The relationship between the hydrothermal response of yield stress and the formation of sandwich compressed wood

Abstract

The effects of yield stress of poplar ( Poplar × euramericana cv. ‘Neva’) on temperature (60–210°C), moisture content (oven dry-30%) and grain response mechanism and as well as its role in the formation of sandwich compressed wood were studied in this paper. The results showed that the yield stress of wood was significantly affected by moisture content(MC), temperature and their interaction. Compared with temperature, the relative change rate of yield stress was nearly 10 times higher for each 1% increase in MC than for each 1°C increase in temperature. The experimental data revealed that the relative change rate of yield stress depended on the softening effect of wood by moisture and temperature. The asymmetry of yield stress in different grain direction also depended on wood hydrothermal softening effect. Raising the temperature or increasing the MC could make wood radial vs tangential asymmetry decrease and radial vs radial tangential asymmetry disappear. In the process of hydrothermal compression, the yield stress gradient caused by the hydrothermal softening inside the wood was the main reason for the formation of sandwich compressed wood, and provided a scientific basis for the controllability of the position and thickness of the compressed layer(s).

Analysis of Deformation Fixation of Thermally Compressed Scots Pine (Pinus sylvestris L.)

“…Because the primary components of the compressed wood do not undergo significant chemical changes, the recovery is predominantly influenced by hydrophilicity and stress accumulated in the macromolecular chains of the wood. However, this stress is typically measured using a stress-strain gauge [22,23], which can analyze stress relaxation and stress-strain relationships in dried wood. During water absorption, it cannot accurately capture the stress-release regularity of modified wood.…”