木材の曲げ試験時のサーモグラフィ

Abstract

木材の変形や破壊に伴う発熱についての知見を得るために, ベイヒ (Chamaecyparis lowsoniana Parl.) の気乾材を用いて三点曲げならびに四点曲げを行ったときの試片側面の表面温度をサーモグラフィ装置で測定し, 試片の変形や破壊と温度上昇の関係について検討した。三点曲げでは, 荷重が比例限度を越えると試片の圧縮側の荷重点下で繊維方向の圧縮破壊に伴って温度が徐々に上昇し, 最大荷重に達するまでに平均で0. 6℃の温度上昇が見られ, 破壊時には引張側で温度が瞬間的に大きく上昇した。四点曲げでも同様の温度上昇が認められたが, 荷重点下以外の部分でも繊維方向の圧縮破壊に伴う温度上昇を示す試片もあった。また, 人為的な欠点として直径3または5mmの穴をあけた試片の三点曲げを試みたところ, 直径5mmの場合には試片の温度上昇に穴の影響が認められたが, 3mmでは穴をあけた効果はほとんど認められなかった。

To examine the thermal behavior of wood during static-bending test, the surface temperature of small airdried specimens of yellow cedar (Chamaecyparis lowsoniana Parl.) was measured during center loading and two-point loading tests by using a thermographic device. The center loaded specimens showed a temperature rise up to av. 0.6℃ immediately below the loading point after the load reached the proportional limit, and showed a sudden rise in temperature around the broken area in the tensile side (Figs. 4, 5 and 6). The temperature rise before the breakage resulted from the compression failure of specimens. The two-point loaded specimens showed a temperature rise in the same manner as the center loaded ones, and some specimens showed a temperature rise also at the center of two loading points (Figs. 7, 8 and 9). In the center loading test of specimens with holes of 3 or 5mm diameter (Fig. 1), it was found that the hole of 5mm diameter distinctly influenced the temperature rise of specimens, especially for the specimens drilled on the tensile side (Figs. 10 and 11).