Comparison of Three Methods for Determining Young's Modulus of Wood

三種測定木材彈性模數方法之比較

卓志隆(Chih-Lung Cho)

《台灣林業科學》 22卷3期 (2007/09) Pp. 297-306

https://doi.org/10.7075/TJFS.200709.0297

摘要

本研究以振動方法探討杉木、紅檜、台灣扁柏、柳杉及樟樹等五種常作為台灣歷史建築物之木材的彈性模數，並與由抗彎試驗得到之結果比較其試驗彈性模數與真實彈性模數之差異。此外，由彎曲及扭轉複合振動方法可同時計算試材的剪斷模數(G)。
試驗結果顯示由縱向振動方法得到之試驗彈性模數(E(下標 L))最高，以抗彎試驗得到之試驗彈性模數(E(下標 s))最低。由不同試驗方法所得到之試驗彈性模數間之差異百分比值會隨E(下標 b)/G值增加而增加。若依Timoshenko樑理論，考慮剪斷變形及旋轉慣性對試材彈性模數之影響，則由複合振動試驗所推導出之真實彈性模數較抗彎試驗所推導出之數值平均大約1.2%，且兩者間具有極高之相關，決定係數為0.999。隨著E(下標 b)/G值降低，試驗彈性模數E(下標 b)與E(下標 s)值的準確性會提高，E/G值可作為預測試驗彈性模數準確性的參考指標。

關鍵字

彈性模數 ； 剪斷模數 ； 振動試驗 ； 抗彎試驗 ； Timoshenko樑理論

並列摘要

Values of Young's modulus of China fir, Taiwan red cypress, Taiwan yellow cypress, Japanese cedar, and camphor wood were investigated in this study. These wood species are most typical of the wood used in historic buildings in Taiwan. Discussions of apparent and true Young's moduli obtained from longitudinal-and complex-vibration tests and a comparison of these results with tests of the same specimens by the static-bending method are presented. A simultaneous determination of the shear modulus (G) of test specimen was obtained by a complex-vibration bending and twisting method. Results showed that the longitudinal-vibration method yielded the highest values for the apparent Young's modulus, and those from the static-bending method were the lowest. Values of the percentage differences between values of Young's modulus obtained from different test methods increased with an increase in E(subscript b)/G values. Based on the Timoshenko beam theory and Hearmon approximate solution method, taking rotary inertia and shear deformation into account, it was observed that a very high correlation (R^2 = 0.999) existed between the true Young's modulus obtained from the complex-vibration and static-bending tests. There was a tendency for the dy-namic measurements to be approximately 1.2% on average higher than the static measurements. The accuracies of the apparent Young's modulus obtained from both the complex-vibration and static-bending tests improved as the E-to-G ratios decreased, and this parameter could be used as a guideline for the expected accuracy of the apparent Young's modulus corresponding to various test methods.

並列關鍵字

Young's modulus ； shear modulus ； vibration test ； static-bending test ； Timoshenko beam theory