STRENGTH AND FRACTURE OF STOICHIOMETRIC POLYCRYSTALLINE UO2

The strength of stoiehiometric polycrystalline UO2 has been determined from 20 to 1500 °C for material of two grain sizes. It is found that the fine grained (~ 8 μm) material is always stronger than the larger grained (~ 25 μm) material. A ductile-brittle transition is observed in both materials at ~ 1200 °C. Below the transition temperature, two modes of fracture are observed. At low temperatures, the fracture stress increases with increase in temperature; fracture occurs by the extension of the large pores which remain after cold pressing and sintering. At intermediate temperatures the strength decreases with increase in temperature; fracture is initiated by plastic flow and occurs at the macroscopic yield stress. © 1969.