Effects of moisture content and density on the stress wave velocity in wood.

In order to measure the moisture content of wood by stress wave, the longitudinal stress wave velocities of wood samples in different radial locations with different moisture content (0% -65%) were examined by a ARBOTOM commercial equipment. The results revealed that the stress wave velocity in wood increased with the decrease of moisture content. Wave velocity increased greatly with the decrease of moisture content when the moisture content was less than the fiber saturation point, the increasing rate was 17.4% -19.5% for beech (Fagus longipetiolata) and 18.2% -20.8% for larch (Larix gmelinii) wood, and the increasing rates were 6.0% - 7.9% for beech and 8.0% - 10.6% for larch when the moisture content was higher than the fiber saturation point. When the moisture content was the same, the stress wave velocity increased with increasing the basic density of wood, and the increase rate for beech wood was 17.5% -20.8% while that of larch wood was 12.7% -14.5%. For the same wood species, a good positive linear correlation between the stress wave velocity and the basic density was found under any moisture content. However, there was no similar correlation among different wood species, which might be due to the differences in the chemical compositions.