THE STRENGTH OF CERAMIC BALLS - THE NOTCHED BALL TEST

摘要

In recent years ceramic balls were used in high performance ball bearings. The strength of ceramic balls depends on the quality of their original surface, which may also depend on machining and handling. Despite information on the strength of balls is essential, simple strength testing methods for balls are missing up to now. Recently, the "Notched Ball Test" (NBT) was established at the Institut fur Struktur- und Funktionskeramik to measure the strength of ceramic balls for structural applications [1]. A notch is cut into the equatorial plane of the ball and the load is induced at the poles by two dies, so that the notch is squeezed together and high tensile stresses occur in the balls surface region opposite the notch root. The stress distribution in notched balls is determined in dependence of notch size and geometry with FE-methods. Strength tests have been performed on commercial silicon nitride balls with different notch geometries and ball diameters.