Previous Biocomposites PhD student
Hygromechanics of wood structures
Clear wood is built from material structures at different scales. For instance, we may identify annual rings, cellular aggregates, cells and cell walls. The inherent properties of the cell walls are those influenced by variations in chemical composition, moisture content, microfibril angle, and chemical modification such as cell wall bulking and heat treatment. The cell wall properties are difficult to measure and therefore the wood material response is used to evaluate effects from the mentioned material composition parameters. The objective of the present project is to develop methods by which the cell wall properties can be measured and interpreted./ These methods will be applied to improve our understanding of how variations in wood composition and wood modification influences the inherent properties of the solid material. This is also a key to improved understanding of how different macroscopic wood properties are controlled by mechanisms at several scales.
The longitudinal properties of clear wood are dominated by the cell wall properties in this direction. However, the stress state at the cell wall level is not simply uniaxial, due to the material microstructure and cell wall anisotropy. In the transverse and radial directions, the material behavior is complicated by deformation mechanisms such as cell wall bending. For this reason, interpretation of cell wall properties in these directions will require a micromechanical analysis.
The experimental methodology will include digital speckle photography, x-ray diffraction for microfibril angle measurements, density determination (optical) and chemical composition analysis. In-situ microscopy (environmental scanning electron microscopy or optical) will also be used as well as mechanical testing and, possibly, moisture swelling experiments. Theoretical analyses will include finite element analysis, analytical micromechanics and classical laminate plate theory. Applications of methods and procedures developed in the project include hygromechanical analysis of glulam beams in order to develop glulam beams and boards of improved performance.
Publications, Presentations and Posters
- CS Modén, LA Berglund, (2007), Elastic deformation mechanisms of softwoods in radial tension – cell wall bending or stretching?, Holzforschung, in press.
- CS Modén, LA Berglund, (2008), A two-phase annual ring model of transverse anisotropy in softwoods, Composites Science And Technology, 68, 3020-3038
- Moden C, On the softness of wood, COST Symposium, Lausanne, 21-23 May, 2007.