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An ASTM standard test method for determination of fracture toughness has been created for advanced ceramics. Standard C 1421-99 includes three test methods and is suitable for ceramics with flat R-curve behavior, but includes some provisions for materials with rising R-curve. The three methods are: chevron notch, single-edge precracked beam, and surface crack in flexure, all of which use beams in bending. Supporting data have been collected through several major international round robin programs conducted under the auspices of the Versailles Advanced Materials and Standards program.
This paper presents the historical evolution of the standard and reflects on the strategies used to overcome the interferences of slow crack growth, R-curve, and stability. It draws parallels to the development of ASTM E 399, and it presents data that show good precision and accuracy for well-behaved materials. Materials with R-curve and susceptibility to slow crack growth have been analyzed following the recommendations in the standard, and the procedure fulfills the objective of identifying such behavior. Standard Reference Material 2100 with certified values of fracture toughness directly complements C 1421.
fracture toughness, R, -curve, slow crack growth, stability, ceramics
Associate professor, Worcester Polytechnic Institute, Worcester, MA
Ceramic engineer, National Institute of Standards and Technology, Gaithersburg, MD
Engineer, NASA Glenn Research Center, Cleveland, OH
Associate professor, University of Washington, Mechanical Engineering Bldg, Seattle, WA