Variations in Ultrasonic Wave Velocity and Dynamic Young's Modulus with Moisture Content for Taiwania Plantation Lumber

Song-Yung Wang, Chih-Ming Chiu, Cheng-Jung Lin

Abstract


The effects of moisture content (MC) on the ultrasonic wave velocity, dynamic Young's modulus (DMOE), and the mobility of free water during desorption from a water-saturated condition were examined for the longitudinal, radial, and tangential directions of Taiwania (Taiwania cryptomerioides Hayta) plantation lumber. The ultrasonic wave velocity in the longitudinal and radial direction tended to increase with decrease in MC, and the effect of MC on the ultrasonic wave velocity of Taiwania lumber below the fiber saturation point (FSP) was stronger than above the FSP. Above the MC of 70%, the ultrasonic wave velocity in the tangential direction tended to decrease with decreasing MC, whereas below the MC of 70%, the ultrasonic wave velocity tended to increase with decreasing MC.

The DMOE curve also showed a significant change around the FSP in a two-stage relationship with MC values. Above the FSP, DMOE values tended to decrease rapidly with decreasing MC, whereas below the FSP, the DMOE values tended to increase gradually with decreasing MC. The k values for the ultrasonic wave propagated through the longitudinal, radial, and tangential direction of Taiwania plantation lumber were equivalent to 0.58, 0.33, and 0.01, respectively. Using the effective density and ultrasonic wave velocity to calculate the longitudinal, radial, and tangential DMOE, it was found that the DMOE tended to remain constant with MC during the MC reducing process from a water-saturated condition to FSP.


Keywords


Taiwania (<i>Taiwania cryptomerioides</i> Hayta);ultrasonic wave velocity;dynamic Young's modulus;moisture content;effective density

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