Browsing by Author "Dazer, Martin"

Now showing 1 - 8 of 8

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 Peter
Modern 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.
Open Access
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.
Open Access
Method for the development of a functional adaptive simulation model for designing robust products
(2014) Kemmler, Stefan; Dazer, Martin; Leopold, Tobias; Bertsche, Bernd
Products have to ensure their function under the inuence of internal and external noise factors in order to remain competitive in the current market. Therefore the step of designing robust products should be integrated in early stages of the Product Development Process (PDP). Robust products are developed using the Robust Design Method SMART (Systematic Method for Axiomatic Robustness-Testing). Thus far, SMART was applied and veri ed based on a simple mechanical machine element. In this paper, the method will be applied to a complex technical system. Additionally, the confict of aiming between the high e orts and the level of detail in the creation of a simulation model are discussed. This confict is brought about owing to the complex functionality of the design. In order to solve the conict, an approach is given for the creation of an adjusted simulation model. Short simulation times are an advantage for the analysis of parameters regarding robustness. The adaptive simulation model discussed in this paper is based on a exible and equation-based model, which is extended with local -structural-mechanical SUB-models for a more detailed analysis. This approach o ers the option of obtaining rst insights about the functionality of the product and the opportunity to complement the simulation model iteratively for the following design phases. This approach complements SMART on the one hand in the simulative design of robust design parameters and, on the other hand, in their reliability prediction in both the Parameter Design and Tolerance Design phase.
Open Access
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.
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, 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%.
Open Access
Statistical power analysis in reliability demonstration testing : the probability of test success
(2022) Grundler, Alexander; Dazer, Martin; Herzig, Thomas
Statistical 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.
Open Access
Vibration analysis for early pitting detection during operation
(2024) Häderle, Philipp; Merkle, Lukas; Dazer, Martin
The economic efficiency of machinery operation is significantly impacted by maintenance strategies. In the realm of condition-based or predictive maintenance strategies, the early detection of fatigue-induced damages is crucial. Therefore, this study focuses on the early detection of pitting damages during operation. Experimental investigations are conducted on a test gearbox acquiring acceleration data for different sizes of pitting damages under diverse operating conditions. A successful detection of the pitting damages during operation is achieved at a very early stage of progression, with a minimum size of 0.41% of an active tooth flank area. The utilization of design of experiments techniques facilitates the identification of factors influencing the detectability of pitting damages. The obtained results are analysed to elucidate the physical basis for the reliable detection of pitting damages across diverse operating conditions.
Open Access
Zuverlässigkeitstestplanung mit Berücksichtigung von Vorwissen aus stochastischen Lebensdauerberechnungen
(Stuttgart : Institut für Maschinenelemente, 2019) Dazer, Martin; Bertsche, Bernd (Prof. Dr.-Ing.)
Diese Arbeit widmet sich zum einen dem Ziel einer individuell anforderungsgerechten Zuverlässigkeitstestplanung im Zielkonflikt zwischen statistischer Genauigkeit, Testkosten und -zeit und zum anderen der Berechnung des dafür benötigten Vorwissens über das Produktausfallverhalten. Bei der Lebensdauer eines technischen Systems handelt es sich um eine Zufallsvariable, die Testingenieure in Kombination mit vielen möglichen Teststrategien und Randbedingungen bei der Planung von Zuverlässigkeitstests vor eine Herausforderung stellt. In einem Zuverlässigkeits-DOE werden die End-of-Life Tests und die ausfallfreien Tests im Spannungsfeld von Genauigkeit, Kosten und Zeit untersucht. Die Resultate zeigen die besten Anwendungsbereiche der jeweiligen Teststrategie und können für die Planung von Zuverlässigkeitstests mit unterschiedlichen Anforderungen verwendet werden. Ausfallfreie Tests, wie der Success Run, benötigen eine hohe Produktüberdimensionierung, um passable Erfolgsaussichten zu garantieren. Ausfallbasierte Teststrategien dagegen, sind zwar häufig kostenintensiver, dafür aber universeller einsetzbar. Durch die eingeführte Normierung aller zeitabhängigen Größen lässt sich das Planungskonzept auf beliebige Produkte übertragen. Das produktspezifische Vorwissen wird im Rahmen dieser Arbeit nicht aus Felddaten oder Vorgängerprodukten gewonnen, sondern mit einem Ansatz zur stochastischen Lebensdauerberechnung ermittelt. Während konventionelle Lebensdauerberechnungskonzepte versuchen, die Streuung von Lebensdauerdaten durch konservative Annahmen und Sicherheitsfaktoren zu kompensieren, wird in diesem Konzept die Streuung zur realitätsnahen Berechnung der Lebensdauer berücksichtigt. Systematische Streuungen der Materialeigenschaften von Toleranzen und der äußeren Lasteinwirkung werden statistisch modelliert und für die Berechnung der Verteilungsfunktionen von Belastung und Belastbarkeit genutzt. Aus deren Überlappung werden die stochastischen Lebensdauerdaten berechnet. Durch Weibullanalyse resultieren die berechneten Lebensdauerdaten im produktspezifischen Ausfallverhalten. Die Anwendbarkeit der stochastischen Lebensdauerberechnung und der daraus abgeleiteten optimalen Testplanung werden anhand eines Nutzfahrzeugbremssattels für strukturmechanisches Versagen unter Beweis gestellt.