DSpace Angular :: Browsing by Author "Poll, Gerhard"

Browsing by Author "Poll, Gerhard"

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A Neural Network for Fast Modeling of Elastohydrodynamic Line Contacts
(SSRN, 2024) Kelley, Josephine; Schneider, Volker; Marian, Max; Poll, Gerhard
When modeling bearings in the context of entire transmissions or drivetrains, there are practical limits to the calculation resources available to calculate single bearings or even contacts. In settings such as these, curve-fitting methods have historically been deployed to estimate the elastohydrodynamic lubrication conditions. Machine learning methods have the potential to enable more sophisticated physical modeling in the context of larger computation environments, as the evaluation time of a trained model is typically negligible. We present a neural network that accurately evaluates the elastohydrodynamic film pressure and film thickness and explore its applications. Employing a neural network for the EHL film thickness calculations can enable a more physically precise modeling strategy at almost no additional computational cost.
Biogenic palm oil-based greases with glycerol monostearate and soy wax: A rheological and tribological study
(2025) Nassef, Belal G.; Moradi, Amirreza; Bayer, Gernot; Pape, Florian; Abouelkasem, Zeyad A.; Rummel, Florian; Schmoelzer, Stefan; Poll, Gerhard; Marian, Max
The increasing environmental concerns associated with conventional lubricants have led to a growing interest in sustainable alternatives, particularly biogenic grease. This study introduces a novel approach to synthesizing and characterizing fully biodegradable greases using palm oil as the base oil and renewable biothickeners, namely glycerol monostearate (GMS) and soywax (SW). The innovation lies in utilizing the distinct properties of these biothickeners to optimize the grease structure and performance for industrial applications. GMS enhances the consistency and mechanical stability, while SW controls the elasticity and oil bleeding. Rheological analysis shows that GMS exhibits the thickening capabilities at room temperature (RT) to achieve common grease consistencies, while SW enhances elasticity, achieving a unique balance of firmness and flexibility. Thermal analysis indicates that GMS-based greases had higher thermal stability, while SW enhance low-temperature performance. Tribological testing reveals a reduction in friction and wear, with an earlier transition to the mixed lubrication regime compared to a reference commercial grease (CG). Under boundary lubrication, GMSbased samples perform better than the CG, particularly under higher contact pressures. In contrast, SW-based formulations demonstrate better lubrication at lower contact pressures. In fluid friction regimes, almost all biobased samples outperform the CG, showing potential for high-speed applications. When tested in angular contact ball bearings under oscillating motion (a typical moderate temperature application), the bio-greases show decent results in preventing false brinelling. This study highlights the potential of these eco-friendly formulations as a viable alternative to conventional greases.
Comprehensive Evaluation of the Rheological, Tribological, and Thermal Behavior of Cutting Oil and Water-Based Metalworking Fluids
(2025) Pape, Florian; Nassef, Belal G.; Schmölzer, Stefan; Stobitzer, Dorothea; Taubmann, Rebekka; Rummel, Florian; Stegmann, Jan; Gerke, Moritz; Marian, Max; Poll, Gerhard; Kabelac, Stephan
Metalworking fluids (MWFs) are crucial in the manufacturing industry, playing a key role in facilitating various production processes. As each machining operation comes with distinct requirements, the properties of the MWFs have to be tailored to meet these specific demands. Understanding the properties of different MWFs is fundamental for optimizing processes and improving performance. This study centered on characterizing the thermal behavior of various cutting oils and water-based cutting fluids over a wide temperature range and sheds light on the specific tribological behavior. The results indicate that water-based fluids exhibit significant shear-thinning behavior, whereas cutting oils maintain nearly Newtonian properties. In terms of frictional performance, cutting oils generally provide better lubrication at higher temperatures, particularly in mixed and full-fluid film regimes, while water-based fluids demonstrate greater friction stability across a wider range of conditions. Among the tested fluids, water-based formulations showed a phase transition from solid to liquid near 0 °C due to their high water content, whereas only a few cutting oils exhibited a similar behavior. Additionally, the thermal conductivity and heat capacity of water-based fluids were substantially higher than those of the cutting oils, contributing to more efficient heat dissipation during machining. These findings, along with the reported data, intend to guide future researchers and industry in selecting the most appropriate cutting fluids for their specific applications and provide valuable input for computational models simulating the influence of MWFs in the primary and secondary shear zones between cutting tools and the workpiece/chiplet.
Effect of Harmful Bearing Currents on the Service Life of Rolling Bearings: From Experimental Investigations to a Predictive Model
(2024) Schneider, Volker; Krewer, Marius; Poll, Gerhard; Marian, Max
This study investigates the effects of harmful bearing currents on the service life of rolling bearings and introduces a model to predict service life as a function of surface roughness. Harmful bearing currents, resulting from electrical discharges, can cause significant surface damage, reducing the operational lifespan of bearings. This study involves comprehensive experiments to quantify the extent of electrical stress caused by these currents. For this purpose, four series of tests with different electrical stress levels were carried out and the results of their service lives were compared with each other. Additionally, a novel model to correlate the service life of rolling bearings with varying degrees of surface roughness caused by electrical discharges was developed. The basis is the internationally recognized method of DIN ISO 281, which was extended in the context of this study. The findings show that the surface roughness continues to increase as the electrical load increases. In theory, this in turn leads to a deterioration in lubrication conditions and a reduction in service life.
Enhancing practical modeling: A neural network approach for locally-resolved prediction of elastohydrodynamic line contacts
(2024) Kelley, Josephine; Schneider, Volker; Poll, Gerhard; Marian, Max
When modeling bearings in the context of entire transmissions or drivetrains, there are practical limits to the calculation resources available to calculate single bearings or even contacts. In settings such as these, curve-fitting methods have historically been deployed to estimate the elastohydrodynamic lubrication conditions. Machine learning methods have the potential to enable more sophisticated physical modeling in the context of larger computation environments, as the evaluation time of a trained model is typically negligible. We present a neural network that accurately evaluates the locally variable elastohydrodynamic film pressure and film thickness distributions and explore its application to (e.g.) cylindrical roller bearings. Employing a neural network for the EHL film thickness calculations rather than the curve-fitted, simplified methods that are today’s standard can enable a more physically precise modeling strategy at almost no additional computational cost.
From Damage to Functionality: Remanufacturing of Thrust Roller Bearings by Tailored Forming
(John Wiley and Sons Inc, 2024) Saure, Félix; Pape, Florian; Poll, Gerhard; Marian, Max
Axial and radial rolling bearings are critical components in various machines, particularly in large-scale applications such as mining and heavy machinery. Failures in these bearings can cause significant operational downtime and high replacement costs. Common failure modes include plastic deformation, abrasive wear, insufficient lubrication, and fatigue, necessitating efficient repair strategies. This article investigates the tailored forming process chain for repairing axial bearing washers, focusing on plasma-transferred arc deposition welding. The repair process involves removing damaged areas, welding, and machining to nominal size. Materials used include a novel alloy and commercially available powders. The repaired bearings undergo rigorous testing, including scanning acoustic microscopy for weld quality assessment and fatigue tests on FE8 test rig. Results indicate that the newly developed alloy exhibits higher fatigue life despite its lower hardness compared to AISI 52100 and AISI 4140 steels. The repaired bearings achieve a service life comparable to new bearings, with the welding process quality significantly impacting longevity. Tribological tests show the new alloy's superior wear resistance, suggesting its potential for extending the service life of repaired bearings. The study concludes that tailored forming processes, combined with optimized welding techniques, can effectively repair rolling bearings, reducing costs and downtime while enhancing performance.
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.
Novel capacitive measuring method to determine the complex impedance behavior of machine elements
(2025) Schneider, Volker; Kelley, Josephine; Lehnhardt, Bela; Krewer, Marius; Bader, Norbert; Marx, Johannes; Poll, Gerhard; Marian, Max
This study focuses on the analysis of the capacitive charging behavior of lubricant films in rolling bearings. A methodology is presented to process experimental data and apply mathematical models for extracting key parameters such as capacitance and parallel resistance of a lubricated bearing. The results provide insights into the electrical properties of the lubricant film, which are crucial for understanding the operational characteristics and durability of rolling bearings.
Residual stress engineering for highly loaded rolling-sliding contacts: Finding the sweet spot for maximum durability by hard turning and deep rolling
(2025) Dechant, Simon; Nordmeyer, Henke; Pape, Florian; Breidenstein, Bernd; Poll, Gerhard; Marian, Max
The durability of highly loaded rolling-sliding contacts, such as those in rolling bearings, is critically determined by subsurface microstructure and residual stresses engineered during manufacturing. This study systematically investigates the interplay between thermal and mechanical process parameters during deep rolling, using bearing inner rings as a representative example, to identify optimal conditions for maximizing fatigue life. By isolating the effects of process temperature (20–400 °C) and deep rolling pressure (200–400 bar), we demonstrate that moderate mechanical loading at room temperature can more than double bearing life through beneficial compressive residual stresses, while excessive pressure or thermal input above 200 °C sharply reduces durability. Notably, we reveal a previously unrecognized mechanism of hidden thermal degradation that limits lifetime, even when conventional hardness or microstructural metrics remain unchanged. These results define a process window for residual stress engineering in bearing steels and provide generic guidelines for hybrid manufacturing of rolling-sliding components subjected to severe tribological loading. The findings advance fundamental understanding of process-induced fatigue mechanisms and offer a framework for the rational design of subsurface-optimized, durable, and sustainable machine elements.
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.
Towards lifetime lubrication of wind turbine gearboxes: Technical and physical investigations on used oils
(Elsevier Ltd, 2025) Liu, Muyuan; Bayer, Gernot; Reimers, Merle; Schunemann, Wilhelm; Konig, Florian; Jacobs, Georg; Schelenz, Ralf; Bader, Norbert; Poll, Gerhard; Marian, Max
Modern geared wind turbines rely on the adequate performance of their lubricant to ensure optimum operation of their main gearboxes. Potential oil ageing mechanisms, such as oxidation or additive depletion, can degrade oil performance over time. An oil that performs satisfactorily throughout the entire life of the turbine can reduce the downtime, resources, and costs associated with oil changes or repairs. Therefore, the purpose of this study is to investigate the ageing of field oil through oil analysis and artificial ageing. In addition, the possibility of oil service life extension by top-treating used oils with additives was investigated. For the field oil evaluation, oil samples were taken from operating wind turbines with lifespans up to 16 years. The deterioration of their copper corrosion, foaming, and wear performance was assessed using standard tests and its influence on gearbox operation was identified. Although these properties had degraded to some extent, most oils continued to perform satisfactorily. To counteract oil ageing, top-treating (adding additives to the field oils) was performed to restore the corresponding properties of oils. Subsequent standard tests confirmed that this approach is generally effective, but there are still some potential problems. To further investigate the oils' lifespan limits, field oils were subjected to artificial ageing. This process involved oil heating and the artificial, accelerated consumption of anti-wear additives. Experimental results indicated that artificial ageing has only a minor influence on wear despite a significant reduction in additive concentration. In conclusion, proper monitoring of oils and timely top-treat have the potential to achieve lifelong wind turbine gearbox lubrication.

Browsing by Author "Poll, Gerhard"

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