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Eingeladener Vortrag
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In this paper, the friction stir welding process was numerically investigated for 6 mm thick aluminum alloy AA2024-T3. The finite element software COMSOL Multiphysics was used to calculate the transient thermal field during welding and the mechanical reaction depending on different mechanical clamping conditions and hardening models subsequently. A thermal pseudo-mechanical (TPM) heat source was implemented.
Softening effects of the material due to precipitation hardening dissolution caused by the frictional heat were accounted for. The transient temperature evolution measured by thermocouple elements at various locations was compared to the numerical results. A good agreement was found for the thermal field. A sensitivity study of the mechanical models showed the strong influence of the clamping conditions and the softening model.
The fatigue crack propagation threshold ΔKth is of paramount importance for any kind of damage tolerant design, but in contrast to this importance, the determination and application of the parameter is not on the firm ground as previously assumed. The paper discusses questions of its experimental determination as well as of its application to components. In both fields, new questions have been raised with the potential to challenge or modify long-standing knowledge. Against this background, the paper is an attempt to systematize the established knowledge as well as questions and open issues.
A fast quantitative model for the energy spectra of radiation emitted by X-ray tubes is described, handling thin as well as thick plane targets of arbitrary materials. The developed model is based on fundamental interaction cross sections, describing electron and photon transport via numerical integration of discretized distributions. While the focus lies on bremsstrahlung production, modeling of characteristic radiation is fully integrated. The model does not include any free parameters. The validity of the model is shown through comparison with measurements and Monte Carlo simulations for several combinations of target material and acceleration potential between 30 kV and 450 kV.
Synchrotron-radiation XPS analysis of ultra-thin silane films: Specifying the organic silicon
(2016)
The analysis of chemical and elemental in-depth variations in ultra-thin organic layers with thicknesses below 5 nm is very challenging. Energy- and angle-resolved XPS (ER/AR-XPS) opens up the possibility for non-destructive chemical ultra-shallow depth profiling of the outermost surface layer of ultra-thin organic films due to its exceptional surface sensitivity. For common organic materials a reliable chemical in-depth analysis with a lower limit of the XPS information depth z95 of about 1 nm can be performed. As a proof-of-principle example with relevance for industrial applications the ER/AR-XPS analysis of different organic monolayers made of amino- or benzamidosilane molecules on silicon oxide surfaces is presented. It is demonstrated how to use the Si 2p core-level region to non-destructively depth-profile the organic (silane monolayer) inorganic (SiO2/Si) interface and how to quantify Si species, ranging from elemental silicon over native silicon oxide to the silane itself. The main advantage of the applied ER/AR-XPS method is the improved specification of organic from inorganic silicon components in Si 2p core-level spectra with exceptional low uncertainties compared to conventional laboratory XPS.
We report an appropriate preparation of binary isotope calibration mixtures of the three stable isotopes of magnesium to be used in the ab initio calibration of multicollector mass spectrometers (ICPMS and TIMS). For each of the three possible combinations of binary mixtures ("24Mg" + "25Mg", "24Mg" + "26Mg", and "25Mg" + "26Mg"), three individual setups have been prepared under gravimetric control, each of them with an isotope ratio close to unity, and a total magnesium mass fraction close to 20 mg kg-1. The preparation was designed to occur via an intermediate dilution of a parent solution of a highly purified specimen of the isotopically enriched magnesium materials. For the application as calibration mixtures, a complete uncertainty budget was set up, and is presented and discussed in detail, including the aspects that went into the design of the dilution and mixing approach to minimize uncertainty. The principle parameters for the purpose of the later calibration of the mass spectrometers are the absolute masses of isotopically enriched magnesium materials in the primary calibration mixtures. For the first time relative expanded uncertainties U (k = 2) for these masses of ≤0.005% could be achieved for all mixtures.
Flexible electrochromic devices (ECDs) based on Fe(II)-metallo-supramolecular polyelectrolytes (Fe-MEPE) and vanadium oxide are studied in operando by means of x-ray absorption fine structure (XAFS) spectroscopy. The ECDs are blue-purple in the colored state at 0.0 V and become light yellow when a voltage of 1.6 V is applied. The XAFS studies at the K-edge of Fe(II) reveals that the absorption edge is shifted toward higher energies by 1.8 eV in the transparent state. Comparison of two different ECDs and different charge cycles demonstrates the reversibility and repeatability of the process. We attribute the shift to a charge transfer and a change of oxidation state of the ions from Fe2+ to Fe3+. The transition is not accompanied by a noticeable structural change of the octahedral coordination geometry as confirmed by analysis of the extended x-ray absorption fine structure (EXAFS) data. (C) 2015 Elsevier B.V. All rights reserved.
The synthesis of peroxycarboxylic esters, as one subgroup of organic peroxides, is characterized by a high thermal hazard potential regarding process safety. In case of failure in the production process, e.g., if the heat of reaction cannot be removed sufficiently fast, decomposition reactions can be triggered, and as a result, remarkable amounts of heat and gas can be released and can cause a high extent of damage. Multifarious technical and organizational measures are necessary to ensure the safe industrial production of peroxides. With the introduction of microreaction technology plenty of possibilities have been opened to carry out highly exothermic reactions in smaller volumes and with more efficient heat removal. In this paper we report the application of three different microstructured reactors, representing different mixing strategies, to synthesize two peroxymonocarboxylic esters, namely tert-butyl peroxypivalate and tert-butyl peroxy-2- thylhexanoate. The following reactor types were considered: an orifice microreactor, a split and recombine microreactor and a capillary tube reactor in combination with ultrasonication. The efficiency of the two Phase liquid/liquid reaction is expressed in comparison of conversion and selectivity. With microreaction technology a remarkable increase in space-time-yield, ranging from 12,500 kg·m−3·h−1 to 414,000 kg·m−3·h−1, is achieved.
Bulk elastic properties, hardness and fatigue of calcium aluminosilicate (CAS) glasses in the technically relevant region of the ternary with intermediate-silica fraction were determined by combining results of Vickers indentation, ultrasonic echography and Archimedian buoyancy at room temperature. Of three studied compositional series, the first series was along the meta-aluminous join, while in the two other series the molar fraction of SiO2 was kept constant. For the first series the elastic moduli and hardness show an almost linear increase with increasing SiO2 fraction. In contrast, increasing the CaO/SiO2 ratio at constant silica content results in a characteristic change when passing the meta-aluminous join. Elastic constants and hardness were lower at the percalcic than on the peraluminous side. Empirical models which relate bulk elastic moduli to internal energy, short-range inter-atomic forces and the packing density of their oxide constituents were found to be in agreement with the experimental data for meta-aluminous glasses, while deviations between the observed and predicted trends were evident for percalcic compositions. Empirical fatigue parameters such as the probability to initiate cracks after indentation reflect the bulk mechanical properties in the CAS system when conducted in inert atmosphere, but are otherwise clearly dominated by environmental effects
In vitro metabolism of the cyanotoxin cylindrospermopsin in HepaRG cells and liver tissue fractions
(2016)
No evidence for phase I metabolites of the cyanotoxin cylindrospermopsin (CYN) was given using HepaRG cells and different liver tissue fractions when studying metabolic conversion. Although the application of ketoconazole, a CYP3A4 inhibitor, led to a decreased cytotoxicity of CYN, no metabolites were detected applying high resolution mass spectrometry. Quantification of non-modified CYN led to recovery rates of almost 100%. Consequently, reduction of CYN toxicity in the presence of metabolism inhibiting agents must be attributed to alternative pathways.
In supplementary work to the one published earlier, experiments with SF6, NF3, CF4 and H2 as new modifier gases for the matrix studied were performed. Our investigations were continued to improve the described analytical method and to achieve additional insights into the mechanism of analyte release. Our new survey is split in two parts. At first fluorinating modifiers were used to investigate the behaviour of a variety of trace elements (Ag, Al, As, Au, Bi, Cd, Co, Cr, Fe, Mg, Mn, Ni, P, Pb, Sb, Se, Si, Sn, Te, Ti, Zn and Zr). Most of them (exceptions Au, Se, and Te) could be effectively released from the copper matrix by thermo-halogenation reactions and by partial sub-sample evaporation. Using SF6 and NF3 as modifier gases, low limits of quantification (LOQs) were achieved for the 19 well released trace elements (typical ≤0.1 mg kg-1). Most elements (exceptions Ag, Mg, and Ni) could be calibrated by using aqueous calibration solutions without any sample pretreatment. For the trace determination of Se, Te, and Au, a further analytical method of ETV-ICP OES is described in the second part based on thermo-hydrogenation reactions by using a hydrogen/argon mixture as a modifier gas. The determination of Se and Te with very high analytical performance (LOQ < 0.1 mg kg-1) can either be carried out in a second analytical step succeeding the halogenation procedure, or the sub-sample is directly treated with H2 without previous halogenation procedure whereby the sub-sample can either be partially or totally evaporated. In this case some other analytes (Ag, Au, As, Bi, Cd, Fe, Mg, Ni, Pb, Sb, Sn, and Zn) can additionally be quantified simultaneously with Se and Te.
Efficient Near UV excited materials (350<λ<400 nm) responding with green line emission are sparse in comparison to higher energy UV excited emitters (λ<350 nm), while corresponding red line emitters are more abundant, albeit typically also restricted to excitation wavelengths below 400 nm. This situation is disadvantageous for several important actual and potential applications. Among these, excitation with high power UV-LEDs and laser diodes are of particular interest. Here we present results on green emitting YBO3:Ce, Tb, which can be excited with 370–380 nm radiation at quantum efficiencies of up to 60% and decay times in excess of 2 ms. Moreover, as powderous phosphors typically require stable matrices to be hosted in, we investigated low melting, lead- and fluoride-free glasses for their capability to accommodate the phosphor and yet retain its optical properties. In these, we even observed an increase of the quantum efficiencies of up to 70% at decay times approaching 3 ms. Finally, we characterized the thermal quenching behavior, which showed a clear advantage of the phosphors in glassy matrices.
In the present study we have investigated whether the effect of water on properties of borate glasses resembles that of alkali oxide. Soda-lime-borate glasses with nominal compositions of x Na2O, 10 CaO, (90-x) B2O3 (x = 5, 15 and 25 mol%) were doped with up to 8 wt.% H2O by processing glass powder + distilled water in platinum capsules in an internally heated gas pressure vessel at 1523 K and 500 MPa. The water content of hydrous glasses was determined by Karl-Fischer titration and near-infrared spectroscopy. The glass transition temperature T-g. was derived from DTA and micropenetration experiments for which the effect of water loss at the surface of the hydrous glasses was studied. Heating glass samples at 10 K min(-1) in the DTA resulted in T-g values which are close to T-12 isokom temperatures confirming the equivalence of enthalpy relaxation and viscous relaxation for borate glasses. For all three glass series it is shown that T-g strongly decreases whereas the liquid fragility strongly increases upon the addition of water. These findings reveal that H2O primarily causes breaking of B-O-B bonds rather than supporting 4-fold coordinated boron as it is well-known for alkali oxides in this concentration range. (C) 2015 Elsevier B.V. All rights reserved.
Within the scope of a DIN INS project, a flash thermography round robin test that evaluates reliability, comparability and efficiency of different testing situations is organized. The results give information about the detectability of defects e.g. by their size and depth, the evaluation method and by the materials used. Besides, the influence of equipment and parameters used by the participants on the results were analysed. All of the quantitative results as well as the feedback given by the participants will be presented in a DIN committee in order to contribute to a flash thermography standard.
The mechanical and microstructural properties of geopolymer concretes were assessed before, during and after high temperature exposure in order to better understand the engineering properties of the material. Fly ash based geopolymer concretes with either quartz aggregate or expanded clay aggregate were exposed to various temperatures up to 750 °C using a thermo-mechanical testing apparatus. Microstructural investigations were also undertaken to better understand the measured changes in the mechanical properties. It was found that dehydration of capillary water caused cracking and strength losses at temperatures ≤300 °C, an effect that was more severe in the quartz aggregate geopolymer due to its lower permeability. At higher temperatures (T ≥ 500 °C) sintering promoted strength increases which enabled both concrete types to yield significant strength advantages over conventional materials. Stress–mechanical strain curves, which form the basis of the fire design of concrete structures, are reported.
Duplex stainless steels have been used for a long time in the offshore industry, since they have higher strength than conventional austenitic stainless steels and they exhibit a better ductility as well as an improved corrosion resistance in harsh environments compared to ferritic stainless steels. However, despite these good properties the literature shows some failure cases of duplex stainless steels in which hydrogen plays a crucial role for the cause of the damage. Numerical simulations can give a significant contribution in clarifying the damage mechanisms. Therefore, a numerical model of a duplex stainless steel microstructure was developed enabling simulation of crack initiation and propagation in both phases. The phase specific stress strain analysis revealed that local plastic deformation occurs in both austenite and δ-ferrite already in the macroscopically elastic range. Altogether, phase specific hydrogen-assisted material damage was simulated for the first time taking into account all main factors influencing hydrogen assisted cracking process. The results agree well with experimental observations and thus allow a better insight in the mechanism of hydrogen-assisted material damage.
A model system was used to simulate the properties of tribofilms which form during automotive braking. The model system was prepared by ball milling of a blend of 70 vol.% iron oxides, 15 vol.% molybdenum disulfide and 15 vol.% graphite. The resulting mixture was characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and various transmission electron microscopic (TEM) methods, including energy dispersive X-ray spectroscopy (EDXS), high resolution investigations (HRTEM) with corresponding simulation of the HRTEM images, diffraction methods such as scanning nano-beam electron diffraction (SNBED) and selected area electron diffraction (SAED). It could be shown that the ball milling caused a reduction of the grain size of the initial components to the nanometer range. Sometimes even amorphization or partial break-down of the crystal structure was observed for MoS2 and graphite. Moreover, chemical reactions lead to a formation of surface coverings of the nanoparticles by amorphous material, molybdenum oxides, and iron sulfates as derived from XPS.
Controlling the dynamics in the weld pool is a highly demanding challenge in deep-penetration laser beam welding with modern high power laser systems in the multi kilowatt range. An approach to insert braking forces in the melt which is successfully used in large-scaled industrial applications like casting is the so-called Hartmann effect due to externally applied magnetic fields. Therefore, this study deals with its adaptation to a laser beam welding process of much smaller geometric and time scale. In this paper, the contactless mitigation of fluid dynamic processes in the melt by steady magnetic fields was investigated by numerical simulation for partial penetration welding of aluminium. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential equations were solved based on temperature-dependent material properties up to evaporation temperature for two different penetration depths of the laser beam. The Marangoni convection in the surface region of the weld pool and the natural convection due to the gravitational forces were identified as main driving forces in the weld pool. Furthermore, the latent heat of solide-liquid phase transition was taken into account and the solidification was modelled by the Carman-Kozeny equation for porous medium morphology. The results show that a characteristic change of the flow pattern in the melt can be achieved by the applied steady magnetic fields depending on the ratio of magnetic induced and viscous drag. Consequently, the weld bead geometry was significantly influenced by the developing Lorentz forces. Welding experiments with a 16 kW disc laser with an applied magnetic flux density of around 500 mT support the numerical results by showing a dissipating effect on the weld pool dynamics.
The identification of different forms of dihydroergocristine (DHEC) was carried out by crystallization from different organic solvents. DHEC was identified as potential template for molecularly imprinted polymers (MIPs) for the epimeric specific analysis of ergot alkaloids (EAs) in food. DHEC was crystallized from different solvents in order to mimic the typical MIP synthesis conditions. Four new solvatomorphs of DHEC were obtained. All solvatomorphs contain a water molecule in the crystal structure, whereas three compounds contain an additional solvent molecule. Based on the conformation of DHEC a comparison with typical EA molecules was possible. The analysis showed that DHEC is a suitable template for MIPs for EAs.
Fluorescence lamps contain considerable amounts of rare earth elements (REE). Several recycling procedures for REE recovery from spent lamps have been established. However, despite their economic importance, the respective recycling is scarce so far, with an REE recovery rate of less than 1%. A reliable analysis of REE and other relevant metals like Yttrium is crucial for a thorough and complete recovery process. This applies both to the solid matter and aqueous phase, since most of the recycling processes include wet-chemical steps. We tested seven different reagent mixtures for microwave-assisted digestion of fluorescent lamp shredder, including hydrofluoric acid, perchloric acid, and hydrogen peroxide. We determined the concentrations of 25 of the most relevant rare earth and other trace elements (Al, P, Ti, V, Cr, Fe, Ni, Cu, Ga, Ge, As, Y, Ag, Cd, Sn, Sb, La, Ce, Eu, Gd, Tb, W, Au, Hg, and Pb) in the respective dilutions. Two independent digestions, one a mixture of perchlorid/nitric/hydrofluoric acid and the other aqua regia, showed the highest concentrations of 23 of these elements, excluding only Sn and Tb. The REE concentrations in the tested lamp shredder sample (stated in g/kg) were 10.2 (Y), 12.1 (La), 7.77 (Ce), 6.91 (Eu), 1.90 (Gd), and 4.11 (Tb).
For the performance of high-strength steel welds by means of load bearing capacity and safety, the information about stress level and distribution due to welding is needed. The interaction between the filler material grade (strength) and heat input on the reaction stresses in high-strength steels, welded under defined restraint conditions were analysed. Butt welds were joined by a multilayer GMAW process in the Instrumented Restraint Cracking test facility (IRC-test). This test facility allowed a defined restraint and, simultaneously, an in-situ analysis of the reaction stresses while welding and cooling. The reaction force build-up of the weld tests showed a significant influence of the used filler materials according to the heat input. Higher strength filler material grades cause a decrease of the welding stresses compared to lower strength grades, if a low heat input is used. The different stress build-up is described in detail for the root welds, filler layers and subsequent cooling to ambient temperature. Residual stresses in the weld, HAZ and base material were measured in loaded and unloaded condition using the incremental hole drilling method.
Anticancer drugs (ACDs) exhibit high biological activity, they are cytotoxic, genotoxic, and are constantly released into the environment as a result of incomplete metabolism. Consequently they pose a serious threat to the environment and human health due to their carcinogenic,mutagenic and/or reproductive toxicity properties. Knowledge of their bioavailability, including their sorption to soils and their impact on the soil–groundwater pathway, is crucial for their risk assessment. Laboratory batch and column leaching tests are important tools for determining the release potential of contaminants from soil or waste material. Batch and column tests were carried out with soils differing in physicochemical properties, each spiked with cyclophosphamide (CK) or ifosfamide (IF). Moreover, due to the fact that environmental pollutants may occur as coexisting compounds in the soil themobility evaluation for ACDs in the mixture with metoprolol (MET; β-blocker) as a co-contaminant was performed. In order to assess appropriateness, the batch and column tests were compared. The release depended on the properties of both the soil and the presence of co-contaminants. The faster release was observed for coarse-grained soil with the smallest organic matter content (MS soil: 90% decrease in concentration until liquid-to-solid ratio (L/S) of 0.3 L kg−1 for all tests' layout) than for loamy sand (LS soil: 90% decrease in concentration until ratio L/S of 0.75 L kg−1). ACDs are highly mobile in soil systems. Furthermore, the decrease of mobility of ifosfamide was observed with the presence of a co-contaminant (metoprolol) in both of the soils (in MS soil a decrease of 29%; in LS soil a decrease of 26%). The mobility of cyclophosphamide does not depend on the presence of a contaminant for MS soil, but also exhibits a decrease of 21% in LS soil.
We demonstrate an approach to overcome Kikuchi pattern misindexing problems caused by crystallographic pseudosymmetry in electron backscatter diffraction (EBSD) measurements. Based on the quantitative comparison of experimentally measured Kikuchi patterns with dynamical electron diffraction simulations, the algorithm identifies the best-fit orientation from a set of pseudosymmetric candidates. Using measurements on framboidal pyrite (FeS2) as an example, we also show the improvement of the orientation precision using this approach.
Trace element concentrations in gold grains from various geological units in South Africa were measured in situ by field emission-electron probe microanalysis (FE-EPMA), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and synchrotron micro X-ray fluorescence spectroscopy (SR-µ-XRF). This study assesses the accuracy, precision and detection limits of these mostly non-destructive analytical methods using certified reference materials and discusses their application in natural sample measurement. FE-EPMA point analyses yielded reproducible and discernible concentrations for Au and trace concentrations of S, Cu, Ti, Hg, Fe and Ni, with detection limits well below the actual concentrations in the gold. LA-ICP-MS analyses required larger gold particles (> 60 µm) to avoid contamination during measurement. Elements that measured above detection limits included Ag, Cu, Ti, Fe, Pt, Pd, Mn, Cr, Ni, Sn, Hg, Pb, As and Te, which can be used for geochemical characterisation and gold fingerprinting. Although LA-ICP-MS measurements had lower detection limits, precision was lower than FE-EPMA and SR-µ-XRF. The higher variability in absolute values measured by LA-ICP-MS, possibly due to micro-inclusions, had to be critically assessed. Non-destructive point analyses of gold alloys by SR-µ-XRF revealed Ag, Fe, Cu, Ni, Pb, Ti, Sb, U, Cr, Co, As, Y and Zr in the various gold samples. Detection limits were mostly lower than those for elements measured by FE-EPMA, but higher than those for elements measured by LA-ICP-MS.
As a chemical metrology tool time-of-flight secondary ion mass spectrometry (ToF-SIMS) has become a very popular technique to monitor the elemental, isotopic and molecular distribution in two or three dimensions. Its reduced sampling depth, high sensitivity, great structural specificity and the direct detection of hydrogen thereby increase the emergence of ToF-SIMS for material and analytical surface science, particularly due to recent instrumental developments improving mass, depth and lateral resolution. For basic surface science, adsorption processes and surface reactivity thus can be investigated in high detail on organic as well as inorganic samples. The use of multivariate data analysis in addition can effectively assist to identify trends in the complex SIMS raw data set and define key co-variances between certain samples or mass spectra. In this contribution the essence of ToF-SIMS is illustrated by discussing two highly relevant energy applications. First, for piezoelectric electroceramics oxygen exchange active zones have been visualized to determine the impact of external field-load to the oxygen vacancy distribution between anode and cathode. As a second case study the interaction of hydrogen species with the microstructure of a duplex stainless steel was investigated. It was concluded that ToF-SIMS has a valuable essence for detailing hydrogen related degradation mechanisms.
Task allocation in social insect colonies is generally organised into an age-related division of labour, termed the temporal polyethism schedule, which may in part have evolved to reduce infection of the colony's brood by pests and pathogens. The temporal polyethism schedule is sensitive to colony perturbations that may lead to adaptive changes in task allocation, maintaining colony homeostasis. Though social insects can be infected by a range of parasites, little is known of how these parasites impact within-colony behaviour and the temporal polyethism schedule. We use honey bees (Apis mellifera) experimentally infected by two of their emerging pathogens, Deformed wing virus (DWV), which is relatively understudied concerning its behavioural impact on its host, and the exotic microsporidian Nosema ceranae. We examined parasite effects on host temporal polyethism and patterns of activity within the colony. We found that pathogens accelerated the temporal polyethism schedule, but without reducing host behavioural repertoire. Infected hosts exhibited increased hyperactivity, allocating more time to self-grooming and foraging-related tasks. The strength of behavioural alterations we observed was found to be pathogen specific; behavioural modifications were more pronounced in virus-treated hosts versus N. ceranae-treated hosts, with potential benefits for the colony in terms of reducing within-colony transmission. Investigating the effects of multiple pathogens on behavioural patterns of social insects could play a crucial role in understanding pathogen spread within a colony and their effects on colony social organisation.
Phosphorus (P) for fertilizer use can be recovered from sewage sludge ash (SSA). To enhance the bioavailability of P and reduce the heavy metal content of SSA, it can be treated thermochemically with Na2CO3 or Na2SO4 at 950 °C in a rotary kiln using dry sewage sludge or lignite as reducing agent. These processes were investigated by thermogravimetry/differential thermal analysis coupled with gas analysis. Reducing conditions in this experimental setup were provided by 2 % hydrogen in the Ar carrier gas. During SSA + Na2CO3 treatment CO2, CO and water were detected in the off-gas. During SSA + Na2SO4 treatment SO2, some CO2 and water were detected. Heavy metal removal was more efficient for SSA + Na2CO3 compared to the sulfate variant. A SSA + Na2SO4 + lignite variant which also formed CO shifted the heavy metal removal to the results obtained with Na2CO3 which was obviously due to the additional reduction potential. However, Zn evaporation was not achieved with the Na2SO4 variants which were most probably due to immobilization as ZnS.
The stress vs. strain curve of materials is affected the rate of imposed straining. Among the methods for dynamic testing the technique known as 'split Hopkinson pressure bar' (SHPB) has evolved into the most widely used one to exert high-speed straining. The theory behind it comprises simple equations to compute stress and strain. The reliability of the strain analysis can be assessed by digital image correlation (DIC). The present results indicate that the visually observed strain is smaller than predicted by theory.
Electron backscatter diffraction (EBSD) and scanning electron microscopy were combined to study the effect of residual defect density on corrosion initiation in aluminium alloy AA2024-T3. EBSD was used to determine the level of misorientation (MO), from pixel to pixel, within individual grains. The MO can be determined with respect to either the average orientation angle of the grain or with respect to the average orientation angle of the surrounding pixels (in this instance, a matrix of 7×7 surrounding pixels has been applied). Herein, the MO, determined using the surrounding pixels, was used as the means for the assessing the level of defect density within a grain. It was found that there was a noteworthy, but not definitive, correlation of MO with corrosion initiation after 1 min exposure to 0.1 M NaCl solution. Additionally, the S and θ-phase particles were also identified using EBSD, displaying a range of MO and therefore defect density.
An energy-based method to determine material constants in nonlinear rheology with applications
(2016)
Many polymer-type materials show a rate-dependent and nonlinear rheological behavior. Such a response may be modeled by using a series of spring-dashpot systems. However, in order to cover different time scales the number of systems may become unreasonably large. A more appropriate treatment based on continuum mechanics will be presented herein. This approach uses representation theorems for deriving material equations and allows for a systematic increase in modeling complexity. Moreover, we propose an approach based on energy to determine thematerial parameters.This method results in a simple linear regression problemeven for highly nonlinearmaterial equations. Therefore, the inverse problem leads to a unique solution. The significance of the proposed method is that the stored and dissipated energies necessary for the procedure are measurable quantities. We apply the proposed method to a 'semi-solid' material and measure its material parameters by using a simple-shear rheometer.
Sewage sludge incineration is extensively practiced in some European countries such as the Netherlands, Switzerland, Austria and Germany. A survey of German sewage sludge ash showed that the recovery potential is high, approx. 19,000 t of phosphorus per year. However, the survey also discovered that the bioavailability of phosphorus in the sewage sludge ash is poor and that more than half of the ashes cannot be used as fertilizers due to high heavy metal content. A new thermochemical process for sewage sludge ash treatment was developed that transforms the ash into marketable fertilizer products. Sewage sludge ash was thermochemically treated with sodium and potassium additives under reducing conditions, whereby the phosphate-bearing mineral phases were transformed into plant available phosphates. High P-bioavailability was achieved with a molar Na/P ratio > 1.75 in the starting materials. Sodium sulfate, carbonate and hydroxide performed comparably as additives for this calcination process. Potassium carbonate and -hydroxide have to be added in a molar K/P ratio > 2.5 to achieve comparable P-solubility. The findings of the laboratory scale investigations were confirmed by an industrial demonstration trial for an ash treatment with sodium sulfate. Simultaneously, the volatile transition metal arsenic (61% removal) as well as volatile heavy metals such as cadmium (80%), mercury (68%), lead (39%) and zinc (9%) were removed via the off-gas treatment system. The product of the demonstration trial is characterized by high bioavailability and a toxic trace element mass fraction below the limit values of the German fertilizer ordinance, thus fulfilling the quality parameters for a P-fertilizer.
Explosion protection of oxidation reactions in micro reactors was investigated. Lange et al. (2014) reported on the possibilities of operating oxidation reactions in catalyst coated micro reactors within the explosion regime, but also warned about hotspot induced thermal runaway and detonation ignition at certain conditions. Methane and ethene, representing the explosion groups IIA1 and IIB (DIN EN ISO 16852), were used in stoichiometric oxygen mixtures with respect to total oxidation, which represents the worst case scenario in terms of safety assessment. Using laser radiation on a ceramic target inside of the micro channel, an artificial, controllable hotspot was generated. The ignition temperatures of fuel gas/oxygen mixtures inside a micro reactor were measured and their dependencies on initial pressure, initial temperature, volumetric flow rate, and micro channel height were examined. Deflagration reactions prior to the detonation were observed for the first time inside a micro reactor.
A discussion is provided on the relation between non-destructive testing (NDT) and fracture mechanics. The basic tasks behind this are to guarantee the safety of a component at a potential hazard loading event, to specify inspection intervals or, alternatively, of demands on NDT for a fixed inspection regime, to plan accompanying measures for cases of temporary continued operation of structures in which cracks have been detected, and, finally, fatigue strength considerations which take into account initial defects.
Hydrophobic guest molecules like organic dyes and metalion complexes can be introduced into aqueous media via adsorption onto inorganic nanoclay host materials such as nm-sized laponite. Dispersions of these organicinorganic hybrid materials show several advantageous properties like minimum light scattering due to their small size in the nanometer regime, ease of modification, low cost, low toxicity, and long-term stability, making them perfect candidates as signaling units and optically active materials in photonics and biotechnology. In this study, we summarize first findings on the easy-to-make, but chemically and optically fairly complex behavior of nanoclay hybrids for biotechnological applications. The latter includes the preparation of nanomaterials, which are colloidally stable in buffers and in the presence of biomolecules like proteins, and methods to control their surface chemistry. For this purpose, we used two red emitting fluorophores, the small organic dye Nile Red and the rare earth complex Eu(ttfa)3(topo)2, and evaluated the interaction of the red nanoclay hybrids with two model proteins, bovine serum albumin and β-lactoglobulin. We were able to monitor the formation of the protein corona around these hybrids using absorption and luminescence spectroscopy.
Poly(alkylene isophthalate)s were prepared by different methods, either in solution or in bulk. The SEC measurements were evaluated in such a way that all oligomers were included. In solution (monomer conc. 0.10.7 mol/L) large fractions of rings were formed and high dispersities (up to 12) were obtained, which disagree with theoretical predictions. Polycondensations in bulk did neither generate cyclics by 'back-biting' nor by end-to-end cyclization, when the maximum temperature was limited to 210 °C. The dispersities of these perfectly linear polyesters were again higher than the theoretical values. Regardless of the synthetic method monomeric cycles were never observed. Furthermore, SEC measurements performed in tetrahydrofuran and in chloroform and SEC measurements performed in three different institutes were compared. Finally, SEC measurements of five samples were performed with universal calibration and a correction factor of 0.71 ± 0.02 was found for normal calibration with polystyrene.
The thermal shock behavior of three commercial-advanced ceramics (SSiC, MgO–PSZ, Al2O3) is characterized in air and vacuum applying a laser thermal shock. The available testing system permits the reproducible setting of defined temperature profiles in thin disks and allows a heating-up thermal shock in various media. Due to the accurate determination of the time- and space-resolved temperature distribution, the local stress state can be calculated as a function of time. It is shown that the thermal shock strength is highest for SSiC and lowest in Al2O3 with MgO–PSZ in between. The approach presented in this work allows quantifying the stress state at failure in terms of tangential tensile stress. The investigated environment does not affect the thermal shock resistance under the studied experimental conditions.
In Germany, a quantity of more than 10 million metric tons of masonry rubble is generated per year. With regard to a sustainable closed substance cycle waste management, these rest masses have to be recovered if possible. The end-of-life (EOL) phase of masonry includes the planning steps of demolition, processing and application. The choice of the most sustainable solution raises questions regarding material technology, plant engineering, economic efficiency and ecological issues. For this purpose, a methodological concept for a holistic assessment of the EOL phase of masonry is developed within the scope of a doctoral thesis. For the assessment the Cost-Effectiveness Analysis (CEA) is adapted. The assessment concept enables a holistic comparison of different EOL scenarios for masonry while integrating all planning steps. It combines Material Flow Analysis (MFA), Life Cycle Analysis (LCA), Life Cycle Working Environment (LCWE), economic evaluation methods and material testing. In future, various scenarios can be evaluated with regard to the goals of the European and German waste management industry.
Applications by fire brigades expose the composite cylinders to harsh temperature and handling conditions. Standards have been used for certifying composite cylinders, which are designed for transport of dangerous goods and do not reflect service conditions specific to fire brigades. In this paper, the residual safety of a design type (fully wrapped with aluminum and carbon fiber composite) at the end of their service life of 15 yrs is analyzed. One sample underwent hydraulic load cycle (LC) tests, another conventional burst tests, and the third slow burst tests (SBTs). The statistical evaluation and the handling of an unexpected high amount of early failures are shown.
Alkaline reactions of paper sludge combustion ash at low temperature (60 °C) were performed using a calcite-rich paper ash (PA 1) and a gehlenite-rich ash (PA 2). Strong alkaline conditions (8, 12, 16 M NaOH) were revealed at reaction times of 1–4 h and 12–24 h. Reactions were performed with pure ashes and in the presence of NaAlO2. The products were characterized by XRD, FTIR, SEM/EDX, gravimetry and chemical analysis. The conversion was found to proceed mainly in the period between 1 and 4 h. Portlandite and hydrogarnet were observed from PA 1 in 8 M NaOH. Onset of formation of Ca4Al2O6CO·311H2O beside Ca(OH)2 could be analyzed after reaction of PA 1 in 12 M and 16 M NaOH. Addition of NaAlO2 favored crystallization of hydrogarnet and Ca4-Al2O6CO·311H2O. For PA 2 gehlenite remained stable, but a high portlandite fraction was observed. Addition of NaAlO2 yielded hydrogarnet beside gehlenite in 8 M NaOH. Higher alkalinities favored crystallization of Ca4Al2O6-CO·311H2O and onset of dissolution of gehlenite. Finally transformation of Ca4Al2O6CO·311H2O into sodium aluminum silicate hydrate was observed. All results were discussed with regard to heavy metal distribution of the initial PA between the alkaline digestion solution and the products. In conclusion suitable applications of the products were proposed.
Insect behavior is a common source of inspiration for roboticists and computer scientists when designing gas-sensitive mobile robots. More specifically, tracking airborne odor plumes, and localization of distant gas sources are abilities that suit practical applications such as leak localization and emission monitoring. Gas sensing with mobile robots has been mostly addressed with ground-based platforms and under simplified conditions and thus, there exist a significant gap between the outstanding insect abilities and state-of-the-art robotics systems. As a step toward practical applications, we evaluated the performance of three biologically inspired plume tracking algorithms. The evaluation is carried out not only with computer simulations, but also with real-world experiments in which, a quadrocopter-based micro Unmanned Aerial Vehicle autonomously follows a methane trail toward the emitting source. Compared to ground robots, micro UAVs bring several advantages such as their superior steering capabilities and fewer mobility restrictions in complex terrains. The experimental evaluation shows that, under certain environmental conditions, insect like behavior in gas-sensitive UAVs is feasible in real-world environments.
Mit der überarbeiteten Version der Vergabegrundlagen des Umweltzeichens Blauer Engel für Bürogeräte mit Druckfunktion (RAL-UZ 171:2012) wurde für die Partikelemission ein Prüfverfahren und ein Prüfwert eingeführt. Dies ergänzt die zahlreichen anderen Kriterien, die bereits Voraussetzungen für die Vergabe des Blauen Engels an Bürogeräte mit Druckfunktion waren. Die Anwendung des Prüfwertes für Partikelemissionen wurde von der Jury Umweltzeichen in 2012 zunächst nur für Geräte unterhalb 250 l Volumen - sogenannte Tischgeräte - beschlossen. Für größere Geräte (> 250 l, sogenannte Standgeräte) wurde eine Dokumentation des Messergebnisses im Rahmen des Prüfberichtes festgelegt. Ein Grund für diese Unterscheidung war die Tatsache, dass zu diesem Zeitpunkt für die Standgeräte keine für eine sinnvolle Festlegung eines Prüfwerts ausreichende Zahl an Messwerten und keine Erfahrungen aus entsprechenden Emissionsprüfungen vorlagen. Notwendig zur beabsichtigten Festlegung des Prüfwerts für die Partikelemission aus großen Bürogeräten war deshalb die systematische Erfassung und Bewertung der durch die anerkannten Prüfinstitute nach Inkrafttreten der RAL-UZ 171 ermittelten Ergebnisse. Dies wurde in diesem Forschungsprojekt durchgeführt. Das Forschungsprojekt befasste sich des Weiteren mit der Ermittlung und Beurteilung der Qualität der Partikelemissionsprüfungen auf Basis der zur Verfügung stehenden Prüfberichte in beiden Größenkategorien. Im Ergebnis stellte sich heraus, dass die Qualität der Prüfungen der Partikelemission insgesamt mit einer Fehlerquote von 3 % ungültiger Prüfungen sehr gut war. Ein weiteres Ergebnis ist, dass keine prüfmethodischen oder qualitätsrelevanten Gründe gegen die Anwendung des bestehenden Prüfwerts auf große Bürogeräte sprechen.