Powdered polystyrene was compacted into specimens having various void fractions. The dynamic mechanical properties of these specimens were measured by the vibratory test method. The mechanical loss factor Q-1 of the compaction-molded specimen was found to increase with increasing void fraction and with increasing strain amplitude of vibration at various temperatures below the glass transition temperature of polystyrene. The dynamic modulus σ0/ε0, which was defined as a ratio of a stress amplitude σ0 to a strain amplitude ε0, varied quite little with increasing strain amplitude and decreased with increasing void fraction. The Q-1 value decreased by sintering of interparticle contact points. Therefore, it was considered that the energy dissipation mechanism was attributed to the friction at a part having weak cohesive force in contact surfaces between adjacent particles. This was also supported by the fact that the Q-1 value increased with decreasing tensile strength which implied decreasing interparticle cohesive force.
