Abstract:

Basing on lab condition, Asian White Birch ( Betula platyphylla )lumbers were dried by conventional methods. The time factor was considered in the drying strains of wood, the polymer′s visco elastic theory and rheology theory were used to analyze the strains of lumber in drying process,slicing method was used to explore development and changing trend for the instant elastic strain、visco elastic strain、mechano sorptive strain which were on the cross section of lumber, the wood traverse strain characters were qualitatively analyzed in one drying cycle.Through research and experiment analysis, the following conclusions can be given:the elastic strains of the surface and center layers are always reverse, simultaneous the maximum elastic strain of surface layer at the drying process could be taken for the reference of steaming disposal. The visco-elastic strain cannot be distinguished from mechano-sorptive strain easily, mechano-sorptive strains of the prophase contain visco-elastic strains, so it can reflect the mechano-sorptive strains approximatively. With the steaming disposal of wood going on at middle stage and final stage of drying process, the mechano-sorptive strains of different layers increase gradually, the wood uneven shrinkage along thickness direction decrease gradually, the elastic strains of surface and center layers decrease, the machano-sorptive strain is one of the main reason of drying stress release.

Key words: Asian White Birch, Wood drying, Elastic strain, Visco elastic strain, Mechano sorptive strain