木材の音波の伝播速度とヤング率について

概要

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Velocity of sound wave propagation in wood were measured on the longitudinal wave by the ultrasonic pulse method. (Fig 1) Direction of sound wave propagation was restricted to the fiber axis of wood and effects of moisture content in the specimen and length of wave propation on velocity of sound was examined. Ultrasonic pulse was the frequency of 30 kHz, pulse width and pulse interval was respectively 1/120 sec. Specimen used was SUGI (Cryptomeria japonica) wood and dimension of the cross section was $10 mm \times 20 mm$ and the side on tangential direction of wood was 10 mm. The results of experiment were shown follows. 1. Velocity of sound wave propagation in wood differs from the length of propagation. The length of sound wave propagation decreases the velocity of propagation. Similarity was noted with steel bar and lead pipe. (Fig. 2,3,4) 2. Moisture in the specimen influences velocity of sound wave propagation. That is to say, velocity gave the maximum value in the state of 0 % moisture content. In the state of 7-8% moisture content, an increase of the decrement in velocity with moisture content was found. (Fig.5) 3. The test value showed that dynamic Young's modulus calculated from velocity of sound wave propagation by 5-40% exceed static Young's modulus from the static compression test of fiber axis direction.(Fig.6,7) 4. Dynamic Young's modulus showed the maximum value in the state of 5% moisture content. (Fig. 7)
九州大学の論文