Relationship between the Fixation Period and Some Mechanical Properties of Pleated Wood

Longitudinally compressed wood (or pleated wood) is much easier bendable compared to untreated wood, even to much smaller curves. Its properties make pleated wood both an economically and environmentally friendly product for performing curved wood products. As a result of longitudinal compression, modulus of elasticity and required bending stress highly decrease, while bendability coefficient increases threefold. The longitudinal compression is usually followed by the fixation process: the degree of compression is held constant for a certain amount of time to relax the internal stresses in the wood. Fixation strengthens the effects of the treatment and it is used by the industry, but unfortunately, there is very slight literary knowledge available in this topic. We try to fill this gap by using different times of fixation and bending tests. The first minute of fixation is the most effective, but for example fixation for more than 10 hours results in a maximum deflection during 4-point bending tests of 675%, in a decrease of modulus of elasticity to 18.6% and in a decrease in bending stress at 5 mm crosshead displacement to 29.3%, compared to untreated specimens. Finally, pleated wood can undergo significant plastic deformation before fracture.