Static bending of Eucalyptus grandis wood: plant spacing and radial variation effect

ABSTRACT Studies that approach the technological parameters of wood with wide use, such as Eucalyptus grandis, are fundamental, since their suitable use and exploitation are dependent on these characteristics. Currently, this species implantation has been expanded and the spacing is a determining factor. Therefore, the aim of present study was to evaluate the plant spacing and radial variation in static bending of Eucalyptus grandis wood. For the experiment conduction, six trees were sampled for each spacing: 2.0 x 1.0 m, 3.0 x 1.0 m and 3.0 x 1.5 m, totalizing 18 specimen at seven years old. Subsequently, the first log of each sample was sectioned into radial boards and then made into test specimens, which were identified at regular intervals in the pith-bark direction, with dimensions of 2.5 x 2.5 x 41.0 cm, to perform the mechanical static bending test, following the ASTM recommendations. The mechanical resistance results showed a variation in the pith-bark direction, where the highest MOE, MOR and TPL values were near to the bark. However, the spacing did not change the modulus of elasticity, modulus of rupture and tension on proportional limit of the material subjected to static bending. Thus, only the radial position influences in the wood quality. The values of the studied mechanical properties had an increase in the pith-bark direction, being more accentuated in the region near the bark.

摘要：针对广泛应用的用材树种（如巨桉（Eucalyptus grandis））开展工艺参数相关研究具有重要意义，因为该树种的合理利用与开发依赖于其相关特性。当前，该树种的种植规模持续扩大，而种植株行距是关键影响因素之一。因此，本研究旨在探究巨桉木材静态弯曲性能随种植株行距及径向的变化规律。为开展本实验，针对2.0×1.0 m、3.0×1.0 m及3.0×1.5 m三种株行距分别选取6株7年生巨桉，共计18株试样材料。随后，将每株试样的第一原木锯切成径向板材，再加工为尺寸2.5×2.5×41.0 cm的抗弯试样，沿髓心-树皮方向按等间距标记，并依据美国材料与试验协会（ASTM）标准开展静态弯曲力学性能测试。力学性能测试结果表明，巨桉木材的力学性能沿髓心-树皮方向存在明显差异，其中弹性模量（MOE）、抗弯强度（MOR）及比例极限拉应力（TPL）的最高值均出现在靠近树皮的区域。但种植株行距对静态弯曲测试下的弹性模量、抗弯强度及比例极限拉应力无显著影响。由此可见，仅径向位置会影响木材品质，所研究的各项力学性能参数沿髓心-树皮方向逐渐升高，且在靠近树皮的区域提升效果更为显著。