Abstract
Properties of the sound transit through wood have been investigated to estimate the moisture content (MC) of wood by the ultrasonic method. In this paper, velocities and damping of longitudinal and transverse waves were measured. The heartwood of Sugi (Cryptomeria japonica D. Don) and Hinoki [Chamaecyparis obtusa (S. and Z.) Endl.] were used in the MC range of the oven-dried to green conditions.
The velocities of ultrasonic waves were reduced as the MC increased. The decrease in ultrasonic velocity per unit moisture content was larger for Hinoki than for Sugi. In the range of MC more than the fiber saturation point (FSP), the ultrasonic velocity was represented by a function of specific gravity. The wood species used were approximately equal in the decrease in velocity per unit specific gravity.
A ratio of the velocity of transverse waves to that of the longitudinal waves tended to increase with increasing MC. In the case of Sugi, the ratio was approximately constant in the range of MC more than the FSP.
Damping of ultrasonic waves increased with increasing MC at the FSP or above. Furthermore, the damping of longitudinal waves was larger than that of transverse waves.
