STP844: Statistical Analysis of Size and Stress State Effects on the Strength of an Alumina Ceramic

    Shetty, DK
    Principal research scientist, research leader, and member of the research council, Battelle-Columbus Laboratories, Columbus, Ohio

    Rosenfield, AR
    Principal research scientist, research leader, and member of the research council, Battelle-Columbus Laboratories, Columbus, Ohio

    Duckworth, WH
    Principal research scientist, research leader, and member of the research council, Battelle-Columbus Laboratories, Columbus, Ohio

    Pages: 24    Published: Jan 1984


    Abstract

    Fracture strengths of an alumina ceramic, surface-finished to obtain an isotropic flaw population, were evaluated in inert and water environments in three qualified tests—four-point and three-point bend tests and a biaxial flexure test featuring uniform-pressure loading of disk specimens. The resulting strengths were examined in terms of a statistical fracture theory that employed fracture criteria derived from fracture mechanics theory and supported by reported experimental results on the fracture from angled surface cracks from indentation. The four-point and three-point bend tests gave fracture strengths, in both inert and water environments, that were consistent with the size effect predicted by the statistical fracture theory. The stress state effect on strength, as indicated by the results of the biaxial test, was predicted by the theory only for the tests in water. The inert biaxial strengths were significantly greater than the statistical theory predictions, irrespective of the fracture criteria employed. The differences in the biaxial strengths predicted from the theory, on the bases of a normal stress (Mode I) and a combined mode fracture criteria, were small because of the relatively small values of the strength scatter in each test. The observed trend in the biaxial fracture strengths in relation to the uniaxial strengths with the change in the test environment suggested more severe strength degradation from slow-crack growth in the biaxial stress state than that in the uniaxial stress state. Implications of this result with respect to long-term reliability of brittle structural components are discussed.

    Keywords:

    brittle materials, structural reliability, fracture strengths, fracture criteria, size effect, mixed-mode fracture, stress state effect, strength distributions, subcritical crack growth, residual stresses, statistical analysis, crack branching


    Paper ID: STP35237S

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP35237S


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