Effect of Temperature on Acoustic Evaluation of Standing Trees and Logs: Part 1—Laboratory Investigation
Keywords:Acoustic velocity, peak energy, logs, moisture content, temperature, trees
AbstractThe goals of this study were to investigate the effect of environment temperature on acoustic velocity of standing trees and green logs and to develop workable models for compensating temperature differences as acoustic measurements are performed in different climates and seasons. The objective of Part 1 was to investigate interactive effects of temperature and moisture state of wood on acoustic properties in a laboratory-controlled environment. Small clear specimens (25.4 x 25.4 x 407 mm) obtained from a freshly cut red pine (Pinus resinosa) log were conditioned to four moisture content levels: green (fresh-cut condition), 24%, 12%, and 0%. All specimens were acoustically tested using an ultrasonic device across a temperature range of -40 to 35°C. Results indicate that wood temperature had a significant effect on acoustic velocity in frozen wood. Below the freezing point, acoustic velocity increased as wood temperature decreased. When wood temperature was well above freezing, velocity decreased linearly at a slow rate as wood temperature increased. We found that wood moisture content had a significant compounding effect on velocity-temperature relationships in the freezing zone (-2.5 to 2.5°C). Temperature effect was much more significant in green wood than in dry wood. In green wood, both velocity and peak energy changed abruptly around the freezing point because of the phase transformation of free water in the cell lumens.
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