Strength of porous oxide microspheres: The role of internal porosity and defects

Abstract

Ceramic oxide green pellets for nuclear fuel or targets are manufactured by powder processes producing detrimental fines. Porous brittle microspheres offer an interesting alternative, providing that their fracture behavior is well controlled during pressing. Here we investigate, using experimental characterization and numerical simulations, the effect of porosity and internal defects on the strength of porous microspheres. We show that although the residual porosity is the main parameter affecting their strength, the shape and location of defects also play a role. Real defects characterized by X-ray tomography are reproduced with discrete element simulations, providing new insights on their fracture behavior. We also investigate the departure from monosized microspheres by simulating the fracture behavior of two microspheres of different sizes, and show that it is the minimum radius that allows for a consistent strength normalization. This study offers a method for anticipating agglomerate strength that can be generalized for any ceramic systems.