Stress wave-based nondestructive evaluation (NDE) methods for wood quality of standing trees.

摘要

The research presented in this dissertation was conducted to further the development and application of stress wave-based nondestructive evaluation (NDE) methods for non-destructively evaluating wood quality of standing trees based on the potential structural quality of products obtained from them. Current stress wave NDE methods for wood quality evaluation are not adaptable to standing trees. In this study, a side-attached stress wave method, which is aimed at in-situ testing in standing trees, was developed and evaluated. It was found that the stress wave could be appropriately generated on the side surface of a tree by impacting a nail driven into the wood. Monitoring the stress-wave trace revealed that this wave generation method provides relatively good signal characteristics in terms of stress wave derivative with respect to time. It was also determined that factors affecting the stress wave generation and measurement could be well controlled to produce repetitive stress wave data.; Stress wave methods were applied to round timber with simple boundary conditions (creosote-treated wood piles) to examine the usefulness of developed side-attached method. It was demonstrated that both end-attached and side-attached stress wave methods can be used to evaluate the potential quality of wood in creosote-treated piles removed from service. Although creosote and surface defects in used piles have an effect on stress wave propagation and stress wave measurements, good correlations were found between stress wave-based MOEd of piles and average MOE of boards, as well as static MOE of small, clear wood obtained from the piles. Experimental investigation on the variation of stress wave properties with a pile revealed that stress waves tend to lead in the bark side while they travel through the piles.; Based on the success achieved in round timber, the side-attached stress wave method was used to evaluate the mechanical properties of wood in standing trees. Results indicated that in-situ stress wave measurements provided relatively accurate and reliable stress wave information which could be utilized to assess the mechanical properties of wood in standing trees. Statistical regression analyses indicate that strong relationships existed between in-situ measured stress wave properties of trees and the strength and stiffness of small, clear samples obtained from trees.