67 research outputs found
Tribological aspects in modern aircraft industry
Preface : The problem of contact materials subject to relative movement is becoming increasingly important for lifetime of the equipment, pollution and cost in energy. One of the aims of tribology is to understand how friction occurs and wear in dynamical contacts. This can vary considerably depending on the choice of the pair of materials and the experimental device. Few milligrams of material lost in a mechanism is sufficient to make it unusable and cause replacement with significant costs. There is still no specific and general formalism to solve the problem of tribology, that is to say, friction, tearing, wear and lubrication of solid and liquid. Friction behavior or wear depends on complex conditions of stress, environment and physicochemical properties of surfaces, themselves dependent on tribological mechanisms. The intrinsic mechanical properties of materials are complementary and play a direct role in the tribological process. The work presented at the ACMAâ14 conferences are multidisciplinary, by interacting mechanics, physical chemistry and materials science on a different scale ranging, the goal is to explain, even if the reactions of the contact surfaces are very complex, the basics of tribology, the process of friction and wear, to apply the test methods on the materials in contact and get material coatings on other surfaces by different methods and processes mechanical, physical and chemical. This special issue of the journal "KEM: Key Engineering Materials" consists of a collection of studies both in the fields of experimental simulation of tribology than the science of surfaces in contact by relative movements in relation to the mechanical properties materials
Speed and Atmosphere Influences on Nanotribological Properties of NbSe2
Nanotribological properties of NbSe2 are studied using an atomic friction force microscope. The friction force is measured as a function of normal load and scan speeds ranging from 10 nm sâ1 to 40 ÎŒm sâ1 under two atmospheres (air and argon). At low speed, no effect of atmosphere is noticed and a linear relationship between the friction and normal forces is observed leading to a friction coefficient close to 0.02 for both atmospheres. At high speed, the tip/surface contact obeys the JKR theory and the tribological properties are atmosphere dependent: the shear stress measured in air environment is three times lower than the one measured under argon atmosphere. A special attention is paid to interpret these results through numerical data obtained from a simple athermal model based on Tomlinson approach
Experimental and theoretical investigations of friction properties of graphite intercalated compounds.
It is classically admitted that the goodfriction properties of lamellar compounds are strongly related to their anisotropic structure and especially to the existence of weak interlayer interactions through the van der Waals gap separating the basal layers. As it is also known, the presence of the van der Waals gap in the structure of lamellar compounds will allow lot of chemical species to be intercalated in the structure leading both to the expansion of structure parameters and inter layer interactions modifications. The present work is concerned with the experimental and theoretical study of friction propertiesof Graphite Intercalated Compounds (GICs) in order to better understand thetribologiclamellar compounds. In order to modulate the interlayer interactions, two types of intercalated species were used, electrophylic species (AlCl3, FeCl3, SbCl5) and nucleophilic species (Li, K, Rb)
High temperature tribological behaviour of metal matrix composites produced by SPS
Materials used as friction components in transportation field are subjected to extreme working conditions: they rapidly reach their structural limits and critical parts require to be regularly replaced. Alternative solutions withstanding higher operating conditions imply to find innovative materials. Steel matrix composites including various solid lubricants, WS2 and h-BN, able to support high temperatures were developed using a Spark Plasma Sintering technique, which makes possible the formation of new microstructures out of reach by conventional means. Sliding tests were conducted using a pin-on-disc tribometer in air at 450°C, with a normal load of 15 N and various velocities ranged from 0.1 to 1.5 m/s. Influence of solid lubricant content and sensitivity to test parameters were studied in terms of friction and wear responses of the contacting materials. Test results reveal an improvement of friction properties for composites containing highest WS2contents. A reduction of wear is quantified for all composites, and the best behaviour is observed for those that contain WS2. In agreement with the third body approach, interpretations are proposed to describe the interphase dynamics within the contact
Evolution des propriétés mécaniques de surface suivie par spectrométrie Raman sur des couples en carbure de silicium et en carbones imprégnés
Les garnitures mĂ©caniques en carbure de silicium (SiC) sont gĂ©nĂ©ralement utilisĂ©es en milieu lubrifiĂ©. Toutefois afin d'accĂ©der Ă de nouvelles applications technologiques, il peut ĂȘtre nĂ©cessaire de les employer en contact sec. Cependant, l'emploi du couple SiC/SiC dans les conditions de frottement sec conduit Ă une usure sĂ©vĂšre des garnitures, voire Ă leur rupture. Afin de dĂ©velopper cette application une des bagues est remplacĂ©e par un matĂ©riau en carbone-graphite (CG) dont les propriĂ©tĂ©s mĂ©caniques et tribologiques sont renforcĂ©es par le procĂ©dĂ© d'imprĂ©gnation qui consiste Ă introduire dans les porositĂ©s du CG un polymĂšre ou un mĂ©tal ductil Ă basse tempĂ©rature. Dans cette Ă©tude, nous avons choisi l'imprĂ©gnation soit par une rĂ©sine phĂ©nolique, du PTFE, ou de l'antimoine. Ces ajouts ont pour effet respectif de renforcer la structure de la bague en CG, de diminuer son Ă©nergie de surface et de permettre l'accomodation par dĂ©formation du film interfacial. Nous proposons d'Ă©tudier les mĂ©canismes de dĂ©gradations tribologiques qui surviennent Ă l'interface entre le couple SiC/CG au moyen d'un tribomĂštre rotatif rĂ©alisant un contact conforme anneau/anneau, Ă tempĂ©rature ambiante, avec une vitesse de glissement de 0,5 m/s et une pression de contact de 0,1 MPa. Les faciĂšs d'usure et les tribofilms sont examinĂ©s par microscopie Ă©lectronique Ă balayage et par spectroscopie de dispersion des rayons X. La spectromĂ©trie Raman vient complĂ©ter l'identification chimique des films tribologiques. Cette technique permet la mesure et la cartographie de la taille des cristallites de graphite et la rĂ©partition des contraintes rĂ©siduelles Ă la surface des bagues en SiC ou en CG.La description des mĂ©canismes de dĂ©gradation des matĂ©riaux s'appuient sur le concept du circuit tribologique qui exprime un bilan des dĂ©bits de matiĂšre dans le contact. Dans le cas des couples SiC/CG, les dĂ©bits sources proviennent principalement des bagues en CG. Les bagues en SIC sont prĂ©servĂ©es de l'usure. Pour tous les couples de frottement, le troisiĂšme corps contient du carbone amorphe et des cristallites de grandes dimensions dont le maintien dans le contact est favorisĂ© par la dynamique du tribomĂštre. L'atmosphĂšre continue Ă jouer un rĂŽle dans l'interface car, bien que le contact soit conforme, l'oxydation de l'antimoine est dĂ©tectĂ©e Ă la surface des bagues qui en sont imprĂ©gnĂ©es. Les tribofilms les plus stables rĂ©duisent le dĂ©bit d'usure et cette stabilitĂ© est fonction de l'imprĂ©gnant employĂ©
Assessment of parameters variations for treatment of CO2 laser carburizing over AISI 4340 steel
This study evaluated the best parameters for the carburizing treatment using a CO2 laser of low power over an AISI 4340 steel previously subjected to heat treatments of quenching and tempering. The coating process used a liquid dispersion of carbon black in ethanol and carboxyl methylcellulose. The laser power was kept constant at 125 W and the resolution is 600 dots per inch. The variable parameter of CO2 laser was the speed. Two speeds were selected for the coating preparation: 1200 and 2000 m/s. After treatment, metallographic preparation and optical microscopy observation were performed in addition to the evaluation of parameter variations through hardness measurements and microscratch tests
Ătablissement dâun critĂšre de qualitĂ© des taillants diamant/WC-Co pour lâexcavation de formations rocheuses
Sous des conditions gĂ©ologiques extrĂȘmes, les outils de forage composĂ©s dâinserts en diamant polycristallins (PDC) sont particuliĂšrement intĂ©ressants au vu de leur performance de coupe [1]. La qualitĂ© des matĂ©riaux innovants utilisĂ©s pour la fabrication de ces outils PDC doit ĂȘtre dĂ©terminĂ©e avec prĂ©cision par la mesure de leur efficacitĂ© de coupe et de leur rĂ©sistance Ă lâusure. Un banc dâusure (tour) composĂ© de roches formĂ©es par un mortier spĂ©cifique a Ă©tĂ© utilisĂ© pour rĂ©aliser les expĂ©riences de cette Ă©tude. Durant les essais, des inserts PDC ont Ă©tĂ© usĂ©s sur une distance dâabrasion supĂ©rieure Ă 15 km avec un effort normal moyen compris entre 3000 et 5000 N, une vitesse de coupe autour de 1,8 m.s-1 et une profondeur de coupe de 2 mm. Les analyses sont basĂ©es sur des modĂšles Ă©tablissant des relations couplĂ©es entre les efforts de coupe et de frottement reliĂ©es aux mĂ©canismes dâexcavation rĂ©alisĂ©s par les outils de coupe [2]. Dans cette Ă©tude, les modĂšles sont implĂ©mentĂ©s dans le but dâĂ©valuer lâefficacitĂ© de coupe et pour estimer la durĂ©e de vie de ces inserts diamantĂ©s. Les inserts testĂ©s ont rĂ©vĂ©lĂ©s des taux dâusure [3] compris entre 1·10-8 et 16·10â8 mm3·N-1·m-1 et des efficacitĂ©s de coupe Ă 10 km Ă©valuĂ©es entre 31 et 55 %. Une approche originale est ensuite dĂ©veloppĂ©e pour Ă©tablir analytiquement un critĂšre de qualitĂ© globale dâun taillant, tenant compte Ă la fois de son comportement tribologique (rĂ©sistance Ă lâusure) et de ses capacitĂ©s dâexcavation (efficacitĂ© de coupe). Une hiĂ©rarchie clairement marquĂ©e a Ă©tĂ© rĂ©vĂ©lĂ©e sur les diffĂ©rents taillants Ă©tudiĂ©s. Les variations de composition des matĂ©riaux et des mĂ©thodes de production distinctes utilisĂ©es pour la mise en Ćuvre des Ă©chantillons en sont Ă lâorigine
Thermal behavior of silicon carbide/carbon tribological tests
During friction, the materials in contact undergo a thermal field that can accelerate their deterioration or promote the creation of protective layers. Silicon carbide/carbon dry contact often experiences these phenomena through an oxidation process and a material transfer. In this study, three carbon samples with different impregnation conditions have been considered. Dry friction experiments using a ring-on-ring tribometer were carried out and thermal fields induced were followed by means of Infrared Thermography. Wear volumes and rates were analyzed as well as the third body generated during the tests. Energetic flows were identified and a wear mechanism for the silicon carbide/carbon dry contact is proposed, with respect to the concept of the third body approach
Analysis of wear mechanism in TPU-steel contact pair by means of long stroke tribometer tests
A complete wear characterisation of a thermoplastic polyurethane (TPU) sliding against steel is presented. Wear tests were performed using a long stroke tribometer under sliding reciprocating movement and dry conditions. The dependence of some of the most significant parameters was studied. Before and after wear tests, complementary observations, analyses and measurements were also performed on both contacting materials. These various characterisations involved weight loss of TPU, physico-chemical and thermo- mechanical analyses of TPU, included topographical measurements and morphological observations of worn surfaces of contacting pairs and calculations of the temperature rise generated by friction
Tribological behaviour of stellite matrix composites for high temperatures applications
Extreme working conditions affect material used as friction components in transportation field: they rapidly reach their limits and critical parts require to be regularly replaced. Alternative solutions withstanding higher operating conditions imply to find innovative materials. Stellite matrix composites including various solid lubricants, WS2 and h-BN, able to admitextreme conditions were developed using a Spark Plasma Sintering technique, which makes possible the formation of new microstructures out of reach by conventional means. Sliding tests were conducted using a pin-on-disc tribometer in air at 450°C, with a velocity of 0,25 m/s and various normal load ranged from 2.5 to 40 N. Influence of solid lubricant content and sensitivity to test parameters were studied in terms of friction and wear responses of the contacting materials. Friction properties are equivalent to Stellite ones and sometimes lesseffective. A reduction of wear is quantified for many composites, and the best behavior is observed for those that contain WS2. In agreement with the third body approach, interpretations are proposed to describe the interphase dynamics within the contact
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