Fracture characteristics of silicon nitride ceramic ball subjected to thermal shock

Abstract

The aim of this study was to clarify the fracture characteristics of ceramic balls, as used in bearings, when subjected to thermal shock. First, water-quench tests were performed on ceramic balls of a range of sizes. The fracture morphology and fracture surface were then observed. The crack propagation and branching behaviors were observed on the surfaces of the ceramic balls after they had been subjected to thermal shock. Manufacturing flaws were then observed on the surface of the fractures in the ruptured ceramic balls. Next, the relationship between the fracture strength, as calculated using a FEM analysis of the temperature difference at thermal shock fracture initiation and the equivalent crack length calculated from the manufacturing flaw size, was theoretically discussed to introduce a virtual crack model. As a result, it was concluded that the relationship can be estimated by applying a virtual crack model based on experimental data obtained from fracture strength tests for the difference fracture type, i.e., the temperature difference depends on the size of the manufacturing flaw. Finally, the temperature difference scatter was theoretically discussed based on the results of the two-parameter Weibull distribution in conjunction with a virtual crack model.

Experimental study on lapping ceramic balls with variable-radius groove plate

“…Si 3 N 4 ceramic ball with low density, high hardness, high stiffness, wear resistance, low thermal expansion coefficient, and other excellent comprehensive performance, is considered to be the most ideal rolling body for high speed and high precision bearings, especially is suitable for extreme environments. 1,2 Ceramic balls are used in groups in bearings, so the geometrical precision, surface quality and consistency of ceramic balls will directly affect the service life of bearings. 3 Therefore, the international standard 4 has put forward the strict requirement to the machining precision and the batch consistency of ceramic balls, the highest precision grade is G3 and the next highest is G5, whose quality and precision indexes are shown in Table 1.…”