Wood is a renewable resource and a popular, sustainable construction material. Complex architectural designs featuring curved or twisted structures, however, pose increasing challenges for the wood construction sector. Reshaping wood currently utilises large machines that consume substantial amounts of energy to press the building elements into the required shapes.
In a study recently published in
Science Advances
, researchers from ETH Zurich and Empa presented a process that has the potential to replace these inefficient mechanical reshaping processes. In collaboration with colleagues from the University of Stuttgart, they have developed an approach that makes solid wooden construction elements bend themselves into a pre-set shape without the use of external mechanical force.
Programmed curvature
The self-shaping process is based on the natural swelling and shrinking of wood caused by the moisture content of the material. When damp wood dries, it contracts more strongly perpendicular to the grain than along the grain. This warpage is normally an undesirable effect, but the researchers have taken advantage of the property by gluing two layers of wood together so that their grain directions are opposed to each other. This bilayer panel constitutes the foundation of the new method.
“As the water content of the bilayer panel decreases, one layer shrinks more than the other. Both layers are firmly glued together, so the wood bends,” explains Markus Rüggeberg, who is affiliated with both Empa and ETH and led the study. Depending on the thickness of the layers, grain direction and moisture content of the wood, the researchers can use a computer model to calculate the precise warpage of the building component during drying. They have dubbed this process “wood programming”.
