Fracture toughness of wood based on experimental near-tip displacement fields and orthotropic theory

Fracture toughness of New Zealand Pinus radiata in TL opening mode was determined from the displacement fields obtained from digital image correlation for about 400 data points within a 7x9 mm² area in front of the tip in conjunction with orthotropic fracture theory. Representative material properties obtained experimentally were used in the theoretical formulae. There was a significant correlation between theory and experiments. Stress intensity factor thus obtained increases nonlinearly with applied load and was consistently higher than that obtained from standard formula revealing a much larger correction factor than that given in handbooks. Fracture toughness obtained from the developed relationship showed a tendency to vary under the combined influence of density and crack angle to RL plane in a nonlinear manner. A relationship was also found to express the combined influence of density and grain angle on the Young's modulus (EL), measured from bending specimens corresponding to fracture specimens. The latter relationship can be used to simulate EL and obtain a simplified expression for fracture toughness in terms of density and crack angle to RL plane