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Paper des Monats
- ja (39)
Low transformation temperature (LTT) welding consumables are an innovative approach to reduce tensile residual stress in weld seams and the surrounding heat affected zone (HAZ). The reduced tensile stress can lead to an improvement in fatigue strength of welded components. LTT alloys are characterized by a chemical composition which reduce the martensite start temperature (Ms) close to room temperature. This article focuses on a hybrid use of LTT filler metals, where the LTT filler is applied as an additional layer to conventional welds on fatigue-critical spots. Conventional gas metal arc welded longitudinal stiffeners are used as specimens. At the face ends of the stiffeners, a second LTT layer was added with various modifications in weld shapes. These different shapes were achieved by changing the welding parameters such as welding speed and offset to the first layer. These samples were used to analyze shape, dilution, resulting Ms, residual stress and fatigue strength. The dilatometer verified Ms and dilution did not change significant, although the area of the 2nd LTT weld seam was varying clear with each modification. However, the weld modification had a significant effect on the residual stress state and the fatigue strength. The X-ray determined residual stress in the HAZ became lower when the weld toe of the LTT layer was further away from the stiffener. All samples with LTT weld exhibit significantly higher fatigue strength values than conventionally single and double-layer welded samples. The lower the residual stress at weld toe, the higher the fatigue strength. The results show that on the one hand LTT filler metals increase the fatigue strength, and on the other hand the impact of LTT fillers materials is not restricted to the dilution and Ms, the shape of the weld seam must also be considered.
Low Transformation Temperature (LTT) Schweißzusätze erzeugen während der Abkühlung Druckeigenspannungen in die Schweißnaht und Wärmeeinflusszone durch eine Volumenexpansion, wodurch die Ermüdungsfestigkeit erhöht werden kann. Um das Potential dieser neuartigen Schweißzusätze besser zu quantifizieren, wurden konventionelle Längssteifen als Probenkörper verwendet, welche an den Stirnseiten mit einer LTT-Zusatznaht geschweißt wurden. Durch Variation der Schweißparameter konnten unterschiedliche Nahtformen realisiert werden. Es konnte, je nach Nahtausführung, eine Erhöhung der Ermüdungsfestigkeit bei 2 Millionen Lastwechseln von 140% festgestellt werden. Somit sind LTT-Zusätze grundsätzlich geeignet, um die Ermüdungsfestigkeit zu erhöhen. Weiterhin wurde festgestellt, dass das Reparaturschweißen mit LTT Schweißzusätzen als Decklage ebenfalls zu einem deutlichen Ermüdungsfestigkeitsanstieg führte.
This work presents the design of air-stable core–shell zero-valent iron–nickel nanofilaments supported on silica and zeolite, developed to overcome the oxidation limitations of nano zero-valent iron in environmental catalysis. The nanofilaments feature ∼ 100 nm iron–nickel cores surrounded by ultrafine iron-rich threads embedded with aluminates and silicates, originating from partial support dissolution during synthesis. By varying the iron reduction time, three catalysts were prepared: one on silica reduced for 30 min, and two on zeolite reduced for 30 and 15 min. They were thoroughly characterized using nitrogen physisorption, X-ray diffraction, electron microscopy with elemental analysis, Mössbauer spectroscopy, and small-angle X-ray scattering. The zeolite-supported catalyst reduced for 15 min showed the highest activity for hexavalent chromium reduction (rate constant 8.054 min−1), attributed to a higher fraction of reactive iron–nickel phases formed under shorter reduction. Its tailored core–shell structure improves air stability and surface reactivity, highlighting its potential as a next-generation zero-valent iron nanocatalyst for aqueous remediation
Probing smartphone-based photogrammetry for part profiling in wire arc directed energy deposition
(2025)
Fast dynamic part profiling during wire arc directed energy deposition (DED-Arc) is required to maintain the dimensional consistency of the fabricated part as it is printed over several overlapped tracks and successive layers. The metrology methods such as laser scanning, though accurate, are costly and less flexible for monitoring of layer-wise deposition. Photogrammetry is an optical measurement technique to reconstruct a 3D geometry using a series of 2D images in different orientations to ensure complete coverage. We propose here a novel attempt for rapid dimensioning of the deposit geometry using smartphone-based photogrammetry for wire arc directed energy deposition (DED-Arc). The recorded images from multiple viewpoints are used for feature extraction and matching and triangulation-based 3D reconstruction of the deposit geometry using open-source software. The reconstructed deposit surface is compared with the original CAD geometry to compare the dimensional consistency of parts during the DED-Arc process. Experimental validation is performed on both simple (cuboid) and complex (hollow cylindrical) aluminum geometries, as well as a steel deposit against laser scanning data. The results demonstrate that the smartphone-based photogrammetry can capture the layer-wise geometry variations with the maximum height deviations well within 15% of the laser scan measurements. Although reconstruction and post-processing times are slightly longer in photogrammetry, the approach provides a flexible, accessible, and cost-effective alternative for part profile monitoring.
In this presentation, the battery and cell test center of BAM is introduced to the Berlin Motion Lab. Points of intersection are identified, and interested students are familiarized with BAM’s research priorities in the field of batteries. The aim is to foster interaction and to inspire young researchers to engage with technologically relevant topics.
The weld pool and keyhole geometries are critical characteristics in evaluating the stability of the high-power laser beam welding (LBW) process and determining the resultant weld quality. However, obtaining these data through experimental or numerical methods remains challenging due to the difficulties in experimental measurements and the high computational demands of numerical modelling. This paper presents a physics-informed generative approach for predicting weld pool and keyhole geometries in the LBW process. With the help of a well experimentally validated numerical model considering the underlying physics in the LBW, the geometries of the weld pool and keyhole under various welding conditions are calculated, serving as the dataset of the generative model. A Conditional Variational Autoencoder (CVAE) model is employed to generate realistic 2D weld pool and keyhole geometries from the welding parameters. We utilize a β-VAE model with the Evidence Lower Bound (ELBO) loss function and include Kullback-Leibler divergence annealing to better optimize model performance and stability during training. The generated results show a good agreement with the ground truth from the numerical simulation. The proposed approach exhibits the potential of physics-informed generative models for a rapid and accurate prediction of the weld pool geometries across a diverse range of process parameters, offering a computationally efficient alternative to full numerical simulations for process optimization and control in laser beam welding processes.
Der Markt für Energiespeicher befindet sich in einer Phase intensiver technologischer Diversifizierung. Neben etablierten Lithium-Ionen-Batterien gewinnen neue Systeme wie Natrium-Ionen-Batterien und künftige Technologien wie Festkörperbatterien zunehmend an Bedeutung. Dies stellt jedoch neue Anforderungen an die Handhabung und Logistik respektiver Systeme und rückt die Klassifizierung von Batterien nach Gefährlichkeit stärker in den Fokus. In diesem Kontext gilt es Transportprozesse zu vereinfachen und simultan die Sicherheit zu erhöhen.
Im Rahmen dieses Vortrags werden aktuelle und kommende Batterietechnologien vorgestellt, die essenziellen Hürden bei deren Handhabung, Transport und Lagerung zusammenfassend dargestellt und ein umfassender Ausblick auf die Regelwerksentwicklung gegeben. Schwerpunkte liegen dabei auf I) der Entwicklung dedizierter Methoden für die Einordnung in Kategorien defekte und kritisch defekte Batteriesysteme, II) Passivierende Verfahren (thermisch und/oder elektrisch) für einen sicheren Transport und III) der Optimierung der Wertschöpfungskette des Gesamtsystems „Batterie“ durch effizientere Batteriekreisläufe und Recyclingverfahren.
Der Markt für Energiespeicher bietet eine kontinuierlich wachsende, technologische Vielfalt. Neben etablierten Lithium-Ionen-Batterien gewinnen alternative Systeme wie Natrium-Ionen-Batterien zunehmend an Bedeutung. Jene Entwicklung steigert aktuell die Anforderungen an Regularien für Logistik und Handhabung ebendieser Systeme und bedarf einer dedizierten jedoch gleichwohl praktikablem Klassifizierung unterschiedlicher Batterien nach deren Gefährlichkeit. Genau dies ist der Schwerpunkt der vorliegenden Präsentation. Ein besonderer Fokus liegt dabei auf dem sicheren Transport kritisch defekter Batteriesysteme durch thermische Passivierung und/oder gezieltes Tiefentladen. Explizit werden aktuelle und zukünftige Batterietechnologien vorgestellt, die wesentlichen Herausforderungen bei Handhabung, Transport und Lagerung zusammengefasst und ein umfassender Ausblick auf die Weiterentwicklung der relevanten Regelwerke gegeben.