Modelling of Recovery of Residual Stress in Densified Wood

摘要

Residual stresses can be generated in manufacturing of densified wood due to structural change in cell walls, and are 'locked' in the final product. Once this wood is exposed to moist conditions, residual stresses are released resulting in dimensional instability such as warping. This study was aimed at directly measuring residual stresses in densified softwoods and modelling the recovery process. Balsam fir and eastern white pine were materials that were densified in the radial direction at three compression ratios, 25%, 50% and 60%. The residual stresses including physical and mechanical parts were measured by soaking densified specimens in hot water of 60°C. It was found that (1) the mechanical residual stress increased with increasing compression ratio, (2) the mechanical residual stress in densified pine wood was slightly larger than densified fir wood, and (3) a mathematical model developed could perfectly describe the recovery of mechanical residual stress.