Experimental investigation of mixed mode fracture of tropical wood material

The process of mixed-mode crack growth of three tropical species of the Gabonese forest, namely iroko (Milicia Excelsa), okume (Pierre Aucoumea klaineana), and padouk (Pterocarpus soyauxii) is studied in this paper. Different tests were carried out at room temperature for different thicknesses. A full-field measurement technique, namely the grid method, was used to obtain both the displacement and deformation maps near the crack tip. The mechanical parameters, the specificities of the wood species, the Arcan system and the grid transfer method are described in the paper. For all the samples, the initial crack was oriented along the fiber direction (RL). Fracture tests were performed using modified Mixed Mode Crack Growth (MMCG) specimen. A thickness of the specimens is 20 mm, and a mixed mode ratio corresponding to 15 were studied. The force-displacement curves, the crack growth process as well as the opening crack were deduced from grid images treated with the grid method. The experimental critical energy release rate Gc was evaluated by the imposed displacement compliance method. The different results show the predominance of mode 1 compared to mode 2. The proportionality of the initial value of the energy release rate with respect to the density of these species is also highlighted. (C) 2018 The Authors. Published by Elsevier B.V.