|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, U.S. Department of Commerce, Gaithersburg, Md., who helped to develop the standard.
ASTM Standard Practice C 1322 was the worlds first consensus standard for fractographic analysis of ceramic materials, he says. 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, in 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, Quinn explains. 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.
Developers of the standard included subcommittee chair Jeffrey J. Swab, ceramic engineer, Research Laboratory, U.S. Army Aberdeen Proving Ground, Aberdeen, Md. The ASTM standard replaces Military Handbook 790, Fractography and Characterization of Fracture Origins in Advanced Structural Ceramics (June 1992), U.S. Army Materials Technology Laboratory, Watertown, Mass. Swab and other subcommittee members approved the document as an efficient and consistent methodology for locating and characterizing fracture origins in advanced brittle ceramics.
Although C 1322 is primarily intended for laboratory test piece analysis, the general concepts and procedures may be applied to component failure analyses. In many cases, component failure analysis may be aided by cutting laboratory test pieces out of the component. Information gleaned from testing the laboratory pieces (for example, flaw types, general fracture features, fracture mirror constants) may aid interpretation of component fractures.
For further technical information, contact George Quinn, NIST, Gaithersburg Md. or Jeffrey Swab, Research Lab, U.S. Army Aberdeen Proving Ground, Aberdeen, Md. Committee C28 meets April 26-27 in Nashville, Tenn., at the Opryland Hotel. For meeting or membership details, contact Gloria Collins, manager, Technical Committee Operations, ASTM International (phone: 610/832-9715). //
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