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Fracture Processes in Germanium

出版	Aeronautical Systems Division, Air Force Systems Command, 1963
URL	http://books.google.com.hk/books?id=IcWixrndHy0C&hl=&source=gbs_api

註釋The fracture strength, sigma sub F, of germanium at constant loading rate was determined over a temperature range from -196 to 500 C sigma sub F decreases slowly up to about 200 C, then increases to about 400 C, followed by subsequent decrease. Sigma sub F is found to be essentially independent of ambient for a wide variety of chemical species. These observations are analyzed in terms of fracture nucleation at a flaw near, but not exposed to, the surface, by a presently unknown kinetic process. The role of dislocations apparently is to inhibit fracture by relaxation of stress concentrations up to about 400 C, above which general plastic defor mation precedes fracture, suggesting the possibility of fracture nucleation by dislocation pileus. The applicability of this analysis to another brittle system, Al2O3, is considered in the light of its reported fracture, deformation, wear and friction characteristics. Striking similarities are found in the behavior of these two crystals, suggesting that the underlying mechanisms must have much in common. The effect of atmosphere on plastic deformation of both single crystal and polycrystalline Al203 was examined. Heat treatment in dry oxygen and nitrogen at temperatures between 1350 and 1580C for periods of up to 50 hours, produced no significant changes in creep behavior.