Effects of Continuous Vibration on Dynamic Viscoelasticity of Wood

Abstract

The effects of the continuous vibration of small amplitude on the dynamic viscoelasticity of wood were studied for seven kinds of species of softwood and hardwood. The free-free flexural vibration method of rectangular beams was used. The vibration test was made in a chamber in which the temperature and humidity was controlled at 20°C and 65% R. H. The vibration was continued for five hours by using a self running oscillation circuit which automatically regulated a resonance frequency of a vibration system. The resonance frequency ranged from 100 to 170 Hz and the amplitude of the vibration was 0.14 mm at the end of a specimen. The dynamic Young's modulus E′ and the loss tangent tan δ were measured at each one hour interval at ten degrees of amplitude in the range from 0.015 to 0.40 mm. The dynamic Young's modulus was not affected by the subjected continuous vibration. On the other hand, the loss tangent decreased until about one or two hours and approached gradually to a constant value as increase of the vibration time. After five hours, the loss tangent decreased by about 5 to 15%. The loss-tangent decreasing process was studied by using the rate process theory, and the qualitative trend of the experiments could be well explained. © 1992, The Society of Materials Science, Japan. All rights reserved.