Cyclic loading tests on ceramic breeder pebble bed by discrete element modeling

Complex mechanics and packing instability can be induced by loading operation on ceramic breeder pebble bed for its discrete nature. A numerical approach using discrete element method (DEM) is applied to study the mechanical performance of the ceramic breeder pebble bed under quasi-static and cyclic loads. A preloaded specimen can be made with servo-control mechanism, the quasi-static and dynamic stress-strain performances are studied during the tests. It is found that the normalized normal contact forces under quasi-static loads have the similar distributions, and increase with increasing loads. Furthermore, the relatively low volumetric strain can be absorbed by pebble bed after several loading and unloading cycles, but the peak normal contact force can be extremely high during the first cycle. Cyclic loading with target pressure is recommended for densely packing, irreversible volume reduction gradually increase with cycles, and the normal contact forces decrease with cycles.