木材の乾燥過程で発生するAEについての二三の考察 (その4) : 吸水 - 乾燥の繰り返しとAE発生

Abstract

乾燥中の木材におけるAEの発生機構を探るための研究の第4報として, スギの辺材と心材から作製した立方体小試片の吸水－乾燥を5回繰り返したときのAE発生, 繊維方向厚さを1 - 10mmとしたヒノキ心材小試片の乾燥過程のAE発生, 備長炭試片の乾燥および吸水過程のAE発生について検討した。スギ試片における吸水－乾燥の繰り返しから, AEは乾燥時のみならず吸水時にも短時間ではあるが発生すること, AEの発生経過及び発生数は辺材と心材でかなり異なることが明らかになった。また, ヒノキ試片におけるAEの発生経過は厚さ4mm前後で異なること, 備長炭試片の乾燥, 吸水過程でもAEが発生することなどが明らかになった。

This is a continuation of three previous reports to examine the generation mechanism of acoustic emission (AE) during wood drying. First, the AE generation during repeated cycles of wetting and drying was examined for small specimens (20X20X20mm) prepared from sapwood and heartwood of sugi (Experiment (1), Fig.1). Secondly, the AE generation during drying was examined for specimens 18mm square of hinoki of different thicknesses, 1-10mm, along the fiber length (Experiment (2), Fig.2). Lastly, the AE generation during drying was examined for a charcoal specimen (13X13X17(L)mm) (Experiment (3), Fig.2). The gain and the threshold for AE signals were set at 70dB and 100mV (Experiment (1) and (3) or 200mV (Experiment (2)) respectively. It was found in Experiment (1) that AEs were generated during both drying and wetting (Figs.4, 5, 7) ; The AE total event count changed with the repetition cycle of wetting and drying (Fig.6) ; AE generation was different between drying and wetting, and also between sapwood and heartwood. In Experiment (2), the process of AE generation during drying varied with the thickness of specimens (Fig.8), and the AE total event was proportional to the thickness (Fig.9). In Experiment (3), it was found that AEs were generated during wetting and drying of charcoal (Fig.10).