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Eingeladener Vortrag
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Highly unrelaxed structural states of metallic glasses have often advantageous mechanical properties. Since metallic glasses continuously relax with time (age) or inherently are well relaxed after processing, methods to uniformly rejuvenate the material are needed. One approach that has received attention is the so-called cryogenic-cycling method, during which a metallic glass is repeatedly immersed into liquid nitrogen. In some cases, cryogenic cycling is truly efficient in increasing the stored excess enthalpy of metallic glasses, but it does not seem to be universally applicable to all alloys and structural states. The origins for these differences remain unclear due to our limited understanding of the underlying structural evolution. In order to shed more light onto the fundamental structural processes of cryogenic cycling, we pursue in-situ x-ray photon correlation spectroscopy (XPCS) to trace the atomic-scale structural dynamics of a Zr-based metallic glass in two different structural states (ribbon and bulk metallic glass). This method allows calculating the relaxation times as a function of time throughout the thermal cycling. It is found that the investigated glasses exhibit heterogeneous structural dynamics at 300 K, which changes to monotonic aging at 78 K. Cryogenic cycling homogenizes the relaxation time distribution for both structural states. This effect is much more pronounced in the ribbon, which is the only structural state that rejuvenates upon cycling. We furthermore reveal how fast atomic-scale dynamics is correlated with long-time average structural relaxation times irrespective of the state, and that the ribbon exhibits unexpected additional fast atomic-scale relaxation in comparison to the plate material. Overall, a picture emerges that points towards heterogeneities in fictive temperature as a requirement for cryogenic energy storage.
Die additive Verarbeitung hochfester Feinkornbaustähle mittels Wire Arc Additive Manufacturing (WAAM) ist ein komplexes, aber zugleich auch effizientes Verfahren, bei dem Werkstoff, Bauteilgeometrie und Schweißprozess gezielt aufeinander abgestimmt sein müssen. Ziel dieser Studie war es, einen Zusammenhang zwischen den Prozessparametern und der generierten Schichtgeometrie zu ermitteln. Dazu wurden definierte Referenzkörper mit einem robotergestützten Schweißsystem additiv gefertigt und hinsichtlich Schichthöhe, Wandstärke und Mikrostruktur analysiert. Fokus der Untersuchung waren sowohl konventionelle als auch für die WAAM-Fertigung speziell entwickelte hochfeste Schweißzusatzwerkstoffe. Die geometrischen Eigenschaften additiv gefertigter Bauteile lassen sich insbesondere durch die Faktoren Drahtvorschubgeschwindigkeit und Schweißgeschwindigkeit gezielt einstellen. Jedoch können diese Parameter nicht beliebig variiert werden, auch aufgrund der rheologischen Eigenschaften der Zusatzwerkstoffe. Zu hohe Streckenenergien führen zu lokalen Überhitzungen und Fehlstellen in der generierten Schicht. Undefinierte Fließ- und Erstarrungsvorgänge im überhitzten Bereich erschweren die maßhaltige Fertigung. Deshalb wird bei speziellen WAAM-Schweißdrähten das Fließverhalten gezielt modifiziert, sodass es über einen größeren Temperaturbereich hinweg konstant ist. Erst die Kenntnis über die komplexen Zusammenhänge zwischen den Prozessparametern und der Bauteilgeometrie ermöglicht die Erzeugung exakter Schichtmodelle für die additive Fertigung. Dies bildet die Grundlage für die Bearbeitung weiterer Fragestellungen auf dem Gebiet der additiven Fertigung mit hochfesten Zusatzwerkstoffen und insbesondere deren Anwendung in modernen hochfesten Bauteilen.
CHG is very different compared to other graphite degenerations or defects;
Filigree, multi-branched string-like, 3d interconnected structure;
Morphology and volumetric amount of CHG cannot be accessed by stereological interpretation of 2d section data;
Field-tested, technically established method to quantify CHG in components not available;
Fatigue: CHG causes substantial reduction in fatigue limit and significant increase in crack growth rate;
Therefore: Avoid or exclude CHG!
High-entropy alloys containing up to 6 platinum group metals can be prepared by thermal decomposition of single-source precursors non requiring high temperature. We prepare the first example of a single-phase hexagonal high-entropy alloy. Heat treat- ment up to 1500 K and compression up to 45 GPa do not result in phase changes, a record temperature and pres- sure stability for a single-phase high-entropy alloy. The alloys show pronounced electrocatalytic activity in methanol oxidation, which opens a route for the use of high-entropy alloys as materials for sustainable energy conversion.
High and medium entropy alloys gained increasing academic and industrial interest as novel materials for engineering applications. This project is aiming to clarify and compare the general and local corrosion properties of high entropy alloy CrMnFeCoNi and medium entropy alloy CrCoNi in different aqueous environments. The focus lies on the local corrosion processes that result either from microstructural imperfections (inclusions, defects at grain boundaries etc.) in the base material or processing related changes in the microstructure and/or local composition.
The corrosion behavior of the alloys was monitored via potentiodynamic polarization experiments and the local corrosion characteristics were further investigated by means of scanning electrochemical microscopy (SECM). Their passivation behavior was analyzed in three different electrolyte systems (NaCl, H2SO4 and NaClO4; c = 0.1M). The characterization of the surface morphology and composition of the passive film was performed by means of atomic force microscopy (AFM), scanning electron microscopy coupled with energy dispersive X-Ray spectroscopy (SEM/EDX) and X-Ray photoelectron spectroscopy (XPS), respectively.
Considering long term corrosion effects, electrochemical work was supported with immersion tests and the analysis of corrosion products by SEM/EDX and XPS depth-profiling. Our results indicate that the medium entropy alloy CrCoNi has a significantly higher corrosion resistance in comparison to the high entropy alloy CrMnFeCoNi. The presentation will summarize some of our results on the mechanistical aspects of the observed high corrosion resistance.
A set of some unexpected and interesting microstructures has put the so-called complex concentrated alloys (CCAs) in the eye of the scientific community. The AlMo0.5NbTa0.5TiZr refractory (r)CCA, aimed at substituting Ni-base superalloys in gas turbine applications, belongs to this alloy family. After a two-stage heat treatment, this rCCA morphologically resembles the typical a two-phase microstructure of the latter. The objective of this work consists in determining the effect of the two stages of the heat treatment on the microstructure of the AlMo0.5NbTa0.5TiZr alloy to eventually improve it in terms of homogeneity and porosity.
The presentation reflects the questions that have been raised by member states and NGOs.
As background information details on the question how to choose a suitable salvage pressure receptacle (SPR) are provided. This leads to the need for deleting the volume limitation for SPRs and to the discussions in 2014 and 2016 on this issue.
As an adequate substitution for deleting the volume limit for SPRs it is proposed to limit the pressure receptacles to be stored in by a maximum pressure-volume-value of 1.5 Mio bar-litres.
After some explanations to standardisation projects currently also tackling this pV-limit, some risk-based safety criteria for a limitation are mentioned with the focus of the consequence level and the general avoidance of catastrophic worst case scenarios.
The presentation starts with some key figures about BAM. Then it introduces BAM's competence centre H2Safety@BAM and shows aspects of special competence of the centre. It closes with information about the engagement of BAM in European research projects on hydrogen and a reference to our bilingual paper about our hydrogen strategy.
Der Vortrag beginnt mit dem erwarteten Bedarf an Wasserstoff und der Frage der Risikosteuerung bei stattfindender Marktdurchsetzung. Dem gegenüber ist an einem Beispiel der Prozess der Regelsetzung gestellt, was die Notwendigkeit pro-aktiven Handelns zeigt.
Es wird über die risikobasierte Definition von Sicherheit gezeigt, welche Bedeutung die Erfassung der Fertigungsstreuung hat und wie die quantitative Erfassung und Bewertung aussehen könnte. Zuletzt wird über den Aspekt der Alterung auf das Potential probabilistischer Zulassungsansätze verwiesen und aufgezeigt, wie die Wirkung von Vorschriften nach dem probabilistischen Sicherheitskriterium bewertet und optimiert werden kann.
First the acceptance rates resulting from the analysis of different minimum burst ratios and standards are displayed and explained. Especially the problems resulting from a further reduction if the minimum burst ratio are shown.
For a better understanding of these results the process of analysing the acceptance rate is explained in detail. This contains the alleged contradiction between safety of samples due to its scatter while the rejected sample provides a higher mean strength.
Then the importance of batch testing is explained and leads to the recommendation to have a strong interaction between provided mean strength and requested maximum of production scatter.
Network modifier ions can decisively influence properties and structure of low melting alkali-zinc-borate glasses and thus cause complex effects on the liquid phase sintering of silver-glass metallization pastes. This effect was studied for X2O-ZnO-B2O3 (X = Li, Na, Rb) glasses for silver-glass metallization pastes. Viscosity and the glass transition temperature, Tg, were measured with rotational viscometry and dilatometry. Dried model pastes with 30 vol% LZB, NZB or RZB glass were prepared for sintering studies by means of heating microscopy measuring the silhouette area shrinkage of uniaxially pressed powder compacts during heating at 5 K/min. For comparison, the silhouette area shrinkage of pure glass and silver powder compacts were determined. Glass-silver wetting was investigated during heating of bulk glass cylinders placed on silver substrates. Glass RZB turned out to have the lowest viscosity among the glasses under study. Its glass transformation temperature, Tg, was found at 444 °C and it caused the lowest sintering onset for its glass and paste powder compacts. Slightly increased values of Tg were found for NZB and LZB (468 °C and 466 °C, respectively) and a slightly retarded sintering was found for both paste powder compacts. These results indicate that liquid phase sintering of silver-glass pastes under air atmosphere is mainly influenced by glass viscosity.
Monodisperse iron oxide nanoparticles as reference material candidate for particle size measurements
(2020)
In order to utilize and rationally design materials at the nanoscale the reliable characterization of their physico-chemical properties is highly important, especially with respect to the assessment of their environmental or biological impact. Furthermore, the European Commission’s REACH Regulations require the registration of nanomaterials traded in quantities of at least 1 ton. Powders or dispersions where 50% (number distribution) of the constituent particles have sizes ≤ 100 nm in at least one dimension are defined as nanomaterials. This creates a need for industrial manufacturers and research or analytical service facilities to reliably characterize potential nanomaterials. Currently, BAM is developing reference nanoparticles, which shall expand the scarce list of worldwide available nano reference materials certified for particle size distribution and will also target other key parameters like shape, structure, porosity or functional properties. In this respect, materials like iron oxide or titanium dioxide are considered as candidates to complement the already available silica, Au, Ag, and polystyrene reference nanoparticles.
The thermal decomposition of iron oleate precursors in high boiling organic solvents can provide large quantities of iron oxide nanoparticles that can be varied in size and shape.[1, 2] The presence of oleic acid or other hydrophobic ligands as capping agents ensures stable dispersion in nonpolar solvents. Such monodisperse, spherical particles were synthesized at BAM and pre-characterized by electron microscopy (TEM, SEM including the transmission mode STEM-in-SEM) and dynamic light scattering comparing cumulants analysis and frequency power spectrum.
1. REACH regulations and nanosafety concerns create a strong need for nano reference materials with diverse properties.
2. Iron oxide nanoparticles are under development as new candidate reference material at BAM.
3. Narrow particle size distribution confirmed by light scattering and electron microscopy.
For hazard Assessment purposes we need models to predict what would happen in case of an accident.
The challenge in hazard assessment consists not only in choosing the right model, but beforehand to define the correct scenario .If models can be found for the physical effect to be simulated, the validation of these models is the next challenge.
Even if experimental data can be found it should always be checked, if these data are correct, even if in general experimental data are considered as “failsafe” or “the absolute truth”.
A new approach towards performance-related design and scientific evaluation of joint sealing systems
(2020)
While there is a permanent improvement of concrete pavement mixtures and pavement construction types over the last decades, the state-of-the-art joint sealing materials and joint constructions seem to stagnate on an antiquated empirical level. This status has been reaffirmed in the latest European standard.
The consequences in the motorway network due to unsatisfying capability and durability of joint sealing systems are unacceptable. In addition, inadequate traffic performance (noise emissions, roll-over comfort) and traffic safety losses in the joint area of concrete pavements are existing challenges. These deficits and weaknesses reflect a demand for joint sealing materials and constructions whose approval requirements take functional aspects into account. Furthermore a sufficient analysis of decisive loads and a practice-oriented method to evaluate the requirements towards performance and durability is still missed.
In this contribution decisive loads to German highways are analyzed. The design of test specimen for representative functional testing of joint sealing systems is discussed. The focus is on the geometry of the test specimens and the used concrete mixture. Finally, a new approach for a function-orientated test concept that considers representative load functions is presented. The potential of this approach to validate the durability and capability of various joint sealing systems is also presented using an example.
Composition and microstructure stability of cement compound under cyclic hydrothermal condition
(2020)
There have been many researches focused on the performance improvement of ultra-high performance concrete (UHPC) by autoclaving treatment. The goal of autoclaving is to increase the pozzolanic reaction, and to densify the cement stone and the transition zone which originates from the incorporation of supplementary cementitious materials (SCMs), such as silica fume, fly ash and blast furnace slag. Due to the superior properties, UHPC can also be utilized under high mechanical load and aggressive condition, for example, the fabrication of water tanks for thermal storage which is of great significance for saving energy and reducing CO2 emission. It is known that mineral stability of the hydration products of an inorganic binder is highly related to the temperature and pressure of the environment. A certain stable composition at room temperature, however, may undergo a phase transformation at high temperature and the performance decrease under this severe condition will generally be more severe. In this way, the rationale behind this deterioration under long-term hydrothermal condition involving many cycles and long duration has to be clarified, and then appropriate optimizing methods will be performed in order to obtain a kind of construction with high durability under aggressive environment. For this purpose, different types and amounts of SCMs are introduced into the standard mixture of UHPC and the phase compositions after autoclaving at 200 °C and 15.5 bar are determined by combined X-ray diffraction and scanning electron microscope. Mercury intrusion porosimeter is used to characterise the microstructure of the samples. In order to establish the relationship between microstructure and macroscopic properties, compressive and flexural strength are also investigated.
Fault detection for linear parameter varying systems under changes in the process noise covariance
(2020)
Detecting changes in the eigenstructure of linear systems is a comprehensively investigated subject. In particular, change detection methods based on hypothesis testing using Gaussian residuals have been developed previously. In such residuals, a reference model is confronted to data from the current system. In this paper, linear output-only Systems depending on a varying external physical parameter are considered. These systems are driven by process noise, whose covariance may also vary between measurements. To deal with the varying parameter, an interpolation approach is pursued, where a limited number of reference models { each estimated from data measured in a reference state { are interpolated to approximate an adequate reference model for the current parameter. The problem becomes more complex when the different points of interpolation correspond to different noise conditions. Then con icts May arise between the detection of changes in the eigenstructure due to a fault and the detection of changes due to different noise conditions. For this case, a new change detection approach is developed based on the interpolation of the eigenstructure at the reference points. The resulting approach is capable of change detection when both the external physical parameter and the process noise conditions are varying. This approach is validated on a numerical simulation of a mechanical system.
In the DECHEMA Virtual Talks, general aspects of the safety and acceptance of hydrogen technologies were presented. How can trust in new technologies be built when past accidents led to myths and fairy tales? The presentation does away with general prejudices and shows that handling hydrogen is neither more unsafe nor safer than handling other fuel gases. The basis for the safe handling of hydrogen is always a risk analysis.
Elastomer seals are used in many industrial applications due to their excellent mechanical properties at a wide range of temperatures. Their high versatility and recovery potential under several load conditions make them well suitable for the application in containers designed for transport, storage and/or disposal of radioactive materials. In containers for low and intermediate level radioactive waste, elastomer seals are used as barrier seals, and as auxiliary seals in storage and transportation casks (dual purpose casks) for heat generating radioactive waste, such as spent fuel and high-level waste. While a seal exchange at defined intervals is typical in many conventional applications, it is impossible or at least hard to perform when principles of minimization of radiation exposure have to be considered and prohibit an unnecessary cask handling. An extensive knowledge of the change of the elastomer’s properties during aging and the availability of reliable end-of-lifetime criteria to guarantee the permanent safe enclosure of the radioactive material is mandatory. As BAM is involved in most of the national cask licensing procedures and in the evaluation of cask-related long-term safety issues, great efforts have been already made and are still planned to scientifically support this task.
Compression stress relaxation and compression set were identified as key indicators of elastomer long-term performance and quantitatively investigated in comprehensive test programs. Among other representative types of elastomers, specimens made from ethylene propylene diene rubber (EPDM) were tested before, during and after aging to capture the most important of their complex mechanical properties.
In the presented study, exemplary results were used to simulate the compression stress relaxation and the compression set of elastomer O-rings during aging. Regarding the influence of temperature, the time temperature superposition principle is applied in the relaxation analysis of elastomer O-rings. The proposed model is implemented in the commercial finite element software ABAQUS/Standard® [1] with a sequential temperature displacement coupling. Numerical results match the experimental compression stress relaxation measurements well. The prediction of compression set values after long-term aging shows a relatively good agreement with the experimental results. Nevertheless, all input parameters derived from the specimen tests, additional assumptions concerning boundary conditions and modeling strategy are discussed with regard to the identified slight discrepancies.
The possibility to extend the finite element model to represent the O-ring seal’s ability to recover after a (fast) partial release is taken into account
In diesem Beitrag werden am Beispiel von Gasturbinen Verfahren zur Charakterisierung des werkstoff-mechanischen Verhaltens sowie der Gefügeentwicklung von Bauteilen für Anwendungen bei hohen Temperaturen aufgezeigt. Gasturbinen sind technisch gesehen sehr interessante Systeme, die in der Energietechnik und in der Luftfahrt von hoher wirtschaftlicher Relevanz sind. Seit Jahrzehnten gelten Gasturbinen als klassische Innovationstreiber, für ihre Entwicklung wurden bereits maßgebliche Erneuerungen im Bereich der Aerodynamik und der Werkstofftechnik hervorgebracht.
Die Bereitstellung von zuverlässigen Werkstoffdaten stand für die Werkstoffprüfung seit dem 19. Jahrhundert in zentraler Stelle. Mit der zunehmender Digitalisierung unserer Gesellschaft gewinnt das Datenmanagement insbesondere im Hinblick auf die Modellierungs- und Simulationsaktivitäten an Bedeutung.
In unserem Beitrag beschreiben wir die gegenwärtigen Aktivitäten in Deutschland – insbesondere die NFDI-MatWerk und die BMBF-Initiative MaterialDigital – sowie in Europa und Übersee. Abschließend heben wir die Auswirkungen auf die technische und akademische Aus- und Weiterbildung.
In this presentation we discuss the online monitoring of metallic AM parts produced by the Laser Powder Bed Fusion (LPBF) process by using optical, thermographic and electromagnetic methods. In a first approach we present the detection of defects generated during the process and discuss how to improve these methods for the optimization of design and production of metallic AM parts.
The mechanical behavior of fiber reinforced composites with polymer matrix is governed by several mechanisms operating at different length scales. In this contribution we describe first non-destructive techniques which are adequate for the characterization of the fiber-matrix interphase at a microscopic level. In a second step we describe on a mesoscopic level the influence of manufacturing related elements on the mechanical properties of rotor blades for wind turbines. We concentrate on thermography, laminography and ultrasound in connection with mechanical testing systems. Finally we present methods for monitoring rotor blades by using embedded optical fibers.
The evaluation of measurement uncertainty is essential for testing and calibration laboratories. This paper provides a general process description for the determination of the measurement uncertainty of quantitative data and its application to the conformity assessment with examples, and how to deal with the uncertainty of qualitative (Boolean) results, e. g. when "Alarm" or "No alarm" occours in an instrument display.
Polymer nanocomposites (PNCs) with inorganic nanofillers dispersed in a polymer matrix have been widely studied from the 1990s, since the pioneering work by Toyota Central Research. The possibility of producing advanced tailor-made, light weight and low-cost materials, inspired academic and commercial research towards numerous potential applications, facilitating PNCs to become a billion-dollar global industry. The introduction of nanoparticles (NPs) to a polymer matrix is expected to result in improved properties. The outstanding performance of PNCs is determined not only by the characteristics of the used components but also by their phase morphology, including the dispersion of NPs and interfacial properties. Understanding of structure-property relationships is particularly important for polymer nanocomposites with high industrial significance, such as epoxy-based materials reinforced with inorganic nanofillers. These PNCs have been successfully adopted by the marine, automotive and aerospace industries, although they are still rarely studied on a fundamental level. Therefore, this thesis aims for a detailed understanding of the structure, molecular mobility and vitrification kinetics first, of two epoxy-based materials with different network structures and second, of the corresponding nanocomposites with different alumina-based nanofillers. The first system considered (EP/T-LDH) was based on bisphenol A diglycidyl ether (DGEBA) cured with diethylenetriamine (DETA) and taurine-modified layered double hydroxide (T-LDH) NPs. The taurine molecule bears additional functionalities that could enhance the interactions between the matrix and the nanofiller, improving the interphase formation. The seconds system (EP/BNP) was based on DGEBA and methyl tetrahydrophtalic acid anhydride (MTHPA) as a hardener, reinforced with boehmite nanoparticles (BNPs). The comparison of the two systems enables for a comparative study on the effect of different hardeners and the morphology and modification of the alumina-based nanofillers on the material behavior. The materials were investigated employing complementary techniques with different sensitivities and frequency windows. The following methodology was used: transmission electron microscopy (TEM), small – and wide – angle X-ray scattering (SAXS/WAXS), broadband dielectric spectroscopy (BDS), calorimetry in a form of conventional DSC and fast scanning calorimetry (FSC), as well as specific heat spectroscopy (SHS) in a form of temperature modulated DSC, temperature modulated FSC and static FSC by calculating the thermal relaxation rates from the cooperativity approach. The FSC method (based on adiabatic chip calorimetry to probe micrometer-sized samples) was successfully employed in this work, exploiting all its possibilities for the first time in literature for a PNC. Moreover, a systematic analysis technique was established to overcome the problem of vague glass transition regions observed for highly loaded PNCs in the heat flow and heat capacity curves.
First, TEM, SAXS/WAXS and indirectly BDS and SHS were employed to obtain the information about the approximate morphology of the PNCs. It was found that epoxy-based materials exhibit a structural heterogeneity in a form of regions with different average crosslinking density. This was indicated by multiple-peak scattering pattern of the polymer matrix and two distinct α-processes (dynamic glass transition) related to the cooperative fluctuation of the epoxy network found by BDS and SHS. This was described for the first time for epoxy-based materials. The two α-relaxations were evidenced differently for the two systems, which is related to different network structures and dipole moments due to the employed hardeners. Nevertheless, structural heterogeneity is an intrinsic feature of these materials, independent of the type of hardener used for the network formation and nanofiller. In addition, matrix inhomogeneities were more pronounced with increasing nanoparticle content. Furthermore, a powerful new technique was applied for X-ray scattering data, using Monte Carlo fits, to describe the NPs dispersion throughout the whole sample volume (as opposed to the local investigations performed by most researches). Additional structural information of the two systems was extracted by BDS and SHS, such as qualitative and quantitative estimation of polymer segments physically adsorbed and/or chemically bonded onto the nanoparticles. Due to the immobilized character of this interphase with respect to the cooperative segmental motions, it is denoted as a rigid amorphous fraction (RAF). For instance, on the contrary to EP/BNP, for EP/T-LDH a dielectrically active process was found, related to the localized fluctuations within RAF. Moreover, the amount of RAF in EP/T-LDH was reaching up to 40 wt % of the system, whereas in EP/BNP it ranged between 1-7 wt %. In the latter case the presence of NPs was found to simultaneously increase and decrease the number of mobile segments, due to the interphase formation and changes in crosslinking density. The difference between the two systems was ascribed to the presence of additional amine functionalities in the T-LDH nanofiller.
Second, employing BDS and SHS, a systematic study on the effect of NPs on the segmental dynamics was performed. For example, depending on the nanofiller, the α-processes related to regions with higher crosslinking density was found to shift to higher and lower temperatures with increasing T-LDH and BNPs concentration, respectively. The observed difference is due to the different synergism of the polymer matrix with the nanofiller.
Third, a detailed investigation of the vitrification kinetics was performed with DSC and FSC. The concentration dependence of the glass transition temperature was found, similar to the behavior of the α-processes. It was shown that, in parallel to the detected main glass transition, epoxy-based materials can exhibit an additional low temperature vitrification mechanism. As expected from the two distinct α-processes, this behavior was however not discussed in prior studies for an unfilled network former. This finding was correlated to the structural heterogeneity evidenced by other techniques.
This thesis, dealing with an in-depth research on the epoxy-based materials that are already successfully employed in numerous applications underlines the necessity of more fundamental research in this field. It shines light on the complexity of these systems and contributes to defining how the structure-property relationships can be determined by combining multiple experimental techniques and analytical methodology.
This study shows that formaldehyde Emission results in micro-scale emission chambers are comparable with results in bigger chambers both for particle boards and wooden toys. On the contrary, the WKI flask method was leading to more variable results depending on sample geometry. Thus, microchambers could be used for reliable routine market surveillance. An exposure assessment led to noticeable formaldehyde indoor air concentration values, pointing out the need for an effective Surveillance of such samples.
Isotope analysis can be used to determine the age and provenance of geological samples or to study dynamic systems like Li-ion batteries. Modern techniques in optical spectrometry allow us a fast and slow-cost isotope analysis. These techniques include high-resolution continuum source molecular absorption spectrometry (HR-CS-MAS) and laser ablation molecular isotopic spectrometry. This seminar will discuss our recent work on precise and accurate isotope analysis of boron, magnesium, and lithium with geology, climate, and energy research applications.
Advances and Applications of Molecular Absorption Spectrometry: from Non-Metals to Isotope Analysis
(2020)
The present work covers two main aspects of high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GFMAS), an analytical technique for elemental trace analysis.
First, a comprehensive mechanistic study of molecule formation in graphite furnaces is presented, which is a key step into the recovery of analytical signals. For this, the molecule formation of CaF was studied, which is used for the indirect analytical determination of fluorine in HR-CS-GFMAS. A zirconium coating catalyzes the CaF formation, and its structure was investigated. The kinetics of this reaction was established by monitoring its molecular spectrum at different atomisation temperatures. An Arrhenius plot showed a pseudo-first order reaction with respect to fluorine (n = 1). An intermediate state was isolated, and its structure was elucidated by spectroscopic methods: scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XANES and EXAFS), and Raman microspectroscopy. Here a mechanism is proposed, where ZrO2 works as a heterogeneous catalyst: after a pyrolytic step, an intermediate state of ZrO(OCaF) is activated, and at higher temperatures, CaF(g) is released from the zirconium-coated graphite surface.
Second, analytical methods were developed by using HR-CS-MAS as detector for non-metals and isotope analysis. Therefore, the determination of organic absorbable chlorine in water, the quantification of fluorine in consume care products with declared perfluorinated ingredients, and the determination of sulfur content in crude oils were investigated. Finally, the high resolution of the instrumentation allows to measure isotopic shifts with high precision in some observed molecular spectra. Consequently, the molecular spectra of enriched isotopes of boron and magnesium were investigated, establishing so the potential of HR-CS-MAS for the accurate and precise determination of isotopic amount ratios.
Isotope analysis can be used to determine the age and provenance of geological samples. Modern techniques in optical spectrometry allow us a stand-off isotope analysis. This seminar will discuss how planetary science with the next Moon and Mars missions drive optical spectrometry into precise and accurate isotope analysis and how BAM will contribute.
Wie lässt sich die Herkunft von Rohstoffen, Lebensmitteln oder Umweltschadstoffen einfacher, schneller und kostengünstiger als mit bisherigen Methoden bestimmen?
Die Dissertation zeigt auf, dass man das grundlegende physikalische Prinzip einer Isotopverschiebung mit in Adlershof entwickelten Optik-Instrumenten für die Herkunftsbestimmung nutzen kann. Die entwickelte Methode ermöglicht es in Zukunft den Ursprung von Rohstoffen, Lebensmitteln oder Umweltschadstoffen kostengünstiger und wesentlich schneller bestimmen, als dies mit bisherigen Methoden möglich ist.
Kann man das grundlegende physikalische Prinzip einer Isotopieverschiebung mit einem Optik-Instrument für die Herkunftsbestimmung nutzen? Carlos Abad hat eine wegweisende Methode entwickelt, die es in Zukunft ermöglicht den Ursprung von Rohstoffen, Lebensmitteln oder Umweltschadstoffen kostengünstiger und wesentlich schneller bestimmen, als dies mit bisherigen Techniken möglich ist.
An established method for characterizing cladding material is the Ring Compression Test (RCT), where a small, cylindrical sample of the cladding tube is subjected to a compressive load. This test is a laboratory representation of a fuel rod load case and has shown a high susceptibility to failure under the occurrence of radial hydrides. Certain hydride morphologies and low temperature might even lead to brittle fracture at very small loads. The BAM research project BRUZL (Fracture mechanical analysis of spent fuel claddings during long-term dry interim storage) aims to study the results of quasi-static RCTs and to establish numerical models to gain an in-depth understanding of the stress state during such experiments. Using a fracture mechanical approach, cases of sudden failure during the RCT procedure are used to characterize the material behaviour and establish a failure criterion.
As an integral part of the project BRUZL, quasi-static Ring Compression Tests have been performed to identify all experimental details, which might be helpful for numerical modelling. Unirradiated samples of the cladding material ZIRLO® have been subjected to hydrogen charging and a thermo-mechanical treatment for radial hydride reorientation. Sample preparation, testing procedures, and analysis results are presented. A numerical model has been established and an elastic-plastic material model was derived from as-received RCT samples by inverse finite element analyses. Cohesive zone modelling has been implemented to reproduce sudden load drops during RCT.
The project is funded by the Federal Ministry for Economic Affairs and Energy (BMWi) under contract no. 1501561.
Understanding the mechanical behaviour of fuel cladding is decisive for an extended dry interim storage period beyond the currently licensed period of 40 years in Germany and subsequent handling, transport, and disposal considering normal and accidental conditions. Since fuel cladding acts as the first barrier for spent fuel, its integrity should be demonstrated to enable safe and secure discharge and handling options after interim storage and subsequent transportation in preparation of final disposal. An established method for characterizing cladding material is the Ring Compression Test (RCT), where a small, cylindrical sample of the cladding tube is subjected to a compressive load. This test is a laboratory representation of a fuel rod load case and has shown a high susceptibility to failure under the occurrence of radial hydrides. Certain hydride morphologies and low temperature might even lead to brittle fracture at very small loads. The BAM research project BRUZL (Fracture mechanical analysis of spent fuel claddings during long-term dry interim storage) aims to study the results of quasi-static RCTs and to establish numerical models to gain an in-depth understanding of the stress state during the experiments. Using a fracture mechanical approach, cases of sudden failure during the RCT procedure are used to characterize the material behaviour and establish a failure criterion. As an integral part of the project BRUZL, quasi-static Ring Compression Tests have been performed to identify all experimental details, which might be helpful for numerical modelling. Unirradiated samples of the cladding material ZIRLO® have been subjected to hydrogen charging and a thermo-mechanical treatment for radial hydride reorientation. Sample preparation, testing procedures, and analysis results are presented. A numerical model has been established and an elastic-plastic material model was derived from as-received RCT samples by inverse finite element analyses. Cohesive zone modelling has been implemented to reproduce sudden load drops during RCT. The project is funded by the Federal Ministry for Economic Affairs and Energy (BMWi) under contract no. 1501561.
In order to shorten time to market of products and to support new developments, the European Community is funding a HORIZON 2020 project called i-TRIBOMAT. In the field of tribology, renowned institutions combine their testing and analytical capabilities to provide the respective services. The later will be offered in Europe via a Single-Entry Point (SEP). Due to this combination of services, a testbed is created consisting of more than 100 tribometers. Thus, a large variety of testers exists, either commercially available or in-house built. Each tester is optimised to simulate a specific tribological contact situation. Currently, there is no standard available for the design of such testers. Especially, the way forces (normal load, friction force) and distances (e.g. stroke, linear wear) are measured, recorded and pre-processed differs from type to type. These forces and distances are essential for the determination of wear/ wear rates and coefficients of friction (COF), the core results of tribo-tests. This matter is complicated by the fact that e.g. for reciprocating motion, there are at least four different ways to determine COF. Depending on the testing conditions, these ways can lead to considerably different results. Currently, it is not obligatory to specify the method used for determining the COF.
In order to make data comparable, there is a need for measures which ensure that each tribometer is delivering similar, at best the same results under the same test conditions, irrespective of its manufacturer, design, location, determination method and even operator. The way forward are improved Round-Robin tests. First results and other challenges faced by creating comparable tribological data will be considered in the present contribution.
Composite Facade Elements with Self-Cleaning Surface made of Ultra-High-Performance Concrete (UHPC)
(2020)
In the framework of the European project H-House various concrete façade elements were developed with the aim to ensure a long service life by combining a very durable material with self-cleaning properties. The façade elements presented are made of a shell of UHPC filled with blocks of aerated autoclaved concrete as insulating material. Self-cleaning properties were realized amongst others by imprinting a microstructure into the surface during casting. The paper focuses on selected technological aspects of the manufacturing process of prototypes which had to be performed in two concreting sections. Furthermore the challenges faced when upscaling the self-cleaning properties are addressed and the strategy to assess the self-cleaning properties by measuring the contact and the roll-off angel is presented. The results show that a successfull upscalaing process requires detailed planning and that the best results can often be achieved with a moderate work effort or material use.
Der Markt von LNG als Transportgut und als Kraftstoff ist seit Jahrzehnten kontinuierlich am Wachsen, wobei das Hauptanwendungsgebiet im Schiffsverkehr lag. LNG ist verflüssigtes Erdgas mit Hauptbestandteil Methan, das neben fossilen, aus erneuerbaren Quellen, wie synthetischen Methan oder Biogas, gewonnen werden kann. LNG hat als Kraftstoff sehr gute Eigenschaften dessen Potenzial als alternativer Kraftstoff zu Diesel im Schwerlast- und Fernverkehr gesehen wird. Dabei weist LNG gegenüber Diesel geringere Emissionen von CO2, Feinstaub, Stickoxiden und Lärm auf und hat gegenüber anderen erneuerbaren Energiespeichern wie CNG, Elektrobatterien oder Wasserstoff die höchste volumetrische und zweitgrößte gravimetrische Energiedichte. Neben seinen Vorteilen zu anderen erneuerbaren Energieträgern birgt LNG durch seine sehr niedrige Temperatur von bis zu 160°C und seiner Brennbarkeit aber auch neue Gefahren für Personen und Infrastrukturen.
Zur Bewertung von Gefahren und zur späteren Durchführung von Risikobewertungen bedarf es Methoden und Modellen deren Untersuchung Ziel des Forschungsprojekts war. Schwerpunkt der Untersuchung stellt die Freisetzung von LNG in Tunnel, mit sich anschließender Stoffausbreitung und verzögerter Zündung des Kraftstoff-Luftgemisches dar. Unfallszenarien mit Brandereignissen in Tunnel haben gezeigt, dass diese meist mit hohen Personen, Bauwerks und volkswirtschaftlichen Schäden verbunden sind. Des Weiteren zeigten Untersuchungen das von Gasexplosionen in Umschließungen wie sie ein Tunnel darstellt, mehr Gefahren ausgehen als von Gasexplosionen im Freifeld.
Im Vortrag werden die untersuchten Modelle und die aus dem Projekt gewonnenen Erkenntnisse für die Stoffausbreitung und Verbrennung der Gasphase von LNG in Umschließungen vorgestellt.
Online quality control of security relevant parts manufactured by Laser Powder Bed Fusion (LPBF) remains to be a challenge due to the highly complex process conditions. Furthermore, the influence of characteristic scan strategy parameters is not sufficiently clarified yet due to the commonly used method of single-track investigations. In this contribution, this topic is addressed by observing large 316L volume sections using in-situ melt pool monitoring by thermography in high temporal and spatial resolution. In detail, the influence of the scan angle on the melt pool geometry is investigated on. Characteristic melt pool features are extracted from the image data and analyzed using statistical methods data for altering scan angles. The results show significant changes in the melt pool dimensions and temperature distribution over the scan angle rotation. A first explanation approach is presented that connects the observed changes to phenomena of beam attenuation by metal vapor plume.
Inacceptable capability and durability of joint sealing systems but also inadequate traffic performance (noise emission; overrolling comfort) up to traffic safety aspects reflect the still enormous demand for data-based description of concrete pavements performance under heavy loading conditions. Especially the deformation behavior of concrete pavement slabs in the joint region in consideration of new pavement construction types and improved concrete mixtures meanwhile established but also under the steeply rising traffic loads is not sufficiently explored. To create a data basis for advanced design rules, evaluation methods and product standards - and with it to improve quality, durability and finally sustainability of pavements - an innovative 3-D sensor system SENSO JOINT adapted to german roadworking requirements and suitable for heavy-duty operating conditions was developed. The contribution introduced describes the development of an extensive technical solution based on the analysis of decisive loads, interactions and boundary conditions. Based on calibration data, results of laboratory testing and finally field-testing on different concrete pavement construction types the outcome of a multi-level evaluation process shall introduce the potential of the new sensor system.
A powerful tool to understand, demonstrate and explain the limits of the pulsed technique in terms of detectability and localizability of AM keyhole pores has been assessed by comparing the active thermographic approach (both experimental and FEM simulations) to Computed Tomography results;
✓ µCT results demonstrate that the intended defect geometry is not achieved; indeed a network of voids (microdefects consisting of small sharp-edged hollows with a complicated, almost fractal, inner surface) was found;
✓ both Exp-PT and FEM results explains clearly why no indication of defect related to the thermal contrasts could be found during the investigation of an uncoated surface. However, the application of further data evaluations focusing on the thermal behavior and emissivity evaluation (PPT post data processing) enable the detection of some defects;
✓ coating facilitates a closer inspection of inner defects, but inhomogeneities of the coating could impair the spatial resolution and lead to the emergence of hotspots (the FEM simulation reached its limit with this extreme geometry where a 25 µm thin disc is considered at a 1 cm thick specimen in millisecond time resolution);
✓ both Exp-PT and FEM results allow the conclusion that very short pulses of 200 ms or shorter should be sufficient to detect these defects below, but near the surface; besides a short duration of the thermal phenomenon it should be emphasized, about 0.04 s (high frame rate camera);
The fourth industrial revolution (also known as “Industry 4.0”) promises to relieve people from manual and physical work by developing cyber-physical systems and smart automation and thereby achieving a more efficient, reliable and safe performance. This will change people’s work from being operators of the system into becoming strategical decision makers and flexible problem solvers. This shift will require a new division of work between people and technical systems, a new division of responsibilities and new ways of interacting with technology, which in turn will pose new demands on people. People will require different physical and cognitive capabilities, different competencies and new strategies to cope with the upcoming challenges. The focus of Industry 4.0 is therefore on designing systems with human in the centre: systems that will extend people’s capabilities, that will allow collaborative work and take advantage of performances in which either people or technology excel. This presentation will focus on the benefits of consideration of human-machine interaction in the context of industry 4.0.
The aim of this presentation is twofold: first, to present the field of psychology including its research methods and, second, to show on an example how psychology can be used in material research. The example is of the study of human factors in non-destructive testing (NDT), in which the author has more than 10 years of experience. The conclusion is that psychological methods can be used to identify human-related problems during different tasks and to generate mitigation strategies that can be used to decrease human error and enhance safety.
This presentation offers a holistic view on the assessment of reliability of NDT including the intrinsic reliability (typically expressed in terms of probability of detection (POD) curves), application, human and organisational factors. In addition to POD, advanced methods such as multiparameter POD, volume POD and POD for combined data are presented. Human and organisational factors in NDT require a systematic approach, i.e. it is not just the individual that determines how the inspections are carried out but also the interactions of individuals with the technology, team, organisation and the extra-organisational environment. Lessons learned from the literature as well as from own studies are presented.
Im Zeitalter von Industrie 4.0 muss die zerstörungsfreie Prüfung (ZfP) mit den Anforderungen Schritt halten. Die erfolgreiche Umsetzung von Digitalisierung, Automatisierung, komplexer Vernetzung, künstlicher Intelligenz, Assistenzsystemen, intelligenten Sensortechnologien usw. hängt stark mit einer erfolgreichen und optimalen Mensch-Maschine-Interaktion (MMI) zusammen. In der ZfP 4.0 wird sich die Rolle des Prüfers zum flexiblen Problemlöser und Entscheider verändern. Dieser Wandel wird andere Anforderungen an die Prüfer stellen und eine andere Organisation der Prüfung, Ausbildung etc. erfordern. Der Mensch wird also weiterhin im Mittelpunkt der ZfP stehen. Zu den Herausforderungen, die dieser Wandel mit sich bringen wird, gehören das Vertrauen in automatisierte Systeme und die Akzeptanz neuer Technologien, für die Wege gefunden werden müssen, um sie zu bewältigen.
Die geringe Zugfestigkeit von zementgebundenen Materialien kann durch die Zugabe von Fasern maßgeblich verbessert werden. Ziel eines gemeinsamen Verbundprojekts mit einem Industriepartner war die Erhöhung der Leistungsfähigkeit von kurzen Polymer- und Carbonfasern durch eine Verbesserung des Verbundes zwischen Faseroberfläche und Zementsteinmatrix.
Von der IONYS AG wurde dazu eine spezielle Funktionalisierung entwickelt, die über eine Hydrophilisierung der Faseroberfläche eine chemische Anbindung an die Zementsteinmatrix gewährleistet. Aufgabe der BAM war es, die Effizienz der neuen Beschichtung bezüglich der Erhöhung der Nachrissbiegezugfestigkeit und der Reduzierung der Schwindrissbildung während der Erhärtungsphase zu quantifizieren. Die Ergebnisse zeigen, dass die Funktionalisierung die Neigung zur Schwindrissbildung für die Carbonfasern und in noch stärkerem Maße für die Polymerfasern reduziert.
Eine Erhöhung der Nachrissbiegezugfestigkeit konnte dagegen nur für die deutlich steiferen Carbonfasern nachgewiesen werden.
Total Reflection X-ray Fluorescence (TXRF) is a small footprint, ressource efficient micro-analytical tool for trace elemental determination. However, depending on the matrix TXRF is also challenging in several ways: the preparation of a representative aliquot maybe difficult for slurries, shading effects and matrix effects may occur and the applicability of an IS maybe hampered by interferences (fitting may be impaired as well) or inhomogeneities. It is therefore crucial to understand and if applicable mitigate the influence of the before mentioned phenomena. We have used the small volume approach using pL droplets to study shading in TXRF previously.Using this approach thin specimens in a favorable geometry are prepared with a well defined morphology; this way minimizing matrix effects and shading. To be used as standard it is also necessary to determine the delivered elemental amounts. Here we will present on the performance of a commercial ink-jet printer cartridge to deliver defined volumes and elemental amounts. The microscopic specimens obtained have been successfully applied to determine relative sensitivities in TXRF and prepare references to study coded apertures in grazing incidence full field micro-XRF.The homogeneous lateral distribution of analyte and IS may be probed by micro-XRF, to obtain information on alikeness of analyte and IS. To study the alikeness of the in depth distribution (film-like or particle-like) angle scans can deliver valuable data. Here we present first results on angle scans using a prototype GIXRF set up and a commercial TXRF instrument.
Composite UHPC facade elements with self-cleaning surface: Aspects of technological manufacturing
(2020)
In the framework of the European collaborative project H-House, which was finished in 2017, large façade elements were developed consisting of a box shaped external shell of ultra-high-performance concrete (UHPC) with a functionalized surface and an insulation of autoclaved aerated concrete (AAC). The exposed concrete of the elements was further refined by adding self-cleaning properties to the surface through imprinting a microstructure in combination with chemical agents directly in the casting process. The paper focuses on selected technological aspects of the manufacturing process of large-scale prototypes. Presented are results of the upscaling process of functionalized surfaces from small specimen up to large UHPC composite facade elements produced for the construction of a demonstrator.
Polymer electrolyte membranes (PEM) are polymers which act as separator in an electrochemical cell and allow ionic charge flow to close the circuit. Widely used membranes are perfluorinated sulfonic-acid (PFSA) ionomers (e.g. Nafion™), a class of ion-conducting polymers with remarkable ion conductivity and chemical-mechanical stability. A nanoscopic water system around the sulfonic acid capped side-chains of the otherwise hydrophobic polymer allows the ion transport. Only approx. 14 molecules of water per sulfonic group are present in the fully hydrated state. In vanadium redox flow batteries (VRFB) ideally only protons are transported. The weak ion selectivity of Nafion™ is the main cause for the transportation of vanadium, briefly vanadium crossover, in VRFBs a system we have investigated more closely, lately. The consequences of crossover are a concentration imbalance and a self-discharge of the battery, which leads to a decrease of the capacity. The development of efficient energy storage systems is crucial for the transformation towards a renewable energy based economy. The VRFB has a great potential as a commercial electrochemical energy storage system due to properties including, but not limited to, no cross-contamination, a long cycle-life and a theoretically unlimited capacity. VRFB consists of two half-cells, which are linked to electrolyte tanks and separated by a membrane. The membrane plays a major role in overall cell performance. So far, vanadium transportation models, which include diffusion, migration, electroosmotic convection and pressure gradients, are inconsistent. There is no agreement in the literature on the diffusion coefficients of vanadium species (e.g. published diffusion coefficients of V2+ are located between 3.13·10-12 m²s-1 and 9.44·10-12 m²s-1) indicate that thevanadium crossover is not well understood and there is a lack on a more fundamental level. Since the membrane transport is the rate-determining step of the crossover as well as of the proton exchange it is extremely important to understand these phenomena on a fundamental level. This will eventually allow us to design better membranes. Alternative materials need to show equivalent performance compared with Nafion™ and ideally be more selective regarding ion cross-membrane transport.There are several options to approach the chemistry i.e. the interaction of dissolved and bound ions inside the confined water body of ionomeric membranes. Vanadium ions are a versatile model as UV/VIS data can be used to distinguish between the 5 species V2+, V3+, VO2+, VO2+ and V2O33+ of the electrolyte. Infrared spectroscopy has been applied to study the interaction of sulfonic groups and the ions. Molecular dynamic modeling is another approach to study the distribution and distances of ions. We now introduce X-ray absorption near edge structure spectroscopy (XANES) to study species and species changes inside Nafion™ and a novel membrane based on poly(1,1-difluoroethylene) (PVDF). We evaluated the methods and investigated the influence of irradiation, temperature and hydration on the measurements.
Vanadium redoxflow batteries (VRFB)are currently one of the most promising candidates for stationary energys torage.For large scale applications the ion conducting membranes currently in use need to be improved. Ideally,they need to become more cost efficient and selective regarding the vanadium crossover.For a better understanding of the vanadium crossover, the development of reliable analytical methods and procedures, that elucidate uptake and transport of vanadium ions in the membrane, is necessary. First, we present the uptake of V2+,V3+,VO2+, VO2+ and V2O33+ in Nafion™ and in a novel membrane based onpoly(1,1-difluoroethylene)(PVDF). In preliminary discharge/charge experiments the ETFE-based membrane, the precursor of PVDF-based membrane, performed comparable to Nafion™. The methods of choice for speciation are UV/Vis and X-ray absorption near edge structure spectroscopy (XANES). According to the results, V2O33+, formed from VO2+ and VO2+, diffuses also into the membrane. In present models, the diffusion of V2O33+ is neglected. In addition,we study whether reactions could take place inside the membranes’ nanoscopic water body using XANES. Exposing Nafion™ from one site with V3+a nd from the other site with VO2+ realized the experiment. The results verified that VO2+ was formed inside the membrane. However,in present models reactions inside the membrane are neglected, too.
Preisträgervortrag Georg-Sachs-Preis der DGM
Röntgencomputertomographie (CT) ist heute ein Standardwerkzeug in der Materialcharakterisierung. Im Vortrag zeigen wir ihre Anwendung für die Untersuchung magnetischer Funktionsmaterialien, additiv gefertigter Bauteile und deren Feedstockpulver und stellen erste CT-Ergebnisse biogener Feedstockpulver vor.
Functional materials for energy conversion are important technology drivers needed for the implementation of low carbon energy. Therefore, researchers commonly focus on improving the intrinsic properties of a functional material. However, for applications, the extrinsic properties are at least as important as the intrinsic ones. Consequently, it is important to investigate and understand the external and internal structure of semi-finished products and especially defect dependent properties. The extrinsic properties may change during application and the life cycle of the material as well as through processing and molding steps. Our studies show how X-ray tomographic (XCT) investigations can contribute to structure investigations in composites and massive samples using the example of magnetic materials for energy conversion.
Thermomagnetic materials are a new type of magnetic energy materials, which enable the conversion of low temperature waste heat to electricity by three routes: Thermomagnetic motors, generators and microsystems. Taking our recent work on thermomagnetic generators as a starting point, in this talk we analyse the material requirements for a more energy and economic efficient conversion. We will describe the influence of magnetisation change and heat capacity on thermodynamic efficiency, as well as the consequences of thermal conductivity on power density. Our analysis will allow selecting the best thermomagnetic materials in Ashby plots and illustrate the substantial different properties compared to magnetocaloric materials. Supported by DFG, project FA 453/14)
Various applications for artificial intelligence in the context of spectroscopy will be presented. in particular, examples from BAMline will be presented. After a short introduction to synchrotron radiation, artificial intelligence algorithms for the quantification of X-ray fluorescence measurement are discussed. In the second example, information retrieval by natural language processing is discussed.
Synchrotron radiation sources with their unique properties in terms of intensity, polarization and adjustability offer a wide range of possibilities in materials research. A basic introduction about the creation and special properties of synchrotron radiation will be given. Examples of current work at BAMline, the high-energy measuring facility of the Federal Institute for Materials Research and Testing at the synchrotron BESSY, are used to illustrate the possibilities and limitations of existing measuring methods.
In this talk, the features of X-ray fluorescence analysis with synchrotron radiation will be presented. First, the basics of the origin of synchrotron radiation and X-ray fluorescence analysis and the experimental setup will be discussed. Then, examples of trace element detection, micrometer resolution, and application of the X-ray color camera will be shown.
Gold ist eines der sieben schon im Altertum bekannten Metalle und wurde wg. seines Glanzes und seiner Seltenheit von alters her als Tauschmittel und zur Herstellung von Schmuck benutzt. Außerdem ist es einfach bearbeitbar und weitestgehend gegen chemische Einflüsse resistent. Die Untersuchungen von Gold mit synchrotronstrahlungsangeregter Röntgenfluoreszenzanalyse sind zerstörungsfrei und geben Auskunft über die in der untersuchten Probe vorhandenen chemischen Elemente. Bei den hier vorgestellten Untersuchungen an der BAMline stehen Fragestellungen wie Herkunft, Herstellungsverfahren und Zusammengehörigkeit von Goldfunden im Vordergrund. Die verschiedenen Fragestellungen werden an einer Reihe von Beispielen erläutert die vom Wikingerschatz aus Hiddensee über die Himmelsscheibe von Nebra bis hin zu Funden aus Ägypten langen. Der Fund von Bernstorf wird ausführlich diskutiert.
Various applications for artificial intelligence in the context of spectroscopy will be presented. in particular, examples from bamline will be featured. After a short introduction to synchrotron radiation, artificial intelligence algorithms for the quantification of X-ray fluorescence measurement are discussed. In the second example, information retrieval by natural language processing is reviewed. As a last example the reconstruction of measurements with the X-ray color camera and coded apertures is presented.
To date, there are only very few technologies available for the conversion of low temperature waste heat to electricity. More than a century ago, thermomagnetic generators were proposed, which are based on a change of magnetization with temperature, switching a magnetic flux, which according to Faraday’s law induces a voltage. In this talk, we first describe the principle of thermomagnetic generators. Then we focus on the impact of topology of the magnetic circuit within thermomagnetic generators. We demonstrate that the key operational parameters strongly depend on the genus, i.e. the number of holes within the magnetic circuit. A pretzel-like topology of the magnetic circuit with genus =3 improves the performance of thermomagnetic generators by orders of magnitude. We will show that this technique is on its way to becoming competitive with thermoelectrics for energy harvesting near room temperature.
Komposit-Druckgefäße für den Gefahrguttransport sowie für Wasserstoff-und Erdgasfahrzeuge bestehen aus einem lasttragenden Komposit und einer gasdichten, metallischen oder polymeren Barriereschicht (Liner).
Zur Untersuchung der Integrität der Druckflaschen wurde die Wirbelstromprüfung eingesetzt. Hierbei wurden verschiedene Frequenzbereiche angewendet, um so die unterschiedlichen Materialien untersuchen zu können. Ziel der Untersuchungen war es, alterungsbedingte Schädigungen rechtzeitig zu detektieren. Der Vortrag stellt diese Ergebnisse vor.
Trace elements are chemical elements whose concentration in a material is very low. The exact definition depends on the application and varies for example between 100 micrograms per gram in analytical chemistry and 1000 micrograms per gram in geology. The ability to detect trace elements fast and quantitatively is of great importance in many areas of science and technology. With its high brilliance and flexibility in the excitation conditions, synchrotron radiation is an ideal tool for detecting traces even in small sample quantities. In this contribution I will report about the use of X-ray fluorescence(XRF)for qualitative and quantitative element sensitiveanalysis. In addition to the fundamentals of XRF and its quantification methods, the advantages and problems of different geometries like e.g. microXRF, Total Reflection X-ray Fluorescence (TXRF)or Double Dispersive XRF (D²XRF) will be discussed. Practical examples from BAMline from the research fields of medicine, geology and archaeometry will complete the lecture.
Additively manufactured metallic materials have already started to find application in safety-relevant components. However, this has only happened for certain materials and specific applications and loading conditions, since there is still an extensive lack of knowledge as well as of historical data regarding their mechanical behaviour. This contribution aims to address this lack of understanding and historical data concerning the creep behaviour of the austenitic stainless steel 316L manufactured by Laser-Powder-Bed-Fusion (L-PBF) and the low-cycle-fatigue behaviour of the titanium alloy Ti-6Al-4V manufactured by Laser-Metal-Deposition (LMD). Furthermore, it aims to assess their mechanical behaviour against their conventional counterparts. With that in mind, specimens from conventional and additive materials are tested and their mechanical behaviour analysed based on characteristic curves. To understand the damage behaviours the materials are characterized by destructive and non-destructive techniques before and after failure.
The development within the offshore wind sector towards more powerful turbines combined with increasing water depth for new wind parks is challenging both the designer as well as the manufacturer of bottom fixed support structures. Besides XL-monopiles, the market developed an innovative and economic jacket support structure which is based on automatically manufactured tubular joints combined with standardized pipes. Besides the improvements for a serial manufacturing process the automatically welded tubular joints show a great potential in terms of fatigue resistance e.g. due to a smooth weld geometry without sharp notches. However, these benefits are not considered yet within the fatigue design process of automatically manufactured jacket substructures according to current standards due to the lack of suitable S-N curves. Therefore, 32 axial fatigue tests on single and double-sided automatically welded tubular X-joints have been performed to determine a new hot spot stress related S-N curve. Based on these constant amplitude fatigue tests a new S-N curve equal to a FAT 126 curve was computed which implicitly includes the benefits of the automatically welding procedure.
We present here a set of conceptual and numerical tools for a micromechanical simulation of general erosion problems involving fluid-saturated granular assemblies, whether frictional or cohesive. We propose a parallel computation using graphical processing units (GPUs) to treat large numbers of degrees of freedom with conventional desktop computers.
The fluid phase is here simulated with a particle-resolved approach in the frame of the Lattice Boltzmann Method (LBM) while the granular solid phase is modelled as a collection of discrete particles from a Molecular Dynamics DEM perspective. The range of possible material behaviors for the solid granular phase is intended here to cover a broad spectrum from purely frictional to viscous cohesive materials with either brittle or transient debonding features. Specific details of the implementation and some validation cases will be put forward.
To conclude we provide some exemplary applications in the field of soil erosion along with details on the parallel performance of the models. The results show that a micromechanical approach can be feasible and useful in practice, providing meaningful insights into complex phenomena like the erosion threshold and kinetics of weakly cemented soils.
Alle nichtmetallischen und metallischen Materialien sowie alle Armaturen und Anlagenteile müssen für Sauerstoff- Anwendungen geeignet sein. Im ersten Teil des Vortrags werden die Prüfverfahren und Untersuchungsmethoden auf dem BAM Stammgelände sowie die Bewertungskriterien vorgestellt. Die BAM Sicherheitsphilosophie setzt bei der Interpretation der Prüfergebnisse teilweise auf strengere oder erweiterte Bewertungskriterien, um somit beispielsweise die bessere Übertragbarkeit der Laborergebnisse auf praktische Anwendungen zu gewährleisten. Im zweiten Teil des Vortrags werden die erweiterten Sauerstoff Untersuchungsmöglichkeiten auf dem BAM Testgelände Technische Sicherheit vorgestellt. Nach der Planung und der technischen Umsetzung konnte im Probebetrieb gezeigt werden, dass die neue, weltweit einzigartige 750 bar Sauerstoff Druckstoßanlage korrekt arbeitet. Da es sich um eine komplette Neuentwicklung für extreme Betriebsbedingungen handelt, wurden für ein korrektes Funktionieren der Anlage teilweise aufwändige Modifikationen notwendig. Für 2021 ist die Inbetriebnahme dieser Prüfeinrichtung geplant.
Moderne Segelflugzeuge sind voll-verklebte tragende FKV-Strukturen. Über die Schwingfestigkeit der Faser-Kunststoff-Verbunde (FKV) und die Lebensdauerabschätzung dieser Werkstoffklasse auf Basis verschiedener Lastspektren wurden insbesondere von Christoph Kensche verschiedenen Arbeiten durchgeführt und auch auf dem Symposium für Segelflugzeugentwicklung vorgestellt. Hingegen ist die Betriebsfestigkeit von Struktur-Klebungen im Anwendungsbereich der CS22 vergleichsweise wenig untersucht worden.
Über die Jahre wurden in verschiedenen Projekten immer wieder Probleme in Struktur-Klebungen (u.a. Betriebsbelastungsversuche an Versuchs-Holmen) identifiziert, analysiert und spezielle Prüfverfahren weiter entwickelt (Projekt „Tragflügel neuer Technologie für die allgemeine Luftfahrt“, FK SIF765). Im Rahmen des LuFo-Vorhabens GeAviBoo (General Aviation Booster) wurde in zwei Arbeitspaketen das Thema erneut aufgegriffen und Betriebsbelastungsversuche an Klebproben durchgeführt. Im Rahmen des Vortrages werden die Erkenntnisse der letzten 10 Jahre aufbereitet und die neusten Ergebnisse vorgestellt.
Kleinere und mittlere Unternehmen agieren heutzutage in einem globalen Umfeld, wodurch diese zu Elementen einer komplexen Wertschöpfungskette werden. Der zunehmende Anstieg der Preise für industriell essenzielle Ressour-cen, wie Primärenergie und Rohstoffe, sowie sich ausweitende klimapolitische Restriktion führen zur Notwendigkeit, die Wettbewerbsfähigkeit durch innovative und ökoeffiziente Fertigungsprozesse langfristig zu sichern. Rahmenbe-dingungen zu schaffen, welche die Positionierung nachhaltiger Produkte und Prozesse innerhalb globaler Wert-schöpfungsketten ermöglicht, ist daher ein wesentliches Ziel der deutschen Industriepolitik [1, 2].
Im Rahmen dieses Beitrages werden aktuelle Forschungsarbeiten zur Bewertung der Umweltwirkungen der schweiß-technischen Fertigungskette anhand ausgewählter Schmelzschweißverfahren unter Berücksichtigung vor- sowie nachgelagerter Fertigungsschritte dargestellt. Das hierzu notwendige Element zur Analyse der Fertigungsprozesse ist die Ökobilanzierung - eine weit verbreitete und standardisierte Methode zur Abschätzung der Umweltwirkungen eines Produktes oder Prozesses. Hierbei stellt die Sachbilanzierung, d.h. die Ermittlung sämtlicher relevanter Ener-gie- und Ressourcenverbräuche während der schweißtechnischen Fertigung, aufgrund des hohen Dokumentations-aufwandes sowie Ableitung assoziierter Wirkkategorien das größte Hindernis für eine Etablierung und Akzeptanz der Ökobilanzierung in der Praxis dar. Gleichwohl wird seitens Unternehmen, welche als Zulieferer von OEM’s agieren, die Dokumentation des fertigungsspezifischen CO2-Verbrauches gefordert.
Ein weiterer Aspekt der Arbeiten beinhaltet folglich Methoden zur automatisierten Erfassung von schweißtechnischen Produktionsdaten sowie deren Nachverfolgbarkeit aufzuzeigen. Anhand unterschiedlicher Schweißverfahren werden die aus den Produktionsdaten abgeleiteten Energie- und Ressourcenverbräuche automatisiert in den relevanten Umweltwirkungen überführt. Die analysierten Schweißprozesse umfassen dabei ein breites für kmU relevantes Spektrum. Durch die softwareseitige Bereitstellung der aufgestellten Umweltprofile ist der Anwender in der Lage, Schweißprozesse unter ökologischen Aspekten zu bewerten und die effizienteste Variante zu identifizieren.
The Dark Side of Science
(2020)
Eine kritische Aufgabe im Rahmen der Etablierung von Prozess-Struktur-Eigenschafts-Performance-Beziehungen bei der additiven Fertigung (AM) von Metallen ist die Ermittlung von zuverlässigen und gut dokumentierten Kennwerten zum Materialverhalten sowie das Schaffen von Wissen über die Struktur-Eigenschafts-Korrelation. Schließlich ist dies die Grundlage für die Entwicklung gezielterer Prozessoptimierungen und zuverlässigerer Lebensdauer-Vorhersagen. In diesem Zusammenhang zielt dieser Beitrag darauf ab, Daten und Erkenntnisse über das Kriechverhalten des austenitischen Edelstahls 316L zu liefern, der mittels Laser-Powder-Bed-Fusion (L-PBF) hergestellt wird. Um dieses Ziel zu erreichen, wurden Proben aus konventionellem warmgewalztem sowie AM-Material gemäß den bestehenden Normen für konventionelles Material geprüft und vor und nach dem Versagen mikrostrukturell charakterisiert. Die Probekörper wurden aus einzelnen Blöcken des AM-Materials gefertigt. Die Blöcke wurden mit einer Standard-Scan- und Aufbaustrategie hergestellt und anschließend wärmebehandelt. Das Kriechverhalten wird anhand der Kriechlebensdauer und ausgewählter Kriechkurven und Kennwerte beschrieben und vergleichend bewertet. Der Einfluss von Defekten und Mikrostruktur auf das Materialverhalten wird anhand von zerstörenden und zerstörungsfreien Auswertungen an ausgewählten Proben analysiert. Der AM-Werkstoff zeigt kürzere Kriechlebensdauern, erreicht das sekundäre Kriechstadium deutlich schneller und bei geringerer Dehnung und weist eine geringere Kriechduktilität im Vergleich zu seinem konventionellen Gegenstück auf. Das Kriechschädigungsverhalten des AM-Werkstoffs ist eher mikrostruktur- als defektgesteuert und ist durch die Bildung intergranularer Kriechrisse gekennzeichnet. Als kritische Merkmale werden die Versetzungsdichte sowie die Versprödung der Korngrenzen identifiziert. Die Mikro-Computertomographie (µCT) erweist sich als Alternative zur Metallographie, um die Kriechschädigung zu analysieren.
Many PhD students are interested in applying machine learning, AI, data science, etc., and there are many good reasons for this. However, there is a disconnect between mainstream data science and materials science, for example, when it comes to the sheer size of the data. This talk will highlight some of the unique challenges in materials informatics and present some interesting approaches to overcome them. Although the field is large, this talk will focus on cases that have some practical relevance to PhD students at BAM.
Data-driven research is considered the new paradigm in science. In this field, data is the new resource from which knowledge is extracted that is too complex for traditional methods. Several factors such as national funding and advances in information technology, are driving the development. In particular, the creation of databases and the analysis of data with artifical intelligence are playing an important role in establishing the new paradigm. However, there are numerous challenges that must be overcome to realize the full potential of data-driven methods. This talk sets the stage for the upcoming workshop by reviewing some of the historical developments and the current state of data-driven science in NDT and materials science.
Explore and Exploit - Strategische Erweiterung der fraktographischen Datenbank mit Machine Learning
(2020)
In diesem Vortrag stellen wir den aktuellen Stand zu einer Masterarbeit zusammen die sich mit dem Thema beschäftigt wie die Generalisierbarkeit von Datenmodellen auf Basis kleiner Datensätze erhöht werden kann. Wir stellen vor, wie die Datenbasis eines fraktogafischen Bildklassifizierers mit einem statistischen Model strategische erweitert, bzw. an eine Anwendung angepasst werden kann.
Im Bereich der Zerstörungsfreien Prüfung (ZfP) im Bauwesen werden eine Vielzahl von Messdaten erfasst. Obwohl Sie als Grundlage für wissenschaftliche Analysen dienen, gibt es noch keine einheitliche Repräsentation der Daten. Eine Analyse verschiedener verteilter Datensätze über unterschiedliche Prüfobjekte hinweg ist daher kaum möglich.
Wir stellen einen Ansatz für ein integriertes Datenmanagement verteilter Datensätze auf Basis von Semantic-Web Technologien vor. Der Ansatz basiert im Kern auf einem mathematischen Modell – der sogenannten Ontologie – welches das Wissen unserer Domäne ZfPBau repräsentiert. Die von uns entwickelte ZfPBau Ontologie wird mit Datenquellen verknüpft und beschreibt so die semantische Bedeutung der Daten. Darüber hinaus fungiert die Ontologie als zentrales Konzept für den Datenbankzugriff. Domänen-fremde Datenquellen können durch die Verknüpfung mit der ZfPBau Ontologie einfach integriert werden und stehen zur generischen Nutzung im Sinne der Digitalisierung direkt zur Verfügung. Basierend auf einer umfangreichen Literaturrecherche, skizzieren wir die Möglichkeiten die sich daraus für die ZfP im Bauwesen ergeben, wie zum Beispiel Messdaten computergestützt zu sortieren, zu analysieren, Zusammenhänge zu erkennen und zu erklären.
Der erwartete Nutzen dieses Ansatzes der Wissensrepräsentation und des Datenzugriffs für die ZfP-Community ist eine Erweiterung des Wissens durch Datenaustausch in der Forschung (Interoperabilität), die wissenschaftliche Verwertung großer existierender Datenquellen mit datenbasierten Verfahren (wie Bilderkennung, Messunsicherheitsberechnungen, Faktoranaylsen, Materialcharackterisierung) und letztlich ein vereinfachter Transfer von ZFP-Daten in Ingenieurmodelle und somit in die Baupraxis.
Ontologien sind bereits Kern vielzähliger intelligenter Systeme wie Building-Information-Modeling oder Forschungsdatenbanken. Der Beitrag gibt einen Überblick über die Werkzeuge die wir derzeit für die Kommunikation mit ihnen schaffen.
We have arrived in the data age. But why is it so difficult for the NDT community to achieve real breakthroughs with data-driven science? In this seminar, we will take a brief look at the evolution of mainstream data science to understand why the most exciting times are perhaps just ahead. We will give an overview of our activities in the junior research group 8.K which are aimed at enabling the next generation of data science methods in NDT. The seminar addresses the two main work fields of our group: semantic data management and the handling of limited data resources.
The first field addresses the problem that a uniform representation of our data is not yet available. However, knowledge creation in data science - whose main contribution lies in the analysis of distributed resources - requires common data access based on a collective understanding. To achieve this, we present an ontology-based approach. Ontologies are already the core of many intelligent systems such as building information models or research databases. We summarize some of the basic principles of this technology and describe our approach to create an NDT ontology.
The second field ties in with the first and addresses the application of data-based methods in engineering practice. Especially in the field of non-destructive testing many successful applications have been published. In most cases, however, the creation of referenced data is extremely expensive and therefore much sparser than in other research areas. As a result, the available data may cover only one scenario, so that common benchmarks often do not reflect the actual performance of the model in practical applications. Estimates that quantify the transferability from one scenario to another are not only necessary to overcome this challenge - they also prove to be a powerful tool for the strategic expansion of what we consider knowledge.
CALM is software for determining the Bravais lattice type and the resulting lattice parameters from a single Kikuchi pattern. It requires the definition of 4 bands and a single bandwidth from which all other band positions as well as bandwidths are derived. For band detection, it uses the Funk transform, which allows detection of twice as many bands as usual. CALM works for any symmetry and requires low-noise patterns of at least 320x240 pixels. The resulting errors are <2% even for such small patterns, assuming good quality. The relative errors are <0.5%. However, this requires a projection centre position best derived from a sample of a cubic phase in CALM. However, this must have been recorded under identical conditions. Hundreds of Kikuchi patterns of phases with different symmetries were examined.
In the field of non-destructive testing (NDT) in civil engineering, a large number of measurement data are collected. Although they serve as a basis for scientific analyses, there is still no uniform representation of the data. An analysis of various distributed data sets across different test objects is therefore only possible with high manual effort.
We present a system architecture for an integrated data management of distributed data sets based on Semantic Web technologies. The approach is essentially based on a mathematical model - the so-called ontology - which represents the knowledge of our domain NDT. The ontology developed by us is linked to data sources and thus describes the semantic meaning of the data. Furthermore, the ontology acts as a central concept for database access. Non-domain data sources can be easily integrated by linking them to the NDT construction ontology and are directly available for generic use in the sense of digitization. Based on an extensive literature research, we outline the possibilities that this offers for NDT in civil engineering, such as computer-aided sorting, analysis, recognition and explanation of relationships (explainable AI) for several million measurement data.
The expected benefits of this approach of knowledge representation and data access for the NDT community are an expansion of knowledge through data exchange in research (interoperability), the scientific exploitation of large existing data sources with data-based methods (such as image recognition, measurement uncertainty calculations, factor analysis, material characterization) and finally a simplified exchange of NDT data with engineering models and thus with the construction industry.
Ontologies are already the core of numerous intelligent systems such as building information modeling or research databases. This contribution gives an overview of the range of tools we are currently creating to communicate with them.
Creep and fracture behavior of conventionally and additively manufactured stainless steel 316L
(2020)
A critical task within the frame of establishing process-structure-property-performance relationships in additive manufacturing (AM) of metals is producing reliable and well-documented material behavior’s data and knowledge regarding the structure-property correlation, including the role of defects. After all, it represents the basis for developing more targeted process optimizations and more reliable predictions of performance in the future. Within this context, this contribution aims to close the actual gap of limited historical data and knowledge concerning the creep behavior of the widely used austenitic stainless steel 316L, manufactured by Laser-Powder-Bed-Fusion (L-PBF). To address this objective, specimens from conventional hot-rolled and AM material were tested under application-relevant conditions according to existing standards for conventional material, and microstructurally characterized before and after failure. The test specimens were machined from single blocks from the AM material. The blocks were manufactured using a standard scan and build-up strategy and were subsequently heat-treated. The creep behavior is described and comparatively assessed based on the creep lifetime and selected creep curves and characteristic values. The effect of defects and microstructure on the material’s behavior is analyzed based on destructive and non-destructive evaluations on selected specimens. The AM material shows shorter creep lives, reaches the secondary creep stage much faster and at a lower strain, and features lower creep ductility compared to its conventional counterpart. The creep damage behavior of the AM material is more microstructure than defect controlled and is characterized by the formation and accumulation of single intergranular damage along the whole volume. Critical features identified are the grain morphology and the grain-boundary as well as the dislocation’s density. Micro-computed tomography (µCT) proves to be an alternative to metallography to analyze the creep damage.
The shape of the parts, created by the technology of laser metal deposition (LMD), is influenced by various parameters, for example, the power and diameter of the laser source spot. The contribution of energy from the laser affects the temperature distribution in the formed layers. The changing temperature in the working area entails a change in the geometry of the layers and affects the stability of the process. In this paper, experiments on the measurement of temperature cycles in the DLMD process with different directions of the filling track are carried out. An infrared camera was used to measure thermal cycles. The calibration of the acquired data (i.e. correspondence table between the intensity of thermal radiation of the material and the absolute temperature) was done with help of two-color pyrometer ex situ and in situ measurements. The experiments are carried out on two materials 316L and Inconel 718. The effect of the maximum temperature on the layer height is shown, and thermal cycles in the formation of layers for different filling strategies are presented.
Hersteller von Geräten für den bestimmungsgemäßen Gebrauch in explosionsfähigen Bereichen müssen, wenn sie unter die Richtlinie 2014/34/EU fallen, für das Inverkehrbringen in EU-Mitgliedsstaaten eine Konformitätsbewertung durchführen. Dazu gehört eine Zündgefahrenbewertung, bei der auch nichtelektrische Zündquellen betrachtet werden müssen, zu denen die mechanischen Schlagvorgänge gehören.
Bei dieser Zündquellenart kommt es infolge eines Schlages und/oder Reibens eines Bauteils auf ein anderes zu einer Energieumwandlung. Dadurch kommt es zu einer Temperaturerhöhung an der Kontaktstelle sowie unter Umständen zu einem Abtrennvorgang kleiner Partikel erhöhter Temperatur. Sowohl die heißen Reibflächen als auch die abgetrennten Partikel stellen potentielle Zündquellen explosionsfähiger Atmosphären dar.
Edelstahl ist für Geräte für die Verwendung zum bestimmungsgemäßen Gebrauch im explosionsgefährdeten Bereich insbesondere in der Chemie ein wichtiger Konstruktionswerkstoff. Die Ergebnisse des Forschungsprojektes "Entwicklung normativer Anforderungen an explosionsgeschützte nichtelektrische Geräte resultierend aus der Zündfähigkeit mechanisch erzeugter Schlagfunken (NAMES)" zeigen, dass Schlagvorgänge mit Edelstählen eine erhebliche Zündgefahr von explosionsfähigen Brenngasgemischen darstellen können. Dabei bestehen jedoch mitunter deutliche Unterschiede zwischen den verschiedenen Brenngasgemischen. Besonders hohe Zündwahrscheinlichkeiten konnten bei Brenngasgemischen mit Brenngasen der IEC-Explosionsgruppe IIC beobachtet werden, die Acetylen bzw. Wasserstoff als Brenngas enthielten. Schläge im Wasserstoff/Luft-Gemisch waren dabei jedoch bedeutend zündwirksamer. In diesem Gasgemisch konnte bei niedrigen maximalen Schlagenergien bis 60 J sogar eine mitunter höhere relative Zündhäufigkeit beobachtet werden als bei Versuchen mit unlegiertem Baustahl.
Im Vortrag wird ein Messfiltertiegel als Zusatztool für die TED-GC/MS vorgestellt, welcher für die Probenaufbereitung von kleinen Partikelfrachten oder kleinen Partikelgrößen genutzt werden kann. Er ist Filtereinheit und Messtiegel in einem, wodurch Verluste bei der Überführung der Probe in das Messgefäß sowie Kontaminationen vermindert werden. Das beispiel ist hier die Filtration von Flaschenwasser mit anschließender Detektion mit der TED-GC/MS.
Mit Hilfe des HIP-Verfahrens („Hot Isostatic Pressing“) werden Poren in der einkristallinen Nickel-Basis Superlegierung CMSX-4 kontinuierlich geschrumpft und dadurch die nach der Erstarrung und der Wärmebehandlung vorhandene Porosität stark reduziert. In diesem Beitrag werden experimentelle und numerische Untersuchungen zu den Mechanismen der Porenschrumpfung zusammengefasst. Es zeigt sich, dass das Verformungsverhalten während Kriechversuchen bei der HIP-Temperatur durch Versetzungsgleitung auf oktaedrischen Ebenen dominiert wird.
Dagegen zeigen Messungen der Porositätsabnahme und Simulationen des Porenschließens, dass die Kinetik der Porenschrumpfung durch das Phänomen der Leerstellendiffusion zwischen Poren und Kleinwinkelkorngrenzen („Low Angle Boundary“, LAB) bestimmt wird. Im Gegensatz führt die klassische Kristallviskoplastizität zu einer systematischen Überschätzung dieser Kinetik. Der scheinbare Widerspruch lässt sich auflösen, wenn man bedenkt, dass auf der Skala der Poren Versetzungsquellen nicht gleichmäßig verteilt sind, wie in der konventionellen Kristallplastizität implizit angenommen wird. Stattdessen wird in einem weiterführenden Modell davon ausgegangen, das Kleinwinkelkorngrenzen (LABs) als Versetzungsquellen fungieren, während die Scherspannungen sehr stark in der Nähe der Poren lokalisiert sind, was die Emission von Versetzungen deutlich reduziert.
A study on building vibrations has been performed by finite element calculations. Family houses, multi-storey residential buildings, office buildings and office towers have been modelled in detail. The frequency-dependent response due to a free-field excitation has been evaluated for walls, columns and floors. The ratio of building amplitudes to free-field amplitudes starts with uB/u0 = 1 at zero frequency and is usually lower than 1 at 50 Hz, the end of the frequency range considered here. In between, amplifications occur due to several reasons. There are „soil resonances“ where the whole building is vibrating on the compliant soil, “column resonances” where the upper storeys are vibrating on the compliant columns, and the “floor resonances” where the floors are vibrating excited by their supports. Results are presented for all building types, but a special focus is set on office buildings. A parameter study shows the influence of the stiffness of the soil, the number of storeys, and the width of the building. It has been found that the “soil resonance” is strongly modified by the low-frequency floor resonances for the normal office building. The main resonance of a twenty-storey office tower is determined equally by the “soil mode” and the “column mode”. It is an important observation for these office buildings that the resonances can differ for different parts of the building such as the centre, the edge, the corner, and the core of the building. This leads to non-uniform vibration modes across the building, which look like another type of “floor resonance” and which have been observed in several real building projects. Experimental results will be shown which can confirm the calculated phenomena.
Der Vortrag berichtet über die Auslagerung von Standardproben nach DIN EN ISO 9223 bis 9226 aus Zink, Stahl, Kupfer und Aluminium auf den verschiedenen atmosphärischen Bewitterungsständen der Bundesanstalt für Materialforschung und -prüfung (BAM). Im Vortrag werden die Masseverluste, Korrosionsgeschwindigkeiten und Korrosivitätskategorien der Standardproben im freibewitterten und überdachten Bereich nach einem Jahr vorgestellt und Unterschiede hinsichtlich der Atmosphärenbedingungen aufgezeigt. Freibewitterte Proben zeigen dabei deutliche Unterschiede hinsichtlich ihres Korrosionsverhaltens im Vergleich zu überdachten Proben. Die ermittelten Korrosivitätskategorien sind sowohl standort- als auch materialspezifisch.
Outcomes of Three Large-Scale Fire Reference Tests Conducted in Propane Gas Fire Test Facility
(2020)
Packages for the transport of high-level radioactive material are designed to withstand severe accidents. Hypothetical severe accident conditions are defined in the IAEA Regulations for the Safe Transport of Radioactive Materials. One of these accident conditions is the thermal test, mainly consisting of a 30 minute fully engulfing 800°C pool fire or an equally severe fire test. The heat fluxes into the package depend substantially on the fire characteristics and the surface temperature of the package. Fire tests can be performed at BAM on a propane gas fire test facility. In order to investigate the heat fluxes over a wide range of surface temperatures in this test facility a fire reference package was designed for multiple use. The package represented the outer geometry of a specific transport cask for radioactive waste. The fire reference package is a closed steel sheet cylinder with a wall thickness of 10 mm, a length of 1500 mm and a diameter of 1050 mm. The package was instrumented with thermocouples and filled with heat resistant insulation material. Three open-air fire tests were performed in the BAM propane gas fire test facility. The flames exposure time period varied slightly for the fire tests. The wind direction as well as the wind speed were measured and changed between and during the tests. Test stand parameters such as wind shield location and propane gas volume flow were chosen constant for the three tests. The locally measured fire reference package steel sheet temperatures were used for the calculation of heat fluxes as function of time and surface temperature. The measured temperatures allowed further calculations. In a first approach effective fire characteristics of the propane gas fire, including the flame temperature, the fire convection coefficient and a radiation exchange coefficient mathematically describing the determined average heat flux over the surface temperature were calculated.
Based on practical examples of analysis with Electron Microscopy and Energy-Dispersive X-ray Spectroscopy, the minimum information requirements for reliable and reproducible nanomaterial characterization data such as particle size and shape distribution and elemental analysis are presented and discussed.
Prediction of dynamic effects of reinforced concrete structures under impact loading is a technical challenge. This is a consequence of the great variability of the physical properties resulting from the wide adaptability of reinforced concrete and a consequence of the wide range of impact loading. Experiments and numerical investigations are normally used on a small scale to address the problem. In this paper, impact tests on reinforced conrete plates with the lateral dimensions of 1.5 m x 1.5 m and a thickness of 30 cm are presented. In bending reinforcement, besides the velocity two properties are varied, the diameter and the spatial distribution of the rebars. Experiments are performed at the Otto-Mohr-Laboratory of the Institute of Concrete Structures of the Technische Universit¨at Dresden. Due to the accelerated fall of the impactor the velocity ranges between 20 and 70 m/s. In addition to the measured quantities such as bearing forces, accelerations are also measured at 4 different positions on and under the plate, as well as the deflection at several positions. The measured data are used for the analysis of the damage form and the numerical examinations with the program Ansys Autodyn and the material model after Drucker-Prager. Numerical investigations support the tests, with detailed analysis of individual effects. These numerical computations and the planar tomographic investigations were carried out at BAM in Berlin. With the help of planar tomographic evaluation, the damaged structure is made visible and compared with the numerical results. Influences of the bending reinforcement are explained on the basis of damage evaluation in the local area and on selected measured values. In addition to the test evaluation, the tomographic and numerical methods are presented.
New developments in legislation and technology development for P-recovery were presented with focus on the situation in Germany.
Für die Bestimmung der Restlebensdauer zyklisch beanspruchter Bauteile kommt dem Schwellenwert für Ermüdungsrissausbreitung ΔKth und dem sich anschließenden Schwellenwertbereich der dadN⁄-ΔK-Kurve große Bedeutung zu. Dem stehen Unsicherheiten bei der Bestimmung und Analyse gegenüber. Der Aufsatz befasst sich mit der Ermittlung des sogenannten intrinsischen Schwellenwerts, der als robuster Eingangsparameter für eine „rissschließfreie“ Analyse der Restlebensdauer von entscheidender Bedeutung ist.