Mode I fracture of tropical woods using grid method. (June 2018)

• Record Type: Journal Article
• Authors: Odounga, Bernard; Moutou Pitti, Rostand; Toussaint, Evelyne; Grédiac, Michel
• Is Part Of: Theoretical and applied fracture mechanics. Volume 95(2018)
• Page Start: 1
• Page End: 17
• Publication Date: 2018-06
• Subjects: Tropical woods -- Fracture analysis -- MMCG and CTS specimens -- Grid method; Fracture mechanics -- Periodicals; 620.1126
• DOI: 10.1016/j.tafmec.2018.02.006
• Languages: English
• ISSNs: 0167-8442

Abstract

Highlights: The cracking of tropical woods from the Gabonese forest by grid method is investigated. The tests are carried out in crack opening mode configuration. The so-called grid method is used to extract the displacements and strains maps allowing to follow the crack opening and the crack tip process. The energy release rate is computed to show the fracture toughness of these tropical species versus the density. Abstract: The cracking properties in opening mode of three tropicals species from the Gabonese forest, namely Iroko (Milicia Excelsa), Okume (Aucoumea klaineana Pierre), and Padouk (Pterocarpus soyauxii), were investigated in this study. Various tests were performed at room temperature and for two different thicknesses. A full-field measurement technique, namely the grid method, was used in order to obtain the displacement and strain maps near the crack during the tests. The mechanical parameters, the specificities of the wood species, the Arcan system and the grid transfer method are first described. For all the specimens, the initial crack length was oriented along the fiber direction (RL). The instantaneous failure tests were performed using two types of specimens: the modified Compact Tension Shear (CTS) and the Mixed Mode Crack Growth (MMCG) specimens. The images of the grid were recorded and analyzed to obtain the displacement maps. The crack opening, the location of the crack tip as well as the strain fields on the surface of the specimens were deduced from these displacement maps. The experimental critical energy release rate Gc was evaluated by the compliance method in imposed displacement. In the case of instantaneous crack with CTS specimens, the comparison of the initial value of Gc for all the samples show that this quantity strongly depends on the thickness and density of the species under study. Crack propagation was observed for a thickness equal to 20 mm only. The results of the crack propagation with the MMCG specimens show the same dependence, and confirm the quasi-brittle fracture behavior of Iroko. The experimental results are scattered, but clear trends can be observed concerning the fracture parameters of the in previous studies described in the literature on wood species with wood species under study. The results are finally compared with those given densities similar to those studied here.