等級內木材強度分佈之變異數研究

Study on the In-grade Variance of Dimension Lumber Strength Distribution

王怡仁(Yi-Ren Wang) ； 陳柏璋(Bor-Jang Chen)

《林產工業》 9卷2期 (1990/06) Pp. 97-109

https://doi.org/10.6561/FPI.1990.9(2).9

摘要

本研究之目的在於驗證理論公式對於經非破壞性檢定分等後，等級內變異數之預測的準確性，同時也對現行之目測分等系統、杉木小徑木平割材之彎曲性質，及其與小試片之關係加以研究。研究方式首先以目測分等方式將杉木之平割材分等，再以比重、靜曲彈性係數及動彈性係數為非破壞性檢定參數，將平割材分等，繼而求其等級內之變異數，然後與由公式所得之預測值相比較。本研究發現經目測分等後，各等級之靜曲強度並沒有顯著的差異，顯示出目測分等方式的精度有待檢討。平割材與小試片間之彎曲性質的相關性偏低，又因為小徑木平割材的缺點與強度之關係尚未究明，對於實大材之性質宜以實大材直接試驗為佳。當以比重、靜曲彈性係數及動彈性係數為非破壞性檢定參數，發現此等參數與靜曲強度之相關性不高，最好的是比重，依次為靜曲彈性係數及動彈性係數，利用非破壞性檢定參數所預測的強度值對平割材分等後，所求得等級內之變異數與公式預測的等級內變異數相比較，發現二者之相關性極高，顯示出理論公式之準確性。

關鍵字

杉木 ； 靜曲強度 ； 靜曲彈性係數 ； 橫振動 ； 動彈性係數 ； 標準差 ； 等級內變異數

並列摘要

The proposed equation which can be used to predict the in-grade variance associated with nondestructive evaluation (NDE) grade is verified. The accuracy of the visual grading system currently employed in the Chinese National Standard (CNS), and the relationship of the bending properties between dimension lumber and the associated small-clear specimen are as well studied. China-fir dimension lumbers are first visually graded by CNS grading rules. Then the specific gravity, the dynamic modulus of elasticity and the modulus of elasticity are chosen as the nondestructive evaluation parameters. The dimension lumbers are graded by the individual NDE parameters. The in-grade variance is obtained and is compared with the one obtained from the proposed equation.It is found that the visual grading rule employed by CNS is not very sensitive in grading China-fir dimension lumbers due to the insignificant difference of bending strengths among grades. Because of the relationship between defects such as knots and juvenile wood and strength is not thoroughly clear, and the low correlation of bending strength between dimension lumber and the relevant small-clear specimen, it is suggested to obtain the strength value of dimension lumber by full-size testing in stead of being predicted by small-clear specimen. The NDE parameters such as specific gravity, dynamic modulus of elasticity and modulus of elasticity do not have high correlation with the bending strength of China-fir dimension lumber. The best predictor of the' bending strength is the specific gravity followed by the modulus of elasticity and the dynamic modulus of elasticity. However, the predicted in-grade variances obtained by the proposed equation are slightly higher than the actual in-grade variances with very high correlation. The equation may be used in predicting in-grade variance with acceptable bias.

並列關鍵字

in-grade variance ； nodestructive evaluation grading ； bending strength modulus of elasticity ； dynamic modulus of elasticity ； China-fir ； flexural vibration