Universität Stuttgart
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Item Open Access Statistical power analysis in reliability demonstration testing : the probability of test success(2022) Grundler, Alexander; Dazer, Martin; Herzig, ThomasStatistical power analyses are used in the design of experiments to determine the required number of specimens, and thus the expenditure, of a test. Commonly, when analyzing and planning life tests of technical products, only the confidence level is taken into account for assessing uncertainty. However, due to the sampling error, the confidence interval estimation varies from test to test; therefore, the number of specimens needed to yield a successful reliability demonstration cannot be derived by this. In this paper, a procedure is presented that facilitates the integration of statistical power analysis into reliability demonstration test planning. The Probability of Test Success is introduced as a metric in order to place the statistical power in the context of life test planning of technical products. It contains the information concerning the probability that a life test is capable of demonstrating a required lifetime, reliability, and confidence. In turn, it enables the assessment and comparison of various life test types, such as success run, non-censored, and censored life tests. The main results are four calculation methods for the Probability of Test Success for various test scenarios: a general method which is capable of dealing with all possible scenarios, a calculation method mimicking the actual test procedure, and two analytic approaches for failure-free and failure-based tests which make use of the central limit theorem and asymptotic properties of several statistics, and therefore simplify the effort involved in planning life tests. The calculation methods are compared and their respective advantages and disadvantages worked out; furthermore, the scenarios in which each method is to be preferred are illustrated. The applicability of the developed procedure for planning reliability demonstration tests using the Probability of Test Success is additionally illustrated by a case study.Item Open Access Comprehensive study of failure mechanisms of field-aged automotive lead batteries(2023) Conradt, Rafael; Schröer, Philipp; Dazer, Martin; Wirth, Jonathan; Jöris, Florian; Schulte, Dominik; Birke, Kai PeterModern vehicles have increasing safety requirements and a need for reliable low-voltage power supply in their on-board power supply systems. Understanding the causes and probabilities of failures in a 12 V power supply is crucial. Field analyses of aged and failed 12 V lead batteries can provide valuable insights regarding this topic. In a previous study, non-invasive electrical testing was used to objectively determine the reasons for failure and the lifetime of individual batteries. By identifying all of the potential failure mechanisms, the Latin hypercube sampling method was found to effectively reduce the required sample size. To ensure sufficient confidence in validating diagnostic algorithms and calculating time-dependent failure rates, all identified aging phenomena must be considered. This study presents a probability distribution of the failure mechanisms that occur in the field, as well as provides insights into potential opportunities, but it also challenges diagnostic approaches for current and future vehicles.Item Open Access Elastohydrodynamic simulation of pneumatic sealing friction considering 3D surface topography(2022) Bauer, Niklas; Baumann, Matthias; Feldmeth, Simon; Bauer, Frank; Schmitz, KatharinaThis contribution presents an elastohydrodynamic lubrication (EHL) model for pneumatic spool valves. For an accurate estimation of the transient friction of this tribological sealing system, the surface topography of the cylindrical sealing counterfaces of the valve housings are measured and analyzed with an optical surface measurement instrument. Based on the surface topography data, tribological properties and flow factors of the system are derived. It has been found that the consideration of the surface topography has a significant influence on the simulation results of the EHL model, lowering the calculated friction force by up to 20 %.Item Open Access Modeling the pumping behavior of macroscopic lead structures on shaft counterfaces of rotary shaft seals(2023) Engelfried, Maximilian; Haffner, Georg; Baumann, Matthias; Bauer, FrankThe leak tightness of the sealing system rotary shaft seal is based on the formation of an active back-pumping effect of the sealing ring. Here, the sealing ring pumps the fluid in the sealing gap back into the housing. However, this active sealing mechanism is disturbed by so-called “lead structures”. Lead structures include all types of directional structures on the sealing counterface which create rotation-dependent axial fluid pumping. Lead-affected sealing counterfaces can thus cause leakage or insufficient lubrication of the sealing contact. To ensure leak tightness, lead must be avoided or tolerated. This article investigates how different structural characteristics of lead affect the amount of fluid pumped by the shaft surface. For this purpose, 26 shafts are subjected to surface analyzing methods and an experimental pumping rate test. The interaction of various geometric features of the lead structures and their combined effect on the pumping capacity is modeled based on the measured data. Appropriated correlation models are discussed and relationships between shaft lead and its pumping effect are shown. The aim is to estimate shaft pumping rates based on surface measurements in future. The results contribute to the derivation of measurable tolerance values for lead and to the prevention of leakage.Item Open Access Influence of protection lips on the frictional torque of rotary shaft seals(2024) Olbrich, Christoph; Feldmeth, Simon; Bauer, FrankRotary shaft seals are used to seal rotating machine parts. In most cases one single sealing lip (main lip) contacts the shaft and separates the fluid on one side from the environment on the other side. To prevent the entry of other fluids and or particles, seals with additional protection lips are used (two lips), especially in heavily contaminated environments. When the protection lip contacts the shaft, a vacuum can form between the main lip and the protection lip, leading to increased contact pressure and friction. The increased frictional torque generates more heat and leads to overheating in the contact area between the lip and the shaft. Test runs conducted on a friction torque test bench with various seal configurations confirm that the two lips influence each other. Higher frictional torques and contact temperatures occur, when the volume between the lips isn't vented. This shows the importance of venting.Item Open Access Assessment of the Lubricity of Grease‐Sealing Rotary Shaft Seals Based on Grease Properties(2022) Hahn, Susanne; Feldmeth, Simon; Bauer, FrankGrease‐lubricated sealing systems have an increased risk of starved lubrication. For this work, the lubricity of 23 greases in a rotary shaft sealing system was evaluated with a new test and evaluation method. The lubricity was then correlated with rheological and other grease properties. These grease properties are either available by the data sheet or can be measured with low effort. The results of the correlation allow a preselection of greases which are expected to lubricate rotary shaft seals well. This can support manufacturers and users in considering the lubrication of the sealing system early in the development process.Item Open Access Realitätsnahe Modellierung und Analyse der Verfügbarkeit von Produktionssystemen in Industrie 4.0(Stuttgart : Institut für Maschinenelemente, 2023) Long, Fei; Bertsche, Bernd (Prof. Dr.-Ing.)Die schnelle Verbreitung des Internets und die rasante Entwicklung der Logistik haben die Globalisierung und Internationalisierung beschleunigt. Durch die Entwicklung und Verbreitung moderner Technologien befindet sich die Industrie an einem Wendepunkt. Um seine internationale Führungsposition und seinen Wettbewerbsvorteil zu sichern, hat Deutschland die Strategie „Industrie 4.0“ umgesetzt. Daraufhin reagierte China mit der Strategie „Made in China 2025“ und Amerika mit „Strategy for American Leadership in Advanced Manufacturing“. Automatisierung, Digitalisierung und Globalisierung machen die Grenzen zwischen Herstellern und Kunden transparenter. Die Globalisierung ermöglicht es den Kunden, auf dem internationalen Markt problemlos eine Vielzahl von Produkten auszuwählen und die gewünschten Produkte mit vergleichbaren Eigenschaften, dem niedrigsten Preis und ausreichender Qualität zu finden. Kunden überzeugen nicht mehr nur die universellen Produkte, sondern auch die Produkte, die zu ihrer eigenen Persönlichkeit passen und ihre Individualität zeigen. Der Trend zur Personalisierung wird immer deutlicher. Darüber hinaus ermutigen die expandierenden sozialen Netzwerke und Online-Echtzeitnachrichten die Industrie, dem Feedback und den Meinungen der Kunden mehr Aufmerksamkeit zu schenken. Die Bedeutung der Kundenzufriedenheit und die Rolle der Kunden auf dem Markt nehmen deutlich zu. Vor dem Hintergrund der Globalisierung suchen die internationalen Wettbewerber nach neuen Strategien und Methoden, um wettbewerbsfähig zu bleiben. Verschiedene Maßnahmen zur Steigerung von Effizienz und Effektivität wurden untersucht und umgesetzt. Es wurden verschiedene Aspekte analysiert, um die Kundenzufriedenheit zu erhöhen und die Produktionskosten zu senken und damit die Rentabilität zu steigern. Durch die Anwendung der automatisierten Technik und Technologie wird der Automatisierungsgrad des industriellen Sektors erhöht und standardisiert. Der erhöhte Automatisierungsgrad und die zunehmende Digitalisierung ermöglichen es der Industrie, kundenspezifische Produkte herzustellen. Auch die Produktqualität kann gewährleistet werden. Um auf dem internationalen Markt Fuß zu fassen und internationale Kunden zu gewinnen, muss die Industrie die kundenspezifischen Anforderungen und Wünsche erfüllen. Daher entstand die Herausforderung, variantenreiche kundenspezifische Produkte in kleinen Losgrößen effizient zu produzieren. Um die Effizienz zu steigern, sollen neue Konzepte von Produktionssystemen in der Industrie 4.0 untersucht werden. In der Literatur werden vielseitige Produktionssysteme, digitale Produktion etc. vorgeschlagen, um dem Trend der Individualisierung und den zukünftigen Herausforderungen zu begegnen. Traditionelle Produktionssysteme basieren auf der Strategie der "Massenproduktion". Aufgrund der hohen Stückzahlen werden die Herstellungskosten gesenkt. Diese Produktionssysteme sind jedoch ineffizient, wenn es darum geht, personalisierte Produkte in kleinen Losgrößen herzustellen. Daher können sie die Anforderung der Individualisierung nicht erfüllen. Im Zukunftsforschungsprojekt Industrie 4.0 wurden neue Konzepte von Produktionssystemen vorgeschlagen. Kernlösung für die Erfüllung der Individualisierung ist die flexible und wandlungsfähige Produktion. Heute besteht die Notwendigkeit, das Konzept vor der Anwendung systematisch zu analysieren, um die möglichen Herausforderungen und Risiken zu untersuchen. Die Literatur hat sich mit dem Design und den Konzepten beschäftigt. Einige haben die vereinfachten Produktionssysteme modelliert. Viele Aspekte können jedoch nicht zusammen betrachtet werden. Es gibt noch keine Methode, um Produktionssysteme unter Berücksichtigung umfassender Aspekte systematisch zu modellieren und realistische, anwendungsreife Ergebnisse zu erhalten. Eine realitätsnahe Modellierung der Verfügbarkeit von Produktionssystemen in der Industrie 4.0 wird dann mögliche Fragestellungen zur Reduzierung von möglichen Verlusten, Schäden und Risiken untersuchen. Im Anschluss daran können konkrete Maßnahmen zur Optimierung der Produktionssysteme vorgeschlagen werden. Für die Auswahl einer geeigneten Methode zur Modellierung von Produktionssystemen in der Industrie 4.0 werden die Fähigkeiten der vorhandenen Methoden zur Modellierung der spezifischen Eigenschaften von Produktionssystemen in der Industrie 4.0 in Bezug auf Netzwerkfähigkeit, Kommunikation, künstliche Intelligenz und Anpassungsfähigkeit bewertet. Die Auswertungen zeigen, dass das Petrinetz für die Modellierung der Produktionssysteme in der Industrie 4.0 sehr gut geeignet ist. Das Hauptziel der Arbeit ist es, die Verfügbarkeit von Produktionssystemen in der Industrie 4.0 mit Petrinetz realistisch zu modellieren. Durch die Modellierung der Produktionssysteme können die möglichen Probleme im Konzept untersucht werden, um mögliche Verluste, Schäden und Risiken zu reduzieren. Anschließend kann eine konkrete Maßnahme zur Optimierung der Produktionssysteme vorgeschlagen werden.Item Open Access Zuverlässigkeitsanalyse neuartiger mechatronischer Systeme(Stuttgart : Institut für Maschinenelemente, 2021) Gröber, Jan; Bertsche, Bernd (Prof. Dr.-Ing.)Item Open Access Multiscale structural mechanics of rotary shaft seals : numerical studies and visual experiments(2023) Grün, Jeremias; Gohs, Marco; Bauer, FrankAlthough rotary shaft seals have been used successfully in many industrial applications for decades, their tribological behavior is still not completely understood. In-depth knowledge of the structural mechanics is essential for the design and optimization of such sealing systems. High complexity results from the multiscale interactions in the tribological system rotary shaft seal. Large macroscopic deformations occur due to the hyperelastic material behavior of elastomers coupled with microscopic tangential distortions of the sealing edge surface in the contact area. This paper includes both numerical and experimental studies on the tribological behavior of rotary shaft seals. A multiscale finite element model provides the simulation of the macroscopic deformations and the microscopic displacements. A test rig equipped with a hollow glass shaft enables in situ visual contact analyses, qualitative determinations of pressure distributions and quantitative measurements of elastomer surface distortions. The optical phenomenon of frustrated total internal reflection enables qualitative evaluations of the pressure distribution. Particle image velocimetry (PIV) is employed to quantify the tangential distortions. The test rig enables the measurement of the friction torque with the same configuration. The results of the numerical and experimental investigations for the radial load, friction torque and tangential distortions are compared and discussed. This serves to validate the simulation methods and the correlation of the measured parameters. This finally results in a solid and validated basis for further tribological investigations of rotary shaft seals.Item Open Access 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, BerndThe 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%.