Influence of the fracture softening behaviour of wood on load-COD curve and R-curve

A cohesive crack model is used to analyse failure of wood in mode I along the grain. Several configurations of the gradual fracture softening behaviour of an interface, meshed with joint-elements located on the potential crack path, are investigated. Different constitutive laws, obtained from a single normalized polynomial function, are tested in order to estimate the influence of parameters such as, the tensile strength, the fracture energy or the ultimate opening of the interface, on the macroscopic response of a fracture specimen. Numerical results are compared with experimental data obtained on DCB specimen. We argue that the fracture energy related to the constitutive law must correspond to the plateau value of the R-curve. Moreover, this study reveals that the peak load of a load-COD (Crack Opening Displacement) curve is strongly affected by the slope of the softening behaviour. Finally, we present a review of the influence of each parameter describing the softening function on: (1) the load-COD curve and (2) the corresponding R-curve.