Effects of Ultrasonic Detection Modes on the Longitudinal Ultrasonic Wave Transmission in Domestic Plantation Lumber
摘要
The performances of different ultrasonic detection applications on the longitudinal wave propagation in Japanese cedar (Cryptomeria japonica) and China fir (Cunninghamia lanceolata var. lanceolata) lumber were evaluated in the study. Results showed that insignificant differences among longitudinal ultrasonic wave velocities measured by transducers from 40 to 1000 kHz were found using the direct transmission method. The average wave velocities were 5074 and 6003 m s^(-1) for Japanese cedar and China fir, respectively. The longitudinal ultrasonic wave velocity obviously decreased with both the surface transmission method and semi-direct transmission method under 500-and 1000-kHz conditions. Good correlations, i.e., R^2 values of between 0.92 and 0.94, among the measured longitudinal ultrasonic wave velocities in the 3 detection methods with a 40-kHz transducer were obtained. Longitudinal ultrasonic wave velocities of wood measured with the different-shaped transducers and coupling methods also had good correlations, with R^2 values of between 0.95 and 0.99. The velocity measured with the flat transducer was 8.8~11.1% higher than that with the tapered transducer. The modulus of elasticity of wood can be estimated using longitudinal ultrasonic wave velocities measured by the 3 different detection methods with R^2 values of between 0.79 and 0.85 for Japanese cedar and China fir. It is expected that ultrasonic detection can be applied to the derivation of allowable strengths of structural lumber from Taiwanese plantations and for field inspections.