Eldorado - Repositorium der TU Dortmund

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Aktuellste Veröffentlichungen

Fundamental characterization of lubrication effects through various cooling lubricants in the chip formation zone
(Springer Science and Business Media LLC, 2024-08-01) Biermann, Dirk; Saelzer, Jannis; Bergmann, Benjamin; Schenzel, Jan; Menze, Christian J.; Gerken, Julian Frederic; Wolf, Tobias; Denkena, Berend; Möhring, Hans-Christian; Zabel, Andreas
Using cooling lubricants in metalworking requires a high consumption of energy and resources. However, cooling lubricants serve to increase the productivity and quality of these processes. Accordingly, it is necessary to expand the efficiency of their application. This requires fundamental understanding of the working mechanisms. Driven by this motivation, this publication compares six cooling lubricants regarding their lubrication effect in orthogonal cutting. Three types of fluid supply, each conducted on a specific special machine tool for chip formation analysis, and two cutting speeds have been used in the tests. In order to analyze the lubricating effect of these different scenarios, force measurements were carried out and the chip formation was recorded with high-speed recordings. It was found that the process improvements due to lubrication is determined by the interaction of fluid properties, supply strategy and cutting speed. Moreover, clear limitations of water-based cooling lubricants (especially oil-water-emulsions) in the ability to lubricate the chip formation zone have been determined and quantified.
Fundamental investigation on the time-variance of process stability
(Springer Science and Business Media LLC, 2024-04-22) Jaquet, Simon; Meijer, Alexander; Baumann, Jonas; Biermann, Dirk
Disturbance factors, such as self-excited tool vibrations, limit the performance of modern machining processes and thus restrict the quality, productivity and sustainability of industrially manufactured components. The dynamic process stability is subjected to significant variances especially at the beginning of the tool life. To precisely quantify these variances, series of milling tests were conducted and analyzed using tools made of high speed steel (HSS) and cemented carbide for the machining of EN AW-7075. In all test series, a critical initial decrease of the stability limit was detected directly at the beginning of the tool life. In the following, a significant increase and subsequent almost constant stability limit was observed. In the case of the HSS cutters the achieved stability limit exceeded the initial level substantially. An increase in the process forces and flank wear was also measured over tool life but the progression cannot directly explain the extend and characteristics regarding the stability limit. The findings described have a considerable impact on the appropriate design of manufacturing processes and experiments to determine the dynamic stability of cutting operations.
Amtliche Mitteilungen der Technischen Universität Dortmund Nr. 16/2026
(Technische Universität Dortmund, 2026-07-08)
In vivo alkaline comet assay: statistical considerations on historical negative and positive control data
(Elsevier BV, 2024-02-22) Tug, Timur; Duda, Julia C.; Menssen, Max; Bruce, Shannon Wilson; Bringezu, Frank; Dammann, Martina; Frötschl, Roland; Harm, Volker; Ickstadt, Katja; Igl, Bernd-Wolfgang; Jarzombek, Marco; Kellner, Rupert; Lott, Jasmin; Pfuhler, Stefan; Plappert-Helbig, Ulla; Rahnenführer, Jörg; Schulz, Markus; Vaas, Lea; Vasquez, Marie; Ziegler, Verena; Ziemann, Christina
The alkaline comet assay is frequently used as in vivo follow-up test within different regulatory environments to characterize the DNA-damaging potential of different test items. The corresponding OECD Test guideline 489 highlights the importance of statistical analyses and historical control data (HCD) but does not provide detailed procedures. Therefore, the working group “Statistics” of the German-speaking Society for Environmental Mutation Research (GUM) collected HCD from five laboratories and >200 comet assay studies and performed several statistical analyses. Key results included that (I) observed large inter-laboratory effects argue against the use of absolute quality thresholds, (II) > 50% zero values on a slide are considered problematic, due to their influence on slide or animal summary statistics, (III) the type of summarizing measure for single-cell data (e.g., median, arithmetic and geometric mean) may lead to extreme differences in resulting animal tail intensities and study outcome in the HCD. These summarizing values increase the reliability of analysis results by better meeting statistical model assumptions, but at the cost of information loss. Furthermore, the relation between negative and positive control groups in the data set was always satisfactorily (or sufficiently) based on ratio, difference and quantile analyses.
Investigation of MHD oxytactic microorganisms with NEPCMs in rectotrapezoidal enclosure with FEM
(Elsevier BV, 2024-01-30) Hussain, Shafqat; Jayavel, Prakash; Almutairi, Bander; Ramesh, Katta
Nanoparticle-enhanced phase change materials (NEPCMs) have gained significant attention in recent years due to their unique ability to enhance the thermal properties and overall performance of phase change materials (PCMs). The present work investigates the bioconvection flow of nano-encapsulated phase change material within a rectotrapezoidal cavity. The left wall of the is fixed at the constant high temperature whereas the right vertical wall is kept at cold temperature. The higher order Galerkin finite element method (GFEM) has been employed to simulate the proposed problem. The discrete systems of nonlinear equations are linearized by implementing the adaptive Newtons method. Influence of various pertinent parameters such as inclined magnetic field, oxytactic bacteria, radiation and Lewis number has been analyzed. It is observed that the average Sherwood and Nusselt number exhibit a positive correlation with the Hartmann and radiation parameter. Moreover, the average heat transfer exhibits a decreasing trend as the Hartmann, bioconvection Rayleigh and Peclet increase.