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Corrigendum: Weather-dependency of the thermographic flow visualization of the laminar-turbulent transition on wind turbines (2024 Meas. Sci. Technol. 35 095301)
No full textThe authors have received additional information from material experts regarding some assumptions made in the article in section 2.2 concerning the heat transfer. Based on the resulting discussion, the corrigendum aims to complement, contextualize and emphasize certain points of the article
Ballasted track on vibrating bridge decks: physical mechanisms, empirical findings, and a proposal for assessment
No full textThis paper summarizes the key findings and physical mechanisms and provides information on open questions and the assessment of railway bridge superstructure vibrations. Bridges are classic disruption points on a railway track. If bridge superstructures are dynamically excited by train traffic, the vertical accelerations of the track must be considered. For a ballasted track, this can lead to the destabilization of the ballast track, as the bridge superstructure acts like a vibrating table. In this respect, the paper explains in more detail what is meant by destabilization, when this destabilization occurs and how various influencing parameters such as acceleration amplitude, the vibration sequence and frequency affect its occurrence. In the InBridge4EU project, gaps in knowledge such as the effect of single impulse loads are being investigated experimentally. A new test facility has been set up for this purpose, the initial results of which are presented here. An essential element in the assessment of this scenario is the stability of the track under high compression forces with simultaneous dynamic excitation of the superstructure. A new approach for the assessment of bridge vibrations with respect to lateral stability is presented
Dilatometry Based Determination of Continuous Cooling Transformation (CCT) Diagrams in Low Alloy Pipeline Steels for Hydrogen transportation
No full textThis study investigates the suitability of low-alloy pipeline steels for hydrogen transportation, focusing on the development of weld microstructures. Previous research has been limited by a deficiency in the understanding of how different microstructural components respond to trapped hydrogen. By developing Continuous Cooling Transformation (CCT) diagrams through dilatometry analysis, this study explores the impact of t8/5-cooling times (the time between 800 °C and 500 °C) on the microstructure and mechanical properties of the HAZ compared to the base material. The findings provide valuable insights into how cooling times influence transformation temperatures and microstructure development, which, in turn, affect hydrogen diffusion and absorption. These findings establish a foundation for future investigations into hydrogen's impact on weld microstructures, including experimental studies, with the aim of optimizing welding practices and enhancing resistance to hydrogen-assisted cracking. Ultimately, this research contributes to improving the safety and reliability of hydrogen transportation systems in commonly used industrial pipeline steels
Synchrotron investigation of heat treatment effects on the 3D residual stress distribution in laser powder bed fused AlSi7Mg alloys
No full textFor the first time, we utilized synchrotron diffraction to determine 3D maps of residual stresses across the entire volume of thick AlSi7Mg alloy prisms produced by PBF-LB. Samples were subjected to different heat treatment processes: direct aging (T5), solution treatment, and solution treatment followed by aging (T6). The T6 heat treatment resulted in the lowest residual tensile strains, while the T5 treatment resulted in significantly higher residual strains. Maximum residual stresses decreased from the as-built condition to the T6 heat-treated specimen. Although the T5 condition provides greater strength, it also retains higher tensile residual stresses near the surface, which can negatively affect fatigue properties
FeNb2O6 as a high-performance anode for sodium-ion batteries enabled by structural amorphization coupled with NbO6 local ordering.
No full textPseudocapacitance-type transition metal oxides have been extensively investigated as anodes materials for lithium-ion batteries. Currently, they are also emerging as promising anodes for sodium-ion batteries due to their low volume change and safety. However, the potential electrochemical performance in sodium energy storage is not fully achieved, primarily due to the larger radius of the Na+-ions. Here, we report for the first time an iron niobate with columbite structure as a high-performance sodium storage anode. The presence of iron in the structure is vital to trigger the loss of long-range order through disorder of the FeO6 octahedra local structure, subsequently allowing reversible Na storage in an amorphous phase. Simultaneously, the formation of short-range ordered zigzag-chain structures within the NbO6 planes creates a “skeleton” that offers abundant active sites for pseudocapacitive ion storage and enhanced ion diffusion pathways. These characteristics of FeNb2O6 make it an effective intercalation host, offering high capacity along with fast Na+ insertion and extraction, as demonstrated through operando and ex-situ characterizations. It leads to an applicable reversible capacity ( 300 mAh g-1) with a favorable average voltage of ca. 0.6 V and excellent rate capability (180.4 mAh g-1 at a current density of 2 A g-1). This study provides insights into the development of intrinsically active transition metal oxides for Na+-ion intercalation
Flammschutz von Faserverbundwerkstoffen: Grundlagen und Konzepte
No full textVor allen Kurz- und Lang-Glasfaser-verstärkte, aber auch Carbonfaser verstärkte Faserverbundwerkstoffe werden in Schienenfahrzeugen eingesetzt. Dabei sind die Brandschutzanforderungen entsprechend EN 45545 zu erfüllen. Der Übersichtsvortrag führt in die Grundlagen des Brandverhaltens und des Flammschutzes von Compositen ein. Anhand von eigenen Arbeiten wird verdeutlicht, dass Flammschutz maßgeschneidert für Composite, die Matrix und für den zu bestehenden Brandtest erforderlich ist
Seasonal PFAS monitoring in surface water via complementary EOF (HR-CS-GFMAS) and target analytics
No full textThe aim of this study was to investigate seasonal shifts in PFAS contamination. Therefore, samples were collected from the River Spree to measure the level of extractable organically bound fluorine (EOF). This was achieved by employing high resolution-continuum source-graphite furnace molecular absorption spectrometry (HR-CS-GFMAS), a method for EOF surface water analysis first described by Metzger et al.. Complementary target-screenings were performed for a small set of relevant PFAS to achieve a more detailed look into the PFAS contamination over time and space and into the identifiable fraction of the EOF. Furthermore, hot spots of relevant PFAS pollution were identified in the river system
Application of the cyclic R-curve analysis to determine the Kitagawa-Takahashi Diagram
No full textThe fatigue limit of metallic materials corresponds to the maximum stress below which all microcracks that were originally able to grow still arrest. In technical alloys, microcracks are normally initiated at material defects. As a result, the fatigue limit of these materials is a function of the defect size. The Kitagawa-Takahashi Diagram (KT-diagram) provides a useful description of this dependency. However, the established methods for its determination are associated with great uncertainties, especially in the technically interesting region corresponding to the short crack regime. In addition, the effect of crack closure and the influence of local stresses are not considered. For this reason, short crack models offer a better alternative for estimating KT-diagrams. In this work, a methodology is presented that incorporates the determination of the fatigue limit based on crack arrest (cyclic R-curve analysis). The crack driving force is determined by FE simulations, while the increase in material resistance with cyclic crack propagation in the region of physically short cracks is described experimentally by the cyclic R-curve. To validate the procedure, fatigue limit tests based on the staircase method are carried out on smooth and notched specimens with 3 different notch sizes. Furthermore, tests are carried out on a low-alloyed steel with two different heat treatments for considering different strengths. The experimental results are compared with the simulations and the possible differences are discussed
Microplastic-microbiome interactions in aquatic ecosystems: a complex story
No full textAs pervasive and persistent pollutants, microplastics exist alongside diverse microbial communities in nature. These hardy substrates accumulate rich polymeric matrices from their surroundings that in turn offer nutrition and protection to diverse communities and their theatre of activity, representing a new ecological niche. With our work, we aim to establish a holistic understanding of the interactions between microplastics and microorganisms within aquatic systems, and how these interactions shape their surrounding environment. In our research, we combine field sampling with in situ experiments, and apply high-throughput sequencing technologies to 16S genes and whole bacterial genomes. We demonstrate through our studies that biofilm communities exhibit no specificity to plastic polymer type but appear rather to be opportunistic colonizers more strongly shaped by spatial and temporal factors. While the polymer surface does not appear to elicit a selective effect on associated biofilms, our studies show that microplastics might shape communities in a different way. Based on our detection of carotenoid synthesis pathways and photosynthetic gene clusters among plastic biofilms, we postulate this new niche to shape a specific functional toolkit, adaptive among its members as a product of prolonged exposure to UV radiation at the sea’s surface. To fully assess the interactions between microplastics and microorganisms, however, one cannot consider plastics singularly but as a component within a more complex and interconnected system. It is known, for instance, that plastics can sorb significant concentrations of polycyclic aromatic hydrocarbons (PAH) in the environment. We show, in our work, that the PAH sorption patterns of microplastics correlate significantly with the structure of associated biofilm communities. Elevated concentrations of specific PAHs on microplastics coincided with the enrichment of selected taxa reportedly capable of hydrocarbon utilisation as well as a reduced diversity among associated biofilm communities. Here, we present a synthesis of our collective research on microplastic biofilms in the aquatic environment, the factors that shape them, and their interactions with nature. To fully comprehend how microplastics impact ecosystems, the entire substrate must be considered, including all chemicals integrated into the polymeric matrix as well as associated biofilms
Machine learning strategies with ensemble voting for ultrasonic damage detection in composite structures under varying temperature or load conditions
No full textIn recent years, the development of machine learning (ML) techniques has led to significant progress in the field of structural health monitoring with ultrasonic-guided waves. However, a number of challenges still need to be resolved for reliable operation in realistic settings. In this work, we consider the complex problem of experimental damage detection under varying temperature or load conditions where damage locations are not included in the training set. The ML techniques proposed here include supervised and unsupervised methods originally developed for image and time series classification combined with ensemble voting. A performance demonstration of the ML techniques is presented using benchmark datasets from the open-guided waves platform. The unsupervised approach is then applied to a new dataset from an experimental campaign carried out on a composite over-wrapped pressure vessel used for hydrogen storage with real defects. Results show that ensemble voting enables the effective combination of the predictions of multiple transducer pairs, even with a limited number of strong individual classifiers. When applied to unsupervised learning, this returns high accuracy also when real damage over the structure is considered