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

This study investigated and clarified the relation between the piezoelectri c voltage and microscopic fracture of hinoki (Chamaecyparis obtusa Endl.), in particular the deformation of the cross-sectional wall of the tracheid i n linear-elastic regions under combined compression and vibration stresses. The piezoelectric voltage-deformation (P-D) curve consisted of a linear re gion starting from the origin followed by a convex curved region. The linea r region of the P-D curve was only about 60% of that of the load-displaceme nt (L-D) curve. By applying combined stresses to a specimen, the cross-sect ional walls of the tracheid were deformed mainly at the radial walls. When a tracheid was regarded approximately as a hexagonal prism, the elastic buc kling stress of the radial wall was estimated from scanning electron micros cope 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 the P-D curve. It is found that there are two consecutive regions before the proportional li mit of the P-D curve: One is the region up to the spot where the radial cel l 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 the P-D curve.