arXiv subjects

Guo-Jie J. Gao

Publications and source records attributed to Guo-Jie J. Gao.

4 recordsLinked to original sources

arXiv2018

Understanding the Local Flow Rate Peak of a Hopper Discharging Discs through an Obstacle Using a Tetris-like Model

Placing a round obstacle above the orifice of a flat hopper discharging uniform frictional discs has been experimentally and numerically shown in the literature to create a local peak in the gravity-driven hopper flow rate. Using frictionless molecular dynamics (MD) simulations, we show that the local peak is unrelated to the interparticle friction, the particle dispersity, and the obstacle geometry. We then construct a probabilistic Tetris-like model, where particles update their positions according to prescribed rules rather than in response to forces, and show that Newtonian dynamics are also not responsible for the local peak. Finally, we propose that the local peak is caused by an interplay between the flow rate around the obstacle, greater than the maximum when the hopper contains no obstacle, and a slow response time, allowing the overflowing particles to converge well upon reaching the hopper orifice.

cond-mat.soft↗

arXiv2018

Studying the Kinetics of a Self-propelled Cruiser in 2D Granular Media under Gravity

We propose a cruiser able to move in a granular medium made of nearly 50-50 bidisperse dissipative particles under gravity. The cruiser has a circular shape with a square indentation on its edge. By shifting and then ejecting granular particles entering its indent-region facing a given direction, the cruiser gains thrust to push itself forward in the same direction, which can be either perpendicular or parallel to gravity. Using molecular dynamics (MD) simulations, we identify three universal phases during one particle-ejection process: 1) acceleration by the ejection thrust, 2) deceleration by the compressed particles ahead and 3) relaxation with the decompressed particles. We also confirm that the cruising capability improves with increasing the particle-ejection strength and with decreasing the interference from gravity.

cond-mat.soft↗

arXiv2018

Incorporating a soft ordered phase into an amorphous configuration enhances its uniform plastic deformation under shear

Amorphous materials of homogeneous structures usually suffer from nonuniform deformation under shear, which can develop into shear localization and eventually destructive shear band. One approach to tackle this issue is to introduce an inhomogeneous structure containing more than one phase, which can reduce the local nonuniform shear deformation and hinder its percolation throughout the system. Using thermostated molecular dynamics (MD) simulations, we compare the deformation behavior between a homogeneous amorphous mixture of bidisperse disc particles, interacting via an n-6 Lennard-Jones potential of tunable softness, with an inhomogeneous one containing an evenly-distributed ordered phase. We change the population ratio of large to small particles to create a homogeneous or an inhomogeneous mixture, where the softness of a chosen phase can be manually adjusted by specifying n of the interparticle potential. Results of applying extensive quasistatic shear on the prepared mixtures reveal that the inhomogeneous amorphous mixture containing a soft ordered phase overall deforms more uniformly than the homogeneous one, which indicates that both the structure inhomogeneity and the inter-phase softness variance play important roles in enhancing the uniformity of the plastic deformation under shear.

cond-mat.mtrl-sci↗

arXiv2013

Studying the elastic properties of nanocrystalline copper using a model of randomly packed uniform grains

We develop a new Voronoi protocol, which is a space tessellation method, to generate fully dense (containing no voids) nanocrystalline models of copper (Cu) with precise grain size control; we also perform uniaxial tensile tests using molecular dynamical (MD) simulations to measure the elastic moduli of the grain boundary and the grain interior components at 300 K. We find that the grain boundary deforms more locally compared with the grain core region under thermal vibrations and is elastically less stiff than the core component at finite temperature. The elastic modulus of the grain boundary is lower than 30% of that of the grain interior. Our results will aid in the development of more accurate continuum models of nanocrystalline metals.

cond-mat.mtrl-sci↗