木材の圧縮試験時のサーモグラフィ (予報)

Abstract

金属材料では, 塑性加工や切削加工における大変形時の発熱挙動について古くから詳細に検討されてきているが, 木材についてはほとんど知見が得られていない。そこで, 木材切削における切削温度の解析およびサーモグラフィによる非破壊試験のための基礎資料を得るため, ヒノキ, スギ, ホワイトセラヤの気乾材に縦, 横および部分圧縮による大変形を与えたときの表面温度をサーモグラフィ装置で測定し, 変形や破壊と温度上昇の関係について検討した。縦圧縮では, 試片の中央付近の温度が上昇した後, せん断破壊による急激な温度上昇が生じた。横圧縮では圧縮破壊が層状に生じ, その場所や数は試片ごとに異なったが, 温度上昇領域は破壊部分に一致していた。また大きな圧縮ひずみが生じている領域では, 温度上昇も大きくなる傾向が認められた。部分圧縮では鋼製のあて板から5mm程度離れた領域にあて板を取り囲むような温度上昇が認められたが, この温度上昇はあて板を通じた熱の流出の影響を受けるようであった。なお本実験で測定した最大の温度上昇は, 縦圧縮で約6℃, 横および部分圧縮で約2℃であった。

Surface temperature of small air-dried wood specimen of sugi (Cryptomeria japonica D. Don), hinoki (Chamaecyparis obtusa Endl.) and white seraya (Parashorea spp.) under three types of compression load was measured by a thermographic device (Figure 1 and 2). The relationships between the strain and fracture of the specimen and the temperature distribution was discussed. On the surface of the specimen compressed longitudinally, rapid increase of the temperature along the plane of maximum shear stress was found, after the temperature in the middle of the surface had once increased (Figure 3). In the test of lateral compression, the compression fracture in a stratified form concentrated in the areas different among the specimen (Figure 4). However, the areas where higher temperature was found on the thermal images, corresponded to those of the fracture (Figure 5). When the specimen was compressed partially by a steel plate, temperature rise was found in the vicinity up to 5mm from the boundary between the specimen and the steel plate (Figure 6 and 7). It was also confirmed that the thermal flow from the specimen into the plate had influenced significantly on the temperature distribution (Figure 9). Analytical approaches have given us some suggestions about the relationships between the strain and the temperature rise (Figure 10). The maximum temperature rises observed in this study were about 6 and 2℃, for the longitudinal compression and the lateral and partial compression tests, respectively.