Chapter 15 Studying the Fracture of Tropical Wood Species with the Grid Method B. Odounga, R. Moutou Pitti, E. Toussaint, and M. Grédiac Abstract The present study consists in studying the initiation and propagation of cracks at room temperature of three tropical species: Okume (Aucoumea Klaineana), Iroko (Pterocarpus Soyauxii) and Padouk (Malicia Excelsa). A short review of the literature shows that only few studies dealing with the fracture mechanics properties of this type of wood species are available. Similar studies are however routinely performed on temperate wood species such as Beech and Douglas, using mixed-mode crack growth (MMCG) specimens for instance [1, 2]. In this paper, tropical wood specimens are studied using the grid method [3] and such MMCG specimens, but made of the three aforementioned tropical species. Keywords Crack growth • Fracture mechanics • Grid method • Tropical wood species • Compliance method 15.1 Extended Abstract The present study consists in studying the initiation and propagation of cracks at room temperature of three tropical species: Okume (Aucoumea Klaineana), Iroko (Pterocarpus Soyauxii) and Padouk (Malicia Excelsa). A short review of the literature shows that only few studies dealing with the fracture mechanics properties of this type of wood species are available. Similar studies are however routinely performed on temperate wood species such as Beech and Douglas, using mixed-mode crack growth (MMCG) specimens for instance [1, 2]. In this paper, tropical wood specimens are studied using the grid method [3] and such MMCG specimens, but made of the three aforementioned tropical species. This paper describes the wood specimens, which are subjected to an opening mode, the experimental device and the background of the grid technique used for tracking the location of the crack tip during the test. The origin and characteristics of the tropical wood species studied here are also given. The experimental results are given and compared in terms of forcedisplacement curves, but also in terms of energy release rate – crack length curves. Typical MMCG specimens made of each of the three different species are shown in Fig. 15.1. The main difference between the three species is their density: Okume (density D0.44) is less dense than Iroko (density D0.64) and Padouk (density D0.79). For all the specimens, the initial crack length is the same: a D20 mm. It is located at mid-height and oriented along the fiber direction, which is horizontal here. The initial crack is completed by a notch (length: 2 mm) made with a cutter in order to initiate correctly crack propagation. A grid, with a regular pitch of 200 microns, was transferred on one face of the specimens, see Fig. 15.1d. The technique presented in [4] is used for this purpose. The experimental device is shown in Fig. 15.2. A 200 kN Zwick/Roel testing machine was used for the tests. A camera was fixed on a tripod at a distance of 67.5 cm from the specimens in order to take images of the grid during the tests. A small sized steel Arcan fixture was used to load the specimens. The lower part was fixed and the upper part was subjected to an imposed displacement. The testing machine was equipped with a force transducer in order to obtain the force-displacement curves, the displacement being obtained with the full-field measurements. The cross-head speed was B. Odounga Ecole Polytechnique de Masuku, Université des Sciences et techniques de Masuku, Franceville, BP 901, Gabon CNRS, Institut Pascal, Université Clermont Auvergne, Clermont-Ferrand, F-63000, France R. Moutou Pitti ( ) CNRS, Institut Pascal, Université Clermont Auvergne, Clermont-Ferrand, F-63000, France IRT, CENAREST, Libreville, 14070, Gabon e-mail: rostand.moutou_pitti@uca.fr E. Toussaint • M. Grédiac CNRS, Institut Pascal, Université Clermont Auvergne, Clermont-Ferrand, F-63000, France © The Society for Experimental Mechanics, Inc. 2018 J. Carroll et al. (eds.), Fracture, Fatigue, Failure and Damage Evolution, Volume 7, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-62831-8_15 111
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