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Chapitre 8.1 Applications en aéronautique

BARRALLIER, Laurent
Fonte: EDP Sciences Publicador: EDP Sciences
FR
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L’installation des nouveaux synchrotrons de haute énergie européens ainsi que la construction de la future source à spallation européenne ouvrent des perspectives nouvelles et inédites de recherche dans le domaine des matériaux et biomatériaux. C’est tout l’enjeu de ce livre qui présente les nouveaux équipements et les évolutions les plus récentes dans les techniques d’analyses des contraintes et des textures. Rayonnement synchrotron, rayons X et neutrons au service des matériaux, fait le point sur les nouvelles thématiques abordées et présente les nouvelles générations de sources synchrotrons et sources à spallation. Dans ce livre, l’analyse de la texture cristallographique dans les matériaux est particulièrement abordée ainsi que l’intérêt de la simulation numérique pour l’analyse des contraintes. Un chapitre entier présente les résultats les plus récents dans les secteurs de l’aéronautique, du ferroviaire à grande vitesse, de la géologie ainsi que dans le domaine des biomatériaux et des matériaux nouveaux. Après une présentation générale et un historique détaillé de la mesure des déformations, les auteurs montrent l’intérêt des neutrons dans la caractérisation des matériaux ainsi que l’utilisation du rayonnement synchrotron en science des matériaux. Une présentation détaillée de la technique et des problèmes rencontrés est faite dans la détermination des contraintes mécaniques par les grands instruments. Le chapitre 8.1 concerne les applications des méthodes diffractométriques par synchrotron et neutrons dans le domaine de l'aéronautique.

Determination of composition, residual stress and stacking fault depth profiles in expanded austenite with energy-dispersive diffraction

JEGOU, Sébastien; CHRISTIANSEN, T.L.; KLAUS, M.; GENZEL, Ch.; SOMERS, M.A.J.
Fonte: Elsevier Publicador: Elsevier
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A methodology is proposed combining the scattering vector method with energy dispersive diffraction for the non-destructive determination of stress- and composition-depth profiles. The advantage of the present method is a relatively short measurement time and avoidance of tedious sublayer removal; the disadvantage as compared to destructive methods is that depth profiles can only be obtained for depth shallower than half the layer thickness. The proposed method is applied to an expanded austenite layer on stainless steel and al- lows the separation of stress, composition and stacking fault density gradients.; Financial support from the Danish Research Council for Technolo- gy and Production Sciences under grant no. 274-07-0344 is gratefully acknowledged.

Stoney formula: Investigation of curvature measurements by optical profilometer

ARDIGO, Maria Rosa; AHMED, Maher; BESNARD, Aurélien
Fonte: Trans Tech Publications inc. Publicador: Trans Tech Publications inc.
EN
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Thin films’ residual stress is often determined by the Stoney formula, using the measurements of the substrate curvature, even if the required hypotheses are not completely respected. In this study, a 2.2 μm titanium nitride coating was deposited by reactive sputtering on a silicon substrate. The Stoney formula was used in order to calculate the residual stress of the film. The radius of curvature was measured, before and after coating by optical profilometer, considering the whole surface of the sample. The effect of the substrate shape (square and rectangular) with various dimensions was investigated. We showed that the shape of the substrate influence strongly the deformation. Moreover, it was highlighted that the choice of the radius (maximum value, minimum value, mean value, with or without initial curvature correction) is critical to the determination of the stress.

Growth of WC-Cr-N and WC-Al-N coatings in a RF-magnetron sputtering process

STANISHEVSKY, Andrei; WALOCK, Michael; ZOU, Yujiao; IMHOFF, Luc; ZAIRI, Amel; NOUVEAU, Corinne
Fonte: Elsevier Publicador: Elsevier
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Tungsten carbide-based coatings have been used in a wide variety of industrial applications such as high speed cutting tools, extrusion dies, drills, aerospace industries, and more. A few reports on ternary and quaternary coatings of WC with other elements indicate good prospects for these material systems. The present study focuses on the formation of quaternary WCeCreN and WCeAleN coatings during the simultaneous reactive RF-magnetron sputtering of tungsten carbide and Al or Cr targets in an argon/nitrogen gas mixture. The resulting coatings, with thicknesses of 3.5 mme8.2 mm, were characterized by using several analytical techniques including X-ray diffraction, SEM/EDS, AFM, and X-ray photoelectron spectroscopy. WCeCreN and WCeAleN coatings with high levels of tungsten (i.e. more than 50 at.% of the total metal content) demonstrated dense microstructure. Coatings with lower tungsten content formed columnar grain microstructure, with different surface morphologies depending on the process parameters. It was proposed that crystalline tungsten carbide (with partial N-substitution of C atoms) and chromium (or aluminum) nitride phases coexist in the coatings when the amount of tungsten was greater than 50 at.% of the total metal content; while at lower tungsten content...

Plasma Nitriding of 90CrMoV8 Tool Steel for the Enhancement of Hardness and Corrosion Resistance

NOUVEAU, Corinne; STEYER, Philippe; MOHAN RAO, Kumar Ram; LAGADRILLERE, Denis
Fonte: Elsevier Publicador: Elsevier
EN
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The aim of the study is to apply a plasma nitriding process to the 90CrMoV8 steel commonly employed in wood machining, and to determine its efficiency to improve both mechanical and electrochemical properties of the surface. Treatments were performed at a constant N2:H2 gas mixture and by varying the temperature and process duration. The structural and morphological properties of nitrided layers were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with EDS microanalyses. Surface hardening and hardness profiles were evaluated by micro hardness measurements. To simulate the woodmachining conditions, electrochemical tests were carried out with an oak wood electrolyte with the purpose of understanding the effects of the nitriding treatment on the corrosion resistance of the tool in operation. X-ray diffraction analyses revealed the presence of both γ′ (Fe4N) and ε (Fe2–3N) nitrides with a predominance of the ε phase. Moreover, α-Fe (110), γ′ and ε diffraction peaks were shifted to lower angles suggesting the development of compressive stresses in the post nitrided steel. As a result, it was shown that nitriding allowed a significant hardening of steel with hardness values higher than 1200 HV. The diffusion layers were always composed of an outer compound layer and a hardened bulk layer which thickness was half of the total diffusion layer one.No white layer was observed. Similarly...

Sputtered tungsten-based ternary and quaternary layers for nanocrystalline diamond deposition

WALOCK, Michael; RAHIL, Issam; ZOU, Yujiao; IMHOFF, Luc; CATLEDGE, Shane Aaron; NOUVEAU, Corinne; STANISHEVSKY, Andrei
Fonte: American Scientific Publishers Publicador: American Scientific Publishers
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Many of today’s demanding applications require thin-film coatings with high hardness, toughness, and thermal stability. In many cases, coating thickness in the range 2–20 m and low surface roughness are required. Diamond films meet many of the stated requirements, but their crystalline nature leads to a high surface roughness. Nanocrystalline diamond offers a smoother surface, but significant surface modification of the substrate is necessary for successful nanocrystalline diamond deposition and adhesion. A hybrid hard and tough material may be required for either the desired applications, or as a basis for nanocrystalline diamond film growth. One possibility is a composite system based on carbides or nitrides. Many binary carbides and nitrides offer one or more mentioned properties. By combining these binary compounds in a ternary or quaternary nanocrystalline system, we can tailor the material for a desired combination of properties. Here, we describe the results on the structural and mechanical properties of the coating systems composed of tungsten chromium-carbide and/or nitride. These WC-Cr-(N) coatings are deposited using magnetron sputtering. The growth of adherent nanocrystalline diamond films by microwave plasma chemical vapor deposition has been demonstrated on these coatings. The WC-Cr-(N) and WC-Cr-(N)-NCD coatings are characterized with atomic force microscopy and SEM...

Thermal Stability and Mechanical Properties of Sputtered Chromium-Molybdenum-Nitride (CrMoN) Coatings

ZOU, Yujiao; WALOCK, Michael; CATLEDGE, Shane Aaron; NOUVEAU, Corinne; STANISHEVSKY, Andrei
Fonte: International OCSCO World Press Publicador: International OCSCO World Press
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Purpose: The purpose of paper is to determinate thermal stability and mechanical properties of sputtered chromium-molybdenum-nitride (CrMoN) coatings. Design/methodology/approach: We have deposited 1.8 m-thick ternary Cr0.5Mo0.5N1.0 films on a CoCrMo alloy using a RF dual magnetron sputtering system, with Cr and Mo targets and N2 as the reactive gas. These films were subjected to various thermal treatments in Ar, air, and microwave plasma. The hardness, Young’s modulus, surface roughness, microstructure, and composition of films were studied by nanoindentation, AFM, x-ray diffraction, and x-ray photoelectron spectroscopy. Findings: The as-prepared CrMoN films consist of an amorphous Cr-rich nitride matrix with Mo-rich nitride crystalline grains, about 15 nm in size. These films are thermally stable up to 600ºC in air. Thermal annealing in the air at 800ºC resulted in an increase in surface roughness and hardness, due to film oxidation, with Cr2O3 as the main crystalline phase. Plasma treatment in a H2/N2 gas mixture, at 800ºC, did not lead to grain growth. Instead, the existing grains were reduced to about 10 nm and a new nanocrystalline phase has been formed. This leads to a decrease in the surface roughness, and an increase in the film hardness. In addition...

Etude de systèmes ternaires à base de Cr et N pour applications mécaniques sur outils de coupe destinés à la transformation du bois

LABIDI, Chafik; NOUVEAU, Corinne; IMHOFF, Luc; MARTIN, Nicolas; GAVOILLE, Joseph; PILLOUD, David; ROUSSELOT, Christophe; MOREL, Anne
Fonte: Société de Chimie Industrielle Publicador: Société de Chimie Industrielle
FR
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Les actes de ce colloque francophone ont été mis sur un CD-Rom, pas en version papier.; Le présent travail se propose d'étudier les propriétés physico-chimiques et mécaniques de revêtements PVD nanocristallins ou nanocomposites (CrAlN, CrSiN) obtenus sur différents substrats et destinés à la première et seconde transformation du bois une fois leur optimisation effectuée. Pour cela, les couches de CrAlN obtenues par magnétron RF ont subit des observations au MEB afin de déterminer la morphologie des couches alors que de la microanalyse EDS a défini leur composition. La structure des couches a été déterminée par diffraction de rayons X. Nous avons alors mesuré l’épaisseur des couches par profilométrie et par interférométrie puis on en a déduit les contraintes internes de celles-ci. L’adhérence et la dureté des couches ont été obtenues par scratch-tests et nanoindentation. Enfin, des analyses plus fines telles que de l’XPS et du SIMS ont été réalisées afin de déterminer les phases en présence dans ces couches. La co-pulvérisation réactive des cibles de Cr et Si en position confocale, est un procedé séduisant pour l’élaboration de films de CrSiN avec une structure nanocomposite du type nc-CrN/a-SiNx. Les analyses EDS et les caractérisations par DRX et nanoindentation confirment dans ces films la présence de phase cristallisée de type CrN et la possibilité de faire varier leur teneur en silicium corrélée avec des changements de dureté.; Conseil Régional de Bourgogne ainsi que le Conseil Régional de Franche-Comté dans le cadre de ce projet transrégional intitulé « ROBUS »...

Etude de la stabilité thermique et de l’influence de l’épaisseur sur les contraintes de couches de Cr et CrN obtenues par pulvérisation cathodique,

NOUVEAU, Corinne; BENLATRECHE, Yacine; CHEKOUR, Lounis; LABIDI, Chafik
Fonte: Société de Chimie Industrielle Publicador: Société de Chimie Industrielle
FR
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Actes sur CD-Rom pas de version papier; Cette étude porte sur des dépôts de couches minces dures de chrome et de nitrures de chrome élaborées par PVD et leur caractérisation. Des films de chrome ont été préparés par pulvérisation cathodique RF. L’influence de l’épaisseur des films, de la puissance appliquée à la cible sur les contraintes résiduelles a été étudiée. L’analyse des contraintes résiduelles par le dispositif des Anneaux de Newton, pour différentes épaisseurs, montre l’existence d’un pic de contraintes entre 170 et 200 nm et ce pour une puissance de l’ordre de 200 W ce qui vérifie d’une part les résultats obtenus lors de précédentes études sur BN, AlN ou ZrBN et d’autre part, le modèle de croissance proposé par Nouveau [1]. En effet des analyses en DRX ont été faites afin de vérifier si un changement de structure avait lieu ou pas en fonction de l’épaisseur des couches. Nous nous sommes ensuite intéressés à la stabilité thermique des couches de CrN. Le suivi de recuits sous azote effectués à différentes températures sur des échantillons revêtus de nitrure de chrome par diffraction X montre que la stabilité thermique de ces films est assurée jusqu’à 800°C.; Programme PAI TASSILI (France-Algérie) 2004-2008

W-Cr-C-N Nanocomposite Thin-Film Coatings via Reactive Magnetron Sputtering

WALOCK, Michael; ZOU, Yujiao; LAGADRILLERE, Denis; NOUVEAU, Corinne; STANISHEVSKY, Andrei
Fonte: Society of Vacuum Coaters Publicador: Society of Vacuum Coaters
EN_US
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While binary tungsten carbide can form smooth, hard films, these suffer from low fracture toughness. Tungsten nitride films are frequently harder, but are more brittle. Chromium nitride has excellent wear and oxidation resistance, but films often form with low hardness. Composites of these binary compounds offer a possibility to tailor the material for a desired combination of properties. To this end, we have used reactive RF-magnetron sputtering with Cr and WC targets to form quaternary composites, with nitrogen as the reactive gas. The coatings were deposited on Si, Ti, and steel substrates. The nitrogen partial pressure was varied to investigate the relationship between the film properties and the deposition conditions. Energy dispersive spectroscopy showed changes in the chemical composition as a result of the change in nitrogen partial pressure. X-ray diffraction illuminated the structure as either a solid solution with a B1 NaCl structure, or a nanocomposite with the average crystallite size under 11 nm. Optical interferometer revealed low compressive stresses. And nanoindentation established that the films are hard and adherent.; U.S. National Science Foundation (DMR-0806521) and the Regional Council of Burgundy, France

Etude des propriétés microstructurales, mécaniques, thermiques et de la porosité des couches minces de CrAlN déposées par PVD sous différents pourcentages d’aluminium

TLILI, Brahim; BENLATRECHE, Yacine; GHRIB, Taher; NOUVEAU, Corinne
Fonte: Société Tunisienne de Physique (S.T.P) Publicador: Société Tunisienne de Physique (S.T.P)
FR
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Several experimental investigations have led to the development of CrAlN (Chrome Aluminum Nitride) hard coatings by varying the aluminum target bias voltage, in preference to the traditional CrN coating. The present work enabled characterisation by physical and mechanical techniques (XRD, AFM, MEB, nano-indentation, Young’s modulus, thermal propriety, Stress, porosity, etc.). Moreover, in order to find improved the adhesion of the different deposition condition of the coatings. The results obtained in this work demonstrate that variation in proportion to aluminum alter the resulting columnar morphology and porosity of the coatings. The thermal properties and the physical property are greatly affected by these morphological alterations. The comparison between the different coating microstructures of CrAlN coatings (columnar and fine-grained) reveals advantages for the fine-grained structure. The results are better wear protection and less profile deviation. Correlation between aluminum proportions in CrAlN coatings and his thermal properties revealed that the conductivity and the diffusivity are influenced primarily by size and shape distribution of the pores and secondarily by decrease of the stitch parameter dimension.

Test d’usure d’outils modifiés ou non lors du déroulage de MDF

AKNOUCHE, Hamid; NOUVEAU, Corinne; BENLATRECHE, Yacine; ROUSSELOT, Christophe; PILLOUD, David; ZERIZER, Abdelattif; MARCHAL, Rémy
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
FR
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Des revêtements à base de nitrure de chrome réalisés par pulvérisation triode ont été testés en déroulage et défonçage du bois. L’efficacité des revêtements triode a été montrée en usinage de MDF (Medium Density Fiberboard), donc dans des conditions sévères de coupe, ainsi qu’en défonçage d’OSB (Oriented Strand Board) où un revêtement CrN de 1μm d’épaisseur permet d’usiner 9 fois plus qu’un outil non revêtu [1]. Le but de cette étude est d’examiner comment on peut améliorer la tenue à l’usure des outils de coupe dans l’opération de déroulage du MDF, en traitant la partie active de l’outil. Les modifications des surfaces actives des couteaux consistent à appliquer des films durs (CrAlN, CrSiN), qui ont déjà donné des résultats prometteurs dans l’opération de défonçage du MDF [2], l’un des facteurs limitant dont il faut nous affranchir est l’adhérence des couches déposées sur les outils de coupe. C’est pourquoi nous avons testé des traitements duplex (nitruration ionique+dépôt magnétron). Ces revêtements ont également été testés en simulant les chocs que peuvent générer les noeuds dans un billon. Les revêtements de CrAlN ont été réalisés par PVD sur un bâti dual magnétron RF alors que les couches de CrSiN ont été obtenues par l’institut FEMTO/ST de Besançon dans le cadre d’un projet de recherche. La nitruration ionique a été réalisée dans un four de traitement thermochimique BMI. Le processus d’usinage a été effectué sur une microdérouleuse instrumentée...

Couches minces dures type Cr-Al-N pour outils de coupe du bois

AKNOUCHE, Hamid; ZERIZER, Abdelattif; NOUVEAU, Corinne; KENNOUCHE, Salim; SITOUAH, N.; BOULAHIA, H.
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
FR
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Les outils de coupe pour l’usinage métallique sont très développés ces dernières années, ainsi plus 90% des outils en carbure et 10% des forets, tarauds en acier sont revêtus, tout en donnant des résultats intéressants, malheureusement cette tendance n’existe pas en usinage bois. Ce travail donc a pour objectif de développer des outils revêtus pour les tester en défonçage du bois de Pin d’Alep une essence très répandues dans le bassin méditerranéen. Notre étude se fera sur des outils de coupe en carbure revêtu en couches minces de CrN et de CrAlN à différent pourcentage respectivement d’Al déposé grâce à un bâti magnétron de marque Nordiko 3500.Les conditions de dépôts sont optimisés lors des précédents travaux, les essais d’usinage sont réalisés sur une défonceuse à commande numérique de marque Recordi. Le comportement à l’usure des outils modifiés est avéré très prometteur, on a constaté que les films en nitrure de chrome résistent d’une manière considérable par rapport aux outils en carbures. L’ajout de l’Aluminium n’améliore pas la résistance à l’usure mais contribue à la cristallisation des films.

Effects of microstructure and local mechanical fields on intergranular stress corrosion cracking of a friction stir welded aluminum–copper–lithium 2050 nugget

DHONDT, Matthieu; AUBERT, Isabelle; SAINTIER, Nicolas; OLIVE, Jean-Marc
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
EN
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The effects of the microstructure and mechanical fields on intergranular stress corrosion cracking (IGSCC) of the nugget zone of heat treated welds obtained by friction stir welding in the AA2050 aluminum alloy have been investigated at different scales. At low strain rate, in 1.0 NaCl aqueous solution, IGSCC develops in the microstructure, whereas only pitting corrosion is observed without any mechanical stress. Based on surface observations, EBSD analysis and X-ray tomography, the key role of sub-millimetric textured bands (induced by the welding process) on the IGSCC is demonstrated. Analyses at a more local scale show the grain boundary (low angle boundary, special coincident site lattice boundary or high angle boundary) do not have a significant effect on crack initiation. Crystal plasticity finite element calculations show that the threshold normal stress at grain boundaries for IGSCC development is about 80% of the macroscopic stress. It is also highlighted by crystal plasticity calculations that there is a drastic effect of the local stress field on the shape of cracks. Finally, it is shown that plasticity induced residual stresses are sufficient for the formation of IGSCC. © 2014 Elsevier Ltd.

Evolution of residual stresses during short time nitriding of 33CrMoV12-9 steel grade

FALLOT, Guillaume; JEGOU, Sébastien; BARRALLIER, Laurent
Fonte: Arts et Métiers ParisTech Publicador: Arts et Métiers ParisTech
EN
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The evolution of residual stresses during short time gas nitriding of 33CrMoV12-9 steel grade is studied. It aims understanding the influence of nitriding parameters (temperature T and nitriding potential Kn) on the generation and evolution of residual stresses in the very first stage of nitriding. The samples are gas nitrided using a thermobalance during 2h30 and 5 hours for various temperatures and nitriding potentials. Residual stress analyses are carried out by laboratory X-ray diffraction.; Projet Nit++

Tribological investigations of TiC+a-C:H Coatings Manufactured on X38CrMoV5-1 Steel Using PVD Technology

GOLABCZAK, Marcin; JACQUET, Philippe; NOUVEAU, Corinne; FLITI, Romain
Fonte: Trans Tech Publications, Switzlerland Publicador: Trans Tech Publications, Switzlerland
EN
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X38CrMoV5-1 steel is a typical tool steel commonly used in forging and plastic moulding industry for production of ejectors, slides, dies, etc. In plastics moulding a lot of these parts sustain relative movement. Because of this, some seizing or micro-welding may appear, especially when lubrication is not used. For many years, the different types of protective coatings were developed to avoid such problems. Most of the obtained solutions relate to the manufacturing of low friction coatings obtained by different nitriding processes and by CVD or PVD methods. In this article, the friction coefficients and the wear resistances of TiC+a-C:H protective coatings manufactured on X38CrMoV5-1 steel samples by using PVD technology are studied. The investigations are based on tribometer tests in different temperature conditions. The process of deposition of PVD coatings was realized by using multisource, hybrid factory-scale equipment of type URM 079. This equipment allows for deposition of coatings by a physical method. The tribological tests were performed using a precision high temperature tribometer under ambient and high temperature conditions with a steel and corundum balls as a counter-samples. In this paper, the results of these tribological tests are presented. It is shown that the measured friction coefficient of steel samples with PVD coatings is significantly lower than the friction coefficient of uncoated steel. It is also shown that X38CrMoV5-1 steel samples with manufactured TiC+a-C:H coatings are characterized by a very low friction coefficient and high wear resistance.

Low friction MoS2TiW Coatings Manufactured on X38CrMoV5-1 Steel Using PVD Method

GOLABCZAK, Marcin; JACQUET, Philippe; NOUVEAU, Corinne; FLITI, Romain
Fonte: Wiley Publicador: Wiley
EN
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In this article the friction coefficients and the wear resistances of MoS2TiW protective coatings manufactured on X38CrMoV5-1 steel samples by using PVD technology are studied. The investi- gations based on tribometer tests which were carried out in different temperature conditions. The process of deposition of PVD coatings was realized by using multisource, hybrid factory- scale equipment of type URM 079. This equipment allows for deposition of coatings by the phys- ical method. The tribological tests were performed using a precision high temperature tribome- ter under ambient and high temperature conditions with a steel and corundum balls as coun- ter-samples. In this paper the results of these tribological tests are presented. It is shown that the measured friction coefficient of steel samples with PVD coatings is significantly lower than the friction coefficient of uncoated steel. It is also shown that X38CrMoV5-1 steel samples with manufactured MoS2TiW coatings are characterized by very low friction coefficient and high wear resistance.

Structure and molecular dynamics of multilayered polycarbonate/polystyrene films.

WALCZAK, M; CIESIELSKI, W; GALESKI, A; POTRZEBOWSKI, M.J.; REGNIER, Gilles; HILTNER, A; BAER, E
Fonte: Wiley Publicador: Wiley
EN
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The definitive version is available at www3.interscience.wiley.com : http://onlinelibrary.wiley.com/doi/10.1002/app.36567/abstract; Multilayered film polycarbonate/polystyrene (PC/PS) comprising 257 layers with total thickness 125 m was made by coextrusion process. The nominal thickness of PC layers was 680 nm, and the nominal thickness of PS layers was 290 nm. Additionally the control samples of PC and PS with the thickness of 125 m were coextruded in the same way. There was reasonably good correlation between the PC and PS layers real thickness as measured by AFM and the estimated thickness determined from the processing parameters. Significant shift of glass transition temperature is observed in multilayer film: for PS component towards higher temperature while PC still being glassy and for PC towards lower temperature while PS being in rubbery phase. In order to investigate the amplitude and geometry of fast segmental motions, the LG-CP NMR technique under fast magic-angle spinning was used. 2D 13C – 1H LG-CP spectra of PC, PS and PC/PS 70/30 were recorded at various temperatures. Cross sections of aromatic carbons spectra show us the influence of PC on PS and vice versa. It gives us also the information about PS and PC segmental motion as a function of temperature: above the glass transition temperature of PS...

Shear-strain step response in linear regime of dilute suspensions of naturally bent carbon nanotubes

CRUZ, Camilo; ILLOUL, Lounès; CHINESTA, Fancisco; REGNIER, Gilles
Fonte: Wiley Publicador: Wiley
EN
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Impressive enhancements of the storage modulus have been documented when low volume fractions of single wall carbon nanotubes (SWNTs) are added to a Newtonian solvent for obtaining dilute suspensions. The intrinsic bending dynamics of carbon nanotubes (CNTs) has been proposed to explain such elasticity. CNTs contain topological defects inducing naturally bent structures in absence of external forces and, hence, a semiflexible filament with a bent configuration at minimal internal-bending-energy is used for mimicking the structure of SWNTs in suspension. Previous continuous model is discretized as a non-freely jointed bead-rod chain with a naturally bent configuration for simulating the rheological behaviour after a shear-strain step in linear regime of SWNT dilute suspension by using a Brownian dynamics (BD) approach. In general, bead-rod chains exhibit an instantaneous relaxation after a high shear-strain step. Bending rigidity and number of constitutive rods are found to be determinant parameters in the internal-energy relaxation behaviour of non-freely jointed bead-rod chains in dilute solution. Proper comparisons between the BD simulation results and the experimental data for treated SWNT dilute suspensions confirm the consistency of the physical model mimicking the structure of a SWNT.

Simulation of the stretch blow moulding process: from the modelling of the microstructure evolution to the end-use elastic properties of polyethylene terephthalate bottles

COSSON, Benoit; CHEVALIER, Luc; REGNIER, Gilles
Fonte: Springer Publicador: Springer
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The original publication is available at www.springerlink.com; The whole stretch blow-moulding process of PET bottles is simulated at the usual process temperature in order to predict the elastic end-use properties of the bottles. An anisotropic viscoplastic constitutive law, coupled with microscopic variables, is dentified from uniaxial tensile tests performed at different strain rates and temperatures. The microstructure evolution is characterised by crystallinity measurements from interrupted tests and frozen samples. For each specimen tested, the Young modulus is measured at room temperature. Numerical simulations of the blow moulding process are run using the C-NEM method. A micromechanical modelling is post-processed after the simulation to predict the elastic properties. Predictions of Young modulus distributions in bottles are in agreement with the ones measured on blow-moulded bottles.