SEDL / STP / STP1201-EB / STP12774S

Fracture Mechanism Maps: Their Applicability to Silicon Nitride

Wiederhorn, SM
Senior NIST Fellow, Materials Science and Engineering Laboratory, The National Institute of Standards and Technology, Gaithersburg, MD

Quinn, GD
Ceramic Engineer, The National Institute of Standards and Technology, Gaithersburg, MD

Krause, R
Research Chemist, The National Institute of Standards and Technology, Gaithersburg, MD

Pages: 26    Published: Jan 1994

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Abstract

Fracture mechanism maps provide a means of assessing the structural reliability of ceramics at elevated temperatures. They can be used to summarize large quantities of data dealing with effects of load, temperature and environment on component lifetime. They also can be used to generate a design envelope that defines stress allowables for a given application. In this paper, we review the history and philosophy behind fracture mechanism maps and then discuss methods of obtaining such maps in an efficient manner. Based on data obtained in simple tensile tests, these methods are illustrated for one of the newer grades of silicon nitride. The map is then used to compare this material with a high temperature structural alloy, and another, older grade of silicon nitride. Finally, we discuss the use of fracture mechanism maps for design.