R-curve on Fracture Criteria for Mixed-mode in Crack Propagation in Quasi-brittle Material: Application for Wood

In this work, Mixed-Mode Bending (MMB) tests are performed on spruce specimens for several mixed mode ratios G(I)/G(II) and in pure Modes (I and II). For each fracture test, the resistance curve (R-curve) is estimated on the basis of the equivalent LEFM by the compliance method. The compliance function used in this study is based on a finite element modeling in which the invariant MO-integral method is applied to separate each mode component. In the quasi-brittle material such as wood, the fracture criterion is usually presented by using the propagation resistance of wood (plateau constant values of the R-curve relative to mode I and mode II components) so that, in this paper, a generalization of the fracture criterion whatever the crack length is proposed. The results show that, in the rising zone and the plateau zone of R-curves, both components (mode I and mode II) of the resistance to crack growth under the mixed mode loading are described with a reasonable accuracy on the basis of the generalized criterion. (C) 2014 Published by Elsevier Ltd.