Effect of knots on the physical and mechanical properties of Scots pine (Pinus sylvestris L.)

This study evaluated the some physical and mechanical properties of Scots pine (Pinus sylvestris L.) wood which has varying amounts of knot area in comparison with control specimens. Wood specimens (prepared according to ISO and Turkish Standard) classified to four different groups based on the knot area in the cross sections (0-25%, 26-50%, 51-75%, and 76-100%) and control specimens were subjected to some physical and mechanical tests. These tests were density, shrinkage, bending, modulus of elasticity in bending, impact bending, compression parallel to grain, tension perpendicular to grain, and hardness. Results showed that density of wood specimens increased as knot area in the cross sections increased. But, shrinkage decreased. Bending strength, modulus of elasticity (MOE), and impact bending values of wood specimens decreased dramatically as knot area increased. Compression strength parallel to grain values of wood specimens containing highest amount of knot area (76-100%) were found to be less compared to control specimens without knots. But, decreasing of between other groups was not important statistically. While values of tension strength perpendicular to grain were not different statistically between 0-25 % and control specimens, 51-75 % and 76-100 % specimens, values of decreasing of between other groups were found to be important statistically. Hardness in the knotted area on the specimens increased however hardness in the knot-free area was lower.