杉木造林木生長應力對製材品翹曲之影響

樹木於生長過程中所產生之內部應力經長年累積後，於伐木、製材時被解放出來，致使原木發生心裂，製材時發生翹曲而降低其利用率。由於材質優良之大徑原木日益減少，為有效利用現有之森林資源，對因樹木生長應力而造成損失之問題，實不容忽視。有鑑於此，因而進行本研究計畫，本試驗以杉木造林木為試材，首先以應變片測定樹幹表面之殘留應變後，又將原木由斷面中央製取厚度2.5cm之含心徑面板，再依序向外製取相同厚度之弦面板，其中含心徑面板由髓心縱切為二，並測定其駝背翹曲量，而弦面板則直接測定其弓形翹曲量。試驗結果顯示：樹幹縱斷面之縱向殘留生長應力在邊材部分為引張應力，靠樹心部分呈壓縮應力，而樹幹表面縱向解放應變之大小與樹高部位及原木直徑並無明顯關係；又含髓心徑面板經帶鋸沿樹心幹軸方向鋸開後之駝背翹曲量有隨原木直徑之增加而減小之傾向，而弦面板之翹曲量與原木直徑及髓心距無明顯關係；樹幹表面解放應變增大時，板材翹曲量略有增大之趨勢；板材縱剖後之駝背翹曲量，實測值較理論值為大。

關鍵字

杉木；生長應力；製材；駝背翹曲；弓形翹曲

並列摘要

In recent years, problems associated with the effective utilization of lumber from plantation forests have been emphasized in Taiwan. It is known that growth stress causes failure during wood utilization and lowers the value of wood products. The equilibrium state of the standing tree will be destroyed by the release of growth stress during processing. As a result, logging and cutting may cause heart crack in logs, while sawing may cause warping which can lower the lumber yield. In this study, planted China fir trees were used for measuring the surface growth strain and strain in the diametral plank. The crooking and bowing of lumber after sawing were also measured. The results obtained were as follows: 1. Variations of surface growth strain over tree height are not apparent. Growth strains have a range of 100-600με, with an average of 400με. 2. Growth stress is tensile at the outer part of the tree trunk and compressive at the inner part. The maximum tensile stress can exceed 120kgf/cm^2, and the maximum compressive stress is about 37kgf/cm^2. 3. There is no obvious relationship between surface growth strain and lumber crook. 4. The crook of quarter-sawn hoards increases with a decrease of log diameter. The average crook is 2mm measured over a span of 100cm. 5. Measured values of crooking of boards after ripping were greater than calculated values.

並列關鍵字

China fir ； growth stress ； lumber ； crooking ； bowing

國際替代計量

杉木造林木生長應力對製材品翹曲之影響

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