The ultrasonic wave velocities of Japanese cedar columns were measured using a non-contact method. An air-coupled ultrasonic wave was propagated through the axial and lateral directions of wood. The velocities in the axial direction (V L) showed the minimum values around the pith. The averaged V L increased from 3600 m/s towards the outside of measurement area and attained the maximum values (=4010 m/s). The velocities in the lateral direction (V RT ) showed no tendency among measurement points. The averaged V RT was 1450 m/s. The velocities obtained using the non-contact method showed a significant positive relationship with those obtained using the contact method. The averaged ratio of V L to V RT was measured to be approximately 2.2 to 2.8. These ratios were in agreement with those from a contact method. These findings suggest that it is possible to measure the velocity in Japanese cedar columns with the non-contact method by using air-coupled ultrasonics.
Japanese cedar is a popular tree cultivated in Japan. The distribution area of Japanese cedar is the largest among planted forestry species, accounting for 26% of the country’s total. In addition, 64% of roundwood production of Japanese cedar is used for sawnwood. The Plan to Create Dynamism through Agriculture, Forestry, and Fisheries and Local Communities was enacted in 2013. Forestry will become a growth industry through the creation of new wood demand and the building of a stable and efficient supply scheme [
Recently, air-coupled ultrasonic waves have been studied for use in the quality control of sawing timber and the maintenance of posts and beams in a wooden construction [
In this study, we tried to measure the ultrasonic wave velocity in Japanese cedar columns with a non-contact method. The air-coupled ultrasonic wave was propagated through the axial and lateral directions in wood. The validity of the ultrasonic wave velocities using the non-contact method was experimentally investigated. In addition, the velocities obtained using the non-contact method were compared with those obtained using the contact method.
Japanese cedar (Cryptomeria japonica D. Don) was used as the test material. Test specimen dimensions were 100 mm (longitudinal) × 100 mm (radial) × 100 mm (tangential). Numbers of test specimens were 3 pieces (S1, S2, S3). The air-dried density and moisture content show in
An air-coupled ultrasonic wave was propagated through air and specimens of wood, as shown in
where L is the propagation distance of wood, T is the propagation time with a wood sample, Ta is the propagation time without a wood sample, and Va is the velocity in air.
Specimens | Density (kg/m3) | Moisture content (%) |
---|---|---|
S1 | 333 | 9.2 |
S2 | 323 | 9.2 |
S3 | 336 | 9.1 |
In addition, the ultrasonic wave velocities were measured using the contact method. The measurement equip- ments were the same as those used in the non-contact method. The ultrasonic velocity (Vc) was calculated using Equation (3).
where L is the propagation distance of wood, Tc is the propagation time with a wood sample, and T0 is the propagation time without a wood sample.
Specimens | VL | VRT | VL/VRT | Frequency | Method |
---|---|---|---|---|---|
(m/s) | (kHz) | ||||
S1 | 3964 ± 283 | 1412 ± 155 | 2.8 | 200 | Non-contact |
S2 | 3515 ± 180 | 1606 ± 92 | 2.2 | ||
S3 | 3468 ± 335 | 1331 ± 235 | 2.6 | ||
S1 | 4118 ± 240 | 1664 ± 147 | 2.5 | 200 | Contact |
S2 | 4164 ± 253 | 1677 ± 84 | 2.5 | ||
S3 | 4096 ± 410 | 1700 ± 130 | 2.4 | ||
Japanese cedara | 4310 ± 339 | 1863 ± 9.0c | 2.3 | 500 | Contact |
1388 ± 15.1d | 3.1 | ||||
Japanese cedarb | 4950 | 2150 c | 2.3 | 2500 | Contact |
1610 d | 3.1 |
aMeasurement by Hasegawa et al. [
the pith. On the other hands, the maximum values show 4414 m/s, 3816 m/s, and 3796 m/s, respectively. Their values existed in the outside point of measurement area. In general, the tracheid length gradually increases toward the outside and attains a constant value. An ultrasonic wave dissipates acoustical energy when it occurs at the end of a fiber [
the test specimens, the propagation path coincides with the radial and tangential directions. As a result, the ultrasonic beam is deflected and shifted laterally with respect to the incident angle [
As shown in
The values of velocity in this study were smaller than those in the previous study, which used a contact method, as shown in
Ultrasonic wave velocities in the axial and lateral directions on Japanese cedar columns can be measured with a non-contact method by using air-coupled ultrasonics. As compared, the velocities were also measured by using the contact method. The velocities in the non-contact method were smaller than those measured using the contact method. The ratios of velocity were the same as those in a contact method. These results in the present study have suggested that the air-coupled ultrasonic wave is a useful tool for non-contact and nondestructive evaluation in Japanese cedar. Most importantly, this study could be considered as the first step toward the application of air-coupled ultrasonics to the nondestructive evaluation in Japanese cedar columns. In the future, the need is envisaged to measure an ultrasonic velocity in a full-sized lumber and to explore the possibility of non-contact and nondestructive evaluation in existing wood constructions using air-coupled ultrasonics.
This work was supported by Grant-in-Aid for Challenging Exploratory Research (No. 23658147) from Japan Society for the Promotion of Science and TOSTEM Foundation for Construction Materials Industry Promotion. The publication was supported in part by the Research Grant for Young Investigators of Faculty of Agriculture, Kyushu University.
MasumiHasegawa,MisakiMori,JunjiMatsumura, (2016) Non-Contact Velocity Measurement of Japanese Cedar Columns Using Air-Coupled Ultrasonics. World Journal of Engineering and Technology,04,45-50. doi: 10.4236/wjet.2016.41005