杉木层状压缩的形成及其密度分布特征OA北大核心CSTPCD

Wood sandwich compression is an advanced technology of compressing wood layers through controlling the position,thickness,and the number of the compressed layers to achieve mechanical property enhancement.By regulating the distribution of temperature and moisture in Chinese fir wood under the desired pressure,the positions and thickness of compressed layers were managed in this study.Furthermore,density distribution in the compressed Chinese fir wood was analyzed to investigate the feasibility of sandwich compression technology to plantation Chinese fir wood and to clearly understand the formation mechanism.The results indicated that when the preheating time ranged from 0.5 to 30 minutes,Chinese fir wood was sandwich compressed with various positions of compressed layers.As the preheating time extended,compressed layers moved from wood surfaces into center and the compressed layer's density exceeded 0.583 g/cm³.By changing the compressing rate and thickness of wood specimen,four types of surface compressed wood with a compression layer thicknesses'range between 3.00～8.07 mm were obtained.The average density of the compressed layer was 28.7%higher than that of the original wood.Combining the technologies for surface compression and centre compression,three distinct compressed layers were formed in the sandwich compressed wood.It was also found that the boundary between the compressed layers and uncompressed layers appeared in the earlywood and the boundary between earlywood and latewood,regardless that compression occurred on wood surface or inside wood.Remarkably,the earlywood cells in the compressed layer underwent significant distortion,leading to the disappearance of almost all cell cavities.On the other hand,latewood cells exhibited little deformation or even remained intact.Based on the density profiles and the calculated characteristic values before and after compression,the maximum density of the compressed earlywood was 210.6%higher than that of the corresponding uncompressed earlywood.