Moisture effects on the ultrasonic velocities in woods

Velocities of 1-MHz ultrasonic waves were measured intermittently for several kinds of wood specimens of varying water content. Results generally show that, with increasing water content up to some point (typically about 30%), the velocities decrease rather sensitively and that this point coincides with the one previously known as the fiber saturation point. Velocity measurements were also performed in three orthogonal directions relative to the fiber axis of wood specimens which were being dried (or moistened) and hence had nonuniform humidity distributions. Rates of water transfer in woods estimated from the measurements are discussed in terms of diffusion theory and the internal structure of woods.<>