Brian K. Brashaw

Stress wave sorting of red maple logs for structural quality

Existing log grading procedures in the United States make only visual assessments of log quality. These procedures do not incorporate estimates of the modulus of elasticity (MOE) of logs. It is questionable whether the visual grading procedures currently used for logs adequately assess the potential quality of structural products manufactured from them, especially those for which MOE is of primary concern. The purpose of this study was to investigate the use of stress wave nondestructive evaluation techniques to sort red maple logs for the potential quality of lumber obtained from them. Ninety-five red maple logs were nondestructively evaluated using longitudinal stress wave techniques and sorted into four stress wave grades. The logs were then sawn into cants and lumber. The same procedure was used to obtain stress wave times in the cants and lumber. The lumber specimens were then dried and graded using a transverse vibration technique. The results of this study showed that good relationships existed between stress wave times measured in logs, cants, and the lumber produced from the logs. It was found that log stress wave grades have positive relationships with the lumber grades. Logs with high stress wave grades produced high-grade lumber. These findings indicate that the longitudinal stress wave technique has potential in sorting logs and cants for the production of high MOE products.

Nondestructive evaluation of incipient decay in hardwood logs

Decay can cause significant damage to high-value hardwood timber. New nondestructive evaluation (NDE) technologies are urgently needed to effectively detect incipient decay in hardwood timber at the earliest possible stage. Currently, the primary means of inspecting timber relies on visual assessment criteria. When visual inspections are used exclusively, they provide no indication of the extent of internal deterioration that may exist in timber. In this study, time-of-flight, stress-wave tomography, and micro-drilling resistance methods were investigated for locating incipient decay in sugar maple logs. We found that the capability of the single-path time-of-flight method for decay detection is very limited, and the method can be used only to identify logs and trees with moderate and severe decay. Resistance-based detection of decay (including early stages) is effective if the resistance drilling device is oriented so that its path goes through the decay zone; however, orienting the drill through the decay is difficult to guarantee. A multi- sensor stress-wave device can overcome the path-dependent detection issue. Results from laboratory testing indicate that the eight-sensor two dimensional stress-wave device has good potential for assisting in the detection of incipient decay in roundwood, such as logs and standing timber. However, to more effectively locate early-stage decay within a hardwood timber, more sensors should be added to the measurement system to obtain a higher resolution two-dimensional tomography image of a cross section. Field studies on standing hardwood timber should further investigate the effectiveness of these NDE methods with improved systems and procedures. This research could benefit field foresters and managers in using NDE technologies to assess the health condition of hardwood timber in the forest and could potentially lead to significant economic savings.

Mechanical and Physical Properties of Thermally Modified Plywood and Oriented Strand Board Panels

Abstract Thermal modification can increase resistance to biological degradation, reduce equilibrium moisture content, and improve the dimensional stability of solid wood. In this study, oriented st...

A critical analysis of methods for rapid and nondestructive determination of wood density in standing trees

Key messageField methods for rapid determination of wood density in trees have evolved from increment borer, torsiometer, Pilodyn, and nail withdrawal into sophisticated electronic tools of resistance drilling measurement. A partial resistance drilling approach coupled with knowledge of internal tree density distribution may offer an alternative solution for wood density surveys in the future.ContextFinding ways to nondestructively assess wood density in trees has been a quest by foresters and wood scientists around the world. In the past several decades, traditional increment borer methods have gradually evolved into sophisticated electronic tools of resistance drilling measurements.AimsWe provide a comprehensive review of research development in the use of several field nondestructive methods for rapid determination of wood density in trees and discuss pros and cons of each method for field applications.ResultsThe use of the increment borer has been a standard method for assessing wood density in trees, and it has been further developed into a system approach allowing the use of outer wood cores and knowledge of internal density distribution for predicting wood density of major tree components. Studies on the use of torsiometer, Pilodyn, and nail withdrawal tools have had very limited success and do not warrant replacement of the increment borer. Resistance drilling, on the other hand, has emerged as a potential tool for more efficient and economical collection of wood density information in trees.ConclusionThe resistance drilling method has considerable advantages over other methods in terms of less damage to trees, faster operation, and higher measurement sensitivity. Internal friction is a key factor that currently hinders further application.

Nondestructive Assessment of Timber Bridges Using a Vibration-Based Method

This paper describes an effort to develop a global dynamic testing technique for evaluating the overall stiffness of timber bridge superstructures. A forced vibration method was used to measure the natural frequency of single-span timber bridges in the laboratory and field. An analytical model based on simple beam theory was proposed to represent the relationship between the first bending mode frequency and bridge stiffness (characterized as EI product). The results indicated that the forced vibration method has potential for quickly assessing superstructure stiffness of timber bridges, but improvements must be made in measurement system to correctly identify the first bending mode frequency in bridges in the field. The beam theory model was found to fit the physics of the superstructure of single-span timber bridges and could be used to correlate first bending frequency to global stiffness if appropriate system parameters are identified.

Stress-wave nondestructive evaluation of green veneer: southern yellow pine and Douglas fir

The potential of using stress wave nondestructive evaluation techniques to sort green southern yellow pine and DOuglas fir veneer into stress grades was evaluated. Stress wave nondestructive evaluation was used to separate green veneer into several grades for use in manufacturing engineered wood composites, most notably laminated veneer lumber. The effect of moisture content and preservative treatment on stress wave determined properties of green (wet) southern yellow pine and Douglas fir veneer was investigated during the preliminary stages of the project. A digital oscilloscope and a commercial stress wave timer were used to measure the transit time it took for an induced stress wave to travel the longitudinal length of each veneer. Stress wave transit times were measured in each piece in the wet condition, during drying, and at a dry equilibrated moisture content of approximately 10 percent. Strong correlative relationships exist between stress wave velocity measured in untreated and preservative treated green (wet) and dry veneer.