A continuum mechanics approach is used by engineering practices to characterize the powder flow properties and to design equipment for the handling and storage of granular materials. However, many studies have highlighted the relevant role of the type and magnitude of the interactions acting between particles on the powder flowability. Therefore, the correlation of a particle-particle approach and a continuum approach may be beneficial to describe the multiscale nature of the mechanical properties of bulk solids for scientific and engineering applications. In this work, the effect of the elastic and plastic behaviour at the contact surface of the particles on the flow behaviour was analysed starting from the powder flow properties measured by a standardized technique. At this purpose, a relationship between interparticle forces and bulk solid tensile strength was derived according to the microscale approaches of Rumpf (1970) and Molerus (1975). The flow properties of Fluid Cracking Catalyst (FCC) samples, corundum and glass bead powders, which were all characterised with a modified Schulze ring shear cell capable of operating at temperatures up to 500°C, were studied. The testing powder conditions were selected so that the van der Waals forces were the most significant particle-particle interactions. The value the mean curvature radius at the contact points which better estimates the measured data was assumed as proper value, according to the SEM images of the material samples. A sensitivity analysis on the main parameters of the model equations, as the porosity of the assembly and the strength of the particle material, was performed for the two cases in which either elastic or plastic deformation of the contact points were assumed. This analysis indicated that the assumption of plastic deformation at contact surfaces, coupled with the decrease in porosity, justified the increase in the tensile strength with the consolidation stress and better describe the flow behaviour of powders. Furthermore, the effect of temperature on the measured flow behaviour was explained with the change in the strength of the material when plastic deformation occurs at the contact points.

The Effect of the Elastic and Plastic Behaviour at the Particle Contact Points on the Flow Properties of Powders

TOMASETTA, IGINO;BARLETTA, Diego;POLETTO, Massimo
2013

Abstract

A continuum mechanics approach is used by engineering practices to characterize the powder flow properties and to design equipment for the handling and storage of granular materials. However, many studies have highlighted the relevant role of the type and magnitude of the interactions acting between particles on the powder flowability. Therefore, the correlation of a particle-particle approach and a continuum approach may be beneficial to describe the multiscale nature of the mechanical properties of bulk solids for scientific and engineering applications. In this work, the effect of the elastic and plastic behaviour at the contact surface of the particles on the flow behaviour was analysed starting from the powder flow properties measured by a standardized technique. At this purpose, a relationship between interparticle forces and bulk solid tensile strength was derived according to the microscale approaches of Rumpf (1970) and Molerus (1975). The flow properties of Fluid Cracking Catalyst (FCC) samples, corundum and glass bead powders, which were all characterised with a modified Schulze ring shear cell capable of operating at temperatures up to 500°C, were studied. The testing powder conditions were selected so that the van der Waals forces were the most significant particle-particle interactions. The value the mean curvature radius at the contact points which better estimates the measured data was assumed as proper value, according to the SEM images of the material samples. A sensitivity analysis on the main parameters of the model equations, as the porosity of the assembly and the strength of the particle material, was performed for the two cases in which either elastic or plastic deformation of the contact points were assumed. This analysis indicated that the assumption of plastic deformation at contact surfaces, coupled with the decrease in porosity, justified the increase in the tensile strength with the consolidation stress and better describe the flow behaviour of powders. Furthermore, the effect of temperature on the measured flow behaviour was explained with the change in the strength of the material when plastic deformation occurs at the contact points.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11386/4130058
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