Mechanical properties in the transverse directions are very important in several technical applications. A few examples of this are mechanical properties in building structures, cupping of drying boards and cracks in the adhesive joints of glulam beams. However,
knowledge of relations between structures and properties in the transverse direction is very limited. Much of the research has only regarded wood as a homogeneous material and tried to relate global properties. In many cases this approach do not give information detailed enough about actual deformation mechanisms in the log.
In this study two experimental techniques, each one capable of localised measurements, are combined. Density measurements from SilviScan are used to characterise the radial density profile of spruce specimen. The characterized specimen are then tested in radial tension, where strain fields are monitored using Digital Speckle Photography (DSP). Both these techniques measures with a spatial resolution of 50 μm.
Strain measurements, combined with the density measurements, are used to calculate the Young’s modulus as a function of density. Modulus is then compared to two different micromechanical models; one where bending of cell walls is the deformation mechanism, and one where the mechanism is stretching of the walls.
Keywords: Transverse mechanical properties, Localized measurements, Micromechanical models
Authors
C.S. Modén
Div. of lightweight structures, KTH
L.A. Berglund
Div of Biocomposites, KTH
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