Browsing by Author "Konopka, Dennis"

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    Location- and time-resolved strain measurement in thrust roller bearings using thin-film sensors
    (2025) Konopka, Dennis; Steppeler, Tobias; Ottermann, Rico; Dencker, Folke; Pape, Florian; Poll, Gerhard; Wurz, Marc Christopher; Marian, Max
    Bearings play a crucial role in a broad range of engineering applications, such as automotive, aerospace and renewable energies. Particularly when it comes to larger and/or hard to replace/repair bearings, such as those in wind turbines, condition monitoring and load control are essential due to their complex and expensive conditions for maintenance and repair. Conventionally, different sensors are used, which are typically positioned outside of the bearing. Thus, a rather low depth of information is achieved, and the bearing condition cannot be assessed optimally. Therefore, this article focuses on the production and evaluation of directly deposited thin-film strain sensor arrays on a rolling bearing within and close to the tribomechanical contact between roller and raceway. The sensor production was carried out using sputtering, photolithography and etching processes. After the static strain gauge characterization concerning temperature, strain and pressure sensitivity on different substrates, a sensor-integrated 81212 thrust roller bearing was investigated in an FE8 bearing test rig. After data processing, the dynamic measurements with a maximum Hertzian pressure of 1 GPa revealed negative sensor resistance changes of up to −1.4 ‰ in the tribomechanical contact and up to 3.8 ‰ positive resistance change right next to the contact zone. Due to the fact that these sensors were subject to wear, sensors were also positioned at a greater distance from the contact that still showed a measurable signal of 0.5 ‰ resistance change that can be used after critical loads when their signal has been correlated to the other sensors in the contact zone when the latter are worn. Furthermore, the time-resolution enables the precise measurement of the rotational speed, and deviations in the roller geometries can be detected as well due to different sensor amplitudes. The location-resolved measurements allow important information about the tribomechanical contact to be derived in real-time, thus enabling intelligent component control, for example concerning rotational speed, lubrication and load before a damage occurs.
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    Self-Regenerative Mo-Based Solid Lubricant Coatings Deposited by APS as a PVD Alternative: Mechanical and Tribological Performance
    (2025) Konopka, Dennis; Crespo Martins, Ricardo; Dukat, Mareike; Pape, Florian; Möhwald, Kai; Poll, Gerhard; Marian, Max
    Solid lubricant coatings are essential for reducing friction and wear in tribo-mechanical systems, particularly in environments where traditional liquid lubricants can’t be used or fail. It has been reported in literature that self-regenerating physical vapor deposition (PVD) coatings can be designed in such a way that they continuously release MoO3 as a solid lubricant through tribo-oxidation. However, a disadvantage of PVD coatings is the limited layer thickness of just a few micrometers and thus the limited solid lubricant reservoir. In contrast, atmospheric plasma spraying (APS) allows the deposition of thicker reservoir layers, potentially extending service life under tribological stressing. Therefore, the aims of this study are to determine whether APS coatings with regenerative properties can be deposited on bearing steel and to assess their tribological performance. The mechanical, tribological, and structural behavior were analyzed using microindentation, ball-on-plate tribometer testing under dry conditions, optical and laser scanning, scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDX). Despite the relatively low hardness of the APS coating, excellent wear resistance protection was demonstrated at various loads and sliding velocities. Additionally, EDX analyses revealed that abrasive wear was prevented and a protective film was formed through tribo-oxidation, effectively shielding the surfaces. The results thus indicate the effectiveness of the APS coating and underline its potential for large-scale machine elements, such as rolling bearings.