1997 Volume 46 Issue 4 Pages 390-394
Dried boxed-heart square timbers of sugi with a split liner were tested for the dimensional stability and tangential stress in surface layer during environmental change. The tests were made under several cyclic conditions of temperature and humidity with reference to the actual day and night condition. The results obtained were as follows;
(1) The change in moisture content with environment was less than 1% by the oven drying method and less than 4% by the high frequency moisture meter method. At the same time, the shrinkage chandes of width were less than 0.4% in the opposite directions for the fluted face and for the other three faces.
(2) When the difference of equilibrium moisture content (ΔE.M.C.) between daytime and nighttime was over 4%, tension stress appeared clearly in the surface layer after changing to the daytime condition.
(3) The above daily change in stress behavior depended on the moisture condition of the dried timber. For the insufficient dried timber with a large moisture gradient, the tension stress in surface layer during the daytime condition increased enough to develope into check.
