Keywords: photonic stress analysis, granular materials, shear stress, contact mechanics, inter-particle interaction.

Several industries process a high proportion of their products in granular form for example, geotechnical, nuclear, pharmaceutical, food, mining and mineral processing industries. For safe handling and efficient processing of granular materials, a clear understanding on the internal behaviour of particulates as a result of the interactions between the constituent particles under mechanical loading is required [1,2,3]. Previous studies on the size effects of particles in sheared granular media show that [1], when the size ratio of an inclusion (large particle), i.e. ratio between diameter of the inclusion in relation to the average diameter of surrounding particles in contact with it, exceeds about 5, the state of average stress in the big particles is dominantly hydrostatic (fluid-like). On the other hand, if the size ratio of an inclusion inside sheared granular media is less than 5 (small particle), the average state of stress of the inclusion is predominantly deviatoric in nature [1]. However, in deriving such conclusions, the effects of wall positions on the nature of stress experienced by particles inside particulate packing are not accounted for.

Based on photonic stress analysis, experimental studies have been performed here to 'sense' the nature of stress distribution of particulate inclusions inside granular compacts. The study shows that, depending on whether particles are within or outside the wall influence zone, their mechanical behaviour changes. The distribution of maximum shear stress 'within' large particles is of a non-homogeneous nature, especially under high load levels and when present inside the wall influence zones - an environment that is more conducive to their breakage [1]. When they reside outside the wall influence zone, which is beyond about three times of their size from wall boundaries, they exhibit the fluid-like, dominantly hydrostatic stress state. Otherwise, they experience strongly anisotropic maximum shear stress which favours their breakage [1]. Though further studies are required, the current research is a step towards providing an elucidation of the mechanical response of particulate materials with respect to process loading conditions.

1

S.J. Antony, "Link between single-particle properties and macroscopic properties in particulate assemblies: role of structures within structures", Philosophical Transactions of the Royal Society of London, Series: A, 365, 2879-2891, 2007. doi:10.1098/rsta.2007.0004

2

S.J. Antony, N.P. Kruyt, "Role of interparticle friction and particle-scale elasticity on shear strength mechanism in three dimensional granular media", Physical Review E, 79, 031308, 2009. doi:10.1103/PhysRevE.79.031308

3

S.J. Antony, N.P. Kruyt, "Force, relative displacement and work networks in granular media subjected to quasi-static deformation", Physical Review E, 75, 051308, 2007. doi:10.1103/PhysRevE.75.051308

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