Fracture characteristics of ThO/sub 2/ ceramics at elevated temperatures
The fracture characteristics of hot-pressed ceramic specimens of unirradiated ThO/sub 2/, and ThO/sub 2/ + 1/8% CaO, have been determined at room temperature and at elevated temperatures up to 1200/sup 0/C. The experimental program included the measurement of fracture strength, fracture toughness, and fracture surface energy of specimens with different surface preparations, and the utilizating of a prestressing procedure, involving preloading at 1200/sup 0/C, followed by slow-cooling to room temperature. Fractographic examination was used in the evaluation of the effects of temperature and microstructure. In the brittle (low temperature) range the fracture strength is independent of temperature, and characteriscally depends on the microstructure and existing flaws of the specimens. In the semi-brittle range the fracture strength was observed to decrease as temperature increases. Dislocation pile-up, grain boundary sliding, microcrack formation and crack link-up mechanisms were used to explain the decrease of fracture strength with temperature. On testing specimens containing flaws produced with Knoop indentations, it was noted that the transition temperature of the brittle and semi-brittle ranges was increased by increasing the crack size. Knoop indentation cracks were investigated using fractographic and dye penetrant methods. The fracture stength at room temperature of specimens with Knoop indentations could be increased significantly by first prestressing them by loading in bending at 1200/sup 0/C, followed by slow-cooling and load-testing. Transgranular type fracture appears dominant in large-grained structures at low temperatures, while intergranular-type fracture seems dominant in small-grained structures at high temperature.
- Research Organization:
- California Univ., Los Angeles (USA)
- OSTI ID:
- 5341467
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
Similar Records
Effect of precrack ``halos`` on fracture toughness determined by the surface crack in flexure method
Fracture from controlled surface flaws
Related Subjects
CERAMICS
FRACTURE PROPERTIES
THORIUM OXIDES
BRITTLENESS
CRACK PROPAGATION
MICROSTRUCTURE
STRESSES
TEMPERATURE EFFECTS
TESTING
VERY HIGH TEMPERATURE
ACTINIDE COMPOUNDS
CHALCOGENIDES
CRYSTAL STRUCTURE
MECHANICAL PROPERTIES
OXIDES
OXYGEN COMPOUNDS
THORIUM COMPOUNDS
360203* - Ceramics
Cermets
& Refractories- Mechanical Properties