Technische Universität Ilmenau

Previous studies have shown that the wear of FSW tools is influenced by process parameters as well as the relation between tool material and workpiece material. However, the effect of tool geometry and the associated material flow on geometrically induced tool wear has not yet been addressed in the existing literature. Against this background, the study systematically investigates the wear behaviour of various shoulder (cylindrical, scroll) and probe geometries (cylindrical, conical, threaded, threaded with flats) as a function of material flow during friction stir welding of the aluminium alloy AA-6060 T66 with a thickness of 5 mm. The wear behaviour was investigated over weld lengths of up to 500 m at a rotational speed of 2000 rpm, a welding speed of 0.5 m/min, and an axial force of 5.5 kN. The study revealed that both horizontal and vertical material flow contribute to wear in the transition zone between the shoulder and the probe. Furthermore, the results showed that reducing tool complexity can significantly reduce tool wear. The experiments were carried out using a force-controlled robotic welding system from Grenzebach Maschinenbau GmbH.

Bimetallic sulfide, with its high theoretical capacity, is one of the preferred anodes for high-energy-density potassium ion batteries (PIBs). However, its low conductivity, high volume expansion, and slow electrode reaction kinetics have limited its practical application. This study developed a freeze-drying-calcination coupled strategy to fabricate a porous nitrogen-doped carbon matrix embedded with Ni3Sn2S2 bimetallic sulfide nanoparticles (Ni3Sn2S2@NC). The enhanced electrochemical kinetics are primarily attributed to the strong electronic interactions between Ni and Sn atoms within the hexagonal crystalline framework. The reduced adsorption energy of potassium ions (K+) and the significantly enhanced diffusion coefficient (∼2.88×10-10cm2/s) are attributed to the electronic coupling effect within the bimetallic sulfide phase. The electronic interaction effectively promotes both K+ transport and electron transfer during charge/discharge cycles, thereby delivering the Ni3Sn2S2@NC composite with good specific capacity (∼667.7mAh/g at 0.1A/g) and ultralong cycling stability at high rates (∼170.6mAh/g under 2.0A/g after 2000cycles). When assembled with perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) as the cathode in PTCDA||KFSI-DME||Ni3Sn2S2@NC, the device achieves a high energy density of ∼226Wh/kg with stable cycling performance. This work introduces a valuable perspective for the kinetic engineering of high-rate electrodes through intrinsic electronic structure modulation.

Near-wall parasitic convective flow is a known phenomenon in stratified thermal energy storages (STES) leading to stratification degradation and exergy destruction. While many features of convective flow in STES have been studied previously, the influence of the storage wall thickness on the near-wall flow, heat transfer and exergy destruction has not yet been addressed. Temperature, heat flux density and optical velocity measurements were carried out in a model experiment for STES at different wall thicknesses. It is found that at a thicker wall, the stratification degradation and the exergy destruction is faster than at a lower wall thickness, caused by an enhanced heat transfer between the storage wall and storage fluid. As time proceeds, the temperature distribution in the storage tank and exergy efficiencies converge for both wall thicknesses. In the flow field, this is reflected in higher maximum velocities at the thicker wall. Furthermore, velocity gradients are larger in this case because of thinner boundary layers. Transient flow fluctuations appear to be stronger at the thicker wall as shown by higher amplitudes and broader spectra of the velocity oscillations. Additionally, the occurrence of maxima in the spectra of the fluctuations at the thicker wall which do not appear at the thinner wall may hint at differences in the transition to turbulence caused by the different wall thicknesses. • Higher parasitic heat transfer in stratified thermal storages with thicker walls. • Thermal stratification and exergy degrade faster at thicker storage walls. • Parasitic near-wall flow is faster at thicker storage walls. • Stronger velocity fluctuations in near-wall flow at thicker walls. • Storage wall thickness influences transition of near-wall flow to turbulence.

Conventional soldering processes in microsystem packaging often induce critical thermo-mechanical stresses, caused by mismatches in the coefficients of thermal expansion (CTEs) of materials such as silicon dies, molding compounds, and substrates. Reactive multilayer systems (RMS) offer a localized heat source that can significantly reduce such stresses, thereby enabling the bonding of heat-sensitive components. To expand the technological possibilities in fabricating heterogeneous microsystems, this study investigates RMS-based bonding of low temperature co-fired ceramics (LTCC) substrates. Two experimental series were conducted. In the first, both reactive foils and deposited RMS structures were used to bond relatively large chips measuring 10 mm x 10 mm under a bonding pressure of 1.5 MPa, with ignition triggered either thermally (up to 350 °C) or resistively, supported by a temperature of 200 °C. In the second series, smaller chips measuring 3 mm x 3 mm were bonded using a reactive foil to achieve a bonding pressure of 100 MPa. Here, ignition was triggered by an electrical spark, supported by a temperature of 160 °C. The bonding interfaces and metallurgical reactions were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The results reveal significant differences between bonding LTCC substrates using prefabricated reactive foils and deposited RMS structures: prefabricated foils generate higher peak temperatures, often exceeding the thermal limits of the metallization system, whereas deposited RMS structures produce lower peak temperatures and offer better compatibility due to the ability to tailor specific parameters.

Thermal spraying is an established technology in the coating industry offering high deposition rates and a broad range of processable materials. In addressing the scale‐up of proton exchange membrane water electrolyzers, thermal spraying presents a promising solution for cell component production, despite several challenges that need to be overcome: Firstly, the substrate material is typically characterized by a relatively thin thickness and complex geometries. Secondly, the coatings often exhibit process‐related roughness. This study demonstrates that this rough coating can be beneficial in enhancing the connection between the bipolar plate (BPP) and the porous transport layer (PTL). The developed coldgas sprayed BPP–PTL coating system was tested in an electrochemical accelerated stress test (AST) as well as in an intermittent long‐term single‐cell test. The results indicate that the BPP–PTL coating system is electrochemically stable during the AST, and subsequent measurements of electrical resistance confirm that the interface is preserved from severe oxidation. In the long‐term test, it was demonstrated that a single cell could be operated with a cell voltage of U cell = 1.9 V at a current density of i = 2 A/cm 2 over 3 months. For the first time, a fully cold gas sprayed BPP–PTL coating system has been tested in a single‐cell test for proton exchange membrane water electrolysis applications.

Accurately quantifying phenological dynamics in vegetated systems is essential as the timing of seasonal plant activity drives water, nutrient, and carbon cycling, but it is also one of the processes most disrupted by environmental changes. Land Surface Models (LSMs) integrate phenology to represent these feedback loops between terrestrial ecosystem functioning and the global climate, but their performance relies on the type and quality of data used for evaluation. Traditional phenological datasets span from point observations (e.g. leaf-on, leaf-off dates), to high resolution ground measurements of greenness and productivity (e.g. GCC), to time series of remote sensed vegetation indexes (e.g. EVI). However, each observation type measures distinct ecosystem properties, and no single data source provides both the temporal and spatial coverage needed to fully represent phenology at regional and global scales. Here we integrate growing season metrics for 89 European temperate forests sites across scales, derived from eddy covariance measurements, phenocam time series, and MODIS remote sensed vegetation indexes. For the first time, we incorporate phenological dates derived from citizen science, drawing data from the Flora Incognita app, GBIF and iNaturalist, to calculate species-specific annual observation curves for 11 characteristic understory species spanning 2020-2024. By combining data streams, we evaluate the advantages and limitations of each for data-model integration, and further assess the potential of opportunistic species observations to scale up non-overlapping phenological data to ecosystems. By simulating the same sites with the QUINCY LSM we also investigate the role of process-based models to bridge between datasets, as the processes underlying growing season that they provide aid the interpretation of differences between observed phenological metrics. This work highlights the potential of integrating multi-scale phenological information, including underutilised contribution from citizen science, to improve our understanding of phenological dynamics. We additionally explore how LSMs can be leveraged together with data for ecological insight beyond evaluation, moving away from the traditional one-way relationship between data and models.

Ultra-short pulse laser radiation (USP) is applied in subtractive high-precision laser material processing, whereby controlled ablation with minimal thermal damage to the components is achieved. In this study, the laser radiation is employed in the context of additive manufacturing, specifically laser-based powder bed fusion (PBF-LB) of borosilicate glass powder materials. The investigations are focused on a comprehensive analysis of the key process parameters, in relation to the material-specific properties of the glass powder. A minimum process temperature of TP = 800 °C is determined to be necessary for the manufacturing of dimensionally stable and dense components. Preheating the powder bed to Tpowder = 400 °C reduces temperature variations between the powder bed and the interaction zone, thereby enabling local heat accumulation and preventing crack formation. High-temperature microscopy identified material-specific viscosity fixed points that align closely with experimentally determined process windows, thus aiding in process control. Cross-sectional analyses of the components reveal the feasibility of achieving consolidated, closed-porosity structures with component densities ρ > 90%. An increase in component density correlates with reduced dimensional accuracy due to the formation of a consolidation zone affecting thermal conduction and powder adhesion. This indicates the capability to manufacture components with rotationally symmetric cavities of up to d = 0.4 mm at a density of ρ = 85%. The study demonstrates the potential of the PBF-USP-LB process for the fabrication of high-density glass components and provides fundamental insights into the underlying process mechanisms that support further advancement of this innovative manufacturing technology.

Anode‐free concept can fully utilize the unmatched theoretical specific energy of lithium‐metal battery. However, the low stability of the anode interface, including both the morphology of Li metal and the solid electrolyte interphase (SEI), hinders the practical battery implementation and creates safety concerns. In this work, sulfolane‐based localized high‐concentration electrolyte (LHCE) is applied as a sustainable and applicable electrolyte for anode‐free Li‐metal batteries (AFLMBs). The effects of important factors, including type of anode current collector, electrolyte properties, and cycling conditions, are explored in terms of clarifying their impact on the structural and functional properties of LFP‖Cu cells. Flammability tests indicate that the electrolyte is nonflammable by direct ignition under the applied conditions, which is highly beneficial for the safety and sustainability of the AFLMB. The performance of SL‐based LHCE is tested for Li plating–stripping reaction on Cu‐engineered substrates, where the microporous Cu substrates display major improvement, which can be attributed to their enlarged active surface area and open and highly interconnected porous structure. The influence of the key operation parameters, state of charge, depth of discharge, and current density is explored, and useful correlations of these factors with the anode structural properties and battery cycling stability are established.

Article 2025 Reisensburg conference on fundamentals of networked and cognitive systems in measurement and automation was published on March 1, 2026 in the journal at - Automatisierungstechnik (volume 74, issue 3).