Size Effect in Crack Shear Strength of Wood

Abstract
It is known for long time that the size of a structure has an important effect on its fracture stress. This phenomenon is called size effect and it seems that it can be attributed to the influence of a damaged zone which develops around the fracture area. Investigations have been made on size effect in shear fracture on two species of wood : Maritime Pine and Norway Spruce. The experimental fracture stresses and energy release rates of geometrically similar specimens of different sizes are analysed according to the size effect law of Bazant. This theoretical model allows an estimation of the evolution of fracture stress and energy release rate in terms of structural size but also an estimation of the dimensional validity areas respectively attributed to non-linear fracture mechanics and to linear elastic fracture mechanics. A comparison of the results was made in order to determine the relative brittleness of Pine and Spruce.