Effect of temperature and deformation rate on fracture strength of sintered uranium dioxide.

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The fracture strength of two kinds of UO2 specimens possessing pores of different maximum sizes (60 and 140 μm) was measured in the range of room temperature 1, 300°C by means of diametral compression testing. The fracture strength thus obtained proved to be smaller than any of the values reported by previous authors who mainly used bending tests. Finite element analysis showed that the method used in the present study should logically yield results close to the true tensile fracture strength. The des-crepancies noted with the results reported from the other studies were attributable to the differences in the methods used for the measurements. The fracture strength was found to remain almost constant in the relatively low temperature region (R.T.800°C) beyond which the value increased with temperature (intermediate temperature region of 1, 0001, 300°C). Electron-microscopic observations of the fractured surface indicated that the brittle-to-ductile transition temperature (Tc) was situated between 800 and 1, 000°C when the strain was applied slowly. Raising the strain rate proved to affect both fracture strength and Tc. These dependences of tem-perature and strain rate on the fracture strength are explained from the relation between dislocation velocity and deformation rate. Griffith's theory is cited to describe the rela-tion between the largest pore size and fracture strength.
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