Study On Biomechanical Properties Of Trees Under Thermal Shock Treated

The growth and the safety reliability of the engineering green trees are effected by the ice and snow disasters with the characteristics of the rapid temperature change-the temperature shock. Therefore the systematical research on the biomechanical response of the greening trees under the temperature shock is particularly important, which not only has important guiding significance for the curing forest and the reasonable scientific restoring the forest after the disasters, as well as can provide a new research idea on the changes in the mechanical and physical properties of the forest when the temperature shock.After the literature study and field research the researching subject of the biomechanical response of the trees under the temperature shock has two parts of the tree trunks and the tree branches according to the method of biomechanical research. Based on the load in temperature shock is bigger than the one under general conditions the branches bending performance was studied. Due to the temperature difference is big in the temperature shock and according to the number of the temperature shocks the study on the biomechanical responses was done. The following study was on the mechanical responses of one tree relative to the temperature shock loads by using numerical modeling. The main research contents and conclusions of the paper are as follows:(1) The experiment about the mechanical properties of dormant branches bending:To the branches of eight kinds of common use trees in afforestation and bamboo the biomechanical experiments were done. By means of the three point bending measurements of the bending strength, the bending modulus and the deformation work of the fresh and dry branches, the biological mechanics performance of the fresh and dry branches have been got, which provide the basic data for the numerical simulation. The experimental results show that the bending elastic modulus and bending strength of the each species of fresh branches is less than dry branches, but the bending deformation and the bending deformation work of the fresh branches is greater than dry branches, and the change degrees are associated with the tree species;(2) The experiment on the mechanical responses of the tree trunks under temperature shock:to the rapid temperature change of pinus tabulaeformis in different temperature difference, and to the different frequency temperature shocks with the same temperature difference, the biological mechanics performance experiments were done, the influences on the mechanical properties of the pinus tabulaeformis were studied according to the temperature differences of temperature shock and the numbers of temperature shock. The following biomechanical experiment conditions were the same temperature difference (the temperature difference has two kinds:normal and extreme) with different times of the temperature shock to the northeast China ash, the Chinese oak, the pinus sylvestris and the moso bamboo. The experimental results indicated that to different cooling temperatures of a temperature shock the influence on the biomechanical properties of pinus tabulaeformis is larger; With the increase of the temperature shock cycle, the flexural strength, the flexural modulus and the rupture work of unit volume continually go down to the all of the pinus tabulaeformis, the Chinese oak, the northeast China ash, the pinus sylvestris and the moso bamboo;(3) Based on the measured data of the mechanical properties of the pinus tabulaeformis under the temperature shock the finite element analysis was down on the biomechanical response of a pinus tabulaeformis tree. By the numerical simulation the stress fields of the trunk and branches of the pinus tabulaeformis tree were calculated. The calculation results show that, when the wind load is fixed, along with the increasing of the ice and snow load, the stress distribution changes in the lower branches and the trunk of the pinus tabulaeformis tree are little, but the stresses in the upper part of the branches and the middle part of the branches of the pinus tabulaeformis tree increase larger. Therefore these branches are more easily to be damaged. To the fixed ice and snow load, with the increasing of wind load, the root stresses of the branches of the pinus tabulaeformis tree and maximum stress in the tree increase sharply, and the pinus tabulaeformis tree could be uprooted.