Segregation of Eucalyptus Lumbers for Finger-jointed Using Longitudinal Vibration

The variation in lumber quality within the supply of eucalypt is large. Effective segregation of the lumber according to "fitness for purpose " is fundamental to enabling the capture of greater value for the finger-jointed. This paper deals with the longitudinal vibration technique as a means of assessing modulus of elasticity (MOE) of solid and finger-jointed specimens made with Eucalyptus grandis × E. urophylla and E. grandis. Dynamic MOE was calculated from resonance frequencies obtained from longitudinal vibration. The dynamic MOE was well correlated to the static bending MOE for solid and finger-jointed lumber from the two eucalyptuses. Correlation coefficients were obtained for the regression of dynamic MOE on static bending MOE for solid and finger-jointed lumber, and were statistically significant. Although the correlation coefficient of finger-jointed was lower than that of solid lumber, the results indicated that the static bending MOE of finger-jointed was strongly correlated with the dynamic MOE of solid lumber, namely, the solid lumber with higher dynamic MOE can produce higher bending MOE finger-jointed. It can be concluded that the longitudinal vibration technique may be useful as a nondestructive method for segregating lumbers for finger-jointed.

Estimating Strength of Finger-jointed Dimension Lumber by Nondestructive Methods

Structural finger-jointed (FJ) lumber was used mainly in structural applications including glue-laminated beams and wooden I-joists and more recently in parallel chord wood trusses. The paper evaluated strength properties of structural FJ lumber by three nondestructive methods (edge-wise bending, longitudinal and transversal vibration) in order to find an alternative to traditional evaluation methods. Lumber was sawn from the logs following a pattern typically used in China to maximize the volume of recovered sawn timbers. After kiln-dried, these rough-sawed lumbers were planned to 4.5 cm thick, 9.0 cm wide and 100cm long. The lumber pieces were assigned to two groups (low-grade and high- grade groups) according to their dynamical modulus of elasticity. FJ lumber was produced by cutting a series of sloping fingers (finger length 20, 25 and 35 mm) on the end of the wood pieces to be joined and interlocking the two pieces. Each finger-jointed lumber with one same finger length had three types: L-L, L-H and H-H. The FJ lumber was nondestructively tested using edge-wise bending, longitudinal and transversal vibration methods. After three methods, tensile and bending strengths of FJ lumber were tested to build dynamical relationships between MOE and strengths. The results showed that dynamic MOEs were good indicators of the static MOE, but both dynamic MOE and static MOE had a bad correlation with tensile strength of finger jointed lumber.

Evaluation of Strength Performance of Finger-jointed Lumbers Using Three Kinds of Nondestructive Techniques

Resonance flexural vibration(Fast Fourier Transform, FFT), ultrasonic wave(Pundit) and stress wave(Metriguard) techniques were examined as means of evaluating the static modulus of elasticity (MOE) and predicting the modulus of rupture (MOR) of finger-jointed lumber specimens made with four kinds of Eucalyptus (Eucalyptus. citriodora, E. exserta, E. grandis x E. urophylla and E. grandis). Dynamic MOE was calculated from frequency and time obtained from forced vibrations and sounds induced in the four species of finger-jointed specimens. It was found that correlation coefficients between density and static MOE and dynamic MOE were statistically significant at the 0.01 level. And it was also found that the three nondestructive techniques can provide rapid and accurate means to determine the MOE, and the dynamic MOE was more accurate to predict static MOE than density. But the correlation coefficient between dynamic MOE, static MOE and MOR were lower than results reported by other researchers for solid wood, and were not statistically significant. It can be concluded that the three nondestructive techniques are useful for evaluating the MOE, but not suitable for predicting the MOR of finger-jointed.