Influence of a single asperity on stresses during lubricated sliding contact on DLC-coated system

http://tribo-lyon2013.sciencesconf.org/18528International audienceExtreme low wear rates of Diamond-Like Carbon (DLC) coatings are one the properties that makes them particularly interesting for numerous applications, like automotive ones. This property is often observed during characterisation tests under basic sollicitations like fretting, sliding, rolling-sliding. However, tests on cam-tappet systems show the coating lifetime can be highly reduced under special coupled conditions, such as the presence of an asperity breaking through the lubrication film into the contact area. Its influence on surface and subsurface stresses has to be quanti ed to eventually obtain a predictive model of the coating lifetime. The purpose of this study is to develop a simpli ed numerical model that is consistent with elasto-hydrodynami-lubrication (EHD) approxima- tions for estimating the stress perturbation due to such an asperity

Mise en évidence et simulation de l’endommagement des revêtements de carbone amorphe pour application moteur à combustion interne

The use of micrometric diamond-like carbon coatings (named DLC) are becoming widely used by automotive manufacturers in order to improve the efficiency of internal combustion engines by reducing the mechanical friction losses. Although DLC coatings generally exhibit excellent tribological properties and very low wear rates, their use in internal combustion engines shows that, subject to complex loadings, many degradation modes are observable. Untimely propagation of these latter upon the entire coated surfaces is a risk to control in order to guarantee the coating function over time. From one hand, this control implies to know and to understand all DLC degradation mechanisms when applied to engine components. On the other hand, it is necessary to possess lifetime simulation tools that can be used to optimize tribological systems in their early design. The work presented in this thesis has been guided by these goals and gathers experimental analyses of DLC-coated components, numerical analyzes, simplified testing protocols and coupling analyses of degradation processes. All these topics finally lead to the definition of a lifetime simulation tool adapted to DLC coated internal combustion engine applicationsL'exploitation de revêtements micrométriques à base de carbone amorphe (les DLC) tend à se généraliser au sein des constructeurs automobiles afin d'améliorer le rendement des moteurs à combustion interne en réduisant les pertes mécaniques par frottement. Si ces revêtements exhibent généralement d'excellentes propriétés tribologiques et de très faibles taux d'usure, leur utilisation au sein des moteurs à combustion interne révèle que, soumis à des sollicitations complexes, de nombreux modes de dégradations sont observables. La propagation prématurée de ces dégradations sur l'intégralité des surfaces revêtues constitue un risque à maîtriser pour garantir la fonction des revêtements dans le temps. Cette maîtrise implique d'une part de connaître et de comprendre les mécanismes de dégradations probables des DLC appliqués aux composants du moteur et d'autre part de disposer d'outils de simulation de leur durée de vie, exploitables pour optimiser les systèmes tribologiques au plus tôt de leur conception. Les travaux présentés dans cette thèse ont été guidés par ces objectifs et rassemblent des expertises de composants revêtus, des développements d'analyses numériques, de protocoles d'essais simplifiés et des recherches de couplages entre modes de dégradations. Autant d'éléments qui permettent de répondre en partie aux questions initialement posées et de proposer, au final, un outil de simulation de durée de vie des DLC adapté aux applications moteur à combustion intern

DLC damage identification and simulation for internal combustion engine application

L'exploitation de revêtements micrométriques à base de carbone amorphe (les DLC) tend à se généraliser au sein des constructeurs automobiles afin d'améliorer le rendement des moteurs à combustion interne en réduisant les pertes mécaniques par frottement. Si ces revêtements exhibent généralement d'excellentes propriétés tribologiques et de très faibles taux d'usure, leur utilisation au sein des moteurs à combustion interne révèle que, soumis à des sollicitations complexes, de nombreux modes de dégradations sont observables. La propagation prématurée de ces dégradations sur l'intégralité des surfaces revêtues constitue un risque à maîtriser pour garantir la fonction des revêtements dans le temps. Cette maîtrise implique d'une part de connaître et de comprendre les mécanismes de dégradations probables des DLC appliqués aux composants du moteur et d'autre part de disposer d'outils de simulation de leur durée de vie, exploitables pour optimiser les systèmes tribologiques au plus tôt de leur conception. Les travaux présentés dans cette thèse ont été guidés par ces objectifs et rassemblent des expertises de composants revêtus, des développements d'analyses numériques, de protocoles d'essais simplifiés et des recherches de couplages entre modes de dégradations. Autant d'éléments qui permettent de répondre en partie aux questions initialement posées et de proposer, au final, un outil de simulation de durée de vie des DLC adapté aux applications moteur à combustion interneThe use of micrometric diamond-like carbon coatings (named DLC) are becoming widely used by automotive manufacturers in order to improve the efficiency of internal combustion engines by reducing the mechanical friction losses. Although DLC coatings generally exhibit excellent tribological properties and very low wear rates, their use in internal combustion engines shows that, subject to complex loadings, many degradation modes are observable. Untimely propagation of these latter upon the entire coated surfaces is a risk to control in order to guarantee the coating function over time. From one hand, this control implies to know and to understand all DLC degradation mechanisms when applied to engine components. On the other hand, it is necessary to possess lifetime simulation tools that can be used to optimize tribological systems in their early design. The work presented in this thesis has been guided by these goals and gathers experimental analyses of DLC-coated components, numerical analyzes, simplified testing protocols and coupling analyses of degradation processes. All these topics finally lead to the definition of a lifetime simulation tool adapted to DLC coated internal combustion engine application

A model for single asperity perturbation on lubricated sliding contact with DLC-coated solids

International audienceIn lubricated sliding contact systems with DLC coated solids, recent studies have shown that DLC coatings are highly sensitive to asperities breaking through the lubricant film within the contact area. Those asperities produce damages similar to those obtained from scratch tests, from where coating delamination can initiate and propagate. To better understand the link between scratches and coating delamination, endurance tests can then be performed on coating with controlled initial scratches. To ensure the scratches’ representativity with respect to the actual asperities’ contact condition, one has to estimate the load transmitted by such asperities as well as the induced perturbation on surface and subsurface stresses. In this paper, a simplified numerical model corresponding to such problems is presented. It is consistent with elasto-hydrodynamic (EHD) lubrication approximations and can be used on coated or uncoated systems. As a simplified model, it can be run quickly on multiple configurations, enabling the creation of representative scratch maps for the given lubricated contact conditions

Usures et endommagements des revêtements DLC sur systèmes came-poussoir

International audienceDes essais sévères réalisés sur systèmes came-poussoir ont montré que la durée de vie des revêtements DLC (Diamond-Like Carbon) pouvait être grandement altérée par rapport à celles couramment observées sous sollicitations élémentaires. Avec l'objectif de proposer à terme un modèle d'estimation de durée de vie de ces revêtements, l'analyse des surfaces usées a permis de construire un scénario d'usure complet où interviennent l'ensemble des processus d'endommagement observés et leurs couplages supposés

Surface analysis of DLC coating on cam-tappet system

Tribomechanical properties of diamond-like carbon (DLC) coatings make them particularly interesting for numerous applications, like automotive ones. But although DLC coatings show a generally high wear resistance, they sometimes can exhibit severe multiple wear. In this study, a surface analysis of worn coated tappets is performed, leading to a complete coupled wear scenario

Influence of scratches on the wear behavior of DLC coatings

International audienceIn lubricated sliding contact systems with Diamond-Like Carbon (DLC) coated solids, several studies have shown that DLC coatings are highly sensitive to asperities breaking through the lubricant film within the contact area. Those asperities produce damages similar to those obtain from scratch tests, from where coating delamination can initiate and propagate. In this work, the influence of initial surface degradations upon the coating lifetime is investigated using wear tests on initially scratched DLC coatings. Results shown that although scratches can be seen as initial damage leading to local spalling, they are likely to break the most prominent roughness peaks of the counterbody and, as a result, to protect the overall coated surface from excessive contact pressure and increase the overall coating lifetim

Mechanical behavior of DLC coatings under various scratch conditions

International audienceIn lubricated sliding contact systems with Diamond-Like Carbon (DLC) coated solids, several studies have shown DLC coatings are highly sensitive to asperities breaking through the lubricant film within the contact area. Those asperities produce damages similar to those obtain from scratch tests, from where coating delamination can initiate and propagate. In the present study, controlled scratches have been performed on DLC-coated samples by varying the tip radius, the normal load and the sliding speed. From one hand, the different fracture mechanisms are compared to those observed on a coated cam-tappet system. They both lead to similar damage and wear, from substrate plasticity to gross spallation, via tensile and angular cracking. On the other hand, a numerical analysis is conducted with a finite element model. It reveals the fracture mechanism can be qualitatively predicted. Additional computations show the scratch severity increases by considering a thinner coating. This upholds the observed experimental coupling between tribochemical wear, scratch networks and coating delamination

Machine learning method to measure the transmission matrix of a multimode optical fiber without reference beam for 3D beam tailoring

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Machine learning method to measure the transmission matrix of a multimode optical fiber without reference beam for 3D beam tailoring

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