Development of elastic strain and mechano-sorptive strain during conditioning of eucalyptus camaldulensis lumber in batch kiln

Abstract

Final conditioning of 25mm thick dried E. camaldulensis lumber was carried out in small capacity batch drying kiln in laboratory, and the elastic (EL) strain and mechano-sorptive (MS) strain was analyzed by slicing method. Mean moisture content(MC) of boards increases 2.5-3.0%, while surface MC increases from 9.8% to 14.2% and center MC always keeps at 12.3% or so. Difference of each slice oven-dried length, through the thickness of the board decreases with the going on of conditioning. Compressive EL strain in the surface decreases significantly during the first 9h of conditioning, and tensile EL strain in the center doesn't change significantly with the going on of conditioning. Compressive EL strain of sub-surface is greater than that of surface during middle and final period of conditioning, so reverse stress gradient is formed. Casehardened surface is softened by moisture picking-up and then complementary shrinkage makes EL strain and MS strain decrease, but because of the effect of drying history, the change of MS strain lags behind that of MC.