Abstract
The study on the anisotropy of the dynamic mechanical properties of wood is an important subject. Among various problems, the effect of grain angle on the modulus of elasticity has been clarified pretty well, but the effect of grain angle on the internal friction has been studied rarely. The only equation treating this effect is the one proposed by R.E. Pentoney3), and so it still remains unsolved.
In order to treat the problem, the grain angle was taken to be the angle between the longitudinal direction and the radial one made by rotating the grain around the fixed tangential-axis, and the effects of grain angle on the dynamic modulus of elasticity and the internal friction of wood were investigated by using a flexural vibration method.
From the examination of the relationship between the internal friction and the grain angle based on Keylwelth's equation, it was found that the relationship between the variations of specific dynamic modulus of elasticity and internal friction for wood with grain angle was expressible by an exponential equation with two constants which depend upon species of wood. From this result, the equation to evaluate the internal friction of wood having grain angle was obtained. The present result disagrees with Pentoney's result which gives a linear relationship between modulus of elasticity and internal friction.
