L’objectif du présent travail est d’étudier expérimentalement et numériquement la fissuration des bois tropicaux issus de la forêt gabonaise, à savoir : le Milicia excelsa (iroko),l’ Aucoumea klaineana pierre (okoumé) et Pterocarpus soyauxii (padouk). Cette étude est axée sur le processus de croissance de la fissure en mode d’ouverture et en mode mixte des trois essences à l’aide d’éprouvettes Compact Tension Shear (CTS) et Mixed Mode CrackGrowth (MMCG) modifiées. Les éprouvettes sont montées dans un système Arcan et placées dans une machine d’essai électromécanique. La méthode de la grille est utilisée pour mesurer les champs de déplacements et de déformations au voisinage de la fissure. Ces cartes ainsi obtenues permettent d’obtenir l’ouverture et la longueur de la fissure tout au long de l’essai. Les courbes force en fonction de l’ouverture de la fissure sont déduites des mesures. La méthode de la complaisance à déplacement imposé est utilisée pour calculer le taux de restitution d’énergie G en mode d’ouverture de fissure et en mode mixte. Les résultats ont montré un effet de l’épaisseur sur la fissuration. Ces résultats ont aussi permis de mettre en évidence une proportionnalité de la densité par rapport aux paramètres de rupture de ces essences. En mode mixte les valeurs de l’évolution de G sont présentées en fonction de la longueur de fissure après découplage des modes (séparation du mode 1 et du mode 2). On observe pour l’okoumé par exemple, que les rapports des taux de restitution d’énergie des deux modes sont constants, ce qui justifie le caractère intrinsèque des paramètres de fissuration obtenus. Des comparaisons faites avec les résultats issus de de la littérature sur les essences tempérées de même densité ont montré des similitudes. / The objective of the present work is to study experimentally and numerically the crackingbehavior of tropical woods from the Gabonese forest, namely : Milicia excelsa (iroko), Aucoumeaklaineana pierre (okume) and Pterocarpus soyauxii (padouk). This study focuseson the crack growth process in crack opening mode and mixed mode of these three speciesusing Modified Tension Shear (CTS) and Mixed Mode Crack Growth (MMCG) specimens.The specimens are mounted in an Arcan system and placed in an electromechanical testingmachine. The grid method is used to measure the displacement and strains fields near the tipcrack. These maps make it possible to obtain the opening and the length of the crack duringthe tests. The curves force showing the face as a function of the crack opening are deducedfrom the measurements. The experimental critical energy release rate G is evaluated by thecompliance method in imposed displacement. The results show an effect of the thickness oncracking. These results also made it possible to demonstrate a proportionality of the densitywith the parameters of rupture of these species. In mixed mode, after decoupling the modes(separation of mode 1 and mode 2), the values of G are presented as a function of to the cracklength. For Okume, for example, it was observed that the ratios of the energy release ratesof the two modes are constant, which justifies the intrinsic character of the cracking parameterswere obtained. Comparisons made with results from the literature review on temperatespecies of the same density showed similarities.

There is a need of substitution woods for the use in musical instruments because of the limited availabil-ity of some commonly used tropical tonewoods. Before substitutions can be found, it is necessary to knowabout the required properties. Hence, in this paper acoustical, mechanical and physical properties of fourcommon tropical hardwoods (Indian rosewood, ziricote, African blackwood and ebony) were determinedbecause there are less literature values for some properties available, e.g. internal friction, hardness orswelling behaviour. The acoustic properties were determined by means of experimental modal analysis,the mechanical properties by means of static bending tests and tests of the Brinell hardness. For the swel-ling behaviour the volume swelling and also the differential swelling coefficients were determined. Withthe results it is possible to look for new ‘tonewoods’ or to specifically modified woods, e.g. thermally trea-ted wood, to substitute tropical wood species.

There is a need of substitution woods for the use in musical instruments because of the limited availabil-ity of some commonly used tropical tonewoods. Before substitutions can be found, it is necessary to knowabout the required properties. Hence, in this paper acoustical, mechanical and physical properties of fourcommon tropical hardwoods (Indian rosewood, ziricote, African blackwood and ebony) were determinedbecause there are less literature values for some properties available, e.g. internal friction, hardness orswelling behaviour. The acoustic properties were determined by means of experimental modal analysis,the mechanical properties by means of static bending tests and tests of the Brinell hardness. For the swel-ling behaviour the volume swelling and also the differential swelling coefficients were determined. Withthe results it is possible to look for new ‘tonewoods’ or to specifically modified woods, e.g. thermally trea-ted wood, to substitute tropical wood species.