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The strength-to-particle size relationship for specially fabricated graphites has been demonstrated and rationalized using fracture mechanics. In the past, similar studies have yielded empirical data using only commercially available material. Thus, experimental verification of these relationships has been difficult. However, the graphites of this study were fabricated by controlling the particle size ranges for a series of isotropic graphites. All graphites that were evaluated had a constant 1.85-g/cm3 density. Thus, particle size was the only variable. The strength-to-particle size relationship revealed that the fracture strength was logarithmically related to initial defect size by an apparent −1/3 power. Application of Dugdale crack extension model with simple modifications accounting for nonspherical pores and variable defect concentrations explains the −1/3 power relationship. This study also considered the particle size effect on other physical properties: coefficient of thermal expansion, electrical resistivity, fracture strain, and Young's modulus.
graphite, particle size, strength, fracture mechanics, microcracking, Dugdale model, physical properties
Associate engineer, Westinghouse Electric Corp., Lester, Pa.
Research staff, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tenn.