Study On The Dynamic Mechanism Of Wood Collapse

Since long ago, the wood collapse source dynamic is thought to result from the tensile capillary forces caused by the air-water meniscus on pit membrane. This tensile capillary force may amount to several megapascals, which causes the wood cell collapse. However, recently, some research results of the botany and the physics actually indicated that the directly measured liquid negative pressure value in the xylem is lower than theoretical value, and possibly the negative pressure in xylem may not be lower than -1MPa. These research results proposed challenge to capillary tension theory in the wood collapse mechanism research. It is necessary to further study the capillary tension theory with the new angle of view.This paper is about research of the wood collapse dynamic mechanism at the earlier period, refers to the glass plate liquid tension measuring technique which is provided by the predecessor studies and further studies the relationship between radius of curvature of air-water meniscus and the liquid tension.The experimental result indicates that, although the radius of curvature of air-water meniscus different greatly, there is not remarkable difference between values of the water film tension, and there is no inevitable relation between the water film tension and the radius of curvature of air-water meniscus. This research results proposes oppugn to point of view that negative pressure caused by tensile capillary forces is the source dynamic of wood collapse and the dynamic value of wood collapse depended on the aperture of pore on pit membrane.The experimental result also shows that the water tension difference is not remarkable when the radius of curvature of air-water meniscus different greatly and with relatively the same water film thickness, and the water film tension is possibly related with the water film thickness. This phenomenon waits for the further thorough research.This paper also selects the dombeyi as the study object which is easy to collapse, and inspects effect of external force on wood collapse. The experimental result indicates that when water saturated wood is dried to fiber saturation point under 70℃drying conditions, the 0.4MPa tensile stress caused the wood collapse quantity drop 27.7%; and when the collapsed wood is treated under 90～95℃steaming, the 0.4MPa compressed stress has been completely suppressed collapse restoration. This indicates that the biggest tension which causes wood collapse certainly is not to be possibly big, and the average collapse restores dynamic is possibly smaller than 0.4MPa.