Investigation And Construction Of Wave Fronts For Stress Wave Propagation In Standing Trees

Nondestructive evaluation(NDE) of wood quality in standing trees is an important procedure in the forest operational value chain worldwide.Current nondestructive testing(NDT) techniques for living trees include two types:one is for detecting internal decay and structural defects,and the other is for assessing mechanical properties of wood.Assessment of wood mechanical properties of standing trees is especially important to the management of forest plantation and the optimal utilization of wood resources.Current research on wood quality evaluation in standing trees is still limited in China.The mechanism of stress wave propagation in trees is not fully understood yet and the interpretation of stress wave measures is largely through empirical relationships.The goal of this paper is to investigate how a stress wave travel in a tree stem as it is introduced into the tree through a mechanical impact.Experimental stress wave data was obtained from freshly cut red pine logs in the laboratory.Two dimensional(2D) and three dimensional(3D) stress wave contour maps were separately generated using 3Dfield and MATLAB software.The 2D and 3D stress wave contour maps represent the wave fronts at a series of locations along the length,which can help to visualize the propagation of stress waves in a tree stem.The experimental simulation of wave fronts in the log specimens shows that stress waves travel as a three dimensional wave initially,then gradually transformed to a quasi one dimensional wave with a non-flat wave front.