Theoretical analysis of structural lumber drying schedules
2002
"Nakao, T. (Shimane Univ., Matsue (Japan))."
"The three dimensional diffusion equation were solved approximately for actual boundary conditions using the commercial software, Excel. With this newly developed program, kiln-drying schedules were analyzed for various kinds of structural lumbers. Moisture content variation and moisture content gradient were estimated. The estimated moisture content variation was in satisfactory agreement with experimental data. The moisture gradients of hinoki and Douglas-fir were in a certain range throughout the drying process, regardless of the lumber thickness. Moisture gradient were higher for sugi for which the drying schedule did not in fact reach a satisfactory level. The high moisture gradient will cause surface checking. The amount of ""drying set"" was calculated from the moisture variation by the finite difference method and the in-plane stress by the finite element method. Using the results, in-plane stress variation in kiln drying was calculated for construction lumber. In the initial stage of high temperature drying, a lower tension stress was estimated at surface by ""drying set"" effect. In the final stage of drying, a large tension stress in the core was estimated by the effect."
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