Fracture Properties of Pine and Spruce in Mode I

Abstract

The fracture behaviour of a quasibrittle material such as wood, characterized by the development of a large fracture process zone (FPZ), is nowadays well-known to be efficiently described by cohesive crack models. The most common applications of fictitious or cohesive crack models used to simulate nonlinear fracture mechanics of quasibrittle materials are considered as variations [1] of a model proposed by Hillerborg and co-workers [2]. These applications need to introduce a cohesive zone at the crack tip, i.e., a fictitious line crack transmitting normal stress dependent on the corresponding opening displacement w. Cohesive crack models are typically applied through finite elements calculations. Interface elements or springs [3] with prearranged strain-softening properties are integrated into the structural model along the most probable crack path. Since the pioneering application of cohesive crack models to wood due to Bostrom [4], a so called bilinear strain-softening model was applied by Stanzl-Tschegg et al. [5] to obtain wood load-deflection curves according to a developed wedge-splitting test protocol.