The effect of juvenility and veneer thickness on bending strength of Douglas-fir laminated veneer lumber
2016
Rahayu, Istie | Denaud, Louis | Ruelle, Julien | Darmawan, Wayan | Nugroho, Naresworo | Marchal, Remy
Most of wood industry requires well conformed logs and middle diameter trees to optimize primary processing yields. The raw material, mostly coming from monoculture plantations, contains a considerable proportion of juvenile wood. The objectives of present study were to identify the transition ring between juvenile and mature wood in Douglas-fir and to analyze the effect of juvenility and veneer thickness on bending strength of Douglas-fir laminated veneer lumber (LVL). Microfibril angle (MFA) and tracheid length from five Douglas-fir logs were measured from pith to bark. Veneers peeled with an instrumented lathe to produce LVL. Total of 140 LVL samples were mechanically characterized by measuring modulus of elasticity (MOE) and modulus of rupture (MOR). The results showed that transition rings from juvenile to mature wood at breast height, according to MFA and tracheid length, were at twentieth and twenty-first, respectively. According to analysis of variance, there was a significant effect of juvenility on LVL bending strength. The advantage of using veneers of mature compare to juvenile wood for LVL was due to an improvement of bending strength in the range of 7–22 %. LVL made of 3 mm veneers has lower stiffness (2.2 %) compare to LVL made of 5.25 mm veneers. High correlation between static and dynamic MOE was noted.
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