木材の圧電異方性(<小特集>木質材料小特集)

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The purpose of this paper is to investigate the piezoelectric anisotropy of wood. It had been considered that the cellulose micelle in wood are oriented in the same direction of fiber axis and consequently wood belongs to the symmetry class ∞2. And so d_<14> and d_<25> had been measured as the piezoelectric moduli of wood. However. we have found that there is a difference in the absolute value between d_<14> and d_<25> determined experimentally ; that is, ∣d_<14>∣>∣d_<25>∣. Therefore. it seems that wood belongs not to the symmetry class ∞2 but to the symmetry class 222. The piezoelectric tensor of the class 222 has three independent piezoelectric moduli d_<14>, d_<25> and d_<36>. In this study, we measured the piezoelectric moduli d_<14>, d_<25> and d_<36> as the symmetry class 222, and found that the modulus of d_<36> exists apparently in our measurement, although it is small compared with d_<14> and d_<25>. Thus, it is reasonable to consider d_<14>, d_<25> and d_<36> as the piezoelectric moduli for wood. The piezoelectric moduli along different directions were also measured by rotating measuring axes, and they were expressed by the components of d_<14>, d_<25> and d_<36>. The causes for the existence of d_<36> and the difference between d_<14> and d_<25> were also examined. The polarization associated with d_<36> is considered to arise from the polarization of ray structure, the components of d_<14> and d_<25>, and d_<36>^<cell> of cellulose crystallites. The difference between d_<14> and d_<25> agrees with that of the moduli of rigidity G_<LT> and G_<LR>, suggesting that the magnitude of piezoelectric polarization depends on that of shearing strain in cellulose crystallites. A correlation is found between the magnitudes of d_<36> and ∣d_<25>/d_<14>∣, and, therefore, the degree of anisotropy of wood can be characterized by either the ratio of ∣d_<25>/d_<14>∣ or the magnitude of d_<36> from the viewpoint of piezoelectricity in wood.
社団法人日本材料学会の論文
1973-10-15

木材の圧電異方性(<小特集>木質材料小特集)

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