Study On The Influence By Seasonal Changes To Mechanical Properties Of Standing Tree Branches

Logging operation caused varying degrees of damage to the branches of remained trees while cutting down the standing trees, affecting the normal growth to the remained trees. Through studying the mechanical properties of branches in different seasons, this paper comparing and analyzing the mechanical properties affected by seasonal changes, providing effective theory basis for the health status and use value assessment of the wood, and then providing evidences for reasonable logging plan.In this paper, bending elastic modulus, dynamic modulus of elasticity and bending strength of branches (birch; poplar; larch) were tested, using the methods of ultrasonic wave, transverse resonance method and universal mechanical testing machine. Laboratory analysis samples were collected from the dates among four seasons. When branches were taken in each season, we immediately produced specimen which meet the requirements of international standard. Part of samples did the test for the determination of moisture content, and the other part of samples did the determination of mechanical properties testing. Test sequences were the ultrasonic wave method, the transverse resonance method, finally the universal mechanical testing machine. Comparing and analyzing all the test data, we got the following conclusions:(1) By the change of seasons, the mechanical properties of the tree branches were also changed a lot. Temperature was one of the important factors affecting the branches’parameters of mechanical properties such as elastic modulus and bending strength;(2) As the temperature getting lower, the static elastic modulus, dynamic modulus and bending strength of the branches increased. Above freezing point, the mechanical properties of the branches influenced by the temperature was not sensitive, the mechanical properties increases slowly when temperature dropped; below freezing point, the mechanical properties of the branches changed significantly influenced by the temperature, and general change trend of three tree species were basically the same. This phenomenon was due to the temperature dropped below freezing point, a large number of inside water of branches caused phase change;(3) There were differences between the three branches’specimens on mechanical properties, the index of birch specimens’ mechanical properties are higher than the specimens of poplar and larch. The mechanics characteristic parameters of larch were the lowest in three tree species. Mechanics characteristic parameters of three branches’specimens were reached maximum in winter and reached minimum in summer;(4) No matter three tree species samples of birch, poplar and larch as an independent sample space, or as a general sample space, the static elastic modulus Es and dynamic elastic modulus of EF, EU basically has significant linear relationship between them. To some degree, it showed the ultrasonic nondestructive test and shear wave resonance method combining with FFT to detect the branch wood has a certain universal significance and it’s practical either.