Intéraction système-matériaux en fretting

Les nombreuses études menées en fretting montrent que les dégradations se traduisent soit par une perte de matière (fretting-usure), soit par l’amorçage de fissures dans les massifs (fretting-fatigue). Ces deux types de réponse dépendent de nombreux paramètres, tant fonctionnels (charge, déplacement, fréquence... imposés ou non) que matériaux (ductiles, fragiles...) et interfaciaux (troisième corps), qui sont parfois retranscrits sous forme de cartes de sollicitations locales ou de réponses des matériaux. Les frontières entre ces différents domaines sont déterminées à partir de critères issus directement des paramètres caractéristiques des cycles de fretting (ouverture du cycle, énergie dissipée), dont l’objectif est de définir le passage entre glissement partiel et glissement total. L’analyse précise des cycles de fretting est donc un élément central de la compréhension du comportement des matériaux sous ce type de sollicitation

Tribolumen: a tribometer for a correlation between AE signals and observation of tribological process in Real-Time—Application to a dry steel/glass reciprocating sliding contact

This paper deals with the development of an original apparatus called TRIBOLUMEN designed specifically for friction experiments on transparent materials. The friction measurement is synchronized with an acoustic emission (AE) sensor and the device is also equipped with a high- speed camera offering a direct view at the interface to gain a deeper understanding of tribological mechanisms. The TRIBOLUMEN device is in ball-on-flat contact configuration with a range of strokes from 5 to 500 μm and an oscillation frequency from 5 to 600 Hz. The experiments showed that this device has an adequate rigidity and can detect subtle friction modifications of the oscillating contacts. The observation of a steel-on-glass contact in real-time highlighted the initiation of Hertzian cracks followed by the formation of debris in the contact. Using the synchronous measurement, these mechanisms were clearly associated with different stages in the friction measurement and in the AE signals, which permitted to identify the AE signature of Hertzian cracks

An environmental tribometer for the study of rubbing surface reactivity

A new tribometer was designed to study the reactivity of rubbing surfaces under controlled environmental conditions. The contacting samples are isolated from the atmosphere by a chamber under secondary vacuum (10−6 mbar) where reactive gasses can be injected. The sample chamber can also be heated up to 900 ◦C by a radiative furnace. The sliding velocity can be varied from 0.05 to 1.5 m/s and the applied load from 5 to 100N (contact pressure ranged between 130MPa and 1.3 GPa). The instrumentation of the tribometer enables continuous measurement of the normal and tangential forces, vertical displacement of the contacting samples, temperature in the vicinity of the contact zone, partial pressure and gas composition in the test chamber and electrical contact resistance. The design difficulties have been exposed and the chosen technological solutions are presented. A test has been carried out to validate the tribological device

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

Conception d’un tribomètre environnemental pour l’étude de la réactivité des surfaces frottantes

En tribologie, un moyen de progresser efficacement dans la compréhension des phénomènes de couplage mécanique/thermique/environnemental sur la réactivité au niveau des surfaces et des interfaces est l’expérimentation où les conditions de contact sont parfaitement contrôlées (en termes de pression partielle d’oxygène, d’humidité ou sous vide, et de température). Pour cela, un tribomètre environnemental a été développé. L’objet de cet article est d’exposer les solutions technologiques adoptées, de présenter l’instrumentation (capteurs de force, de déplacement, de pression, de température, de résistance de contact, analyseur de gaz in situ), et de décrire les performances de ce prototype

Établissement d’un critère de qualité des taillants diamant/WC-Co pour l’excavation de formations rocheuses

Sous des conditions géologiques extrêmes, les outils de forage composés d’inserts en diamant polycristallins (PDC) sont particulièrement intéressants au vu de leur performance de coupe [1]. La qualité des matériaux innovants utilisés pour la fabrication de ces outils PDC doit être déterminée avec précision par la mesure de leur efficacité de coupe et de leur résistance à l’usure. Un banc d’usure (tour) composé de roches formées par un mortier spécifique a été utilisé pour réaliser les expériences de cette étude. Durant les essais, des inserts PDC ont été usés sur une distance d’abrasion supérieure à 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 basées sur des modèles établissant des relations couplées entre les efforts de coupe et de frottement reliées aux mécanismes d’excavation réalisés par les outils de coupe [2]. Dans cette étude, les modèles sont implémentés dans le but d’évaluer l’efficacité de coupe et pour estimer la durée de vie de ces inserts diamantés. Les inserts testés ont révélés des taux d’usure [3] compris entre 1·10-8 et 16·10−8 mm3·N-1·m-1 et des efficacités de coupe à 10 km évaluées entre 31 et 55 %. Une approche originale est ensuite développée pour établir analytiquement un critère de qualité globale d’un taillant, tenant compte à la fois de son comportement tribologique (résistance à l’usure) et de ses capacités d’excavation (efficacité de coupe). Une hiérarchie clairement marquée a été révélée sur les différents taillants étudiés. Les variations de composition des matériaux et des méthodes de production distinctes utilisées pour la mise en œuvre des échantillons en sont à l’origine

Wear mechanisms of WC-Co drill bit inserts against alumina counterface under dry friction: Part 2 — Graded WC-Co inserts

The tribological behaviour of innovative graded cemented carbide inserts were studied by using a rotary tribometer and abrasive alumina counterfaces. This work completes the study made on commercial inserts with homogeneous cobalt content. Inserts with three types of graduation processes were considered: inserts with borides WCoB phases, imbibed inserts and inserts combining both processes (i.e. inserts with reactive imbibition). Physicochemical and mechanical measurements show that the WCoB phases increase the hardness towards the active surface and the imbibition increases the insert core fracture toughness. The wear tests indicate that the boride phases lower the friction coefficient. In addition, as for the commercial inserts, cemented carbide volumes with higher cobalt content also reduce the friction coefficient. Concerning the wear results, the boride phases improve the abrasion resistance. By applying a third body approach, the WCoB phases limit the introduction of cobalt binder in the source flow, the cohesion of alumina particles in the internal flow and the formation of an abrasive paste in the contact. The imbibition process, where the cobalt migration is controlled, does not affect the wear resistance by avoiding a cobalt enrichment of the cemented carbide near the active surface

Interaction between systems and materials in fretting

Most fretting studies analyze material׳s responses using criteria directly issued from characteristic parameters of the fretting loops (loop aperture, dissipated energy, contact stiffness…). The present study concerns the influence of the device, first element of the tribological triplet, on the gross slip response of a ball-on-flat contact. The role of the static and dynamic device stiffness (vibratory analysis), of the control system mode (imposed displacement or imposed actuator force) and of the material type (ductile or brittle) on the loop shape is analyzed in order to distinguish the respective contributions of devices and materials

Development of an in-house cutting forces simulation for fir tree broaching process

This article proposes a simulation of cutting forces in broaching of fir tree slots. Every step needed to build an in-house fir tree broaching simulation is presented. This simulation is based on the discretization of each tooth of the broach, computation of elementary cutting forces of each discretized section, and finally the summation of each elementary cutting force into a global axes system. This work also presents orthogonal cutting experiments to implement realistic specific cutting forces into the model. The simulation obtained is compared with the real force signals of a fir tree broach to evaluate the quality of the simulation. At the end, the application to industrial context is developed

An experimental study of the high speed interaction between a labyrinth seal and an abradable coating in a turbo-engine application

A new high-speed test rig was designed to simulate the interactions between labyrinth seals and abradable coatings in similar turbo-engine operating conditions. To determine a solution for turbo-engine efficiency enhancement, we investigated the clearance reduction between the rotary parts in air systems, the successive starts and stops, the thermal expansion and the vibrations that might cause direct rub interactions between a rotary seal, known as a labyrinth seal, and a turbo-engine housing coated with a sacrificial abradable material. High interaction speeds from 0 to 130 m s−1 were obtained using a 5-axis milling machine fitted with a unique magnetic bearings spindle developed specifically for the study. The purpose of this paper is to study the interaction phenomena between an abradable material (Al–Si 6%) and a nickel alloy (Alloy 718) to obtain a first contact assessment under different turbo-engine operating conditions. The experimental results are first presented by visual observations of the posttest samples, as specified by accurate profile measurements. A quantitative approach to the interaction forces recorded during the tests and micrographic observations complete the preliminary study. This work provides new basic data for a preliminary study of the interaction between labyrinth seal teeth tips and abradable coatings in turbo-engine applications