Influence of anatomy on transverse compressive mechanical properties of Norway spruce

• Main Author: Hernandez Estrada, Albert
• Other Authors: Tukiainen, Pekka, Kemian tekniikan korkeakoulu, School of Chemical Engineering, Puunjalostustekniikan laitos, Hughes, Mark, Aalto-yliopisto, Aalto University
• Format: Master Thesis
• Language: English
• Published: 2011
• Subjects: mechanical properties; mesoscale; compression; Norway spruce; Young's modulus; size effect; Norway; Sea ice
• Online Access: https://aaltodoc.aalto.fi/handle/123456789/99646

Wood is an anisotropic material which exhibits different mechanical properties depending on the direction in which it is tested. In the longitudinal direction, Young's modulus is around 10 times higher than in the transverse one, but also different orientations in the transverse direction exhibit different mechanical properties. In this current research, two different sizes of Norway spruce specimens have been tested in compression in the transverse direction, radially and tangentially, to find how morphology affects the mechanical properties and how these properties differ from one direction to another. The important role of rays acting as beams keeping the integrity of the structure, as well as the differences between earlywood and latewood under external strains, has been elucidated. At the same time, some techniques have been developed in the production of small specimens, razor blade cutting being the most important one, being able to produce a flat surface and minimizing the damage in the cell walls, allowing the further possibility of imaging the surface at the mesoscale level with the microscope to obtain images of the cell's deformation. As a consequence of testing different specimen sizes, an unexpected effect associated with the specimen size arose that affected the values of mechanical properties. It was found that this effect was previously called size effect, and it is not only affecting wood but it is common in other cellular materials such aluminium or polyurethane foams, ceramics or sea ice.