Evaluating Distance to the Pith as a Parameter for Strength Grading of Douglas Fir (Pseudotsuga menziesii (Mirb.) Franco)
2025
Guillaume Pot | Joffrey Viguier | Anders Olsson
Distance to the pith is a parameter that is known to be correlated with the mechanical properties of wood, but it is not utilized in strength grading machines. This study aimed to investigate how different the mechanical properties and grading yields are for Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) boards with small and large distances to the pith, respectively, and whether the distance to the pith could be an interesting parameter to use for strength grading in combination with other predictor variables. For this purpose, 221 boards were scanned to obtain fiber orientation and local density. Their dynamic modulus of elasticity and distance to the pith were measured, and they were finally tested in bending. The boards were classified into two categories: corewood if a board&rsquo:s cross-section was entirely located within a radius of 200 mm from the pith, and outerwood otherwise. The results show that corewood presents lower mechanical properties than outerwood, explained especially by the higher knottiness of corewood. Distance to the pith improves the grading yields of a machine based on fiber orientation measurements, but using the dynamic modulus of elasticity rather than the distance to the pith leads to better results. Distance to the pith can be used as a single or secondary parameter to predict timber strength if the dynamic modulus of elasticity is not used.
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