Comparing Nano and Macroindentation in Search of Microfibril Angle in Spruce

The present paper describes experimental measurements of wood stiffness and analytical homogenization to provide estimates of the Micro-fibril angle (MFA). It is known that the orientation of fiber-like aggregates of crystalline cellulose in S2 layer of the wood cell with respect to the alignment of lumens considerably influences the overall stiffness of wood. Recently an inverse approach exploiting the results of nanoindentation at the level of wood cell and analytical homogenization has been proposed as a suitable tool for the MFA determination. A simpler methodology based on the results of indentation at the structural level using the Pilodyn 6J testing device has also been advocated as an alternative appealing particularly to engineering practice. Comparison of the two approaches suggesting their advantages as well as drawbacks is the principal objective of this contribution. As an example, an application to spruce as the most common type of wood used in building structures is considered.