Modeling analysis of the bending modulus of elasticity for branches in the period of dormancy

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. Totally 176 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 the least-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.