Piezoelectric behavior of wood under combined compression and vibration stresses II: Effect of the deformation of cross-sectional wall of tracheids on changes in piezoelectric voltage in linear-elastic region

This study investigated and clarified the relation between the piezoelectric voltage and microscopic fracture of hinoki (Chamaecyparis obtura Endl.), in particular the deformation of the cross-sectional wall of the tracheid in linear-elastic regions under combined compression and vibration stresses. The piezoelectric voltage-deformation (P-D) curve consisted of a linear region starting from the origin followed by a convex curved region. The linear region of theP-D curve was only about 60% of that of the load-displacement (L-D) curve. By applying combined stresses to a specimen, the cross-sectional walls of the tracheid were deformed mainly at the radial walls. When a tracheid was regarded approximately as a hexagonal prism, the elastic buckling stress of the radial wall was estimated from scanning electron microscope images and our method based on a modification of the Gibson and Ashby method. As a result, it was estimated that the elastic buckling stress was only about 80% of the stress at the proportional limit of theP-D curve. It is found that there are two consecutive regions before the proportional limit of theP-D curve: One is the region up to the spot where the radial cell wall generates the elastic buckling, and the other is the region starting from the end of the aforementioned region up to the proportional limit of theP-D curve.Part of this paper was presented at the 47th annual meeting of the Japan Wood Research Society, Kochi, April 3–5, 1997