熱處理木材的彎曲強度機構與其AE行為

Bending Strength Mechanism and Acoustic Emission Behavior of Heat-treated Wood

本研究係以無瑕疵之雲杉（Picea sitchensis）氣乾材，作為評估木材受熱處理後之彎曲強度機構與其在彎曲強度試驗時所發生的音射（AE）行為。試材在不同溫度（40、80、120、160及200°C），加熱時間（8、24、72及120 h）等條件組合熱處理後，測定其彎曲強度，彈性係數及變形量，並同時偵測在彎曲強度試驗所發生之音射事件（AE events）。AE試驗使用共振周波數140 kHz之AE感應器（sensor），將其裝置於試材下方離載重3公分處。結果顯示，在溫度超過160°C以上，彎曲強度隨加熱時間增加而降低。彈性係數於加熱溫度的40至160°C與其加熱時間為8至120 h時無明顯變化，但在溫度200°C時，隨加熱時間增加則有顯著影響。同時得知，試材受熱處理，AE事件由最初微小破壞開始發生並連續累積直到最大（破壞）載重。又知材內之應變能量因其韌性降低（即塑性領域之變形量減少）而減少，因此導致在破壞載重前，AE事件相對的增加。本研究得知應用AE偵測技術在彎曲強度試驗時，能進一步探討木材經熱處理後之彎曲強度機構的破壞行為。 Air-dried clear spruce (Picea sitchensis) specimens after heat-treated under various temperature and time conditions were used to clarify the bending strength mechanisms and the Acoustic Emission (AE) characteristics during static bending tests. The specimens were heat-treated using 20 different conditions with combination of temperatures (40, 80, 120, 160 and 200°C) and time (8, 24, 72 and 120 h). In these experiments an AE sensor with a resonant frequency of 140 kHz was mounted onto the tensile side of the specimen. The AE sensor location was about 30 mm left side from the center of the specimen. The modulus of rupture (σ), static Young's modulus (E), deflection and AE events were measured. The σ decreased with the increase in heating time at temperatures above 160°C. The E insignificantly varied the heat-treated woods in the range from 40 to 160°C with the heating time from 8 to 120 h. However, the E was remarkably influenced under the treatments at 200°C with heating duration. The AE events continuously accumulated from the initial minute fracture to the load at failure according to the structural mechanics of the wood that were changed as a result of the heat treatment effect. Moreover, AE events before reaching the failure load level increased relatively, recognizing that the strain energy stored in the beat-treated wood due to the reduction in toughness (the decrease of the deflection in plastic region) decreased. These results indicate that using AE monitoring techniques in the static bending tests to evaluate the heat-treated woods could assess the variations in the bending strength mechanism.

Air-dried clear spruce (Picea sitchensis) specimens after heat-treated under various temperature and time conditions were used to clarify the bending strength mechanisms and the Acoustic Emission (AE) characteristics during static bending tests. The specimens were heat-treated using 20 different conditions with combination of temperatures (40, 80, 120, 160 and 200°C) and time (8, 24, 72 and 120 h). In these experiments an AE sensor with a resonant frequency of 140 kHz was mounted onto the tensile side of the specimen. The AE sensor location was about 30 mm left side from the center of the specimen. The modulus of rupture (σ), static Young's modulus (E), deflection and AE events were measured. The σ decreased with the increase in heating time at temperatures above 160°C. The E insignificantly varied the heat-treated woods in the range from 40 to 160°C with the heating time from 8 to 120 h. However, the E was remarkably influenced under the treatments at 200°C with heating duration. The AE events continuously accumulated from the initial minute fracture to the load at failure according to the structural mechanics of the wood that were changed as a result of the heat treatment effect. Moreover, AE events before reaching the failure load level increased relatively, recognizing that the strain energy stored in the beat-treated wood due to the reduction in toughness (the decrease of the deflection in plastic region) decreased. These results indicate that using AE monitoring techniques in the static bending tests to evaluate the heat-treated woods could assess the variations in the bending strength mechanism.