Centre des Matériaux

A qualitative analysis of the various outcomes of a drop impact on solid surfaces with different roughness and wettability is carried out. Water, ethanol, different mixtures of glycerin and water, liquid alloys, and silicone oil were used to provide a wide range of material properties such as surface tension, viscosity, and density. The impact velocity was varied by moving the drop generator vertically with respect to the plate. Also two drop diameter classes were considered. A variation of roughness amplitude and wavelength was achieved using a laser ablation process on polyvinyl chloride and glass substrates, creating a deterministic microstructure. A highly nonwettable rough surface was prepared with alkylketene dimer (AKD) [1]. A first classification of the different outcomes, in terms of splash, rebound, partial rebound, deposition, and other features, is presented.

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The past 20 years have seen substantial work on the modeling of ductile damage and fracture. Several factors explain this interest. (i) There is a growing demand to provide tools which allow to increase the efficiency of structures (reduce weight, increase service temperature or load, etc.) while keeping or increasing safety. This goal is indeed first achieved by using better materials but also by improving design tools. Better tools have been provided which consist (ii) of material constitutive equations integrating a physically-based description of damage processes and (iii) of better numerical tools which allow to use the improved constitutive equations in structural computations which become more and more realistic. This article reviews the material constitutive equations and computational tools, which have been recently developed to simulate ductile rupture.

This review summarizes recent advances in the area of tribology based on the outcome of a Lorentz Center workshop surveying various physical, chemical and mechanical phenomena across scales. Among the main themes discussed were those of rough surface representations, the breakdown of continuum theories at the nano- and microscales, as well as multiscale and multiphysics aspects for analytical and computational models relevant to applications spanning a variety of sectors, from automotive to biotribology and nanotechnology. Significant effort is still required to account for complementary nonlinear effects of plasticity, adhesion, friction, wear, lubrication and surface chemistry in tribological models. For each topic, we propose some research directions.

ABSTRACT: : Edible chitosan coatings showed anti‐ Listeria monocytogenes effect evaluated by numeration and epifluorescence methods, imparting a strong localized functional effect at the food surface by active packaging. The use of film‐forming solution in culture liquid medium showed a known flocculant phenomenon combined with bactericidal activity, keeping 20% of the initial microbial charge as viable cells in flocculant, which could develop subsequently. However, chitosan film showed 100% of L. monocytogenes inhibition for at least 8 d, completed by bactericidal activity measured by epifluorescence assays. A decrease in antibactericidal effect with time was obtained, most probably due to a decreasing availability of amino‐groups of chitosan. Latter results were validated on Emmental cheese samples using L. innocua as model strain because of its nonpathogenicity.

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Abstract The major scientific and technological advances and breakthroughs of advanced high strength steels (AHSS) were achieved due to the strong demands of automotive industry. The development of AHSS began in the early 1980s with the aim of improving passenger safety and weight‐saving. The present paper presents the driving forces and logic of development of various AHSS for automotive applications since 1980s. The importance of crash performance, weight‐saving, formability, and rigidity are critically reviewed for the development of new steel grades for automotive applications. The logical sequences of the development of dual phase (DP) steel, transformation induced plasticity (TRIP) steels, tempered DP steels, complex phases (CP) steels, Ferrite‐Bainite steels, hot‐stamping technology, twinning induced plasticity (TWIP) steels, Quench and Partitioning (Q&P) steels, Medium Mn steels, and steels–polymer composites are presented.

A new fabrication method to produce homogeneously fluorescent nanodiamonds with high yields is described. The powder obtained by high energy ball milling of fluorescent high pressure, high temperature diamond microcrystals was converted in a pure concentrated aqueous colloidal dispersion of highly crystalline ultrasmall nanoparticles with a mean size less than or equal to 10 nm. The whole fabrication yield of colloidal quasi-spherical nanodiamonds was several orders of magnitude higher than those previously reported starting from microdiamonds. The results open up avenues for the industrial cost-effective production of fluorescent nanodiamonds with well-controlled properties.

Abstract A series of fracture experiments were carried out at various strain-rates on pre-cracked silicon single crystals between – 196° and 1000°C. The surface energy for cleavage was determined from many tests to be 2500 erg/cm2. A transition from pure cleavage to general yielding at the crack-tip was found to occur over several degrees centigrade. The brittle-to-ductile transition was rate dependent and obeyed an activation energy close to that for thermally-activated dislocation glide. A mechanism based on crack-tip blunting through dislocation nucleation and glide was developed to explain the abruptness of the brittle-to-ductile transition. The crack-tip dislocation arrangements were analysed by Lang X-ray topography.

Diamond nanoparticles (nanodiamonds) have been recently proposed as new labels for cellular imaging. For small nanodiamonds (size <40 nm), resonant laser scattering and Raman scattering cross sections are too small to allow single nanoparticle observation. Nanodiamonds can, however, be rendered photoluminescent with a perfect photostability at room temperature. Such a remarkable property allows easier single-particle tracking over long time scales. In this work, we use photoluminescent nanodiamonds of size <50 nm for intracellular labeling and investigate the mechanism of their uptake by living cells. By blocking selectively different uptake processes, we show that nanodiamonds enter cells mainly by endocytosis, and converging data indicate that it is clathrin-mediated. We also examine nanodiamond intracellular localization in endocytic vesicles using immunofluorescence and transmission electron microscopy. We find a high degree of colocalization between vesicles and the biggest nanoparticles or aggregates, while the smallest particles appear free in the cytosol. Our results pave the way for the use of photoluminescent nanodiamonds in targeted intracellular labeling or biomolecule delivery.

Biomaterials play an increasing role in modern health care systems. Biocompatibility poses a significant challenge for manufacturers of medical devices and contemporary intelligent drug delivery technologies from materials development to market approval. Despite a highly regulated environment, biocompatibility evaluation of biomaterials for medical devices is a complex task related to various factors that include mainly chemical nature and physical properties of the material, the contact tissue and duration of contact. Although international standards, such as ISO 10993-1, are generally employed to prove regulatory compliance needed for market clearance or for initiating clinical investigations, they may not offer sufficient guidance, or risk-management perspective when it comes to choosing materials or appropriate in vitro biocompatibility screening methods when developing medical devices. The global normative approach towards the biocompatibility evaluation of medical devices is presented in this review, with a focus on in vitro studies. Indeed, a risk-management approach towards the judicial choice of in vitro tests throughout the development and production of medical devices and drug delivery systems will facilitate rapid regulatory approval, avoid unnecessary animal studies, and ultimately reduce risks for patients. A detailed overview towards the construction of a comprehensive biological evaluation plan is described herein, with a focus on polymer-based materials used in medical applications. Polymeric materials offer a broad spectrum of applications in the manufacturing of medical devices. They are extensively employed within both conventional and innovative drug delivery systems with superior attributes supporting robust, extended use capacity, capable of meeting specific requirement such as adhesion, drug release, and more. Various methods of biocompatibility assessment are detailed within, with an emphasis on scientific analysis. This review may be of interest to those involved in the design, manufacturing and in vitro testing of medical devices and innovative drug delivery technologies, specifically with respect to a risk-management approach towards the biocompatibility assessment of polymer-based devices.

A micro-macro model derived from slip theory is shown. It is applied to the modeling of nickel base single crystal superalloys. The experimental data include monotonic and cyclic solicitations at 950°C. The general agreement between tests and numerical simulations is good for all the studied orientations: 〈001〉, 〈011〉, 〈111〉, and 〈123〉. The model is simple enough to be implemented in a finite element code as shown in a future part of the paper.

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Legume root architecture is characterized by the development of two de novo meristems, leading to the formation of lateral roots or symbiotic nitrogen-fixing nodules. Organogenesis involves networks of transcription factors, the encoding mRNAs of which are frequently targets of microRNA (miRNA) regulation. Most plant miRNAs, in contrast with animal miRNAs, are encoded as single entities in an miRNA precursor. In the model legume Medicago truncatula, we have identified the MtMIR166a precursor containing tandem copies of MIR166 in a single transcriptional unit. These miRNAs post-transcriptionally regulate a new family of transcription factors associated with nodule development, the class-III homeodomain-leucine zipper (HD-ZIP III) genes. In situ expression analysis revealed that these target genes are spatially co-expressed with MIR166 in vascular bundles, and in apical regions of roots and nodules. Overexpression of the tandem miRNA precursor correlated with MIR166 accumulation and the downregulation of several class-III HD-ZIP genes, indicating its functionality. MIR166 overexpression reduced the number of symbiotic nodules and lateral roots, and induced ectopic development of vascular bundles in these transgenic roots. Hence, plant polycistronic miRNA precursors, although rare, can be processed, and MIR166-mediated post-transcriptional regulation is a new regulatory pathway involved in the regulation of legume root architecture.

Responsive surfaces composed of cylindrical or square micrometer-sized thermoresponsive pillars made of thiol-ene nematic main-chain liquid crystalline elastomers (LCEs) are produced by replica molding. The individual pillars behave as microactuators, showing ultralarge and reversible contractions of around 300-400% at the nematic to isotropic phase transition. The nematic main-chain LCE microactuators described here present contractions as large as the best macroscopic systems reported in the literature. Moreover, the contraction observed for this new system outperforms the best values already reported for other LCE microsystems.

Preparation by morphosynthesis–the chemical construction and patterning of inorganic materials with complex forms–will only be technologically relevant if inexpensive routes with high product yields can be developed. A facile, one-step, high-yield preparation of vaterite (calcium carbonate) microsponges is presented, the proposed mechanism for the formation of which is illustrated in the Figure.

Routine preparation of mesostructured nanoparticles (see Figure) at room temperature is possible using the simple quenching procedure presented here. Silica particles with mesostructured interiors and diameters as small as 15 nm can be synthesized as can organo-silica derivatives with chemically functionalized mesopores. Preliminary insights into the mechanism of growth of these materials are also gained.

The degradation of A1N powder in excess H 2 O at room temperature for up to 24 h was investigated. Samples were characterized by various techniques (IR; XRD; SEM; XPS; C, H, N analysis; surface area, particle size, and weight change measurements). The reaction rate was found to be significant, with 80% of the A1N being consumed in 24 h. The initial reaction product was found to be a porous, amorphous, hydrated alumina with stoichiometry near AlOOH. After ∽16 h a crystalline phase, bayerite Al(OH) 3 , was detected which became the predominant phase after 24‐h contact. The kinetics of the A1N consumption were found to be first order and the reaction rate linear. The kinetic data fitted an unreacted core model with a porous product layer where the surface chemical reaction controlled the overall kinetics.

Abstract The properties of chitosan depend on several parameters including its origin (shrimp, squid, fungi etc), characteristics (mol fraction of N ‐acetylation; molecular weight) and treatments used to condition it (dissolving, precipitation, drying). These parameters can influence the material's sorption properties for metal ions. It has been suggested that the changes in sorption properties are related to the crystallinity of the material. The present work focuses on the study of the crystallographic properties of samples prepared from shrimp, squid and fungi sources, with different characteristics and conditioned by several physical treatments (dissolving, reprecipitation and drying, including oven‐drying, freeze‐drying), prior to subsequent studies of their sorption properties for platinum (discussed in Part II of this manuscript). © 2003 Society of Chemical Industry

Abstract Rate form constitutive equations of elasto‐viscoplastic type are expressed in a manner similar to that of classical metals, but the viscoplastic part, which is no longer incompressible, is related to the rate of variation of porosity. An incremental and implicit algorithm has been implemented in a finite element program in order to simulate hot isostatic pressing of an Astroloy powder. Temperature distributions are shown to induce strong density variations in real parts during hot isostatic pressing (HIP). For one particular turbine disk, we tested the sensitivity of the final shape to different processing parameters. Computed final shapes compare well with experimental ones.