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Najeeb, Mussab; Schwalbe, Ulf
State of health estimation for second life lithium-ion batteries: indicators and considerations. - In: IEEE Xplore digital library, ISSN 2473-2001, (2024), insges. 6 S.

This study aims to provide valuable insights into state of health estimation of second-life lithium-ion batteries in stationary energy storage systems by conducting an analytical examination of key technical indicators and considerations. By considering these factors, we can enhance our understanding of the estimation process and make informed decisions regarding the conditions of utilizing these batteries in their second life. The approach, presented in this paper, focuses on two main aspects. Firstly, it takes into account the unique characteristics of these batteries, which exhibit different responses to operational factors compared to their initial life cycle in electrical vehicles. Secondly, it considers monitoring conditions of stationary storage systems to develop an enhanced monitoring system which leads to an efficient performance of batteries in their second-life. By addressing these aspects, we aim to optimize the utilization of second-life batteries in stationary storage systems and ensure their reliable operation. This methodology, which utilizes Kalman filter and empirically derived data, has demonstrated significantly improved reliability and accuracy compared to other methodologies. By leveraging Kalman filter, we were able to enhance the estimation process and achieve a more precise estimation of state of health in stationary energy storage systems.

Neitzel, Benedikt; Puch, Florian
Formation of voids due to transitions in permeability and cavity diameter during resin injection processes. - In: AIP conference proceedings, ISSN 1551-7616, Bd. 3012 (2024), 1, 020013, S. 020013-1-020013-9

The specific mechanical properties of fiber reinforced composite components are unmatched, considering their low weight. To optimize the lightweight potential of fiber reinforced composites, fiber volume contents have to be maximized and imperfections must be eliminated. However, during the production of fiber reinforced composite laminates via resin injection processes, the formation of microscopic voids is nearly inevitable. Even low amounts of imperfections can cause significant deteriorations in the mechanical properties of the material. To reduce the number of voids inside composite components, understanding the formation and transport of voids is essential. Numerous renowned models describe said formation of voids in dependence of local flow front conditions during the impregnation of textile preforms with thermoset resins. State of the art are models emphasizing the formation of meso-and microvoids in dependence of the modified capillary number. These models show plausible correlations when applied to unidirectional preforms or fabrics with constant permeability along the direction of flow. However, the formation of voids remains to be investigated at points of transitioning permeability, such as alterations in the setup of layers or abruptly changing cavity diameters. To expand the applicability of the existing models onto preforms with local changes in permeability, an experimental setup for gradually increasing cavity diameter and varying layer setup is introduced. A planar mold with three increasing levels of cavity height is used to induce changes in permeability. The rate of change in permeability is controlled by defining the slope between each level. In this study, injection pressure as well as flow front velocity were optically traced, and material data was measured. Resulting local void volume contents were quantified by calcination. It is demonstrated how alterations of diameter and layup take effect on the resulting local porosity. The observed impact on void formation is put in context to changes in tow permeability due to local differences in fiber volume content. By including the slope dependent rate of change in tow permeability into the existing model for calculation of void formation by GUEROULT ET AL., the accuracy of the model can be increased. Comparing the unaltered model to experimental results, the deviations between calculations and measurements were diminished when using the newly introduced factors. Although the error of prediction is being significantly reduced, calculations are still flawed since additional effects like overflow at level edges need to be considered. This discourse is meant to administer a starting point for considering rates of change in tow permeability into the commonly established use of shape factors of models of void formation.

Langgemach, Wiebke; Rädlein, Edda
A new method for evaluating the influence of coatings on the strength and fatigue behavior of flexible glass. - In: Journal of electronic materials, ISSN 1543-186X, Bd. 53 (2024), 8, S. 4390-4400

Flexible glass is an interesting substrate for a variety of displays, especially bendable or foldable ones, as it shows excellent surface properties and appealing haptics. With the necessary skill, flexible glass can be coated with thin films of different functionality, such as electrical or optical thin films, using plasma processes. In displays, thin film coatings such as transparent conductive electrodes and/or antireflective layer stacks are of major importance. Despite its attractive surface properties, however, flexible glass is still brittle, and its strength must be examined and monitored during any functionalization process, especially with regard to the fatigue behaviour. Currently, specific setups for cyclic fatigue testing of coated flexible glass are not available. Therefore, a new test method is presented herein for easy-to-handle rapid strength and fatigue testing using an endurance testing machine. This method overcomes two issues with the commonly used two-point bending test: the correct insertion of specimens is much easier, and both strength and fatigue testing using the same setup are now possible. Finite element method (FEM) simulation outcomes and first experimental simple fracture tests show that results comparable to those with a two-point bending test setup can be achieved with less effort. This makes it possible to analyze the fracture behaviour of flexible glass under cyclic loading and to evaluate the influence of thin film stress and other coating properties on its performance.

Najeeb, Mussab; Schwalbe, Ulf; Herget, Mathias
Improved approach for online monitoring of second life lithium-ion batteries to optimize the performance in stationary storage systems. - In: 2023 14th International Renewable Energy Congress (IREC), (2024), insges. 6 S.

Monitoring lithium-ion batteries in their second life is of great importance when using them in stationary storage systems for grid support or in any other energy system, due to the expected different behavior and operational conditions in their second life compared to their first life. The idea of this study based on the fact that each estimation method has its advantages and drawbacks depending on the application in which the batteries will be used, and that monitoring batteries in their second life required to be integrated with the battery management system to balance cells, optimize performance, and prevent overheating. The contribution of our study can be summarized in the integration of specific methods, aiming to benefit from most of their advantages and neutralizing their drawbacks as much as possible to provide more accurate and reliable online monitoring of batteries. The combination presented in this study, consisting, for state of charge estimation, of an artificial neural network and an Unscented Kalman Filter with adjusting the filtering process using Coulomb counting, and Kalman Filter for state of health estimation, showed much better reliability and accuracy than if each method was used alone. This combination has been trained and adjusted using empirical data of second-life batteries, extracted from used electric vehicle battery bank, to obtain the best possible performance, considering the specificity of these batteries in terms of operating voltage range, lower current ratio, and other parameters.

Wöste, Andreas; Hergert, Germann; Silies, Martin; Wang, Dong; Groß, Petra; Lienau, Christoph
Photon-induced near-field interaction in ultrafast point-projection electron microscopy. - In: CLEO, (2023), JTu2A.133, insges. 2 S.

We report the first study of ultrafast, slow (<100 eV) free electron wavepackets with optical near fields. This interaction is probed in a point-projection-microscope with 50fs temporal resolution using strongly localized fields around a nano-antenna.

Günther-Müller, Sarah; Strehle, Steffen
Dielectrophoretic actuation in a microfluidic system with coplanar electrode configuration. - In: IEEE BioSensors 2023 conference proceedings, (2023), insges. 4 S.

This paper presents the analysis of the motion characteristics of droplet transport induced by liquid dielectrophoresis (LDEP). Hereby, a novel fluidic system is demonstrated, which enables droplet transport across a planar surface using a coplanar electrode configuration with adjacent electrodes. The droplet displacement is analyzed by high-speed video imaging and digital image processing. It is demonstrated that droplet motion can be initiated through simplified electrode geometries and the experimental results provide deeper insights into LDEP driven droplet manipulation.

Glaser, Marcus; Matthes, Sebastian; Riegler, Sascha Sebastian; Hildebrand, Jörg; Bergmann, Jean Pierre; Schaaf, Peter; Gallino, Isabella
Characterization of plastic-metal hybrid composites joined by means of reactive Al/Ni multilayers - evaluation of occurring thermal regime. - In: Engineering for a changing world, (2023), 4.3.056, S. 1-16

Present challenges in material science and joining technology are ever more subject to the desire for lightweight construction and engineering. Plastic-metal composites are suitable material combinations but also require the development and investigation of appropriate joining technologies. A particularly promising approach is the application of reactive multilayer foils. As an innovative method, these foils provide the possibility of flexible and low-distortion joining of dissimilar materials. The underlying reaction mechanism offers fast exothermic reaction propagation with well-known exothermic power output while the energy source is introduced directly into the joining zone. In this work, hybrid lap joints between semi-crystalline polyamide 6 and structured austenitic stainless steel X5CrNi18-10 were joined using reactive Al/Ni multilayer foils. The self-propagating reaction provides immediate temperatures that are well above the melting point of used plastic but decays rapidly after only a few milliseconds. To support ongoing investigations regarding composite formation, analysis of occurring thermal regime is in the focus of this work. Conducted experiments are supported by accompanying thermal simulation in ANSYS Workbench. Besides the estimation regarding sensitivity of thermal material parameters the evaluation of formed melting zone and resulting thermally influenced area is a central topic.

Hiller, Benedikt T.; Rennert, Mirko; Nase, Michael
Comparison of the properties of biogenic wine by-products stabilized biocomposites compounded with a miniaturized single-screw extruder and a co-rotating twin-screw extruder. - In: Engineering for a changing world, (2023), 2.3.010, S. 1-13

Bioplastics research is hindered by high material prices and limited availability of biopolymers. For conventional compounding, even on lab-scale, large quantities of material are required. In this study, an alternative process for compounding biocomposites was evaluated to investigate the potential of wine-derived biogenic by-products as functional fillers. Formulations based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and wine grape pomace (WP) with filler contents up to 10 wt.-% were prepared. The materials were processed with a modified miniaturized single-screw extruder (MSE) and compared to a lab-scale twin-screw extruder (TSE). Thermal and rheological properties of the materials were determined using GPC, MFR, DSC, TGA and OIT. The mixing quality of both extruders was evaluated by optical microscopy imaging. The results revealed that the MSE represents an efficient alternative for research purposes, but differences in the dominant degradation mechanisms during processing must be considered. Thermal analysis showed that WP successfully suppressed the thermo-oxidative degradation of PHBV.

Mohammadkarimi, Shiva; Neitzel, Benedikt; Puch, Florian
Influence of the recycling process parameters on CFRTP waste properties. - In: Engineering for a changing world, (2023), 2.3.002, S. 1-12

Nowadays, the combination of continuous fibers and thermoplastic polymers as the matrix to continuous fiber-reinforced thermoplastics (CFRTP) is receiving increasing attention due to their potential advantages such as excellent weight-specific mechanical properties, short cycle times, storability, repeated meltability, good formability and the use of alternative joining processes enabling automated large volume manufacturing processes which allow various applications in different industries including transportation, construction among others. As the production rate of these materials increases, the amount of waste for disposal increases, for which recycling strategies need to be established to ensure the sustainability of CFRTP. Hence, these recycling strategies must be developed and evaluated economically and ecologically to close the loop and achieve a circular economy to process recycled fiber-reinforced pellets from CFRTP waste to valuable products e.g., by injection molding. This study presents a mechanical recycling approach from CFRTP waste to injection molded test specimens and evaluates the impact of the individual recycling steps along the recycling chain on the fiber length as the fiber length is detrimental to the resulting mechanical properties. First, the CFRTP waste processability is investigated and conditions for size reduction by cutting and shredding into feedstock for extrusion are defined. Second, fiber-reinforced pellets are produced by twin-screw extrusion. The fiber volume content and the process parameters screw speed and temperature during compounding are varied and the influence of these parameters on the fiber length is determined. Third, the extruded pellets are further processed by injection molding. Here, the influence of screw speed, back pressure, and processing temperature as well as the initial fiber length in the extruded granules on the resulting properties is investigated. Quantitative correlations between material properties and processing parameters are presented and suggestions for gentle processing during recycling are given.

Puch, Florian; Richter, Bastian
Influence of the processing on the properties of continuous fiber reinforced thermoplastic sheets prepared by extrusion. - In: AIP conference proceedings, ISSN 1551-7616, Bd. 2884 (2023), 1, 050005, S. 050005-1-050005-14

Continuous fiber reinforced thermoplastics (CFRT) are composite materials consisting of continuous fibers and a thermoplastic matrix and offer outstanding mechanical properties, low densities, short cycle times and recyclability. CFRT can be classified into unidirectional tapes and sheets utilizing various semi-finished textiles as reinforcement. CFRT sheets are of interest for area measured products or multiaxial loads. Various discontinuous and semi-continuous methods to prepare CFRP sheets are described in the literature. All these methods either feature high cycle times or high investment costs and require double melting of the polymer, e.g., first to produce a polymer film and second to produce the CFRT sheet. An energy efficient alternative to produce CFRT sheets is extrusion, which allows to spare one melting step. A twin-screw extruder melts the polymer, which is then conveyed by a melt pump to the film extrusion dies and applied to both sides of the semi-finished textile, which is wetted and consolidated using a calendar. Due to the high melt viscosity and the line load at the calendar the major challenge is to achieve full void-free impregnation of the semi-finished textile. The mechanical properties of a CFRT sheet are determined by fiber and void volume content. Hence, the influence of the processing conditions on the fiber and void volume content as well as the mechanical properties were examined applying a parametric study of the die temperature, the haul-off speed, and the gap between the calendar rolls. The properties of the extruded CFRT sheets were compared to compression molded sheets. The fiber volume content was directly adjusted by the haul-off speed and the extruder throughput. An increasing die temperature lowers the melt viscosity and results in an increased fiber volume content. Scanning electron microscopy shows complete macro impregnation between the fiber bundles but not completely wetted individual filaments within fiber bundles.