DAMPING PROPERTIES OF WOOD/POLYMER COMPOSITES .3. INFLUENCE OF GEOMETRY ON FLEXURAL VIBRATION OF LAMINATES

The damping of wood/polymer composite depends on dynamic mechanical properties of the polymer layer as well as on the structural geometry. The dynamic tensile properties of ethylene vinyl acetate copolymer (EVA)/Terpene Phenol resin (TP) blends were measured. It was observed that the peaks of E'' and tan delta shifted toward higher temperatures and the width of the glass transition region was broadened as the amount of TP incresed. The damping factor (tan delta(c)) and the dynamic bending modulus (E(c)*) of wood/EVA-TP laminates was measured over the frequency range 3.5 to 110 Hz and the approximate temperature range -100 to 150 degrees C using a Rheovibron instrument in a bending mode. The master curve of the composite damping factor (tan delta(c)) was determinded by means of the time (frequency)-temperature superposition principle. Damping of a sandwich structure correlated with the loss factor (tan delta), and that of a coated structure correlated with the loss modulus (E'') of polymer layer. In case of a three-layer sandwich structure, a symmetric configuration was found to be more effective in damping than were unsymmetric ones of the same overall thickness but the latter was stiffer. Although the total thicknesses of the wood and polymer layer was the same, the damping could be increased still further by malting a multiple-layer sandwich structure. The peak of damping shifted toward the lower temperature side, which was also the larger modulus side of the polymer layer as the modulus of the substrates became greater. This result suggests that the damping of composites depends on the stiffnesses of substrates as well.