The Effect of Drying Schedule on Internal Stresses of Sugi (Cryptomeria japonica) Pithless Square Timber

Abstract

In this study, the effect of drying schedule on internal stresses of sugi (Cryptomeria japonica) pithless square timber was determined. The released strain distribution of the timber was measured using a slicing method. Square timbers with cross-sectional dimensions of 120 mm × 120 mm were dried under three different conditions. After drying, cross-cut specimens of 15 mm thickness were cut from the center of the timber and divided using four different methods. The released strain distribution was measured using images of the specimen surface before and after splitting. The surface layer of the timber showed a large positive released strain, indicating a large compressive stress. This tendency was remarkable at higher initial dry-bulb temperature. The released strain at the surface showed a strong positive correlation to the released strain gradient, indicating that the released strain at the surface could be used to estimate the released strain gradient. These findings were already known for boxed-heart square timber, and this study shows that the same is true for pithless square timber.