5种桉树木材物理力学性质的差异比较

分析5种桉树幼龄材的物理力学性质的差异，为研究不同桉树材性变异规律及提高桉树木材利用效率提供参考。以采自广东湛江南方国家级林木种苗示范基地大田区的2.5年生和4年生赤桉、2.5年生尾巨桉及6年生尾细桉无性系L-9、M-11等5种不同林龄的桉木为研究对象，按照国家标准测量木材物理性质指标木材密度（基本密度、气干密度、全干密度）、气干（径向、弦向、体积）干缩率、全干（径向、弦向、体积）干缩率，以及力学性质指标抗弯强度、抗弯弹性模量、顺纹抗剪强度、顺纹抗压强度、硬度（弦面硬度、径面硬度、端面硬度），以SPSS、Excel等数据分析软件对其进行数理统计和分析，分析其差异和变异规律。5种桉树基本密度差异不显著，其余物理力学指标差异极显著。5种桉树的基本密度0.428～0.460 g/cm³，气干密度0.494～0.543 g/cm³，全干密度0.482～0.525 g/cm³，各品系间变异较小。气干干缩率在不同品系间存在着较大的变异，2.5年生赤桉＞4年生赤桉＞L-9＞M-11＞尾巨桉，径向干缩率变异最大。桉树随着林龄的增长干缩率值增大，说明林龄大的桉木更容易开裂。不同品种间力学性质差异显著。5种桉树木材密度与径面硬度和端面硬度呈正相关关系，说明桉树木材密度越大，其木材硬度越高。由木材密度指标看，桉树可作为纸浆材和纤维板材的原材料，随着林龄的增加，桉树木材物理力学性质指标值增加。按照木材物理力学指标分级标准可知，5种桉树木材密度属于小级；赤桉干缩率属于Ⅱ级，尾巨桉干缩率属于Ⅱ-Ⅲ级，L-9干缩率属Ⅳ级，M-11干缩率属于Ⅳ级；5种桉树木材抗弯强度和抗弯弹性模量均属于Ⅱ级，剪切强度属于Ⅴ级，端面硬度均属Ⅲ级。

Difference in Wood Physical and Mechanical Properties of Five Kinds of Eucalyptus

In order to provide references for understanding the wood variation rules of different Eucalyptus species and improving the utilization efficiency,differences in wood physical and mechanical properties of five kinds of juvenile woods were analyzed.Samples of 5 Eucalyptus timbers were collected from South China Experimental Nursery in Zhanjiang,Guangdong,including E.camaldulensis (2.5，and 4-year-old),E.urophylla×E.grandis (2.5-year-old),clone L-9 and M-11 of E.urophylla×E.tereticornis (6-year-old ).The wood density (basic density,air-dry density,absolute-dry density),air-dry (radial,tangential,volume) shrinkage rate and absolute-dry (radial,tangential,volume) shrinkage rate,and mechanical properties including bending strength,modulus of elasticity of bending,shear strength,compressive strength,hardness (tangential,radial,end) were measured according to the national standards.The differences and variations were analyzed by SPSS,Excel,DPS and other data analysis software.There was no significant difference in the wood basic density among 5 timbers,but significant differences in other physical and mechanical indexes were observed.The basic density,the air-dry density,and the total dry density ranged from 0.344 to 0.558,0.373 to 0.665,and 0.380 to 0.664 g/cm³,respectively,with little variations.The air-drying shrinkage rate varied greatly with an order of 2.5-year-old E.camaldulensis>4-year-old E.camaldulensis>L-9>M-11>E.urophylla×E.grandis,and the radial shrinkage rate varied most significantly.The shrinkage increased with stand age,which indicated that the older Eucalyptus timber was easy to crack.There were also significant differences in mechanical properties.Wood density of all five timbers was positively correlated with diameter hardness and end hardness,which indicated that the higher the wood density,the higher the wood hardness.From the view of wood density,Eucalyptus woods could be used as materials to make paper pulp and fiber board.The values of Eucalyptus wood physical and mechanical properties increased with age.According to the classification standard of wood physical and mechanical indexes,the wood density of five Eucalyptus timbers was in low grade; the dry shrinkage rates of E.camaldulensis,E.urophylla×E.grandis,L-9 and M-11 were in grade Ⅱ,Ⅱ-Ⅲ,Ⅳ,and Ⅳ,respectively.The bending strength and modulus of bending elasticity of five timbers were fitted into grade Ⅱ; the shear strength belonged to grade Ⅴ; and the hardness of end surface belonged to grade Ⅲ.