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Use of Time-of-Flight Ultrasound to Measure Wave Speed in Poplar Seedlings

1
School of Technology, Beijing Forestry University, Beijing 100083, China
2
Joint International Research Institute of Wood Nondestructive Testing and Evaluation, Beijing Forestry University, Beijing 100083, China
3
USDA Forest Service, Forest Products Laboratory, Madison, WI 53726-2398, USA
*
Author to whom correspondence should be addressed.
Forests 2019, 10(8), 682; https://doi.org/10.3390/f10080682
Received: 28 June 2019 / Revised: 6 August 2019 / Accepted: 9 August 2019 / Published: 13 August 2019
(This article belongs to the Special Issue Wood Properties and Processing)
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Abstract

In this study, 145 poplar (Populus × euramericana cv.’74/76’) seedlings, a common plantation tree species in China, were selected and their ultrasonic velocities were measured at four timepoints during the first growth year. After that, 60 poplar seedlings were randomly selected and cut down to determine their acoustic velocity, using the acoustic resonance method. The effects of influencing factors such as wood green density, microfibril angle, growth days, and root-collar diameter on acoustic speed in seedlings and the relationship between ultrasonic speed and acoustic resonance speed were investigated and analyzed in this work. The number of specimens used for investigating growth days and root-collar diameter was 145 in both cases, while 60 and two specimens were used for investigating wood density and the microfibril angle, respectively. The results of this study showed that the ultrasonic speed of poplar seedlings significantly and linearly increased with growth days, within 209 growing days. The ultrasonic velocity of poplar seedlings has a high and positive correlation with growth days, and the correlation was 0.99. However, no significant relationship was found between the ultrasonic velocity and root-collar diameter of poplar seedlings. Furthermore, a low and negative relationship was found between wood density and ultrasonic speed (R2 = 0.26). However, ultrasonic velocity significantly decreased with increasing microfibril angle (MFA) in two seedlings, and thus MFA may have an impact on ultrasonic speed in poplar seedlings. In addition, ultrasonic velocity was found to have a strong correlation with acoustic resonance velocity (R2 = 0.81) and a good correlation, R2 = 0.75, was also found between the dynamic moduli of elasticity from ultrasonic and acoustic resonance tests. The results of this study indicate that the ultrasonic technique can possibly be used to measure the ultrasound speed of young seedlings, and thus early screen seedlings for their stiffness properties in the future. View Full-Text
Keywords: ultrasonic speed; poplar seedlings; acoustic resonance; density; microfibril angle; root-collar diameter ultrasonic speed; poplar seedlings; acoustic resonance; density; microfibril angle; root-collar diameter
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Liu, F.; Xu, P.; Zhang, H.; Guan, C.; Feng, D.; Wang, X. Use of Time-of-Flight Ultrasound to Measure Wave Speed in Poplar Seedlings. Forests 2019, 10, 682.

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