfstöße, Kreuzstöße und Längssteifen), die aus warmgewalzten Stahlplatten produziert wurden. Die analytische Modellierung basierte auf drei wichtigen Aspekten: Quantitative Beschreibung der Rissausbreitung mechanisch-kurzer Risse; Statistische Effekte infolge der Variabilität der lokalen Schweißnahtgeometrie; Modellierung der Mehrfachrissinitiierung und des Mehrfachrisswachstums. Im Folgenden wird die Methodik vorgestellt und ihre Validierung an einem ausgewählten Beispiel diskutiert.
The failure of composites is initiated by imperfections on microscale. The interface between fiber and matrix is a key parameter concerning failure initiation. In order to get an improved understanding of local failure processes a fracture mechanical analysis of interfacial failure in a composite ply under transverse stresses is performed. The mixed mode energy release rate is calculated. In addition the failure of interfaces under cyclic loading is studied on a single fiber model. The quasistatic debonding process is compared with the interfacial failure under fatigue loading. It is shown that the tan delta can be used as an indicator for the damage propagation.
The premise for the development of improved failure criteria for fiber reinforced composites is the understanding of the failure processes on microscale. On microscale the local behaviour of the matrix polymer is crucial. It significantly differs from that found in macroscopic measurements. The present study is focused on the plastic material behaviour of a standard epoxy resin. Local plastic strains are measured in tensile test by using digital image correlation. A multilinear plastic law is implemented by the experimental data. The stress field arising in an idealised representative volume element of a unidirectional ply is analysed by finite element calculations. The change of the stress and strain field due to plastic deformation according to the multilinear plastic law is shown. The change leads to a shift of the critical locations where failure is likely to initiate. In addition, the failure type changes from stress based to strain based failure. The dominant role of the shear strains is shown.
In diesem Aufsatz wird eine analytische Prozedur zur bruchmechanischen Beschreibung des Schwingverhaltens von Schweißverbindungen beschrieben, die im Rahmen des DFG-AiF-Clusters IBESS entwickelt wurde. Es wurden drei Verbindungen untersucht (Stumpfstöße, Kreuzstöße und Längssteifen), die aus warmgewalzten Stahlplatten produziert wurden. Die analytische Modellierung basierte auf drei wichtigen Aspekten: Quantitative Beschreibung der Rissausbreitung mechanisch-kurzer Risse; Statistische Effekte infolge der Variabilität der lokalen Schweißnahtgeometrie; Modellierung der Mehrfachrissinitiierung und des Mehrfachrisswachstums. Im Folgenden wird die Methodik vorgestellt und ihre Validierung an einem ausgewählten Beispiel diskutiert.
The problems of the limits of continuum mechanics are shown on some examples. The fiber-matrix debonding and subsequent crack propagation in fiber reinforced composites is studied. While Finite Element Analyses predict clear crack surfaces, either following the interface or bridging to the neighbouring fiber forming planes, the actual surfaces are very cliffy. Due to the much larger fracture surfaces and the completely different stress states on the cliffy fracture surfaces the continuum mechanical prediction is far from the actual local behaviour. The phenomenon of local high stresses which re much higher than the macroscopically measured strength of the material is also encountered in general fracture mechanics.
The scale dependency of materials is shown on indentation tests conducted on different scales. From a continuum mechanical point of view it makes no difference if the indentation test is performed on a nano-, micro- or macroscale, because it is a matter of self-similarity. However, in nano- or microindentation tests on a pure polymer using e.g. a Berkovic indentor, the extremely high stress concentrations arising at the indentor tip are domination more or less the whole region around the indentor. In case of a macroscopical test, this zone covers only a small part of the material loaded by the indentor. Accordingly, the results of the different test cannot be scaled up.
The paper addresses the ‘Determining the influence of preparation and measurement conditions on bonding strength using CAT-Technology’ and the follow points are discussed in more detail: Motivation, CAT – Technology, Influence of bonding area on bonding strength, Influence of storing & measurement temperatures and Influence of substrate thickness and coating support.
Packages for the transport of radioactive material are often equipped with impact limiters consisting of wood, encapsulated by steel sheets. These impact limiters shall ensure the transport cask meets the mechanical and thermal IAEA regulatory test requirements. After damage caused by the mechanical tests the package has to withstand a severe fire scenario. According to the regulations during and following the thermal test, the specimen shall not be artificially cooled and any combustion of materials of the package shall be permitted to proceed naturally.
Corresponding to results of the French institute IRSN combustion and smouldering of wood inside the impact limiter occurred during and after the fire test. An additional energy supply from a pre-damaged impact limiter to the cask could be the consequence for the safety assessment of the containment.
BAM started a first test phase to examine the issue of combustion for such kind of package components. The goal was to understand the phenomena under the consideration of relevant regulatory boundary conditions. Several metal buckets were filled with wood and equipped with thermocouples. The test specimens have been prepared with different damage arrangements to take the influence of the mechanical tests into account. This paper shows the experimental setup and the conduction of the tests. The first test shows that pre-damaged metal encapsulations can lead to smouldering of the wood and with this to a supplement energy release after the end of the 30 minute fire. BAM is in the preparation process for a second test phase. A thermal test will take place with a wood filled test specimen weighing about 2Mg.