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[February 2003]
Ceramic Engineers Upgrade ASTM Fractography Standard
Testers of brittle materials can determine where a break originates and why with new methodology in ASTM C 1322 Standard Practice for Fractography and Characterization of Fracture Origins in Advanced Ceramics (2002)."Fractographic analysis can identify the exact origin of fracture, the stress state, and even the magnitude of stresses in fractured glasses, structural, electrical and biological ceramics," says George Quinn, ceramic engineer, National Institute of Standards and Technology, US Department of Commerce, Gaithersburg, MD, USA. "ASTM Standard Practice C 1322 provides guidance in interpretation and reporting of fractographic features in ceramics and glasses. The standard is applicable to laboratory strength test specimen analysis as well as component failure analysis."
Quinn and co-members of ASTM Subcommittee C28.05 on Characterization and Processing (part of ASTM Committee C28 on Advanced Ceramics) "dramatically upgraded" the standard. "One major revision in 2002 was the addition of a wealth of new information on the detection and characterization of machining damage cracks," explained George Quinn. "Machining cracks often are difficult to detect, but C 1322 now includes illustrative schematics and examples that will aid the recognition of critical tell tale features.
"In many cases, it is possible to use simple optical microscopy techniques to diagnose that small machining cracks were at the fracture origin. The standard also now includes a huge compilation of fracture mirror constants that will enable users to estimate stresses in the part at the instant of breakage if a fracture mirror is present."
The ASTM standard replaces Military Handbook 790, Fractography and Characterization of Fracture Origins in Advanced Structural Ceramics (June 1992). Although C 1322 is primarily intended for laboratory test piece analysis, the general concepts and procedures may be applied to component failure analysis.
ENDS