Kyung-Jin Yoon

Influence of humidity on the flexural strength of alumina

The influence of humidity on the flexural strength of alumina was investigated. The strengths tested at relatively high relative humidities (>45%) were smaller than those tested at relatively low relative humidities (<45%) as much as ∼10%. It was demonstrated by a round robin test that the influence of the humidity could produce a problem in the reproducibility of the strength data. It was discussed, that the problem in the reproducibility can be avoided by testing and using the inert strength in the comparison of strength data. It was recommended that, to test the inert strength, the strength measurement be made after the specimens had been coated with oil to protect them from contact with environmental moisture.

Effects of environmental temperature and humidity on the flexural strength of alumina and measurement of environment-insensitive inherent strength

Abstract In the range of temperature, 10–55 °C, and relative humidity, 20–80%, it has been demonstrated that the flexural strength of alumina decreases significantly with increasing temperature and relative humidity. It has been also demonstrated that the environment-insensitive inherent strength may be obtained by testing under nitrogen gas atmosphere after coating specimens with liquid paraffin, vacuum grease or polyurethane.

Surface Strengthening of Zirconia Toughened Alumina (ZTA) Using Glass Infiltration Technique

Molten Soda lime glass (SLG) was penetrated into the surface of ZTA at 1500°C for the holding time of 1 to 10 h. The depth of the glass penetration increased with increasing holding time. The thermal expansion mismatch and elastic property mismatch between the penetrated glass and ZTA produced residual compression in the surface region during cooling. This residual compression enhanced the flexural strength and fracture toughness remarkably.

Effects of the Loading Rate and Humidity in the Fracture Toughness Testing of Alumina

To test the fracture toughness of alumina, a Surface-Crack-in-Flexure (SCF) method, a Single-Edge-Precracked-Beam (SEPB) method and a Single-Edge-V-Notched-Beam (SEVNB) method were used at crosshead rates ranging from 0.005 ㎜/min to 2 ㎜/min and relative humidity ranging from 15% to 80%. The results show that the fracture toughness tested by the SCF method increases with either an increasing loading rate or decreasing relative humidity; in contrast, the toughness by the SEPB method and the SEVNB method does not depend on the loading rate or the relative humidity. Theoretical analysis of the way slow crack growth affects the apparent fracture toughness indicates that the three testing methods have different effects with respect to the loading rate and the relative humidity; moreover, these differences are attributable to differences in the size of the cracks or notches.