Acoustic evaluation of the impact of moist spherical granules and glass beads

• The coefficient of restitution decreases with increasing moisture content.
• The coefficient of restitution decreases with increasing surface roughness.
• The coefficient of restitution is a parameter with an individual distribution.
• The coefficient of restitution depends on the inelasticity parameter.

The impact behavior of spherical dominant elastic-plastic γ-Al2O3 granules, elastic-plastic zeolite 4A granules and elastic glass beads has been investigated using free fall tests. The elastic sonic waves generated at impact within the plate have been recorded by an acoustic sensor and have been used to determine the normal coefficient of restitution (CoR).Moreover, the influences of impact velocity, moisture content, surface roughness of the plate and the ratio of particle diameter to plate thickness have been investigated. Due to various influences, the impact behavior of the granules is characterized as to be in the elastic-plastic range. However, the materials exhibit almost constant values of the CoR within the investigated range of impact velocities. Furthermore, with increasing moisture content and surface roughness, the coefficient of restitution slightly decreases. The influence of elastic waves has been evaluated with the model of Zener.

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