Title: Modeling temperature and moisture state effects on acoustic velocity in wood
Author: Gao, Shan; Wang, X.; Wang, L.; Bruce, R.B.
Source: In: Proceedings, 17th International Nondestructive Testing and Evaluation of Wood Symposium, Sopron, Hungary, 14-16 September. p. 411-418.
Description: Previous research has proved the concept of acoustic wave propagation methods for evaluating wood quality of trees and logs during forest operations. As commercial acoustic equipment is implemented in field for various purposes, one has to consider the influence of operating temperature on acoustic velocity — a key parameter for wood property prediction. Our field study on acoustic monitoring of standing trees and logs over one-year cycle showed a significant change in acoustic velocity as seasonal temperature changed. The purpose of this study is to further investigate the effects of temperature and moisture state of wood on acoustic properties in a laboratory-controlled environment. Small clear specimens (25.4 x25.4 x407 mm) obtained from a freshly-cut red pine (Pinus resinosa) log were conditioned to four moisture content (MC) levels: green (fresh-cut condition), 24% MC, 12% MC and 0% MC. All specimens were acoustically tested using an ultrasonic device over a temperature range of -45 °C and 35 °C. The results indicated 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 in green wood was not significantly affected by temperature change. It was found that wood moisture content had a significant compounding effect on the velocity-temperature relationships. Temperature effect was much more significant in green wood than in dry wood. In green wood, both velocity and energy loss changed abruptly around the freezing point (-2.5°C~ 2.5°C) due to the phase transformation of free water in the cell lumens.
Keywords: Acoustic velocity, energy loss, logs, moisture content, temperature, trees
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Gao, Shan; Wang, X.; Wang, L.; Bruce, R.B. 2011. Modeling temperature and moisture state effects on acoustic velocity in wood. In: Proceedings, 17th International Nondestructive Testing and Evaluation of Wood Symposium, Sopron, Hungary, 14-16 September. p. 411-418.
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