Processing of Ceramics--Surface Finishing Studies.
Final technical rept. 22 Jan 69-21 Mar 70,
STANFORD RESEARCH INST MENLO PARK CA
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An expanded ring test has been used for a comparison of tensile strength between alumina specimens having as-fired surfaces and specimens diamond ground to final dimensions. The irregular geometry of the as-fired specimens prevented quantitative comparisons however, the as-fired specimens exhibited a lower average tensile strength than the diamond ground specimens. An apparatus has been built to permit the use of the expanded ring test under vacuum. The tensile strength of the ground specimens has been determined at two different stress rates in air and under vacuum. At the stress rate of 30 psisec the vacuum strength of alumina has been found to be up to 40 higher than the strength in air. This difference in strength is considerably higher than the difference produced by changing grinding variables andor surface finish. The data obtained are correlated with previous results and the phenomenon of delayed fracture in ceramics is discussed. Author
- Ceramics, Refractories and Glass