以打音非破壞試驗推定木材含水率變化之研究

Estimation of Moisture Content Change in Wood by Tap Tone Non-destructive Testing

黃彥三(Yan-San Huang) ； 陳欣欣(Shin-Shin Chen)

《台灣林業科學》 11卷4期 (1996/12) Pp. 367-372

https://doi.org/10.7075/TJFS.199612.0367

摘要

木材之水分管理在人工乾燥過程或乾燥後之加工及使用過程頗為重要，惟由生材至平衡含水率之水分管理則較少受到重視。生材或飽水材經由天然乾燥使其含水率降低，重量減輕，除可減少運輸費用外，並可減少往後人工乾燥所需時間及能源消耗。在天然乾燥過程中，時時檢測含水率變化，在效率化的水分管理上是必要的。因此，開發一種簡便的非破壞測定技術，用以推定生材在天然乾燥時的含水率與重量變化，可說是具有實用上的價值。由於打音試驗係就長棒測定其固有縱振動頻率，並據以計算音速及彈性係數，此時木材中之水分可視為完全參與振動，故測得之音速乃該含水率下之平均音速。本研究就台灣杉生材在天然乾燥過程中，試材含水率與重量變化對打音音速測值之影響加以探討，並檢討將打音技術應用於水分管理之可行性。
試驗結果顯示：木材中之自由水分在打音時完全表現在生材之密度變化上，因此打音音速完全遵守音速與材質關係之基本物理定律，故在含水率高於纖維飽和點之生材狀態，利用音速變化來推定木材重量變化或含水率變化具有相當高的精度，是合理可行的。

關鍵字

打音 ； 音速 ； 非破壞試驗 ； 台灣杉 ； 含水率

並列摘要

Moisture control during the wood drying process and the utilization stage after drying is very important. yet, it is seldom emphasized between saturation to E. M. C. conditions. The air drying of wet wood reduces the moisture content and weight of wood, so that the time needed for kiln drying and energy consumption are reduced and, in addition, transportation costs are lowered. It is necessary to effectively manage moisture during air drying by monitoring the changes of moisture content of the wood. The development of an easy non-destructive testing method which can estimate moisture changes during the air drying process would be valuable. In this study, water saturated Taiwania (Taiwania cryptomerioides) lumber was air dried, and the tap tone method was used to measure the sound speed changes during the drying process. The relationships between sound speed changes and weight changes of specimens are discussed. The following results were obtained.
1. The free water in wood is very closely related to the density change of wood during drying, so that the sound speed measured by tap tone completely obeys the physical law relating sound speed and properties of solid materials.
2. When moisture contents are higher than the fiber saturation point, the weight changes or the moisture content changes of the wood can be estimated with high accuracy by measuring the changes of sound speed using the tap tone method.

並列關鍵字

tap tone ； sound speed ； non-destructive testing ； Taiwania cryptomerioides ； moisture content