Computational study of the elastic modulus of single size pebble beds for fusion applications

Abstract

In this paper, the discrete element method (DEM) was used to report the mechanical behaviors and elastic moduli of single size pebble beds. The effect of cyclic pressure p and the subtle difference in particle sizes within the granular system were considered. In this study, we re-confirmed the nonlinear elastic stress-strain relation, the much lower elastic moduli of a granular system than that of solid materials and the faster growth of moduli than the p1/3 law predicted by the effective medium theory (EMT). We also observed that cyclic pressure (mechanical excitation) would stiffen the granular system, but this effect will become smaller as the cycle number increases. This indicates that the stability of system will become stronger under this effect. Besides, the subtle difference in grain sizes was observed to soften the system although it caused a little higher packing density. Furthermore, although the effective moduli of different granular materials Es are diverse, they were found to nearly collapse to the same distribution when both Es and p are non-dimensionalized by particle moduli Ep. This can actually also be derived from the EMT theory.