Modelling the effect of pressure on the critical shear stress of MgO single crystals

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Modeling the mechanical properties of nanoparticles: a review

International audienceNanoparticles are commonly used in various fields of applications such as electronics, catalysis or engineering where they can be subjected to a certain amount of stress leading to structural instabilities or irreversible damages. In contrast with bulk materials, nanoparticles can sustain extremely high stresses (in the GPa range) with ductility, even in the case of originally brittle materials. This review article focuses on the modeling of the mechanical properties of nanoparticles, with an emphasis on elementary deformation processes. Various simulation methods are described, from classical molecular dynamics calculations, the best suited method when applied to the modeling the mechanics of nanoparticles, to dislocation dynamics based hybrid methodologies. We detail the mechanical behaviour of nanoparticles for a large array of material classes (metals, semiconductors , ceramics, etc.), as well as their deformation processes. Regular crystalline nanoparticles are addressed, as well as more complex systems such as nanoporous or core-shell particles. In addition to the exhaustive review on the recent works published on the topic, challenges and future trends are proposed, providing solid foundations for forthcoming investigations

Deformation mechanism of cerium oxide nanocubes - an in situ transmission electron microscopy study

Cerium oxide nanoparticles are used in many industrial products, among which solid oxide fuel cell electrodes or catalysts. However, their mechanical properties are rarely taken into account and few studies dealt with the determination of their deformation mechanism [1, 2]. Please click Download on the upper right corner to see the full abstract

Dislocation motion and instability

The Peach-Koehler expression for the stress generated by a single (non-planar) curvilinear dislocation is evaluated to calculate the dislocation self stress. This is combined with a law of motion to give the self-induced motion of a general dislocation curve. A stability analysis of a rectilinear, uniformly translating dislocation is then performed. The dislocation is found to be susceptible to a helical instability, with the maximum growth rate occurring when the dislocation is almost, but not exactly, pure screw. The non-linear evolution of the instability is determined numerically, and implications for slip band formation and non-Schmid behaviour in yielding discussed

Atrasentan and renal events in patients with type 2 diabetes and chronic kidney disease (SONAR): a double-blind, randomised, placebo-controlled trial

Background: Short-term treatment for people with type 2 diabetes using a low dose of the selective endothelin A receptor antagonist atrasentan reduces albuminuria without causing significant sodium retention. We report the long-term effects of treatment with atrasentan on major renal outcomes. Methods: We did this double-blind, randomised, placebo-controlled trial at 689 sites in 41 countries. We enrolled adults aged 18–85 years with type 2 diabetes, estimated glomerular filtration rate (eGFR)25–75 mL/min per 1·73 m 2 of body surface area, and a urine albumin-to-creatinine ratio (UACR)of 300–5000 mg/g who had received maximum labelled or tolerated renin–angiotensin system inhibition for at least 4 weeks. Participants were given atrasentan 0·75 mg orally daily during an enrichment period before random group assignment. Those with a UACR decrease of at least 30% with no substantial fluid retention during the enrichment period (responders)were included in the double-blind treatment period. Responders were randomly assigned to receive either atrasentan 0·75 mg orally daily or placebo. All patients and investigators were masked to treatment assignment. The primary endpoint was a composite of doubling of serum creatinine (sustained for ≥30 days)or end-stage kidney disease (eGFR <15 mL/min per 1·73 m 2 sustained for ≥90 days, chronic dialysis for ≥90 days, kidney transplantation, or death from kidney failure)in the intention-to-treat population of all responders. Safety was assessed in all patients who received at least one dose of their assigned study treatment. The study is registered with ClinicalTrials.gov, number NCT01858532. Findings: Between May 17, 2013, and July 13, 2017, 11 087 patients were screened; 5117 entered the enrichment period, and 4711 completed the enrichment period. Of these, 2648 patients were responders and were randomly assigned to the atrasentan group (n=1325)or placebo group (n=1323). Median follow-up was 2·2 years (IQR 1·4–2·9). 79 (6·0%)of 1325 patients in the atrasentan group and 105 (7·9%)of 1323 in the placebo group had a primary composite renal endpoint event (hazard ratio [HR]0·65 [95% CI 0·49–0·88]; p=0·0047). Fluid retention and anaemia adverse events, which have been previously attributed to endothelin receptor antagonists, were more frequent in the atrasentan group than in the placebo group. Hospital admission for heart failure occurred in 47 (3·5%)of 1325 patients in the atrasentan group and 34 (2·6%)of 1323 patients in the placebo group (HR 1·33 [95% CI 0·85–2·07]; p=0·208). 58 (4·4%)patients in the atrasentan group and 52 (3·9%)in the placebo group died (HR 1·09 [95% CI 0·75–1·59]; p=0·65). Interpretation: Atrasentan reduced the risk of renal events in patients with diabetes and chronic kidney disease who were selected to optimise efficacy and safety. These data support a potential role for selective endothelin receptor antagonists in protecting renal function in patients with type 2 diabetes at high risk of developing end-stage kidney disease. Funding: AbbVie

Multi-scale modeling of the plasticity of magnesium oxyde single crystal : from laboratory conditions to the Earth’s mantle

Les évènements géologiques de surface, comme le volcanisme ou les séismes, sont le fruit d'une dynamique qui vise à dissiper la chaleur interne de notre planète. Dans le manteau terrestre, les roches sont déformées plastiquement dans des conditions extrêmes de pression, de température et de vitesse de déformation. Malgré les récentes avancées expérimentales, il est impossible de reproduire de telles conditions de déformation en laboratoire. C'est pourquoi nous proposons, dans ce travail de thèse, une approche numérique, basée sur la modélisation multi-échelle de la plasticité, des conditions du laboratoire à celles qui caractérisent le manteau terrestre. Nous avons choisi d'appliquer cette méthode à MgO, phase importante du manteau inférieur.À partir des propriétés de cœur des dislocations, nous avons utilisé la théorie des double-décrochements afin de décrire la mobilité d'une dislocation isolée en fonction de la température et de la contrainte. Nous avons ensuite implémenté, dans un code de Dynamique des Dislocations (DD), les paramètres de mobilité des différents défauts afin de décrire le comportement collectif des dislocations lors d’essais numériques de déformation. Les résultats montrent que les propriétés mécaniques de MgO dépendent fortement de la pression et de la vitesse de déformation.Surface geological events, like volcanos and earthquakes, are due to the internal dynamics of the Earth which tends to release its internal heat. Inside the Earth's mantle, solid rocks are plastically strained under extreme conditions of pressure, temperature and strainrate. In spite of recent experimental progress, it is still impossible to reach such conditions of deformation. This is why we propose an alternative approach, based on the multi-scale modeling of plasticity, from the laboratory conditions to the Earth's mantle. We have choosen to apply our model to magnesium oxide which is a phase present in the lower mantle.From core properties, we modeled a dislocation thermally activated mobility law based on the kink pair theory. Then, we have incorporated it inside a Dislocation Dynamics code to describe the collective behaviour of dislocations throughout numerical strain experiments. Here we show that MgO mechanical properties depends significantly on pressure and strainrate

Mechanical properties and dislocation nucleation in nanocrystals with blunt edges

International audienceThe deformation of blunt nanocrystals under uniaxial compression is modelled using molecular dynamics simu- lations. Ni3Al blunt nanoparticles are built using a simple algorithm that allows continuous shape design from perfectly-sharp nanocubes to nanospheres including a large set of cuboid shapes. Simulation results show that blunt nanoparticles are significantly stronger in comparison to their perfectly cubic counterparts and deform due to the nucleation of partial dislocations and deformation twins. Furthermore, while the early plastic deforma- tion of nano-objects is generally attributed to the nucleation of dislocations from the surface, here we show that homogeneous dislocation nucleation may also happen in blunt nanoparticles and a size-dependent transition pa- rameter is defined. This study emphasizes how much the design of virtual samples is crucial when modeling nano-objects mechanical properties using molecular dynamics simulations and provides new insights onto po- tential incipient plasticity features at the nanoscale

Deformation of ultra-hard ceramic nanocrystals using atomistic simulations

International audienceNucléation de dislocation dans des nanocubes de MgO, approche par MD et NE

Multi-Objective Optimization Method for the Mixed-Model-Line Assembly Line Design Problem

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Efficient multi-objective optimization method for the mixed-model-line assembly line design problem

This paper presents a mathematical model and an adaptation of the Strength Pareto Evolutionary Algorithm II (SPEA2) for the Mixed-Model Assembly Line balancing and equipment selection problem. The SPEA2 was enriched with a task and equipment reassignment procedure and aims at supporting the planners to find better solutions in the earliest phases of a production system planning project