MODELLING THE EFFECT OF THREE-DIMENSIONAL GRAIN ANGLE ON THE TENSION STRENGTH OF BIRCH WOOD

In the present paper, the effect of three-dimensional grain direction on the tension strength of small-scale birch wood specimens is investigated. The grain angles are measured on all four surfaces of the specimens using laser light scattering technique, and afterwards, the specimens are destructively tested in tension. A numerical model is developed to predict the tensile strengths. The model is a combination of a linear elastic finite element model, with local orthotropic material orientations defined based on the measured grain orientations, and stress-based phenomenological failure criteria, with stress averaging. Strength predictions from the numerical model are compared to the experimental results, and, additionally, material strength properties are calibrated by minimizing the difference between the predictions and experimental results. A simple analytic model is further investigated and evaluated against the numerical model. Results indicate that the numerical model can predict the tensile strength of the specimens based on the measured grain angles. Stress averaging improved strength predictions by reducing localized stress peaks. Calibrated strength properties further improved the predictions and are compared with the literature. With only grain angle information, however, the numerical model does not significantly improve predictions, relative to the simple analytical model.