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Polymers were slid on rough hard steel surfaces with normal loads which caused full penetration (real and apparent areas equal) and partial penetration (real less than apparent area). Wear data for polyvinylchloride (PVC) and polychlorotrifluoroethylene (PCTFE) was obtained on a pin-on-disk machine using neutron activation analysis A (NAA). Observations of the wear process were made in the scanning electron microscope (SEM) both before, during, and after the wear experiment. It was observed that these polymers along with Nylon 6-6 tend to wear in discrete sites rather than continuous films. At these discrete sites the polymer shears at an angle which is dependent on the mechanical properties of the polymer and on the asperity angle. There appears to be a minimum shear angle beyond which no wear occurs. / Ph. D.

An investigation of interfacial and bulk friction-induced dissipation in model epoxy-based composite materials reinforced with carbon fillers, as well as pure epoxy, is a challenge of this PhD thesis. While the interfacial dissipation depends mostly on surface properties of very thin material layer, the bulk dissipation involves high volume deformations. Firstly, an experimental friction investigation on carbon fibre- and carbon nanopearl-reinforcedepoxies of different filler volume friction under soft tribological conditions is carried out. In order to understand the results, a generalized frictional law for interfacial friction between two composites is proposed. It is based on Bowden and Tabor theory applied to multimaterial contact and requires a contact in-plane geometry parameter and local friction coefficients. Depending on applied assumption, effective shear stress or effective hardness for all composite phases, it results in direct or inverse proportionality frictional law. These analytical results complete and explain the experimentally obtained tendencies: the direct law should be applied to the composite/epoxy contact, while the inverse law is valid for the composite/composite contact. The second part of the experimental work deals with pure epoxy and carbon fibre-reinforced epoxy under severe tribological conditions. It aims to investigate bulk frictional dissipation and associated wear. A two-scale approach is established, which consists in calculation of macro parameters, such as wear rate, dissipated frictional energy, friction coefficient and relative contact temperature rise, and their coupling with damaged surface observations. This approach allows us to distinguish several wear modes, as two-body and three-body abrasion, adhesion, fatigue and thermal effects, and to associate their appearance and evolution to macro parameters. In contrast to pure epoxy, carbon fibre-reinforced epoxy tends to be more wear resistant.

The radioactive ion implantation wear measuring method (RII) has been used for many years as a tool to make highly sensitive real-time in-situ measurements of wear and corrosion in metallic or ceramic materials. The method consists of the controlled implantation of radioactive ions of limited decay time in a thin layer at the surface of the material. The progressive abrasion of the material results in a decline in radioactivity which is followed to monitor material losses. The application of RII to control the wear of polymers is potentially of interest, but it has been lagging behind because of uncertainties related to possible changes in material properties during and after the implantation, and to the exact shape of implantation profiles. In this thesis, we investigate these issues on two thermoplastic elastomers typically used for making the soles of sport shoes, among which one contains radiation-sensitive unsaturated bonds, using as ions 7Be, 7Li and Kr. The results of the sample characterisation indicate that the 7Be and 7Li implantations, under properly-selected conditions, do not induce significant modifications in the materials. The implantation of a stack of polymer thin films and the activity measurements performed to determine the implantation profile are also presented. The experimental results on the ion implantation profiles and the determination of calibration curves are presented and discussed in comparison with simulated results. The results indicate that it is possible to predict the implantation profile by means of simulations. This bodes well for the application of the RII method to polymer materials. In the last part, an experimental study is presented regarding the possible redistribution of the implanted 7Be after implantation. Since very few existing experimental techniques are able to detect light elements implanted in polymer targets at fluences less or equal to 1012 cm-2, with implantation depths of a few µm, a new method is presented, which implies the use of plasma etching techniques in order to remove layers of polymers and measuring the remaining activity after each step. Our results indicate that a redistribution of the implanted ions takes place during the implantation process, resulting in a scrambling of the initial implantation profile. Nevertheless, provided a suitable methodology be used, wear measurements in polymers by using the RII method are still possible, as we propose in the thesis.

L’enjeu de ce travail concerne la dissipation interfaciale et volumique induite par le frottement dans les matériaux composites modèles á base d’époxy renforcée par du carbone, ainsi que dans l’époxy pure. Alors que la dissipation interfaciale dépend surtout des propriétés d’une couche mince de surface, la dissipation volumique induit des déformations de volume importantes. Dans un premier temps, nous avons effectué une étude expérimentale de frottement sur les résines époxy renforcées par des fibres et des nanoperles de carbone en différentes concentrations sous des conditions tribologiques faibles. Afin de comprendre les résultats obtenus, une loi de frottement généralisée pour le frottement interfacial entre deux composites a été proposée. Basée sur la théorie de Bowden et Tabor et appliquée au contact des composites, elle requiert un paramètre géométrique de contact et des coefficients de frottement locaux. En fonction de l’hypothèse appliquée, la contrainte de cisaillement ou la dureté effective pour toutes les phases du composite, elle découle sur une loi de proportionnalité directe ou inverse. Ces résultats analytiques complètent et expliquent les tendances obtenues expérimentalement : la loi directe doit être appliquée pour le contact composite/époxy, tandis que la loi inverse est valide pour le contact composite/composite. La deuxième partie du travail expérimental est consacrée á l’étude sur l’époxy pure et celle renforcée par des fibres de carbone sous des conditions tribologiques plus sévères. Son objectif est d’étudier la dissipation volumique et l’usure associée. Dans ce cadre, une approche multi-échelle est établie, qui consiste d’abord á calculer les paramètres macroscopiques, comme le taux d’usure, l’énergie dissipée par le frottement, le coefficient de frottement et l’augmentation de la température. Ces paramètres sont ensuite couplés avec les observations des surfaces endommagées. Cette approche nous permet de distinguer plusieurs régimes d’usure, i.e. l’abrasion á deux et trois corps, l’adhésion, la fatigue et les effets thermiques, et associer leur apparence et leur évolution avec les paramètres macroscopiques. Contrairement á l’époxy pure, le composite renforcé par des fibres de carbone s’avère être plus résistant á l’usure. / An investigation of interfacial and bulk friction-induced dissipation in model epoxy-based composite materials reinforced with carbon fillers, as well as pure epoxy, is a challenge of this PhD thesis. While the interfacial dissipation depends mostly on surface properties of very thin material layer, the bulk dissipation involves high volume deformations. Firstly, an experimental friction investigation on carbon fibre- and carbon nanopearl-reinforcedepoxies of different filler volume friction under soft tribological conditions is carried out. In order to understand the results, a generalized frictional law for interfacial friction between two composites is proposed. It is based on Bowden and Tabor theory applied to multimaterial contact and requires a contact in-plane geometry parameter and local friction coefficients. Depending on applied assumption, effective shear stress or effective hardness for all composite phases, it results in direct or inverse proportionality frictional law. These analytical results complete and explain the experimentally obtained tendencies: the direct law should be applied to the composite/epoxy contact, while the inverse law is valid for the composite/composite contact. The second part of the experimental work deals with pure epoxy and carbon fibre-reinforced epoxy under severe tribological conditions. It aims to investigate bulk frictional dissipation and associated wear. A two-scale approach is established, which consists in calculation of macro parameters, such as wear rate, dissipated frictional energy, friction coefficient and relative contact temperature rise, and their coupling with damaged surface observations. This approach allows us to distinguish several wear modes, as two-body and three-body abrasion, adhesion, fatigue and thermal effects, and to associate their appearance and evolution to macro parameters. In contrast to pure epoxy, carbon fibre-reinforced epoxy tends to be more wear resistant.