Micromechanical analysis of inclusions in particulate media using digital photo stress analysis tomography

Abstract

Abstract. An experimental study aimed at sensing the stress distribution characteristics of inclusions inside particulate assemblies subjected to axial compaction is presented. The particulate assemblies are made of powders and grains, in which photoelastic inclusions are embedded along the central axis of the assemblies at different elevations. Digital photo stress analysis tomography is used to obtain the contours of maximum shear-stress distribution and the direction of major principal stress within the inclusions under the external loading. Using this, an analysis is performed for understanding the implications of using Hertz theory based on discrete element modeling for simulating stresses in relatively big inclusions surrounded by particulates. In the case of the inclusions surrounded by the grains, the location at which the peak value in maximum shear stresses occurs within the inclusions deviates from that of Hertzian analysis. This effect is dominant in the case of inclusions residing close to the loading surface. Unlike granular materials, shear-stress distribution characteristics of inclusions in powder surroundings tend to display continuum-like behavior under external compression and points to the need for a deeper understanding of the effects of the surrounding materials in particulate beds with inclusions.

Interplay between the inclusions of different sizes and their proximity to the wall boundaries on the nature of their stress distribution within the inclusions inside particulate packing

“…Detailed explanations on the working principles of photo stress analysis methodology for granular assemblies can be found elsewhere [24,25], however briefly stated here. Basically, birefringent particles optically respond to stress when viewed under a circular polariscope setup [9,24,25]. Depending on the level of the induced stress, they display contours of fringes of different orders depending on the retardation of light passing through the fast and slow optical axes at the point of interest.…”

“…It is widely recognised that the force-transmission inside granular assemblies occurs via inter-particle contacts in a non-homogeneous manner through a chain-like networks of contacts, often referred to as force chains [2][3][4][5]. Such observations have been made from photo elastic studies of birefringent grains [6][7][8][9], computer simulations using discrete element method (DEM) [10] and combined FEM-DEM [11]. For the granular materials, photo elastic studies were mostly reported for the two dimensional conditions whereas the DEM simulations accounted for both the two dimensional and three dimensional conditions [4,[10][11][12][13].…”

“…In DEM, average stress calculations are based on interparticle contact forces and, variations of stresses within particles, are not rigorously accounted for the stress calculations [10]. In the present work, we use PSAT methodology [8,9] to obtain insights on the interplay between the size effects of the inclusions and their proximity to wall boundaries, with an emphasis on the nature of stress distribution experienced by them inside granular assemblies subjected to axial compression.…”

“…In these studies, a known size of two dimensional inclusions (circular disk) was surrounded by three dimensional grains in such a way that the thickness of the inclusion and the grains were the same (quasi-3D experiments). Studies were performed using a number of positions for a single-size inclusion from the wall boundaries [8], or different sizes of inclusion positioned far away from walls [9] to sense the shear stress distribution experienced by the inclusion inside the granular assemblies under mechanical loading. They help to advance understandings on the stress distribution characteristics within single-particle scale.…”

Micromechanical Analysis of Compaction and Drilling of Granular Media- A Review

“…Micromechanical analysis of compaction and particulate/granular materials has been of significance to academics and industrial communities, from beach sandcastles to chemical, pharmaceutical, food, mechanical, civil, mining and petroleum engineering as well as underground reservoir industry, and materials processing sectors [2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Granular media are thermal, quite normal after all, usually with different particle-scale properties and inter-particle interactions, which are responsible for their complex behaviors at the low gravitational environment and macroscopic scale and difficult to assess experimentally [6,11,12,[16][17][18][19][20][21][22]. Several researchers have proposed calibration procedures relating the micro parameters to macro properties of the granular material [23][24][25].…”