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This paper presents the results of Discrete Element Modelling (DEM) which quantitively examine the effect of coal fouling on the deformation and degradation of ballast upon cyclic loading. The degradation model described herein considers the Weibull distribution effects in tandem with a granular medium hardening law that incorporates the maximum contact criterion to capture surface abrasion and corner breakage of angular ballast. The DEM model had been calibrated initially with laboratory data obtained from large-scale direct shear testing. Subsequently, a series of cubical shear test simulati...

The mechanical behaviour and stability of coal mining engineering underground is significantly affected by ground water. In this study, nuclear magnetic resonance imaging (NMRI) technique was employed to determine the water distribution characteristics in coal specimens during saturation process, based on which the functional rule for water distribution was proposed. Then, using discrete element method (DEM), an innovative numerical modelling method was developed to simulate water-weakening effect on coal behaviour considering moisture content and water distribution. Three water distribution n...

This paper presents a study of the mechanical behaviour of ballast contaminated by different fouling agents such as coal and subgrade clay. Large-scale direct shear tests were carried out to examine the strength and deformation properties for coal-fouled and clay-fouled ballast. The experimental results show that fouled ballast (both clay and coal) exhibits a lower peak shear strength and decreased dilation during shearing. The clay-fouled ballast shows higher shear strength and smaller dilation compared to coal-fouled ballast. The relationship between shear stress and dilatancy of ballast und...

 E-Mail IMAGE: Pebble-bed reactors use passive natural circulation to cool down, making it theoretically impossible for a core meltdown to occur. view more  Credit: Dr. Jean Ragusa and Dr. Mauricio Eduardo Tano Retamales/Texas A&M University Engineering When one of the largest modern earthquakes struck Japan on March 11, 2011, the nuclear reactors at Fukushima-Daiichi automatically shut down, as designed. The emergency systems, which would have helped maintain the necessary cooling of the core, were destroyed by the subsequent tsunami. Because the reactor could no longer cool itself...

Abstract This paper introduces a three-dimensional (3D) simulation to model the elasto-plastic deformation of ductile materials by discrete element method (DEM) using cohesive plastic beam approach. The Euler–Bernoulli beam theory is applied to calculate force and torque reactions of the cohesive beam bond that can account for plastic strain. In order to simulate the elasto-plastic behavior of materials, a coupled model of plasticity and damage is proposed for the cohesive beam bond. The von Mises yield criterion, a modified perfectly plastic law and an exponential damage law are implemente...