07 Fakultät Konstruktions-, Produktions- und Fahrzeugtechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/8
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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 Enhanced scaling of material removal rate with high surface quality through combined laser processes(2023) Buser, Matthias; Hofele, Markus; Menold, Tobias; Riegel, Harald; Michalowski, AndreasAbstractIn the field of ultrashort pulse laser processing, the effective utilization of average power provided by todays laser systems presents an almost unsolvable challenge. This study aims to address this challenge in the context of laser volume ablation. We propose a solution for utilization of high average power while producing a high-quality finish, even when starting from arbitrary surfaces. The approach combines closed loop laser volume ablation, laser cleaning and laser polishing in a subsequent process strategy. The closed loop approach enables ablative laser processes to be used to produce precise target geometries and surfaces, even if the initial geometry of the component is very different from the target geometry. One application example is the post-processing of components manufactured using additive processes such as laser powder bed fusion. Therefore, we demonstrate automated removal of support structures and finishing of a sample made of AlSi10Mg material by laser powder bed fusion. The combination of laser ablation and laser polishing made it possible to significantly increase the productivity of the post-processing and achieving a surface roughness of Ra = 0.3 µm.Item Open Access Dielectric properties of PEEK/PEI blends as substrate material in high-frequency circuit board applications(2024) Scherzer, Tim; Wolf, Marius; Werum, Kai; Ruckdäschel, Holger; Eberhardt, Wolfgang; Zimmermann, AndréSubstrate materials for printed circuit boards must meet ever-increasing requirements to keep up with electronics technology development. Especially in the field of high-frequency applications such as radar and cellular broadcasting, low permittivity and the dielectric loss factor are key material parameters. In this work, the dielectric properties of a high-temperature, thermoplastic PEEK/PEI blend system are investigated at frequencies of 5 and 10 GHz under dried and ambient conditions. This material blend, modified with a suitable filler system, is capable of being used in the laser direct structuring (LDS) process. It is revealed that the degree of crystallinity of neat PEEK has a notable influence on the dielectric properties, as well as the PEEK phase structure in the blend system developed through annealing. This phenomenon can in turn be exploited to minimize permittivity values at 30 to 40 wt.-% PEI in the blend, even taking into account the water uptake present in thermoplastics. The dielectric loss follows a linear mixing rule over the blend range, which proved to be true also for PEEK/PEI LDS compounds.