摘要
利用在回归方程中加入虚拟变量的方法分析休眠期常绿乔木和落叶乔木的枝龄、含水率、密度等对抗弯弹性模量的影响。以2012年12月从北京鹫峰国家森林公园采集的休眠期7个树种(40年的油松,30年的侧柏,12年的臭椿,20年的刺槐,30年的栾树,40年的白杜,35年的元宝枫)的176株新鲜树枝为研究对象。通过实验测得枝龄、含水率、密度、抗弯弹性模量参数,枝龄通过数枝条法进行测量后,在实验室制作试件时再通过数年轮法进行复测。含水率参照《木材含水率测定方法》标准GB/T 1931—2009中的规定获得。密度参照《木材密度测定方法》标准GB/T 1933—2009中的规定获得,其中体积采取排水法测量树枝的体积。新鲜树枝的抗弯弹性模量参照《木材抗弯弹性模量测定方法》标准GB/T 1936.2—2009中的规定,采用三点弯曲实验获得新鲜树枝的抗弯弹性模量。通过用EViews7.0对实验得到的休眠期176株新鲜树枝的力学性能参数进行最小二乘回归研究发现,在初冬休眠期,新鲜树枝的枝龄与抗弯弹性模量显著相关,随着枝龄的增加,新鲜树枝的抗弯弹性模量成曲线状下降;而新鲜树枝的含水率与密度对抗弯弹性模量影响并不显著。新鲜树枝的树种对抗弯弹性模量的变化有较大影响。
This paper analyzes the effects of branch age,moisture content and density of fresh branches of evergreen and deciduous trees during the period of dormancy on the modulus of elasticity（ MOE） by adding the dummy variable into regression model. These branches were from the seven species（ five deciduous trees and 2 evergreen trees in December 2012,including 40-year-old Pinus tabulaeformis,30-year-old Platycladus orientalis,12-year-old Ailanthus altissima,20-year-old Robinia pseudoacacia,30-year-old Koelreuteria paniculata,40-year-old Euonymus maackii,and 35-year-old Acer truncatum. Totally176 fresh twigs as research samples were collected in the Experimental Forest Farm of Beijing Forestry University. The twig age was firstly measured by using the branch sequence method,and then confirmed by counting the annual rings when test specimen was produced in the laboratory. Moisture content was measured in accordance with the national standard ＂method for determination of the moisture content of wood＂GB / T 1931-2009（ ISO 3130： 1975 MOD）. Density was obtained in compliance with the national standard ＂method for determination of the density of wood＂GB / T 1933- 2009,in which the volume of branch was measured by the water drainage method. MOE measurement was in compliance with the national standard ＂method for determination of the MOE in static bending of wood＂GB / T 1936. 2-2009.The MOE of the fresh twigs was obtained by three-point bending test. The EViews7. 0 was used for theleast-square regression analysis of the mechanical performance parameters of the 176 fresh dormant twigs,and the results indicated that there was significant correlation between MOE and the age of fresh twig in the initial phase of dormancy. The MOE of fresh twigs decreased in curved line with the increase of age.The effects of moisture content and density of fresh twigs on MOE are not significant. The tree species have marked effect on the change of MOE.
出处
《北京林业大学学报》
CAS
CSCD
北大核心
2014年第6期130-134,共5页
Journal of Beijing Forestry University
关键词
休眠期
树枝
抗弯弹性模量
枝龄
含水率
密度
树种
period of dormancy
branch
modulus of elasticity（MOE）
branch age
moisture content
density
species
