Grain angle determination of silver birch by laser light scattering and tensile fracturing

Reliable non-destructive methods for grain angle determination are essential for the evaluation of mechanical properties of timber. In the present study, the detection of grain angle by means of laser light scattering patterns is investigated on small-scale specimens and timber boards of silver birch, along with the relationship to fracture angle and tensile strength. Results on small-scale specimens indicate applicability of laser scattering method, as the detected grain angles and the fracture angles show a strong correlation, r = 0.94. Three-dimensional grain angles, derived from surface grain angles, show a well defined relationship to strength, which can be described with wood-based failure criteria from literature. Furthermore, the paper presents new findings regarding the detection of flame wood through laser scattering. It was shown that small-scale specimens with flame wood tend to have higher grain angles, higher density, and lower strength, relative to specimens without. Nevertheless, for timber boards, the influence of flame wood on the strength was insignificant.