| Summary: | 碩士 === 國立中興大學 === 森林學系 === 89 === The purpose of this study was to apply the nondestructive ultrasonic wave to test the ultrasonic velocity of wood and wood based materials, and to use destructive universal testing machine to test their strength.
The finding of this study were summarized as follows：
Ultrasonic velocity is increased with the density of the increased particleboard. The coefficients of determination (R2) of the regression analysis between density and longitudinal wave and between density and surface wave were 0.93 and 0.92, respectively. However, the density and ultrasonic velocity of solid wood showed that they had no relations because of the structure of solid wood.
Fiber angle of wood affected the transport velocity of ultrasonic. Also, the velocity is decreased with fiber being angle increased. Producing flow direction of merchant particleboard and fiberboard had a little impact on ultrasonic velocity. That was to say, the directionality of panels wasn’t obvious. Surface layer direction of plywood had also a little impact on ultrasonic velocity.
The velocity of longitudinal wave is decreased with the increased specimen length, but the relationships among them were not obvious. When the length of specimen was longer than 15cm, velocity of surface wave is increased with the increased specimen length, and the relationships among them were not obvious, either. The relationships between thickness and ultrasonic velocity of particleboard and fiberboard were not obvious, but the ultrasonic velocity of plywood is decreased with the increased thickness.
The ultrasonic was applied to test the mechanical property of wood based panels. The relationship between MOE and the velocity of longitudinal wave or surface wave was statistically significant, and R2 values of them are 0.86 and 0.85, respectively. The relationships between MOR and their velocities were also statistically significant, and their R2 values were 0.84 and 0.83, respectively. IB specimen was tested with longitudinal wave which frequency was 40 and 100 KHz, and R2 values of them are 0.74 and 0.75, respectively.
Based the result of this study, it showed that the ultrasonic was not suitable to test the artificial defect with hole, if the wavelength was larger than the size of artificial defected hole. As the results mentioned above, results applied to test in wood based panels of longitudinal wave and surface wave were similar. These results showed the longitudinal wave and surface wave could cooperate with each other.
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