Research Projects

Cohesion between particles in a granular ensemble is fairly common especially in stored powders, food grains, and naturally occurring geomaterials. This presence of cohesion arrests the relative movement of particles and dramatically changes the ensemble mechanical response. A fundamental understanding of the physics and mechanics of force propagation in granular materials has impacted the engineering of these systems dramatically. Similarly the mechanisms of force propagation in cohesive granular system will have an impact on sectors including 3D printing, infrastructure, food storage and pharmaceutical processing. The research envisioned in this proposal would parse the fundamental physics and mechanics of force transfer in cohesive granular materials. The experiments will require high energy x rays for imaging of these model cohesive granular systems and hence the experiments will be performed in a synchrotron. Two model granular materials – single crystal quartz and single crystal sapphires will be used in these experiments. Cohesive binders of different strengths and amounts will be used for these experiments. The synchrotron facilities available in Raja Ramanna Center for Advanced Technologies (RRCAT)- Indore and Cornell High Energy Synchrotron Source (CHESS)- Cornell, will be used for these experiments. X ray diffraction measurements will be made along with X ray computed tomography using the synchrotron source. Interrupted compression tests and confined compression tests will be carried out in this research programme. The fabric and structure generated in these granular ensembles will be studied through the X ray CT measurements. Features such as localization, bifurcation and shear banding will be investigated. By calculating the strains from the XRD measurements it is possible to determine inter-particle forces in these realistic granular materials. This imaging will be followed by extensive image analysis and visualization. This research will build on similar experiments that have been recently carried out on frictional granular materials to understand force propagation. An improved formulation for force interference in the presence of cohesion between particles will be brought to the fore. The force propagation mechanism as a function of the cohesive binder content will be understood, impacting the understanding of a range of materials including dense suspensions, concrete, soft rock etc. These results will provide the experimental underpinning necessary for developing a constitutive model for cohesive granular systems at multiple length scales.