Characterization and mechanical behavior of ceramic rings

Diametral compression is usually used to determine the mechanical resistance of cylindrical ceramic specimens. This work deals with the possibility of employing diametral compression in order to evaluate the mechanical response of ceramic rings, by testing two sets of rings (used as pump seals) that had two different sizes. The rings were characterized by different techniques: qualitative X-ray diffraction, apparent density and porosity measurements, determination of Vickers hardness, surface roughness, and microstructural analysis. a-alumina was identified as the majority crystalline phase in both types of rings. The porosities were rather similar, even though the observed mean grain size of the large rings was slightly larger. Significant differences were observed in the average roughness. Diametral compression tests at room temperature were carried out on a statistical number of each ring set. The fracture features were analyzed by ocular inspection and SEM observation of the fracture surfaces. Several approaches were used to estimate the fracture strengths: three analytical formulae with and without an empirical constant, and a finite element calculation. The simplest approach, an analytical formula that only requires the knowledge of the geometrical magnitudes of rings besides de fracture loads, gave a conservative estimation of the mechanical strength of rings and a limited explanation of fracture features. On the other hand, the numerical model being the most complex and informative of the approaches, gave the complete stress distributions.