Study On Stress Wave Propagating Velocity And Effect Factors In Standing Trees And In Logs In Frozen State

In recent years, certain achievements on physical properties, growth characteristics, mechanical properties, and defects of wood detected by stress wave non-destructive test technology has been made. Nevertheless, researches on stress wave non-destructively evaluating standing trees and logs were still relatively less, moreover, most of those researches were conducted in normal temperature. However, in northeast China, forest cutting is mainly and usually carried out in winter and early spring, when the temperature is often lowest in a year and trees are in dormant state. Meanwhile, during this period of a year, various properties, such as density and moisture content, exhibit quite different comparing to those in growth period, which have close relationship with stress wave propagation characteristics in standing trees and logs. Accordingly, felling, trimming and branching are taken on to process trees into tree-length, further, skidding operation was introduced to deliver to tree-length to log yard. Then through log scaling referring to log standards, log building, and log sorting, then bunching operation is taken.Before log loading and timber marketing, log quality inspection is needed while log grading is a especially indispensable process in log quality examination. Logs of different will be sold after grading. According to corresponding literature, one of the most substantial reference documents when grading is dynamic modulus of elasticity of standing trees and logs, which have close relation with stress wave propagating velocity in standing trees and logs. Therefore, for monitoring and predicting growth, health situation, and internal defect of trees, stress wave non-destructive evaluation technology was introduced to measure stress wave propagating velocity and its effecting factors in healthy and various standing trees and logs of Betula platyphylla, Populus pseudo-simonii, Larix olgensis, and Abies nephrolepis species with of Heartwood decay, intergrown knots, and radial shake of different grades, respectively. As a result, grade prediction could be performed before trees felling to provide more reference to standing and log grading, which could also consolidate theoretical support for reasonable bucking and play as a positive role in log optimum utilization. T-test, correlation analysis, and simple linear regression of statistical analysis software SPSS were used to analyze and compare stress wave propagating velocity and its effecting factors in healthy and various standing trees and logs of Betula platyphylla, Populus pseudo-simonii, Larix olgensis, and Abies nephrolepis species with of heartwood decay, intergrown knots, and radial shake of different grades, respectively. The results showed that:(1) In frozen state, longitudinal stress wave propagating velocity in healthy standing trees and logs of Betula platyphylla, Populus pseudo-simonii, Larix olgensis, and Abies nephrolepis species decreased as moisture content of sapwood increased linearly while there existed no correlation between radial stress wave propagating velocity and moisture content of sapwood in healthy standing trees and logs of these four species.(2) In frozen state, light conditions had less effect on longitudinal stress wave propagating velocity, radial stress wave propagating velocity, and moisture content of sapwood in in healthy standing trees and logs of Betula platyphylla, Populus pseudo-simonii, Larix olgensis, and Abies nephrolepis species.(3) In frozen state, when propagating in trees and log of Betula platyphylla, Populus pseudo-simonii, Larix olgensis, and Abies nephrolepis species with first, second, and third heartwood decay, intergrown knots, and radial shake, radial stress wave propagating velocity decreased linearly as the sizes of heartwood decay and radial shake, moreover, radial longitudinal wave propagating velocity decreased linearly as the sizes of intergrown knots.