Fracture toughness and shear yield stress determination from quasi-linear cutting tests of Scots pine (Pinus sylvestris L.) with a normalisation process by local density aided by X-ray computed tomography

The Atkins model has been widely adopted for determining mechanical properties of wood, such as fracture toughness and shear yield stress, which are typically normalised by global density for cutting force and power predictions. This study explores the feasibility of determining these mechanical properties for knotty and clear Scots pine (Pinus sylvestris L.) using local densities revealed by X-ray computed tomography scanning. Six wood workpieces, three from Poland and three from Sweden, were scanned and subsequently cut on a custom single-tooth quasi-linear cutting machine. Cutting forces for both clear and knotty regions were recorded and normalised by local densities. Results indicate that clear Polish pine exhibits higher local-density-normalised fracture toughness and shear yield stress than Swedish pine, suggesting that wood origin influences mechanical properties beyond mere density differences. Knots display significantly lower local-density-normalised shear yield stress compared to clear wood, despite their higher density. The large variation in normalised fracture toughness observed in knots is attributed to differences in cutting direction relative to knot orientation. The study highlights the effectiveness of computed tomography scanning to provide detailed insights into wood density and structure, enabling more accurate normalization of cutting forces and enhancing the understanding of wood machinability across different origins and structural characteristics.