Nihon Kikai Gakkai ronbunshu (Jul 2024)
Damping properties and optical observation of particles behavior in particle dampers with particle diameters of sub-mm or less (The case of gravity direction vibration)
Abstract
Particle dampers (PD) can be embedded in structures fabricated via selective laser melting (SLM) because the raw powder (particle diameter : several tens of micrometers) remains in closed spaces during SLM. However, most PD studies have focused on coarse particle sizes larger than 1 mm and low frequencies below 100 Hz; there is insufficient evaluation of PD attenuation characteristics and particle behavior for particle sizes from tens of micrometers to sub-millimeters and in the 100 to 1000 Hz band. In this study, the equivalent viscous damping coefficients of spherical zirconia balls with nominal sizes of 0.05, 0.10, 0.20, and 0.40 mm are measured under different vibration accelerations (from 9 to 148 m/s2(rms)) and frequencies (from 100 to 800 Hz) to experimentally investigate the effect of fine particle diameters on the damping properties. It is deduced that in the frequency range above 200 Hz, the equivalent viscous damping coefficients of the coarse particle diameter are greater than those of fine particles at accelerations below the range of 15.7–22.4 m/s2(rms). In contrast, the equivalent viscous damping coefficients of the fine particles are greater than those of the coarse particles at accelerations above the 15.7–22.4 m/s2(rms) range. In addition, to determine the reason for these tendencies, the behavior of particles with a nominal size of 0.05 mm, which is close to the raw powder, is observed through a window using a high-speed microscope camera. The results reveal that in the low acceleration range, the inertial force does not overcome the static friction force owing to poor flowability caused by adhesion force, and the particles are always stationary with respect to the sealed container.
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