Fracture characteristics of silicon nitride ceramic ball subjected to thermal shock

摘要

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.