Research Projects

Granular material is a special class of complex systems composed of many interacting constituents behaving collectively. On top of the inherent complex behaviour of granular material, the response of granular media under high speed impact is notoriously difficult to model analytically since the impact process never reaches a steady state. The existing constitutive laws for the granular materials are applicable for steady fully developed flow conditions whereas the granular impact process leads to unsteady and complex flow. Due to this complexity, the mathematical modelling of the impact process is still limited to the phenomenological modelling such as describing the macroscopic drag force as a function of the depth and velocity of the intruder heuristically. The grain scale picture of such heuristic model is lacking in the literature. In a recent investigation by the present author, it is shown that the conventional drag force models fail to capture the dynamics in the high speed limit, and the drag force cannot be written as a combination of depth-independent inertial drag and depth-dependent static pressure as commonly employed in the literature. The apparent contradiction between the phenomenological drag models and the simulation observation calls for a detailed investigation of the impact dynamics in the high speed regime. Moreover, the mechanism of energy dissipation under high speed impact is largely unexplored. The energy transfer and dissipation can happen via energy transport through phonons, continuous transitions between different metastable states and anharmonic dissipation. A fundamental question that needs to be addressed is how the initial high impact energy gets distributed amongst different dynamic modes of collective grain motions and eventually dissipated. A very recent study suggests a universal scaling for the peak forces in the early stages of impact as a function of impact velocity, which appears to be largely unaffected by spatial dimensions and numerous other system parameters. Contradictory to this observation,the present author convincingly showed that this scaling is not universal and can change with the spatial dimension. This intriguing observation prompts the need for a deeper investigation into the nature of initial forces during impacts in granular media. The proposed work will employ large scale simulations to erect a microscopic picture of the highly dynamic impact phenomenon and accordingly build a theoretical framework to explain the drag force on the intruder in the high speed limit. We also aim to understand the origin of the maximum on the intruder force response very early in the impact process and its scaling with the relevant system parameters. The proposed study will also undertake extensive numerical simulations complemented by theory to unravel the dissipation mechanism in such amorphous materials and consequently set the right conditions for it to be used as a protective barrier against projectile impact. The findings from the proposed research will be of immense interest in the space industries, ballistics and any other process involving high speed impact. The results of this study will help us understand how the impact energy gets dissipated in an amorphous media, leading to the efficient formulation of cost-effective materials that can absorb and dissipate the high impact energy very fast.