以應力波探討花旗松立木性質與其板材製品彈性模數之關係

Stress-wave Measurements of Douglas-fir Trees for Evaluating Its Lumber Modulus of Elasticity

吳四印(Shih-Yin Wu)

《林產工業》 24卷4期 (2005/12) Pp. 271-281

摘要

選擇位於美國愛達荷州的三個樣區內共24株Douglas fir （Pseudotsuga menziesii）立木，檢測應力波在每株立木縱向及橫向的傳送速率，並依據應力波的速率發展出立木性質指標數，作為立木性質評估之用。立木伐倒後製成名義尺寸2×6之板材，並使用E-Computer量測每塊板材製品之彈性係數，求取每株立木產出板材之平均彈性係數（Modulus of Elasticity, MOE）後，檢驗立木性質與板材彈性係數間之關係。研究結果顯示，在120、240及360公分的量測跨距所測得的應力波縱向速率與該立木製成板材之平均彈性係數之決定係數R^2（coefficients of determination）分別為0.3786、0,4425及0.4070；而在從立木基點起每隔120公分的高度所測得之應力波橫向速率與立木平均MOE間的決定係數為0.3713、0.3585、0.3877及0.36370立木性質指標數為該立木縱向速率及橫向速率平方之乘積換算而得，在採用立木指標數作為該立木製品平均MOE的預測結果，可提高其預測之正確性：在120、240及360公分的量測跨距下，立木指標數與該立木製材平均MOE間之決定係數提高為0.5479、0.6092及0.5131。

關鍵字

應力波 ； 縱向速率 ； 橫向速率 ； 彈性模數

並列摘要

Stress-waves were induced longitudinally and transversely into 24 living Douglas fir (Pseudotsuga menziesiiy trees located at 3 different sites in Idaho. Stress wave velocities in the longitudinal and transverse directions were used as parameters to estimate the Modulus of Elasticity (MOE) of lumber manufactured from the trees. In addition, a stress wave index value, based on the stress-wave velocities propagated both longitudinally and transversely, was also used as an estimating parameter. These nondestructive test (NDT) parameters were used to estimate the MOE of 2 by 6 dimension lumber manufactured from the selected trees. The coefficients of determination(R^2) between the stress-wave velocities in longitudinal direction and the average MOE of lumber sawn from the trees were 0.3786, 0.4425 and 0.4070 for the 120 cm, 240 cm and 360 cm measuring spans, respectively. R^2 values that between average transverse stress-wave velocities and average lumber MOE were 0.3713, 0.3585, 0.3877, and 0.3637 at 0, 120 cm, 240 cm and 360 cm heights from the base of the tree. In this study, an index value was developed by multiplying the square of the longitudinal velocity and the square of the transverse velocity. The accuracy of the lumber quality predictions can be improved by using this index value. The R^2 value for index values and average lumber MOE were 0.5479, 0.6092 and 0.5131 for 120 cm, 240 cm and 360 cm lengths, respectively.

並列關鍵字

StressWave ； Longitudinal velocity ； Transverse velocity ； Modulus of Elasticity