Dissipation of vibration energy using viscoelastic granular materials

This work addresses the way in which a viscoelastic granular medium dissipates
vibration energy over broad ranges of frequency, amplitude and direction of
excitation.
The viscoelastic properties (modulus and loss factor) of polymer particles are
obtained experimentally both by deriving the master curve of the material and by
measuring the stiffness of these spherical particles at different frequencies using a
test rig designed for this purpose. Three dimensional Discrete Element Method
(DEM) is used to develop a numerical model of the granular medium and is
validated by comparison with experimental results. Despite the simplifications the
model was found to be in good agreement with experiments under vertical and
horizontal vibrations with different numbers of particles over a range of frequencies
and amplitudes of excitation.
The study is extended to investigate different phases that occur under vibrations of
granular materials. The low amplitude vibrations when the particles are permanently
in contact without rolling on each other is called solid phase. In this phase, most
energy is dissipated internally in the material. A theoretical/numerical approach is
considered for this phase and it is validated by experiment. At higher amplitude
vibrations when the particles start to move and roll on each other (the convection
phase) there is a trade-off between energy dissipation by friction and
viscous/viscoelastic effects. Energy dissipation is relatively insensitive to the
damping of individual particles. At extremely high amplitude vibrations particles
spend more time out of contact with each other (the particles are separated from each
other – gas region). It can be seen the particles with lower damping reach the gas
region earlier because they are less sticky and more collisions can happen so
although the damping for each individual particle it less, the total damping increases.
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The effect of parameters of particles on energy dissipation is also studied using
sensitivity analysis. The benefit of doing this is to better understand how each
parameter influences the total system damping.