DEM study on the force chain evolution of biaxial compression of pebble bed

Abstract

Li4SiO4 and Li2TiO3 are granular materials in the pebble bed of fusion reactors, and their physical parameters and mechanical properties directly affect the working status and structural design of the pebble bed. The force chain can be employed to intuitively describe the mechanical properties of the pebble bed in the particle aggregate. Based on the discrete element method, we conducted a numerical study on the evolution characteristics of the force chain of Li4SiO4 and Li2TiO3 pebble beds under biaxial compression and explored the friction coefficient and pebble bed effect of the aspect ratio on the force chain distribution. The results revealed that as the particle friction coefficient increased, the force chain tended to be isotropically distributed, indicating that the friction mechanism was more conducive to a uniform distribution of the force chain. During compression, the average coordination number of the pebble bed increased with the friction coefficient. The Li2TiO3 particles had larger gravity than the Li4SiO4 pebble bed therefore, the Li2TiO3 pebble bed accounted for more force chains in the vertical direction. When the aspect ratio of the pebble bed was less than 0.5 or greater than 2.5, the distribution of force chains exhibited strong anisotropy. Conversely, when the pebble bed aspect ratio ranged between 0.5 and 2.5, the distribution of force chains tended towards an isotropic trend. Moreover, the number of force chains in each direction varied with changes in the aspect ratio of the pebble bed, characterized by a high concentration at the edges and a lower concentration in the middle. The results can provide an in-depth understanding of the force chain distribution and evolution characteristics in the pebble bed and provide a theoretical basis for designing and analyzing tritium breeding pebble beds.