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Eingeladener Vortrag
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Für die Berücksichtigung mechanischer Belastungen unterhalb der Streckgrenze ist im Rahmen einer zuverlässigen Bauteilauslegung die Kenntnis der elastischen Konstanten von besonderer Bedeutung. Für die experimentelle Bestimmung des Elastizitätsmoduls wurde eine Vielzahl von Verfahren entwickelt, die zum Teil werkstoffspezifisch Eingang in die Normung gefunden haben. Prinzipiell können diese Verfahren in zwei Gruppen unterteilt werden; die statischen und die dynamischen Prüfverfahren. Die statischen Verfahren beruhen auf der direkten Messung des Spannungs-Dehnungs-Zusammenhangs während einer mechanischen Belastung im elastischen Verformungsbereich (Zug, Biegung, Druck). Die dynamischen Verfahren basieren auf der Schwingungsanregung eines Prüfkörpers und der Analyse der resultierenden Schwingungen (Resonanzmethode oder Impulsanregungsmethode) oder auf der Messung der Ultraschallausbreitungsgeschwindigkeit. Stellvertretend für die dynamischen Verfahren wird im ersten Teil dieses Beitrages die Resonanzmethode vorgestellt. Der zweite Teil dieses Beitrages fasst die werkstoffabhängigen Ergebnisse der E-Modulbestimmung mit statischen Verfahren im Zug- und Biegeversuch zusammen.
Study of elastic properties of aero-engine metallic materials is of paramount importance because it forms one of the foundations of engineering design of components. Nine isotropic aero-engine metallic materials were studied for their elastic properties for a temperature range varying from ambient to operating limit. Test was carried out in vacuum to prevent oxidation of specimens. Dimensional corrections of the specimen due to thermal expansion were taken into account. Dynamic elastic modulus was evaluated as the average of the moduli that was obtained through first flat and edge flexural mode frequencies. Dynamic shear modulus was established through the first torsional mode of frequency.
Conventional indentation hardness measurements to obtain load independent Vickers hardness values for the different phases in multifilamentary superconducting (SC) wires are described. The concept of composite hardness is validated for a binary metalmatrix metalfilament NbTi/Cu composite wire. The tensile materials properties of the individual wire components are estimated from their indentation hardness. The potential and limitations of this approach are critically discussed, based on a comparison with ensile test results obtained for wires and extracted NbTi filaments.
The load-independent Vickers hardness (HV) of the individual phases in a non-reacted Nb3Sn
wire has been measured and the yield strength (YS) of the individual components estimated
from the HV values. The YS and tensile strength (Rm) of the composite wire are calculated
according the rule of mixtures (ROM). Calculated tensile properties are compared with tensile
test results that were obtained for the entire composite wire, for the wire after removal of the
Cu stabiliser and for single Nb-7.5wt.%Ta fibres.
The tribological behaviour under dry sliding conditions of Magneli phase Ti4O7 and e-phase Ti2Cr2O7 with α-alumina as a sliding partner has been characterised at room temperature by oscillating sliding. The mechanical properties as well as Vickers hardness measurements do not reveal big differences between the materials, and 4-point bending strengths are around 200 MPa for both materials. Although the friction coefficients are in the medium range of 0.6 and do not differ much between the materials, the wear behaviour is very different. At room temperature, the wear coefficient of Ti2O7 is strongly dependent on relative humidity, and wear is highest under dry conditions when relative humidity is low as it is typically found for many ceramic materials. Ti2Cr2O7 shows remarkably different wear behaviour with the lowest wear in dry conditions. The measured coefficients of wear at low relative humidity of 4% are more than 2 orders of magnitude lower than those for Ti2O7.
Thermal barrier coatings allow increasing the operating temperature and efficiency of land-, sea-, or air-based turbines. As failure of the coating may result in serious damage of the turbine, reliable estimation of its lifetime is essential. To assess the lifetime, cyclic tests are conceived to combine thermal loading by heating the surface of the coating with laser irradiation and nondestructive methods for damage determination. Using laser irradiation allows a high reproducibility of the thermal load. The temperature of the sample surface during thermal loading is determined by an infrared-camera which also enables the possibility to detect damage in the coating via thermography. Additionally, four acoustic sensors, attached to the experimental setup, are used to detect damage in the sample and determine the source of acoustic events. Results of acoustic emission correlate well with thermographic images that visualize the formation and evolution of damage through delaminations in the samples.
Characterization of Ti-6Al-4V fabricated by multilayer laser powder-based directed energy deposition
(2022)
Laser powder-based directed energy deposition (DED-L) is increasingly being used in additive manufacturing (AM). As AM technology, DED-L must consider specific challenges. It must achieve uniform volume growth over hundreds of layers and avoid heat buildup of the deposited material. Herein, Ti–6Al–4V is fabricated using an approach that addresses these challenges and is relevant in terms of transferability to DED–L applications in AM. The assessment of the obtained properties and the discussion of their relationship to the process conditions and resulting microstructure are presented. The quality of the manufacturing process is proven in terms of the reproducibility of properties between individual blanks and with respect to the building height. The characterization demonstrates that excellent mechanical properties are achieved at room temperature and at 400 °C.
The elastic properties of the single-crystal nickel-base superalloy CMSX-4 used as a blade material in gas turbines were investigated by the sonic resonance method in the temperature interval between room temperature and 1300 °C. Elastic constants at such high temperatures are needed to model the mechanical behavior of blade material during manufacturing (hot isostatic pressing) as well as during technical accidents which may happen in service (overheating). High reliability of the results was achieved using specimens of different crystallographic orientations, exciting various vibration modes as well as precise measurement of the material density and thermal Expansion required for modeling the resonance frequencies by finite element method. Combining the results measured in this work and literature data the elastic constants of the gamma and gamma' phases were predicted.
This prediction was supported by measurement of the temperature dependence of the gamma'fraction.
All data obtained in this work are given in numerical or analytical forms and can be easily used for different scientific and engineering calculations.
In nickelbasierten Superlegierungen, die für Gasturbinenschaufeln verwendet werden, sind bei hohen Betriebstemperaturen und -belastungen Kriechschäden, Ermüdung, Korrosion und Oxi-dation zu beobachten. Die betroffenen Turbinenschaufeln müssen ersetzt oder repariert werden, um Effizienzverluste und ein eventuelles Bauteilversagen zu vermeiden. In letzter Zeit wurden additive Fertigungs- und Lötverfahren für die Reparatur und das Fügen von Nickelbasiswerk-stoffen entwickelt, um die Einschränkungen der traditionellen Reparaturverfahren zu überwinden. Für eine auslegungsrelevante Bewertung des Risswachstumsverhaltens in den Fügezonen, die durch diese neuen Technologien erzeugt werden, sind Rissfortschrittsuntersuchungen erfor-derlich. Entsprechende Untersuchungen an gefügten Proben werden in diesem Beitrag vorge-stellt. Die Rissfortschrittsversuche werden an gefügten SEN-Proben (Single Edge Notch) bei einem Spannungsverhältnis von 0,1 und einer Temperatur von 950 °C durchgeführt. Das Riss-wachstum wird mit der DCPD-Methode (Direct Current Potential Drop) überwacht, und die ge-messenen Potenzialsignale werden anhand der optisch vermessenen Risslänge und einer Finite-Elemente-Analyse kalibriert. Der Spannungsintensitätsfaktor (SIF) für die gefügte SEN-Geometrie wird mit Hilfe von Finite-Elemente-Analysen berechnet. Auf diese Weise können Rissfortschrittskurven aus den experimentellen Daten abgeleitet werden.