Abstract
The opposite-roller contact test has been used for the strength measurement of Si₃N₄ and SiC based ceramics and the results have been compared to the results of the four-point bending strength test. Ceramographic and fractographic methods have been used for the characterisation of the strength degrading defects. The characteristic strength values for the silicon nitride ceramics are very similar in contact and bending strength tests but for the silicon carbide the characteristic strength in bending mode is lower compared to the value of contact strength. This is caused by the presence of the relatively large processing flaws in the SiC ceramics. The Weibull moduli obtained for the investigated materials using contact strength method are approximately half of the moduli of bending methods. Contact end cracks, median and lateral cracks have been found as the main damage mechanisms which lead to the fracture of the specimens in contact strength test.

Key words
contact strength, bending strength, cylinder loading, Weibull parameters

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