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.
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    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.
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    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.
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    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.
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    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.
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    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.