Hiroaki Makino

Strength Degradation of Ceramics Caused by Residual Stress Around Impression

The surface of the specimens of three kinds of silicon nitrides and two kinds of sialons was indented with a conical diamond indenter. The flexural strengths of the specimens decreased over certain indentation loads, which were dependent on the material properties, especially on the hardness. It was thought from the observation of the fracture surfaces that the strength degradation was due to the residual stress formed around impressions. The residual stress was evaluated by the method based on a plasticity theory. With an increase in the hardness of the materials, the evaluated indentation load causing residual stress decreases. The evaluation of the residual stress indicates that the material with higher hardness has greater resistance against the localized contact stress. The experimental results coincided with the estimation.