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Eingeladener Vortrag
- nein (443)
Even for the basic measurements of material data for design and engineering of composite structures there is a need to upgrade standards. With a new shear frame test rig more precise values can be obtained.
With advanced methods in the research on the fatigue behaviour of FRP it was found a load level of infinite life for GFRP and CFRP. This is in the range of typical strain values of airliners and rotor blades in normal operation.
Statistically the mean time between damage events on rotor blades is 6 years (Deutscher Windenergie Report 2006). Due to imperfection in the production the shell structures get cracks after a few years fare before the designed life time. A shell test rig was built at BAM for efficient research on the effects of defects in production.
Test blades of ~10m are an efficient way for SHM research and evaluation of NDT-methods and blade geometry.
The Interdisciplinary Alchemist: Reproduction and Study of Black Inks from the Islamicate World
(2019)
The identification of the materials constituting an artefact is the basis of any correct conservation project, for this reason (among others) in the last 50 years analytical techniques have been applied to the study of manuscripts. Unfortunately, the scientific investigation of Arabic books is still uncommon, focusing mainly on single case studies, often producing unclear results, especially for black inks. This lack of knowledge prompted a recent research in which black ink recipes have been collected from written Arabic sources on bookmaking, their feasibility has been assessed, and finally some of them have been reproduced. These samples were artificially aged and analysed through an array of analytical techniques, mostly non-invasive and non-destructive, in order to build a database of Arabic inks and their ingredients and also to verify the detection limits of the portable equipment employed. In this talk I will present some instances of how this approach can help textual criticism, for example in evaluating variants and determining the competence of authors and compilers. At the same time the research highlights how much this scientific work depends on textual studies, especially concerning the identification of ingredients. Moreover, I will focus on some of the problematics I faced both during the textual interpretation and the actual reproduction of the recipes and how they influenced the results of the scientific analyses. In particular I’ll look into the role played by the degree of purity of the components and the function (real and perceived) of some of the ingredients.
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. The components are tested non-destructively in 3D in order to localize and characterize cracks, pores, inclusions as well as other defects and their influence on the functional properties and also “in-time” during the life cycle of the material. Exsitu and in-situ experiments performed with non-destructive XCT are predestinated to follow damaging mechanisms of materials under certain load conditions, atmospheres or liquids, e.g. went through several working cycles of a functional material. By combining microtomography with other methods of magnetic and classical material characterization, unique statements about the structure and the functional properties can be made.
From the applications point of view, sometimes complex, three-dimensional geometries are needed to fully exploit the functional properties of the materials, e.g. to ensure a high surface area for heat exchange. Since many functional materials are brittle and difficult to form, shaping is often a big challenge. In principle, additive manufacturing processes offer the possibility to produce complex, porous components from poorly formable alloys.
If all stages of additive manufacturing are accompanied by X-ray tomographic imaging, the process of finding the optimal parameters for material processing can be significantly accelerated.
Based on the quality control of the initial powder material used and also investigations of the shape and arrangement of defects within the molten structure and their relationship with the melting path scanning strategy, Xray tomography has proven to be an ideal tool for additive manufacturing, even for functional materials. Overall, tomographic methods are important tools for the development of functional materials to application maturity.
The deep penetration laser beam welding (LBW) has developed to one of the most promising metal joining methods in the modern manufacturing industry. It has well-known advantages of good penetration capacity, low heat input, high reachable welding speed and low welding distortion in comparison to conventional arc welding techniques. However, there are still challenges in LBW making the realization of the advantages difficult, such as porosity or inhomogeneous element distribution when using filler material. The magnetohydrodynamics technique is a promising way to solve these issues by introducing a suitable electromagnetic field, and correspondingly Lorentz force, to control the Transport phenomena in the weld pool.
The underlying physics in wire feed laser beam welding with electromagnetic stirring were investigated numerically and experimentally. A three-dimensional transient heat transfer and fluid flow model coupled with dynamic keyhole, magnetic induction and element transport was developed for the first time. The electromagnetic behaviour as well as the temperature and velocity profiles, solidification parameters, keyhole evolution and element transport are calculated.
The model is well tested against the experimental results. The beneficial effects from electromagnetic stirring (element homogenization and grain refinement) are explained quantitatively using the numerical data and the results from high-speed imaging, OM, EDX and EBSD.
In this presentation the main requirements of BAM-GGR 016 regarding maintenance and periodic inspections were explained. BAM ensures during acceptance of the quality management program that specific and relevant instructions for maintenance and periodic inspections are developed and handed to the operator of the packaging. Examples are given.
It was found for inorganic/polymer nanocomposites that a so-called Rigid Amorphous Phase (RAF) is formed in the interfacial region by adsorption of polymer segments onto the nanoparticles. The segmental dynamics of RAF is expected to be altered, as compared to the pure matrix, which might percolate into the entire system, affecting the overall nanocomposite properties. Here, the structure and molecular mobility of epoxy-based PNCs with different nanofillers (layered double hydroxide and boehmite) was studied by a combination of calorimetric and X-Ray scattering techniques. Temperature modulated DSC (TMDSC) showed that depending on the nanofiller, RAF can reach up to 40 wt % of the system or, on the contrary, the overall mobility of the matrix might increase due to the presence of particles. Such contrasting results, including the high amount of RAF, which was never shown before for epoxy-based PNCs, emphasize the importance of interfaces. Additionally, glass transition and glassy dynamics were investigated by a novel technique, Flash DSC (heating rates up to 10 kK/s) employed for the first time to a thermosetting system and electrospun fibers, which did not result in their degradation. It was used to study both the vitrification kinetics and glassy dynamics of the PNCs, for instance further confirming the presence of RAF and its impact on the overall material properties.
Tuff ist in vielen historischen Objekten in Deutschland verbaut, hat aber wegen seiner Porosität und hygrischen Eigenschaften eine schlechte Verwitterungsresistenz. Ziel des Vorhabens ist die Entwicklung eines gesteinsmehlmodifizierten Schutzsystems auf Kieselsäurebasis (GEMOSK) zur Konservierung verbauter Tuffe. Für die Schutzmittelherstellung wird eine geeignete Mischung aus Kieselsol und feinen Gesteinsmehlen aus Steinbruchrückständen und Tuffabfällen verwendet. Bei erfolgreichem Abschluss des Projektes kann GEMOSK im Denkmalpflegebereich eingesetzt werden. Dadurch werden die Bausubstanz besser erhalten, Tuffsteinressourcen eingespart und Tuffabfälle wiederverwertet.
Das Fügeverfahren Kleben bietet viele Vorteile, wie z.B. das Verbinden unterschiedlicher Materialklassen, geringe thermische Belastung (und damit ggf. verbundene Strukturveränderung/-schwächung) der Fügeteile und eine Lastverteilung über den gesamten Fügebereich. Die Auswahl an verfügbaren Klebstoffen und Vorbehandlungsoptionen sind dabei - wie die Applikationen auch - vielfältig. Es werden vier Applikationsbeispiele zu Referenzklebverbunden aus Edelstahl, zur Plasmaaktivierung von Niedrigenergie-Polymeren, zur Bestimmung der Haftfestigkeit von Lackierungen auf GFK und zur Wirkung von Primern vorgestellt. Einige Polymere weisen z.B. Eigenschaften auf, die eine Herstellung von festen und dauerhaft beanspruchbaren Kleb-verbindungen erschweren. Im Allgemeinen geht dies mit geringen Oberflächenenergien einher. Mittels Oberflächenvorbehandlung, z.B. durch Plasmafeinreinigung bzw. Plasmaaktivierung, können die Grenzflächen solcher Polymere - bezogen auf die Eignung als Fügeteile (Klebfestigkeit) oder als Substrat (Haftfestigkeit) – optimiert bzw. die Oberflächenenergie erhöht werden. Schnelle, zuverlässige und statistisch abgesicherte Prüfverfahren zur Ermittlung von Verbund-eigenschaften sind dabei unverzichtbar.
Challenges in Traceable Size Measurement of Non-Spherical, Non-Monodisperse Nanoparticles - nPSize
(2019)
Size measurement of nanoparticles (NP) becomes a challenging analytical problem when non-spherical shapes must be traceably measured. However, most industrial NPs have irregular shapes and broad size distribution making it often more complex to follow European regulatory to identify a material as a nanomaterial according to which accurate measurement of the smallest dimension and its size Distribution is necessary.
The European research project nPSize - Improved traceability chain of nanoparticle size measurements aims to fill this gap by developing potential non-spherical reference nanoparticles, measurement procedures and physical modelling to improve the traceability chain, comparability and compatibility for NP size measurements between different methods. Therefore, new model NP with well-controlled shape has been synthesized and are supposed to be systematically characterized using the traceable methods scanning/transmission electron microscopy, atomic force microscopy and small angle X-ray scattering.
Following NP candidates are under investigation with respect to their homogeneity and stability: (i) titania nanoplatelets (10-15 nm thickness x 50-100 nm lateral), (ii) titania bipyramides (~60 nm length x 40 nm width), (iii) titania acicular particles (100 nm length x 15-20 nm width; aspect ratio 5.5/6), (iv) gold nanorods (~10 nm width x 30 nm length), and (v) gold nanocubes (~55 nm x 55 nm x 55 nm). In addition, sample preparation procedures as well as measurement analysis procedures with evaluation of appropriate measurands and descriptors for each material class and method are being developed to support standardization. To underpin the traceability of the size measurement of nonspherical NP, physical modelling of the signals in e.g. electron microscopy techniques will be used and in combination, the implementation of machine learning is aimed to facilitate measurement Analysis procedures, especially regarding the accurate thresholding/segmentation of the NPs.zeige mehr
Die Präsentation gibt einen Überblick bezüglich der von der BAM im Rahmen des SimCoLas Verbundprojekts durchgeführten Arbeiten zum Thema "Photonische Prozessketten". Die numerisch abgebildete Prozesskette Tiefziehen/Laserstrahlschweißen wird darsgestellt und diskutiert. Fokus der Diskussion ist die entwickelte Methodik zur konsistenten Abbildung numerischer Prozessketten mit der Applikation Heissrisskritikalität beim Laserstrahlschweißen.
Der Vortrag gibt einen Überblick über Arbeiten im Rahmen der Themenstellung "photonische Prozessketten" des SimCoLas Projekts. Es werden Ergebnisse zur Datendurchgängigkeit der Prozesskette Umformen/Laserstrahlschweißen sowie erste Ergebnisse zu numerischen Schweißstruktursimulationen zur Bewertung der Heissrisskritikalität eines tiefgezogenen Napfes beim Laserstrahlschweißen gegeben.
Laser beam welding of aluminum die casting is challenging. A large quantity of gases (in particular hydrogen) is absorbed by aluminum during the die-cast manufacturing process and is contained in the base material in solved or bound form. After re-melting by the laser, the gases are released and are present in the melt as pores. Many of these metallurgic pores remain in the weld seam as a result of the high solidification velocities. The natural (Archimedean) buoyancy is not sufficient to remove the pores from the weld pool leading to process instabilities and poor mechanical properties of the weld. Therefore, an electromagnetic (EM) system is used to apply an additional buoyancy component to the pores. The physical mechanism is based on the generation of Lorentz forces, whereby an electromagnetic pressure is introduced into the weld pool. The EM system exploits the difference in electrical conductivity between poorly conducting pores (inclusions) and the comparatively better conducting aluminum melt to increase the resulting buoyancy velocity of the pores. Within the present study, the electromagnetic supported degassing is investigated in dependence on the laser beam power, welding velocity and electromagnetic flux density. By means of a design of experiments a systematic variation of these parameters is carried out for partial penetration laser beam welding of 6 mm thick sheets of wrought aluminum alloy AlMg3 and die-cast aluminum alloy AlSi12(Fe) where the wrought alloy serves as a reference. The proportion of pores in the weld seams is determined using X-ray images, computed tomography (CT-) images and cross-section images. The results prove a significant reduction of the porosity up to 70 % for both materials as a function of the magnetic flux density
Diffraction-based experimental determination of Residual Stress in AM parts: A critical discussion
(2019)
Additive manufacturing (AM) technologies have experienced an exceedingly rapid growth, not always paralleled by the knowledge about the materials properties and performance. In particular, residual stress (RS) has been soon recognized as an issue in AM parts, so that parts are always post-heat-treated. Moreover, much effort has been spent on simulating RS, especially using finite element methods.
The experimental determination of RS has thereby become increasingly important, and even simple data constitute (to date) a piece of knowledge to fill the above-mentioned gap. In particular, diffraction methods, which are basically non-destructive, offer enormous possibilities to gain knowledge on real components, since neutrons and synchrotron radiation can penetrate even heavy metals up to several millimeters (or even centimeters). Indeed, some success has been obtained, and the knowledge about the origins of the RS fields, as well as their variation as a consequence of heat or mechanical treatments, has been greatly expanded.
In this talk, a few success stories will be outlined. It will be shown how the determination of RS in metallic parts (with focus on those produced by laser powder bed fusion) has even allowed showing that process parameters that were considered unimportant play a major role in the onset of stress.
However, while RS is starting to be considered in the part design, deposition strategy (e.g. build plate temperature), and even in the definition of the relevant metric to assess the quality of a part, much is still to be investigated about the hypotheses underlying its experimental determination. Therefore, some aspects to be aware of, or even to date unclear will also be discussed, such as the determination of the reference unstrained samples and of the principal axes of stress. All these aspects will draw the path towards a comprehensive understanding of the process-structure-performance relationships in AM materials and parts.
Die zunehmenden Nachweise von Kunststoffen in verschiedenen Umweltmedien erfahren in den letzten Jahren weltweit ein zunehmendes wissenschaftliches, gesellschaftliches und politisches Interesse. Besondere Aufmerksamkeit erfahren Kunststoffpartikel von 1-1.000 µm sogenanntes Mikroplastik. Es wurde mittlerweile in Wasser, Böden, Luft und Biota nachgewiesen. Obwohl die Wirkungen auf die natürlichen Umweltfunktionen noch unklar sind und kontrovers diskutiert werden, ist allein durch die ubiquitäre Präsenz eine systematische Erfassung von Eintragsquellen und Verbleib der Partikel über alle Umweltmedien notwendig, um Maßnahmen zur Reduktion der Einträge zu veranlassen.
Für eine zuverlässige Erfassung sind medienübergreifende Verfahren zu entwickeln, welche die drei analytischen Schritte, Probennahme, Probenaufbereitung und Detektion beinhalten. Die Verfahren adressieren unterschiedliche Zielgruppen, welche verschiedene analytische Informationen fordern. Für die akademische Bewertung werden Verfahren mit hohem analytischen Aufwand favorisiert, welche möglichst detaillierte Information über Partikelsorte, -größe, -zahl und -oberflächenbeschaffenheit geben. Im Gegensatz dazu, fordern Anwender aus der Praxis schnelle und einfache Monitoring Verfahren, welche die Bestimmung eines Massengehaltes, bzw. eines Grenzwertes zulassen. Allen ist gemeinsam, dass ein hoher interdisziplinärer Anspruch besteht, der sowohl technische Voraussetzungen zur repräsentativen Probennahme und die Limitationen von Detektionsverfahren berücksichtigt, als auch die Fachkompetenz von Biologen, Umweltwissenschaften, Analytiker und Polymerwissenschaftler einschließt.
Verfahren zum Mikroplastiknachweis müssen auch verschieden Proben mit sehr unterschiedlichen Gehalten an natürlicher Matrix gerecht werden. So müssen allein für Wasser Verfahren entwickelt werden, die Mikroplastik verschiedener Form (sphärische Partikel, komplexe Bruchstücke, Fasern) aus Medien mit sehr variablen Partikelanteil (u.a. Trinkwasser, Oberflächenwasser, Abwasser) repräsentativ erfassen sowie schnell und kostengünstig sind – einschließlich der notwendigen Probenaufbereitung. Die jeweiligen Detektionsverfahren müssen z.B. einzelne Partikel oder integrale Gehalte über drei Dekadenklassen für thermoplastische und insbesondere auch elastomere Partikelsorten erfassen können.
Im Vortrag werden Ergebnisse eines Forschungsvorhabens des DVS vorgestellt, in dem ein Verfahren zur Vermeidung von Schweißimperfektionen im Überlappbereich einer laserstrahlhybridgeschweißten Rundnaht entwickelt wird. Die Strategie der Prozessführung beim Schließen der Rundnaht sieht hervor, dass ein fehlerfreier Überlappbereich durch die Kontrolle der Erstarrungsbedingungen am Schweißnahtende erreicht wird. Die kontrollierte Wärmeführung wird durch eine Anpassung der Parameter von beiden beteiligten Schweißprozessen, dem Laserstrahl- sowie MSG-Schweißprozess realisiert. Es konnte gezeigt werden, dass eine Defokussierung des Laserstrahls von bis zu 40 mm über den Weg von max. 15 mm während der Bewegung des Schweißkopfes zu einer deutlich besseren Nahtausbildung im Überlappbereich führt. Es konnte eine günstige kelchförmige Schweißnahtform ohne eine Tendenz zur Rissbildung erzielt werden.
Extensometer sind seit Jahrzehnten im Einsatz und bilden die Basis für eine präzise Dehnungsmessung in werkstoffmechanischen Versuchen. Jedoch ist die Temperaturstabilität von Extensometern häufig noch nicht ausreichend beachtet worden, um Fehler verursacht durch Temperaturschwankungen zu minimieren. Dieses wird derzeit nicht nur in Deutschland, sondern auch international zunehmend diskutiert. Datenblätter von Extensometern sind teils unvollständig besonders hinsichtlich von Temperatureinflüssen. Extensometer für den Einsatz bei höheren Temperaturen sollen z.B. laut Normen für dehnungsgeregelte Ermüdungsversuche mit Luft oder Wasser aktiv gekühlt werden. Jedoch schreiben die Normen keine Temperatur-Toleranzen für Extensometer vor. Dehnungsfehler verursacht durch Temperaturschwankungen am Extensometer bleiben meist verborgen, da die Temperatur des Extensometers standardmäßig gar nicht gemessen wird. Die Ursache von Einflüssen zur Temperaturstabilität von Extensometern wird erläutert. Ein einfaches Rechenbeispiel zeigt die Empfindlichkeit von Extensometern gegenüber Temperaturschwankungen und die Auswirkungen auf den Dehnungsfehler. Lösungsmöglichkeiten zur Optimierung werden aufgezeigt. Der Anwender von Extensometern soll sensibilisiert werden, um der Temperaturstabilität von Extensometern sowohl hinsichtlich Herstellerspezifikationen als auch bei der Anwendung von Extensometern im Prüflabor mehr Aufmerksamkeit zu schenken, um letztlich die Qualität von Versuchsergebnissen zu verbessern. Empfehlungen an Extensometerhersteller werden formuliert. Dieses Thema wird zukünftig auch in Prüfnormen mehr Aufmerksamkeit geschenkt werden. Es werden Maßnahmen zur Verbesserung der Temperaturstabilität von Extensometern Einzug in Prüfnomen finden, um letztlich verlässlichere Versuchsergebnisse zu erhalten. Es ist beabsichtigt, eine Verbesserung der Temperaturstabilität von Extensometern z.B. bei der nächsten Revision der Prüfnormen ISO 12106 und ISO 12111 für dehnungsgeregelte LCF- und TMF-Versuche zu berücksichtigen.
Localized laser surface treatments are able to produce tailor-made surface properties to fulfill requirements of a variety of technical applications. Especially micrometric surface topologies can be beneficial for optimizing tribological contact situations. Structures with lowered surface features are already utilized for bearings or cylinders of combustion engines. There are also other fields of application, where the potential of protruding surface features is known, e. g. for metal forming tools.
A promising approach for a tailored surface treatment working in the microsecond range is the localized dispersing of hard ceramic particles by pulsed laser radiation, the so-called laser implantation. This technique is able to produce micrometric surface structures and to improve simultaneously the wear resistance by creating metal matrix composites.
In this talk, the laser implantation technique is described and compared to the state of the art. The potential to adjust the geometry as well as the mechanical properties of laser implanted surfaces is demonstrated by means of microstructural and topographical investigations of different ceramic materials and steel substrates. Finally, results of research projects are presented aiming on the application of such structured surfaces. Their capability to change and optimize friction and wear are demonstrated for fully lubricated contacts, tools for hot sheet metal forming and tools for cold rolling of sheets for automotive applications.
Das Prozessmonitoring stellt einen wichtigen Baustein für eine Qualitätssicherung additiv gefertigter Bauteile dar, insbesondere bei kleinen Losgrößen. Der Vortrag zeigt einen Überblick aktueller Entwicklungen der BAM im Bereich des Prozessmonitorings für das Laserstrahlschmelzen (laser powder bed fusion) metallischer Werkstoffe. Durch Vergleich mit der Referenzmethode Computertomografie wird am Beispiel der thermografischen Verfahren gezeigt, wie relevante Defekte in Bauteilen detektiert werden können und Einsatzpotenziale sowie Limitierungen aufgezeigt.
Polymers of intrinsic microporosity (PIMs) have recently emerged as novel materials for a broad range of high-performance applications from gas separation to electronic devices. The very rigid, contorted polymer chains show only limited molecular mobility and therefore pack inefficiently giving rise to intrinsic microporosity with pore sizes generally smaller than 1 nm resulting in BET surface areas larger than 700 m2/g. Using conventional thermal analysis techniques, no glass transition temperature (Tg) of PIMs could be unambiguously detected up to now. Employing fast scanning calorimetry (FSC) based on a one chip sensor, decoupling the time scales responsible for the glass transition and the thermal decomposition is a reliable strategy to overcome this limitation. The FSC device is capable to heat and cool a small sample (ng-range) with ultrafast rates of several ten thousand K/s. Evidence of a glass transition is obtained for a series of PIMs with different chain rigidities. Local small-scale fluctuations are held responsible for the glass transition of highly rigid PIMs rather than segmental motions as in conventional polymers.
In diesem Verbundvorhaben werden standardisierte Messverfahren für hybride Gemische erarbeitet, die der Bestimmung sicherheitstechnischer Kenngrößen des Explosionsschutzes dienen. Unter einem hybriden Gemisch wird dabei ein mehrphasiges System aus Brenngas oder brennbarem Dampf, sowie Luft und brennbarem Staub verstanden. Die Veröffentlichung der Ergebnisse erfolgt in einem Abschlussbericht und als DIN-Spezifikation (DIN SPEC). Diese DIN SPEC versetzt Prüfinstitute und Industrie in die Lage, Explosionsgefahren beim Betrieb technischer Anlagen mit hybriden Gemischen einzuschätzen und damit Prozesse sowohl sicherer als auch effizienter zu steuern. Dieses Projekt wird im Rahmen des WIPANOProgramms (Wissens- und Technologietransfer durch Patente und Normen) vom BMWi gefördert.
Demonstrationsexperimente
(2019)
Korrosionsprüfung
(2019)
The combination of tomographic, microstructural data with other experimental techniques and with modeling is paramount, if we want to extract the maximum amount of information on material and component properties. In particular, quantitative image analysis, statistical approaches, direct discretization of tomographic reconstructions represent concrete possibilities to extend the power of the tomographic 3D representation to insights into the material and component performance. This logic thread equally holds for industrial and academic research and valorizes expensive experiments such as those carried out at synchrotron sources, which cannot be daily repeated.
I will show a few examples of possible use of X-ray tomographic data for quantitative assessment of damage evolution and microstructural properties, as well as for non-destructive testing. Examples of micro-structured inhomogeneous materials will be given, such as Composites, Ceramics, Concrete, and Additively manufactured parts. I will also show how X-ray refraction computed tomography (CT) can be highly complementary to classic absorption CT, being sensitive to internal interfaces.
Additionally, I will show how Neutron Diffraction, which is extremely well suited to the study of internal stresses, both residual and under external load, can well be coupled to the microstructural framework gained by CT, allowing understanding the microstructure-property relationships in materials.
Finally, I will show that BAM is very active in standardization and certification, including production of Reference Materials and Methods.
The combination of tomographic, microstructural data with other experimental techniques and with modeling is paramount, if we want to extract the maximum amount of information on material and component properties. In particular, quantitative image analysis, statistical approaches, direct discretization of tomographic reconstructions represent concrete possibilities to extend the power of the tomographic 3D representation to insights into the material and component performance. This logic thread equally holds for industrial and academic research and valorizes expensive experiments such as those carried out at synchrotron sources, which cannot be daily repeated.
I will show a few examples of possible use of X-ray tomographic data for quantitative assessment of damage evolution and microstructural properties, as well as for non-destructive testing. Examples of micro-structured inhomogeneous materials will be given, such as Composites, Ceramics, Concrete, and Additively manufactured parts. I will also show how X-ray refraction computed tomography (CT) can be highly complementary to classic absorption CT, being sensitive to internal interfaces.
Additionally, I will show how Neutron Diffraction, which is extremely well suited to the study of internal stresses, both residual and under external load, can well be coupled to the microstructural framework gained by CT, allowing understanding the microstructure-property relationships in materials.
Es besteht die grundsätzliche Anforderung, dass alle nichtmetallischen und metallischen Materialien nur dann in Sauerstoffanwendungen eingesetzt werden dürfen, wenn sie sicherheitstechnisch auch für die entsprechenden Betriebsbedingungen geeignet sind. Der Vortrag stellt nicht nur die gängigen Prüfverfahren und Beurteilungskriterien. Es werden auch die folgenden Fragen beantwortet, die häufig von Wirtschaftsunternehmen und Verbänden gestellt werden:
- Welchen praktischen Anwendungsfall bilden die Prüfungen ab?
- Welche Untersuchungsmethoden führt die BAM durch?
- Warum verwendet die BAM ergänzende Beurteilungskriterien bei der sicherheitstechnischen Interpretation von Prüfergebnissen?
- Warum empfiehlt die BAM chargenbezogene Materialprüfungen?
- Worin unterscheiden sich die zwei von der BAM verwendeten Methoden zur Beurteilung der Ausbrennsicherheit von Armaturen und Anlagenteilen und welche Vor- und Nachteile bietet jede dieser Methoden?
Grundsätzlich dürfen alle nichtmetallischen und metallischen Materialien nur dann in Sauerstoffanwendungen eingesetzt werden, wenn sie sicherheitstechnisch für die Betriebsbedingungen geeignet sind. Neben allgemeinen Sauerstoff-spezifischen Anforderungen stellt der Vortrag die standardisierten Prüfverfahren und die Untersuchungsmöglichkeiten der BAM vor. Die Beurteilungskriterien für die Prüfverfahren werden kritisch betrachtet und es wird erklärt, in welchen Fällen und aus welchen Gründen die BAM ergänzende Beurteilungskriterien verwendet. Um den tatsächlichen, praktischen Anwendungsfall abzubilden, ist unter gewissen Umständen die Anpassung des Prüfumfangs möglich. Außerdem wird dargestellt, warum die BAM chargenbezogene Materialprüfungen empfiehlt.
Auch Sauerstoff- Armaturen und Anlagenteile müssen sicherheitstechnisch für die Betriebsbedingungen geeignet sein. Zur Beurteilung der Ausbrennsicherheit werden die zwei an der BAM praktizierten Vorgehensweisen mit ihren jeweiligen Vor- und Nachteilen vorgestellt: Untersuchung der Armatur als komplette Funktionseinheit bzw. Beurteilung der Armatur auf Basis der Untersuchungen der eingesetzten Materialien. Neben den Anforderungen aus produktspezifischen Normen wird auch für diesen Fall kurz erklärt, in welchen Fällen und aus welchen Gründen die BAM ergänzende Beurteilungskriterien verwendet bzw. den Prüfumfang anwendungsfallbezogen anpasst.
Force-distance curves have been recorded on thin films of lubricants. The lubricants wet the AFM tip, which causes a capillary force. This force depends on the shape of the tip, as well as on physical properties like viscosity and surface tension, which have been determined additionally with other methods. This way, their influence on the shape of the curves could be analyzed.
At BAM, which is a federal institute for materials research and testing in Germany, it is one of our tasks to evaluate the safety of casks designed for transport and/or storage of radioactive material. This includes assessment of elastomeric seals applied in the casks. One of the aims is to identify a suitable method for estimating the service lifetime of the seals with regard to the requirements for long-term safety (40 years and more) of the containers. Therefore, we started an accelerated ageing programme with selected rubbers often used for seals (HNBR, EPDM and FKM) which are aged at four different temperatures (75 °C, 100 °C, 125 °C and 150 °C) for up to five years. In order to assess sealability, O-rings were aged in compression by 25 % (corresponding to the compression during service) between plates as well as in flanges that allow leakage rate measurements. For comparison, uncompressed O-rings were aged as well. In order to understand the underlying ageing mechanisms in each material, material properties such as hardness, density and tensile properties were examined. Additionally, compression set (CS), which represents the recovery behaviour of a seal after release from compression, is measured. For obtaining results closely related to practical conditions, O-rings with a full-scale cord diameter of 10 mm were aged. However, this set-up can lead to heterogeneous ageing caused by diffusion-limited oxidation (DLO) effects especially for HNBR, resulting in distorted bulk properties such as compression set. However, if DLO-affected data is excluded, extrapolations of CS data are possible using time-temperature shifts.
For selecting an appropriate end-of-lifetime criterion, leakage rate measurements were performed, since leakage rate is the only characteristic directly correlated to the performance of the sealing system. A significant increase in leakage rate was considered as the end of the lifetime. However, the O-rings remained leak tight under static conditions even though material properties had already degraded strongly. For this reason, a modified, more demanding leakage test involving a fast small decompression of the seal was developed that allowed determining a more conservative end-of-lifetime criterion with a safety margin for EPDM seals. FKM, which is a very heat and oxidation resistant material, exhibited only little degradation, even though it had the smallest activation energy.
At the Stakeholder meeting of the EMPIR project “Multifunctional ultrafast microprobes for on-the-machine measurements”, details about two measurement modes were presented. Force distance curves and contact resonance measurements are compared. The basic principles are explained and exemplary measurements concerning mechanical properties of polymers are shown.
High heat input leads to grain coarsening and softening in WM and HAZ; the tensile strength is reduced. Low heat input leads to inadmissible hardening in the WM; the impact strength is reduced.
The proposed t8/5-time of 3 s to 15 s could be achieved through the reduced welding velocity.
The concept of electromagnetic weld pool support system allowed single-pass welds in flat position without gravity drop-outs even for reduced welding speeds; in this way the heat input can be controlled.
The adaptation of the electromagnetic weld pool support system to laser and laser hybrid welding process can dramatically increase the potential field of application of these technologies for real industrial implementation.
Schwerpunkte:
Strategie zur Vermeidung von Schweißimperfektionen im Überlappbereich beilaserhybridgeschweißten Rundnähten für 9.5 mm dicke Rohre.
Anpassung der Laserleistung in Kombination mit der Defokussierung des
Laserstrahls sowie einer Endkraterfüllung am Ende der Schweißnaht führte zu einer besseren Nahtausbildung.
Herausrampung der Energie des Schweißprozesses, sodass ein Übergang von Durchschweißung zu einer Einschweißung mit gewünschter kelchförmiger Nahtgeometrie stattfand.
Einstellung eines Wärmestaus durch Defokussierung und Verschiebung des
Laserstrahls führt zu einem gut ausgebildeten Überlappbereich ohne Poren, Risse.
Schweißungen an Rohrabschnitten mit einer max. Wandstärke von 15 mm, bei gegebenenfalls weiteren Parameteranpassungen.
Microstructure ageing of stainless steel AISI 316L manufactured by selective laser melting (SLM)
(2019)
Additive manufacturing (AM) processes, such as SLM, offer a variety of advantages compared to conventional manufacturing. Today AM parts are still comparatively less cost-effective if they are manufactured in large quantities. To make the AM parts more cost-efficient, the AM process has to be improved. It requires a good understanding of microstructure formation, microstructure-property-relations and ageing processes affected by different loads.
In this work the ageing behavior of SLM manufactured AISI 316L stainless steel is evaluated. The microstructure effected by mechanical, thermal and corrosive loads are investigated and compared to as-built microstructure. Tensile tests are used for mechanical ageing. For thermal and corrosive loads the typical application conditions of 316L apply. The methods of microstructure investigation include SEM, TEM, CT and EBSD. The main object of this work is the description of microstructure and ageing processes of AM parts.
Additive manufacturing (AM) offers diverse advantages compared to conventional manufacturing. In this work the microstructure of austenitic steel 316L, manufactured with Selective Laser Melting (SLM), was analyzed and compared to microstructure of 316L hot rolled material. Methods used for analysis are microprobe, optical microscopy and electron backscatter diffraction.
The distributed measurement of relative humidity is a sought-after capability for a wide range of applications in civil engineering and structural health monitoring. We show that polymethyl methacrylate (PMMA) optical fi-bers can be employed as a sensor medium to conduct distributed humidity measurement by analyzing Rayleigh backscattering traces obtained by OTDR. We make use of the effect that water penetrates the fiber core and directly influences the local fiber attenuation and Rayleigh backscatter coefficient. We conducted distributed backscattering analysis for two different pulse wavelengths: 500 nm and 650 nm. The 650 nm results are susceptible to both, attenuation changes and backscatter changes, whereas backscatter results at 500 nm are not affected by humidity-induced attenuation and only exhibit a change of Rayleigh backscattered power as a function of humidity. The combined measurement and analysis of both parameters at these two wavelengths has the advantage that cross-sensitivities on backscatter change and attenuation, such as strain and tempera-ture changes, could be separated from the humidity response of the fiber. We present laboratory results for a humidity range between 30% and 90% for both pulse wavelengths: including step responses, humidity cycles and hysteresis analysis. In addition to the attenuation and backscatter coefficient dependence, we also analyze optical runtime changes as a function of humidity. POFs have the advantage that they can be directly embed-ded into materials such as concrete or soil to measure water content or localize water ingress. Standard step-index PMMA POFs can be used as a distributed relative humidity sensor up to 200 m distance.
Composite pressure vessels for transporting dangerous goods and for hydrogen and natural gas vehicles consist of a load-bearing composite and a gas-tight, metallic or polymeric barrier layer (liner). To investigate the aging behavior of such composite pressure vessels, BAM carried out the interdisciplinary project COD-AGE. The aim of the project was the development of methods and models for the description and determination of the aging behavior of carbon fiber composites using the example of pressure vessels in order to better predict aging and safe working life. One focus of this project was the provision of suitable NDT methods. These included both test-related tests and the possible development of test equipment for later practical use.
In the lecture, test results of the age-related eddy current test on composite pressure vessels are presented.
In aging tests, pressure vessels made of an approximately 4 mm thick aluminum liner and approx. 8 mm thick CFRP layer were examined. Typical application of such pressure vessels are respiratory protective devices of the fire department. The pressure vessels were tested using conventional eddy current technology from the outer and inner side as well as with high-frequency eddy current technology. Both damage to the metallic liner and structures of the CFRP could be detected. A particular mechanical challenge was the inspection of the inside of the liners, since a cylindrical surface with an inside diameter of 150 mm has to be tested with an access of only 15 mm diameter.