Diameter effect on stress-wave evaluation of modulus of elasticity of logs

Recent studies on nondestructive evaluation (NDE) of logs have shown that a longitudinal stress-wave method can be used to nondestructively evaluate the modulus of elasticity (MOE) of logs. A strong relationship has been found between stress-wave MOE and static MOE of logs, but a significant deviation was observed between stress-wave and static values. The objective of this study was to investigate the effect of log diameter on stress-wave evaluation of MOE of logs and to develop a new stress-wave model by relating stress-wave MOE to log diameter for static MOE prediction. A total of 201 small-diameter logs, including jack pine (Pinus banksiana Lamb.), red pine (Pinus resinosa Ait.), Douglas-fir (Pseudotsuga menziesii), and ponderosa pine (Pinus ponderosa Dougl. ex Laws), were nondestructively evaluated. The results of this study indicate that the longitudinal stress-wave technique is sensitive to the size and geometrical imperfections of logs. As log diameter increases, the deviation between stress-wave MOE and static MOE increases. It was also found that log diameter has an interactive effect that contributes significantly to MOE prediction when used in conjunction with the fundamental wave equation. The newly developed multivariable prediction model relating static MOE to stress-wave speed, log density, and log diameter was found to better predict MOE during stress-wave evaluation of logs than did the fundamental wave equation. This could allow for the prediction of static bending properties of logs using the longitudinal stress-wave technique at levels of accuracy previously considered unattainable.