Nondestructive evaluation techniques for assessing modulus of elasticity and stiffness of small-diameter logs

Many of the forests in the United States have large areas that contain trees of small diameter, mixed species, and undefined quality. Because these areas are overstocked, they are at risk from attack by insects, disease, and uncontrollable wildfires. Therefore, it is essential to find cost-effective products for the fiber from these trees. A critical need is the development of nondestructive technologies for evaluating the potential quality of stems and logs obtained from trees in such ecosystems. Longitudinal stress wave and transverse vibration nondestructive evaluation (NDE) techniques are frequently used to assess the modulus of elasticity (MOE) of lumber. Strong correlations between MOE values obtained from these techniques and the static MOE of lumber have been shown to exist. The objective of this research was to investigate the use of these NDE techniques to evaluate the flexural stiffness and MOE of small-diameter logs. A total of 159 red pine and jack pine logs were obtained from Northern Michigan in the United States and assessed nondestructively using longitudinal stress wave, transverse vibration, and static bending techniques. Statistical relationships between stiffness and MOE values obtained from each technique were then examined. Results of this study demonstrated that strong relationships exist between the log properties determined by longitudinal stress wave, transverse vibration, and static bending techniques. Longitudinal stress wave and transverse vibration techniques can be used to sort small-diameter logs with reasonable accuracy.