• Physique/Mécanique/Mécanique des matériaux
  
• Sciences de l'ingénieur/Acoustique
  
• Sciences de l'ingénieur/Matériaux
  
• Sciences de l'ingénieur/Mécanique/Mécanique des matériaux
  
• Sciences de l'ingénieur/Mécanique/Thermique
  
• Sciences de l'ingénieur/Mécanique/Vibrations
  

Spruce wood specimens were treated under mild temperatures 130°C and 150°C and different relative humidity from 0% to 25%. EMC reduced significantly for all the treatments. Weight loss (WL) increased insignificantly while the colour parameter, L*, decreased dramatically. Tanδ reduced significantly while the E/d has increased. After reconditioning, the partially reversibility has been achieved for EMC, tanδ and E/d. But, still an irreversible changes remains, which suggested being due to the chemical changes in wood polymers. While reversible changes has been resulted from the annealing of amorphous polymers. Since, the mild hygrothermal treatment applied to the specimens coincided with no significant WL, there was no obvious damage in wood structure while the irreversible changes present an improvement in vibrational properties by decrease in damping (tanδ), which could be due to the intermediate relative humidity of the treatment.

Le bois est couramment utilisé pour la fabrication d’instruments de musique. Les procédés employés consistent souvent en traitements modifiant le matériau en volume ou en surface. Ce travail s’est focalisé sur deux espèces employées dans les instruments à cordes et représentatives de différentes cultures: L’épicéa (Picea abies Karst.) utilisé en Europe et le Mûrier blanc (Morus alba L.) utilisé en Iran. Pour chacune l’effet d’un traitement thermique modéré (<150°C) et d’un revêtement par vernis sur plusieurs propriétés physiques et mécaniques ont été étudiés. Les principaux résultats sont les suivants. A la différence de l’Epicéa, le Mûrier présente un très faible degré d’anisotropie mécanique. Chez les deux espèces, le traitement thermique entraîne une forte chute dde l’amortissement, particulièrement dans la direction radiale pour l’Epicéa, ainsi que du taux d’humidité d’équilibre, sans dégradation marquée comme indiqué par la faible perte de masse. Toutefois, après reconditionnement à haute humidité, une part importante de la modification est récupérée. L’application d’un vernis à base solvent sur le Mûrier entraîne une rigidification continue, tandis que la forte augmentation de l’amortissement observée après l’application est suivie par un retour au bout d’environ 2 mois aux niveau du bois non traité. Pour l’Epicéa, des vernis à base d’huile siccative ont été appliqués et divers paramètres du procédé ont été testé. Dans ce cas la cintétique de stabilisation des propriétés est très lente et des variations notables continuaient à être observée au bout de 5 mois.

The influence of vanishing process on the vibrational properties of the wood+coating systems was studied using different types and recipes of instrument making varnishes, used in traditional Iranian string instruments making, or in European violin-quartet making. The focus is on the time evolution of these properties, that can be involved in the changing behaviour of newly made instruments. The different tested varnishes recipes were applied on wood representative of each culture, studied both along-the-grain and cross-grain, and monitored through time for up to more than one year. The different effects, both immediate and their kinetics through time after application, are discussed.

Mild thermal treatments (below 160°C) are increasingly considered as a mean to accelerate some beneficial effects of wood ageing. In this work, treatments were done in a pressurized reactor which has controlled conditions of temperature and relative humidity. We performed 5 treatments, each one applied to poplar (for study of dimensional stability in view of panel paintings applications) and to spruce (for study of axial and radial acoustic properties in view of musical applications). Three groups were treated at 150°C with, respectively, 0% (constant) relative humidity (RH), 25% constant RH, and cyclic variations between these 2 RH. The same protocol was applied to three other groups at a temperature of 130°C. The oven-dry weight, dimensions and colorimetric properties and the air-dry (3 weeks at 20°C and 65% RH) weight, dimensions and viscoelastic vibrational properties were measured before and after treatment. Intermediate data were also measured in the course of the treatments for weight, dimensions and colorimetric properties, in order to model the kinetics of modification. Although oven-dry weight loss were moderate (maximum 4%) in these relatively mild conditions, properties were significantly improved. Moisture sorption and swelling/shrinkage were significantly reduced, as well as vibration damping, without negative effects of the rigidity. The effect of reconditioning at high relative humidity was also investigated.