Experimental study of the brittle–ductile transition in hot cutting of SG iron specimens

http://www.sciencedirect.com/science/article/pii/S0924013612002579The present paper investigates the brittle-ductile transition (BDT) of the primary shear zone during cutting of spheroidal graphite (SG) iron in the austenitization temperature range (around 1000 °C). The experimental tests were performed using a cutting test bench in the cutting speed range of 0.8 to 1.6m.s-1. The cut surfaces were studied using optical microscopy and Scanning Electron Microscope (SEM) analysis techniques. The obtained results revealed either consequent deep fractured regions governed by a brittle-cracking regime (BCR) or a crack-free cut surface governed by a ductile-shear regime (DSR) with large plastic deformations. When cutting data were discussed with respect to the influences of cutting parameters and obtained cut surface, the correlation is significantly rich. Both cut surface integrity, cutting force curves and metallographic results show a BDT indicating a change in the dominating hot cutting process mechanism. Such a transition is associated with the dynamic recrystallization promoting strain softening and hot cutting by ductile shearing

Digital image correlation as a usefful tool of analysis of hot cutting process

This study deals with the use of Digital Image Correlation (DIC) to investigate the physical phenomena taking place during the orthogonal cutting of a SG iron specimen at high temperature (around 1,000 °C). After h aving recalled the scientific and industrial context, the experimental procedure developed to record the pictures of the tool covered with a speckle pattern at a frequency of 10,000 Hz (thanks to a high speed camera) is explained. The quantitative exploitation of these recordings is leading to a first set of results showing how the cutting speed and the rake angle of the tool have an influence on the physics of the cutting operation.Arts et Métiers ParisTech - DGAR

Trapping efficiency of plastic bottle "wickertraps" for population assessment of river Macrobrachium (Crustacea : Decapoda)

Small wickertraps made from plastic bottles are used to sample #Macrobrachium communities (#Crustacea Decapoda) in the rivers of Nuku-Hiva (Marquesas Islands, French Polynesia). Relations are established between sampling effort (number of traps per m2), number of crustacea caught, and surface of the pool. Catch per trap decreased with increasing trap density up to a threshold of about 8 traps per m2. Escape measurements, in a river and in the laboratory, help to describe the behaviour of the shrimps towards the traps. Escape was greater at night than during the day. The number of shrimps entering the traps was inversely proportional to the number of shrimps already in the traps. Sampling efficiency of the traps was estimated, in a single trial, at 40-47% for a trap density of 8.3 traps per m2. (Résumé d'auteur

Etude d'une méthode d'échantillonnage des populations de chevrettes (Macrobrachium lar. et M. australe) des rivières de Nuku Hiva (Marquises, Polynésie française)

Une méthode d'échantillonnage des #Macrobrachium, macrocrustacés dulçaquicoles, est étudiée dans le cadre d'un suivi de la faune non cible aux traitements des rivières de l'île de Nuku-Hiva (Marquises) visant l'éradication du "nono noir des vallées" (#Simulim buissoni). Plusieurs engins de pêche ont été étudiés dont de petites nasses fabriquées à l'aide de bouteilles plastiques. Le "comportement" de ces bouteilles en regard des captures échantillonnées est abordé par comparaison avec les captures d'autres types de pièges (grandes nasses et pêche électrique), divers types de bouteilles (appâtées, colorées), et différentes orientations des bouteilles dans la rivière. L'abondance des captures est analysée en fonction de l'échappement et des fluctuations de l'effort d'échantillonnage (nombre de bouteilles/unité de surface). L'efficacité des bouteilles transparentes quant à l'abondance des prises est étudiée après des estimations du nombre total de chevrettes dans le milieu résultant d'opérations de marquage-recapture et de comptages visuels de nuit. Enfin, une interprétation de l'abondance et de la densité des chevrettes par des variables écologiques descriptives du milieu est proposée. (Résumé d'auteur

Enhancing Graph Neural Networks with Quantum Computed Encodings

Transformers are increasingly employed for graph data, demonstrating competitive performance in diverse tasks. To incorporate graph information into these models, it is essential to enhance node and edge features with positional encodings. In this work, we propose novel families of positional encodings tailored for graph transformers. These encodings leverage the long-range correlations inherent in quantum systems, which arise from mapping the topology of a graph onto interactions between qubits in a quantum computer. Our inspiration stems from the recent advancements in quantum processing units, which offer computational capabilities beyond the reach of classical hardware. We prove that some of these quantum features are theoretically more expressive for certain graphs than the commonly used relative random walk probabilities. Empirically, we show that the performance of state-of-the-art models can be improved on standard benchmarks and large-scale datasets by computing tractable versions of quantum features. Our findings highlight the potential of leveraging quantum computing capabilities to potentially enhance the performance of transformers in handling graph data.Comment: arXiv admin note: text overlap with arXiv:2210.1061

Développement d'une méthode de mesure de champs cinématiques pour étudier la coupe à chaud

Ce travail se concentre sur le développement d'une technique de mesure de champs cinématiques pour l'étude des phénomènes se déroulant lors de la découpe à chaud d'alliages métalliques. Le développement d'une méthode de mesure permettant d'observer le comportement mécanique à ces températures élevées (environ 1000 °C) reste un challenge. Ce travail se propose de relever ce défi. Des cartes de déformations et de vitesses de déformation ont été obtenues grace à l'élaboration d'un mouchetis résistant à la température couplé avec un système d'observation ad hoc pour permettre une étude cinématique locale lors de la découpe à chaud de la pièce à l'aide de la corrélation d'images numériques

Competition and facilitation between the marine nitrogen-fixing <i>cyanobacterium</i> Cyanothece and its associated bacterial community

N2-fixing cyanobacteria represent a major source of new nitrogen and carbon for marine microbial communities, but little is known about their ecological interactions with associated microbiota. In this study we investigated the interactions between the unicellular N2-fixing cyanobacterium Cyanothece sp. Miami BG043511 and its associated free-living chemotrophic bacteria at different concentrations of nitrate and dissolved organic carbon and different temperatures. High temperature strongly stimulated the growth of Cyanothece, but had less effect on the growth and community composition of the chemotrophic bacteria. Conversely, nitrate and carbon addition did not significantly increase the abundance of Cyanothece, but strongly affected the abundance and species composition of the associated chemotrophic bacteria. In nitrate-free medium the associated bacterial community was co-dominated by the putative diazotroph Mesorhizobium and the putative aerobic anoxygenic phototroph Erythrobacter and after addition of organic carbon also by the Flavobacterium Muricauda. Addition of nitrate shifted the composition toward co-dominance by Erythrobacter and the Gammaproteobacterium Marinobacter. Our results indicate that Cyanothece modified the species composition of its associated bacteria through a combination of competition and facilitation. Furthermore, within the bacterial community, niche differentiation appeared to play an important role, contributing to the coexistence of a variety of different functional groups. An important implication of these findings is that changes in nitrogen and carbon availability due to, e.g., eutrophication and climate change are likely to have a major impact on the species composition of the bacterial community associated with N2-fixing cyanobacteria

Effect of Si, Cu and processing parameters on Al-Si-Cu HPDC castings

Chemical composition of secondary Al-Si-Cu alloys and working variables of high-pressure die casting process (HPDC) may change for the same casting parts from one country to another in the world. They can even sometimes vary from one manufacturing site to another within the same country. An experimental study on the influence of alloying elements contents (Si and Cu), casting temperature and injection pressure on mechanical properties of die cast aluminum alloys was carried out to support the automotive industry suppliers in designing their cast parts. The microstructural features and the porosity level were also investigated and assessed. The primary objective is to highlight the modification mechanisms of the achieved properties using tensile tests, hardness measurements and microstructural observations performed on a HPDC casting parts. Low pressure and low temperature increase the rate of porosity, promote the formation of coarse Fe-rich intermetallic compounds and change the morphology of α-Al phases. These in turn deteriorate mechanical tensile properties. However, variation of alloying elements contents modifies the optimum properties achieved when part is made at constant casting processing parameters. Finally, the interactions between the studied parameters of HPDC and the chemical alloying elements show also a significant influence on the tensile properties

Effect of laser irradiation on failure mechanism of TiCp reinforcedtitanium composite coating produced by laser cladding

Laser cladding is an effective technique to coat a metallic substrate with a layer of a different nature.It has been widely reported that the most important combined parameters controlling the quality ofthe coating are the specific energy (E) and the powder density ( ). In the present work, clad depositsof Ti6Al4V + 60 wt.% TiC were prepared on a Ti6Al4V substrate using an optimum combination of Ec= 24 J/mm2 and c= 3 mg/mm2. These experiments were performed using a laser power of 400 and600 W, in order to study the effect of laser power on the properties of the clad. The microstructure, phasecomposition and nanohardness of the coatings were investigated by optical microscopy, scanning elec-tron microscopy and X-ray diffraction. During laser processing, TiC can be partially converted to TiCX(X = 0.5) due mainly to the TiC dissolution into the laser-generated melting pool and subsequent precipi-tation during cooling. It was observed that the lower laser power limit reduces primary TiC dissolution butit also promotes secondary carbide alignment at the interface. On the other hand, the damage mechanisminduced by high laser power is dominated by primary TiC particle cracking by the high stress concentra-tion at the particle matrix interface followed by ductile failure of the matrix. It is also remarkable thatirradiance affects the TiC/TiCxratio despite Ecand care fixed and it determines hardness distributioninside the coating.Authors thank MINECO funding in special the Training of Research Staff programme with the help BES-2009-013589 and the support of the Comision Interministerial de Ciencia y Tecnologia (CICYT), Spain, under Grant MAT2012-39124. This work was developed at the Materials Technology Unit of the Polytechnic University of Valencia associated to CSIC through the National Centre for Metallurgical Research (CENIM). Finally, thank the EU for the funding received through the FEDER help in the project UPOV08-3E-005 for the purchase of equipment and the Generalitat Valenciana for the help ACOMP/2012/094.Candel Bou, JJ.; Jiménez, J.; Franconetti Rodríguez, P.; Amigó Borrás, V. (2014). Effect of laser irradiation on failure mechanism of TiCp reinforcedtitanium composite coating produced by laser cladding. Journal of Materials Processing Technology. 214(11):2325-2332. https://doi.org/10.1016/j.jmatprotec.2014.04.035S232523322141

Dynamic recrystallization behaviour of spheroidal graphite iron. Application to cutting operations

To increase the competitiveness of manufacturing processes, numerical approaches are unavoidable. Nevertheless, a precise knowledge of the thermo-mechanical behaviour of the materials is necessary to simulate accurately these processes. Previous experimental studies have provided a limited information concerning dynamic recrystallization of spheroidal graphite iron under hot cutting operations. The purpose of this paper is to develop a constitutive model able to describe accurately the occurrence of this phenomenon. Compression tests are carried out using a Gleeble 3500 thermo-mechanical simulator to determine the hot deformation behaviour of spheroidal graphite iron at high strains. Once the activation range of the dynamic recrystallization process is assessed, a constitutive model taking into account this phenomenon is developed and implemented in the Abaqus/Explicit software. Finally, a specific cutting test and its finite element model are introduced. The ability of the numerical model to predict the occurrence of dynamic recrystallization is then compared to experimental observations