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Luminescence and structural properties of europium doped titania in the 600–750 °C range
No full textInternational audienceIn this study, europium doped titania nanophosphors are synthetized and characterize in order to understand the relationship between structural changes induced by heat treatments and luminescence properties. After heat treatments, phase changes are observed between 600 °C and 700 °C and characterized using X-ray diffraction and Raman spectroscopy. These phase changes include the anatase – rutile transition and the apparition of secondary phases such as europium oxide and pyrochlore phase (Eu2Ti2O7). Along with the phase changes and crystallite size evolution, the luminescence intensity of the 5D0→ 7F2 transition and the lifetime decay are measured after green laser excitation (532 nm). The europium concentration is a key parameter to obtain a monotone and bijective relationship between the temperature and the luminescence behavior
Mode I and mode II fracture behavior in nano‐engineered long fiber reinforced composites
No full textInternational audienceDelamination still remains one of the common concerns in continuous fibers reinforced polymer composites. In the literature, the incorporation of nanoconstituents into constitutive composites plies has been suggested with the aim of improving interface toughness. In this study, vertically aligned carbon nanotubes forests (VACNTs) are transferred at composites interfaces, and mode I (DCB tests) and mode II (ENF tests) fracture tests carried out on composite samples. Microscopic analysis of reference and nano-engineered composites help to understand fracture behavior and toughness. While the crack path in ENF samples is observed at interlaminar VACNTs-resin interfaces, the crack path in DCB samples is intralaminar, located within the unidirectional carbon fiber plies. These microscopic observations give explanation for unstable crack propagation in nano-engineered ENF samples and the unchanged toughness from the nano-engineered to the reference zone in DCB samples
Crystallization and freezing processes assisted by power ultrasound
No full textInternational audiencePower ultrasound may be used to control crystal properties in solutions and melts.The first part of this chapter concerns the thermodynamics and kinetics of crystallization.The second part reviews several studies dealing with ultrasound-assisted crystallization or freezing processes. The influence of operating conditions (dissipated acoustic power or intensity, frequency, duration, ultrasonic device) on crystals’ properties and process rate is discussed.The third part investigates elementary mechanisms (temperature, pressure, diffusive, and chemical effects) underlying the sonocrystallization process according to the literature but also on the ground of authors’ own results. A special paragraph is devoted to ice crystallization in super-cooled aqueous solutions
Solar pyrolysis of algae in molten salt for capacitive carbon preparation
No full textInternational audiencePyrolysis of algae in molten carbonates driven by concentrated solar energy is proposed as an economical and environmentally friendly method to obtain capacitive carbon for supercapacitors. The effects of molten carbonates on pyrolysis process and electrochemical performance at different temperatures (800, 850 and 900 °C) are investigated. Na2CO3–K2CO3 leads to a relatively high carbon yield and superior microstructure at around 900 °C compared with other molten salts, which is beneficial for capacitive carbon production. The as-prepared carbon possesses a high specific surface area of 2009.26 m2/g and a hierarchical porous structure mainly consisting of micropores and mesopores. Moreover, it contains abundant oxygen- and nitrogen-containing functional groups, such as Cdouble bondO, –OH, pyrrolic–N and quaternary–N. These features play an important multiple synergy for the preparation of desirable capacitive carbon, which has a high specific capacitance of 230.2 F/g at 0.25 A/g, a capacitance retention of 75.54% at 2 A/g and an energy density of 31.97 Wh/kg at 999.94 W/kg. This work provides a green and promising approach for the production of heteroatom-doped capacitive carbon with superior porosity and specific surface area
Comment on “Unraveling the role of cobalt in the direct conversion of CO2 to high-yield liquid fuels and lube base oil” by Jo et al. [Appl. Catal., B 2022, 305, 121041]
No full textInternational audienceThe IR work reported in the paper by Jo et al. is critically re-analyzed and different interpretations are proposed that invalidate some of the conclusions proposed by the authors
Monte-Carlo estimation of geometric sensitivities in Solar Power Tower systems of flat mirrors
No full textInternational audienceOptical optimizations for a Concentrated Solar Power (CSP) system are currently limited largely to gradient-free methods, since the gradient is hard to obtain by using the existing numerical optics tools available in the community. This article aims to build new algorithms of the Monte-Carlo type, which numerically estimate the gradient of power impacting the receiver with respect to the geometric parameters that characterize the geometric status of the heliostats in the heliostats field, for a Solar Power Tower (SPT) system.Physical models will be built for the specific intensity and also for its derivatives to the geometric parameters of the heliostats, also called geometric sensitivities of intensity. Similar to the intensity but with their own models, they are regarded as physical quantities emitted, absorbed and reflected in the system. They carry the perturbations of intensity as information, corresponding to the relations between the geometric parameters and the physical events in the SPT system: blocking, spillage, shadowing, etc. These relations will be distinguished and discussed.Finally, not only the gradient but also the contributions of physical events (blocking, spillage, shadowing, etc.) to the gradient can be estimated for further sensitivity analysis and optimization processes
Simulation-based Assessment of Hyperconnected Humanitarian Supply Chains Response Readiness
No full textInternational audienceThe escalating disasters and increasingly complex external environment are forcing humanitarian organizations to continually improve their operations to provide better humanitarian relief. Transformation towards hyperconnected humanitarian supply chains is one of the most promising paths and the Physical Internet could provide a paradigm for this evolution. However, the impact of this shift on the humanitarian supply chain's performance, particularly readiness, has been understudied. To address this issue, a simulation-based assessment of hyperconnected humanitarian supply chains' response readiness is conducted. Different combinations of multiple potentials of the Physical Internet are simulated, and the corresponding effects on relief operations are analyzed. The findings of this work provide greater insight into the transformation towards hyperconnectivity and thus are helpful for decision-makers to design appropriate evolutionary avenues for today's humanitarian supply chains
Excellent Balance of Ultimate Tensile Strength and Ductility in a Ti–6Al–2Sn–4Zr–2Mo–Si Alloy Having Duplex α + α′ Microstructure: Effect of Microstructural Factors from Experimental Study and Machine Learning
No full textInternational audienceThis research focuses on the systematic study of a Ti–6Al–2Sn–4Zr–2Mo–Si titanium alloy and the characterization of α + β (equiaxed and bimodal) and α + α′ (duplex) microstructures. It provides more insights on the outstanding advantages of the duplex (α + α′) microstructure, especially on its exceptional work hardening and strength-ductility balance. The heat treatment conditions required to form equiaxed, bimodal and duplex microstructures and their effects on the grain size and the phase proportion are discussed. It shows how the microstructural parameters can be controlled thanks to the heat treatment temperatures, the holding times and possible aging processes. The influence of such microstructural factors on the tensile properties of each alloy is investigated, especially on strength (proof stress, ultimate tensile strength), ductility (plastic elongation) and work hardening properties. The duplex (α + α′) microstructure is compared with the equiaxed and bimodal microstructures and its advantages are displayed, highlighting the better strength-ductility balance and superior work hardening properties of the duplex microstructure. Indeed, the deformed microstructure of the duplex (α + α′) microstructure reveals more homogeneous strain partitioning than that of the bimodal (α + β) microstructure. Thus, this work proved the potential of an optimized duplex (α + α′) microstructure for the enhanced tensile properties at room temperature. Finally, a machine learning model using gradient boosting regression trees is used to quantify the importance of the microstructural factors (type of microstructure, grain size and phase ratio) on the mechanical properties
Review
No full textInternational audienceA Safety Science focus on research in the science and technology of human and industrial safety. Critical Infrastructures (CIs), as a crucial part of urban technological systems, are highly correlated with urban safety management in terms of their resilience when cities are facing a crisis or disaster. According to many studies, indicator-based resilience assessment has been used frequently to manage CIs in recent decades. Defining and characterising indicators can be useful for managers of human and industrial safety, as it could help monitor and improve the capacities and performance of CIs. In recent years, critical infrastructures (CIs) have been damaged with increasing frequency (and will be so in the future) following natural or technological disasters. CIs, such as buildings, transportation networks and power systems, play an indispensable role in our society due to their importance for maintaining critical societal functions, economic organisation and national defence. Therefore, the popularity of "critical infrastructure resilience" has exploded in both academic and policy discourses. Indicator-based assessment is a convenient and common tool to help understand, analyse and improve CI resilience in the scientific field. This paper produces a state-of-the-art review of the existing indicator-based assessment of CI resilience. After a terminology presentation, which helps clarify the objective of this study, this paper will show: 1) two methods for selecting the current scientific papers applying indicators to assess CI resilience; and 2) analysis of the indicators in these papers based on the study objective. The results show that there are many indicators and they do not have a uniform standard system, which means an indicator system for CI resilience assessment must be established
Approches micromécaniques pour l'étude du couplage oxydation-mécanique
No full textMa thématique de recherche porte sur le comportement mécanique, la réactivité de surface et la durabilité de matériaux métalliques pour applications transports/aéronautiques/production de l'énergie en environnements complexes. Je m’intéresse plus particulièrement à la synergie "oxydation-déformation localisée" à l’échelle de la microstructure afin d’appréhender les prémices d’endommagement sous chargement mécanique à haute température en atmosphère réactive. Mes travaux portent sur divers matériaux métalliques structurels ou modèles afin d'aborder différents mécanismes de déformation localisée (bandes de glissement, maclage, glissement aux joints de grains, etc.) mais aussi de réactivité de surface (oxydation externe et interne, dissolution d'éléments de faible taille, etc.) : les superalliages à base de nickel, les alliages de titane, d’aluminium, certains revêtements pour la tenue à l’oxydation. L'oxydation des matériaux entraîne une consommation sélective d'éléments chimiques et le matériau - sous cette couche d'oxyde - peut voir sa composition chimique, sa microstructure, ses propriétés mécaniques et physiques évoluer sur de faibles profondeurs. Cette zone affectée par l'oxydation peut néanmoins impacter l'intégrité mécano-chimique des matériaux en question. Ainsi, mes activités de recherche visent à comprendre comment le matériau et ses propriétés évoluent dans cette zone affectée par l'oxydation sous chargement mécanique. À ce jour, mon objectif est de développer différents outils expérimentaux et un savoir-faire dans la caractérisation macro- et micromécanique de matériaux dans une large gamme de température et sous différents environnements afin de sonder les propriétés mécaniques dans la zone affectée par l'oxydation. La finalité de ces caractérisations expérimentales couplées à des modèles et simulations numériques serait de mieux comprendre l'impact du comportement de cette zone affectée sur le comportement et l'intégrité mécanique de pièces structurelles en service. A ce jour, j'ai développé un savoir-faire en préparation d'échantillons ultraminces (10 µm d'épaisseur pour quelques cm de long) qui me permet d'étudier les effets d'épaisseur à la fois sur (i) le comportement mécanique (transition de comportement polycristallin à multricristallin en présence d'une surface libre), (ii) le comportement en oxydation (effet réservoir du fait de la consommation sélective des éléments) et (iii) le couplage "oxydation-mécanique" au travers d'éprouvettes minces présentant une forte surface réactive au regard du volume sollicité. De plus, le développement d’outils de mesures de champ cinématique multi-échelles (techniques de corrélation d’images) m’ont permis d’appréhender, d’identifier et de quantifier la localisation de la déformation dans une large gamme de température à l’échelle de la microstructure-celle des grains-mais aussi de la mesostructure-celle des fibres de textures notamment-qui amène une certaine variabilité sur le comportement local de la matière. Je contribue également au développement de modèles et simulations numériques en relation avec l’anisotropie des propriétés de matériaux métalliques à l’échelle du grain, notamment par le dialogue essai-simulation à partir de données issues d'essais de corrélation d'images, mais aussi nouvellement de nanoindentation