KJ Ceramics 31

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Detailed Program

Paper Number : ST-O11

Time Frame : 14:20~14:40

Presentation Date : Friday, 28, November

Session Name : Structual Ceramics & Refractory materials

Session Chair 1# : Young-Wook Kim

Session Chair 2# : Kouichi Yasuda

Measurement of Local Fracture Toughness of Soda-lime Glass and Si3N4 Ceramics Using Microcantilever Beam Specimens

Junichi TATAMI

Yokohama National University

Keywords: Fracture toughness, soda-lime glass, Si3N4

Local mechanical properties are important to understand the nature of the mechanical properties of bulk ceramics and glass. In this study, the local mechanical properties, in particular fracture toughness, of soda-lime glass and Si3N4 ceramics were measured using microcantilever beam specimens prepared by focused ion beam technique.
The size of the sample for strength measurement was 2.5×2×15m and their section profile was pentagonal. A sharp single notch was also machined along a target to measure the fracture toughness. After bending test, the grain boundary fracture toughness was calculated by displacement method based on finite element analysis.
Table 1 shows the fracture toughness near the surface of soda-lime glass. In this study, the target to measure the fracture toughness is as-received and HF-eched surfaces. The fracture toughness of the HF-eched surface is higher than that of the as-received surface. Since the chemical composition in soda-lime glass changes from the surface toward the inner part, the difference in the fracture toughness between the as-received and the HF-etched surfaces probably resulted from the chemical composition. It has been reported that removal of the surface by HF-etching improved the strength of soda-lime glass. In consideration of the result of the present study, it was shown that removal of the defects by etching has a great effect on the improvement of the strength.
Table 2 shows the fracture toughness of grain and grain boundary of Si3N4 ceramics. The fracture toughness of the Si3N4 grain was 2.77 MPam1/2, which is higher than the estimation by calculation. The difference should result from the dissipative energy other than formation of new fracture surfaces. The grain boundary fracture toughness of Si3N4 ceramics depended on the added rare earth oxide, which is higher than the fracture toughness of SiAlON glass. It was suggested that structure of the intergranular glassy film should be different from that of the bulk SiAlON glass. The dependence of the grain boundary fracture toughness on the added rare earth oxide was explained by the difference in the grain boundary structure.

Acknowledgements :

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