John W. Forsman

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.