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Institute: search.filters.UBSInstitut.Fakultätsübergreifend / Sonstige EinrichtungAuthor: search.filters.author.Bertsche, Bernd

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Now showing 1 - 4 of 4
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    Reliability as a key driver for a sustainable design of adaptive load-bearing structures
    (2022) Efinger, Dshamil; Ostertag, Andreas; Dazer, Martin; Borschewski, David; Albrecht, Stefan; Bertsche, Bernd
    The consumption of construction materials and the pollution caused by their production can be reduced by the use of reliable adaptive load-bearing structures. Adaptive load-bearing structures are able to adapt to different load cases by specifically manipulating internal stresses using actuators installed in the structure. One main aspect of quality is reliability. A verification of reliability, and thus the safety of conventional structures, was a design issue. When it comes to adaptive load-bearing structures, the material savings reduce the stiffness of the structure, whereby integrated actuators with sensors and a control take over the stiffening. This article explains why the conventional design process is not sufficient for adaptive load-bearing structures and proposes a method for demonstrating improved reliability and environmental sustainability. For this purpose, an exemplary adaptive load-bearing structure is introduced. A linear elastic model, simulating tension in the elements of the adaptive load-bearing structure, supports the analysis. By means of a representative local load-spectrum, the operating life is estimated based on Woehler curves given by the Eurocode for the critical notches. Environmental sustainability is increased by including reliability and sustainability in design. For an exemplary high-rise adaptive load-bearing structure, this increase is more than 50%.
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    Parameter assessment for reliability modeling of machine components using heuristic screening
    (2023) Arndt, Marco; Dazer, Martin; Raither, Wolfram; Bertsche, Bernd
    For the investigation of influence of various parameters on properties and outputs of components or systems, Design of Experiments (DOE) offers the most efficient approach to create a comprehensive empirical insight into product performance. However, especially if product lifetime is treated as the investigation objective, the main focus of attention must be placed on the efficiency of testing - if only to comply with the principle of DOE, even before testing begins. Without actual test runs, a pre-selection of relevant factors influencing the target quantity can be performed here and strategically adjusted in scale compared to the subsequent method. In this work, common heuristic tools and methods are analyzed and evaluated with respect to a deliberate preselection of influencing factors versus the challenges in lifetime testing and degradation behaviors. Several factors as well as their interactions are taken into account to achieve this. For this purpose, these methods are partially extended and adapted in their focus in order to finally be made applicable in a suitable procedure. An illustration of this is also provided in a selected use case with limited empirical and experimental prior-knowledge, in which a sample of relevant influences is identified through qualitative heuristic decision making with respect to parameters that influence product lifetime.
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    Lebensdaueranalyse auf Basis von multidimensionaler Zuverlässigkeits- und Robust Design Simulation : integrale Betrachtung der robusten Zuverlässigkeit
    (2017) Kemmler, Stefan; Dazer, Martin; Leopold, Tobias; Bertsche, Bernd
    Konventionelle Methoden des Robust Design verfolgen größtenteils Ansätze zur Varianzbetrachtung, die potentiell über der Produkteinsatzzeit auftreten können. Daher geben diese Methoden keine genauen Informationen über das zeitlich funktionale Verhalten der sich verändernden Produkteigenschaften und -anforderungen sowie deren Lebensdauer. Um genaue Lebensdauerprognosen bezüglich dieser Funktionserfüllung zu beschreiben, ist eine kontinuierliche Merkmalsänderung in Form von sogenannten Degradationsmodellen von Vorteil. Diese werden im Allgemeinen durch reale Versuche mit einem hohen Grad an zeitlichem und kostenintensivem Aufwand durchgeführt. Für eine effizientere Ermittlung der Modelle sollten bereits in frühen Phasen des Produktentwicklungsprozesses, virtuelle Degradationsmodelle entwickelt werden. Durch die genaue Kennung von Funktionsausfällen über der Zeit können nicht nur Produkte zielgerichtet ausgelegt, sondern auch unnötige Ressourcen eingespart werden.
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    Coefficient of friction behavior of gear oils and significance for the meshing process of spur gears : lubrication for improved properties
    (2022) Baumann, Axel; Bertsche, Bernd
    The mechanical properties of oils are determined using test methods. There are standardized test methods for determining viscosity and density. The characterization of transmission oil based on its dynamic viscosity alone is not sufficient for the physical explanation of different levels of noise emissions in vehicle transmissions. For this reason, the test procedure for determining the coefficient of friction is used in the following to enable a further differentiation between the oils according to mechanical properties. In gear transmissions with involute gear teeth, rolling friction occurs in the gear pair meshing along the line of action due to the variation in the equivalent curvature radii throughout the meshing cycle. This is rolling friction on which a sliding friction component, so-called slip, is superimposed. Pure rolling friction only occurs in the pitch point. From the pitch point to the start and end of the meshing, there is a superimposed sliding friction component that increases with increasing distance from the pitch point. Slip values occur in the range of 5-50% depending on tooth geometry. These friction conditions during tooth flank lubrication can be assessed using the Stribeck curve. The Stribeck curve represents the coefficient of friction as a function of the speed. A mini traction machine from PCS Instruments with a ball/plate measurement setup was used to determine the coefficient of friction behavior of gear oils. This allows the coefficient of friction of an oil to be assessed at low speeds in the range from boundary and mixed friction to elastohydrodynamic fluid friction at high speeds. The investigations show that the coefficient of friction behavior of a gear oil depends on the oil viscosity and above all on the chemical composition. The lower the coefficient of friction, the less energy is required to shear the lubricating film and the lower the power transmission through the fluid. The coefficient of friction is a property that is dominated by the type of base oil and the type of VI improver in the area of mixed and fluid friction, especially with additional sliding in contact. It will be shown in the paper that the use of a gear oil that has been optimized with regard to the coefficient of friction curve can reduce the entry impacts of meshing gear pairs under vibration excitation and the gear transmission thus generates lower noise emissions.