Abstract
Small-scale mechanical testing has been used to isolate the properties of individual grain boundaries and regions of the lattice in undoped UO2 polycrystals. Notched microcantilever specimens were prepared by focused ion beam milling and tested in bending. Fracture toughness values were calculated from finite element analysis of the sample geometry at fracture load using the J-integral method. Lattice and grain boundary fracture toughness values of 1.17 ± 0.16 MPa m1/2 and 1.08 ± 0.08 MPa m1/2, respectively, were obtained. The similarity between the lattice and grain boundary fracture toughness values is consistent with the preference for transgranular room-temperature fracture in UO2. The grain boundary and lattice fracture toughness values also agree well with the toughness of dense polycrystals, which suggests that microstructural-scale toughening mechanisms are limited in such samples.
