On the Fractographic Analysis of Machining Cracks in Ground Ceramics: A case Study on Silicon Nitride

G. D. Quinn, L. K. Ives, and S. Jahanmir, On the Fractographic Analysis of Machining Cracks in Ground Ceramics: A case Study on Silicon Nitride, NIST-SP 996 (2003), Government Printing Office, Washington, DC.

Meticulous fractographic analysis of broken flexural strength specimens was used to characterize the size, shape, and severity of grinding flaws in a commercial silicon nitride. The cylindrical rods and rectangular bars were prepared by a varietyof grinding procedures. Grinding flaw size correlated strongly with grinding direction and wheel grit size. Cracks depths from as small as 12 mm to as large as 80 mm were measured. Copious illustrations of machining cracks are provided. Some grinding treatments had no deleterious effect on strength since the machining cracks were very small and fracture occurred from the material’s inherent flaws. Tell tale signs of machining damage were found with conventional low power opticalmicroscopy using simple fractographic techniques. The tell tale signs are summarized in a new series of schematic drawings which will aid pattern recognition for engineers and fractographers. These schematics will make detection of machining cracks much easier. Machining damage maps for silicon nitride are presented.

 


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