Interactions « tribologie –- vibrations » entre une lamelle vibrante et la surface en contact avec celle-ci.

Dans différentes applications techniques, il est nécessaire de déterminer l'état de surface des matériaux. Différentes méthodes de mesure d'état de surface existent mais il est parfois difficile de comparer différentes structures. Afin de pouvoir réaliser cela, un nouveau capteur, développé dans notre laboratoire, permet de mesurer n'importe quelle surface périodique ou non, ayant des aspérités de hauteurs comprises entre 10 μm à 2 mm. Il s'agit d'une fine lamelle d'acier frottant sur la surface et vibrant selon ses fréquences propres de vibration. Dans cette étude, les paramètres d'état de surface (rugosité, frottement et compressibilité) de différentes surfaces ont été mesurés et comparés aux valeurs des énergies et de fréquences de la lamelle. Il y est montré que cette méthode est capable de lier ces paramètres tribologiques avec les valeurs des énergies et des fréquences. Cependant, la représentation 2D actuelle est parfois insuffisante pour discriminer les classes de surfaces. Le principal résultat de ce travail est une nouvelle représentation 3D incluant la compressibilité des surfaces et capable de discriminer les classes de surfaces

Influence du mode de polymérisation de composites verre/polyester sur leur comportement mécanique

L’objet de cette communication est d’analyser les propriétés mécaniques de composites unidirectionnels verre/polyester obtenus par deux procédés différents de polymérisation : un procédé conventionnel thermique et un procédé photochimique. Les propriétés mécaniques de surface ont été étudiées par micro-indentation afin d’observer l’influence des conditions d’élaboration sur la réponse du composite à une pénétration. Il apparait que la dureté d’indentation HIT et le taux de conversion de la résine ne sont pas suffisants pour discriminer les échantillons. Les propriétés d’élasticité et de fluage sont également nécessaires pour comparer et comprendre le comportement des différents composites. Le procédé de photopolymérisation de la résine améliore les propriétés mécaniques du composite ainsi élaboré

Characterisation by indentation of glass / polyester composites: effect of the resin polymerisation process

http://euromat2017.fems.eu/programme/final-scientific-program/For several years, the use of photochemical resins to produce composites has encountered problems related to the manufacturing process. It is clear that the UV rays could be dangerous, but the difficulty of controlling the flux, and its penetration within the composite, make impossible to keep the percentage of polymerised resin under control. Recently, some advanced technologies using robot-based deposition systems and the introduction of LED lamps have put again this technology forward. It is well known that the progress of the resin polymerization have a strong influence on the mechanical behavior. The purpose of this work is to present and compare the mechanical properties of unidirectional glass / polyester composites. Two different processes: conventional thermal polymerization and photochemical polymerization were used to polymerize the polyester resin. The surface mechanical properties were studied by micro-indentation carried out with a Berkovich indenter under a maximum load of 500 mN. The speed of charge and discharge and the time during that the maximum load remains constant was chosen to analyze the creep behavior of the material. The indentation hardness HIT is not sufficient to discriminate the samples. Elasticity and viscoelasticity properties are necessary to compare the differen composites. For the composites elaborated by thermal polymerization, a post curing step improves the hardness and decreases the creep. For photo cured composites, a long step of vacuum allows a better fiber impregnation by the resin. As a consequence, the hardness and stiffness of the structure are enhanced. Finally, this work shows that photopolymerised composites exhibit better mechanical properties compared to conventional one obtained by thermal process. The differences in hardness and indentation modulus are quantified and related to the elaboration proces

Influence du mode de polymérisation de composites verre/polyester sur leur comportement mécanique

This paper aims to analyze the mechanical properties of unidirectional glass / polyester composites manufactured by two different processes: a conventional thermal polymerization and a photochemical process. The mechanical surface properties were studied by micro-indentation in order to observe the influence of the elaboration conditions on the response of the composite to penetration. It was demonstrated that the indentation hardness HIT and the degree of conversion are not sufficient to discriminate the samples. The elasticity and creep properties are also necessary to understand the behavior of the various composites. The photochemical resin improves the mechanical properties of the composite.L’objet de cette communication est d’analyser les propriétés mécaniques de composites unidirectionnels verre/polyester obtenus par deux procédés différents de polymérisation : un procédé conventionnel thermique et un procédé photochimique. Les propriétés mécaniques de surface ont été étudiées par micro-indentation afin d’observer l’influence des conditions d’élaboration sur la réponse du composite à une pénétration. Il apparait que la dureté d’indentation HIT et le taux de conversion de la résine ne sont pas suffisants pour discriminer les échantillons. Les propriétés d’élasticité et de fluage sont également nécessaires pour comparer et comprendre le comportement des différents composites. Le procédé de photopolymérisation de la résine améliore les propriétés mécaniques du composite ainsi élaboré

Understanding indentation, scratch and wear behavior of UV-cured wood finishing products

In the wood furniture and flooring industry, the protection and aesthetic properties of the final product often rely, at least partially, on the coatings applied on the wood surface. For flat surfaces, UV-cured coatings are often preferred due to their multiple advantages, such as high curing speeds, low volatile organic compounds (VOC) content, low energy consumption and high crosslinking densities. To increase the durability of interior wood products, the behavior of the protective coatings, while subjected to wear and deterioration, has to be understand in order to be enhanced. According to the type of solicitation, mar (i.e. shallow defect), scratches or indentations can be formed, which impact the coating’s appearance and can shatter the perception of the whole product. In this work, formulations based on different monomer-oligomer couples were prepared and photo-polymerized to investigate their performances. First, the glass transition temperature and the crosslinking density were determined to understand the contribution of both components in the polymeric network formed upon UV-curing. Then abrasion resistance, hardness, scratch and wear resistance were studied. The results showcased the importance of monomer and oligomer structure, functionality and main physical properties. In scratch experiments, hard and brittle coatings tend to display failures at lower loads than soft and ductile ones, whereas hard coatings are able to better withstand higher forces during indentations experiment. Friction experiments also caused subsurface tearing and fissuring in the soft coatings while generating several fractures in harder ones. Furthermore, the best overall mechanical resistance was obtained for the couples achieving high crosslinking density and a correlation between the crosslinking density of UV-cured coatings and their hardness was found. Interestingly, the investigation of tracks after scratch and wear experiments revealed a significant amount of information toward coatings behavior under various mechanical loads