Static and dynamic stressing of elastic, plastic and viscous granules

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Almost perfectly elastic to viscoelasto-viscoplastic model granules will be experimentally tested (individually) by uniaxial static compression and normal dynamic low-velocity impact (free-fall) tests; the corresponding force-displacement-time and the impact-rebound events will be recorded respectively. From the compression tests, the force-displacement and the force-displacement rate behavior will be approximated using suitable contact models to arrive at the micro-mechanical properties such as micro-yield strength, stiffness, etc. Product failure by macro-breakage (resulting due to simultaneously acting normal and shear stresses) will be expressed in terms of breakage probability functions and moreover the mechanism in case of instantaneous and fatigue failure will be described. The influences of binder content and cyclic moisture loading-unloading on the micro-yield and macro-breakage probability will be studied. Furthermore, the influence of displacement-controlled loading velocity on the viscous micro-mechanical properties will be examined. From the recorded digital images during the events at impact and rebound, the impact and rebound velocities can be arrived at, from which the impact number i.e. the coefficient of restitution will be determined. The influence of layer thickness of moisture and powder layers at contact during impact will be investigated. We expect that by the completion of the first funding period (24 months), the above described multi-scale experimentation would successfully conclude, paving a well-defined path to the numerical simulations which will be performed during the second funding period (12 months). Three dimensional numerical simulations will be performed according to the discrete element method using the software PFC3D. The outcome of this project would provide an excellent improvement towards controlling and reducing undesired deformation and breakage of granules (particle collectives in the millimeter range composed of primary particles in the micrometer range), by defining specific energetic limits to optimize future industrial handling of granules and establish qualitative standards to granulate designer products for niche markets and high value process (agricultural, food and pharmaceutical) industries.