DSpace Angular :: Browsing by Author "Rothammer, Benedict"

Browsing by Author "Rothammer, Benedict"

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Combining multi-scale surface texturing and DLC coatings for improved tribological performance of 3D printed polymers
(2023) Marian, Max; Zambrano, Dario F.; Rothammer, Benedict; Waltenberger, Valentin; Boidi, Guido; Krapf, Anna; Merle, Benoit; Stampfl, Jürgen; Rosenkranz, Andreas; Gachot, Carsten; Grützmacher, Philipp G.
Polymer components fabricated by additive manufacturing typically show only moderate strength and low temperature stability, possibly leading to severe wear and short lifetimes especially under dry tribological sliding. To tackle these shortcomings, we investigated the combination of single- and multi-scale textures directly fabricated by digital light processing with amorphous diamond-like carbon (DLC) coatings. The topography of the samples and conformity of the coatings on the textures are assessed and their tribological behaviour under dry conditions is studied. We demonstrate that the surface textures have a detrimental tribological effect on the uncoated samples. This changes with the application of DLC coatings since friction substantially reduces and wear of the textures is not observed anymore. These trends are attributed to the protection of the underlying polymer substrate by the coatings and a reduced contact area. The best tribological performance is found for a coating with highest hardness and hardness-to-elasticity ratios. Moreover, multi-scale textures perform slightly better than single-scale textures due to a smaller real contact area. Summarizing, we verified that the high flexibility and low production costs of 3D printing combined with the excellent mechanical and tribological properties of DLC results in synergistic effects with an excellent performance under dry sliding conditions
Designing amorphous carbon coatings using numerical and experimental methods within a multi-scale approach
(2020) Tremmel, Stephan; Marian, Max; Rothammer, Benedict; Weikert, Tim; Wartzack, Sandro
Amorphous carbon coatings have the potential to effectively reduce friction and wear in tribotechnical systems. The appropriate application of amorphous carbon layers requires both, a very good understanding of the tribological system and knowledge of the relationships between the fabrication of the coatings and their properties. In technical practice, however, the coatings’ development and their selection on the one hand and the design of the tribological system and its environment on the other hand are usually very strongly separated. The present work therefore aims to motivate the integrated development of tribotechnical systems with early consideration of the potential of amorphous carbon coatings. An efficient integrated development process is presented, which makes it possible to determine the boundary conditions and the load collective of the tribological system based upon an overall system and to derive the requirements for a tailored coating. In line with the nature of tribology, this approach must cover several scales. In this respect, the development process follows a V-model. The left branch of the V-model is mainly based upon a simulation chain including multibody and contact simulations. The right branch defines an experimental test chain comprising coating characterization to refine the contact simulation iteratively and tribological testing on different levels to validate the function fulfillment. Within this contribution, the outlined approach is illustrated by two use cases, namely the cam/tappet-pairing and the total knee replacement.
Diamond-like Carbon coatings for artificial implants
(Wiley, 2025) Rothammer, Benedict; Marian, Max
This chapter delves into the enhancement of implant performance through diamond-like carbon (DLC) coatings, recognized for their exceptional mechanical, chemical, and biocompatible properties, making them ideal for various biomedical applications. The chapter focuses on orthopedic applications, where DLC coatings improve wear resistance and longevity of implants, and promote osteointegration by enhancing cell adhesion and proliferation. In dental implants, DLC coatings boost biocompatibility and reduce infection risk, while also enhancing the durability of orthodontic brackets. This chapter details the requirements for DLC coatings in artificial implants and reviews their use in load bearing and dental implants, respectively. The chapter concludes with a summary of findings and identifies future research challenges, emphasizing the need for translating model-level advancements to component-level applications and addressing the reproducibility issues in dental applications. Overall, DLC coatings show significant potential to improve patient outcomes, reduce revision surgeries, and enhance comfort in both orthopedic and dental medicine.
Evaluation of DLC, MoS2, and Ti3C2T thin films for triboelectric nanogenerators
(2022) Tremmel, Stephan; Luo, Xiongxin; Rothammer, Benedict; Seynstahl, Armin; Wang, Bo; Rosenkranz, Andreas; Marian, Max|Zhu, Laipan
Due to their cost-effective fabrication, easy integration, and low frequency working range, triboelectric nanogenerators (TENGs) demonstrate tremendous potential in green energy harvesting to power smart devices and the internet of things (IoT). However, there is an urgent need to synergistically maximize their output and improve their durability to ensure a long-lasting high performance. This study aims at elucidating the performance of protective thin films deposited on the wear-prone PTFE surface of TENGs including doped and undoped, single- and multi-layer hydrogenated DLC films, MoS2 coatings fabricated by physical vapor deposition and multi-layer Ti3C2Tx (MXene) films. The deposited coatings are characterized by electron microscopy, and Raman spectroscopy. Their triboelectric performance is analyzed for TENGs operating in contact separation and freestanding sliding modes. We verified that MXenes outperformed the other films in contact separation mode due to the good electron gain ability of functional oxygen and fluorine groups. In sliding mode, the undoped a-C:H coating performed on a comparable level to the uncoated reference and superior to the tungsten-doped DLC and MoS2 films. The film withstood long-term tests without notable signs of wear; merely the output slowly decreased with time due to graphitization and thus potential material transfer to the mating body.
Evaluation of the wear-resistance of DLC-coated hard-on-soft pairings for biomedical applications
(2023) Rothammer, Benedict; Neusser, Kevin; Bartz, Marcel; Wartzack, Sandro; Schubert, Andreas; Marian, Max
Diamond-like carbon (DLC) coatings deposited on the articulating surfaces of total hip or knee arthroplasties have the potential to enhance the overall biotribological behavior and longevity. In this contribution, we employ an ultrahigh molecular weight polyethylene ball-on-three cobalt chromium or titanium alloy pin configuration lubricated by simulated body fluid to effectively carry out screening tests. Thus, the influence of the choice of the coated component (metallic and/or polymeric) as well as the differences between a higher and lower load case with non- and conventionally cross-linked polyethylene were studied. The studied coating systems featured excellent mechanical properties with a substantial enhancement of indentation hardness and elastic modulus ratios. The adhesion of the coatings as determined in modified scratch tests can be considered as very good to polymeric and as satisfactory to metallic substrates, thus confirming the potential for the use in total joint arthroplasties. Although the coatings predominantly led to an increase in friction due to the considerably higher roughness, wear was substantially reduced. While only the metallic components were mostly coated in studies reported in literature, our investigation showed that a coating of the polymer component in particular is of decisive importance for enhancing the wear performance and increasing the service life of load-bearing implants. Moreover, single sided coating results in higher wear of the uncoated counter-part. Therefore, coating systems deposited on both articulating surfaces, polymeric and metallic, should be pursued in the future
Experimental study on the tribological behavior of ceramic disks for application in mixer taps under different lubrication conditions
(2023) Ziegler, Marlene Kristin; Rothammer, Benedict; Bartz, Marcel; Wartzack, Sandro; Beau, Patrick; Patzer, Gregor; Henzler, Stephan; Marian, Max
Purpose: The evaluation of the haptics of water taps and wear-related changes during usage usually involves time- and cost-intensive testing. The purpose of this paper is to abstract the tribo-system between technical ceramic disks of water tap mixer cartridges to the model level and study the tribological behavior. Design/methodology/approach: The friction and wear behavior was studied by means of an alumina ball-on-original alumina disk setup at different temperatures as well as under dry conditions and under lubrication by different greases. Thereby, the frictional behavior was measured in situ, and the wear losses were analyzed by means of laser scanning microscopy. Findings: It was shown that friction and wear can behave in a contrasting way, whereby one grease might lead to low friction, that is, an easy-going movability of the water tap, but to increased wear losses. The latter, in turn, is an indicator for the usability and service life, which cannot be explained from friction alone. Thereby, the viscosity of the base oil, the grease consistency and additives were identified as relevant grease formulation parameters to allow for fluid film (re-)formation and removal of wear particles. Originality/value: To the authors’ best knowledge, this is the first approach to systematically analyze the friction and wear behavior of technical ceramic disks of water tap mixer cartridges in dependency on the temperature as well as the used lubricating grease. This approach is relevant for developing screening test strategies as well as for the selection of lubricants for water tap applications.
Frictional Behaviour and Surface Topography Evolution of DLC-Coated Biomedical Alloys
(2025) Nečas, David; Gelnar, Adam; Rothammer, Benedict; Marian, Max; Ranuša, Matúš; Wartzack, Sandro; Vrbka, Martin; Křupka, Ivan; Hartl, Martin
Advanced engineering coatings offer a promising solution to enhance the longevity and performance of medical biomaterials in orthopaedic implants. This study hypothesises that diamond-like carbon (DLC) coatings exhibit distinct frictional performance based on substrate and counterface material. Three different DLC coatings were tested using a pin-on-plate test in four material combinations. Virgin and DLC-coated CoCrMo and Ti6Al4V pins were tested under sliding against UHMWPE and glass plates with simulated body fluid lubrication. Results revealed that coating composition significantly impacts frictional performance, with silicon- and oxygen-doped coatings showing great potential to minimise friction. Surprisingly, reducing contact pressure had either a neutral or somewhat negative effect. Future investigations will focus on long-term testing and lubrication analyses of these material combinations.
Subject-specific tribo-contact conditions in total knee replacements: a simulation framework across scales
(2023) Rothammer, Benedict; Wolf, Alexander; Winkler, Andreas; Schulte-Hubbert, Felix; Bartz, Marcel; Wartzack, Sandro; Miehling, Jörg; Marian, Max
Fundamental knowledge about in vivo kinematics and contact conditions at the articulating interfaces of total knee replacements are essential for predicting and optimizing their behavior and durability. However, the prevailing motions and contact stresses in total knee replacements cannot be precisely determined using conventional in vivo measurement methods. In silico modeling, in turn, allows for a prediction of the loads, velocities, deformations, stress, and lubrication conditions across the scales during gait. Within the scope of this paper, we therefore combine musculoskeletal modeling with tribo-contact modeling. In the first step, we compute contact forces and sliding velocities by means of inverse dynamics approach and force-dependent kinematic solver based upon experimental gait data, revealing contact forces during healthy/physiological gait of young subjects. In a second step, the derived data are employed as input data for an elastohydrodynamic model based upon the finite element method full-system approach taking into account elastic deformation, the synovial fluid’s hydrodynamics as well as mixed lubrication to predict and discuss the subject-specific pressure and lubrication conditions.
Ti₃C₂T_x-UHMWPE Nanocomposites-Towards an Enhanced Wear-Resistance of Biomedical Implants
(2024) Rothammer, Benedict; Feile, Klara; Werner, Siegfried; Frank, Rainer; Bartz, Marcel; Wartzack, Sandro; Schubert, Dirk W.; Drummer, Dietmar; Detsch, Rainer; Wang, Bo; Rosenkranz, Andreas; Marian, Max
There is an urgent need to enhance the mechanical and biotribological performance of polymeric materials utilized in biomedical devices such as load-bearing artificial joints, notably ultrahigh molecular weight polyethylene (UHMWPE). While two-dimensional (2D) materials like graphene, graphene oxide (GO), reduced GO, or hexagonal boron nitride (h-BN) have shown promise as reinforcement phases in polymer matrix composites (PMCs), the potential of MXenes, known for their chemical inertness, mechanical robustness, and wear-resistance, remains largely unexplored in biotribology. This study aims to address this gap by fabricating Ti3C2Tx-UHMWPE nanocomposites using compression molding. Primary objectives include enhancements in mechanical properties, biocompatibility, and biotribological performance, particularly in terms of friction and wear resistance in cobalt chromium alloy pin-on-UHMWPE disk experiments lubricated by artificial synovial fluid. Thereby, no substantial changes in the indentation hardness or the elastic modulus are observed, while the analysis of the resulting wettability and surface tension as well as indirect and direct in vitro evaluation do not point towards cytotoxicity. Most importantly, Ti3C2Tx-reinforced PMCs substantially reduce friction and wear by up to 19% and 44%, respectively, which was attributed to the formation of an easy-to-shear transfer film.
Wear Mechanism of Superhard Tetrahedral Amorphous Carbon (ta-C) Coatings for Biomedical Applications
(2023) Rothammer, Benedict; Schwendner, Michael; Bartz, Marcel; Wartzack, Sandro; Boehm, Thomas; Krauss, Sebastian; Merle, Benoit; Schroeder, Stefan; Uhler, Maximilian; Kretzer, Jan Philippe; Weihnacht, Volker; Marian, Max
Tetrahedral amorphous carbon (ta-C) coatings have the potential to protect biomedical implants from wear and increase their service life. This study elucidates the biocompatibility, mechanical properties, adhesion, and wear resistance of ta-C coatings fabricated by physical vapor deposition on cobalt-chromium-molybdenum (CoCr) and titanium (Ti64) alloys as well as ultrahigh molecular weight polyethylene (UHMWPE). Satisfactory cytocompatibility is verified using contact angle and surface tension measurements as well as indirect and direct cell testing. Scratch testing demonstrates excellent adhesion to the substrates and as confirmed by nanoindentation, the coatings represent an up to 13-fold and 182-fold increase in hardness on the hard and soft materials. In metal pin-on-UHMWPE disk sliding experiments under simulated body fluid lubrication, the wear rates of the disk are reduced by 48% (against CoCr) and 73% (against Ti64) while the pin wear rates are reduced by factors of 20 (CoCr) and 116 (Ti64) compared to uncoated pairings. From optical and laser scanning microscopy, Raman measurements, and particle analyses, it is shown that the underlying substrates remain well protected. Nonetheless, focused ion beam scanning electron microscopy revealed coating process-related and thermally driven subductions as well as tribologically induced near-surface fatigue, which can potentially constitute critical wear mechanisms.

Browsing by Author "Rothammer, Benedict"

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