EFFECTS OF VOLUME FRACTION OF BUNDLE-SHEA TH ON THE VIBRATIONAL PROPERTIES OF BAMBOO

This paper describes relationships between the vibrational properties and the volume fraction of bundle sheath (V-f) of bamboo. The cylinder wall of bamboo consists of a bundle sheath and a parenchyma. The shap e and distribution of bundle sheath change in the radial direction of the cylinder, so that the cylinder walls of mousouchiku (Phyllostachys pubescens Mazel) and madake (P. reticulata C. Koch) were divided into three layers and two layers in the radial direction, respectively. V- f increased from the inner layer toward the outer layer over a range o f 0.10-0.45. The density (rho), dynamic elastic modulus (E') and dynam ic loss modulus (E '') increased with an increase in V-f, whereas the loss tangent (tan delta) decreased. Very high linear relationships exi sted between V-f and these propertises. rho, E' and E '' for madake we re a little larger than those for mousouchiku, and tan ic for madake w as less than that for mousouchiku. The ratio of measured value to the one calculated from those of the above linear relationships ranged fro m 0.9 to 1.1. The structure of the cylinder wall in the longitudinal d irection was expressed simply by a parallel model which consisted of a bundle sheath and a parenchyma. rho and the vibrational properties of each tissue were calculated from mixture rules based on this model an d those above linear relationships, with the results that rho and the vibrational properties were very different between bundle sheath and p arenchyma. rho and E '' for bundle sheath were about four times those of parenchyma, E' was 40-80 times, and the specific dynamic modulus (E '/rho) was 10-20 times as much. On the other hand, the specific loss m odulus (E ''/rho) for parenchyma was almost equal to that of bundle sh eath, and tan delta for parenchyma was 10-20 times as much as that of bundle sheath. From the above results, it was concluded that the vibra tional properties in the longitudinal direction of bamboo were much de pendent on V-f, and the bundle sheath showed elastic behavior, while t he parenchyma had more viscose behavior.