Contact strength and crack formation in monolithic ceramic materials

The paper deals with the strength meaurement and characterization of strength data of monolithic Si3N4 and SiC ceramics using unconventional contact tests between opposite rollers and opposite spheres. The results are compared to the results of conventional four-point-bending test. Ceramographic and fractographic methods are used for the characterization of strength degrading defects represented by processing flaws and by cracks of different types arising during the loading. The processing flaws influenced the Weibull parameters mainly in the bending mode, and the strength and its scatter in contact modes was influenced by lateral, median and contact end cracks, originating during the contact test using rollers, and by cone cracks originating during the contact test using spheres. The influence of the radius of the spheres on length and an angle of the cone cracks has been determined too.