A Simple Size Effect Model for Tension Perpendicular to the Grain

The strength in tension perpendicular to the grain is known to decrease with an increase in the stressed volume. Usually this size effect is explained on a stochastic basis, that is, an explanation relying on the increased probability of encountering a strength reducing flaw when the volume of the material under stress is increased. This paper presents an experimental investigation on specimens with a well-defined structural orientation of the material. The experiments exhibit a large size effect and the nature of the failures encountered suggests that the size effect can be explained on a deterministic basis. Arguments for such a simple deterministic explanation of size effect is found in finite element modelling, using the orthotropic stiffness characteristics in the transverse plane of wood.