Abstract
The paper deals with the determination of strength of ceramic materials and a microstructural analysis of strength-degrading defects. Strength is determined by mechanical tests in bending and contact modes. The bending and contact modes are simulated by a four-point bending test and single-cycle contact tests using rollers or spheres, respectively. The determination of strength is based on the Weibull analysis which is used for the determination of the characteristic strength σ₀ and the Weibull modulus m . Accordingly, numerical values of σ_0,bend and σ_0,cont related to the four-point bending test and the single-cycle contact test using rollers, respectively, enable to define a relationship between σ_0,bend and σ_0,cont. Similarly, the same relationship is determined between numerical values of m_bend and m_cont. These relationships confirm the validity of the Fett's theory. In case of the bending mode, the strength-degrading defects are represented by flaws, which originate during the processing of a material. In case of the contact modes, different types of cracks, which are formed during mechanical loading, represent the strength-degrading defects. A detailed analysis of parameters of the cracks is also presented. The mechanical tests were applied to monolithic and composite ceramic materials represented by Si₃N₄, SiC and MoSi₂+10%Si, respectively.

Key words
nitrides, carbides, ceramic matrix composites, fracture, bending test, contact test

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