Bending and Contact Strength of Monolithic Ceramic Materials

Abstract

The article deals with the determination of strength of monolithic ceramic materials by mechanical tests, in bending and contact modes, simulated by a four-point bending test and single-cycle contact test using rollers or spheres, respectively. In general, the determination of strength of ceramic materials results from statistical methods, usually represented by the Weibull analysis comprising of the determination of the characteristic strength σ₀ and the Weibull modulus m. Accordingly, the characteristic strength σ_0,bend and σ_0,cont as well as the Weibull moduli m_bend and m_cont, related to the four-point bending test and the single-cycle contact test using rollers, are determined, respectively. Additionally, the comparison of numerical results of σ_0,bend/σ_0,cont, m_bend/m_cont confirms the validity of the Fett's theory. Along with this verification and the Weibull analysis for mechanical loading by spheres, a microstructural analysis of strength-degrading defects as fraction origins is performed for the bending and contact modes which induce different types of crack. Finally, the determination of mechanical loading causing material failure and an analysis of parameters of the cracks is also presented. The mechanical tests were applied to monolithic Si₃N₄ and SiC ceramic materials.